JP2011154275A - Polarization inversion wavelength converting element, and light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization inversion wavelength converting element capable of sufficiently reducing a speckle contrast while emitting an output laser beam having high light output power. <P>SOLUTION: The element includes a polarization inversion structure, where regions D1 to D3 having a polarization inversion structure are arrayed side by side. Among basic laser beams 300 that are made incident on an incident surface 201, the element converts wavelengths of a plurality of fundamental waves with wavelength bands separated from one another, and emits the plurality of converted waves with wavelength bands separated from one another. The element emits an output laser beam 400 from an exit surface 203, the output laser beam including converted waves emitted from the respective regions of the polarization inversion structure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polarization inversion wavelength conversion element and a light source, and more particularly to a polarization inversion wavelength conversion element and a light source for use in a green laser light source of a scanning laser projector.

  Full-color scanning laser projectors using red, blue and green laser beams have been proposed. A scanning laser projector projects an image on a screen by reflecting and scanning laser light using a MEMS (Micro Electro Mechanical Systems) mirror, so that there is no need for focus adjustment, and the image has a non-flat shape. There is an advantage that even if it is projected on the screen, there is no out-of-focus blur.

  As a green laser light source used for a scanning laser projector, a wavelength conversion light source provided with an SHG (Second Harmonic Generation) element is usually used. The wavelength conversion light source uses the SHG element to convert the wavelength of the basic laser light from the laser element, converts the basic laser light into output laser light having a different wavelength, and emits it.

  In recent years, a wavelength conversion light source that converts the wavelength of the basic laser beam using an SHG element having a periodically poled structure has been developed. An SHG element having a periodically poled structure is also called a polarization inversion wavelength conversion element, and generates basic phase laser light and output laser light by generating quasi phase matching (QPM) in the basic laser light and output laser light. Has been converted. Since the polarization inversion wavelength conversion element has a higher wavelength conversion efficiency for converting the basic laser light into the output laser light as compared with the conventional SHG element, the output laser light with high optical output power can be emitted.

  Note that the wavelength band of the basic laser beam in which the quasi phase matching occurs is determined according to the polarization inversion period which is the period length of the domain inversion structure. Therefore, the wavelength band of the basic laser beam that can be converted in the polarization inversion wavelength conversion element changes according to the polarization inversion period. Hereinafter, the wavelength band of basic laser light capable of wavelength conversion in the polarization inversion wavelength conversion element may be referred to as a wavelength conversion region.

  FIG. 74 is a conceptual diagram showing another example of a green laser light source using a polarization inversion wavelength conversion element.

In the green laser light source shown in FIG. 74, the semiconductor laser light 15 having a wavelength of 808 nm band is emitted from the semiconductor laser array 11. The semiconductor laser beam 15 is excited by an Nd: YVO ₄ (Neodymium Doped Yttrium Orthovanadate) crystal 12, converted into a red external laser beam 16 having a wavelength of 1060 nm, and emitted. The red line laser beam 16 is incident on a resonator composed of a pair of resonator mirrors 13A and 13B.

In the resonator, a PPSLT (periodically poled stoichiometric LiTaO ₃ ) crystal 14 which is a polarization inversion wavelength conversion element is provided on the optical path of the red external laser light 16, and the red external laser light 16 is converted into the PPSLT 14. Is converted into green laser light 17 having a wavelength of 530 nm and emitted from the resonator mirror 13A.

  The green laser light source shown in FIG. 74 can emit green laser light, but has a problem that it is difficult to use for a scanning laser projector.

  Laser light sources for scanning laser projectors include: 1. It is possible to emit a single beam of output laser light that can be scanned with a MEMS mirror. 2. High-speed modulation of output laser light is possible. 3. Small size and low cost. 4. It is possible to emit an output laser beam having a high optical output power. It is required to be able to emit an output laser beam that realizes a projection image with weak speckles.

  Note that speckle is speckled noise generated by interference of light scattered at each point on the screen when light having coherence such as laser light is projected onto the screen. The strength of speckle can be evaluated by a value called speckle contrast. The speckle contrast takes a value from 0% to 100%, and the smaller the value, the weaker the speckle. Further, in the scanning laser projector, if the speckle contrast is about 10% or less, it is possible to make the observer of the projected image feel less speckle.

  The green laser light source shown in FIG. 74 can emit a single beam of output laser light. Further, this green laser light source is small and low-cost, and can perform high-speed modulation of laser light. This is because the DBR laser 1 of the green laser light source is small and low-cost, and can perform high-speed modulation up to about several GHz.

  However, the green laser light source shown in FIG. 74 has a problem that an output laser beam having a high optical output power is emitted and a projection image with a weak speckle cannot be realized.

  The green laser light source shown in FIG. 74 can emit green laser light with high optical output power by increasing the light intensity of the semiconductor laser light incident on the PPLN crystal, which is a polarization inversion wavelength conversion element. . However, when a semiconductor laser beam having a high light intensity is incident on the PPLN crystal, photorefractive damage may occur in the PPLN crystal and the PPLN crystal may be damaged. For this reason, it is necessary to be able to emit an output laser beam having a high optical output power while reducing the intensity of the semiconductor laser beam incident on the PPLN crystal to a certain level.

  The wavelength conversion efficiency in a polarization inversion wavelength conversion element such as a PPLN crystal increases in proportion to the square of the length of the polarization inversion wavelength conversion element. For this reason, in order to obtain output laser light with high optical output power, it is necessary to lengthen the polarization inversion wavelength conversion element. Normally, if the length of the polarization inversion wavelength conversion element is about 10 mm, the optical output power of the output laser light is applied to the scanning laser projector by using semiconductor laser light that does not cause photorefractive damage to the PPLN crystal. The required 50 mW or more can be achieved.

  However, the longer the polarization inversion wavelength conversion element, the smaller the wavelength conversion region in the polarization inversion wavelength conversion element, so the wavelength width of the output laser light becomes smaller. As the wavelength width of the output laser beam is smaller, the speckle of the projection image becomes larger. Therefore, if the polarization inversion wavelength conversion element is lengthened to obtain an output laser beam having a high optical output power, the speckle of the projection image becomes stronger. Therefore, it is not possible to realize a projected image that emits laser light with high optical output power and weak speckles.

  In general, in a polarization inversion wavelength conversion element having a length of about 10 mm, the wavelength conversion region is as extremely small as about 0.16 nm. However, in order to make the speckle contrast about 10%, the wavelength conversion region needs about 5 nm to 10 nm.

  As a technique capable of emitting an output laser beam having a high optical output power and widening the wavelength conversion region, there is an optical wavelength conversion element described in Patent Document 1. FIG. 75 is a conceptual diagram showing the optical wavelength conversion element described in Patent Document 1.

  In FIG. 75, the optical wavelength conversion element has a single wavelength conversion element 21 and chirp structure portions 22 and 23 arranged on both sides of the single wavelength conversion element 21.

  FIG. 76 is a diagram showing the relationship between the distance along the traveling direction of the basic laser light and the polarization inversion period in the optical wavelength conversion element. As shown in FIG. 76, in the single wavelength conversion element 21, the polarization inversion period is constant. In the chirp structure portions 22 and 23, the polarization inversion period continuously changes along the traveling direction of the laser light. Further, the polarization inversion period continues at the boundary between the single wavelength conversion element 21 and the chirp structure portions 22 and 23.

  76. By providing the chirp structure portions 22 and 23 having the polarization inversion period as shown in FIG. 76, the wavelength conversion regions in the chirp structure portions 22 and 23 are connected to the wavelength conversion region in the single wavelength conversion element 21. Is possible. Therefore, the wavelength conversion region of the optical wavelength conversion element can be made wider than the wavelength conversion region of the single wavelength conversion element 21.

  Specifically, when the optical wavelength conversion element is about 10 mm, the width of the wavelength conversion region of the optical wavelength conversion element is about 0.5 nm.

  Therefore, the wavelength conversion region can be widened without shortening the polarization inversion wavelength conversion element, so that the optical output power can be increased and the width of the wavelength conversion region can be widened.

JP 2000-321610 A

  In the optical wavelength conversion element described in Patent Document 1, the width of the wavelength conversion region is about 0.5 nm. In a scanning laser projector, it is desired that the speckle contrast is about 10% or less, but in order to make the speckle contrast about 10% or less, the wavelength conversion region needs to be at least about 5 nm to 10 nm. Become.

  Therefore, the optical wavelength conversion element described in Patent Document 1 has a low rate of increase / decrease in the width of the wavelength conversion region, and the speckle contrast cannot be sufficiently lowered, so that it is difficult to apply to a scanning laser projector. There is a problem.

  An object of the present invention is to provide a polarization inversion wavelength conversion element and a light source that solve the problem that the speckle contrast, which is the above-mentioned problem, cannot be sufficiently lowered while emitting an output laser beam having a high optical output power. That is.

  The polarization inversion wavelength conversion element according to the present invention includes an incident surface on which incident light is incident and a plurality of regions having a polarization inversion structure, and each region has a wavelength band of incident light incident on the incident surface. Each of the plurality of separated fundamental waves is converted, and each of the plurality of converted waves having a separated wavelength band is emitted. And an exit surface that emits the exit light including the converted wave.

  The light source by this invention has the said polarization inversion wavelength conversion element and the light output part which radiate | emits the said incident light to the said polarization inversion wavelength conversion element.

  According to the present invention, it is possible to sufficiently reduce speckle contrast while emitting an output laser beam having a high optical output power.

It is the block diagram which showed the structure of the laser light source of the 1st Embodiment of this invention. It is the conceptual diagram which showed the more detailed structure of the laser light source of the 1st Embodiment of this invention. It is the circuit diagram which showed the structure of the high frequency LD driver power supply. It is the figure which showed the relationship between the transmittance | permeability of a dichroic mirror, and a wavelength. It is the figure which showed the structure of the polarization inversion wavelength conversion element. It is the figure which showed the relationship between the wavelength of a fundamental wave, and a polarization inversion period. It is an external view of a polarization inversion wavelength conversion element. It is the figure which showed the more detailed structure of the polarization inversion wavelength conversion element. It is the figure which showed the relationship between the wavelength conversion efficiency of a polarization inversion wavelength conversion element, and the wavelength of a fundamental wave. It is the figure which showed the relationship between interaction length when a wavelength conversion window turns into a flat window, and a conversion wavelength space | interval. It is the figure which showed an example of the wavelength dependence of wavelength conversion efficiency. It is the figure which showed an example of the wavelength dependence of wavelength conversion efficiency. It is the figure which showed an example of the wavelength dependence of wavelength conversion efficiency. It is the figure which showed an example of the wavelength conversion spectrum of a polarization inversion wavelength conversion element. It is the figure which showed the other example of the wavelength conversion spectrum of a polarization inversion wavelength conversion element. It is the figure which showed the relationship between the change rate of a speckle contrast, and a wavelength difference. It is a figure for comparing the wavelength conversion spectrum of the polarization inversion wavelength conversion element of 1st embodiment, and a single conversion element. It is the figure which showed an example of the spectrum of the basic laser beam. It is the figure which showed an example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed an example of the spectrum of the output laser beam from a single conversion element. It is the block diagram which showed the structure of the laser light source of the 2nd Embodiment of this invention. It is another external view of a polarization inversion wavelength conversion element. It is the figure which showed the other structural example of the polarization inversion wavelength conversion element. It is the figure which showed the other example of the wavelength dependence of wavelength conversion efficiency. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed an example of the wavelength spectrum of a fundamental wave. It is the figure which showed the beam shape of the laser beam in a PPLN crystal | crystallization. It is the figure which showed the beam shape of the laser beam in the air. It is the figure which showed the relationship between the beam shape of the laser beam in a PPLN crystal | crystallization, and beam waist width. It is the block diagram which showed the structure of the laser light source of the 3rd Embodiment of this invention. It is the figure which showed the other example of the spectrum of the basic laser beam. It is the figure which showed the other example of the structure of the polarization inversion wavelength conversion element. It is the figure which showed the other example of the wavelength dependence of the wavelength conversion efficiency of a polarization inversion wavelength conversion element. It is the figure which showed an example of the relationship between a speckle contrast, optical output power, and beam waist width. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of the basic laser beam. It is the figure which showed the other example of the relationship between a speckle contrast, optical output power, and beam waist width. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of the basic laser beam. It is the figure which showed the other example of the relationship between a speckle contrast, optical output power, and beam waist width. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of output laser beam. It is the block diagram which showed the structure of the laser light source of the 4th Embodiment of this invention. It is another external view of a polarization inversion wavelength conversion element. It is the figure which showed the other example of the structure of the polarization inversion wavelength conversion element. It is the figure which showed an example of the relationship between the spectrum of a fundamental wave, and interaction length. It is the figure which showed an example of the relationship between the spectrum of a fundamental wave, and interaction length. It is the figure which showed an example of the spectrum of output laser beam. It is the figure which showed an example of the dependence with respect to the element length of green light output power. It is the figure which showed the other example of the dependence with respect to the element length of green light output power. It is the figure which showed an example of the dependence with respect to the excitation light output power of green light output power. It is the figure which showed an example of the dependence with respect to pumping light output power of element length. It is the figure which showed the other example of the dependence with respect to the element length of green light output power. It is the figure which showed the other example of the dependence with respect to the element length of green light output power. It is the figure which showed the other example of the dependence with respect to the excitation light output power of green light output power. It is the figure which showed the other example of the dependence with respect to pumping light output power of element length. It is the figure which showed the spectrum and interaction length distribution of the basic laser beam. It is the figure which showed an example of the dependence with respect to the distribution parameter of a speckle contrast. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed an example of the spectrum of the basic laser beam, and a wavelength conversion spectrum. It is the figure which showed the other example of the spectrum of the fundamental laser beam, and the wavelength conversion spectrum. It is the figure which showed the spectrum and interaction length distribution of the basic laser beam. It is the figure which showed the other example of the dependence with respect to the distribution parameter of a speckle contrast. It is the figure which showed the other example of the spectrum of output laser beam. It is the figure which showed the other example of the spectrum of the fundamental laser beam, and the wavelength conversion spectrum. It is the block diagram which showed the structure of the laser light source of the 2nd Embodiment of this invention. It is the block diagram which showed the structure of the laser light source of the 2nd Embodiment of this invention. It is the conceptual diagram which showed an example of the laser light source which is related technology. It is the conceptual diagram which showed the optical wavelength conversion element of patent document 1. It is the figure which showed the polarization inversion period in the optical wavelength conversion element of patent document 1.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, components having the same function may be denoted by the same reference numerals and description thereof may be omitted.

  FIG. 1 is a block diagram showing the configuration of the laser light source according to the first embodiment of the present invention. In FIG. 1, the laser light source includes a light output unit 100 and a polarization inversion wavelength conversion element 200.

  The light output unit 100 emits the basic laser light 300 to the polarization inversion wavelength conversion element 200.

  The polarization inversion wavelength conversion element 200 is an SHG element having a periodic polarization structure. The fundamental laser light 300 emitted from the light output unit 100 is incident on the polarization inversion wavelength conversion element 200. Therefore, the basic laser light 300 becomes incident light of the polarization inversion wavelength conversion element 200.

  The polarization inversion wavelength conversion element 200 converts the wavelength of the basic laser light 300 and emits the output laser light 400. Note that the output laser beam 400 may be referred to as emitted light.

  FIG. 2 is a conceptual diagram showing a more detailed configuration of the laser light source shown in FIG. In FIG. 1, the laser light source includes a light output unit 100 and a wavelength conversion unit 101 including a polarization inversion wavelength conversion element 200. The light output unit 100 and the wavelength conversion unit 101 are provided on the substrate 50.

  The optical output unit 100 includes LD modules 111 </ b> A to 111 </ b> C, a high frequency LD driver power source 112, a temperature control unit 113, reflecting mirrors 114 and 115, dichroic mirrors 116 and 117, and a half-wave plate 118.

  The LD modules 111A to 111C emit laser light. Hereinafter, the laser light of the LD module 111A is referred to as laser light 301A, the laser light of the LD module 111B is referred to as laser light 301B, and the laser light of the LD module 111C is referred to as laser light 301C. The laser beams 301A to 301C become the basic laser beam 300 as will be described later.

  The center value of the wavelength band of the laser beam 301A is λa, the center value of the wavelength band of the laser beam 301A is λa + Δ, and the center value of the wavelength band of the laser beam 301A is λa + 2Δ. Note that λa and Δ are positive values. In the following, it is assumed that λa = 1.58 μm and Δ = 1 nm. Further, it is assumed that the differences in the median values of the wavelength bands of the laser beams 301 to 301C are all equal.

  It is assumed that the polarization directions of the laser beams 301 </ b> A to 301 </ b> C are parallel to the substrate 50. Hereinafter, a direction parallel to the substrate 50 is referred to as a horizontal direction, and a direction perpendicular to the substrate 50 is simply referred to as a vertical direction.

  Each of the LD modules 111 </ b> A to 111 </ b> C includes an LD chip 121, a collimator lens 122, and a heat sink 123.

  The LD chip 121 is a semiconductor laser element for excitation. The LD chip 121 is subjected to high-frequency superposition driving by a high-frequency LD driver power source 112, and outputs a laser beam corresponding to the high-frequency superposition driving.

  The high-frequency superimposed drive is a drive method for driving a semiconductor laser element using a high-frequency superimposed current obtained by superimposing a high-frequency component on the drive current of the semiconductor laser element. Therefore, the light output unit 100 emits the basic laser light 300 using a semiconductor laser element that is driven by high-frequency superposition.

  The collimator lens 122 outputs the laser light from the LD chip 121 as parallel light. The heat sink 123 diffuses the heat generated by the LD chip 121.

  The high-frequency LD driver power source 112 is a drive unit for the LD chip 121, performs high-frequency superposition driving of the LD chip 121 of the LD modules 111A to 111C, and emits laser beams 301A to 301C from the LD chip 121 of the LD modules 111A to 111C. Let

  FIG. 3 is a circuit diagram showing the configuration of the high frequency LD driver power supply 112. In FIG. 3, the high frequency LD driver power source 112 includes a current source V0, a high frequency power source Vrf, and an LC resonance circuit including a coil L and a capacitor Cn.

  The current source V0 generates a drive current for the LD modules 111A to 111C. The high frequency power supply Vrf generates a high frequency component. The LC resonance circuit superimposes a high-frequency component on the drive current, thereby converting the drive current into a high-frequency superimposed current and supplying it to the LD chips 121 of the LD modules 111A to 111C. In the present embodiment, the frequency of the high frequency superimposed current is about 300 MHz to 600 MHz.

  The high-frequency LD driver power supply 112 periodically changes the current value of the high-frequency superimposed current within a range from a first value smaller than the threshold current of the LD chip 121 to a second value larger than the threshold current. As a result, the carrier density inside the LD chip 121 fluctuates and relaxation vibration occurs in the LD chip 121, so that the wavelength of the laser light output from the LD chip 121 fluctuates. For this reason, the wavelength band of the laser beams 301A to 301C can be widened.

  Further, if the high frequency LD driver power supply 112 stops outputting the high frequency superimposed current at the end of one period of the relaxation oscillation, the high frequency LD driver power source 112 has a time width determined from the LD chip 121 according to the maximum value of the relaxation oscillation frequency. Optical pulses can be output as laser light. Thereby, the optical output power of the laser beam from the LD chip 121 can be increased. In general, when an LD chip outputs an optical pulse as laser light, it can output laser light having an optical output power of about 1 W to 2 W.

  In this case, since the optical output power of the laser beams 301A to 301C can be increased, the optical output power of the output laser beam 400 emitted from the laser light source can be increased. Moreover, since the temperature rise of the LD chip 121 can be reduced, the wavelength stability of the laser beams 301A to 301C can be improved.

  Returning to the description of FIG. The temperature control unit 113 measures the temperature of the LD chip 121 in the LD modules 111A to 111C and adjusts the temperature of the heat sink 123 in the LD modules 111A to 112C so that the temperature becomes constant.

  The reflecting mirror 114 reflects the laser beam 301B from the LD module 111B and enters the dichroic mirror 116. The reflecting mirror 115 reflects the laser beam 301C from the LD module 111C and enters the dichroic mirror 117.

  The dichroic mirrors 116 and 117 have a wavelength-dependent transmittance and transmit only light in a specific wavelength band.

  FIG. 4 is a diagram showing the relationship between the transmittance of the dichroic mirrors 116 and 117 and the wavelength. As shown in FIG. 4, the transmittance of the dichroic mirror 116 is approximately 1 below the wavelength λa, sharply decreases in the range from the wavelength λ to λa + Δ, and approximately 0 above the wavelength λa + Δ. On the other hand, the transmittance of the dichroic mirror 117 is approximately 1 below the wavelength λa + Δ, sharply decreases in the range from the wavelength λa + Δ to λa + 2Δ, and approximately 0 above the wavelength λa + 2Δ.

  Returning to the description of FIG. The dichroic mirror 116 combines the laser light transmitted through the dichroic mirror 116 in the laser light 301A and the laser light reflected by the dichroic mirror 116 in the laser light 301B so that the optical axes thereof coincide with each other. The mirror 117 is arranged so as to be emitted as laser light 302. Further, the dichroic mirror 117 combines the laser light transmitted through the dichroic mirror 117 in the laser light 302 and the laser light reflected by the dichroic mirror 117 in the laser light 301C so that the optical axes thereof coincide with each other. The half-wave plate 118 is arranged so as to be emitted as the basic laser beam 300. Thereby, the basic laser beam 300 becomes a laser beam having the laser beams 301A to 301C. Moreover, since the wavelength bands of the laser beams 301A to 301C are separated, the wavelength band of the basic light is separated.

  In the present embodiment, the polarization direction of the basic laser light 300 is the horizontal direction.

  The half-wave plate 118 is arranged so that the delay axis is inclined 45 degrees with respect to the polarization direction of the basic laser light 300. As a result, the half-wave plate 118 converts the polarization direction of the basic laser beam 300 into the vertical direction and emits it to the wavelength conversion unit 101.

  The wavelength conversion unit 101 includes an element support 131, a temperature control unit 132, a condenser lens 133, an outgoing light adjustment lens 134, and a polarization inversion wavelength conversion element 200. The element support 131 is disposed on the substrate 50, and the temperature controller 132, the condenser lens 133, the outgoing light adjustment lens 134, and the polarization inversion wavelength conversion element 200 are disposed on the element support 131.

  The temperature control unit 132 has a heat sink. The temperature control device 132 measures the temperature of the polarization inversion wavelength conversion element 200 and adjusts the temperature of its own heat sink so that the temperature becomes constant.

  The condensing lens 133 may be called a 1st condensing part. The condensing lens 133 condenses the basic laser light 300 so that the minimum value d of the diameter of the basic laser light 300 in the polarization inversion wavelength conversion element 200 is included in a desired range. Incident on the incident surface. The desired range is desirably 50 μm ≦ d ≦ 500 μm, and more desirably 70 μm ≦ d ≦ 150 μm.

  The polarization inversion wavelength conversion element 200 is an SHG element formed of a PPLN crystal having a periodic polarization inversion structure. In the periodically poled structure, a plurality of domains in which two dielectric regions having opposite polarization directions are arranged in parallel are arranged. The length of the domain is called a polarization inversion period (domain pitch) of the periodic polarization inversion structure.

In addition, the PPLN crystal that is the polarization inversion wavelength conversion element 200 is formed of LN (LiNbO ₃ : lithium niobate) in the present embodiment. However, the PPLN crystal is not limited to LN but may be formed of various ferroelectric materials having a periodically poled structure. For example, the PPLN crystal may be formed of LT (LiTaO ₃ : lithium tantalate), KTP (KTiOPO ₄ : potassium titanate phosphate), KN (KNbO ₃ : potassium niobate), or the like.

  The polarization inversion wavelength conversion element 200 converts the wavelength band of the basic laser light 300 incident via the condenser lens 133 and outputs the converted laser light as the output laser light 400 to the emission light adjusting lens 134. In the present embodiment, the output laser light 400 is assumed to be green laser light.

  The emitted light adjusting lens 134 emits the output laser light 400 emitted from the polarization inversion wavelength conversion element 200 as parallel light.

  Next, the polarization inversion wavelength conversion element 200 will be described in detail.

  FIG. 5 is a diagram showing the configuration of the polarization inversion wavelength conversion element 200. In FIG. 5, the polarization inversion wavelength conversion element 200 has an incident surface 201, a polarization inversion structure portion 202, and an exit surface 203.

  The basic laser beam 300 is incident on the incident surface 201.

  In the domain-inverted structure 202, a plurality of periodic domain-inverted regions (hereinafter simply referred to as regions) having a domain-inverted structure are arranged in parallel.

  Each region converts each wavelength of a plurality of fundamental waves, which are a plurality of wavelength components separated from each other in the fundamental laser light 300, and outputs each of a plurality of converted waves separated from each other in the wavelength band. To do. In addition, it is desirable that the difference in the median values of the wavelength bands adjacent to each other among the wavelength bands of the fundamental wave whose wavelength is converted in each region is equal. In addition, among the wavelength bands in which the wavelengths are converted in each region, it is preferable that the difference δ between the adjacent wavelength bands satisfies 0.5 μm ≦ δ ≦ 2 μm, and 0.8 μm ≦ δ ≦ 1. It is further desirable to satisfy 5 μm.

  More specifically, the polarization inversion period of each region is determined according to the wavelength band of each fundamental wave so that each fundamental wave and the second harmonic of each fundamental wave satisfy the quasi phase matching condition.

  In the region, if the fundamental wave and the second harmonic satisfy the quasi phase matching condition, the electric field component of the fundamental wave parallel to the polarization direction of the domain-inverted structure can be converted into the second harmonic and emitted. It becomes possible. Accordingly, each region converts each wavelength of the fundamental wave included in the fundamental laser beam, and emits a plurality of second harmonics separated from each other in wavelength band as converted waves. Hereinafter, the converted wave will be described as the second harmonic.

FIG. 6 is a diagram showing the relationship between the wavelength of the fundamental wave and the polarization inversion period when the fundamental wave and the second harmonic satisfy the quasi-phase matching condition. FIG. 6 further shows the relationship between the wavelength of the fundamental wave and the refractive index of the PPLN crystal that is the domain-inverted structure 202.
The refractive index is represented by a solid line, and the polarization inversion period is represented by a dotted line.

  Since the polarization inversion period and the refractive index change according to the temperature, when the temperature of the polarization inversion wavelength conversion element 200 changes, the conversion efficiency for converting the fundamental wave to the second harmonic decreases, and the output laser light 400 The optical output power may be low. In the present embodiment, as described above, the temperature control unit 132 adjusts the temperature of the polarization inversion wavelength conversion element 200 to be constant, thereby suppressing a decrease in the optical output power of the output laser light 400 due to a temperature change. FIG. 6 shows the relationship between the wavelength of the fundamental wave and the polarization inversion period at about room temperature (20 ° C.).

  Returning to the description of FIG. In the present embodiment, the domain-inverted structure 202 has three regions D1 to D3 as periodic domain-inverted regions.

  The emission surface 203 emits output laser light 400 including three second harmonics converted in the regions D1 to D3. In the output laser beam 400, the three second harmonics are aligned on the same optical axis.

  Next, an example of a method for manufacturing the polarization inversion wavelength conversion element 200 will be described.

  First, an LN substrate formed of LN is prepared. More specifically, an LN substrate formed of a Z-cut LN having a thickness of 2 mm and an MgO addition concentration of 5 mol% is prepared. Since the LN substrate has a large nonlinear optical constant, the polarization inversion wavelength conversion element 200 with high wavelength conversion efficiency can be realized. Further, the composition of the LN substrate may be a congruent composition that is a coincidence melting composition or a stoichiometric composition that is a stoichiometric composition.

  Subsequently, an electrode for forming a domain-inverted structure in the LN substrate is formed on the surface of the LN substrate.

More specifically, one of the surfaces in the thickness direction of the LN substrate (hereinafter referred to as the + Z plane) is near the room temperature (20 to 60 ° C.) with respect to a laser beam having a wavelength of 1064 nm, which is a fundamental wave. Comb electrodes are formed with a period of about 7 μm so that quasi phase matching occurs. For example, a Ta thin film (100 nm thickness) and a SiO ₂ thin film (200 nm thickness) are formed by vapor deposition on the + Z plane, and these films are exposed using a photolithography technique to form a comb-shaped electrode.

  Further, a solid electrode is formed on the surface of the LN substrate facing the + Z plane (hereinafter referred to as the −Z plane).

  Thereafter, a high voltage power source is connected to the comb-shaped electrode and the solid electrode, and the LN substrate is set to 140 ° C. so that the potential on the + Z plane becomes positive and the potential on the −Z plane becomes negative. Then, using a high-voltage power supply, a voltage pulse having a voltage equal to or higher than the coercive voltage of the LN substrate (for example, 10 kV) is applied to the LN substrate to form a periodically poled structure on the LN substrate. When a voltage higher than the coercive voltage is applied to the LN substrate, the spontaneous polarization in the LN substrate can be aligned with the direction of the electric field.

  Further, a portion of a predetermined length is cut out from the LN substrate, and both end faces thereof are optically polished to form a polarization inversion wavelength conversion element.

  Then, one of the surfaces perpendicular to the ± Z plane of the polarization inversion wavelength conversion element is used as the incident surface 201, and the incident surface 201 is coated with a dielectric film that functions as an antireflection film for reducing the reflection of the basic laser light 300. To do. As the dielectric film of the incident surface 201, for example, a dielectric film having a reflectance of 0.2% or less with respect to laser light with a wavelength of 1064 nm and a reflectance of 90% or more with respect to laser light with a wavelength of 530 nm is used. .

  In addition, the other surface perpendicular to the ± Z plane of the polarization inversion wavelength conversion element is used as the emission surface 202, and the emission surface 202 functions as an antireflection film for reducing the reflection of the output laser beam 400. The polarization inversion wavelength conversion element 200 is produced by coating with As the dielectric film on the emission surface 202, a dielectric film having a reflectance of 0.2% or less with respect to 530 nm laser light is used.

  A portion of the polarization inversion wavelength conversion element manufactured using the above manufacturing method is immersed in a mixed solution having a ratio of hydrofluoric acid and nitric acid of 1: 3 to perform selective etching, and then a cross section is observed with an electron microscope. As a result, the polarization inversion ratio of the LN substrate substantially coincided with the ideal value of 50%.

  In addition, the manufacturing method of the polarization inversion wavelength conversion element 200 is not limited to the above example, and can be changed as appropriate.

  Next, the polarization inversion wavelength conversion element 200 will be described in more detail.

  FIG. 7 is an external view of the polarization inversion wavelength conversion element 200. In FIG. 7, the polarization inversion wavelength conversion element 200 includes an incident surface 201, a polarization inversion structure 202, an exit surface 203, and dielectric films 201A and 203A. The polarization inversion wavelength conversion element 200 is disposed on the heat sink 132A of the temperature control unit 132.

  Further, FIG. 7 shows an upper dielectric polarization region 202A and a lower dielectric polarization region 202B, which are dielectric regions constituting the domain of the domain-inverted structure 202.

  The polarization direction of the upward dielectric polarization region 202A is upward in the vertical direction, and the polarization direction of the downward dielectric polarization region 202B is downward in the vertical direction.

  As described above, since the second harmonic is generated from an electric field component parallel to the polarization direction of the fundamental wave, the polarization direction of the fundamental wave and the polarization direction of the domain-inverted structure 202 are the same. The conversion efficiency for converting the fundamental wave to the second harmonic becomes the highest. In this embodiment, since the polarization direction is the vertical direction, the polarization direction of the basic laser light 300 is set to the vertical direction using the half-wave plate 118.

  The dielectric film 201A is formed on the incident surface. In the dielectric film 201A, the light transmittance in the wavelength band of the basic laser light 300 is high, and the light transmittance in the wavelength band of the output laser light 400 is low. Therefore, the dielectric film 201 </ b> A functions as an antireflection film that reduces reflection of the basic laser light 300. The dielectric film 201A is an example of a first antireflection film.

  The dielectric film 203A is formed on the emission surface. In the dielectric film 203A, the light transmittance in the wavelength band of the basic laser light 300 is low, and the light transmittance in the wavelength band of the output laser light 400 is high. Therefore, the dielectric film 203A functions as an antireflection film that reduces reflection of the output laser light 400. The dielectric film 203A is an example of a second antireflection film.

  FIG. 8 is a diagram showing a more detailed configuration of the polarization inversion wavelength conversion element. In FIG. 8, the regions D1 to D3 in the domain-inverted structure 202 are shown. The interaction lengths of the regions D1 to D3 are L1 to L3. The interaction length is a length along the traveling direction of the basic laser beam 300.

  In each of the regions D1 to D3, a plurality of subregions that convert wavelengths included in each of a plurality of subwavelength bands obtained by dividing the wavelength band of the fundamental wave that converts the wavelength itself are arranged in parallel. In the present embodiment, each of the regions D1 to D3 has three subregions. More specifically, the region D1 has sub-regions D11 to D13, the region D2 has sub-regions D21 to D23, and the region D3 has sub-regions D31 to D33.

The interaction lengths of the subregions D11 to D13 are L11 to L13, the interaction lengths of the subregions D21 to D23 are L21 to L23, and the interaction lengths of the subregions D31 to D33 are L31. ~ L33. In the present embodiment, it is assumed that the interaction lengths L11 to L33 of each sub-region are all L ₀ = 13 mm.

  In the sub-regions D11 to D33, the n wavelength components included in each of the plurality of sub-wavelength bands obtained by dividing the wavelength band of the fundamental wave in which the region including the sub-region is converted are converted.

In the following, the sub fundamental wavelengths, which are the median values of the wavelength bands of the fundamental waves converted in the sub-regions D11 to D13, are denoted by λ _D1 = 1.06000 μm, λ _D2 = 1.06015 μm, and λ _D3 = 1.06030 μm. The sub fundamental wavelengths converted in the sub-regions D21 to D23 are λ _D4 = 1.06105 μm, λ _D5 = 1.06120 μm, and λ _D6 = 1.06135 μm, and are converted in the sub-regions D31 to D33. The sub fundamental wavelengths are λ _D7 = 1.06210 μm, λ _D8 = 1.06225 μm, and λ _D9 = 1.06240 μm.

  Further, the polarization inversion periods of the sub-regions D11 to D13 are determined so that the fundamental wavelength converted in the sub-region satisfies the quasi phase matching condition from the relationship between the wavelength and the polarization inversion period shown in FIG. .

  Here, the second harmonic converted in the sub-region will be described.

Assuming that the traveling direction of the fundamental laser light is the L direction, when the polarization inversion wavelength conversion element is a single conversion element having a single polarization inversion period, the electric field intensity distribution E ⁽² ω ⁾ ( L) is the differential equation

It is represented by Where i is the imaginary unit, ω is the angular frequency of the fundamental wave, μ is the permeability of the PPLN crystal forming the subregion, ε is the dielectric constant of the PPLN crystal, d _eff is the effective nonlinear optical constant of the PPLN crystal, E ⁽ ω ⁾ (L) is the electric field strength of the fundamental wave. Further, .DELTA.k (lambda) is twice the fundamental wave of the wave number k of wavelength lambda ^(omega), the difference in wave number k of the second harmonic ^{(2 omega),} using the wavelength of the fundamental wave lambda,

It is expressed as Note that n ₀ (λ) is the normal light refractive index of the PPLN crystal in the light of wavelength λ, and using the Selmeier dispersion formula,

It is represented by In addition, the polarization inversion period Λ when quasi phase matching occurs is a function of the fundamental wavelength λ,

It is expressed as

  Solving the differential equation shown in Equation 1,

It becomes. Note that when the conversion from the fundamental wave to the second harmonic occurs, the electric field strength of the fundamental wave decreases, but the conversion efficiency is very small, so the calculation was performed assuming that the electric field strength of the fundamental wave does not change. That is, the electric field intensity E ⁽ ω ⁾ (L) of the fundamental wave is set as a constant E ⁽ ω ⁾ .

From Equation 5, the spectrum conversion function f (λ, λ ₀ , L ₀ ) representing the spectrum (electric field strength) of the second harmonic is

It is expressed as Since the light intensity is the square of the absolute value of the electric field intensity, the light intensity conversion function F ₀ representing the light intensity of the second harmonic is

It becomes. Therefore, the optical output power P ₀ of the second harmonic is

It becomes. Here, S is the cross-sectional area of the PPLN crystal, P is the optical output power of the fundamental wave, c is the speed of light, and ε ₀ is the dielectric constant of vacuum. As shown in Equation 6, the optical output power P ₀ of the second harmonic is proportional to the square of the interaction length L ₀ of the sub-region and proportional to the square of the optical output power P of the fundamental wave. is doing.

  In addition, when the polarization inversion wavelength conversion element has N + 1 sub-regions, it can be considered that N + 1 single conversion elements are arranged in parallel. Therefore, the electric field intensity of the output laser light from the polarization inversion wavelength conversion element is Sum of field strengths of second harmonics transformed in the region

It is represented by Note that the converted wavelength of the second harmonic converted in each sub-region is λ _k (k = 0, 1, 2,... N), and the interaction length of each sub-region is L _k . More specifically, in order from the sub-region closer to the incident surface 201, the converted wavelengths of the second harmonics converted in the sub-region are λ ₀ , λ ₁ ... Λ _N, and the interaction length of the sub-region is L ₀ , L ₁ ... L _N.

Therefore, the spectrum conversion function F (λ, {λ _k }, {L _k }) of the polarization inversion wavelength conversion element is

It is expressed. As shown in Equation 10, the spectral conversion function is an interference factor representing the second harmonic interference generated in each sub-region.

Have For this reason, since the electric field strength of each second harmonic in the output laser light is subject to interference of other second harmonics, the electric field strength of the output laser light is easily affected by the wavelength variation of the fundamental wave, The optical output power of the output laser beam becomes unstable. Hereinafter, the spectral conversion function of each sub-region including the interference factor is assumed to be F _k . That means

And

The spread width Δλ on one side of the spectrum indicated by the spectral conversion function F _k of each sub-region depends on the interaction length L _k . The relationship between the spread width Δλ and the interaction length L _k is such that the spectral conversion function F _k becomes zero.

From

It is expressed as That is, the interaction length L and the spread width Δλ are inversely proportional to each other. If the conversion wavelength interval Δλ _k = λ _k −λ _k−1, which is the difference between the conversion wavelengths λ _k of the second harmonics converted in the sub-regions adjacent to each other, is sufficiently large from this spread width, conversion is performed in each sub-region. The interference of the generated second harmonic can be ignored. That means

If so, the interference of the second harmonic generated in each sub-region can be ignored. For example, since the spread width Δλ when the interaction length L ₀ = 10 mm at which the second harmonic wave has sufficient light intensity is 0.13 nm, each conversion wavelength interval satisfies Δλ _k >> 0.13 nm. The second harmonic interference generated in the sub-region can be ignored.

  In this case, the spectral conversion function F is

It becomes. Therefore, the spectrum conversion function F of the polarization inversion wavelength conversion element is the sum of the spectrum conversion functions F _k of each sub-region, and it can be considered that the second harmonics generated in each sub-region are independent from each other. In this case, the optical output power of the output laser light is relatively stable with respect to the wavelength variation of the fundamental wave. According to the experiment, when the interaction length L ₀ = 10 mm, the interference of the second harmonic converted in each sub-region can be ignored if the interval Δλ _k > 0.5 nm of the conversion wavelength λ _k is satisfied, It can be considered that those second harmonics are independent of each other.

In FIG. 8, the interaction length L ₀ of each sub-region is set to 13 mm as described above so that the spread width on one side of the spectrum of the second harmonic converted in each sub-region is 0.15 nm. Yes.

  FIG. 9 is a diagram showing the relationship between the wavelength conversion efficiency of the polarization inversion wavelength conversion element 200 and the wavelength of the fundamental wave.

  As shown in FIG. 9, in the polarization inversion wavelength conversion element 200, wavelength conversion windows W1 to W3 corresponding to the regions D1 to D3 are formed. The wavelength conversion window is a wavelength band of basic light converted in each region.

  The widths of the wavelength conversion windows W1 to W3 are all 0.45 μm. The difference between the fundamental wavelengths, which are the center wavelengths of the wavelength conversion windows W1 and W2, is λD5−λD2 = 1.06120 μm−1.06015 μm = 1.05 nm, and the difference between the fundamental wavelengths of the wavelength conversion windows W2 and W3 is λD8−λD5 = 1.06225 μm−1.06 120 μm = 1.05 nm. Therefore, in the polarization inversion wavelength conversion element 200, the wavelength conversion windows W1 to W3 having an interval of 1.05 nm are formed.

  In each of the wavelength conversion windows W1 to W3, if the wavelength conversion efficiency of the fundamental wave in the wavelength conversion window is constant, the optical output power of the converted wave does not change much even if the wavelength of the fundamental wave changes somewhat. That is, stable output laser light can be obtained with respect to the wavelength change of the basic laser light 300. Hereinafter, a wavelength conversion window having a constant wavelength conversion efficiency is referred to as a flat window.

In order to make the wavelength conversion window corresponding to each of the regions D1 to D3 flat, the converted wavelength λ _k of the outgoing light converted in the sub-region within the region is converted into the spectral conversion of the sub-region adjacent to the sub-region. What is necessary is just to set to the wavelength from which the function F _k-1 becomes zero. Therefore, when the incident laser beam is in the 1060 nm band, the conversion wavelength interval Δλ _k and the interaction length L ₀ are

If this condition is satisfied, the wavelength conversion windows corresponding to the regions D1 to D3 can be made flat.

FIG. 10 is a diagram showing the relationship between the interaction length L ₀ and the conversion wavelength interval Δλ _k when the wavelength conversion window is a flat window. In FIG. 10, a round dot is a point where the flat window calculated | required from simulation was obtained. The relationship between the interaction length L ₀ and the conversion wavelength interval Δλ _k shown in FIG. 10 matches the relationship between the interaction length L ₀ and the conversion wavelength interval Δλ _k shown in Equation 17. Note that the number of sub-regions does not affect the condition for obtaining a flat window.

Each of FIG. 11 to FIG. 13 is a diagram showing the wavelength dependence of the wavelength conversion efficiency in a region where the number of sub-regions is nine. In each of FIGS. 11 to 13, the interaction lengths of the sub-regions are 12 mm, 13 mm, and 14 mm. Further, the conversion wavelength interval Δλ _{k is set} to 0.15 nm.

Even if the number of sub-regions is 9 as shown in FIGS. 11 to 13, when the conversion wavelength interval Δλ _k is 0.15 nm, a flat window can be obtained only when the interaction length is 13 mm. .

  14 and 15 are diagrams showing the wavelength conversion spectrum of the polarization inversion wavelength conversion element. More specifically, FIG. 14 shows a wavelength conversion spectrum of a polarization inversion wavelength conversion element having nine wavelength conversion windows with an interaction length of 10 mm and a conversion wavelength interval of 1.0 nm, and FIG. The wavelength conversion spectrum of a polarization inversion wavelength conversion element having nine wavelength conversion windows with an interaction length of 10 mm and a conversion wavelength interval of 0.5 nm is shown.

  As shown in FIGS. 14 and 15, when the conversion wavelength interval is narrow, a flat window cannot be obtained, the light intensity of the second harmonic is reduced, and the speckle of the projected image by the output laser light is increased. . This is due to the influence of the interference factor of the spectral conversion function. In this embodiment, in order to reduce speckles, the wavelength interval is preferably 0.5 nm or more, and more preferably 1 nm or more.

  Next, speckle contrast will be described.

We have conducted detailed research on speckle. In general, the speckle contrast of multiple laser beams obtained by combining multiple single-wavelength laser beams with different wavelengths on the same optical axis is the wavelength λ _{k of the} multiple laser beams. Is a _k (k = 1, 2... N), the speckle pattern correlation function Cor (λk, λi) is used.

I realized that I can express it. C ₀ is the speckle contrast of the single wavelength laser beam. Furthermore, we have found from experiments that the correlation function can be expressed as an exponential function. Therefore, the speckle contrast of the multiple laser light is

It is expressed as Here, μ is called a wavelength correlation length. The wavelength correlation length generally depends on the wavelength of the single wavelength laser beam. As shown in Equation 19, when the wavelength correlation length is doubled, the value of the correlation function is 1 / e ² times.

  As the wavelength interval of the single-wavelength laser light included in the multiple laser light increases, the correlation between the single-wavelength laser lights decreases, so that the speckle pattern of the multiple laser light is averaged and the speckle contrast is reduced. In the limit where the wavelength correlation length is low, the speckle contrast of multiple laser light is

It becomes. As shown in Expression 20, when the light intensity of the multiple laser light is made constant, the speckle contrast becomes minimum when the light intensities of the single wavelength laser lights are all equal.

On the other hand, in the extreme correlation length is large, the C = C _0. This means that even if the single wavelength laser light is emitted from different light sources, the speckle contrast cannot be reduced if the wavelength is the same.

  Further, as the wavelength of the single wavelength laser beam becomes longer, the wavelength correlation length becomes longer. The reason why the wavelength correlation length is increased when the wavelength is large is that when the wavelength is large, speckle patterns are difficult to be averaged because the speckle spots are increased.

  There are two single-wavelength laser lights in the multiple laser light, the light intensity of each single-wavelength laser light is halved for both a1 and a2, and the wavelength difference of the single-wavelength laser light is δλ. Le Contrast C

It becomes. Therefore, the change rate ΔC / C ₀ of the speckle contrast of the multiple laser light and the speckle contrast of the single wavelength laser light is

It is expressed as The wavelength correlation length is obtained by comparing Equation 22 with the experimental results. The wavelength correlation length obtained in this way is not limited to the case where there are two single-wavelength laser beams, but is the same value for general multiple laser beams.

FIG. 16 is a diagram showing the relationship between the speckle contrast change rate ΔC / C ₀ and the wavelength difference δλ. FIG. 16 shows the relationship between the speckle contrast change rate ΔC / C ₀ and the wavelength difference δλ when the frequency bands of the multiplexed laser light are the 1062 nm band, the 660 nm band, the 630 nm band, and the 402 nm band, respectively. Note that when the frequency band of the green multiple laser light is the 530 nm band, the wavelength correlation length μ is about 0.23 μm.

  As shown in FIG. 16, in the case of the green multiple laser light, when the wavelength difference δλ is 0.25 nm or more, the correlation between the two single-wavelength laser lights in the multiple laser light is reduced, and the speckle contrast is reduced. Decrease. In particular, when the wavelength difference δλ is 0.5 nm or more, the reduction rate of speckle contrast increases.

As explained above, green laser light with low speckle
1. Multiple single-wavelength laser beams with separate wavelength bands are multiplexed (that is, having multiple wavelength peaks)
2. The wavelength difference between the wavelength peaks of the single-wavelength laser beams needs to be 0.25 nm or more (more desirably, 0.5 nm or more). Furthermore, the green laser light is
3. 3. The wavelength difference of each wavelength peak is all equal. If the wavelength intensity distribution of each single wavelength laser beam is satisfied, speckle can be further reduced.

  In order to emit green laser light satisfying the above conditions as output laser light 400 from the polarization inversion wavelength conversion element 200, the basic laser light 300 needs to have a wavelength twice that of the green laser light. The difference between the fundamental wavelengths of the fundamental waves in the fundamental laser beam 300 needs to be 0.5 nm or more (more desirably 1 nm or more). Further, since the wavelength band of the green laser light is 520 nm to 540 nm, when the wavelength difference of each wavelength peak of the green multiple laser light is 0.5 nm or more, the number of wavelength peaks is 40 or less. As described above, since the wavelength band is limited, it is possible to effectively reduce speckle by equalizing the wavelength difference between the wavelength peaks.

  The polarization inversion wavelength conversion element 200 converts each of a plurality of incident lights included in a range of 1.040 μm to 1.080 μm into second harmonics. In the polarization inversion wavelength conversion element 200, 1. A plurality of wavelength conversion windows are formed; 2. 2. the difference between the central wavelengths of the wavelengths of the wavelength conversion windows is about 1 nm; The differences in the center wavelengths are all equal.

  Therefore, the polarization inversion wavelength conversion element 200 converts a plurality of incident lights having a wavelength included in the range of 1.040 μm to 1.80 μm to 1. 1. has a plurality of wavelength peaks; 2. the wavelength difference of each wavelength peak is 0.5 nm or more; All of the wavelength differences at the respective wavelength peaks can be converted into outgoing light. In the domain-inverted wavelength conversion element 200, since the interaction lengths of the sub-regions are the same, the light intensity of the light beams emitted from the LD modules 111A to 111C can be made equal to obtain the wavelength intensity distribution of the emitted light. It can be made uniform.

  Therefore, by using the polarization inversion wavelength conversion element 200, green laser light with low speckle can be obtained.

  FIG. 17 is a diagram for comparing the wavelength conversion spectrum of the polarization inversion wavelength conversion element that forms a single wavelength conversion window and the wavelength conversion spectrum of the polarization inversion wavelength conversion element 200 that forms a plurality of wavelength conversion windows. is there.

  In FIG. 17, the interaction length of each sub-region of the polarization inversion wavelength conversion element 200 is 7 mm. There are nine wavelength conversion windows at 1 nm intervals. The element length of the polarization inversion wavelength conversion element 200 is 63 mm. In this case, a wavelength width of 8 nm is obtained. On the other hand, the conventional polarization inversion wavelength conversion element requires a wavelength conversion region for 28 wavelengths, and the element length is 196 mm.

  Therefore, the element length of the polarization inversion wavelength conversion element 200 can be shortened conventionally. In the conventional polarization inversion wavelength conversion element, since the element length is long, it is difficult to manufacture the polarization inversion wavelength conversion element from a single LN substrate. However, in the polarization inversion wavelength conversion element 200, it is also easy. .

  The green laser beam was scanned at a horizontal scanning frequency of 10 kHz and a vertical scanning frequency of 60 Hz using a MEMS (Micro Electro Mechanical Systems) mirror and projected onto the diffusion plate. The speckle pattern of the scanned image reflected on the diffuser was photographed with a CMOS camera simulating the optical structure of the human eye, and the image was processed to obtain the speckle contrast. When the green laser beam is a single wavelength laser beam, the speckle contrast of the scanned image was 25%.

  When the high-frequency LD driver power source 112 is not performing high-frequency superposition driving, the spectrum of the basic laser light 300 is the spectrum shown in FIG. 18, and the spectrum of the output laser light 400 is the spectrum shown in FIG.

  In this case, the speckle contrast of the scanned image by the output laser beam 400 from the polarization inversion wavelength conversion element 200 was 14.4%. Therefore, the reduction rate of speckle contrast is 42%.

  When the high frequency LD driver power source 112 performs high frequency superposition driving, the spectrum of the output laser beam 400 is the spectrum shown in FIG. In this case, the speckle contrast of the scanned image by the output laser beam 400 was 12.5%. Therefore, the reduction rate of speckle contrast is 50%.

  FIG. 21 is a diagram showing a spectrum of output laser light from a single conversion element. Laser light generated by high frequency superposition driving is incident on the wavelength conversion element.

  In this case, the speckle contrast of the scanned image by the laser beam output from the single conversion element was 20%. Therefore, the reduction rate of speckle contrast was as low as 20%.

  According to this embodiment, in the domain-inverted structure 202, regions D1 to D3 having domain-inverted structures are arranged in parallel. Of the fundamental laser light 300 incident on the incident surface 201, the wavelength of each of the plurality of fundamental waves separated in wavelength band is converted, and each of the plurality of converted waves separated in wavelength band is emitted. Further, the output laser beam 400 including the converted wave emitted from each region of the domain-inverted structure 202 is emitted from the emission surface 202.

  In this case, the wavelengths of the plurality of fundamental waves separated from each other in the regions D1 to D3 are converted, and each of the plurality of converted waves separated from the wavelength band is emitted. Then, an output laser beam 400 including those converted waves is emitted. For this reason, it is possible to sufficiently reduce the speckle contrast while emitting the output laser beam 400 having a high optical output power.

In the present embodiment, in the regions D1 to D3, three subregions for converting the fundamental wave included in each of the three subwavelength bands obtained by dividing the wavelength band of the fundamental wave to which the wavelength is converted into three. Are placed side by side. Further, the interaction length {L _k [mm]} of each sub-region and the conversion wavelength interval {Δλ _k }, which is the median interval between adjacent sub-wavelength bands, satisfy Expression 17.

  In this case, since the wavelength conversion efficiency in each region can be made constant, it is possible to reduce the deterioration of the optical output power of the output laser beam 400 due to the wavelength change of the basic laser beam 300.

  Moreover, in this embodiment, the difference of the median value of the mutually adjacent wavelength band is equal among the wavelength bands of the fundamental wave in which the wavelength is converted in each of the regions D1 to D3. In this case, the speckle reduction rate can be further increased.

  In the present embodiment, among the wavelength bands in which wavelengths are converted in each region, the difference δ between the median values of adjacent wavelength bands is 0.5 μm ≦ δ ≦ 2 μm or 0.8 μm ≦ δ ≦. Fills 1.5 μm. In this case, the correlation between the second harmonics in the output laser beam 400 can be lowered, and the speckle reduction rate can be further increased.

  Next, a second embodiment of the present invention will be described.

  FIG. 22 is a block diagram showing the configuration of the laser light source of this embodiment. In FIG. 22, in the laser light source, the light output unit 100 further includes an LD module 111D and a reflecting mirror 119 in addition to the configuration shown in FIG. The laser light source includes a dichroic mirror 115A instead of the reflecting mirror 115, and a polarization inversion wavelength conversion element 500 that is a waveguide type polarization inversion wavelength conversion element instead of the polarization inversion wavelength conversion element 200.

  The LD module 111D has the same configuration as the LD modules 111A to 111C. The LD module 111 </ b> D emits laser light 301 </ b> D corresponding to high frequency superposition driving performed by the high frequency LD driver power source 112.

  The reflecting mirror 119 reflects the laser beam 301D from the LD module 111D and enters the dichroic mirror 115A.

  The dichroic mirror 115A has a wavelength-dependent transmittance similar to the dichroic mirrors 116 and 117. More specifically, the transmittance of the dichroic mirror 115A is approximately 1 below the wavelength λa + 2Δ, sharply decreases in the range from the wavelength λa + 2Δ to λa + 3Δ, and approximately 0 above the wavelength λa + 3Δ.

  The dichroic mirror 115A is a dichroic mirror in which the laser light transmitted through the dichroic mirror 115A in the laser light 301D and the laser light reflected by the dichroic mirror 115A in the laser light 301C are combined so that their optical axes coincide. 117 is arranged to be emitted as laser light 303. The dichroic mirror 117 combines the laser light transmitted through the dichroic mirror 117 in the laser light 302 and the laser light reflected by the dichroic mirror 117 in the laser light 303 so that the optical axes thereof coincide with each other. The half-wave plate 118 is arranged so as to be emitted as the basic laser beam 300. For this reason, in this embodiment, the basic laser light 300 has four wavelength peaks.

  FIG. 23 is an external view of the polarization inversion wavelength conversion element 500. 23, in addition to the configuration shown in FIG. 7, the polarization inversion wavelength conversion element 500 further includes a waveguide 501 for confining and propagating the basic laser light 300 in a space having a predetermined cross-sectional area. The waveguide 501 is formed in the domain-inverted structure 202.

  If the width of the waveguide 501 is smaller than 4 μm, the optical coupling efficiency for guiding the basic laser light 300 to the waveguide 501 is lowered, and further, the PPLN crystal forming the polarization inversion wavelength conversion element 500 is likely to be damaged by light. Become. In addition, when the width of the waveguide 501 is larger than 6 μm, the second harmonic generated in the polarization inversion wavelength conversion element 500 tends to be multimode. Therefore, the width of the waveguide 501 is desirably 4 μm to 6 μm.

  FIG. 24 is a diagram showing a configuration of the polarization inversion wavelength conversion element 500. In FIG. 5, the domain-inverted wavelength conversion element 500 includes an incident surface 201, a domain-inverted structure 202, an exit surface 203, and a waveguide 501.

  In the present embodiment, the domain-inverted structure 202 has regions D1 to D4. Each of the regions D1 to D4 has three subregions as in the first embodiment.

Hereinafter, each of the sub-regions of the region D4 is referred to as sub-regions D41 to D43. The interaction length of the region D4 is L4, and the interaction lengths of the subregions D41 to D43 are L41 to L43. In addition, it is assumed that the interaction lengths L11 to L43 of the respective sub-regions are all equal and L ₀ = 13 mm.

Further, the fundamental wavelengths converted in the sub-regions D11 to D13 are set to λ _D1 = 1.06000 μm, λ _D2 = 1.06015 μm, and λ _D3 = 1.06030 μm, as in the first embodiment. The fundamental wavelengths converted in the regions D21 to D23 are set to λ _D4 = 1.06105 μm, λ _D5 = 1.06120 μm, and λ _D6 = 1.06135 μm, as in the first embodiment. Further, the fundamental wavelengths converted in the sub-regions D31 to D33 are λ _D7 = 1.06225 μm, λ _D8 = 1.06240 μm, and λ _D9 = 1.06255 μm, respectively, and converted in the sub-regions D41 to D43. The fundamental wavelengths are λ _D10 = 1.06345 μm, λ _D11 = 1.06360 μm, and λ _D12 = 1.06375 μm.

  FIG. 25 is a diagram showing the wavelength dependence of the wavelength conversion efficiency of the polarization inversion wavelength conversion element 500. As shown in FIG. 25, in the polarization inversion wavelength conversion element 500, wavelength conversion windows W1 to W4 corresponding to the regions D1 to D4 are formed.

  The widths of the wavelength conversion windows W1 to W4 are all 0.45 μm. The wavelength interval between the wavelength conversion windows W1 and W2 is 1.05 nm, the wavelength interval between the wavelength conversion windows W2 and W3 is 1.2 nm, and the wavelength interval between the wavelength conversion windows W3 and W4 is 1.2 nm. It is. Thus, the polarization inversion wavelength conversion element 500 is different from the polarization inversion wavelength conversion element 200 described in the first embodiment, the wavelength conversion windows are not evenly spaced, but each wavelength conversion window has a width. It is possible to reduce the deterioration of the optical output power of the output laser beam 400 due to the wavelength change of the basic laser beam 300.

  Next, an example of a method for manufacturing the waveguide 501 will be described.

  The waveguide 501 was formed using the proton exchange method described below. The width of the waveguide 501 is 4 μm to 6 μm, and the depth of the waveguide 501 is 2 μm to 4 μm.

  An LN substrate formed of LN is prepared, and a chromium film is deposited on the + Z plane of the LN substrate. Then, using a photolithography technique, a proton exchange mask having openings matching the width and length of the optical waveguide is formed.

Next, the LN substrate is immersed in a melt of benzoic acid (C ₆ H ₅ COOH) at 200 ° C. for 120 minutes, and proton exchange of the LN substrate is performed. A benzoic acid melt as a proton exchange melt is prepared by adding 1 mol% of lithium benzoic acid C ₆ H ₅ COOLi to 500 g of benzoic acid and melting the additive in a glass container. Since the melting temperature of this additive is lower than the boiling point of benzoic acid, which is 249 ° C., the substrate is immersed while the upper surface of the glass container is opened.

Here, induced defects due to proton exchange are reduced by supplementing lithium with benzoic acid using lithium benzoic acid (C ₆ H ₅ COOLi). Further, by exchanging Li + in the LN substrate and H + in the benzoic acid melt by the proton exchange method, a step-type high refractive index region can be formed as a waveguide on the surface of the LN substrate. .

  When the immersion treatment of the LN substrate is performed for 120 minutes, the LN substrate is taken out of the benzoic acid solution, and the proton exchange mask is removed from the LN substrate. Thereafter, the LN substrate is heated at 350 ° C. for 120 minutes in order to optimize the refractive index distribution by diffusing the high refractive region of the LN substrate into the substrate and optimizing the H + concentration in the high refractive region. Do.

  Further, the polarization inversion wavelength conversion element is formed by cutting out a predetermined length from the LN substrate and optically polishing both end faces thereof. Then, one of the planes perpendicular to the ± Z plane of the polarization inversion wavelength conversion element is used as an incident plane, and the reflectance of the incident plane is 0.2% or less with respect to a laser beam having a wavelength of 1064 nm, and a wavelength of 530 nm. Coating is performed with a dielectric film so that the reflectance with respect to the laser beam is 90% or more.

  Next, the speckle reduction rate is evaluated.

  When the high-frequency LD driver power source 112 is not performing high-frequency superposition driving, the speckle contrast of the scanned image of the output laser light 400 is 12.5%. Therefore, since the speckle contrast of the scanned image is 25% when the green laser beam is a single wavelength laser beam, the reduction rate of the speckle contrast of the light source of this embodiment is 50%. This coincides with the case where the green laser light has four independent laser lights having different wavelengths.

  Further, when the high frequency LD driver power source 112 performs high frequency superposition driving, the speckle of the output laser light 400 has a spectrum shown in FIG. In this case, the speckle contrast of the scanned image by the output laser beam was 11.2%. Therefore, the reduction rate of speckle contrast is 55.2%.

  Next, a third embodiment will be described.

  In the first and second embodiments, the case where the light intensity of the fundamental wave included in the fundamental laser beam 300 is the same has been described, but in this embodiment, the case where the light intensity of the fundamental wave is different will be described.

  Since the light intensity of the second harmonic output from the polarization inversion wavelength conversion element is proportional to the square of the light intensity of the fundamental wave, the light intensity of the second harmonic wave corresponding to the wavelength component having a low light intensity in the fundamental wave. Is significantly reduced, the wavelength width of the second harmonic is reduced. For this reason, the reduction rate of speckle becomes low.

  In order to solve the above problem, in the polarization inversion wavelength conversion element of the present embodiment, each region is emitted from each region according to the light intensity of each fundamental wave and the position of the beam waist of the fundamental laser beam. They are arranged along the traveling direction of the basic laser beam so that the light intensity of the peak wavelength of the second harmonic becomes uniform. More specifically, each region is arranged so that the wavelength is converted at a position where the diameter of the fundamental laser beam is larger as the fundamental wave has a higher light intensity.

  First, the shape of the basic laser light incident on the polarization inversion wavelength conversion element will be described.

  FIG. 27 is a diagram showing an example of the wavelength spectrum of the basic laser beam. As shown in FIG. 27, the spread width σ of the wavelength spectrum of the basic laser light is 3 nm. The spread width σ is a length from a wavelength at which the light intensity is maximum to a wavelength at which the light intensity is 1 / e of the maximum value.

  FIG. 28 is a diagram showing the beam shape of laser light in a PPLN crystal, and FIG. 29 is a diagram showing the beam shape of laser light in air. 28 and 29, the beam shape of green laser light (wavelength: 530 nm) and the beam shape of infrared laser light (wavelength: 1060 nm) are shown.

  As shown in FIGS. 28 and 29, the laser beam has a smaller beam diameter spread as the wavelength is smaller. Further, since the refractive index of the PPLN crystal is higher than the refractive index of air, the spread of the diameter of the laser light in the PPLN crystal is smaller than the spread of the diameter of the laser light in the air.

  FIG. 30 is a diagram showing the relationship between the beam shape of the laser light in the PPLN crystal and the beam waist width of the laser light. FIG. 30 shows the beam shape of the laser light when the beam waist width is 50 μm, 100 μm, and 150 μm. As shown in FIG. 30, as the waist width becomes smaller, the spread of the diameter of the laser light becomes larger. However, when the waist width is 100 μm and 150 μm, the diameter of the laser light is not so different.

  Next, the laser light source of this embodiment will be described.

  FIG. 31 is a block diagram showing the configuration of the laser light source of the present embodiment. In FIG. 31, the laser light source includes a light output unit 600 and a wavelength conversion unit 601. The light output unit 600 and the wavelength conversion unit 601 are disposed on the substrate 50.

  The optical output unit 600 includes an LD module 611, a high frequency LD driver power source 612, a temperature control unit 613, and a half-wave plate 614.

  The LD module 611 includes an LD chip 621, a collimator lens 622, and a heat sink 623.

  The LD chip 621 emits basic laser light 350 that is multi-wavelength infrared laser light having a plurality of wavelength peaks. In the present embodiment, the basic laser beam 350 has nine wavelength peaks.

  The collimator lens 622 outputs the basic laser beam 350 output from the LD chip 621 as parallel light. The heat sink 623 diffuses the heat generated by the LD chip 621.

  The high frequency LD driver power supply 612 may be called a drive unit. The high frequency LD driver power source 612 performs high frequency superposition driving of the LD module 611 and emits the basic laser light 350 from the LD module 611.

FIG. 32 is a diagram showing the spectrum of the basic laser beam 350. As shown in FIG. 32, the basic laser beam 350 has wavelength peaks λ _{1 to} λ ₉ with a wavelength interval of 1 nm. Note that λ ₁ <λ ₂ <λ ₃ <λ ₄ <λ ₅ <λ ₆ <λ ₇ <λ ₈ <λ ₉ is satisfied. Moreover, the spread width σ of the spectrum of the basic laser beam 350 is 4 nm.

  Returning to the description of FIG. The temperature control unit 613 measures the temperature of the LD chip 621 in the LD module 611 and adjusts the temperature of the heat sink 623 in the LD module 611 so that the temperature becomes constant.

  The half-wave plate 614 converts the multi-wavelength infrared laser light to the wavelength conversion unit 601 after converting the polarization direction to the vertical direction.

  The wavelength conversion unit 601 includes an element support base 631, a temperature control unit 632, a condenser lens 633, an emitted light adjustment lens 634, and a polarization inversion wavelength conversion element 700. Note that the temperature controller 632, the condenser lens 633, the outgoing light adjustment lens 634, and the polarization inversion wavelength conversion element 700 are disposed on the element support base 631.

  The temperature control unit 632 includes a heat sink, and controls the temperature of the polarization inversion wavelength conversion element 700 to be constant using the heat sink.

  The condensing lens 633 may be called a first condensing unit. The condensing lens 633 condenses the basic laser beam 350 to the first desired aperture and enters the incident surface of the polarization inversion wavelength conversion element 700.

  The polarization inversion wavelength conversion element 700 is a bulk SHG element and has a periodic polarization structure. The polarization inversion wavelength conversion element 700 converts the wavelength of the basic laser light 350 incident through the condenser lens 633 and outputs the converted laser light as output laser light 450 to the outgoing light adjustment lens 134.

  The emitted light adjusting lens 634 emits the output laser light 450 emitted from the polarization inversion wavelength conversion element 700 as parallel light.

  FIG. 33 is a diagram showing a more detailed configuration of the polarization inversion wavelength conversion element 700. In FIG. 33, the polarization inversion wavelength conversion element 700 has an incident surface 701, a polarization inversion structure portion 702, and an exit surface 703.

  The basic laser beam 350 is incident on the incident surface 701.

  In the domain-inverted structure portion 702, a plurality of regions having domain-inverted structures are arranged in parallel. Each region converts each wavelength of a plurality of fundamental waves, which are a plurality of wavelength components separated from each other in the fundamental laser beam 350, and outputs each of a plurality of converted waves separated from each other in the wavelength band. To do.

In FIG. 33, the domain-inverted structure portion 702 includes nine regions D1 to D9 each having a domain-inverted periodic structure. The interaction lengths of the regions D1 to D9 are all 10 mm (= L ₀ ).

The fundamental wavelengths of the fundamental waves whose wavelengths are converted in each of the regions D1 to D9 are λ ₁ , λ ₂ ... Λ _{9 in} order from the region D1. Therefore, the region D1 is quasi-phase matched with the fundamental wave with the wavelength λ ₁ , the region D2 is quasi-phase matched with the fundamental wave with the wavelength λ ₂ , and the region D3 is quasi-phase matched with the fundamental wave with the wavelength λ ₃ , region D4 is to the fundamental wave and the quasi phase matching wavelength lambda _4, area D5 is to the fundamental wave and the quasi-phase matching wavelength lambda _5, region D6 is to the fundamental wave and the quasi-phase matching wavelength lambda _6, region D7 Is quasi-phase matched with the fundamental wave of wavelength λ ₇ , domain D 8 is quasi-phase matched with the fundamental wave of wavelength λ ₈ , and domain D 9 is quasi-phase matched with the fundamental wave of wavelength λ _9. The polarization inversion period of the structure portion 702 is set. Each region is set to be quasi-phase matched at 40 ° C.

  In the regions D1 to D9, the light intensity of the peak wavelength of the second harmonic emitted from the regions D1 to D9 is uniform according to the light intensity of each fundamental wave and the position of the beam waist of the fundamental laser beam 350. Are arranged along the traveling direction of the basic laser beam 350. More specifically, each region is arranged so that the wavelength of the fundamental wave with higher light intensity is converted at a position where the diameter of the fundamental laser beam 350 is larger. In FIG. 33, regions D5, D4, D3, D2, D1, D9, D8, D7, and D6 are arranged in this order from the incident surface 701.

In FIG. 33, the fundamental wavelengths of the fundamental waves converted in the regions D1 to D9 are λ ₅ , λ ₄ , λ ₃ , λ ₂ , λ ₁ , λ ₉ , λ ₈ , λ ₇ , λ ₆ from the incident surface 701. Are in order. Therefore, the condensing lens 633 is provided so that the beam waist of the basic laser beam 350 is located at the boundary between the regions D5 and D6. When the beam waist width of the basic laser beam 350 is 100 μm, the diameter (diameter) of the basic laser beam 350 on the incident surface 701 is 310 μm, and when the beam waist width of the basic laser beam 350 is 50 μm, The diameter of the basic laser beam 350 is 610 μm.

  FIG. 34 is a diagram showing the relationship between the wavelength conversion efficiency of the polarization inversion wavelength conversion element 700 and the wavelength of the fundamental wave. As shown in FIG. 34, the wavelength conversion efficiency has nine peaks corresponding to each of the regions D1 to D9.

  Next, speckle will be described.

  First, the case where the spread width σ of the wavelength spectrum of the basic laser beam 350 is 4 nm will be described.

  FIG. 35 is a diagram showing the relationship between the speckle contrast of the projected image of the output laser beam 450, the optical output power of the output laser beam 450, and the beam waist width of the basic laser beam 350. In FIG. 35, the solid line indicates the speckle contrast, and the dotted line indicates the optical output power.

  As shown in FIG. 35, the speckle contrast is minimized when the beam waist width is 80 to 100 μm. Further, the optical output power becomes maximum when the beam waist width is 100 to 130 μm.

  When the beam waist width is 50 μm, the speckle contrast is 10.1% and the optical output power is 18.6 mW. When the beam waist width is 100 μm, the speckle contrast is 8.4% and the optical output power is 30 mW. Further, when the beam waist width is 150 μm, the speckle contrast is 8.9% and the optical output power is 28.1 mW.

  36 to 38 are diagrams showing the spectrum of the output laser beam 450. FIG. 36, the beam waist width of the output laser beam 450 is 50 μm, the beam waist width of the output laser beam 450 is 100 μm in FIG. 37, and the beam waist width of the output laser beam 450 is 150 μm in FIG. It is.

  As shown in FIGS. 36 to 38, when the beam waist width is 100 μm, the light intensity distribution of the output laser beam 450 is relatively uniform.

  Next, the case where the spread width σ of the wavelength spectrum of the basic laser beam 350 is 3 nm will be described.

  FIG. 39 is a diagram showing a wavelength spectrum of the basic laser beam 350 having a spread width σ of 3 nm. FIG. 40 is a diagram showing the relationship between the speckle contrast of the projected image of the output laser beam 450, the optical output power of the output laser beam 450, and the beam waist width of the basic laser beam 350. In FIG. 40, the solid line indicates speckle contrast, and the dotted line indicates optical output power.

  As shown in FIG. 40, the speckle contrast is minimized when the beam waist width is 50 to 60 μm. Further, the optical output power becomes maximum when the beam waist width is 120 to 150 μm.

  When the beam waist width is 50 μm, the speckle contrast is 8.4% and the optical output power is 12 mW. When the beam waist width is 100 μm, the speckle contrast is 9.2% and the optical output power is 27 mW. When the beam waist width is 150 μm, the speckle contrast is 10.0% and the optical output power is 29.8 mW.

  41 to 43 are diagrams showing the wavelength spectrum of the output laser beam 450. FIG. In FIG. 41, the beam waist width of the output laser beam 450 is 50 μm, in FIG. 42, the beam waist width of the output laser beam 450 is 100 μm, and in FIG. 43, the beam waist width of the output laser beam 450 is 150 μm. It is.

  As shown in FIGS. 41 to 43, when the beam waist width is 50 μm, the light intensity distribution of the output laser light 450 is relatively uniform, but the light output power is relatively small. In addition, the speckle contrast increase rate is higher when the beam waist width is larger than when the spread width σ of the wavelength spectrum of the basic laser beam 350 is 4 nm. However, if the beam waist width is reduced, the optical output power becomes very small. Therefore, when the spread width σ of the wavelength spectrum of the basic laser beam 350 is 3 nm, the speckle contrast is slightly increased, but the beam waist width is about 100 μm. Is good.

  Next, a case where the spread width σ of the wavelength spectrum of the basic laser beam 350 is 5 nm will be described.

  FIG. 44 is a diagram showing a wavelength spectrum of the basic laser beam 350 having a spread width σ of 5 nm. FIG. 45 is a diagram showing the relationship between the speckle contrast of the projection image of the output laser beam 450, the optical output power of the output laser beam 450, and the beam waist width of the basic laser beam 350. In FIG. 45, the solid line indicates speckle contrast, and the dotted line indicates optical output power.

  As shown in FIG. 45, the speckle contrast is minimized when the beam waist width is 100 to 150 μm. Further, the optical output power becomes maximum when the beam waist width is 70 to 130 μm.

  When the beam waist width is 50 μm, the speckle contrast is 11.6% and the optical output power is 24.7 mW. When the beam waist width is 100 μm, the speckle contrast is 8.5% and the optical output power is 32 mW. When the beam waist width is 150 μm, the speckle contrast is 8.5% and the optical output power is 28.1 mW.

  46 to 48 are diagrams showing the wavelength spectrum of the output laser beam 450. FIG. 46, the beam waist width of the output laser beam 450 is 50 μm, the beam waist width of the output laser beam 450 is 100 μm in FIG. 47, and the beam waist width of the output laser beam 450 is 150 μm in FIG. It is.

  As shown in FIGS. 46 to 48, when the width of the beam waist becomes 100 μm or more, the optical output power decreases, and when the width of the beam waist becomes 100 μm or less, the speckle contrast increases. In order to obtain a sufficient optical output power while lowering the speckle contrast, the width of the beam waist may be about 100 μm to 150 μm.

  According to the present embodiment, in the domain-inverted structure portion 702, the region where the wavelength of the fundamental wave having a higher light intensity is converted is provided at a position where the diameter of the fundamental laser beam 350 is larger.

  In this case, even if the light intensity of the fundamental wave is not equal, the light intensity of the peak wavelength of the second harmonic can be made uniform, and the reduction rate of speckle contrast can be increased.

  Next, a fourth embodiment will be described.

  FIG. 49 is a block diagram showing the configuration of the laser light source of the present embodiment. 49, the laser light source has a polarization inversion wavelength conversion element 710 instead of the polarization inversion wavelength conversion element 700, as compared with the laser light source shown in FIG.

  The polarization inversion wavelength conversion element 710 is a waveguide type SHG element and has a periodic polarization structure. The polarization inversion wavelength conversion element 710 converts the wavelength of the basic laser beam 350 incident through the condenser lens 633 and outputs the converted laser beam as the output laser beam 450 to the emission light adjustment lens 134.

  FIG. 50 is a diagram showing a configuration of the polarization inversion wavelength conversion element 710. In FIG. 50, the polarization inversion wavelength conversion element 710 has an entrance surface 711, a polarization inversion structure portion 712, an exit surface 713, and dielectric films 711A and 713A. The polarization inversion wavelength conversion element 710 is disposed on the heat sink 632A of the temperature control unit 632.

  The basic laser beam 350 is incident on the incident surface 711.

  In the domain-inverted structure portion 712, a plurality of regions having domain-inverted structures are arranged in parallel. Each region converts each wavelength of a plurality of fundamental waves, which are a plurality of wavelength components separated from each other in the fundamental laser beam 350, and outputs each of a plurality of converted waves separated from each other in the wavelength band. To do.

  In addition, a waveguide 720 for confining and propagating the basic laser beam 350 in a space having a predetermined cross-sectional area is formed in the domain-inverted structure portion 712.

  The output surface 713 emits the output laser beam 450 generated by the domain-inverted structure portion 712. The dielectric film 711 </ b> A is formed on the incident surface 711 and functions as an antireflection film that reduces the reflection of the basic laser beam 350. The dielectric film 713A is formed on the emission surface 713, and functions as an antireflection film that reduces the reflection of the output laser beam 450.

  FIG. 51 is a diagram showing a configuration of the polarization inversion wavelength conversion element 710. In FIG. 51, the polarization inversion wavelength conversion element 710 includes an entrance surface 711, a polarization inversion structure portion 712, an exit surface 713, and a waveguide 720.

  As shown in FIG. 51, in the domain-inverted structure portion 712, regions D1 to D9 are arranged in parallel from the incident surface 711.

  In this embodiment, the interaction lengths L1 to L9 of the regions D1 to D9 are set according to the light intensity of each fundamental wave so that the light intensity at the peak wavelength of each converted wave in the output laser light 450 is uniform. Is done. More specifically, the interaction lengths L1 to L9 of the regions D1 to D9 are shorter as the region in which the fundamental wave having higher light intensity is converted.

  52 and 53 are diagrams showing the relationship between the spectrum of the basic laser beam 350 and the interaction length of each region.

  In FIG. 52, the spread width σ of the wavelength spectrum of the fundamental wave is 3 nm, and the element length L of the polarization inversion wavelength conversion element 710 is 30 mm. In this case, the interaction lengths L1 to L9 of each region are L1 = 7.51 mm, L2 = 3.45 mm, L3 = 1.98 mm, L4 = 1.42 mm, L5 = 1.27 mm, L6 = 1. 42, L7 = 1.98 mm, L8 = 3.45 mm, and L9 = 7.51 mm.

  In addition, when the spread width σ of the wavelength spectrum of the fundamental wave is 3 nm and the element length L of the polarization inversion wavelength conversion element 710 is 25 mm, the interaction lengths L1 to L9 of each region are L1 = 6.26 mm, L2 = 2.88 mm, L3 = 1.65 mm, L4 = 1.18 mm, L5 = 1.06 mm, L6 = 1.18 mm, L7 = 1.65 mm, L8 = 2.88 mm, L9 = 6.26 mm.

In FIG. 53, the spread width σ of the wavelength spectrum of the fundamental wave is 4 nm, and the element length L of the polarization inversion wavelength conversion element 710 is 30 mm. In this case, the interaction lengths L _{1 to} L ₉ of each region are L1 = 5.57 mm, L2 = 3.60 mm, L3 = 2.63 mm, L4 = 2.18 mm, L5 = 2.05 mm, L6 = 2. .18 mm, L7 = 2.63 mm, L8 = 3.60 mm, and L9 = 5.57 mm.

When the spread width σ of the wavelength spectrum of the fundamental wave is 4 nm and the element length L of the polarization inversion wavelength conversion element 710 is 25 mm, the interaction lengths L _{1 to} L ₉ of each region are L1 = 4.64 mm, L2 = 3.00 mm, L3 = 2.19 mm, L4 = 1.82 mm, L5 = 1.71 mm, L6 = 1.82 mm, L7 = 2.19 mm, L8 = 3.00 mm, L9 = 4.64 mm Become.

Next, a specific method for determining the interaction length will be described. If the element length of the polarization inversion wavelength conversion element 710 is L, and the interaction length of the region that is pseudo-phase matched with the fundamental wave of the fundamental wavelength λ _k is L _k ,

Meet. Also, assuming that the optical output power of the fundamental laser beam 350 is A and the light intensity a _k of the fundamental wave of the fundamental wavelength λ _k is

Meet. In this case, the optical output power P _k of the emitted light having the wavelength λ _k / 2 in the output laser beam 450 is

Can be expressed as At this time, the optical output power P of the output laser beam 450 is

The speckle contrast C of the output laser beam 450 is

It is.

It is desirable to select the interaction length L _k so that the optical output power P of the output laser beam 450 is as large as possible and the speckle contrast C of the projected image by the output laser beam 450 is as small as possible.

When the output laser beam 450 is a green laser beam, each second harmonic is considered to be independent if the interval between the converted wavelengths λ _k / 2 of the emitted light is greater than 0.5 nm. The optical output power P _k of the wave is considered to contribute to speckle independently. In this case, the speckle contrast C of the output laser beam 450 is expressed by each interaction length L _k .

The speckle contrast C can be minimized. In this case, the optical output power P _k of the second harmonic is

And does not depend on k. Therefore, a flat output laser beam 450 having a constant light intensity of each second harmonic is obtained. At this time, the speckle contrast C of the output laser beam 450 is

It becomes.

FIG. 54 is a diagram showing a spectrum of the output laser beam 450 when each interaction length L _k satisfies Equation 28. In FIG. 54, the wavelength interval of each second harmonic in the output laser beam 450 is 0.5 nm. Therefore, since the wavelength interval of each second harmonic is sufficiently large, each second harmonic independently contributes to speckle. Therefore, in the present embodiment, since the output laser beam 450 has nine wavelength peaks, the speckle contrast reduction rate is １ ／ at the maximum.

  For example, when the speckle contrast of the scanned image when the green laser beam is a single wavelength laser beam is 25%, the speckle contrast of the scanned image when the green laser beam is the output laser beam of this embodiment is 8.3 (= 25/3)%.

  Note that if a plurality of laser beams are combined into a single beam by an optical fiber or the like, the optical output power of the basic laser beam 350 can be increased, but the apparatus becomes larger. For this reason, in consideration of the optical output power of the laser beam that can be output by the single mode LD element, the optical output power of the basic laser beam 350 is set to 0.5 w to 2.5 W.

  The element length of the polarization inversion wavelength conversion element is a target value of 10 mm to 30 mm. In order to emit 10 to 20 lumens of white light with the scanning projector using the laser light source of the present embodiment, the light output power of the green laser light is preferably about 60 mW in view of optical loss.

  Since the output laser beam 450 is proportional to the square of the element length of the polarization inversion wavelength conversion element 710 and the optical output power of the basic laser beam 350, when the optical output power of the green laser beam is made constant, If the optical power is large, the element length of the polarization inversion wavelength conversion element 710 can be reduced. When the spread width σ of the wavelength spectrum of the basic laser beam 350 is 4 nm, the optical output power of the basic laser beam 350 is 1.5 W, the element length of the polarization inversion wavelength conversion element 710 is 28 mm, and the waveguide width W is 5 μm. In this case, a green laser beam of 60 mW was obtained as the output laser beam 450. The speckle contrast C of the scanned image is 8.3% regardless of the element length of the polarization inversion wavelength conversion element.

  Next, the relationship between the optical output power of the basic laser beam 350, the optical output power of the output laser beam 450, the element length, and the width W of the waveguide 720 will be described. Hereinafter, the wavelength band of the basic laser beam 350 is set to 1060 nm to 1068 nm. In addition, the optical output power of the basic laser beam 350 may be referred to as excitation light output power, and the optical output power of the optical output power of the output laser beam 450 may be referred to as green light output power.

  First, the case where the spread width σ of the wavelength spectrum of the basic laser beam 350 is 3 nm will be described.

  FIG. 55 is a diagram showing the dependency of the green light output power PG on the element length L. In FIG. 55, the pumping light output power PE is 1.5 W.

  As shown in FIG. 55, if the element length L is constant, the green light output power PG increases as the width W of the waveguide 720 decreases. For example, when the element length L is 30 mm, the green light output power PG is 40 mW when the width W of the waveguide 720 is 5 μm, and the green light output power PG is 60 mW when the width W of the waveguide 720 is 4 μm. .

  FIG. 56 is a diagram showing the dependency of the green light output power PG on the element length L. In FIG. 56, the width W of the waveguide 720 is 5 μm.

  As shown in FIG. 56, if the element length L is constant, the green light output power PG increases as the pump light output power PE increases. In order to set the green light output power to 60 mW, if the pump light output power is 1.5 W, the element length L needs to be 36 mm.

  FIG. 57 is a diagram showing the dependency of the green light output power PG on the pumping light output power PE. In FIG. 57, the width W of the waveguide 720 is 5 μm.

  As shown in FIG. 57, in order to set the green light output power to 60 mW, when the element length L is 30 mm, 1.8 W is required as the excitation output power.

  FIG. 58 is a diagram showing the dependency of the element length L on the pumping light output power PG. In FIG. 58, the width W of the waveguide 720 is 5 μm. As shown in FIG. 58, the relationship between the pumping light output power PG and the element length L is inversely proportional.

Next, a case where the spread width σ of the wavelength spectrum of the basic laser beam 350 is 4 nm will be described. In this case, it is advantageous for downsizing of the apparatus by the extent that the spread width σ is widened.

FIG. 59 is a diagram showing the dependency of the green light output power PG on the element length L. In FIG. 59, the pumping light output power PE is 1.5 W.

As shown in FIG. 59, if the element length L is constant, the green light output power PG increases as the width W of the waveguide 720 decreases. For example, when the element length L is 30 mm, when the width W of the waveguide 720 is 5 μm, the green light output power PG is 70 mW. When the element length L is 25 mm, the width W of the waveguide 720 is 5 μm. The green light output power PG is 50 mW.

FIG. 60 is a diagram showing the dependency of the green light output power PG on the element length L. In FIG. 60, the width W of the waveguide 720 is 5 μm.

  As shown in FIG. 60, if the element length L is constant, the green light output power PG increases as the pump light output power PE increases. In order to set the green light output power to 60 mW, if the pumping light output power is 1.5 W, the element length L needs to be 28 mm.

  FIG. 61 is a diagram showing the dependency of the green light output power PG on the pumping light output power PE. In FIG. 61, the width W of the waveguide 720 is 5 μm.

  As shown in FIG. 61, in order to set the green light output power to 60 mW, when the element length L is 30 mm, 1.4 W is required as the excitation output power.

  FIG. 62 is a diagram showing the dependency of the element length L on the pumping light output power PG. In FIG. 62, the width W of the waveguide 720 is 5 μm. As shown in FIG. 62, the relationship between the pumping light output power PG and the element length L is inversely proportional.

  As described above, the green light output power PG depends on the spread spectrum σ of the wavelength spectrum of the basic laser light 350, the pump light output power PE, the element length L, and the width W of the waveguide 720. Since these parameters are limited, the speckle contrast C may be minimized and a desired green light output power may not be obtained.

  Hereinafter, a method for reducing speckle contrast C as much as possible while obtaining a desired green light output power will be described.

Using the distribution parameter q that determines the interaction length L _k of the region D _k, the interaction length L _k

It expresses. The distribution parameter q is a real number from 0 to 1.

When the distribution parameter q is 0, the interaction length L _k is a value L _k (0) = L / N _obtained by equally dividing the element length L. When the distribution parameter q is 1, the speckle contrast C is minimized. The interaction length. The element length L does not depend on the distribution parameter.

  FIG. 63 is a diagram showing the spectrum of the basic laser beam 350 and the interaction length distribution. In FIG. 63, the element length L is 35 mm, and the spread spectrum σ of the wavelength spectrum of the basic laser beam 350 is 3 nm.

  As shown in FIG. 63, when the distribution parameter q is 0.53, the interaction lengths L1 to L9 of the respective regions are L1 = 6.47 mm, L2 = 3.96 mm, L3 = 3.05 mm, L4 = 2.70 mm, L5 = 2.61 mm, L6 = 2.70 mm, L7 = 3.05 mm, L8 = 3.96 mm, L9 = 6.47 mm. Further, when the distribution parameter q is 0.81, the interaction lengths L1 to L9 of each region are L1 = 7.84 mm, L2 = 4.00 mm, L3 = 2.61 mm, L4 = 2.08 mm, L5 = 1. .94 mm, L6 = 2.80 mm, L7 = 2.61 mm, L8 = 4.00 mm, L9 = 7.84 mm.

  FIG. 64 is a diagram showing the dependence of the speckle contrast on the distribution parameter. In FIG. 64, the element length L is 35 mm, and the spread spectrum σ of the wavelength spectrum of the basic laser beam 350 is 3 nm.

  As shown in FIG. 64, the larger the distribution parameter q, the higher the speckle contrast but the higher the green light output power. For example, when the distribution parameter q is 1, when the excitation light power is 1.2 W, the speckle contrast C is 8.4% which is the minimum value, but the green light output power is slightly low at 38 mW. On the other hand, when the distribution power q is 0.53, the speckle contrast is slightly high at 9.5%, but the green light output power is also high at 60 mW.

  When distribution power q is 0.53, the spectrum of output laser beam 450 is as shown in FIG. 65, and the spectrum and wavelength conversion spectrum of basic laser beam 350 are as shown in FIG. When the distribution power meter q is 0, the spectrum of the basic laser beam 350 and the wavelength conversion spectrum are as shown in FIG. 65 to 66, the spread width σ of the wavelength spectrum of the basic laser beam 350 is 3 nm, and the element length L is 35 mm.

  Next, a case where the spread width σ of the wavelength spectrum of the basic laser beam 350 is 4 nm will be described.

  FIG. 68 shows the wavelength spectrum of the basic laser beam 350 and the interaction length distribution. In FIG. 68, the element length is 35 mm.

  As shown in FIG. 68, when the distribution parameter q is 0.59, the interaction lengths L1 to L9 of the respective regions are L1 = 4.65 mm, L2 = 3.49 mm, L3 = 2.92 mm, L4 = 2.65 mm, L5 = 2.58 mm, L6 = 2.65 mm, L7 = 2.92 mm, L8 = 3.49 mm, L9 = 4.65 mm.

  FIG. 69 is a diagram showing the dependence of speckle contrast on the distribution parameter. In FIG. 69, the element length is 35 mm.

  As shown in FIG. 69, the larger the distribution parameter q, the higher the speckle contrast, but the higher the green light output power. However, the dependence of the green light output power on the distribution parameter is smaller than when the spread width σ is 3 nm.

  For example, when the distribution parameter q is 0.59, if the pumping light power is 1.1 W, the green light output power is 60 mW, and the speckle contrast C is 8.6%. When the distribution parameter is 1, when the pumping light power is 1.2 W, the green light output power is 62 mW and the speckle contrast C is 8.3%.

  When the distribution power meter q is 0.59, the spectrum of the output laser beam 450 is as shown in FIG. 70, and the spectrum and wavelength conversion spectrum of the basic laser beam 350 are as shown in FIG.

  According to the present embodiment, the interaction length of each region becomes shorter as the region in which the fundamental wave having higher light intensity is converted. In this case, even if the light intensity of the fundamental wave is not equal, the light intensity of the peak wavelength of the second harmonic can be made uniform, and the reduction rate of speckle contrast can be increased.

  Next, a fifth embodiment will be described.

  In the present embodiment, there will be described a laser light source in which a plurality of polarization inversion wavelength conversion elements are provided, and a light output unit makes basic laser light incident on each polarization inversion wavelength conversion element. The number of polarization inversion wavelength conversion elements is 2 in this embodiment, but actually, it may be plural.

  FIG. 72 is a block diagram showing the configuration of the laser light source of the present embodiment. In FIG. 72, the laser light source includes a light output unit 800 and a wavelength conversion unit 801.

  The optical output unit 800 includes an LD array module 811, a high frequency LD driver power source 812, a temperature control unit 813, and a half-wave plate 814.

  The LD array module 811 includes LD chips 821A and 821B, collimator lenses 822A and 822B, and a heat sink 823.

  Each of the LD chips 821A and 821B emits multi-wavelength infrared laser light having a plurality of wavelength peaks. Hereinafter, the multi-wavelength infrared laser light emitted from the LD chip 821A is referred to as basic laser light 350A, and the multi-wavelength infrared laser light emitted from the LD chip 821B is referred to as basic laser light 350B.

  In the present embodiment, the wavelength peaks of the basic laser beams 350A and 350B have a constant wavelength interval. Specifically, the wavelength peak of the basic laser beam 350A is 1.060 μm, 1.061 μm, 1.062 μm, 1.063 μm, and 1.064 μm, and the wavelength peak of the basic laser beam 350B is 1.065 μm, 1.066 μm, 1.067 μm, 1.068 μm, and 1.069 μm.

  The collimator lens 822A emits the basic laser light 350A emitted from the LD chip 621A as parallel light, and the collimator lens 822B emits the basic laser light 350B output from the LD chip 621B as parallel light. The heat sink 823 diffuses the heat generated in the LD chips 621A and 621B.

  The high frequency LD driver power supply 812 may be called a drive unit. The high-frequency LD driver power source 812 performs high-frequency superposition driving of the LD array module 811 to emit the basic laser beams 350A and 350B from the LD array module 811.

  The half-wave plate 814 converts the polarization directions of the basic laser beams 350 </ b> A and 350 </ b> B emitted from the LD array module 811 to the vertical direction and emits them to the wavelength conversion unit 801.

  The wavelength conversion unit 801 includes an element support 831, a temperature control unit 832, condenser lenses 833 A and 833 B, polarization inversion wavelength conversion elements 834 A and 834 B, and a combining unit 835. The temperature control unit 832 and the polarization inversion wavelength conversion elements 834A and 834B are disposed on the element support 831.

  The temperature controller 832 has a heat sink, and controls the temperature of the polarization inversion wavelength conversion elements 834A and 834B to be constant using the heat sink.

  The condensing lens 833A may be referred to as a first condensing unit. The condensing lens 833A condenses the basic laser beam 350A so that the minimum value d of the diameter of the basic laser beam 350A in the polarization reversal wavelength conversion element 834A is included in a desired range, and the polarization reversal wavelength conversion element 834A. Incident.

  The condensing lens 833B may be referred to as a first condensing unit. The condensing lens 833B condenses the basic laser beam 350B to the polarization inversion wavelength conversion element 834B so that the minimum value d of the diameter of the basic laser light 350B in the polarization inversion wavelength conversion element 834B is included in a desired range. Incident.

  Accordingly, since the basic laser beams 350A and 350B output from the light output unit 800 are incident on the polarization inversion wavelength conversion elements 834A and 834B, the light output unit 800 transmits the basic laser light to the plurality of polarization inversion wavelength conversion elements. Will be incident.

  Each of the polarization inversion wavelength conversion elements 834A and 834B has a configuration similar to that of the polarization inversion wavelength conversion element 710 shown in FIG. The domain-inverted wavelength conversion element 834A has a plurality of regions that satisfy each of the peak wavelengths of the basic laser light 350A and the pseudo-polarization matching condition, and the domain-inverted wavelength conversion element 834B has each of the peak wavelengths of the basic laser light 350B. And a plurality of regions that satisfy the pseudo-polarization matching condition.

  Therefore, the polarization inversion wavelength conversion element 834A converts the wavelengths of the five fundamental waves including each of the five wavelength peaks in the fundamental laser light 350A, and converts the first output laser light including the five second harmonics. It will be emitted. Further, the polarization inversion wavelength conversion element 834B converts the wavelengths of the five fundamental waves including each of the five wavelength peaks in the fundamental laser light 350B, and outputs the second output laser light including the five second harmonics. It will be emitted.

  For this reason, the wavelength peaks of the first output laser light are 0.530 μm, 0.5305 μm, 0.531 μm, 0.5315 μm, and 0.532 μm. The wavelength peaks of the second output laser light are 0.5325 μm, 0.533 μm, 0.5335 μm, 0.534 μm, and 0.5345 μm.

  The multiplexing unit 835 combines the first output laser beam and the second output laser beam emitted from the polarization inversion wavelength conversion elements 834A and 834B, respectively, and emits the output laser beam 850.

  The multiplexing unit 835 includes outgoing light adjusting lenses 841A and 841B, a half-wave plate 842, a reflecting mirror 843, and a polarization beam multiplexer 844.

  The emitted light adjusting lens 841A emits the first output laser beam emitted from the polarization inversion wavelength conversion element 834A as parallel light. The emitted light adjusting lens 841B emits the second output laser light emitted from the polarization inversion wavelength conversion element 834B as parallel light.

  The half-wave plate 842 rotates the polarization direction of the first output laser light emitted from the emitted light adjustment lens 841A by 90 degrees and emits it to the polarization beam combiner 844.

  The reflecting mirror 843 reflects the second output laser light emitted from the outgoing light adjustment lens 841B and emits it to the polarization beam combiner 844. As a result, the polarization direction of the second output laser beam is rotated by 90 degrees.

  The polarization beam combiner 844 combines the first output laser beam emitted from the half-wave plate 842 and the second output laser beam emitted from the reflecting mirror 843 to obtain an output laser beam 850. Exit.

  As described above, the laser light source of the present embodiment can emit green laser light of a unit beam having ten wavelength peaks. In the laser light source of this embodiment, the speckle contrast of the scanned image is 7.9, and the speckle contrast reduction rate is 68%.

  According to the present embodiment, since a plurality of basic laser beams are used, the optical output power of the output laser beam 850 can be increased. Further, since it is not necessary to install a plurality of polarization inversion wavelength conversion elements in series, the length of the polarization inversion wavelength conversion element along the traveling direction of the basic laser light can be reduced.

  Normally, light having a wavelength distance of 10 nm or more in light near 530 nm is recognized as light having a different hue by humans. Therefore, when the laser light source of this embodiment is used as a green laser light source, The width of the wavelength band is desirably less than 10 nm. For this reason, it is desirable that the combined wavelength band of the basic laser beams 350A and 350B is 20 nm. More specifically, the combined wavelength band of the basic laser beams 350A and 350B is preferably 4 nm or more and 10 nm or less.

  Next, a sixth embodiment will be described.

  FIG. 73 is a block diagram showing the configuration of the laser light source of the present embodiment. In FIG. 73, the laser light source includes a light output unit 600 and a wavelength conversion unit 901. In the present embodiment, the light output unit 600 makes the basic laser beam 350 incident on the wavelength conversion unit 901.

  The wavelength conversion unit 901 includes an element support 931, a temperature control unit 932, condenser lenses 933 and 940, polarization inversion wavelength conversion elements 934 to 936, triangular prisms 937 to 939, and an outgoing light adjustment lens 941. Have. The temperature controller 932, the condenser lens 933, the polarization inversion wavelength conversion elements 934 to 936, the triangular prism 937, and the outgoing light adjustment lens 941 are disposed on the element support 931.

  The condensing lens 933 may be called a 1st condensing part. The condensing lens 933 condenses the basic laser beam 350 to the first desired aperture and enters the polarization inversion wavelength conversion element 934. Therefore, the light output unit 600 makes the basic laser beam 350 incident on any of the polarization inversion wavelength conversion elements 934 to 936.

  The polarization inversion wavelength conversion elements 934 to 936 have the same configuration as the polarization inversion wavelength conversion element 710 shown in FIG. In each region of the polarization inversion wavelength conversion elements 934 to 936, the polarization inversion period is determined so that the polarization inversion wavelength conversion elements 934 to 936 convert wavelengths of fundamental waves having different wavelength bands included in the basic laser light 350. It has been.

  Further, the emission surfaces of the polarization inversion wavelength conversion elements 934 and 935 emit not only the output laser beam including the second harmonic but also the basic laser beam 350. Hereinafter, output laser light emitted from the polarization inversion wavelength conversion element 934 is referred to as first output light, and output laser light emitted from the polarization inversion wavelength conversion element 935 is referred to as second output light.

  The triangular prisms 937 to 940 and the condenser lens 940 constitute a light guide unit. The light guide unit reflects the basic laser light 350 and the output laser light emitted from the polarization inversion wavelength conversion element so that the basic laser light 350 enters each of the polarization inversion wavelength conversion elements 934 to 936, The light enters the polarization inversion wavelength conversion element.

  Specifically, the triangular prism 937 reflects the first output light emitted from the polarization inversion wavelength conversion element 934 twice and enters the polarization inversion wavelength conversion element 935. Further, the triangular prism 938 reflects the second output light emitted from the polarization inversion wavelength conversion element 935 and emits it to the triangular prism 939 via the condenser lens 940. The triangular prism 940 reflects the second output light and enters the polarization inversion wavelength conversion element 936.

The condensing lens 940 may be called a second condensing unit. The condensing lens 940 condenses the second output laser beam and the basic laser beam 350 to a predetermined aperture. The emission light adjusting lens 941 emits the output laser beam emitted from the polarization inversion wavelength conversion element 935 as parallel light. To do.

  According to the present embodiment, since it is not necessary to install a plurality of polarization inversion wavelength conversion elements in series, the length of the polarization inversion wavelength conversion element along the traveling direction of the basic laser light can be reduced.

  Further, the provision of the condensing lens 940 makes it possible to suppress the spread of the basic laser beam 350 and to increase the wavelength conversion efficiency.

  In each embodiment described above, the illustrated configuration is merely an example, and the present invention is not limited to the configuration.

  For example, the polarization inversion wavelength conversion element used in the fifth and sixth embodiments may be the polarization inversion wavelength conversion element 200 or 500.

50 Substrate 100, 600, 800 Light output unit 101, 601, 801, 901 Wavelength conversion unit 111A to 111D, 611 LD module 112, 612, 812 High frequency LD driver power supply 113, 132, 613, 632, 813, 832, 932 Temperature Control unit 114, 115, 119 Reflective mirror 115A, 116, 117 Dichroic mirror 118, 614, 814, 842 Half-wave plate 121, 621, 821A, 821B LD chip 122, 622, 822A, 822B Collimator lens 123, 132A, 623, 632A, 823 Heat sink 131, 631, 831, 931 Element support 133, 633, 833A, 833B, 933, 940 Condensing lens 134, 634, 841A, 841B, 941 Emission light adjusting lens 20 , 500, 700, 710, 834A, 834B, 934 to 936 Polarization inversion wavelength conversion element 201, 701, 711 Incident surface 201A, 203A, 711A, 713A Dielectric film 202, 702, 712 Polarization inversion structure part 203, 703, 713 Surface 300, 350 Basic laser light 400, 450 Output laser light 501, 720 Waveguide 811 LD array module 835 Combined part 937-939 Triangular prism D1-D9 area D11-D43 Sub area

Claims (17)

An incident surface on which incident light is incident;
A plurality of regions having a domain-inverted structure are arranged in parallel, and each region converts the wavelengths of a plurality of fundamental waves separated from each other in the incident light incident on the incident surface, and the wavelength band is A polarization inversion structure that emits each of the plurality of separated converted waves; and
A polarization reversal wavelength conversion element comprising: an exit surface that emits outgoing light including a converted wave emitted from each region of the domain-inverted structure. The polarization inversion wavelength conversion element according to claim 1,
When n is an integer of 2 or more, in each region, n subregions that convert wavelengths included in each of the n subwavelength bands obtained by dividing the wavelength band of the fundamental wave that converts the wavelength into n in each region {D _k : k = 1, 2,... N} are juxtaposed,
The length {L _k [mm]} along the traveling direction of the incident light of each sub-region {D _k : k = 1, 2,... N} and the median value {λ _k [nm] of adjacent sub-wavelength bands ]} Interval {Δλ _k = λ _k −λ _k−1 }

A polarization reversal wavelength conversion element that satisfies the requirements. The polarization inversion wavelength conversion element according to claim 1 or 2,
The polarization inversion wavelength conversion element, wherein the converted wave is a second harmonic of the fundamental wave. The polarization inversion wavelength conversion element according to any one of claims 1 to 3,
Polarization inversion wavelength conversion element in which the difference between the medians of wavelength bands adjacent to each other among the wavelength bands of fundamental waves whose wavelengths are converted in each region is the same The polarization inversion wavelength conversion element according to any one of claims 1 to 4,
A polarization inversion wavelength conversion element in which a median difference δ of wavelength bands adjacent to each other among wavelength bands in which wavelengths are converted in each region satisfies 0.5 μm ≦ δ ≦ 2 μm. In the polarization inversion wavelength conversion element according to claim 5,
The polarization inversion wavelength conversion element, wherein the median difference δ satisfies 0.8 μm ≦ δ ≦ 1.5 μm. The polarization inversion wavelength conversion element according to any one of claims 1 to 6,
The domain-inverted wavelength conversion element, wherein the domain-inverted structure section includes a waveguide for confining and propagating the incident light in a space having a predetermined cross-sectional area. The polarization inversion wavelength conversion element according to any one of claims 1 to 7,
A first antireflection film for reducing reflection of the incident light is formed on the incident surface, and a second antireflection film for reducing reflection of the emitted light is formed on the emission surface. , Polarization inversion wavelength conversion element. The polarization inversion wavelength conversion element according to any one of claims 1 to 8,
A light output unit that emits the incident light to the polarization reversal wavelength conversion element. The light source according to claim 9,
Each region is a light source arranged such that the wavelength is converted at a position where the diameter of the incident light is larger as the fundamental wave has a higher light intensity. The light source according to claim 9 or 10,
A light source in which the length of each region along the traveling direction of the incident light is shorter in a region where a fundamental wave having a higher light intensity is converted. The light source according to any one of claims 9 to 11,
The incident light emitted from the light output unit is condensed to the polarization inversion wavelength conversion element so that the minimum value d of the diameter of the incident light in the polarization inversion wavelength conversion element satisfies 50 μm ≦ d ≦ 500 μm. A light source having an incident first light collecting portion. The light source according to claim 12,
The first condensing unit condenses the incident light so that a minimum value d of the diameter of the incident light satisfies 70 μm ≦ d ≦ 150 μm. The light source according to any one of claims 9 to 13,
The light output unit is a light source that emits the incident light using a semiconductor laser element that performs high-frequency superposition driving. The light source according to any one of claims 9 to 14,
There are a plurality of the polarization inversion wavelength conversion elements,
The light output unit makes the incident light incident on each polarization inversion wavelength conversion element,
A light source further comprising a multiplexing unit that multiplexes and emits light emitted from each polarization inversion wavelength conversion element. The light source according to any one of claims 9 to 14,
There are a plurality of the polarization inversion wavelength conversion elements, and the exit surface of each polarization inversion wavelength conversion element further emits the incident light,
The light output unit makes the incident light incident on any of the plurality of polarization inversion wavelength conversion elements,
A light source having a light guide unit that makes the outgoing light and incident light emitted from the polarization inversion wavelength conversion element incident on another polarization inversion wavelength conversion element so that the incident light enters each polarization inversion wavelength conversion element . The light source according to claim 16,
The light guide unit includes a second light collecting unit that collects the emitted light and incident light to a predetermined aperture.

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