JP2020086137A - Light modulator and optical comb generator - Google Patents

Abstract

To stabilize resonator control without deformation of a transmission mode waveform of an optical guide.SOLUTION: A light modulator comprises an optical guide 12 which is formed as a region where a guide mode is present only for a single polarization component on a substrate 11 which has at least an electrooptic effect so as to penetrate from an incident-side reflection film 93 to an emission-side reflection film 94 which constitutes resonance means. Members 86, 87 having a hardness equal to that of the substrate are provided in an upper part of the optical guide 12 so that at least one end surface thereof forms the same plane as an end surface of the substrate including the light incident end or light emission end on the optical guide 12. The incident side reflection film 93 and the emission side reflection film 94 which are formed by polishing end surfaces of the members 86, 87 and end surfaces of the substrate 11 are deposited.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical modulator applied to a field requiring a standard light source having high coherence at multiple wavelengths such as optical communication, optical CT, an optical frequency standard, or a light source that can also utilize coherence between wavelengths, Regarding the optical comb generator.

With the development of optoelectronics in recent years, a waveguide type optical resonator that resonates the light confined in an optical waveguide in order to meet the demands of laser light control for frequency multiplex communication and frequency measurement of absorption lines distributed over a wide range. Has become popular.

When the optical frequency is measured with high accuracy, the light to be measured is interfered with other light, and heterodyne detection is performed to detect an electric signal of the generated optical beat frequency. The band of light that can be measured in this heterodyne detection is limited to the band of the light receiving element used in the detection system, and is approximately several tens GHz.

On the other hand, it is necessary to further expand the measurable band of light in order to perform optical control for frequency multiplex communication and frequency measurement of absorption lines distributed over a wide range.

In order to meet the demand for expanding the measurable band, a wideband heterodyne detection system using an optical comb generator has been conventionally proposed (see, for example, Patent Document 1). This optical comb generator generates comb-shaped sidebands arranged at equal intervals on the frequency axis over a wide band, and the frequency stability of this sideband is almost equal to the frequency stability of incident light. is there. By heterodyne-detecting the generated sideband and the measured light, it is possible to construct a wideband heterodyne detection system over several THz.

Further, an optical comb generator and an optical modulator have been proposed in which not only the light propagating in the forward direction of the optical waveguide but also the light propagating in the backward direction are subjected to phase modulation (for example, see Patent Document 2). ).

Furthermore, by suppressing chipping and rounding during processing of the corners of the end face of the waveguide, and by stably depositing each reflective film without peeling off at the uppermost corners of the end face, the reflectance of the reflective film and the optical resonator can be improved. We have proposed an optical resonator, an optical modulator, an optical comb generator, and an optical oscillator that improve the finesse and improve the function of the device itself. (For example, refer to Patent Document 3).

That is, a member having the same hardness as the substrate for forming the optical waveguide from the upper surface is formed, and at least one of the end faces forms the same plane as the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. As described above, the incident side reflection film and the emission side reflection film that constitute the resonance means are provided on the plane formed by polishing the end face of the member and the end face of the substrate. Since it is attached, it is possible to suppress chipping and rounding at the time of processing the corners of the waveguide end face, and it is possible to adhere stably without peeling off at the corners of the uppermost end face of each reflection film. It is possible to improve the finesse of the optical resonator and enhance the function of the device itself.

Conventionally, in a waveguide type optical resonator that resonates light confined in an optical waveguide, an optical waveguide that transmits a polarization component in which orthogonal modes are mixed is used, and when an optical modulator or an optical comb generator is constructed, The obtained optical output also contained a polarization component in which orthogonal modes were mixed.

JP, 2003-202609, A Japanese Patent No. 3891977 Japanese Patent No. 4781648

By the way, in the conventional optical comb generator, when the optical comb is used for measurement, in order to obtain a stable output, a part of the light emitted from the optical resonator is detected by the photodetector, and a predetermined value is detected. Although the resonance length of the optical resonator is feedback-controlled so that the resonance length is obtained, a circle is added to FIG. 22 because an optical waveguide that transmits a polarization component in which orthogonal modes are mixed is used. As shown by the above, the transmission mode waveform due to the orthogonal polarization components may be deformed. Moreover, the places where the transmission mode waveform is deformed by the orthogonal polarization components (relative positions with respect to the main mode) are scattered and there are a plurality of local minimum portions, which becomes an instability factor when controlling the resonance length.

That is, in the optical comb generation in the optical comb generator using the waveguide type optical resonator that resonates the light confined in the optical waveguide, orthogonal polarization components cause the resonance frequency of the optical comb generator to match the laser frequency. May cause instability in the control of the control point, cause a shift of the control point, oscillation of the control, etc., and when using the optical comb in a measuring device that measures the distance or height to the measurement target, the orthogonal polarization The component was the cause of the measurement error.

Therefore, in view of the conventional situation as described above, an object of the present invention is to make it possible to stabilize resonator control without causing deformation in the transmission mode waveform of the optical waveguide.

Another object of the present invention is to suppress the output of orthogonal polarization components that do not contribute to the generation of an optical comb, improve the polarization extinction ratio, and obtain an optical comb output with an increased single polarization degree. Especially.

Still another object of the present invention is to make it possible to stabilize the optical comb generator, improve the accuracy of a measuring device including the optical comb, and reduce errors.

Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of the embodiments described below.

The present invention is an optical modulator, comprising an optical waveguide formed as a region in which a waveguide mode exists only for a single polarization component in a substrate having at least an electro-optical effect, and the optical waveguide. An optical modulator formed on the path for propagating the modulation signal in the forward direction or the backward direction, and an optical modulation means for modulating the phase of the light propagating in the optical waveguide according to the modulation signal supplied to the electrode; , A member having the same hardness as the substrate of the optical waveguide, and at least one end face of the member forms the same plane as the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. And an end face protection means disposed above the optical waveguide, wherein the optical waveguide has a light incident end face and a light emitting end face which are respectively formed on a flat surface by polishing the end face of the member and the end face of the substrate. It is characterized by having.

In the optical modulator according to the present invention, the optical waveguide may be formed as a region in which a waveguide mode exists only for the single polarization component by proton exchange, for example. ..

Further, in the optical modulator according to the present invention, the optical waveguide may be made of, for example, a nonlinear optical crystal.

Further, in the optical modulator according to the present invention, in the optical modulation means, for example, a reflection means for reflecting a modulation signal supplied from the oscillation means to one end side of the electrode is provided only on the other end side of the electrode. That is, the phase of light propagating in the forward direction is modulated by the modulation signal propagating in the forward direction without causing the supplied modulation signal to resonate, and the phase of light propagating in the backward direction is changed to the return path. It may be modulated by a modulation signal propagating in the direction.

Further, the optical modulator according to the present invention is, for example, as the reflecting means, a reflector for reflecting a modulation signal supplied from the other end to one end of the electrode, and a phase of the reflected modulation signal. It is possible to arrange a phase shifter for adjusting.

Further, in the optical modulator according to the present invention, the phase shifter determines, for example, the phase of the reflected modulation signal according to the shape of the electrode, the frequency of the modulation signal, and the group refractive index of the optical waveguide. It can be adjusted.

Further, in the optical modulator according to the present invention, the electrode of the optical modulator may have a ridge structure, for example.

Further, the present invention is an optical comb generator, comprising an oscillating means for oscillating a modulated signal of a predetermined frequency, an incident side reflection film and an emission side reflection film which are parallel to each other, and the In the resonance means for resonating the incident light and the substrate having at least the electro-optical effect so as to penetrate from the reflection film on the incident side to the reflection film on the emission side, the waveguide mode is generated only for a single polarization component. An optical waveguide formed as an existing region, and an electrode for propagating the modulation signal, which is formed on the optical waveguide and supplied from the oscillating means, in the forward direction or the backward direction, and includes the incident side reflection film. It is formed so as to penetrate through to the emission side reflection film, modulates the phase of the light resonated by the resonating means in accordance with the modulation signal supplied from the oscillating means, and sets the center of the frequency of the incident light. The optical comb generating means for generating sidebands at the frequency intervals of the modulated signal and a member having the same hardness as the substrate of the optical waveguide, and at least one end face of the member is incident on the optical waveguide. An end face or a light emitting end, the end face protecting means disposed on the optical waveguide so as to form the same plane as the end face of the substrate, the incident side reflection film and the emission side reflection film, It is characterized in that it is adhered to a flat surface formed by polishing the end surface of the member and the end surface of the substrate.

In the optical comb generator according to the present invention, the optical waveguide may be formed as a region in which a waveguide mode exists only for the single polarization component by proton exchange, for example. it can.

In the optical comb generator according to the present invention, the optical waveguide may be made of, for example, a nonlinear optical crystal.

Further, in the optical comb generator according to the present invention, in the optical modulation means, for example, a reflection means for reflecting a modulation signal supplied from the oscillation means to one end side of the electrode is provided only on the other end side of the electrode. The phase of the light propagating in the forward direction is modulated by the modulating signal propagating in the forward direction without causing the modulation signal supplied from the oscillating means to resonate, and the light propagating in the backward direction is also modulated. Can be modulated by the modulation signal propagating in the backward direction.

Further, the optical comb generator according to the present invention is, for example, as the reflection means, a reflector for reflecting a modulation signal supplied from the other end to one end of the electrode, and a reflection signal of the reflected modulation signal. A phase shifter for adjusting the phase may be provided.

Further, in the optical comb generator according to the present invention, the phase shifter determines, for example, the phase of the reflected modulation signal according to the shape of the electrode, the frequency of the modulation signal, and the group refractive index of the optical waveguide. Can be adjusted.

Further, in the optical comb generator according to the present invention, the electrode of the light modulating means may have a ridge structure, for example.

Further, the optical comb generator according to the present invention includes, for example, a photodetecting unit that detects a part of the optical comb obtained by the optical comb generating unit, and the resonance unit from the photodetection signal obtained by the photodetecting unit. The control means for generating a control signal for zeroing the error of the resonance length with respect to the control target and controlling the resonance length of the resonance means can be provided.

According to the present invention, an optical waveguide formed as a region in which a waveguide mode exists only for a single polarization component in a substrate having at least an electro-optical effect so as to penetrate from the incident end to the emission end Therefore, only a single polarized component of the light incident through the incident side reflection film is propagated through the optical waveguide, phase-modulated, and emitted from the emission end. By providing the incident side reflection film and the emission side reflection film that form the resonance means, it is possible to generate an optical comb as an optical modulation output of only a single polarization component via the emission side reflection film. Further, a member having the same hardness as the substrate for forming the optical waveguide from the upper surface is formed, and at least one end face thereof forms the same plane as the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. As described above, the incident side reflection film and the emission side reflection film that constitute the resonance means are provided on the plane formed by polishing the end face of the member and the end face of the substrate. Since it is attached, it is possible to suppress chipping and rounding at the time of processing the corners of the waveguide end face, and it is possible to adhere stably without peeling off at the corners of the uppermost end face of each reflection film. It is possible to improve the finesse of the optical resonator and enhance the function of the device itself.

Therefore, according to the present invention, since the transmission mode waveform is not deformed by using the optical waveguide that allows only a single polarization component to pass, the resonator control can be stabilized, and the optical comb generator can be used. Can be stabilized, the accuracy of the measuring device including the optical comb can be improved, and errors can be reduced.

It is a perspective view which shows the structure of the optical modulator to which this invention is applied. It is a side view of the said optical modulator. FIG. 4 is a vertical cross-sectional view of a main part in each step for explaining the manufacturing method of the optical modulator. It is a perspective view of the board|substrate which provided three optical waveguides produced in order to measure the end surface reflectance of the optical modulator to which this invention is applied. It is a front view which shows the incident side end surface of the said board|substrate. It is a top view of the said board|substrate. It is a figure which shows the structure of the optical modulator of a reciprocal modulation type to which the present invention is applied. It is a figure which shows the intensity distribution in each frequency (wavelength) of a sideband at the time of applying this invention to an optical comb generator. It is a perspective view showing the composition of the optical comb generator to which the present invention is applied. It is a side view of the said optical comb generator. It is a front view which shows the plane in which the incident side reflection film in the said optical comb generator is formed. It is a perspective view showing the composition of the optical modulator (optical comb generator) which has the electrode which has the ridge structure to which the present invention is applied. FIG. 6 is a longitudinal sectional view of a main part in each step for explaining a method for manufacturing the optical modulator (optical comb generator). It is a perspective view showing a substrate which forms an electrode which has a ridge structure of the above-mentioned optical modulator (optical comb generator). It is a principal part longitudinal cross-sectional view which shows the electrode which has the ridge structure of the said optical modulator (optical comb generator). It is a figure for demonstrating the result of having measured the change of the drive voltage (AC Vpi) in 25 GHz by the presence or absence of the ridge structure of an electrode about the optical modulator to which this invention is applied. FIG. 6 is a diagram for explaining the results of actual measurement of changes in DC drive voltage (DC Vpi) depending on the presence/absence of a ridge structure of electrodes in the optical modulator to which the present invention is applied. It is a block diagram which shows the structural example of the optical comb generator using the low power type optical comb module to which this invention is applied. It is a block diagram which shows the other structural example of the optical comb generator using the low power type optical comb module to which this invention is applied. It is a block diagram which shows the structural example of the optical comb light source constructed|assembled using the low power type optical comb module to which this invention is applied. FIG. 6 is a characteristic diagram showing a transmission mode waveform without deformation obtained when feedback controlling the resonance length of an optical resonator in an optical comb generator using an optical waveguide that allows only a single polarization component to which the present invention is applied. In a conventional optical comb generator that uses an optical waveguide that transmits polarization components with mixed orthogonal modes, a characteristic diagram showing the deformation of the transmission mode waveform due to orthogonal polarization components that occurs when the resonance length of the optical resonator is feedback controlled. Is.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that common components will be described with common reference numerals in the drawings. Further, it is needless to say that the present invention is not limited to the following examples and can be arbitrarily modified without departing from the gist of the present invention.

The present invention is applied to, for example, a waveguide type optical modulator 8 having a structure as shown in FIGS. FIG. 1 is a perspective view showing a configuration of an optical modulator 8 to which the present invention is applied, and FIG. 2 is a side view of the optical modulator 8.

This waveguide type optical modulator 8 includes a substrate 11, an optical waveguide 12 formed on the substrate 11 for modulating the phase of a single polarization component of propagating light, and an optical waveguide 12 on the substrate 11. The buffer layer 14 laminated so as to cover it, the electrode 83 provided on the upper surface of the optical waveguide 12 so that the direction of the modulation electric field becomes substantially perpendicular to the light propagation direction, and the electrode layer 83 via the optical waveguide 12. The first end face 84 and the second end face 85 provided so as to face each other, and the first protective material 86 disposed on the upper part of the optical waveguide 12 so as to form the same plane as the first end face 84. And a second protective material 87 disposed on the optical waveguide 12 so as to form the same plane as the second end surface 85, a first end surface 84 and an end surface 86a of the first protective material 86. Between the incident-side antireflection film 63 deposited on the flat surface 91 formed between the second end surface 85 and the end surface 87a of the second protective material 87. The emission side antireflection film 64, an oscillator 16 arranged at one end of the electrode 83 for oscillating a modulation signal of the frequency f _m , and a terminating resistor 18 arranged at the other end of the electrode 83. There is.

The substrate 11 is obtained by cutting a large crystal such as LiNbO ₃ or GaAs having a diameter of 3 to 4 inches grown by a pulling method into a wafer. The ridges 20 for forming the electrodes 83 are provided on the cut-out substrate 11 by subjecting it to mechanical polishing, chemical polishing, or the like.

The optical waveguide 12 has a waveguide mode only for a single polarized component in the substrate 11 having at least an electro-optical effect so as to penetrate from the incident side antireflection film 63 to the emission side antireflection film 64. It is formed as a region.

The light incident on the optical waveguide 12 via the incident-side antireflection film 63 propagates while only a single polarization component is totally reflected at the boundary surface of the waveguide 12.

Here, the optical waveguide 12 that allows only a single polarization component to pass through the substrate 11 having the electro-optical effect is formed by the optical waveguide formation method that causes a change in the refractive index only to a specific polarization component, for example, the proton exchange method. Can be formed as a region having a high refractive index only for the polarized wave component.

The optical waveguide 12 can be formed, for example, on the substrate 11 made of LiNbO ₃ or the like as a region where a waveguide mode exists only for a single polarization component by the proton exchange method.

Further, when the optical waveguide 12 is manufactured by diffusing Ti atoms in the substrate 11 or by epitaxially growing it on the substrate 11, the waveguide mode is changed to a single polarization by devising the refractive index distribution. It can be formed as a limited region. As the optical waveguide 12, for example, a LiNbO ₃ crystal optical waveguide can be used and can be formed by diffusing Ti on the surface of the substrate 11 made of LiNbO ₃ or the like. The region in which Ti is diffused has a higher refractive index than other regions and can confine light of a single polarization component, so that light of a single polarization component can be propagated. The waveguide 12 can be formed. Although the refractive index is high for both polarization components orthogonal to each other, there is also a condition that the guided mode is established only for a single polarization component.

The LiNbO ₃ crystal type optical waveguide 12 manufactured based on such a method has electrical properties such as the Pockels effect in which the refractive index changes in proportion to the electric field and the Kerr effect in which the refractive index changes in proportion to the square of the electric field. Since it has an optical effect, the light of a single polarization component can be modulated by utilizing such a physical phenomenon.

The buffer layer 14 covers the optical waveguide 12 in order to suppress the propagation loss of the light of a single polarized component. By the way, if the buffer layer 14 is made too thick, the electric field strength is lowered and the modulation efficiency is lowered. Therefore, the film thickness is set as thin as possible within a range in which the propagation loss of light of a single polarization component does not increase. You may do so.

The electrode 83 is made of, for example, a metal material such as Ti, Pt, or Au, and drives the modulation signal of the frequency f _m supplied from the oscillator 16 into the optical waveguide 12 to phase the light propagating in the optical waveguide 12. Apply modulation.

The first protective material 86 and the second protective material 87 are each composed of a member corresponding to the material of the substrate 11. The first protective material 86 and the second protective material 87 may be made of the same material as the substrate 11. Further, the end face 86a and the first end face 84 of the first protective material 86 forming the flat surface 91 may be processed so as to have the same crystal orientation, and similarly the flat surface 92 forming the flat surface 92 may be formed. The end surface 87a and the second end surface 85 of the second protective material 87 may be processed so as to have the same crystal orientation.

The incident-side antireflection film 63 is deposited on the flat surface 91 formed between the first end surface 84 and the end surface 86a of the first protective material 86. The emission-side antireflection film 64 is deposited on the flat surface 91 formed between the second end surface 85 and the end surface 87a of the second protective material 87. These antireflection films 63 and 64 may be made of a low reflection film, or may be made uncoated to obtain the same effect as when the low reflection film is applied. ..

The terminating resistor 18 is a resistor attached to the terminating end of the electrode 83, and prevents the reflection of the electric signal at the terminating end to prevent the waveform from being disturbed.

Next, a method of manufacturing the optical modulator 8 to which the present invention is applied will be described with reference to FIG.

First, in step S11, a photoresist pattern 13 is formed on the surface of the substrate 11 made of LiNbO ₃ crystal.

Next, in step S12, the LiNbO ₃ crystal substrate 11 having the photoresist pattern 13 formed on the surface is heated while being immersed in a proton exchange liquid such as benzoic acid to remove Li in the surface layer portion of the substrate 11. By the proton exchange method of substituting with H ⁺ , the optical waveguide 12 is formed as a region where the guided mode exists only for a single polarized component.

The step of manufacturing the optical waveguide 12 in steps S11 and S12 is not limited to the proton exchange method. For example, in step S11, the photoresist pattern 13 is formed on the surface of the substrate 11 made of LiNbO ₃ crystal. Then, Ti is vapor-deposited on the surface of the substrate 11 made of LiNbO ₃ crystal, and the photoresist is removed to produce a Ti fine line having a width of micron size. By heating the substrate 11 on which the thin wire of Ti is formed, the Ti atoms are thermally diffused in the substrate 11 and the optical waveguide 12 is formed as a region where the waveguide mode exists only for a single polarization component. This may be replaced by the Ti diffusion method to be formed.

Next, in step S13, the resist pattern 13 is removed and a SiO ₂ thin film as the buffer layer 14 is deposited on the surface of the substrate 11. In this step S13, the buffer layer 14 may be formed by a method of attaching a SiO ₂ wafer to the surface of the substrate 11. In such a case, in consideration of the electrode attachment region in the next step S14, the vapor-deposited buffer layer 14 may be polished so as to be controlled to have an appropriate film thickness.

Next, in step S14, the electrode 83 is formed on the buffer layer 14.

Next, in step S15, the protective materials 86 and 87 are adhered to the upper portion of the optical waveguide 12. Regarding the method of adhering the protective materials 86 and 87, they may be attached by an adhesive, or they may be directly joined based on another method. When the substrate 11 is made of LiNbO ₃ crystal, the protective materials 86 and 87 may be made of the same material, LiNbO ₃ . In this step S15, it is possible to form flat surfaces 91 and 92 between the end surfaces 86a and 87a of the attached protective materials 86 and 87 and the first end surface 84 and the second end surface 85, respectively. And cut them into pieces.

Finally, in step S16, the obtained flat surfaces 91 and 92 are polished. Then, the incident side antireflection film 63 and the emission side antireflection film 64 are formed on the polished flat surfaces 91 and 92, respectively, over the entire surface. Incidentally, in this step S16, the incident side antireflection film 63 and the emission side antireflection film 64 may be first formed on the flat surfaces 91 and 92, and then they may be polished.

As described above, in the optical modulator 8 to which the present invention is applied, since the protective materials 86 and 87 are attached at each end portion, the end surface of the optical waveguide 12 that is conventionally located at the corner of the top end surface is formed. Moves to substantially the center of the plane 91 (92). As a result, even if the corners of the flat surface 91 (92) are chipped during the polishing in step S16, the end faces of the optical waveguide 12 are not chipped. That is, it becomes possible to make the end face of the optical waveguide 12 less likely to be chipped. This makes it possible to suppress light loss from each end face of the optical waveguide 12 as much as possible.

Further, by configuring the material of the protective materials 86, 87 to be an optimum material corresponding to the material of the substrate 11, the polishing rate in step S16 can be adjusted from the first end surface 84, the second end surface 85 to the end surface 86a of the substrate 11. It is possible to make it uniform over 87a. As a result, the end face of the optical waveguide 12 does not become round during processing, flat surfaces 91 and 92 made of flat polished surfaces can be obtained, and reflection loss at the end face of the optical waveguide 12 can be minimized. Become. Further, the reflection loss can be further suppressed by making the crystal orientations of the end faces forming the planes 91 and 92 the same.

Further, by intentionally providing the protective materials 86 and 87, the polishing accuracy in step S16 is improved, and the perpendicularity of the obtained flat surface 91 (92) to the optical waveguide 12 is also improved. As a result, it is possible to minimize the light loss due to the deviation of the verticality.

Further, the incident-side antireflection film 63 and the emission-side antireflection film 64 are formed over a wide range from the first end face 84, the second end face 85 to the end faces 86a, 87a of the substrate 11, and thus are very stable. Therefore, peeling is less likely to occur, and the reproducibility of film formation can be improved.

In practice, in order to experimentally verify the effect of providing the protective materials 86 and 87, the flat surface 91 (92) after the protective materials 86 and 87 were attached was polished, and the end face of the optical waveguide 12 was polished. It is possible to confirm that the optical polishing is performed flat, which is suitable for depositing the incident side antireflection film 63 and the emission antireflection film 64 without any chipping or bending in the part.

Particularly, the first protective material 86 and the second protective material 87 are made of the same material as the substrate 11, and the end surfaces 86a, 87a and the first end surface 84 of the protective materials 86, 87 forming the flat surfaces 91, 92 are formed. By processing so that the second end surface 85 and the second end surface 85 have the same crystal orientation, the hardness of the crystal becomes the same between the two, so that the planes 91 and 92 do not tilt due to the difference in polishing rate.

In the optical modulator 8 having such a configuration, light of only a single polarization component that is incident through the incident-side antireflection film 63 and propagates in the optical waveguide 12 is modulated at the frequency f _m supplied from the oscillator 16. The signal is phase-modulated by the signal and emitted through the emission-side antireflection film 64. Moreover, in the optical modulator 8 to which the present invention is applied, the end faces of the optical waveguide 12 can be moved to the substantially central portion of the flat surface 91 (92) by attaching the protective material 86, 87 at each end portion. The chipping or rounding of the end face of the optical waveguide 12, the verticality between the optical waveguide 12 and the planes 91, 92 can be secured, and the polishing accuracy on the planes 91, 92 can be improved, and the yield can be improved.

Here, only a single polarization type optical waveguide made by the proton exchange method in which only a single polarization component of incident light is propagated and only orthogonal polarization components of the incident light are propagated Regarding the orthogonal polarization type optical waveguide manufactured by the Ti diffusion method, as shown in FIGS. 4, 5 and 6, width W ₁ =1.9 [mm], length L ₁ =27.4 [mm], Three optical waveguides 12A, 12B and 12C are formed on a LiNbO ₃ crystal substrate 11 having a thickness T ₁ =0.5 [mm], and a width W _{2 is} 1.9 [mm] above the optical waveguides 12A, 12B and 12C. ], the length L ₂ =1.5 [mm], and the thickness T ₂ =0.5 [mm], the protective materials 86 and 87 are adhered, and the end surfaces of the protective materials 86 and 87 and the end surface of the LiNbO ₃ crystal substrate 11 are bonded. by polishing the three optical waveguides 12A, 12B, the incident surface and the exit surface of the 12C as LiNbO ₃ crystal substrate blocks and finished flat, three optical waveguides 12A respectively, 12B, 12C optical path width _{W 3} of 10 samples of 6 types of 6.0 [μm], 6.3 [μm], 6.6 [μm], 6.9 [μm], 7.2 [μm], 7.5 [μm] After being manufactured, the reflectances on the incident surfaces A ₁ , B ₁ , C ₁ and the emission surfaces A ₂ , B ₂ , C ₂ of the three optical waveguides 12A, 12B, 12C were measured, and the finesse and the transmittance of each sample were measured. Was obtained, the following results were obtained.

That is, the finesse of the orthogonal polarization type optical waveguide was about 30 to 45, whereas the finesse of the single polarization type optical waveguide was about 50 to 65. Further, the transmittance of the orthogonal polarization type optical waveguide was about 12.5 to 25[%], whereas the transmittance of about 20 to 32.5[%] was obtained with the single polarization type optical waveguide. Has been.

The present invention is not limited to the above embodiment. For example, the invention can be applied to a reciprocal modulation type optical modulator 51 as shown in FIG. Regarding the configuration and elements of the optical modulator 51 that are the same as those of the optical modulator 8 described above, the description in FIGS. 1 and 2 is cited, and the description thereof is omitted here.

As shown in (a) of FIG. 7, the optical modulator 51 is formed as a substrate 11 and a region on the substrate 11 in which a guided mode exists only for a single polarization component. The optical waveguide 12 that modulates the phase of light to be generated, the buffer layer 14 that is laminated on the substrate 11 so as to cover the optical waveguide 12, and the direction of the modulation electric field is substantially perpendicular to the light propagation direction. The electrode 83 provided on the upper surface of the optical waveguide 12, the first protective material 86 and the second protective material 87 provided on the upper portion of the optical waveguide 12, and the antireflection film 63 deposited on the flat surface 91. And an emission-side reflection film 94 attached on the flat surface 92.

When actually using the optical modulator 51, as shown in FIG. 7B, the input light from a light source (not shown) is transmitted or the output light output from the optical modulator 51 is changed. An optical system including an optical transmission line 23 configured by an optical fiber or the like for transmitting to the outside, an optical circulator 21 for separating the input light and the output light, and a focuser 22 optically connected to the optical circulator 21. Is further provided, and an oscillator 16 disposed on one end side of the electrode 83 for oscillating a modulation signal having a frequency f _m and a terminating resistor 18 disposed on the other end side of the electrode 83 are further disposed.

The antireflection film 63 is deposited on the flat surface 91 formed between the first end surface 84 and the end surface 86a of the first protective material 86. The antireflection film 63 may be formed of a low reflection film, or may be formed uncoated to obtain the same effect as when the low reflection film is applied.

The focuser 22 focuses the input light that has passed through the optical circulator 21 on the end portion of the optical waveguide 12, collects the output light that has passed through the antireflection film 63 from the end portion of the optical waveguide 12, and collects the output light. Send to. The focuser 22 may be composed of a lens or the like for optically coupling the input light so that the spot diameter corresponds to the diameter of the optical waveguide 12.

In the optical modulator 51 having such a configuration, one end of the optical waveguide 12 formed as a region in which a guided mode exists only for a single polarization component is emitted as a high reflection film. By providing the side reflection film 94 and providing the antireflection film 63 at the other end, it operates as a so-called reciprocal modulation type optical modulator. The input light incident on the optical waveguide 12 is modulated while propagating only a single polarized component in the optical waveguide 12, is reflected by the exit side reflection film 94 on the end face, and then propagates again in the optical waveguide 12. After passing through the antireflection film 63, it is emitted to the focuser 22 side and becomes output light having only a single polarization component. At the same time, the electrical signal of the frequency f _m supplied from the oscillator 16 is absorbed by the terminal resistor 18 after propagating on the electrode 83 while modulating the input light.

Further, as shown in (c) of FIG. 7, this optical modulator 51 is provided with an oscillator 25 and a terminating resistor 27 on one end side of an electrode 83 to propagate an electric signal supplied from the oscillator 25 on the electrode 83. Then, this may be reflected on the other end side of the electrode 83. At this time, an isolator 26 for separating the electric signal supplied from the oscillator 25 and the electric signal reflected on the other end side of the electrode 83 may be provided. Further, in this optical modulator 51, an incident side reflection film 93 having a high reflectance is applied. This allows light to resonate inside the optical waveguide 12. Further, as an alternative to the incident side reflection film 93, the above-mentioned antireflection film 63 having a low reflectance may be applied. This makes it possible to perform phase modulation while the light reciprocates once in the optical waveguide 12.

In the optical modulator 51, the reflection phase of the electric signal is adjusted according to the phase of the light reflected by the emission side reflection film 94, so that the phase of the light can be modulated by each electric signal reciprocating through the electrode 83. Therefore, the modulation efficiency can be increased. In particular, by attaching the protective materials 86 and 87, the peeling and chipping of the films 63 and 94 can be suppressed as described above, and the optical modulator 51 with improved finesse can further increase the optical modulation efficiency. Becomes

Further, when these optical modulators 51 are applied to an optical comb generator, it is possible to perform reciprocal modulation on light that resonates in the optical waveguide 12 by an electric signal that reciprocates through the electrodes. In such a case, the intensity distribution at each frequency (wavelength) of the generated sideband is as shown in FIG. 8 when the modulation frequency of the electric signal applied to the electrode 83 is 25 GHz and its power is 0.5 W. In, the modulation index expressed as the magnitude of the modulation applied in the optical waveguide 12 is π radian per propagation direction. From this result, it can be seen that the half-wave voltage Vπ defined as the voltage required to move the phase by half a wavelength is 7.1V.

The optical modulator 51 may divide the output of the oscillator 16 as a signal source, instead of reflecting the electric signal, to separately drive and input the electric signal from both ends of the electrode 83. This may be performed by connecting different oscillators 16 to both ends of the electrode 83.

Here, in the optical modulators 8 and 51 according to the present invention, the electrode 83 provided on the upper surface of the optical waveguide 12 to which the modulation signal is supplied has a ridge structure to further improve the optical modulation efficiency. Can be made

Here, in the optical modulators 8 and 51 thus produced, as shown in FIGS. 9 and 10, in the step S16, the flat surfaces 91 and 92 are polished parallel to each other, and the polished flat surfaces are obtained. By forming an incident-side reflection film 93 and an emission-side reflection film 94 on 91 and 92 instead of the incident-side antireflection film 63 and the emission-side antireflection film 64, respectively, an optical comb is generated. It functions as a container 1.

That is, in the optical comb generator 1, the incident side reflection film 93 and the emission side reflection film 94 are provided so as to be parallel to each other in order to resonate the light incident on the optical waveguide 12. The optical resonator 5 is configured to resonate the light passing therethrough to resonate.

Light of frequency ν ₁ is incident on the incident side reflection film 93 from a light source (not shown). Further, the incident side reflection film 93 reflects the light of the single polarization component reflected by the emission side reflection film 94 and having passed through the optical waveguide 12. The emission side reflection film 94 reflects the light of the single polarization component that has passed through the optical waveguide 12. Further, the emission side reflection film 94 emits the light of the single polarization component passing through the optical waveguide 12 to the outside at a constant rate.

Although the incident-side reflection film 93 and/or the emission-side reflection film 94 may be formed over the entire planes 91 and 92, they are formed so as to cover only the end of the optical waveguide 12 at a minimum. It should have been done.

The terminating resistor 18 is a resistor attached to the terminating end of the electrode 83, and prevents the reflection of the electric signal at the terminating end to prevent the waveform from being disturbed.

FIG. 11 shows the plane 91 on which the incident side reflection film 93 is formed, from the direction A in FIG.

The first end surface 84 including the light incident end of the optical waveguide 12 and the end surface 86a of the protective material 86 form the same plane 91. The formed plane 91 has an inclination of 0.05° or less. The loss when light with a 1/e ² beam diameter of 10 μm is reflected by an end face with an inclination of 0.05° with respect to the plane 91 with an inclination of 0.05° is 4×10 ⁻⁴ It is negligibly smaller than the reflectance of the side reflection film 93.

By thus forming the first end face 84 and the second end face 85 substantially perpendicular to the optical waveguide 12, the incident side reflection film 93 and the emission side reflection film 94 attached to the optical waveguide 12 form a single unit. The polarized light can be efficiently resonated.

In the optical comb generator 1 having the above-described configuration, the light incident from the outside through the incident-side reflection film 93 has a single polarized light component propagating in the optical waveguide 12 in the outward direction and exiting side. The light is reflected by the reflective film 94 and partially transmitted to the outside. The light of the single polarization component reflected by the emission side reflection film 94 propagates in the optical waveguide 12 in the backward direction and is reflected by the incidence side reflection film 93. By repeating this, light with a single polarization component resonates in the optical waveguide 12.

Further, by inputting the electric signal synchronized with the time when the light of the single polarization component travels back and forth in the optical waveguide 12 through the electrode 83 as a driving input, the light of the single polarization component is converted into the optical modulator. It is possible to perform deep phase modulation several tens of times or more as compared with the case where the signal passes through the inside 8 only once. Also, hundreds of sidebands can be generated over a wide band around the frequency ν ₁ of the incident light. Incidentally, the frequency intervals of the generated sidebands are all equal to the frequency f _{m of the} input electric signal. Therefore, the light modulator 8 has a single polarization band composed of a large number of side bands by replacing the incident side antireflection film 63 and the emission side antireflection film 64 with the incident side reflection film 93 and the emission side reflection film 94. It functions as an optical comb generator 1 that generates an optical comb of wave components.

The optical comb generator 1 guides only a single polarization component on the substrate 11 having at least the electro-optical effect so as to penetrate from the incident side reflection film 93 to the emission side reflection film 94 which form the resonance means. Since the optical waveguide 12 formed as the region where the mode exists is provided, only a single polarization component of the light incident through the incident side reflection film 93 is propagated through the optical waveguide 12, An optical comb can be generated as an optical modulation output of only a single polarization component via the emission side reflection film 94.

As described above, in the optical modulators 8 and 51 to which the present invention is applied, since the protective materials 86 and 87 are attached to the respective end portions, the optical waveguide 12 that is conventionally located at the uppermost corner of the end face. As a result, the end surface of the optical waveguide 12 is moved to the substantially central portion of the flat surface 91 (92), so that even if the corner of the flat surface 91 (92) is chipped during the polishing in step S17, the end surface of the optical waveguide 12 is not chipped. That is, it becomes possible to make the end face of the optical waveguide 12 less likely to be chipped. This makes it possible to suppress the optical loss from each end face of the optical waveguide 12 as much as possible. Moreover, by providing the protective materials 86 and 87, it is possible to suppress a change in the film thickness due to the incident side reflection film 93 and the emission side reflection film 94 to be adhered from the flat surfaces 91 and 92 to other side surfaces. . Therefore, the film thickness near the end face of the optical waveguide 12, which is important for ensuring the reflectance, can be optimized, and the reflectance can be further improved.

Further, the incident-side reflection film 93 and the emission-side reflection film 94 are extremely stable because they are formed over a wide range from the first end face 84, the second end face 85 to the end faces 86a, 87a of the substrate 11. Further, it is difficult to peel off, and it is possible to improve the reproducibility of film formation.

In practice, in order to experimentally verify the effect of providing the protective materials 86 and 87, the flat surface 91 (92) after the protective materials 86 and 87 were attached was polished, and the end face of the optical waveguide 12 was polished. It is possible to confirm that flat optical polishing suitable for deposition of the incident-side reflection film 93 and the emission-side reflection film 94 is performed without any chipping or bending in the part.

Particularly, the first protective material 86 and the second protective material 87 are made of the same material as the substrate 11, and the end surfaces 86a, 87a and the first end surface 84 of the protective materials 86, 87 forming the flat surfaces 91, 92 are formed. By processing so that the second end surface 85 and the second end surface 85 have the same crystal orientation, the hardness of the crystal becomes the same between the two, so that the planes 91 and 92 do not tilt due to the difference in polishing rate.

As described above, in the optical modulator 8 and the optical comb generator 1 to which the present invention is applied, the end faces of the optical waveguide 12 are flattened as shown in FIG. Since it can be moved to the substantially central part of (92), the end face of the optical waveguide 12 is chipped or rounded, the verticality between the optical waveguide 12 and the planes 91, 92 is secured, and the polishing accuracy on the planes 91, 92 is improved. It is possible to suppress peeling and wraparound of the incident-side reflection film 93 and the emission-side reflection film 94, improve the reflectance of the incident-side reflection film 93 and the emission-side reflection film 94, realize designed reflection characteristics, and improve the performance reproducibility of the reflection film. It will be possible. As a result, it is possible to improve the finesse of the optical resonator 5 composed of the incident side reflection film 93 and the emission side reflection film 94, and to manufacture an optical modulator and an optical comb generator with good reproducibility with good reproducibility. It becomes possible and the yield can be improved.

Further, the present invention is applied to, for example, a waveguide type optical modulator 8A (optical comb generator 1A) having a configuration as shown in FIG.

In this waveguide type optical modulator 8A (optical comb generator 1A), the electrode 83 in the waveguide type optical modulator 8 (optical comb generator 1A) shown in FIGS. 1 and 2 (FIGS. 9 and 10) has a ridge structure. For the same configuration and elements as those of the optical modulator 8 (optical comb generator 1) described above, the description in FIGS. 1 and 2 (FIGS. 9 and 10) is cited. Is omitted.

In this waveguide type optical modulator 8A (optical comb generator 1A), the substrate 11 is obtained by cutting a large crystal such as LiNbO ₃ or GaAs having a diameter of 3 to 4 inches grown by a pulling method into a wafer shape. is there. The ridges 20 for forming the electrodes 83A having a ridge structure are provided on the cut-out substrate 11 by subjecting it to mechanical polishing, chemical polishing, or the like.

The optical waveguide 12 is formed so as to penetrate from the entrance end to the exit end by the proton exchange method or the Ti diffusion method, and guides only the single polarization component in order to propagate the light of the single polarization component. It is formed as a formation where the wave modes are present.

The refractive index of the layer forming the optical waveguide 12 is set higher than that of other layers such as the substrate 11 only for a single polarized component. In the light incident on the optical waveguide 12, only a single polarization component propagates while being totally reflected at the boundary surface of the optical waveguide 12.

The LiNbO ₃ crystal type optical waveguide 12 manufactured based on such a method has electrical properties such as the Pockels effect in which the refractive index changes in proportion to the electric field and the Kerr effect in which the refractive index changes in proportion to the square of the electric field. Since it has an optical effect, the light of a single polarization component can be modulated by utilizing such a physical phenomenon.

The electrode 83A having a ridge structure has a main electrode formed on the ridge portion 20, and is made of a metal material such as Ti, Pt, or Au. The electrode 83A having a ridge structure in which the main electrode is formed on the ridge portion 20 propagates in the optical waveguide 12 by inputting the modulated signal of the frequency f _m supplied from the oscillator 16 to the optical waveguide 12. Phase modulation is applied to the light.

A method of manufacturing the waveguide type optical modulator 8A (optical comb generator 1A) having such a structure will be described with reference to FIG.

That is, first, in step S21, a photoresist pattern 13 is formed on the surface of the substrate 11 made of LiNbO ₃ crystal.

Next, in step S22, the LiNbO ₃ crystal substrate 11 having the photoresist pattern 13 formed on the surface thereof is heated while being immersed in a proton exchange liquid such as benzoic acid to remove Li in the surface layer portion of the substrate 11. By the proton exchange method of substituting with H ⁺ , the optical waveguide 12 is formed as a region where the guided mode exists only for a single polarized component.

The step of producing the optical waveguide 12 in steps S21 and S22 is not limited to the proton exchange method. For example, in step S21, the photoresist pattern 13 is formed on the surface of the substrate 11 made of LiNbO ₃ crystal. Then, Ti is vapor-deposited on the surface of the substrate 11 made of LiNbO ₃ crystal, and the photoresist is removed to produce a Ti fine line having a width of a micron size. By heating the substrate 11 on which the thin wire of Ti is formed, the Ti atoms are thermally diffused in the substrate 11 and the optical waveguide 12 is formed as a region where the waveguide mode exists only for a single polarization component. This may be replaced by the Ti diffusion method to be formed.

Next, the process proceeds to step S23, the resist pattern 13 of the substrate 11 on which the optical waveguide 12 is formed is removed, and the electrode 83A having a ridge structure is formed by a process such as mechanical polishing or chemical polishing, as shown in FIG. A ridge portion 20 for forming the ridge is provided.

Next, in step S24, a SiO ₂ thin film as the buffer layer 14 is deposited on the surface of the substrate 11. In this step S24, the buffer layer 14 may be formed by a method of attaching a SiO ₂ wafer to the surface of the substrate 11. In such a case, the vapor deposition buffer layer 14 may be polished to control the film thickness to an appropriate thickness in consideration of the electrode attachment region in step S25 described later.

Next, the process proceeds to step S25, and an electrode 83A having a ridge structure is formed on the buffer layer 14 of the substrate 11 as shown in the vertical cross section of the main part of FIG.

Next, in step S26, the protective materials 86 and 87 are adhered to the upper portion of the optical waveguide 12. Regarding the method of adhering the protective materials 86 and 87, they may be attached by an adhesive, or they may be directly joined based on another method. When the substrate 11 is made of LiNbO ₃ crystal, the protective materials 86 and 87 may be made of the same material, LiNbO ₃ . In this step S26, it is possible to form flat surfaces 91 and 92 between the end surfaces 86a and 87a of the attached protective materials 86 and 87 and the first end surface 84 and the second end surface 85, respectively. And cut them into pieces.

In the optical modulator 8A to which the present invention is applied, in the final step S27, the obtained planes 91 and 92 are polished, and the incident side antireflection film 63 and the emission side reflection are provided on the polished planes 91 and 92. The prevention films 64 are formed over the respective surfaces.

In addition, in the optical comb generator 1A to which the present invention is applied, the flat surfaces 91 and 92 are polished in parallel with each other in step S27, and the incident-side antireflection film 63 and the outgoing light are emitted onto the polished flat surfaces 91 and 92. Instead of the side anti-reflection film 64, an incident side reflection film 93 and an emission side reflection film 94 are formed over one surface.

In the optical modulator 8A and the optical comb generator 1A having such a configuration, the oscillator 16 is provided in the electrode 83A having the ridge structure with respect to only the light of a single polarization component which is incident from the incident end and propagates through the optical waveguide 12. The phase modulation can be efficiently performed by the modulation signal of the frequency f _m supplied from

In addition, in the optical modulator 8A and the optical comb generator 1A to which the present invention is applied, the end faces of the optical waveguide 12 are made substantially central in the plane 91 (92) by attaching the protective materials 86 and 87 at each end. Since it can be moved, chipping or rounding of the end face of the optical waveguide 12, securing verticality between the optical waveguide 12 and the planes 91, 92, and improving polishing accuracy on the planes 91, 92 are possible, thus improving the yield. Will also be possible.

Further, in the optical comb generator 1A, only a single polarization component of the light incident from the outside through the incident side reflection film 93 propagates in the optical waveguide 12 in the outward direction and is reflected by the emission side reflection film 94. It also partially penetrates to the outside. The light of the single polarization component reflected by the emission side reflection film 94 propagates in the optical waveguide 12 in the backward direction and is reflected by the incidence side reflection film 93. By repeating this, the light of the single polarization component resonates in the optical waveguide 12.

Further, by inputting an electric signal synchronized with the time when the light of the single polarization component makes a round trip in the optical waveguide 12 as a driving input through the electrode 83A, the light of the single polarization component is converted into the optical modulator. It is possible to perform deep phase modulation several tens of times or more as compared with the case where the signal passes through the inside 8 only once. Also, hundreds of sidebands can be generated over a wide band around the frequency ν ₁ of the incident light. Incidentally, the frequency intervals of the generated sidebands are all equal to the frequency f _{m of the} input electric signal. Therefore, the optical modulator 8A functions as an optical comb generator 1A that generates an optical comb having a single polarization component configured by a number of sidebands.

As described above, in the optical comb generator 1A to which the present invention is applied, a single polarization is formed on at least a substrate having an electro-optical effect so as to penetrate from the incident side reflection film 93 forming the resonance means to the emission side reflection film 94. Since the optical waveguide 12 formed as a region where the guided mode exists only for the wave component is provided, only a single polarization component of the light incident through the incident side reflection film 93 is After being propagated through the optical waveguide 12, an optical comb can be generated as an optical modulation output of only a single polarization component via the emitting side reflection film 94, and the protective material 86, 87 is attached at each end. Since it is attached, the end face of the optical waveguide, which has been positioned at the uppermost corner of the end face in the past, moves to the substantially central portion of the plane 91 (92). As a result, even when the corner of the flat surface 91 (92) is chipped during the polishing in step S27, the end face of the optical waveguide 12 is not chipped. That is, it becomes possible to make the end face of the optical waveguide 12 less likely to be chipped. This makes it possible to suppress light loss from each end face of the optical waveguide 12 as much as possible.

Moreover, this optical modulator 8A is provided with the electrode 83A having the ridge structure formed on the buffer layer 14 of the substrate 11 as shown in the longitudinal cross section of the main part of FIG. 15, so that the modulation efficiency is further improved. Can be made

Here, in this optical modulator 8A, the ridge width RW of the electrode 83A having a ridge structure formed on the buffer layer 14 of the substrate 11 is 10, 12, 14, 16, and 18 [μm], and the average of the ridge grooves is A sample of the optical modulator 8A having depths AVD (Average depths) of 3.3, 2.96, 4.79, and 4.72 [μm] was prepared, and the drive voltage (AC Vpi) at 25 GHz and DC The drive voltage (DC Vpi) was measured and the results are shown in FIGS. Vpi is the voltage required to modulate the phase by π radians.

That is, in the conventional optical modulator having an electrode structure having no ridge structure, the drive voltage (AC Vpi) at 25 GHz is about 8 to 10 V, and the DC drive voltage (DC Vpi) is about 6 to 6.5 V. On the other hand, in the optical modulator 8A including the electrode 83A having the ridge structure, the drive voltage (AC Vpi) at 25 GHz is about 3.5 to 7.5 V, and the DC drive voltage (DC Vpi) is 5 to 6 V. It has become a degree.

By providing the ridge structure in this way, the drive voltage (AC Vpi) at 25 GHz is reduced to about 70% of the original average voltage as compared with the case without the ridge structure, and the power is about 50%. Equivalent to a decrease in Further, the DC drive voltage (DC Vpi) has an average voltage reduced to about 80% of the original voltage as compared with the case without the ridge structure, which corresponds to a reduction of about 50% in electric power.

That is, the optical modulator 8A and the optical comb generator 1A are composed of a member having the same hardness as the substrate 11 of the optical waveguide 12, and at least one end face of the member is a light incident end or a light in the optical waveguide 12. A first protective material 86 and a second protective material 87, which are disposed on the optical waveguide 12 so as to form the same plane as the end surface of the substrate 11 including the emission end, are provided. Since the incident-side antireflection film 63 or the incident-side reflection film 93 and the emission-side antireflection film 63 or the emission-side reflection film 94 are respectively deposited on the plane formed by polishing the end face of the substrate, the optical waveguide end face is formed. It is possible to prevent the occurrence of chipping in the optical fiber, stabilize the attachment of the high reflection film, and improve the finesse of the optical resonator 5 including the incident side reflection film 93 and the emission side reflection film 94. Driving power can be reduced by providing the electrode 83A having a ridge structure.

Therefore, in the optical modulators 8 and 8A and the optical modulator 51 having the above-described configuration, at least one of the members 86 and 87 having the same hardness as the substrate 11 for forming the optical waveguide 12 from the upper surface is provided. Is disposed above the optical waveguide 12 so that its end face forms the same plane as the end face of the substrate 11 including the light incident end or the light emitting end of the optical waveguide 12, and the end faces of the members 86 and 87. Since the incident-side reflection film 93 and the emission-side reflection film 94 that form the resonance means are deposited on the plane formed by polishing the end face of the substrate 11, chipping during corner processing of the waveguide end face may occur. Suppresses rounding and allows each reflective film to be deposited stably without peeling off at the corners at the top of the end face. It improves the reflectance of the reflective film and the finesse of the optical resonator, and enhances the function of the device itself. A waveguide mode exists only for a single polarization component in the substrate 11 having at least the electro-optical effect so as to penetrate from the incident side reflection film 93 constituting the resonance means to the emission side reflection film 94. By providing the optical waveguide 12 formed as a region in which the light is incident, only a single polarization component of the light incident through the incident side reflection film 93 is propagated through the optical waveguide 12 and the emission side reflection film. An optical comb capable of generating a stable optical comb as an optical modulation output of only a single polarization component via 94 functions as the generators 1 and 1A.

The optical waveguides 12 in the optical modulators 8 and 8A and the optical modulator 51 as described above have a single polarization in the substrate 11 having at least an electro-optical effect so as to penetrate from the incident side reflection film 93 to the emission side reflection film 94. A low-power laser light source or optical comb that can output a laser beam or optical comb with only a single polarization component by being formed as a region where a guided mode exists only for the wave component. A generator can be built.

Next, the configuration of the optical comb generator 110 using the low power type optical comb module to which the present invention is applied is shown in the block diagram of FIG.

The optical comb generator 110 includes an optical coupler 111 that branches a part of the optical comb output from the low-power type optical comb module 100A to which the present invention is applied, and an optical detector that detects the light branched by the optical cup 111. And a control circuit 113 to which a photodetection signal obtained by the photodetector 112 is supplied.

The optical comb module 100A receives laser light from a laser light source (not shown) and inputs an RF modulation signal through the bias tee 114, so that a single polarization component of the incident laser light is received. An optical comb is generated and output by performing phase modulation with the RF modulation signal. In this optical comb module 100A, the resonance length of the resonance means by the incident side reflection film and the emission side reflection film provided in the optical waveguide is controlled by the temperature control by the temperature adjustment circuit 119.

The control circuit 113 obtains an error with respect to the control target from the light detection signal, generates a control signal that makes the error zero, and supplies the control signal to the bias tee 114.

By adding to the DC bias of the optical comb module 100A, the resonant frequency of the optical comb module 100A can be made to follow the input laser frequency.

The control circuit 113 may be a printed circuit board alone or a combination of an RF mixer or an isolator and a printed circuit board. By mixing the photodetection signal of the photodetector 112 and the synchronizing signal, a control signal corresponding to the amount of error from the control target is generated.

A part of the output of the RF modulation signal source can be used as the synchronization signal. In that case, the operating band of the photodetector 112 needs to be equal to or higher than the RF driving frequency.

In the control circuit 113, the low frequency component of the signal obtained by inputting the photodetection signal and the synchronizing signal to the mixer via the phase adjuster is taken as the error signal. Alternatively, another modulation signal (dither signal) can be used as the RF drive signal as the synchronization signal. The laser frequency or the resonance frequency of the optical comb module 100A is modulated with a smaller amplitude than that of the resonance mode FSR, and the output signal of the photodetector 112 and the synchronizing signal are mixed. If the dither signal frequency is low, it is also possible to convert the photodetection signal into a digital signal by an analog-digital converter and then generate an error signal by a product-sum operation of digital signal processing.

The adjusted frequency characteristic of the error signal is added as a control signal to the DC bias of the optical comb module 100A via the bias tee 114. Generally, the error signal is input to a circuit having functions of proportional, integral, and derivative, and the frequency characteristics of the control loop are determined by adjusting the amplitudes of these components, and the resonance frequency of the optical comb module 100A is the input laser. It is controlled so as to follow the oscillation frequency.

The block diagram of FIG. 19 shows the configuration of the optical comb generator 120 using the low power type optical comb module to which the present invention is applied.

The optical comb generator 120 performs resonator control by utilizing the reflected light of the low power type optical comb module 100A to which the present invention is applied, and a part of the reflected light of the low power type optical comb module 100A is optical. It is branched by the coupler 111 and is incident on the photodetector 112.

Each constituent element of the optical comb generator 120 is the same as the constituent element of the optical comb generator 110 shown in FIG. 18, and corresponding constituent elements are designated by the same reference numerals in FIG. 19 and detailed description thereof is omitted. To do.

The control circuit 113 obtains an error with respect to the control target from the photodetection signal obtained by the photodetector 112, and outputs a control signal such that the error becomes zero. By applying the control signal to the DC bias of the optical comb module, the resonance frequency of the optical comb module 100A can be made to follow the input laser frequency.

Further, in the low power type optical comb module to which the present invention is applied, for example, the optical comb light source 130 configured as shown in FIG. 20 can be constructed.
The optical comb light source 130 includes a laser light source 131 that oscillates a single frequency, a separation optical system 132 such as an optical coupler or an optical beam splitter that separates a single frequency laser light emitted from the laser light source 131 into two laser lights, A frequency shifter 135 for shifting the frequency of one of the laser beams separated by the separation optical system 132, two optical comb generators (OFCG1, OFCG2) 130A, 130B each using a low power type optical comb module, and the like are provided.

In this optical comb light source 130, the laser light emitted from one single-frequency-oscillation laser light source 131 is separated into two laser lights by a separation optical system 132, and two optical comb generators (OFCG1 and OFCG2) are provided. It is adapted to be input to 130A and 130B.

The two optical comb generators 130A and 130B are driven by oscillators 133A and 133B that oscillate at different frequencies f _m +Δf _m and frequency f _m . The respective oscillators 133A and 133B are phase-locked by the common reference oscillator 134, so that the relative frequencies of f _m +Δf _m and f _m become stable. A frequency shifter 135 such as an acousto-optic frequency shifter (AOFS) is provided in front of the optical comb generator (OFCG1) 130A, and the input laser light is given an optical frequency shift of frequency f _a by this frequency shifter 135. It is like this. As a result, the beat frequency between the carrier frequencies is not a DC signal but an AC signal of frequency f _a . As a result, convenient to the phase comparison for the beat signal of the beat signal and the low-frequency sideband of the frequency sideband of the carrier frequency is generated in the opposite frequency domain across the beat frequency f _a between the carrier frequency of the beat signal good.

The two optical comb generators (OFCG1 and OFCG2) 130A and 130B are each configured by a low power type optical comb module to which the present invention is applied, and only a single polarization component of the input laser light is phased. By modulating, it is possible to output an optical comb having a single polarization component. This optical comb light source 130 uses two laser light sources 131 of single frequency oscillation in common and two optical comb generators (OFCG1, OFCG2) 130A and 130B having different center frequencies and frequency intervals. For example, the first and second light sources in the range finder and the optical three-dimensional shape measuring instrument according to Japanese Patent No. 5231883 previously proposed by the present inventor, that is, the intensity or phase, respectively, are generated. Are modulated, and two optical comb generators (OFCG1 and OFCG2) are used by using the above-mentioned optical comb light source 130 as the first and second light sources for emitting the reference light and the measuring light having the interfering property and the modulation periods different from each other. An optical comb output for measurement of a single polarization component emitted from 130A and 130B is irradiated while scanning the surface of the object to be measured, and reflected light from the surface is detected for each irradiation point to obtain a distance. By performing the (height) calculation, it is possible to construct a measuring system for a range finder or an optical three-dimensional shape measuring machine that performs a stable measuring operation. The surface shape of the object can be obtained from the coordinates of the scan and the distribution of the distance (height). There are various forms of scanner optics. The use of telecentric optics makes it possible for the light to be incident almost vertically on the object in the measuring range.

In addition, for example, the light source in the vibration measuring device according to Japanese Patent No. 5336921 or Japanese Patent No. 5363231 previously proposed by the inventor of the present invention, that is, a spectrum with a predetermined frequency interval, the modulation frequency and the central frequency are different from each other, By using the optical comb light source 130 as a light source unit for emitting the reference light and the measurement light that are phase-locked and coherent, a single light emitted from the two optical comb generators (OFCG1, OFCG2) 130A and 130B is used. It is possible to construct a measurement system of a vibration measuring device that performs a stable multipoint vibration measurement operation by irradiating an optical comb of a polarization component to a different place depending on the wavelength through an element that divides for each wavelength.

Here, in the measuring device using the optical comb obtained by the optical comb generator using the optical waveguide that transmits the polarization component in which the orthogonal modes are mixed, as shown by circles in FIG. The transmission mode waveform may be deformed, and the locations (relative positions with respect to the main mode) that occur may vary, and multiple local minima may cause unstable control, but only a single polarization component As shown in FIG. 21, by using the optical waveguide that passes through, the transmission mode waveform is not deformed, stabilizing as an optical comb generator, improving the accuracy of the measuring device including the optical comb, reducing errors, etc. Can be planned.

That is, when the optical comb is used for measurement, the polarization component orthogonal to the generation of the optical comb causes a measurement error of the distance and the height, and the polarization component orthogonal to the generation of the optical comb is generated by the optical comb generator. The control for matching the resonance frequency to the laser frequency may become unstable, which may cause a shift in the control point and oscillation of the control. Also, when using the optical comb for measurement, measure the distance and height. Although it has been a factor of error, by generating an optical comb using an optical waveguide that passes only a single polarization component, the output of the orthogonal polarization component that does not contribute to the generation of the optical comb is suppressed, and the polarization of the optical comb output is reduced. The extinction ratio can be improved, the degree of single polarization can be increased, the resonator control can be stabilized, unnecessary interference signals can be removed, and measurement errors in distance measurement and shape measurement using an optical comb can be eliminated. It is possible to improve the measurement accuracy and the reliability of the entire system.

1, 1A, 110, 120, 130A, 130B optical comb generator, 8, 51 optical modulator, 11 substrate, 12 optical waveguide, 14 buffer layer, 16 oscillator, 18 termination resistor, 20 ridge, 21 optical circulator, 22 Focuser, 63 Antireflection Film, 83, 83A Electrode, 84 First End Face, 85 Second End Face, 86 First Protective Material, 86a, 87a End Face, 87 Second Protective Material, 91, 92 Plane, 93 Incident side reflection film, 94 Emission side reflection film, 100A low power type optical comb module, 111 optical coupler, 112 photodetector, 113 control circuit, 114 bias tee, 130 optical comb light source, 131 laser light source, 132 separation optical system , 135 frequency shifter

Claims (15)

An optical waveguide formed as a region in which a guided mode exists only for a single polarized component in a substrate having at least an electro-optical effect,
Light that is formed on the optical waveguide and that comprises an electrode for propagating a modulation signal in the forward direction or the backward direction, and that modulates the phase of the light that propagates in the optical waveguide according to the modulation signal supplied to the electrode Modulation means,
It is composed of a member having the same hardness as the substrate of the optical waveguide, and at least one end face of the member forms the same plane as the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. An end face protection means disposed on the optical waveguide,
The optical modulator, wherein the optical waveguide has a light incident end surface and a light emitting end surface, which are respectively formed on a flat surface by polishing the end surface of the member and the end surface of the substrate. The optical modulator according to claim 1, wherein the optical waveguide is formed as a region where a waveguide mode exists only for the single polarized component by proton exchange. The optical modulator according to claim 1, wherein the optical waveguide is made of a non-linear optical crystal. In the light modulating means, the reflecting means for reflecting the modulation signal supplied from the oscillating means to the one end side of the electrode is provided only on the other end side of the electrode, without resonating the supplied modulation signal. A phase of light propagating in the forward direction is modulated by a modulation signal propagating in the forward direction, and a phase of light propagating in the backward direction is modulated by a modulation signal propagating in the backward direction. The optical modulator according to any one of claims 1 to 3. As the reflecting means, a reflector for reflecting the modulation signal supplied from the other end and a phase shifter for adjusting the phase of the reflected modulation signal are provided at one end of the electrode. The optical modulator according to claim 4, wherein: The phase shifter adjusts the phase of the reflected modulation signal according to the shape of the electrode, the frequency of the modulation signal, and the group refractive index of the optical waveguide. Light modulator. The optical modulator according to any one of claims 1 to 4, wherein the electrode of the optical modulator has a ridge structure. Oscillation means for oscillating a modulation signal of a predetermined frequency,
Resonant means configured of an incident side reflection film and an emission side reflection film that are parallel to each other, and resonating means for resonating light incident through the incident side reflection film,
An optical waveguide formed as a region in which a waveguide mode exists only for a single polarization component in a substrate having at least an electro-optical effect so as to penetrate from the incident side reflection film to the emission side reflection film. When,
It is composed of an electrode for propagating the modulation signal supplied from the oscillating means on the optical waveguide in the forward direction or the backward direction, and is formed so as to penetrate from the incident side reflection film to the emission side reflection film, The phase of the light resonated by the resonating means is modulated according to the modulation signal supplied from the oscillating means, and sidebands centered on the frequency of the incident light are generated at intervals of the frequency of the modulation signal. Optical comb generating means
It is composed of a member having the same hardness as the substrate of the optical waveguide, and at least one end face of the member forms the same plane as the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. An end face protection means disposed on the optical waveguide,
The optical comb generator, wherein the incident side reflection film and the emission side reflection film are respectively adhered to a plane formed by polishing the end face of the member and the end face of the substrate. 9. The optical comb generator according to claim 8, wherein the optical waveguide is formed as a region in which a waveguide mode exists only for the single polarization component by proton exchange. The optical comb generator according to claim 8, wherein the optical waveguide is made of a non-linear optical crystal. The light modulating means is provided with a reflecting means for reflecting the modulation signal supplied from the oscillating means to the one end side of the electrode only at the other end side of the electrode, and is provided with the modulation signal supplied from the oscillating means. Without resonating, the phase of the light propagating in the forward direction is modulated by the modulation signal propagating in the forward direction, and the phase of the light propagating in the return direction is modulated by the modulation signal propagating in the return direction. The optical comb generator according to any one of claims 8 to 10, characterized in that. As the reflecting means, a reflector for reflecting the modulation signal supplied from the other end and a phase shifter for adjusting the phase of the reflected modulation signal are provided at one end of the electrode. The optical comb generator according to claim 11, wherein: The phase shifter adjusts the phase of the reflected modulation signal according to the shape of the electrode, the frequency of the modulation signal, and the group refractive index of the optical waveguide. Optical comb generator. The optical comb generator according to any one of claims 8 to 13, wherein the electrode of the light modulating means has a ridge structure. A light detecting means for detecting a part of the optical comb obtained by the optical comb generating means,
Control means for generating a control signal for zeroing the error of the resonance length of the resonance means with respect to the control target from the light detection signal obtained by the light detection means, and controlling the resonance length of the resonance means. The optical comb generator according to any one of claims 8 to 14.