JP3761060B2 - Waveguide type optical device and light source and optical apparatus using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser light source and an optical system used in the field of optical information processing and optical applied measurement control, to which a coherent light source is applied.
[0002]
[Prior art]
In an optical information recording / reproducing apparatus, higher density can be realized by using a light source having a shorter wavelength. For example, a compact disk device that has been widely used conventionally uses near-infrared light of 780 nm, whereas a digital versatile disk (DVD) that realizes higher-density information reproduction uses a red semiconductor laser of 650 nm. In addition, in order to realize a higher density next-generation optical disk device, a blue laser light source having a shorter wavelength has been actively developed. For example, a wavelength conversion element using a nonlinear optical material has been developed as a small and stable blue laser light source.
[0003]
FIG. 14 is a schematic view of an example of a blue light source using a second harmonic generation element (hereinafter abbreviated as SHG element). First, the SHG light source will be described with reference to FIG.
[0004]
A high refractive index region having a width of about 3 microns and a depth of about 2 microns is formed on the optical material substrate 114 by a proton exchange method, and serves as an optical waveguide 115. Infrared light having a wavelength of 850 nm emitted from the semiconductor laser 111 is condensed on the incident side end surface 139 of the SHG element 117, propagates in the optical waveguide 115 on the SHG element 117, and becomes fundamental wave guided light [fundamental guided wave]. .
[0005]
The lithium niobate crystal of the optical material substrate 114 has a large nonlinear optical constant, and excites harmonic guided light having a wavelength of 425 nm, which has been converted from a fundamental electric field to a half wavelength.
[0006]
In addition, a domain inversion region 116 is periodically formed on the waveguide 115 to compensate for the propagation constant difference between the fundamental wave and the harmonics, and the harmonics excited over the entire waveguide 115 are coherent. The light is added and emitted from the emission-side end face 138 of the waveguide 115.
[0007]
Here, in order to accurately compensate for the difference in propagation constant between the fundamental wave and the harmonic wave, it is necessary to keep the wavelength of the fundamental wave accurately constant, and the semiconductor laser 111 is a DBR laser whose wavelength fluctuation due to temperature or the like is extremely small. Used. The DBR laser not only has a small wavelength variation, but also has the features of high coherence and low RIN noise due to oscillation at a single wavelength.
[0008]
Next, the operation will be described with reference to a schematic diagram of a blue light source optical disk pickup using the SHG element 117 shown in FIG. The harmonic blue light emitted from the SHG element 117 passes through the collimating lens 113, the polarization separation beam splitter 120, the quarter wavelength plate 121, and the objective lens 122 and is collected on the optical disk 124.
[0009]
The light modulated by the optical disk 124 is reflected by the polarization beam splitter 120 and guided to the photodetector 125 by the condenser lens 123 to obtain a reproduction signal.
[0010]
At this time, linearly polarized light parallel to the paper surface is emitted from the SHG element 117, but the light travels back and forth through the quarter-wave plate 121 and becomes perpendicular to the paper surface, and the reflected light from the optical disk 124 is polarized. The beam splitter 120 is totally reflected and does not return to the light source side.
[0011]
[Problems to be solved by the invention]
In the section of the prior art, the configuration in which the reflected light from the optical disk is reflected by the polarizing beam splitter and does not return to the light source side is described. However, since the actual optical disk 124 has birefringence, it is generated on the disk. The unnecessary polarized component passes through the polarization beam splitter 120 and returns to the light source side.
[0012]
During the reproduction of the optical disk 124, the position of the objective lens 122 is controlled so as to be accurately focused on the optical disk 124. Therefore, the exit side end surface 138 of the SHG element 117 and the optical disk 124 are confocal optical systems [confocal optical system. The reflected light from the optical disk 124 is accurately condensed on the exit side end surface 138 of the optical waveguide 115 of the SHG element 117.
[0013]
As described above, various techniques for avoiding the problem of returning reflected light to the light source have been proposed as return light induced noise of an optical system using a semiconductor laser as a light source.
[0014]
For example, a plurality of longitudinal modes are generated by modulating a semiconductor laser with a high-frequency signal, or a self-excited oscillation is caused in the semiconductor laser to realize a plurality of longitudinal mode oscillations.
[0015]
In the field of optical communication, when condensing light from a semiconductor laser onto an optical fiber, an optical isolator using a magneto-optical effect is generally inserted between the two.
[0016]
Alternatively, a method for obliquely polishing the incident side end face of an optical fiber or optical waveguide to reflect reflected light obliquely so as not to return to the semiconductor laser is disclosed in Japanese Patent Laid-Open No. 5-323404.
[0017]
These techniques reduce the return light-induced noise caused by the return light fed back into the light source of the semiconductor laser.
[0018]
We conducted an optical pickup reproduction experiment using the waveguide type SHG element 117 shown in FIG. 15, and found noise generated by a mechanism different from the conventional return light induced noise.
[0019]
That is, this is interference noise generated by the return light collected on the output side end surface 138 of the optical waveguide 115 being reflected by the output side end surface 138 of the waveguide 115 and interfering with the light output from the inside of the waveguide 115. .
[0020]
Due to this interference effect, it appears that the output light power of the light source changes from the optical disk 124 side, and the reproduction signal of the optical disk 124 is modulated by low frequency noise, resulting in signal degradation.
[0021]
While the return light induced noise (mode hop noise) in the semiconductor laser is generated by the interaction between the light inside the semiconductor laser 111 and the return light reflected by the incident side end face 139, the above interference noise is a light source. This is different in that it is generated by interference between the outgoing light from the light and the return light reflected by the outgoing side end face 138.
[0022]
Further, by further detailed examination, a part of the return light from the external optical system (collimator lens 113) is excited again as guided light in the waveguide 115 of the waveguide optical device, and the incident side end face 139 of the waveguide 115 is excited. It was found that the noise is reflected in the same way and causes interference noise.
[0023]
As described above, the optical system using the waveguide optical device reflects two kinds of noises, that is, light emitted from the light source and returns to the light emitting side end surface 138, and the optical system outside the light source. There are low-frequency interference noise causing interference and mode hop noise caused by the inside of the semiconductor laser 111.
[0024]
Various techniques have been proposed to reduce the latter mode hop noise, but interference noise outside the former light source has not been noticed so far, and a method for fundamentally solving this has been proposed. Absent.
[0025]
An object of the present invention is to reduce interference noise outside the light source.
[0026]
Another object of the present invention is to use a waveguide type optical device capable of reproducing an optical disc with low noise without being affected by the return light even when there is return light from the optical disc. It is to provide a light source and an optical device.
[0027]
[Means for Solving the Problems]
The waveguide type optical device according to the present invention is a waveguide type optical device including an optical material substrate and a waveguide formed on the optical material substrate, wherein the optical material substrate and the waveguide are second harmonics. Forming a generating element, the waveguide having a longitudinal axis, an emission side end surface formed at an angle shifted from a right angle with respect to a plane perpendicular to the longitudinal axis, and a plane perpendicular to the longitudinal axis; An incident side end face formed at an angle deviated from a right angle with respect to, The angle of the exit-side end face is set so as to prevent interference between the return light from the external optical system and the exit light from the waveguide when reflected by the exit-side end face. The angle is set so that the return light from the external optical system is not incident on the waveguide when reflected from the incident-side end surface from the exit-side end surface. On the incident side end face, The return light An antireflection film for reducing the reflectivity of the harmonics is formed, thereby achieving the above object.
[0039]
An optical apparatus according to the present invention includes a waveguide optical device according to the present invention, and a condensing optical system that condenses the light emitted from the waveguide onto an observation object. Said The waveguide optical device and the object to be observed are arranged so as to have a confocal relationship, thereby achieving the above-described object.
[0040]
An angle θ formed by a plane perpendicular to the exit-side end face and the waveguide, an effective refractive index n of the waveguide, and a substantial numerical aperture NA on the exit side of the waveguide of the condensing optical system are expressed as NA A relationship of ≦ sin (θ × n) may be satisfied.
[0041]
The observed object may include an optical disk.
[0042]
Another waveguide type optical device according to the present invention is a waveguide type optical device including an optical material substrate and a waveguide formed on the optical material substrate, and is emitted from the waveguide in a first direction to an external object. Thus, the light reflected to the emission side end surface is emitted in the second direction different from the first direction at the emission side end surface, thereby achieving the above object.
[0043]
The optical material substrate and the waveguide may form a second harmonic generation element.
[0044]
According to a certain aspect of the present invention, the effect of returning light can be effectively reduced by a simple configuration in which the emission side is formed obliquely.
[0045]
In the waveguide type optical device formed on both the incident side and the output side at an angle with respect to the waveguide, reflection at both end faces is reduced, and the influence of return light interference can be almost completely eliminated. By forming it obliquely, the return light to the semiconductor laser due to reflection at the incident side end face of the optical waveguide can be suppressed, and the effect of reducing the mode hop noise of the semiconductor laser is also obtained.
[0046]
A waveguide type optical device characterized in that the incident-side end surface and the emission-side end surface of the optical material substrate are formed substantially in parallel has an effect that it is easy to manufacture.
[0047]
According to another aspect of the present invention, since the collimating optical system of the light source is arranged at the center of the light distribution from the waveguide optical device, the light returning to the semiconductor laser light source can be reduced.
[0048]
According to still another aspect of the present invention, the optical device prevents the return light from the external optical system from being reflected by the end face of the waveguide and interferes with the outgoing light, and provides a stable light source free from interference noise. By forming the incident-side end face also at an angle, not only does the return light from the external optical system return to the incident-side end face of the waveguide and reflect it, but also the return light to the semiconductor laser light source is reduced. Have
[0049]
DETAILED DESCRIPTION OF THE INVENTION
In this specification, unless otherwise specified, the “outgoing side end face” includes both the surface of the optical material substrate and the surface of the waveguide from which light is emitted. The optical material substrate may have an emission side end face different from the emission side end face of the waveguide. The optical material substrate and the waveguide may have an emission side end face in the same plane.
[0050]
Unless otherwise specified, the “incident side end face” includes both the surface of the optical material substrate and the surface of the waveguide through which light enters from the light source. The optical material substrate may have an incident side end face different from the incident side end face of the waveguide. The optical material substrate and the waveguide may have an incident side end face in the same plane.
[0051]
“Emitted light” means light emitted from the waveguide.
[0052]
(Embodiment 1)
FIG. 1 shows a schematic configuration diagram of an optical apparatus 100 using a waveguide optical device 10 of the present invention. The waveguide optical device of the present invention is not limited to the SHG element, but the example of FIG. 1 shows an example in which an SHG element that converts infrared light into blue light is used as the waveguide element.
[0053]
The optical device 100 includes a light source device 101 and a condensing optical system 102. The light source device 101 includes a semiconductor laser 11 as a light source, a condensing lens 12, a waveguide optical device 10, and a collimating lens 13. The condensing optical system 102 includes a polarizing beam splitter 20, a quarter-wave plate 21, and an objective lens 22.
[0054]
The waveguide optical device 10 includes an optical material substrate 14 and an optical waveguide 15 formed on the optical material substrate 14. In the embodiment described below, an SHG element including the optical material substrate 14 and the optical waveguide 15 will be described as an example, but the present invention is not limited to this. In the present invention, other types of elements can be used as the optical material substrate and the optical waveguide.
[0055]
Light having a wavelength of 850 nm is emitted from the semiconductor laser 11, and blue light having a wavelength converted to a half is generated while propagating through the optical waveguide 15 formed on the SHG element 17. Blue light having a wavelength of 425 nm is emitted.
[0056]
The outgoing light 30 from the SHG element 17 passes through the collimating lens 13 and the polarization beam splitter 20 and is condensed on the optical disk 24 by the objective lens 22.
[0057]
The reflected light from the optical disk 24 is reflected by the polarization beam splitter 20 and guided to the photodetector 25. However, when the base material of the optical disk 24 has birefringence, unnecessary polarization components pass through the polarization beam splitter 20. To return to the SHG element 17.
[0058]
Here, since the position of the objective lens 22 is controlled so as to be accurately condensed on the optical disk 24, the emission side end face 38 of the SHG element 17 and the optical disk 24 form a confocal system, and the return light 31 from the optical system is The light is condensed on the emission side end face 38.
[0059]
The waveguide device according to the present invention shown in FIG. 1 is characterized in that the exit-side end face 38 has a surface 50 perpendicular to the exit-side end face 38 having an oblique angle θ with respect to the longitudinal axis A of the optical waveguide 15. Is formed. That is, the emission side end face 38 has an oblique angle θ with respect to a plane perpendicular to the longitudinal axis A of the optical waveguide 15. In this specification, it expresses that the positional relationship of such an output side end surface and an optical waveguide is formed diagonally with respect to an optical waveguide.
[0060]
The outgoing light 30 from the optical waveguide 15 is emitted at an angle of an outgoing angle θ1 with respect to the surface 50 perpendicular to the outgoing side end face 38. The emission angle θ1 at this time is Snell's law,
θ1 = n × sin θ (Formula 1)
And is defined by the refractive index n of the optical waveguide and the angle θ formed by the optical waveguide and the output side end face.
[0061]
As described above, since the light emitted from the optical waveguide 15 is emitted obliquely with respect to the optical waveguide 15, the SHG element 17 and the optical pickup optical system (the collimating lens 13, the polarization beam splitter 20, and the objective lens 22) are not shown. As shown in FIG. For this reason, the end face reflected light 32 of the return light 31 from the optical system has an angle deviation of 2 × θ1 from the outgoing light 30, and the end face reflected light 32 is not captured by the collimating lens 13 and avoids interference with the outgoing light 30. Is done.
[0062]
As can be seen from FIG. 1, the collimating lens 13 is arranged in an oblique direction with respect to the optical waveguide 15, which is in the center of the distribution of the outgoing light 30 emitted at an angle defined by Snell's law. 13 is placed.
[0063]
Compared with the configuration in which the collimating lens 13 is disposed at a right angle to the optical waveguide 15, the angle formed by the return light 31 from the optical system and the end surface reflected light 32 is larger, so that the emitted light 30 is the most. It can be used efficiently.
[0064]
Although the angle θ formed between the optical waveguide 15 and the output side end face 38 in FIG. 1 is not particularly limited, it is effective in reducing interference noise, but the output angle θ1 of the output light 30 and the light source side NA of the optical pickup optical system 103 are effective. (Numerical aperture)
NA <sin (θ × n) (Formula 2)
By setting to such a condition, the outgoing light 30 and the end surface reflected light 32 can be completely separated, and interference between the outgoing light 30 and the end surface reflected light 32 can be completely eliminated.
[0065]
Here, the light source side NA of the optical pickup optical system 103 does not simply indicate the NA of the collimating lens 13. For example, in the optical pickup optical system 103 of FIG. 1, the collimating lens 13 has an effective diameter larger than that of the objective lens 22, and the effective beam diameter of the optical pickup optical system 103 is defined by the effective diameter of the objective lens 22.
[0066]
In this case, NA in (Expression 1) indicating the condition under which the influence of the end surface reflected light 32 is completely removed is the effective beam diameter of the optical pickup optical system 103, that is, the effective diameter r of the objective lens 22 and the collimating lens. From 13 focal lengths f
NA = sin (r / f) (Formula 3)
NA is expressed by the following formula. The angle θ formed between the optical waveguide 15 and the emission side end face 38 may be set within a range where (Equation 1) is established with respect to this NA.
[0067]
For example, in a general optical pickup optical system of DVD or CD, when a lithium niobate waveguide having an effective beam radius of 2 mm, a collimating lens focal length f of about 15 mm, and a refractive index of 2.2 is used, The angle θ formed between the optical waveguide 15 and the emission side end face 38 may be set to 3.5 degrees or more. The upper limit of the angle is determined by the total reflection critical angle. However, since the angle dependency of the end face transmittance increases as the angle increases, the angle θ formed between the optical waveguide 15 and the emission side end face 38 is set to about 20 degrees or less. Is realistic.
[0068]
FIG. 2 shows an example of an optical device having a configuration in which the inclination angle of the emission side end face is further reduced. The waveguide optical device 10A includes an SHG element 17A. The SHG element 17A includes a proton exchange waveguide 15A. The surface 51 perpendicular to the emission side end face 38A of the SHG element 17A has a smaller angle with respect to the longitudinal axis A of the proton exchange waveguide 15A than the emission side end face 38 of FIG.
[0069]
When the proton exchange waveguide 15A is used as the waveguide optical device 10A, the far-field image of the output light 30A from the optical waveguide 15A is an elliptical shape that is wide in the vertical direction and narrow in the horizontal direction as shown in FIG. Often have.
[0070]
FIG. 3 is a cross-sectional view of the emitted light 30A at the cross section 3-3 in FIG. As shown in FIG. 3, the height h of the far-field image is larger than its width d.
[0071]
In such a case, an aperture plate 37A that matches the shape of the far-field image of the outgoing light 30A can be inserted to reduce the horizontal NA of the optical system without greatly losing the amount of light.
[0072]
4A is a cross-sectional view of the aperture plate 37A at the cross-section 4A-4A of FIG. As shown in FIG. 4A, the height h of the aperture of the aperture plate 37A is larger than its width d. The aperture plate 37A is adapted to the far field image of the outgoing light 30A in FIG. By using the aperture plate 37A in this way, the NA in the width d direction (FIG. 3) of the optical pickup optical system can be reduced.
[0073]
In FIG. 2, the angle θ at which the interference of the reflected light can be completely removed is determined by using the aperture width d of the aperture plate 37A.
NA = sin {(d / 2) / f} (Formula 4)
(Equation 1) should be satisfied with respect to the NA expressed by the equation (1), and the inclination angle θ of the exit side end face 38A can be made smaller than the inclination angle in the structure shown in FIG.
[0074]
In a typical proton exchange waveguide, the vertical spread (height h shown in FIG. 3) of the far-field image is about twice the horizontal spread (width d shown in FIG. 3). In this case, the inclination angle θ of the emission side end face 38A can be reduced to one half of the value corresponding to (Expression 2). When applied to the specific example of the optical pickup described above, the inclination angle θ is 1.8 degrees or more. In practice, it is appropriate to set the inclination angle θ to 2 degrees or more in consideration of the installation position error of the lens and the light source. It is realistic to set the upper limit of the inclination angle θ to about 20 degrees or less. The upper limit of the inclination angle θ is determined by the total reflection critical angle, but the angle dependency of the end face transmittance increases as the angle increases.
[0075]
FIG. 2 shows an example where the far-field image shape from the optical waveguide 15A is wide in the vertical direction (height h shown in FIG. 3), but the far-field image shape is horizontal (depending on the structure of the optical waveguide 15A). In the case of a wide width d) shown in FIG. 3, an aperture plate having a long shape in the horizontal direction (width d shown in FIG. 3) may be inserted in accordance with the shape of the far field image.
[0076]
The aperture shape is not limited to an elliptical shape, and may be any shape that has different vertical and horizontal spreads, such as a rectangle (37B) and a band shape (37C), as shown in FIGS. 4B and 4C.
[0077]
A technique for preventing the end face reflection of the guided light by forming the end face of the waveguide obliquely is disclosed in, for example, Japanese Patent Application Laid-Open No. 61-22311. This has the effect of preventing reflection of the end face of the guided light by forming the fiber end face obliquely. On the other hand, the feature of the waveguide type optical device of the present invention is that, as described above, the reflected light from the external optical system is reflected at an angle when it is re-reflected at the end face of the waveguide. This is to prevent interference with the emitted light, and is a technique that is different in configuration and effect from the technique that prevents reflection of guided light.
[0078]
FIG. 2 is a plan view of the waveguide optical device 10A. The axis A passes through the proton exchange waveguide 15A. Surface B is perpendicular to the longitudinal axis A. The axis C intersects the plane of the paper and is perpendicular to the longitudinal axis A. The emission side end face 38A is formed so as not to be parallel to the face B and to intersect the axis C. The emission side end face 38 shown in FIG.
[0079]
1 and 2 show an example in which the exit-side end faces 38 and 38A are inclined in the horizontal direction, the same applies to the waveguide type optical device 10B shown in FIG. 5 in which the exit-side end face 38B is inclined in the vertical direction. Interference between the end surface reflected light 32 and the emitted light 30 can be avoided.
[0080]
Referring to FIG. 5, axis D intersects the page and is perpendicular to longitudinal axis A. The exit side end face 38B is formed so as not to be parallel to the face B and to intersect the axis D.
[0081]
The configuration in which the exit-side end face is formed obliquely with respect to the waveguide can be easily realized by obliquely polishing the entire exit-side end face as shown in FIGS. 1, 2, and 5, as shown in FIG. As described above, the same effect can be obtained even when only the waveguide end face portion 38C of the substrate is formed obliquely.
[0082]
As a manufacturing method for realizing the configuration of FIG. 6, there is a method by dicing. For example, if a blade with surface roughness # 6000 is used, a cross section close to optical polishing can be formed. By forming a notch of width 38w, for example, about 10 μm, in the vicinity of the surface of the optical waveguide 15C, the output end face 38C of the optical waveguide can be formed. Further, by performing only about 10 μm of dicing, mirror surface processing becomes easy, blade consumption is small, and processing with a high yield is easy.
[0083]
As described above, the optical device in which the interference noise due to the influence of the reflected light from the optical system is reduced by forming the emission-side end face obliquely has been described. As described above, the influence of the return light can be reduced only by forming the exit side end face obliquely. However, in order to reduce interference noise more completely, it is necessary to consider the reflection on the entrance side end face. is there.
[0084]
That is, as indicated by a dotted line in the SHG element 17 in FIG. 1, a part of the return light 31 from the optical system enters the optical waveguide 15 and is reflected by the incident side end face 39 to become the waveguide beam reflected light 33. The light is emitted from the emission side end face 38. This light cannot be removed even if the emission side end face 38 is formed obliquely, and interferes with the emission light 30 and causes noise.
[0085]
(Embodiment 2)
An example of a waveguide type optical device that reduces reflection at the incident side end face is shown in FIG. In the waveguide type optical device 10D of FIG. 7, the incident side end face 39D of the SHG element 17D of the optical waveguide 15D is also formed obliquely with respect to the optical waveguide 15D.
[0086]
The return light from the optical system at this time is incident on the optical waveguide 15D, is reflected by the incident side end face 39D, and becomes a waveguide beam reflected light 33D that travels in a different direction from the waveguide 15D. The waveguide beam reflected light 33D is emitted into the waveguide optical device 10D while diffusing without entering the waveguide 15D, and does not reach the exit-side end face 38D.
[0087]
As in the example of FIG. 5, in the waveguide-type optical device 10D in which both the incident-side end surface 39D and the emission-side end surface 38D are formed obliquely with respect to the waveguide 15D, the incident-side end surface 39D and the emission-side end surface 38D The reflection is reduced, and the influence of interference between the return light 31 and the outgoing light 30 can be removed almost completely.
[0088]
Further, since the incident-side end face 39D is formed obliquely, the return light to the semiconductor laser 11 due to reflection at the incident-side end face 39D of the optical waveguide 15D can be suppressed, and the effect of reducing the mode hop noise of the semiconductor laser 11 is also achieved. Have both.
[0089]
(Embodiment 3)
In addition, in the waveguide type optical device in which both the incident side end face and the emission side end face are formed obliquely, an effect of preventing a reduction in device productivity is produced by forming both end faces in parallel.
[0090]
A waveguide type optical device is usually cut after a large number of waveguides are collectively produced on a material substrate having a large area, and undergoes a polishing process to smooth the end face.
[0091]
FIG. 8A shows the arrangement of the waveguide type optical device 10H on the optical material substrate. As shown in FIG. 8A, the waveguide optical device 10H in which the incident-side end surface and the emission-side end surface are formed in parallel can densely arrange the waveguide-type optical device 10H without generating a useless space in the optical material substrate 14. At the same time, there is an effect that cutting and polishing of all devices for one row can be processed at a time.
[0092]
That is, first, a lump cut along the cutting line 48 at the end face of the waveguide is performed, and a polishing process that requires a relatively long time is a waveguide optical device for one column cut along the cutting line 48. After performing 10H collectively, the side surface of the waveguide is cut along the cutting line 47.
[0093]
As shown in FIG. 8B, when the incident side end face and the emission side end face are not parallel, the cutting lines of the waveguide end faces of the individual waveguide type optical devices 10J on the substrate 14A do not coincide with each other.
[0094]
For this reason, since the individual waveguide optical devices 10J cannot be cut together along the cutting line of the waveguide end face, the one row of waveguide optical devices 10J cut along the cutting line can be batched. It cannot be polished.
[0095]
As a result, the waveguide optical device 10J has to be polished individually, and a problem arises in that productivity is significantly reduced as compared with a waveguide optical device having end faces formed at right angles.
[0096]
By forming the incident side end surface and the emission side end surface in parallel, it is possible to prevent a decrease in productivity even in a configuration in which the end surface is formed obliquely.
[0097]
Next, examples of other configurations for reducing reflection on the incident side end face are shown in Embodiments 4 to 6 (FIGS. 9 to 11). In these examples, a second harmonic generation element is used in a waveguide type optical device, and a long wavelength fundamental wave is incident from the incident side of the device, and a shorter wavelength harmonic is emitted from the emission side. It is effective.
[0098]
(Embodiment 4)
In FIG. 9, an antireflection film 34 for harmonics is formed on the incident side end face 39E of the waveguide optical device 10E. In an ordinary SHG element, an incident-side end face 39E is usually loaded with an antireflection film for the fundamental wave in order to prevent the fundamental wave from returning to the semiconductor laser. In the SHG element 17E of FIG. Since the side end face 39E is formed obliquely with respect to the optical waveguide 15E, the return light to the semiconductor laser is prevented, so that it is not necessary to reduce the reflectance of the fundamental wave.
[0099]
On the other hand, with respect to the harmonic return light 31E from the optical pickup optical system side (collimator lens 13 side), even if the incident side end surface 39E is formed obliquely, the reflectance is not completely eliminated. The antireflection film 34 for harmonics can be formed to further reduce the reflectance.
[0100]
The antireflection film 34 may be formed at a position away from the incident side end face 39E.
[0101]
(Embodiment 5)
FIG. 10 is a schematic configuration of a waveguide-type optical device 10F configured to reduce the return light 31F from the optical system side (collimator lens 13 side) by the harmonic absorbing element 35. The harmonic absorbing element 35 is provided on the waveguide 15F in the vicinity of the incident side end face 39F of the SHG element 17F of the waveguide optical device 10F.
[0102]
When near infrared light of 860 nm is used for the fundamental wave 61F and blue light of 425 nm is used for the harmonic, a material such as titanium oxide, zinc selenide, gallium phosphide, amorphous silicon, or the like is used as the harmonic absorber 35. Can be used. These materials are transparent to the infrared region, have a spectral characteristic of absorbing blue light, and can be loaded in the form of a thin film on the waveguide 15F by a technique such as sputtering.
[0103]
For a device using a wavelength different from the above example, such as using red light for the fundamental wave and ultraviolet light for the harmonic wave, another substance is used as the harmonic absorption element 35.
[0104]
(Embodiment 6)
FIG. 11 shows a schematic configuration of a waveguide type optical device 10G configured to prevent interference by diffracting and scattering the return light 31G from the optical system side (collimator lens 13 side) using the grating 36.
[0105]
A short-period grating 36 is formed in the vicinity of the incident side end face 39G of the waveguide optical device 10G, and the period Λ is determined by using the wavelength λ1 of the fundamental wave in vacuum and the effective refractive index n of the waveguide.
λ / (4 × n) <Λ <λ / (2 × n) (Formula 5)
By setting the value within a certain range, only the harmonics are diffracted and the fundamental wave is not diffracted.
[0106]
Vector diagrams for the harmonics and the fundamental wave at this time are shown in FIGS. 12 and 13, respectively. On the vector diagram shown in FIG. 12, a wave vector 40 of the harmonic guided light, a wave vector 42 of the grating, a wave vector 43 of the diffracted light into the air, and a wave vector 44 of the diffracted light into the substrate are displayed. .
[0107]
On the vector diagram shown in FIG. 13, a wave number vector 41 of the fundamental wave guided light and a wave number vector 42 of the grating are displayed. The direction of each vector corresponds to the propagation direction, and the magnitude of each vector corresponds to the wave number.
[0108]
The procedure for obtaining the direction of the diffracted light when the guided light is diffracted by the grating using a vector diagram is as follows. Since the wavelength of the radiated light in the air and in the substrate is uniquely determined, the wave vector of the radiated light (diffracted light into the air and diffracted light into the substrate) is on the semicircles R1 and R2 in FIG. It has terminations on the semicircles R3 and R4 in FIG.
[0109]
In addition, in order for the guided light to be diffracted light into the substrate or diffracted into the air by the grating, the wave number vector of the radiated light (diffracted light into the air and diffracted light into the substrate) and the guided light Only when the horizontal component of the difference from the wave vector 40 matches the wave vector 42 of the grating. For this reason, the wave number vectors of the radiated light (diffracted light into the air and diffracted light into the substrate) have terminations on the straight lines DL1 and DL2 shown by dotted lines in FIGS.
[0110]
That is, in the diffraction of the harmonic wave guide light shown in FIG. 12, the radiated light (diffracted light into the air and diffracted light into the substrate) in the direction of the intersections 43A and 44A between the semicircular arcs R1 and R2 and the dotted line DL1. Will occur.
[0111]
Here, in FIG. 13, since the dotted line DL2 and the semicircles R3 and R4 have no intersection, the fundamental wave guided light does not become radiated light and propagates through the grating region without loss.
[0112]
Thus, the return light reflection at the incident side end face can also be reduced by using a grating having a period satisfying the relationship of (Equation 5).
[0113]
As mentioned above, although the Example of this invention was described giving the example which used the SHG element for the waveguide type optical device, the waveguide type optical device which concerns on this invention is not restricted to a SHG element in particular. For example, high-speed modulation elements, phase shifters, frequency shifters, and polarization control elements can be used as waveguide optical devices with various functions and configurations. For all optical systems using such waveguide optical devices and coherent light sources, The waveguide type optical device of the present invention can be applied.
[0114]
However, since a light source using an SHG element often generates high coherence harmonics using a semiconductor laser having high coherence as a semiconductor laser, conversely, interference noise is likely to be generated. Interference noise can be reduced particularly effectively by combining with a wave type optical device.
[0115]
Although the optical pickup optical system has been described as an example of the confocal optical system, it is needless to say that the present invention can be applied to other coherent optical systems such as a laser scanning microscope and a laser printer.
[0116]
However, in the optical pickup optical system, the optical disk of the object to be measured has a high reflectance, the objective lens is position-controlled so that the light is always focused on the optical disk, and the confocal system is maintained, and the optical disk is moved up and down. The waveguide optical device of the present invention is particularly effective for an optical disk pickup because the interference condition changes every moment due to movement and interference noise is likely to be generated.
[0117]
【The invention's effect】
As described above, in the waveguide type optical device of the present invention, the return light from the external optical system is reflected by the waveguide end surface and interferes with the output light by forming the output side end surface of the waveguide obliquely. To provide a stable light source free from interference noise.
[0118]
In addition, the incident side end face is also formed obliquely to prevent return light from the external optical system from being reflected back to the incident side end face of the waveguide and to reduce return light to the semiconductor laser light source. Also has an effect.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical apparatus using a waveguide optical device according to a first embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a waveguide-type optical device according to Embodiment 1 of the present invention.
FIG. 3 is a cross-sectional view of a far-field image of light from the light source device according to Embodiment 1 of the present invention.
FIG. 4A is a schematic configuration diagram of an aperture plate of the waveguide type optical device according to the first embodiment of the present invention.
FIG. 4B is a schematic configuration diagram of another aperture plate of the waveguide optical device according to the first embodiment of the present invention.
4C is a schematic configuration diagram of still another aperture plate of the waveguide optical device according to Embodiment 1 of the present invention. FIG.
FIG. 5 is a schematic configuration diagram of another waveguide type optical device according to the first embodiment of the present invention.
FIG. 6 is a schematic configuration diagram of still another waveguide optical device according to the first embodiment of the present invention.
FIG. 7 is a schematic configuration diagram of a guided wave optical device according to a second embodiment of the present invention.
FIG. 8A is a layout view of a waveguide optical device according to a third embodiment of the present invention on an optical material substrate.
FIG. 8B is a layout view of a waveguide optical device according to Embodiment 3 of the present invention on an optical material substrate.
FIG. 9 is a schematic configuration diagram of a waveguide-type optical device according to Embodiment 4 of the present invention.
FIG. 10 is a schematic configuration diagram of a waveguide-type optical device according to a fifth embodiment of the present invention.
FIG. 11 is a schematic configuration diagram of a waveguide-type optical device according to a sixth embodiment of the present invention.
FIG. 12 is a diagram showing a wave vector diagram for harmonics on the grating of the waveguide optical device according to Embodiment 6 of the present invention.
FIG. 13 is a diagram showing a wave vector diagram for the fundamental wave on the grating of the waveguide optical device of the present invention according to Embodiment 6 of the present invention.
FIG. 14 is a schematic configuration diagram of a conventional waveguide type optical device of a second harmonic generation element.
FIG. 15 is a schematic configuration diagram of an optical disc pickup optical system using a conventional waveguide type optical device.
[Explanation of symbols]
10 Waveguide type optical device
11 Semiconductor laser
13 Collimating lens
14 Optical material substrate
15 Optical waveguide

Claims (5)

An optical material substrate;
In a waveguide optical device including a waveguide formed in the optical material substrate,
The optical material substrate and the waveguide form a second harmonic generation element,
The waveguide is offset from a right angle with respect to a longitudinal axis, an exit end face formed at an angle deviated from a right angle with respect to a plane perpendicular to the longitudinal axis, and a plane perpendicular to the longitudinal axis. An incident side end face formed at an angle,
The angle of the exit side end face is set so as to prevent interference with the exit light from the waveguide when the return light from the external optical system is reflected by the exit side end face,
The angle of the incident-side end face is such that return light from an external optical system is not incident on the waveguide when it is incident on the incident-side end face from the exit-side end face and reflected on the incident-side end face. Set to
A waveguide type optical device, wherein an antireflection film for reducing a reflectance of a harmonic wave as the return light is formed on the incident side end face. A waveguide type optical device according to claim 1;
A light source including a collimating lens that substantially collimates the light emitted from the waveguide,
The collimating lens is a light source disposed at the center of the distribution of the emitted light from the waveguide. A waveguide type optical device according to claim 1;
A condensing optical system that condenses the light emitted from the waveguide onto the object to be observed,
An optical apparatus in which the waveguide optical device and the observed object are arranged so as to have a confocal relationship. An angle θ formed by a plane perpendicular to the exit-side end face and the waveguide, an effective refractive index n of the waveguide, and a substantial numerical aperture NA on the exit side of the waveguide of the condensing optical system,
NA ≦ sin (θ × n)
The optical device according to claim 3, wherein the following relationship is satisfied.   The optical apparatus according to claim 3, wherein the observed object includes an optical disk.

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