JP7152761B2 - Optical comb generator - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention is an optical comb generator applied to fields requiring standard light sources with multiple wavelengths and high coherence, such as optical communications, optical CT, and optical frequency standards, or light sources that can also utilize coherence between wavelengths. Regarding.

Along with the recent development of optoelectronics, a waveguide type optical resonator that resonates light confined in an optical waveguide in order to meet the demand for laser light control for frequency multiplexing communication and frequency measurement of absorption lines distributed over a wide area. has come to be used frequently.

In order to measure the optical frequency with high accuracy, heterodyne detection is performed to detect the electrical signal of the generated optical beat frequency by interfering the light to be measured with other light. The band of light measurable in this heterodyne detection is limited to the band of the light receiving element used in the detection system, and is approximately several tens of GHz.

On the other hand, it is necessary to further expand the measurable band of light in order to control light for frequency multiplex communication and to measure the frequency 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-like sidebands arranged at equal intervals on the frequency axis over a wide band, and the frequency stability of these sidebands is almost the same as that of the incident light. be. By heterodyne-detecting the generated sideband and the light to be measured, it is possible to construct a wide-band heterodyne detection system over several THz.

Further, an optical comb generator and an optical modulator have been proposed that phase-modulate not only the light propagating in the forward direction but also the light propagating in the backward direction through an optical waveguide (see, for example, Patent Document 2). ).

In addition, by suppressing chipping and rounding of the corners of the waveguide end face during processing, and by stably coating each reflective film on the uppermost corner of the end face without peeling off, the reflectance of the reflective film and the optical resonator can be improved. We are proposing optical resonators, optical modulators, optical comb generators, and optical oscillators that improve the finesse of the device and enhance the functionality of the device itself. (See Patent Document 3, for example).

That is, a member having the same hardness as that of a substrate for forming an optical waveguide from above is formed so that at least one end face thereof is flush with the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. and an incident-side reflecting film and an exit-side reflecting film constituting resonance means are coated on the plane formed by polishing the end face of the member and the end face of the substrate. Therefore, chipping and rounding during processing of the corners of the waveguide end face can be suppressed, and each reflective film can be stably adhered without peeling off at the uppermost corner of the end face. It is possible to improve the finesse of the optical resonator and enhance the function of the device itself.

Conventional waveguide-type optical resonators that resonate light confined in optical waveguides use optical waveguides that transmit polarized components in which orthogonal modes are mixed. The resulting optical output also contained polarization components mixed with orthogonal modes.

Japanese Patent Application Laid-Open No. 2003-202609 Japanese Patent No. 3891977 Japanese Patent No. 4781648

By the way, in the conventional optical comb generator, in order to obtain a stable output when the optical comb is used for measurement, part of the light emitted from the optical resonator is detected by a photodetector, and a predetermined The resonance length of the optical resonator was feedback-controlled so as to obtain the resonance length. As shown in , there may be deformation in the transmission mode waveform due to the orthogonally polarized components. Moreover, the positions (relative positions with respect to the main mode) where the transmission mode waveform is deformed by the orthogonally polarized components are scattered and have a plurality of minimum parts, which becomes an unstable factor when controlling the resonance length.

That is, in the generation of an optical comb in an optical comb generator using a waveguide type optical resonator that resonates light confined in an optical waveguide, the orthogonal polarization component is used to match the resonance frequency of the optical comb generator with the laser frequency. control can be destabilized, causing control point shifts and control oscillations. The component was a factor of the measurement error.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention, in view of the conventional circumstances as described above, to stabilize the resonator control without causing deformation of 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 degree of single polarization. That's what it is.

Another object of the present invention is to stabilize the optical comb generator, improve the accuracy of the 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 clearer from the description of the embodiments described below.

The present invention is an optical comb generator, comprising a single-frequency oscillation laser light source and a plurality of optical comb generators into which a plurality of laser beams emitted from the laser light source are separated and entered, each of the optical comb generators includes an oscillating means for oscillating modulated signals having different frequencies with a predetermined frequency difference phase-locked by a common reference oscillator, and an incident-side reflecting film and an output-side reflecting film parallel to each other. and a substrate having at least an electro-optical effect penetrating from the incident-side reflecting film to the emitting-side reflecting film. An optical waveguide formed as a region in which a waveguide mode exists only for a polarization component, and a modulated signal formed on the optical waveguide and supplied from the oscillation means for propagating in the forward or backward direction. and is formed so as to penetrate from the incident-side reflecting film to the exit-side reflecting film, and modulates the phase of light resonated by the resonance means in accordance with the modulation signal supplied from the oscillation means. By generating sidebands centered on the frequency of the incident light at intervals of the frequency of the modulated signal, single polarized light beams having mutually different modulation frequencies and center frequencies, which are phase-synchronized and coherent with each other, are generated. An optical comb generating means for outputting an optical comb of wave components, a light detecting means for detecting a part of the optical comb of a single polarization component obtained by the optical comb generating means, and light obtained by the light detecting means. and control means for generating, from the detection signal, a control signal that makes an error of the resonance length of the resonance means with respect to a control target zero, and controlling the resonance length of the resonance means.

In the optical comb generation device according to the present invention, the plurality of optical comb generators may be used as a light source unit for a measuring device that emits coherent reference light and measurement light with mutually different modulation periods. can.

In the present invention, each of the plurality of optical comb generators includes an incident side reflecting film and an output side reflecting film which are parallel to each other, and resonates the light incident through the incident side reflecting 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 reflecting film to the exit-side reflecting film; By providing, in each optical comb generator, only a single polarized wave component of light incident through the incident side reflecting film is allowed to pass through the optical waveguide, and a single polarized wave component is transmitted through the output side reflecting film As an optical modulation output of only the components, an optical comb of single polarization components whose modulation frequencies and center frequencies are different from each other and which are phase-locked and coherent with each other can be generated. In other words, the output of the orthogonal polarization component that does not contribute to the generation of the optical comb is suppressed, the polarization extinction ratio of the optical comb output is improved, the single polarization degree can be increased, the cavity control is stabilized, and the unnecessary interference signal can be removed and an optical comb can be generated as an optical modulation output of only a single polarized wave component through the reflection film on the output side, and measurement errors in distance measurement and shape measurement using multiple optical combs By removing it, it is possible to improve the measurement accuracy, improve the reliability of the entire system, and the like.

Therefore, according to the present invention, by using a plurality of optical comb generators included in the optical comb generator as a light source unit for a measuring device that emits coherent reference light and measurement light with mutually different modulation periods, It is possible to construct a measurement system for a rangefinder or an optical three-dimensional shape measuring machine that performs stable measurement operations, or to construct a measurement system for a vibration measurement device that performs stable multi-point vibration measurement operations.

1 is a perspective view showing a configuration of an optical modulator to which the invention is applied; FIG. It is a side view of the said optical modulator. 4A to 4C are longitudinal cross-sectional views of main parts in each step for explaining the method of manufacturing the optical modulator; FIG. 3 is a perspective view of a substrate provided with three optical waveguides, which is manufactured for measuring end face reflectance of an optical modulator to which the present 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. 1 is a diagram showing the configuration of a reciprocating optical modulator to which the present invention is applied; FIG. FIG. 5 is a diagram showing intensity distributions at respective frequencies (wavelengths) of sidebands when the present invention is applied to an optical comb generator; It is a perspective view which shows the structure of the optical comb generator to which this 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. 1 is a perspective view showing a configuration of an optical modulator (optical comb generator) having electrodes having a ridge structure to which the present invention is applied; FIG. 4A to 4C are longitudinal cross-sectional views of main parts in each step for explaining a method of manufacturing the optical modulator (optical comb generator); FIG. 4 is a perspective view showing a substrate on which electrodes having a ridge structure of the optical modulator (optical comb generator) are formed; FIG. 3 is a vertical cross-sectional front view of a main part showing an electrode having a ridge structure of the optical modulator (optical comb generator); FIG. 10 is a diagram for explaining the results of actual measurement of changes in driving voltage (AC Vpi) at 25 GHz depending on the presence or absence of the ridge structure of the electrode for the optical modulator to which the present invention is applied; FIG. 10 is a diagram for explaining the result of actually measuring changes in the direct-current driving voltage (DC Vpi) depending on the presence or absence of the electrode ridge structure for 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. FIG. 4 is a block diagram showing another configuration example of an optical comb generator using a low-power optical comb module to which the present invention is applied; It is a block diagram which shows the structural example of the optical comb light source built using the low-power type optical comb module to which this invention is applied. FIG. 4 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 passes only a single polarized component to which the present invention is applied. Characteristic diagram showing the deformation of the transmission mode waveform due to the orthogonal polarization components that occurs when feedback-controlling the resonance length of the optical resonator in a conventional optical comb generator using an optical waveguide that transmits polarized components in which orthogonal modes are mixed. is.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that common constituent elements will be described by attaching common reference numerals in the drawings. Further, 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, for example, to a waveguide type optical modulator 8 configured as shown in FIGS. FIG. 1 is a perspective view showing the 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. As shown in FIG.

This waveguide type optical modulator 8 comprises a substrate 11, an optical waveguide 12 formed on the substrate 11 for modulating the phase of a single polarized component of propagating light, and the optical waveguide 12 on the substrate 11. The buffer layer 14 laminated so as to cover, the electrode 83 provided on the upper surface of the optical waveguide 12 so that the direction of the modulation electric field is substantially perpendicular to the light propagation direction, and the optical waveguide 12 A first end surface 84 and a second end surface 85 provided to face each other, and a first protective material 86 disposed on the upper portion of the optical waveguide 12 so as to form the same plane as the first end surface 84. , a second protective member 87 disposed above the optical waveguide 12 so as to form the same plane as the second end face 85, and an end face 86a of the first end face 84 and the first protective member 86. The incident-side antireflection film 63 is deposited on a plane 91 formed between an output-side antireflection film 64, an oscillator 16 arranged on one end side of the electrode 83 for oscillating a modulated signal of frequency _fm , and a terminating resistor 18 arranged on the other end side of the electrode 83. there is

The substrate 11 is, for example, a wafer cut out of a large crystal of LiNbO ₃ or GaAs with a diameter of 3 to 4 inches grown by a pulling method. The cut out substrate 11 is subjected to processing such as mechanical polishing or chemical polishing to provide the ridges 20 for forming the electrodes 83 .

The optical waveguide 12 has a waveguide mode only for a single polarized wave 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 exit-side antireflection film 64 . It is formed as an area where

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

Here, the optical waveguide 12 through which only a single polarized component passes is formed by a substrate 11 having an electro-optical effect by an optical waveguide forming method, such as a proton exchange method, which causes a change in refractive index only for a specific polarized component. can be formed as a region with a high refractive index only for the polarization component of .

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

When the optical waveguide 12 is fabricated by diffusing Ti atoms in the substrate 11 or epitaxially growing on the substrate 11, the waveguide mode is changed to single polarized light by devising the refractive index distribution. It can be formed as a limited area. For this 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. This Ti-diffused region has a higher refractive index than other regions, and can confine light of a single polarization component. A wave path 12 can be formed. Although the refractive index is high for both orthogonal polarization components, there are also conditions under which a 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 an electrical effect such as the Pockels effect, in which the refractive index changes in proportion to the electric field, or the Kerr effect, in which the refractive index changes in proportion to the square of the electric field. Since it has an optical effect, it is possible to use such a physical phenomenon to modulate light of a single polarization component.

The buffer layer 14 covers the optical waveguide 12 in order to suppress propagation loss of light of a single polarization component. Incidentally, if the film thickness of the buffer layer 14 is too thick, the electric field intensity will decrease and the modulation efficiency will decrease. You may make it

The electrode 83 is made of, for example, a metal material such as Ti, Pt, or Au. By driving and inputting the modulated signal of frequency _fm supplied from the oscillator 16 into the optical waveguide 12, the phase of the light propagating in the optical waveguide 12 is changed. modulate.

The first protective material 86 and the second protective material 87 are each made of a material 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 of the first protective member 86 forming the plane 91 and the first end face 84 may be processed so as to have the same crystal orientation. The end face 87a of the second protective member 87 and the second end face 85 may be processed so as to have the same crystal orientation.

The incident-side antireflection film 63 is deposited on a plane 91 formed between the first end face 84 and the end face 86 a of the first protective material 86 . The exit-side antireflection coating 64 is deposited on a plane 91 formed between the second end face 85 and the end face 87 a of the second protective material 87 . These anti-reflection films 63 and 64 may be composed of low-reflection films, or may be uncoated to obtain the same effect as coating low-reflection films. .

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

Next, a method for 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 a substrate 11 made of LiNbO ₃ crystal.

Next, in step S12, the LiNbO ₃ crystal substrate 11 with the photoresist pattern 13 formed on the surface is immersed in a proton exchange liquid such as benzoic acid and heated to remove Li from the surface layer of the substrate 11. An optical waveguide 12 is formed as a region in which a waveguide mode exists only for a single polarization component by a proton exchange method for H ⁺ substitution.

The process of manufacturing the optical waveguide ₁₂ in steps S11 and S12 is not limited to the proton exchange method. Ti is vapor-deposited on the surface of the substrate 11 made of LiNbO ₃ crystals, and the photoresist is removed to fabricate a thin Ti line having a width of micron size. By heating the substrate 11 on which the thin Ti wires are formed, Ti atoms are thermally diffused into the substrate 11 to form the optical waveguide 12 as a region in which a waveguide mode exists only for a single polarization component. A forming Ti diffusion method may be substituted for this.

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 substrate 11 surface. In this step S13, the buffer layer 14 may be formed by a method of attaching a _SiO2 wafer to the substrate 11 surface. In such a case, the thickness of the deposited buffer layer 14 may be controlled to an appropriate thickness by polishing the deposited buffer layer 14 in consideration of the electrode mounting area in the next step S14.

Next, the process proceeds to step S 14 to form the electrode 83 on the buffer layer 14 .

Next, in step S15, protective materials 86 and 87 are adhered to the upper portion of the optical waveguide 12. Next, as shown in FIG. As for the method of adhering the protective members 86 and 87, they may be adhered with an adhesive, or may be directly joined based on other techniques. When the substrate 11 is made of LiNbO ₃ crystal, the protective members 86 and 87 may be made of LiNbO ₃ as the same material. In this step S15, the end surfaces 86a and 87a of the affixed protective materials 86 and 87 are arranged so that planes 91 and 92 can be formed between the first end surface 84 and the second end surface 85, respectively. , trim.

Finally, the process proceeds to step S16 to polish the planes 91 and 92 thus obtained. Then, an incident-side antireflection film 63 and an exit-side antireflection film 64 are formed on the polished flat surfaces 91 and 92, respectively. Incidentally, in this step S16, the incident side antireflection film 63 and the exit side antireflection film 64 may be first formed on the flat surfaces 91 and 92, and then polished.

As described above, in the optical modulator 8 to which the present invention is applied, since the protective materials 86 and 87 are adhered to the respective ends, the end surface of the optical waveguide 12, which was conventionally positioned at the uppermost corner of the end surface, moves to substantially the center of the plane 91 (92). As a result, even if the corner of the plane 91 (92) is chipped during polishing in step S16, the end surface of the optical waveguide 12 is not chipped. That is, it is possible to obtain a configuration in which the end face itself of the optical waveguide 12 is less likely to be chipped. This makes it possible to minimize optical loss from each end surface of the optical waveguide 12 .

In addition, by configuring the protective members 86 and 87 with an optimum material corresponding to the material of the substrate 11, the polishing rate in step S16 can be changed from the first end surface 84, the second end surface 85 to the end surface 86a, 87a can be made uniform. As a result, the end face of the optical waveguide 12 is prevented from being rounded during processing, and the planes 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, by making the crystal orientations of the end faces forming the planes 91 and 92 the same, it is possible to further suppress the reflection loss.

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

In addition, since the incident-side antireflection film 63 and the exit-side antireflection film 64 are formed over a wide range from the first end face 84 and the second end face 85 to the end faces 86a and 87a of the substrate 11, they are very stable. Therefore, it is difficult to peel off, and it is possible to improve the reproducibility of the film formation.

In order to experimentally verify the effect of providing the protective members 86 and 87, the plane 91 (92) after the protective members 86 and 87 were attached was polished. No chipping or bending occurs in any part, and it can be confirmed that a flat optical polishing suitable for adhering the incident-side antireflection film 63 and the output antireflection film 64 is performed.

In particular, the first protective member 86 and the second protective member 87 are made of the same material as the substrate 11, and the end faces 86a, 87a of the protective members 86, 87 forming planes 91, 92 and the first end face 84 , and the second end face 85 are processed so as to have the same crystal orientation, the hardness of the crystal becomes the same between them, so that the planes 91 and 92 are not tilted due to the difference in polishing rate.

In the optical modulator 8 having such a configuration, only the single polarized component light that is incident through the incident-side antireflection film 63 and propagated through the optical waveguide 12 is modulated at the frequency _fm supplied from the oscillator 16. The light is phase-modulated by the signal and emitted through the exit-side anti-reflection film 64 . Moreover, in the optical modulator 8 to which the present invention is applied, the end surface of the optical waveguide 12 can be moved to the substantially central portion of the plane 91 (92) by attaching the protective materials 86 and 87 to the respective end portions. , chipping or rounding of the end face of the optical waveguide 12, ensuring the perpendicularity between the optical waveguide 12 and the planes 91 and 92, and improving the polishing accuracy of the planes 91 and 92 are possible, and the yield can be improved.

Here, both the single polarization optical waveguide fabricated by the proton exchange method in which only a single polarization component of the incident light is propagated and the orthogonal polarization component of the incident light are propagated. As shown in FIGS. 4, 5 and 6, the orthogonally polarized optical waveguide produced by the Ti diffusion method has a width W ₁ =1.9 [mm], a length L ₁ =27.4 [mm], Three optical waveguides 12A, 12B, and 12C are formed on the LiNbO ₃ crystal substrate 11 with a thickness T ₁ =0.5 [mm], and the width W ₂ =1.9 [mm] above the optical waveguides 12A, 12B, and 12C. ], length L ₂ =1.5 [mm] _, and thickness T ₂ =0.5 [mm]. By polishing the three optical waveguides 12A, 12B and 12C, the entrance surface and the exit surface of the three optical waveguides 12A, 12B and 12C are finished to be flat as a LiNbO ₃ crystal substrate block, and the optical path width W ₃ of the three optical waveguides 12A, 12B and 12C is obtained. 6.0 [μm], 6.3 [μm], 6.6 [μm], 6.9 [μm], 7.2 [μm], 7.5 [μm] 10 samples The reflectance at the entrance planes A ₁ , B ₁ , C ₁ and the exit planes A ₂ , B ₂ , C ₂ of the three optical waveguides 12A, 12B, 12C was measured, and the finesse and transmittance of each sample were measured. was obtained, the following results were obtained.

That is, while the orthogonally polarized optical waveguide has a finesse of about 30-45, the single-polarized optical waveguide provides a finesse of about 50-65. Further, while the transmittance of the orthogonally polarized optical waveguide was about 12.5 to 25 [%], the single polarized optical waveguide obtained a transmittance of about 20 to 32.5 [%]. It is

The present invention is not limited to the above-described embodiments. For example, it can be applied to a reciprocating optical modulator 51 as shown in FIG. In this optical modulator 51, the same configuration and elements as those of the above-described optical modulator 8 are referred to the explanations in FIGS.

As shown in FIG. 7(a), the optical modulator 51 is formed of a substrate 11 and a region on the substrate 11 in which a waveguide mode exists only for a single polarization component. An optical waveguide 12 for modulating the phase of the light to be transmitted, a buffer layer 14 laminated on the substrate 11 so as to cover the optical waveguide 12, and a modulation electric field direction substantially perpendicular to the light propagation direction. An electrode 83 provided on the upper surface of the optical waveguide 12, a first protective material 86 and a second protective material 87 arranged on the upper part of the optical waveguide 12, and an antireflection film 63 coated on the plane 91. and an exit-side reflecting film 94 deposited on the plane 92 .

Further, when the optical modulator 51 is actually used, as shown in FIG. An optical system comprising an optical transmission line 23 composed of an optical fiber or the like for transmission 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 mounted, an oscillator 16 arranged on one end side of the electrode 83 to oscillate a modulated signal of frequency _fm , and a terminating resistor 18 arranged on the other end side of the electrode 83 are further arranged.

The antireflection film 63 is deposited on a plane 91 formed between the first end face 84 and the end face 86 a of the first protective material 86 . The anti-reflection film 63 may be composed of a low-reflection film, or may be uncoated to obtain the same effect as that obtained by applying a low-reflection film.

The focuser 22 converges the input light that has passed through the optical circulator 21 to the end of the optical waveguide 12, converges the output light that has passed through the antireflection film 63 from the end of the optical waveguide 12, and directs it to the optical circulator 21. 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 waveguide mode exists only for a single polarization component is used as a highly reflective film for emitting light. By providing the side reflection film 94 and providing the anti-reflection film 63 at the other end, it operates as a so-called reciprocating modulation type optical modulator. The input light that has entered the optical waveguide 12 is modulated while propagating through the optical waveguide 12 with only a single polarized component, and after being reflected by the exit-side reflecting film 94 on the end face, propagates through the optical waveguide 12 again. The light is transmitted through the antireflection film 63 and emitted to the focuser 22 side, and becomes an output light having only a single polarized wave component. At the same time, the electrical signal of frequency _fm supplied from the oscillator 16 is absorbed by the terminating resistor 18 after propagating on the electrode 83 while modulating the input light.

7(c), the optical modulator 51 is provided with an oscillator 25 and a terminating resistor 27 on one end side of the electrode 83 so that an electrical signal supplied from the oscillator 25 is propagated on the electrode 83. In addition, the light may be reflected at the other end of the electrode 83 . At this time, an isolator 26 may be provided to separate the electrical signal supplied from the oscillator 25 and the electrical signal reflected at the other end of the electrode 83 . Also, in this optical modulator 51, an incident-side reflecting film 93 having a high reflectance is applied. Thereby, light can be resonated inside the optical waveguide 12 . Further, instead of the incident-side reflecting film 93, the antireflection film 63 having the low reflectance described above may be applied. This makes it possible to apply phase modulation while reciprocating the light only once in the optical waveguide 12 .

In this optical modulator 51, by adjusting the reflection phase of the electrical signal in accordance with the phase of the light reflected by the exit-side reflecting film 94, the phase of the light can be modulated by each of the electrical signals reciprocating through the electrode 83. Therefore, the modulation efficiency can be increased. In particular, by attaching the protective materials 86 and 87, peeling and chipping of the films 63 and 94 are suppressed as described above, and in the optical modulator 51 with improved finesse, it is possible to further increase the optical modulation efficiency. becomes.

Further, when these optical modulators 51 are applied to an optical comb generator, it is possible to apply reciprocating modulation to the light resonating in the optical waveguide 12 by means of electrical signals reciprocating through the electrodes. In such a case, the intensity distribution at each frequency (wavelength) of the generated sideband is, as shown in FIG. , the modulation index, expressed as the magnitude of the modulation applied within the optical waveguide 12, is .pi. radians per direction of propagation. From this result, it can be seen that the half-wave voltage Vπ defined as the voltage required to shift the phase by half a wavelength is 7.1V.

Instead of reflecting the electric signal, the optical modulator 51 may divide the output of the oscillator 16 as the signal source so that the electric signal is separately driven and input from both ends of the electrode 83. , by connecting separate oscillators 16 across electrodes 83, respectively.

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, thereby further improving the optical modulation efficiency. can be made

Here, as shown in FIGS. 9 and 10, the optical modulators 8 and 51 manufactured in this manner are polished at the step S16 so that the flat surfaces 91 and 92 are parallel to each other, and the polished flat surfaces are Instead of the incident-side antireflection film 63 and the exit-side antireflection film 64, an incident-side reflecting film 93 and an exit-side reflecting film 94 are formed on the surfaces 91 and 92, respectively, to generate an optical comb. It functions as vessel 1.

That is, in the optical comb generator 1, the incident-side reflecting film 93 and the output-side reflecting film 94 are provided so as to be parallel to each other in order to resonate the light incident on the optical waveguide 12. An optical resonator 5 that resonates by reciprocatingly reflecting light passing through is constructed.

Light of frequency ν1 is incident on the incident-side reflecting film 93 from _a light source (not shown). The incident-side reflecting film 93 also reflects light of a single polarized component that has been reflected by the output-side reflecting film 94 and passed through the optical waveguide 12 . The output-side reflecting film 94 reflects light of a single polarization component that has passed through the optical waveguide 12 . Further, the output-side reflecting film 94 outputs light of a single polarization component that has passed through the optical waveguide 12 to the outside at a constant rate.

The incident side reflecting film 93 and/or the output side reflecting film 94 may be formed over the planes 91 and 92, respectively, but they are formed so as to cover only the ends of the optical waveguide 12 at a minimum. It is good if it is.

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

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

The same plane 91 is formed by the first end face 84 including the light incident end of the optical waveguide 12 and the end face 86a of the protective material 86. As shown in FIG. The formed plane 91 has an inclination of 0.05° or less. Calculating the loss in the case where light with a 1/e ² beam diameter of 10 μm is reflected at the end surface with an inclination of 0.05° with respect to the plane 91 with an inclination of 0.05°, the loss is 4×10 ⁻⁴ , and the incident It is so small that it can be ignored compared to the reflectance of the side reflecting film 93 .

By forming the first end face 84 and the second end face 85 substantially perpendicularly to the optical waveguide 12 in this manner, the entrance-side reflection film 93 and the exit-side reflection film 94 attached thereto form a single optical waveguide. It is possible to efficiently resonate the light of the polarized wave component.

In the optical comb generator 1 configured as described above, the light incident from the outside through the incident-side reflecting film 93 propagates in the optical waveguide 12 in the outgoing direction as light of a single polarization component, 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 output-side reflecting film 94 propagates in the optical waveguide 12 in the backward direction and is reflected by the incident-side reflecting film 93 . By repeating this, the light of a single polarization component resonates in the optical waveguide 12 .

In addition, by inputting an electric signal through the electrode 83 in synchronization with the reciprocating time of the light of a single polarization component in the optical waveguide 12, the light of a single polarization component can be output to this optical modulator. Compared to the case of passing through 8 only once, it is possible to apply deep phase modulation several tens of times or more. In addition, several hundred sidebands can be generated over _a wide band centering on the frequency ν1 of the incident light. Incidentally, the frequency intervals of the generated sidebands are all equal to the frequency _fm of the input electric signal. Therefore, the optical modulator 8 replaces the incident-side antireflection film 63 and the exit-side antireflection film 64 with the incident-side reflective film 93 and the exit-side reflective film 94 to form a single polarized light composed of many side bands. 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 polarized wave component through the substrate 11 having at least an electro-optical effect so as to penetrate from the incident-side reflecting film 93 to the emitting-side reflecting film 94 constituting the resonance means. Since the optical waveguide 12 is formed as a region in which a mode exists, only a single polarized component of the light incident through the incident-side reflecting film 93 is propagated through the optical waveguide 12, An optical comb can be generated as an optically modulated output of only a single polarized wave component via the output-side reflecting film 94 .

As described above, in the optical modulators 8 and 51 to which the present invention is applied, the protective materials 86 and 87 are attached to the ends of the optical modulators 8 and 51. Therefore, in the conventional art, the optical waveguide 12 located at the uppermost corner of the end face As a result, the end face of the optical waveguide 12 is not chipped even if the corner of the plane 91 (92) is chipped during polishing in step S17. That is, it is possible to obtain a configuration in which the end face itself of the optical waveguide 12 is less likely to be chipped. This makes it possible to minimize optical loss from each end face of the optical waveguide 12 . Moreover, by providing the protective materials 86 and 87, it is possible to suppress changes in film thickness caused by the entrance-side reflection film 93 and the exit-side reflection film 94 to be adhered to wrap around from the flat surfaces 91 and 92 to the other side surfaces. . Therefore, the film thickness near the end surface of the optical waveguide 12, which is important for ensuring the reflectance, can be optimized, and the reflectance can be further improved.

In addition, since the incident side reflecting film 93 and the emitting side reflecting film 94 are formed over a wide range from the first end face 84 and the second end face 85 to the end faces 86a and 87a of the substrate 11, they are very stable. , it is difficult to peel off, and it is possible to improve the reproducibility of film formation.

In order to experimentally verify the effect of providing the protective members 86 and 87, the plane 91 (92) after the protective members 86 and 87 were attached was polished. It can be confirmed that no chipping or bending occurs at all, and that flat optical polishing suitable for adhering the incident-side reflecting film 93 and the exit-side reflecting film 94 is performed.

In particular, the first protective member 86 and the second protective member 87 are made of the same material as the substrate 11, and the end faces 86a, 87a of the protective members 86, 87 forming planes 91, 92 and the first end face 84 , and the second end face 85 are processed so as to have the same crystal orientation, the hardness of the crystal becomes the same between them, so that the planes 91 and 92 are not tilted 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 protective materials 86 and 87 are attached to the ends of the optical waveguide 12 so that the end face of the optical waveguide 12 is flat 91 as shown in FIG. Since it can be moved to the approximate center of (92), the end face of the optical waveguide 12 is chipped or rounded, ensuring the perpendicularity between the optical waveguide 12 and the planes 91 and 92, improving the polishing accuracy on the planes 91 and 92, Suppression of peeling and wraparound of the incident-side reflecting film 93 and the exit-side reflecting film 94, improvement of the reflectance of the incident-side reflecting film 93 and the exit-side reflecting film 94, realization of designed reflection characteristics, and improvement of the performance reproducibility of the reflecting film. It becomes possible. As a result, the finesse of the optical resonator 5 composed of the incident-side reflecting film 93 and the exit-side reflecting film 94 can be improved, and a high-performance optical modulator and optical comb generator can be manufactured with good reproducibility. It becomes possible, and it becomes possible to improve the yield.

Further, the present invention is applied to a waveguide type optical modulator 8A (optical comb generator 1A) configured as shown in FIG. 12, for example.

This waveguide type optical modulator 8A (optical comb generator 1A) has a ridge structure instead of the electrodes 83 in the waveguide type optical modulator 8 (optical comb generator 1A) shown in FIGS. 1 and 2 (FIGS. 9 and 10) for the same configuration and elements as the above-described optical modulator 8 (optical comb generator 1). is omitted.

In this waveguide type optical modulator 8A (optical comb generator 1A), the substrate 11 is a wafer cut out of a large crystal such as LiNbO ₃ or GaAs having a diameter of 3 to 4 inches and grown by, for example, a pulling method. be. The cut substrate 11 is subjected to a process such as mechanical polishing or chemical polishing to form the ridges 20 for forming the electrodes 83A having a ridge structure.

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

The refractive index of the layers forming the optical waveguide 12 is set to be higher only for a single polarization component than other layers such as the substrate 11 . The light incident on the optical waveguide 12 propagates while only a single polarized component is 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 an electrical effect such as the Pockels effect, in which the refractive index changes in proportion to the electric field, or the Kerr effect, in which the refractive index changes in proportion to the square of the electric field. Since it has an optical effect, it is possible to use such a physical phenomenon to modulate light of a single polarization component.

The electrode 83A having a ridge structure has a main electrode formed on the ridge 20 and is made of a metal material such as Ti, Pt, Au, or the like. 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 applying a modulated signal of frequency _fm supplied from the oscillator 16 to the optical waveguide 12 as a driving input. 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.

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

Next, in step S22, the LiNbO ₃ crystal substrate 11 with the photoresist pattern 13 formed on the surface is heated while immersed in a proton exchange liquid such as benzoic acid to remove Li from the surface layer of the substrate 11. An optical waveguide 12 is formed as a region in which a waveguide mode exists only for a single polarization component by a proton exchange method for H ⁺ substitution.

The steps S21 and S22 for fabricating the optical waveguide ₁₂ are not limited to the proton exchange method. Ti is vapor-deposited on the surface of the substrate 11 made of LiNbO ₃ crystals, and the photoresist is removed to form a thin Ti line having a micron-sized width. By heating the substrate 11 on which the thin Ti wires are formed, Ti atoms are thermally diffused into the substrate 11 to form the optical waveguide 12 as a region in which a waveguide mode exists only for a single polarization component. A forming Ti diffusion method may be substituted for this.

Next, in step S23, the resist pattern 13 on the substrate 11 having the optical waveguide 12 formed thereon is removed, and furthermore, the electrode 83A having a ridge structure is formed by mechanical polishing, chemical polishing, or the like, as shown in FIG. A ridge 20 is provided for forming the .

Next, in step S24, a SiO ₂ thin film as the buffer layer 14 is deposited on the substrate 11 surface. In this step S24, the buffer layer 14 may be formed by a method of attaching an _SiO2 wafer to the substrate 11 surface. In such a case, the thickness of the deposited buffer layer 14 may be controlled to an appropriate thickness by polishing the deposited buffer layer 14 in consideration of the electrode mounting area in step S25 described later.

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

Next, in step S26, protective materials 86 and 87 are adhered to the upper portion of the optical waveguide 12. Next, as shown in FIG. As for the method of adhering the protective members 86 and 87, they may be adhered with an adhesive, or may be directly joined based on other techniques. When the substrate 11 is made of LiNbO ₃ crystal, the protective members 86 and 87 may be made of LiNbO ₃ as the same material. In this step S26, the end surfaces 86a and 87a of the attached protective materials 86 and 87 are arranged so that planes 91 and 92 can be formed between the first end surface 84 and the second end surface 85, respectively. , trim.

In the optical modulator 8A to which the present invention is applied, the obtained flat surfaces 91 and 92 are polished in the final step S27, and the incident side antireflection film 63 and the emission side reflection film are formed on the polished flat surfaces 91 and 92. An anti-film 64 is formed over each surface.

Further, in the optical comb generator 1A to which the present invention is applied, the planes 91 and 92 are ground parallel to each other in the step S27. Instead of the side anti-reflection film 64, an incident-side reflecting film 93 and an exit-side reflecting film 94 are respectively formed over one surface.

In the optical modulator 8A and the optical comb generator 1A having such a configuration, the oscillator 16 is connected to the electrode 83A having a ridge structure for only a single polarization component of light that is incident from the incident end and propagated through the optical waveguide 12. Phase modulation can be efficiently performed by the modulation signal of frequency _fm supplied from .

Moreover, in the optical modulator 8A and the optical comb generator 1A to which the present invention is applied, the protective materials 86 and 87 are affixed to the ends of the optical waveguide 12 so that the end surface of the optical waveguide 12 is aligned substantially in the center of the plane 91 (92). Since it can be moved, chipping or rounding of the end face of the optical waveguide 12, securing of perpendicularity between the optical waveguide 12 and the planes 91 and 92, and improvement of the polishing accuracy on the planes 91 and 92 are possible, thereby improving the yield. is also possible.

In the optical comb generator 1A, only a single polarized wave component of light incident from the outside through the incident-side reflecting film 93 propagates in the forward direction in the optical waveguide 12 and is reflected by the exit-side reflecting film 94. and partially permeate to the outside. The light of the single polarization component reflected by the output-side reflecting film 94 propagates in the optical waveguide 12 in the backward direction and is reflected by the incident-side reflecting film 93 . By repeating this, light of a single polarization component resonates in the optical waveguide 12 .

In addition, by inputting an electric signal synchronous with the reciprocating time of the light of a single polarization component through the electrode 83A, the light of a single polarization component is output to this optical modulator. Compared to the case of passing through 8 only once, it is possible to apply deep phase modulation several tens of times or more. In addition, several hundred sidebands can be generated over _a wide band centering on the frequency ν1 of the incident light. Incidentally, the frequency intervals of the generated sidebands are all equal to the frequency _fm of the input electric signal. Therefore, the optical modulator 8A functions as an optical comb generator 1A that generates an optical comb of a single polarization component composed of multiple sidebands.

As described above, in the optical comb generator 1A to which the present invention is applied, the substrate having at least the electro-optical effect penetrates from the incident-side reflecting film 93 to the exit-side reflecting film 94 constituting the resonance means, and a single polarized light is generated. Since the optical waveguide 12 is formed as a region in which a waveguide mode exists only for wave components, only a single polarized wave component of light incident through the incident-side reflecting film 93 is Propagating through the optical waveguide 12, an optical comb can be generated as an optically modulated output of only a single polarized wave component via the output-side reflecting film 94, and protective materials 86 and 87 are attached to each end. As a result, the end face of the optical waveguide, which was conventionally positioned at the uppermost corner of the end face, moves to substantially the center of the plane 91 (92). As a result, even if the corner of the plane 91 (92) is chipped during polishing in step S27, the end surface of the optical waveguide 12 is not chipped. That is, it is possible to obtain a configuration in which the end face itself of the optical waveguide 12 is less likely to be chipped. This makes it possible to minimize optical loss from each end surface of the optical waveguide 12 .

Moreover, the optical modulator 8A is provided with an electrode 83A having a ridge structure formed on the buffer layer 14 of the substrate 11, as shown in the longitudinal section of the main part of FIG. 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 ridge groove is Samples of the optical modulator 8A with average depths (AVD) of 3.3, 2.96, 4.79, and 4.72 [μm] were prepared, and the driving voltage (AC Vpi) at 25 GHz and the DC The driving voltage (DC Vpi) was actually measured and the results are shown in FIGS. 16 and 17. FIG. Vpi is the voltage required to modulate the phase by π radians.

That is, in a conventional optical modulator having an electrode structure that does not have a 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 electrodes 83A having a ridge structure, the driving voltage (AC Vpi) at 25 GHz is about 3.5 to 7.5 V, and the DC driving voltage (DC Vpi) is about 5 to 6 V. It is about

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 and about 50% of the power compared to the case without the ridge structure. equivalent to a decrease in In addition, the DC drive voltage (DC Vpi) has an average voltage drop of about 80% of the original voltage compared to the case without the ridge structure, which corresponds to a power drop of about 50%.

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 surface of the member corresponds to the light incident end or the light incident end of the optical waveguide 12. A first protective member 86 and a second protective member 87 are provided above the optical waveguide 12 so as to form the same plane as the end face of the substrate 11 including the output end, and the end face of the member and the second protective member 87 are provided. Since the incident-side antireflection film 63 or the incident-side reflecting film 93 and the output-side antireflection film 63 or the output-side reflecting film 94 are each coated on the flat surface formed by polishing the end face of the substrate, the end face of the optical waveguide is In addition to preventing the occurrence of chipping, it is possible to stabilize the mounting of the high reflection film, improve the finesse of the optical resonator 5 composed of the entrance side reflection film 93 and the exit side reflection film 94, and Driving power can be reduced by providing the electrode 83A having a ridge structure.

Therefore, the optical modulators 8 and 8A and the optical modulator 51 configured as described above have at least one of the members 86 and 87 having the same hardness as the substrate 11 for forming the optical waveguide 12 from above. is disposed above the optical waveguide 12 so that the end face of the optical waveguide 12 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 entrance-side reflection film 93 and the exit-side reflection film 94 constituting the resonance means are adhered on the flat surface formed by polishing the end face of the substrate 11, chipping of the corners of the waveguide end face during processing is avoided. Suppresses rounding and enables stable deposition of each reflective film on the uppermost corner of the end face without peeling off, improving the reflectance of the reflective film and the finesse of the optical cavity, and enhancing the functionality of the device itself. A waveguide mode exists only for a single polarization component in the substrate 11 having at least an electro-optical effect so as to penetrate from the incident side reflecting film 93 to the emitting side reflecting film 94 constituting the resonance means. By providing the optical waveguide 12 formed as a region with a reflective film 93 on the incident side, only a single polarized wave component of the light incident through the reflective film 93 on the incident side propagates through the optical waveguide 12 and reaches the reflective film on the exit side. An optical comb capable of generating a stable optical comb as an optically modulated output of only a single polarization component via 94 functions as generators 1 and 1A.

The optical waveguide 12 in the optical modulators 8 and 8A and the optical modulator 51 as described above has a single polarized light on the substrate 11 having at least an electro-optical effect so as to penetrate from the incident-side reflecting film 93 to the exit-side reflecting 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 forming a region in which a waveguide mode exists only for a wave component. You can build generators.

Next, the block diagram of FIG. 18 shows the configuration of an optical comb generator 110 using a low-power optical comb module to which the present invention is applied.

This optical comb generator 110 includes an optical coupler 111 that branches a part of the optical comb output from the low-power optical comb module 100A to which the present invention is applied, and a photodetector that detects the light branched by the optical coupler 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 receives an RF modulation signal via the bias tee 114, so that for a single polarization component of the incident laser light, An optical comb is generated and output by applying phase modulation with an RF modulated signal. In the optical comb module 100A, temperature control by the temperature control circuit 119 controls the resonance length of the resonance means by the incident-side reflecting film and the exit-side reflecting film provided on the optical waveguide.

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

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

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

A portion of the output of the RF modulated signal source can be used as the synchronization signal. In that case, the operating band of photodetector 112 should be equal to or greater than the RF drive frequency.

In the control circuit 113, the low-frequency component of the signal obtained by inputting the photodetection signal and the synchronization signal to the mixer through the phase adjuster is taken as an error signal. Alternatively, it is possible to use a different modulation signal (dither signal) from the RF drive signal as a synchronization signal. The laser frequency or the resonance frequency of the optical comb module 100A is modulated with an amplitude smaller than the FSR of the resonance mode, and the output signal of the photodetector 112 and the synchronization 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 the error signal by the product-sum operation of digital signal processing.

A control signal obtained by adjusting the frequency characteristics of the error signal is applied to the DC bias of the optical comb module 100A via the bias tee 114 . In general, the error signal is input to a circuit having proportional, integral, and differential functions, and the frequency characteristics of the control loop are determined by adjusting the amplitude of these components, and the resonance frequency of the optical comb module 100A becomes the input laser. It is controlled to follow the oscillation frequency.

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

This optical comb generator 120 performs resonator control using reflected light from the low-power optical comb module 100A to which the present invention is applied. The light is branched by the coupler 111 and is incident on the photodetector 112 .

Each component in this optical comb generator 120 is the same as the component in the optical comb generator 110 shown in FIG. 18, and the corresponding components are given the same reference numerals in FIG. 19, and detailed description thereof is omitted. do.

The control circuit 113 obtains the error with respect to the control target from the photodetection signal obtained by the photodetector 112, and outputs a control signal that makes the error zero. By adding 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.

Furthermore, the low-power optical comb module to which the present invention is applied can construct an optical comb light source 130 configured as shown in FIG. 20, for example.
The optical comb light source 130 includes a single-frequency oscillation laser light source 131, a separation optical system 132 such as an optical coupler or an optical beam splitter that separates the 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 laser beam separated by the separation optical system 132, two optical comb generators (OFCG1, OFCG2) 130A and 130B each using a low-power optical comb module, and the like are provided.

In this optical comb light source 130, a laser beam emitted from one single-frequency oscillation laser light source 131 is separated into two laser beams by a separation optical system 132, and two optical comb generators (OFCG1, OFCG2) are generated. 130A and 130B.

The two optical comb generators 130A and 130B are driven by oscillators 133A and 133B that oscillate _at different frequencies _fm + _Δfm and fm. The respective oscillators 133A, 133B are phase-locked by a common reference oscillator 134 to stabilize the relative frequencies of _fm + _Δfm and _fm . A frequency shifter 135 such as an acousto-optical 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 fa by this frequency shifter 135. It's like This causes the beat frequency between the carrier frequencies to be an AC signal of frequency fa rather than _a DC signal. As a result, the beat signal in the high-frequency side band of the carrier frequency and the beat signal in the low-frequency side band of the carrier frequency are generated in opposing frequency regions across the beat frequency _fa between the carrier frequencies of the beat signal, which is inconvenient for phase comparison. good.

The two optical comb generators (OFCG1, OFCG2) 130A, 130B are each composed of a low-power optical comb module to which the present invention is applied, and phase only a single polarization component of the input laser light. By modulating, an optical comb of a single polarization component can be output. This optical comb light source 130 uses one single-frequency oscillation laser light source 131 in common, and two optical combs with different center frequencies and frequency intervals of two optical comb generators (OFCG1, OFCG2) 130A and 130B. For example, the first and second light sources in the rangefinder and the optical three-dimensional shape measuring machine according to Japanese Patent No. 5231883 previously proposed by the present inventor, that is, the intensity or phase, respectively, periodically are modulated, and by using the optical comb light source 130 as the first and second light sources for emitting coherent reference light and measurement light with mutually different modulation periods, two optical comb generators (OFCG1, OFCG2) The surface of the object to be measured is irradiated with the optical comb output for measurement of a single polarization component emitted from 130A and 130B while being scanned, and the reflected light from the surface is detected for each irradiation point and the distance is determined. By performing (height) calculation, it is possible to construct a measurement system for a rangefinder or an optical three-dimensional shape measuring machine that performs stable measurement operations. The surface shape of the object can be obtained from the scan coordinates and distance (height) distribution. There are various forms of scanner optical systems. The use of telecentric optics allows the light to enter the object almost perpendicularly within the measurement range.

Further, 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 present inventor, that is, the spectrum at a predetermined frequency interval, the modulation frequency and the center frequency are different from each other, and By using the optical comb light source 130 as a light source for emitting phase-locked and coherent reference light and measurement light, the two optical comb generators (OFCG1, OFCG2) 130A and 130B emit single It is possible to construct a measurement system of a vibration measuring apparatus that performs stable multi-point vibration measurement operation by irradiating an optical comb of polarized wave components to different locations depending on the wavelength through an element that splits for each wavelength.

Here, in a measurement device using an optical comb obtained by an optical comb generator using an optical waveguide that transmits polarized components in which orthogonal modes are mixed, as shown by the circle in FIG. Deformation may occur in the transmission mode waveform, and the places where it occurs (relative position to the main mode) are scattered, and there are multiple minimum parts, which causes unstable control, but only for a single polarization component. As shown in FIG. 21, the use of an optical waveguide through which the light passes through eliminates the deformation of the transmission mode waveform. can be planned.

In other words, the polarization component orthogonal to the optical comb generation causes measurement errors in distance and height when using the optical comb for measurement, and the polarization component orthogonal to the optical comb generation is a factor of the optical comb generator. The control for matching the resonance frequency to the laser frequency may become unstable, causing deviation of the control point and control oscillation. Although it was 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. It improves the extinction ratio, increases the degree of single polarization, stabilizes the cavity control, removes unnecessary interference signals, and eliminates measurement errors in distance measurement and shape measurement using an optical comb. It is possible to improve the measurement accuracy, improve the reliability of the entire system, and the like.

1, 1A, 110, 120, 130A, 130B optical comb generator, 8, 51 optical modulator, 11 substrate, 12 optical waveguide, 14 buffer layer, 16 oscillator, 18 terminating resistor, 20 ridge, 21 optical circulator, 22 focuser, 63 antireflection film, 83, 83A electrode, 84 first end surface, 85 second end surface, 86 first protective member, 86a, 87a end surface, 87 second protective member, 91, 92 plane, 93 Incident Side Reflective Film 94 Output Side Reflective Film 100A Low Power 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 (2)

a single-frequency laser light source;
Equipped with a plurality of optical comb generators into which the laser light emitted from the laser light source is divided into a plurality and entered,
Each of the plurality of optical comb generators includes:
oscillating means for oscillating modulation signals having different frequencies and having a predetermined frequency difference phase-locked by a common reference oscillator;
a resonance means composed of an incident-side reflecting film and an exit-side reflecting film parallel to each other and resonating the light incident through the incident-side reflecting 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 reflecting film to the exit-side reflecting film. When,
an electrode formed on the optical waveguide for propagating a modulated signal supplied from the oscillation means in the forward or backward direction, and formed so as to penetrate from the entrance-side reflection film to the exit-side reflection film, According to the modulation signal supplied from the oscillation means, the phase of the light resonated by the resonance means is modulated, and sidebands centered on the frequency of the incident light are generated at intervals of the frequency of the modulation signal. an optical comb generation means for outputting an optical comb of a single polarization component having mutually different modulation frequencies and center frequencies, phase synchronization with each other, and coherence by generation;
an optical detection means for detecting a part of the optical comb of a single polarization component obtained by the optical comb generation means;
control means for controlling the resonance length of the resonance means by generating a control signal for zeroing the error of the resonance length of the resonance means with respect to a control target from the photodetection signal obtained by the photodetection means;
An optical comb generator . 2. The optical comb generation device according to claim 1, wherein the plurality of optical comb generators are used as a light source unit for a measurement device that emits coherent reference light and measurement light with mutually different modulation periods. .

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