JP7100906B2 - Method for manufacturing optical resonators and light modulators - Google Patents

Description

The present invention is an optical resonator and an optical resonator applied to a field that requires a standard light source having high coherence at multiple wavelengths such as optical communication, optical CT, and an optical frequency standard, or a light source that can also utilize coherence between each wavelength. The present invention relates to a method of manufacturing an optical modulator .

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

When measuring the optical frequency with high accuracy, heterodyne detection is performed by interfering the measured light with other light and detecting the 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 about several tens of GHz.

On the other hand, with the development of optoelectronics in recent years, 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 expansion of the measurable band, a wide band heterodyne detection system using an optical frequency comb generator (see, for example, Patent Document 1) has been conventionally proposed. This optical frequency 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 the same as the frequency stability of incident light. Is. By heterodyne detection of the generated sideband and the light to be measured, it is possible to construct a wideband heterodyne detection system over several THz.

FIG. 32 shows the principle structure of this conventional optical frequency comb generator 1003.

As the optical frequency comb generator 1003, an optical resonator 1000 including an optical phase modulator 1031 and reflectors 1032 and 1033 installed so as to face each other via the optical phase modulator 1031 is used.

The optical resonator 1000 resonates the light Lin incident through the reflecting mirror 1032 with a slight transmittance between the reflecting mirrors 1032 and ₁₀₃₃ , and emits a part of the light L _out through the reflecting mirror 1033. Let me. The optical phase modulator 1031 is composed of an electro-optical crystal for optical phase modulation whose refractive index changes by applying an electric field, and the frequency applied to the electrode 1036 with respect to the light passing through the optical resonator 1000. Phase _modulation is applied according to the electric signal of fm.

In this optical frequency comb generator 1003, the optical phase modulator 1031 is operated only once by driving and inputting an electric signal synchronized with the time when light reciprocates in the optical resonator 1000 from the electrode 1036 to the optical phase modulator 31. It is possible to apply a deep phase modulation that is several tens of times or more deeper than when passing through. As a result, hundreds of high-order side bands can be generated, and the frequency intervals _fm of adjacent side bands are all equal to the frequency _fm of the input electric signal.

Further, the conventional optical frequency comb generator is not limited to the bulk type described above. For example, as shown in FIG. 33, it can also be applied to a waveguide type optical frequency comb generator 1020 using an optical waveguide.

The waveguide type optical frequency comb generator 1020 is composed of a waveguide type optical modulator 1200. The waveguide type optical modulator 1200 includes a substrate 1201, an optical waveguide 1202, an electrode 1203, an incident side reflecting film 1204, an emitting side reflecting film 1205, and an oscillator 1206.

The substrate 1201 is obtained by cutting out 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. The cut out substrate 1201 is subjected to processing such as mechanical polishing and chemical polishing.

The optical waveguide 1202 is arranged to propagate light, and the refractive index of the layer constituting the optical waveguide 1202 is set higher than that of other layers such as the substrate 1201. The light incident on the optical waveguide 1202 propagates while being totally reflected at the boundary surface of the optical waveguide 1202. Generally, the optical waveguide 1202 can be manufactured by diffusing Ti atoms in the substrate 1201 or by epitaxially growing it on the substrate 1201.

As the optical waveguide 1202 _, a LiNbO3 crystal optical waveguide may be applied. This LiNbO ₃ crystal optical waveguide can be formed by diffusing Ti on the surface of the substrate 1201 made of LiNbO ₃ or the like. When actually producing this LiNbO ₃ crystal optical waveguide, a photoresist pattern is first produced on the surface of the substrate 1201, Ti is vapor-deposited on the pattern, and then the photoresist is removed to obtain a micron-sized pattern. A thin line of Ti composed of width is produced. Next, by heating this thin wire of Ti, it is thermally diffused in the substrate 1201.

Incidentally, when this Ti is thermally diffused into the substrate 1201 made of LiNbO ₃ , light can be confined in the region where the Ti is diffused, where the refractive index is higher than in other regions. That is, an optical waveguide 1202 capable of propagating light in a region where such Ti is diffused is formed. Since the LiNbO ₃ crystal type optical waveguide 1202 produced based on such a method has an electro-optical effect, the refractive index can be changed by applying an electric field to the optical waveguide 1202.

The electrode 1203 is made of a metal material such as Al, Cu, Pt, and Au, and drives and inputs an electric signal having a frequency of _fm supplied from the outside to the optical waveguide 1202. Further, the light propagation direction in the optical waveguide 1202 and the traveling direction of the modulated electric field are the same. By adjusting the width and thickness of the electrode 1203, the speed of light propagating through the optical waveguide 1202 and the speed of the electric signal propagating on the electrode 1203 may be matched. This makes it possible to keep the phase of the electric signal felt by the light propagating through the optical waveguide 1202 constant.

The incident-side reflective film 1204 and the outgoing-side reflective film 1205 are provided to resonate the light incident on the optical waveguide 1202, and resonate by reciprocating the light passing through the optical waveguide 1202. The oscillator 1206 is connected to the electrode 1203 and supplies an electrical signal with a frequency of _fm .

The incident side reflecting film 1204 is arranged on the light incident side of the waveguide type optical modulator 1200, and light having a frequency ν ₁ is incident from a light source (not shown). Further, the incident side reflecting film 1204 reflects light that is reflected by the emitting side reflecting film 1205 and has passed through the optical waveguide 1202.

The light emitting side reflective film 1205 is arranged on the light emitting side of the waveguide type optical modulator 1200, and reflects the light that has passed through the optical waveguide 1202. Further, the emission-side reflective film 1205 emits light that has passed through the optical waveguide 1202 to the outside at a constant rate.

In the waveguide type optical frequency comb generator 1020 having the above configuration, an electric signal synchronized with the time when light reciprocates in the optical waveguide 1202 is used as a drive input from the electrode 1203 to the waveguide type optical modulator 1200. Compared with the case of passing through the optical phase modulator only once, it is possible to apply a deep phase modulation several tens of times or more. As a result, it is possible to generate an optical frequency comb having a sideband over a wide band as in the bulk type optical frequency comb generator 1003, and the frequency intervals of the adjacent sidebands are all the frequencies _fm of the input electric signal. Is equivalent to.

The feature of this waveguide type optical frequency comb generator 1020 is that the interaction region between light and electric signal is small. Since light is confined and propagates in the optical waveguide 1202 on the order of micron, which has a higher refractive index than the surroundings, by attaching the electrode 1203 in the very vicinity of the optical waveguide 1202, the electric field strength in the optical waveguide 1202 is locally adjusted. It will be possible to increase. Therefore, the electro-optic effect generated in the optical waveguide 1202 is larger than that of the bulk type optical frequency comb generator 1003, and it is possible to obtain a large modulation with a small amount of power.

However, in the conventional waveguide type optical frequency comb generator 1020 described above, it is difficult to polish the incident side reflective film 1204 and the outgoing side reflective film 1205 and the end surface to which they are adhered due to the structure of the optical waveguide 1202. Therefore, it was difficult to make a resonator with high finesse with good reproducibility. In order to improve the performance of the waveguide type optical frequency comb generator 1020, it is indispensable to improve the finesse of the resonator composed of the incident side reflecting film 1204 and the emitting side reflecting film 1205. Even if the modulation index in the optical waveguide 1202 is high only in the outward or return direction, if the finesse itself is low, the number of round trips of light cannot be increased, so that a high-intensity sideband is generated over a wide band. Because it cannot be done.

Further, there have been proposed an optical comb generator and an optical modulator in which phase modulation is applied not only to the light propagating in the outward path direction but also to the light propagating in the return path direction (see, for example, Patent Document 2). ).

Further, FIG. 34 shows the end face of the waveguide type optical frequency comb generator 1020 on which the incident side reflecting film 1204 is formed. According to FIG. 34, an optical waveguide 1202 is formed on the upper end of the substrate 1201, a thin buffer layer is laminated on the optical waveguide 1202, and an electrode 1203 is further formed on the thin buffer layer. That is, the optical waveguide 1202 is located at the uppermost corner of the end face of the waveguide type optical frequency comb generator 1020. Since the uppermost corner of the end face is sharp, a chip is often generated as shown in FIG. 34 during polishing. When the uppermost part of the end face is chipped, the light to be resonated is scattered and becomes a loss.

Further, depending on the state of end face polishing, the corners may be rounded even if the corners at the uppermost portion of the end face are not chipped. When the corners are rounded, a part of the reflected light deviates from the waveguide mode of the optical waveguide 1202, resulting in loss.

Further, in rare cases, it may be possible to polish in a state where the corners are not chipped at the uppermost portion of the end face and the corners are not rounded. Have a problem. A high-reflection film such as the incident-side reflective film 1204 is usually produced by alternately depositing a film having a high refractive index and a film having a low refractive index. As a result of the film thickness changing as the material of the highly reflective film wraps around from the end face to the side surface, there is also a problem that the film thickness cannot be controlled as designed.

That is, in an optical waveguide in which a core is formed in a substrate by diffusion or the like, the core is formed on the surface of the substrate, so that at least one side of the outer periphery of the core is located on the outer periphery of the substrate on the end face. When an optical thin film such as a reflective film is formed on the end face of such an optical waveguide by a vapor deposition method, a sputtering method, a chemical vapor phase growth method, etc. Since the film-formed particles flying from the side surface direction wrap around to the end face, it is difficult to obtain a uniform film thickness on the outer peripheral portion of the end face of the substrate. Therefore, it is very difficult to form a film thin enough to act as a reflective film or the like and having a small film thickness distribution on the end face of the core located on the outer peripheral portion of the end face of the substrate.

Here, the applicant of the present application suppresses chipping and rounding at the time of processing the corners of the end face of the optical waveguide, and stably adheres each reflective film to the uppermost corner of the end face without peeling. We have previously proposed optical cavities, optical modulators, optical comb generators, and optical oscillators that have improved reflectivity and finesse of optical cavities and enhanced the functions of the device itself. (See, for example, Patent Document 3).

That is, a protective member having the same hardness as the substrate for forming the optical waveguide from the upper surface, at least one end surface thereof has the same plane as the end surface of the substrate including the light incident end or the light emitting end in the optical waveguide. An incident side reflecting film and an emitting side reflecting film constituting the resonance means on the plane formed by polishing the end face of the protective member and the end face of the substrate, which are arranged on the upper part of the optical waveguide so as to be formed. By applying the light, it is possible to suppress chipping and rounding of the corners of the optical waveguide end face during processing, and to stably coat each reflective film without peeling off at the uppermost corner of the end face. It is possible to improve the reflectance and the finesse of the optical resonator and enhance the function of the device itself.

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

By the way, in the conventional waveguide type optical frequency comb generator 1020, since the end face of the optical waveguide 1202 is located at the uppermost corner of the end face, the optics of the reflective film or the like by the vapor deposition method, the sputtering method, the chemical vapor deposition method or the like. When a single-layer or multi-layered vapor deposition film is formed on the end face as a thin film, the film-forming particles wrap around to the side surface and the film-forming particles flying from the side surface wrap around to the end face at the outer peripheral portion of the end face of the substrate. Therefore, it is difficult to obtain a uniform film thickness on the outer peripheral portion of the end face of the substrate, and it is thin enough to act as a reflective film or the like on the end face of the core located on the outer peripheral portion of the end face of the substrate, and the film thickness is distributed. There was a problem that it was very difficult to form a film with a small amount of particles.

Further, when the end face of the optical waveguide 1202 is polished, the corners of the end face of the optical waveguide 1202 are easily chipped during processing, and the corners of the end face of the optical waveguide 1202 may be rounded during processing. There is a problem that the formed reflective film is easily peeled off at the uppermost corner of the end face.

These problems are a decrease in the reflectance of the reflective film adhered to the end face of the optical waveguide 1202, a decrease in the finesse of the cavity composed of the incident side reflective film 204 and the outgoing side reflective film 1205, and a waveguide type optical frequency comb. Since the function of the generator 1020 itself is deteriorated and it depends on the manufacturing environment, the performance of the waveguide type optical frequency comb generator 20 and the waveguide type Fabry-Perot resonator to which the same is applied is considered. Reproducibility could not be guaranteed, which was a factor in lowering the yield.

Further, conventionally, in a waveguide type optical cavity 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 an optical modulator or an optical frequency comb generator is constructed. The light output obtained in this case also contained a polarization component in which orthogonal modes were mixed.

In the conventional optical frequency comb generator, when the optical frequency comb is used for measurement, a part of the light emitted from the optical resonator is detected by the optical detector in order to obtain a stable output, and a predetermined value is obtained. The resonance length of the optical cavity was controlled by feedback so that it would be the resonance length. As shown in the above, the transmission mode waveform due to the orthogonal polarization component may be deformed. Moreover, the locations where the transmission mode waveform due to the orthogonal polarization component is deformed (relative positions with respect to the main mode) are scattered and have a plurality of extremely small portions, which becomes an unstable factor when controlling the resonance length.

That is, in the optical frequency comb generation in the optical comb generator using the waveguide type optical resonator that resonates the light confined in the optical waveguide, the orthogonal polarization components match the resonance frequency of the optical frequency comb generator with the laser frequency. When the optical frequency comb is used as a measuring device for measuring the distance or height to the measurement target, for example, it may cause the control to be unstable, which may cause the control point to shift or the control to oscillate. The orthogonal polarization components were a factor in the measurement error.

Further, as described above, a protective member having the same hardness as the substrate for forming the optical waveguide from the upper surface is provided with at least one end surface thereof and the end surface of the substrate including the light incident end or the light emitting end in the optical waveguide. An incident side reflective film constituting the resonance means on the plane formed by arranging the upper part of the optical waveguide so as to form the same plane and polishing the end face of the protective member and the end face of the substrate. By adhering the light emitting side reflective film, it is possible to suppress chipping and rounding at the time of processing the corners of the end face of the optical waveguide, and it is possible to stably adhere each reflective film without peeling off at the uppermost corner of the end face. It is possible to improve the reflectivity of the reflective film and the finesse of the optical resonator and enhance the function of the device itself. Thermally curable optical adhesives such as acrylic or photocurable optical adhesives may dissipate gas components when heated even after curing, and the incident side reflective film and the outgoing side reflective film may be emitted. There is a problem that the amount of the emitted gas increases as the vapor deposition temperature rises, and the emitted gas deteriorates the optical characteristics of the vapor phase growth film.

Further, the optical adhesive has a problem that the adhesive itself deteriorates when the glass transition temperature is exceeded, and the strength of the adhesive portion is lowered or the deformation causes physical deformation of the gas phase growth film.

Therefore, the present invention has been devised in view of the above-mentioned conventional problems, and the purpose of the present invention is to provide a protective member for suppressing chipping and rounding of the corners of the end face of the optical waveguide as an optical waveguide. Without adverse effects such as deterioration of the optical properties of the gas phase growth film due to the emitted gas due to the heating of the optical adhesive for adhesively fixing to the upper part of the cavity and physical deformation of the gas phase growth film due to the decrease in the strength of the bonded part. By stably adhering a single-layer or multi-layer gas phase growth film as each reflective film without peeling off at the uppermost corner of the end face, the reflectance of the reflective film and the finesse of the cavity are improved, and the device It is an object of the present invention to provide a method for manufacturing an optical resonator and a modulator having enhanced functions thereof .

Another object of the present invention is to make it possible to stabilize the resonator control without deforming the transmission mode waveform of the optical waveguide.

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

Further, another object of the present invention is to stabilize the optical frequency comb generator, improve the accuracy of the measuring device including the optical frequency comb, reduce the error, and the like.

Other objects of the invention, the specific advantages obtained by the present invention, will be further clarified from the description of the embodiments described below.

The present invention relates to a method for manufacturing an optical resonator that propagates and resonates light incident through the incident side reflective film by an optical waveguide formed so as to penetrate from the incident side reflective film to the outgoing side reflective film. An optical waveguide forming step of forming the optical waveguide from the upper surface of the substrate, and a protective member having the same hardness as the substrate, the substrate having at least one end face including a light incident end or a light emitting end in the optical waveguide. By polishing the end face of the protective member and the end face of the substrate arranged in the arrangement step of the optical waveguide so as to form the same plane as the end surface of the optical waveguide. As a flat polishing surface including the light incident end or the light emitting end of the waveguide, a polishing step of forming a plane perpendicular to the optical waveguide, and the incident side reflective film or the above-mentioned incident side reflective film or the above-mentioned incident side reflection film on the above-mentioned plane formed in the above-mentioned polishing step. The light emitting side reflective film has a reflective film coating step of adhering a single-layer or multi-layered gas phase growth film, and in the disposing step, the protective member is attached to the upper part of the optical waveguide with an adhesive. In the process of adhering the reflective film, the temperature is lower than the heat resistant temperature of the adhesive over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate. It is characterized in that the incident side reflective film or the outgoing side reflective film is formed in a plane perpendicular to the optical waveguide by adhering a single-layer or multi-layer gas phase growth film under the conditions.

In the method for manufacturing an optical cavity according to the present invention, in the reflection film coating step, the light incident end or light emission of the optical waveguide is relative to the loss rate according to the crystal length in the light propagation direction of the optical waveguide. It is possible to adhere a single-layer or multi-layer gas phase growth film having an optimized film thickness in the end face region including the end.

The present invention relates to a method for manufacturing an optical modulator that propagates and modulates light incident on an incident side through an incident side reflective film by an optical waveguide on which an incident side reflective film and an outgoing side reflective film are formed. An optical waveguide forming step of forming the light waveguide from the upper surface of the substrate, a laminating step of laminating a buffer layer on the substrate so as to cover at least the optical waveguide formed in the optical waveguide forming step, and an electric field applied to the optical waveguide. An electrode forming step of forming an electrode for applying on a buffer layer laminated in the laminating step, and a protective member having the same hardness as the substrate, at least one end surface thereof is a light incident end or light in the optical waveguide. The arrangement step of arranging the upper part of the optical waveguide so as to form the same plane as the end surface of the substrate including the emission end, and the end surface of the protection member arranged in the arrangement step and the end surface of the substrate are polished. By doing so, as a flat polishing surface including the light incident end or the light emitting end of the optical waveguide, a polishing step of forming a plane perpendicular to the optical waveguide and the polishing step formed in the polishing step on the plane. It has a reflective film attachment step of adhering a single layer or a multilayer gas phase growth film as the incident side reflective film or the outgoing side reflective film, and in the disposing step, the protective member is placed on the upper part of the optical waveguide. The adhesive is attached and arranged with an adhesive, and in the reflective film adhesion step, the adhesive is applied over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate. By adhering a single-layer or multi-layered gas phase growth film under temperature conditions lower than the heat-resistant temperature, the incident-side reflective film or the outgoing-side reflective film is formed on a plane perpendicular to the optical waveguide. It is characterized by.

In the method for manufacturing an optical cavity according to the present invention, in the reflection film coating step, the light incident end or light emission of the optical waveguide is relative to the loss rate according to the crystal length in the light propagation direction of the optical waveguide. It is possible to adhere a single-layer or multi-layer gas phase growth film having an optimized film thickness in the end face region including the end.

Further, in the method for manufacturing an optical resonator according to the present invention, in the reflective film coating step, in the optical waveguide forming step, a single polarization component is formed by proton exchange from the upper surface of the substrate having at least an electro-optical effect. The optical waveguide can be formed as a region in which the waveguide mode exists only.

Further, the method for manufacturing an optical resonator according to the present invention includes a ridge structure forming step of forming a ridge structure on the substrate, and is laminated on the substrate on which the ridge structure is formed in the laminating step in the electrode forming step. An electrode having a ridge structure can be formed on the buffer layer as an electrode for applying an electric field to the optical waveguide.

The present invention is an optical resonator, which is composed of an incident side reflecting film and an emitting side reflecting film, and has a resonance means for resonating light incident through the incident side reflecting film and the above emitting light from the incident side reflecting film. It is composed of an optical waveguide that is formed so as to penetrate through the side reflective film and propagates the light resonated by the resonance means, a substrate on which the optical waveguide is formed from the upper surface, and a protective member having the same hardness as the substrate. The protective member is attached to the upper part of the optical waveguide with an adhesive so that at least one end surface of the protective member forms the same plane as the end surface of the substrate including the light incident end or the light emitting end of the optical waveguide. The end face protection means is provided with end face protection means attached and arranged, and the end face protection means is a light incident end or light emission in the optical waveguide at a substantially center of a plane formed by the end face of the protection member and the end face of the substrate. Arranged so that the ends are located, the incident-side reflective film and the outgoing-side reflective film cover the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate. Temperature conditions lower than the heat resistant temperature of the adhesive over all the planes perpendicular to the optical waveguide formed as a flat polished surface including the light incident end or the light emission end of the optical waveguide by polishing. It is characterized by being a monolayer or multilayer vapor growth film adhered underneath.

In the optical resonator according to the present invention, the incident-side reflecting film and the emitting-side reflecting film have the light incident end of the optical waveguide or the light incident end of the optical waveguide with respect to the loss rate according to the crystal length in the light propagation direction of the optical waveguide. It can be a single-layer or multi-layer gas phase growth film with an optimized film thickness in the end face region including the light emitting end.

Further, in the optical waveguide according to the present invention, the protective member constituting the end face protecting means is made of the same material as the substrate, and the end face of the protective member forming the plane and the end face of the substrate are the same as each other. The end face protection means is such that one end face of the protection member forms the same plane as the end face of the substrate including the light incident end in the optical waveguide, and the other end face protection member of the protection member. It can be arranged on the upper part of the optical waveguide so that the end surface of the optical waveguide forms the same plane as the end surface of the substrate including the light emitting end of the optical waveguide.

The present invention is an optical modulator, which is composed of an oscillating means for oscillating a modulated signal of a predetermined frequency, an incident side reflecting film and an emitting side reflecting film, and resonates light incident through the incident side reflecting film. The resonance means is formed so as to penetrate from the incident side reflecting film to the emitting side reflecting film, and the phase of the light resonated by the resonance means is modulated according to the modulated signal supplied from the oscillating means. It is composed of an optical waveguide, a substrate on which the optical waveguide is formed from the upper surface, and a protective member having the same hardness as the substrate, and at least one end surface of the protective member is a light incident end or a light emitting end in the optical waveguide. The light waveguide is provided with an end face protecting means in which the protective member is attached and disposed with an adhesive so as to form the same plane as the end face of the substrate including the above, and the end face protecting means is provided with the protection. The light incident end or the light emitting end in the optical waveguide is arranged so as to be located at the substantially center of the plane formed by the end surface of the member and the end surface of the substrate, and the incident side reflecting film and the emitting side reflecting film are arranged. By polishing over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate, a flat polished surface including the light incident end or the light emitting end of the optical waveguide. It is characterized by being a single-layer or multi-layered vapor-phase growth film adhered under a temperature condition lower than the heat-resistant temperature of the adhesive over all the planes perpendicular to the optical waveguide formed as. ..

In the light modulator according to the present invention, the incident side reflecting film and the emitting side reflecting film have the light incident end of the optical waveguide or the light incident end of the optical waveguide with respect to the loss rate according to the crystal length in the light propagation direction of the optical waveguide. It can be a single-layer or multi-layer gas phase growth film with an optimized film thickness in the end face region including the light emitting end.

The present invention is an optical modulator, which is composed of an incident side reflecting film and an emitting side reflecting film, and has a resonance means for resonating light incident through the incident side reflecting film and the above emitting light from the incident side reflecting film. It consists of an optical waveguide formed so as to penetrate through the side reflective film, a substrate on which the optical waveguide is formed from the upper surface, and an electrode formed on the substrate for propagating a modulation signal in the outward path direction or the return path direction. The protective member comprises an optical modulation means that modulates the phase of light propagating in the optical waveguide according to the wavelength of an electric signal supplied to the electrode, and a protective member having the same hardness as the substrate. The protective member is attached and arranged on the upper part of the optical waveguide with an adhesive so that at least one end face forms the same plane as the end face of the substrate including the light incident end or the light emitting end in the optical waveguide. The end face protecting means is provided so that the light incident end or the light emitting end of the optical waveguide is located substantially at the center of a plane formed by the end face of the protective member and the end face of the substrate. The incident side reflective film and the outgoing side reflective film are arranged and polished over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate. All of the planes perpendicular to the optical waveguide formed as a flat polished surface including the light incident end or the light emission end of the optical waveguide were adhered under temperature conditions lower than the heat resistant temperature of the adhesive. It is characterized by being a single-layer or multi-layered gas phase growth film.

Further, in the light modulator according to the present invention, the incident side reflecting film and the emitting side reflecting film have a loss rate according to the crystal length in the light propagation direction of the optical waveguide, and the light incident of the optical waveguide. It can be a single-layer or multi-layer gas phase growth film with an optimized film thickness in the end face region including the end or the light emitting end.

Further, in the optical modulator according to the present invention, the optical waveguide is formed on the substrate having at least an electro-optic effect as a region in which a waveguide mode exists only for a single polarization component. Can be.

Further, in the light modulator according to the present invention, the electrodes of the light modulation means may have a ridge structure.

The present invention is an optical frequency comb generator, which is composed of an oscillating means for oscillating a modulated signal of a predetermined frequency, an incident side reflecting film, and an emitting side reflecting film, and the light incident through the incident side reflecting film. And the phase of the light resonated by the resonance means according to the modulation signal supplied from the oscillation means and formed so as to penetrate from the incident side reflection film to the emission side reflection film. An optical waveguide that is modulated to generate a sideband centered on the frequency of the incident light at intervals of the frequency of the modulated signal, a substrate on which the optical waveguide is formed from the upper surface, and a substrate formed on the substrate for modulation. An optical modulation means that comprises electrodes for propagating a signal in the outward or return direction and modulates the phase of light propagating in the optical waveguide according to the wavelength of an electric signal supplied to the electrodes, and a substrate. The optical waveguide is composed of a protective member having the same hardness as that of the optical waveguide so that at least one end surface of the protective member forms the same plane as the end surface of the substrate including the light incident end or the light emitting end of the optical waveguide. The protective member is provided with an end face protecting means to which the protective member is attached and arranged by an adhesive, and the end face protecting means is provided at substantially the center of a plane formed by the end face of the protective member and the end face of the substrate. The light incident end or the light emitting end of the optical waveguide is arranged so as to be located, and the incident side reflecting film and the emitting side reflecting film are the end face of the protective member attached with the adhesive and the end face of the substrate. By polishing over all the planes formed by It is characterized by being a single-layer or multi-layer gas phase growth film adhered under a temperature condition lower than the heat resistant temperature of the adhesive.

In the optical frequency comb generator according to the present invention, the incident side reflecting film and the emitting side reflecting film have a loss rate according to the crystal length in the light propagation direction of the optical waveguide, and the light incident of the optical waveguide. It can be a single-layer or multi-layer gas phase growth film with an optimized film thickness in the end face region including the edge or the light emitting edge.

The present invention is an optical oscillator, which is composed of an incident side reflecting film and an emitting side reflecting film, and has a resonance means for resonating light incident through the incident side reflecting film or light generated by laser amplification. An optical waveguide formed so as to penetrate from the incident side reflecting film to the emitting side reflecting film, amplify the light resonated by the resonance means, and emit the light to the outside through the emitting side reflecting film, and the above. The optical waveguide consists of a substrate formed from the upper surface and an electrode formed on the substrate for propagating a modulation signal in the outward path direction or the return path direction, and the optical waveguide is formed according to the wavelength of an electric signal supplied to the electrode. It is composed of an optical modulation means that modulates the phase of light propagating inside and a protective member having the same hardness as the substrate, and at least one end surface of the protective member is a light incident end or a light emitting end in the optical waveguide. The protective member is provided with an end face protection means disposed on the upper part of the optical waveguide so as to form the same plane as the end face of the substrate including the above, and the end face protection means is provided with the protection. The light incident end or the light emitting end in the optical waveguide is arranged so as to be located at the substantially center of the plane formed by the end surface of the member and the end surface of the substrate, and the incident side reflecting film and the emitting side reflecting film are arranged. By polishing over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate, a flat polished surface including the light incident end or the light emitting end of the optical waveguide. It is characterized in that it is a single-layer or multi-layer gas phase growth film adhered under a temperature condition lower than the heat-resistant temperature of the adhesive over all the planes perpendicular to the optical waveguide formed as. ..

In the optical oscillator according to the present invention, the incident side reflecting film and the emitting side reflecting film have a loss rate according to the crystal length in the light propagation direction of the optical waveguide, and the light incident end or light of the optical waveguide. It can be a single-layer or multi-layer gas phase growth film with an optimized film thickness in the end face region including the emission end.

Further, in the optical waveguide according to the present invention, the optical waveguide absorbs the light incident through the incident side reflective film and diffuses the medium having amplification characteristics with respect to the wavelength of the light peculiar to the medium. Can be.

Further, in the optical oscillator according to the present invention, the optical waveguide can be made of a nonlinear optical crystal.

The present invention is an optical oscillator, which is an oscillating means for oscillating a modulated signal having a predetermined frequency.
A resonance means that resonates light incident on the incident side reflective film and light generated by laser amplification, which is composed of an incident side reflective film and an outgoing side reflective film, and the outgoing side reflection from the incident side reflective film. An optical waveguide that is formed so as to penetrate through a film, amplifies the light resonated by the resonance means in response to the modulation signal supplied from the oscillation means, and emits the light to the outside through the reflection film on the exit side. The optical waveguide is composed of a substrate formed from the upper surface and an electrode formed on the substrate for propagating a modulation signal in the outward path direction or the return path direction, depending on the wavelength of the electric signal supplied to the electrode. It is composed of an optical modulation means that modulates the phase of light propagating in the optical waveguide and a protective member having the same hardness as the substrate, and at least one end surface of the protective member is a light incident end or an optical incident end in the optical waveguide. The end face protection means is provided with an end face protection means in which the protection member is attached and arranged with an adhesive on the upper part of the optical waveguide so as to form the same plane as the end face of the substrate including the light emission end. The light incident end or the light emitting end of the optical waveguide is arranged so as to be located at the substantially center of the plane formed by the end surface of the protective member and the end surface of the substrate, and the incident side reflective film and the emitted side reflection are arranged. The film is flat including the light incident end or the light emitting end of the optical waveguide by polishing over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate. A single-layer or multi-layered vapor-phase growth film adhered under a temperature condition lower than the heat-resistant temperature of the adhesive over all the planes perpendicular to the optical waveguide formed as a polished surface, and is a laser. It is characterized by taking phase synchronization between oscillating multimodes.

Further, in the optical oscillator according to the present invention, the incident side reflecting film and the emitting side reflecting film have a loss rate according to the crystal length in the light propagation direction of the optical waveguide, and the light incident end of the optical waveguide. Alternatively, it can be a single-layer or multi-layer gas phase growth film in which the film thickness in the end face region including the light emission end is optimized.

In the present invention, the protective member having the same hardness as the substrate for forming the optical waveguide from the upper surface is the same as the end surface of the substrate including the light incident end or the light emitting end in the optical waveguide at least one end surface thereof. By attaching and arranging the optical waveguide on the upper part of the optical waveguide with an adhesive so as to form a flat surface and polishing the end face of the protective member and the end face of the substrate, the light incident end or the light emission end of the optical waveguide is formed. As the including flat polished surface, a plane perpendicular to the optical waveguide can be formed. Further, a single layer or a multilayer vapor phase under a temperature condition lower than the heat resistant temperature of the adhesive over the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate. Since the growth film is adhered, the optical characteristics of the gas phase growth film due to the emitted gas due to the heating of the adhesive are not deteriorated, and the physical deformation of the gas phase growth film due to the decrease in the strength of the bonded portion is not adversely affected. As each reflective film, a single-layer or multi-layered gas phase growth film can be stably adhered without peeling at the uppermost corner of the end face. As a result, chipping and rounding during processing of the corners of the optical 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, and the reflectance and resonance of the reflective film can be achieved. It is possible to improve the finesse of the vessel and enhance the function of the device itself.

Further, in the present invention, an optical waveguide formed as a region in which a waveguide mode exists only for a single polarization component on a substrate having at least an electro-optical effect so as to penetrate from the incident end to the emitted end. Therefore, only a single polarization component of the light incident through the incident side reflective film is propagated through the optical waveguide, phase-modulated, and emitted from the exit end. By providing the emission side reflection film from the incident side reflection film constituting 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, in the present invention, it corresponds to a modulation signal supplied to an electrode having a ridge structure formed on an optical waveguide formed of a substrate having at least an electro-optical effect and for propagating a modulation signal in the outward path direction or the return path direction. By providing the optical modulation means for modulating the phase of the light propagating in the optical waveguide, the power of the microwave used as the modulation signal required for driving can be reduced.

That is, according to the present invention, by polishing the end face of the protective member having the same hardness as the substrate for forming the optical waveguide and the end face of the substrate, the corners of the optical waveguide end face are chipped or rounded during processing. By using an optical waveguide having a single-layered or multi-layered gas phase growth film as a light incident end face and a light emitting end face formed in a plane perpendicular to the optical waveguide, and having an electrode having a ridge structure. It is possible to provide optical modulators and optical comb generators that realize low power drive, save energy, reduce heat generation, reduce size and weight, improve reliability, and reduce costs.

It is a figure which shows the structure of the optical modulator to which this invention is applied. It is a side view of the optical modulator to which this invention is applied. It is a figure which shows the plane in which the incident side reflection film is formed in the light modulator to which this invention is applied. It is a flowchart for demonstrating the manufacturing method of the optical modulator to which this invention is applied. It is a figure for demonstrating the experimental result of the loss characteristic of the optical modulator to which this invention is applied. It is a figure which shows the structure of the optical modulator which has a wafer which plays the role of a protective member and a buffer layer together. It is a figure which shows the structure of the reciprocating modulation type optical modulator to which this invention is applied. It is a figure which shows the intensity distribution at each frequency (wavelength) of a side band when this invention is applied to an optical frequency comb generator. It is a figure which shows the structure of the optical waveguide type laser oscillator to which this invention is applied. It is a figure which shows the structure of the laser oscillator to which this invention is applied. It is a figure which shows the structure of the modified FP electro-optic modulator to which this invention is applied. It is a figure for demonstrating the example of the communication system which mounted the optical modulator to which this invention is applied in the base station. It is a figure for demonstrating the case which limits the length of the optical modulator to which this invention is applied. It is another figure for demonstrating the case which limits the length of the optical modulator to which this invention is applied. It is a perspective view which shows the other structural example of the optical modulator to which this invention is applied. It is a side view of the said optical modulator. It is sectional drawing of the main part in each process for demonstrating the manufacturing method of the said optical modulator. It is a perspective view of the substrate provided with three optical waveguides manufactured for measuring the end face reflectance of the optical modulator to which this invention is applied. It is a front view which shows the incident side end face of the said substrate. It is a top view of the said substrate. It is a perspective view which shows the structure of the optical modulator (optical comb generator) provided with the electrode which has the ridge structure to which this invention is applied. It is a vertical sectional view of the main part in each process for explaining the manufacturing method of the said optical modulator (optical comb generator). It is a perspective view which shows the substrate which forms the electrode which has the ridge structure of the said optical modulator (optical comb generator). It is a vertical sectional front view of a main part 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 driving voltage (AC Vpi) at 25GHz with and without the ridge structure of an electrode about the optical modulator to which this invention was applied. It is a figure for demonstrating the result of having measured the change of the direct current drive voltage (DC Vpi) by the presence or absence of the ridge structure of an electrode about the optical modulator to which this invention was 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 configuration 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 by using the low power type optical comb module to which this invention was applied. It is a block diagram which shows the structure of the optical comb rangefinder configured by using the said optical comb light source. It is a characteristic diagram which shows the transmission mode waveform without deformation obtained when the resonance length of an optical resonator is feedback-controlled in the optical comb generator using the optical waveguide which passes only a single polarization component to which this invention is applied. It is a figure which shows the principle structure of the conventional optical frequency comb generator. It is a figure which shows the principle structure of the conventional waveguide type optical frequency comb generator. It is a figure which shows the end face which the incident side reflection film is formed in the conventional waveguide type optical frequency comb generator. Characteristic diagram showing deformation of transmission mode waveform due to orthogonal polarization component generated when feedback control of resonance length of optical cavity is performed in a conventional optical comb generator using an optical waveguide that transmits a polarization component in which orthogonal modes are mixed. Is.

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

The present invention applies to the light modulators 8 shown in FIGS. 1 and 2. The optical modulator 8 includes a substrate 11, an optical waveguide 12 formed on the substrate 11 that modulates the phase of propagating light, and a buffer layer 14 laminated so as to cover the optical waveguide 12 on the substrate 11. And the electrode 83 provided on the upper surface of the optical waveguide 12 so that the direction of the modulated electric field is substantially perpendicular to the light propagation direction, and the first provided so as to face each other via the optical waveguide 12. A first protective member 86 arranged on the upper part of the optical waveguide 12 so as to form the same plane as the end surface 84 and the second end surface 85 and the first end surface 84 and adhered by an adhesive, and a second. A second protective member 87 arranged on the upper part of the optical waveguide 12 so as to form the same plane as the end surface 85 and adhered by an adhesive, and an end surface 86a of the first end surface 84 and the first protective member 86. An incident side reflective film 93 made of a single-layer or multi-layered gas phase growth film adhered on a plane 91 formed between the two under a temperature condition lower than the heat resistant temperature of the adhesive, a second end face 85, and the like. Emission side reflection composed of a single-layer or multi-layer gas phase growth film adhered on a flat surface 92 formed between the end surface 87a of the second protective member 87 under a temperature condition lower than the heat resistant temperature of the adhesive. It includes a film 94, an oscillator 16 arranged on one end side of the electrode 83 and oscillating a modulation signal having a frequency _fm , and a termination resistor 18 arranged on the other end side of the electrode 83.

The substrate 11 is obtained by cutting out 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. The cut out substrate 11 is subjected to processing such as mechanical polishing and chemical polishing.

The optical waveguide 12 is formed so as to penetrate from the incident side reflective film 93 to the outgoing side reflective film 94, and is formed to propagate the resonated light. The refractive index of the layers constituting the optical waveguide 12 is set higher than that of other layers such as the substrate 11. The light incident on the optical waveguide 12 propagates while being totally reflected at the boundary surface of the optical waveguide 12. Generally, the optical waveguide 12 can be manufactured by diffusing Ti atoms in the substrate 11 or by epitaxially growing it on the substrate 11.

As the optical waveguide 12 _, a LiNbO3 crystal optical waveguide may be applied. This LiNbO ₃ crystal optical waveguide can be formed by diffusing Ti on the surface of the substrate 11 made of LiNbO ₃ or the like. In the region where Ti is diffused, where the refractive index is higher than in other regions, light can be confined, so that an optical waveguide 12 capable of propagating light can be formed. The LiNbO ₃ crystal type optical waveguide 12 produced based on such a method has electricity 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, it is possible to modulate light by utilizing such a physical phenomenon.

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

The electrode 83 is made of a metal material such as Ti, Pt, or Au, and is phased with light propagating in the optical waveguide 12 by driving and inputting a modulation signal having a frequency _fm supplied from the oscillator 16 to the optical waveguide 12. Modulate.

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

The incident side reflecting film 93 and the emitting 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, and reciprocally reflect the light passing through the optical waveguide 12. The optical resonator 5 that resonates with the above is configured.

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

The incident side reflective film 93 and the outgoing side reflective film 94 are subjected to a temperature condition lower than the heat resistant temperature of the above-mentioned vapor adhesive by using a vapor deposition method, an ion plating method, a chemical vapor deposition method (CVD), a sputtering method or the like. It is formed over one plane 91 and 92 as a single-layer or multi-layer vapor deposition film made of a thin-film film, a sputter film, or the like.

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

FIG. 3 shows the plane 91 on which the incident side reflective film 93 is formed from the direction A in FIG.

The same plane 91 is formed by the first end surface 84 including the light incident end of the optical waveguide 12 and the end surface 86a of the protective member 86. 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 the end face with a slope of 0.05 ° with respect to the plane 91 with a slope of 0.05 ° is 4 × 10 ^-4 , which is incidental. It is negligibly small compared to the reflectance of the side reflective film 93.

By forming the first end face 91 and the second end face 92 substantially perpendicular to the optical waveguide 12 in this way, the incident side reflective film 93 is adhered to the first end face 91 and the second end face 92 as a single-layer or multi-layer gas phase growth film. In addition, the light can be efficiently resonated by the light emitting side reflective film 94.

In the light modulator 8 having the above-described configuration, the light incident from the outside through the incident side reflecting film 93 propagates in the optical waveguide 12 in the outward path direction, is reflected by the emitting side reflecting film 94, and is partially external. Permeate to. The light reflected by the light emitting side reflecting film 94 propagates in the optical waveguide 12 in the return direction and is reflected by the incident side reflecting film 93. By repeating this, the light resonates in the optical waveguide 12.

Further, by using an electric signal synchronized with the time when the light reciprocates in the optical waveguide 12 as a drive input via the electrode 83, the light passes through the light modulator 8 only once, as compared with the case where the light passes through the light modulator 8 only once. It is possible to apply deep phase modulation several tens of times or more. In addition, hundreds of sidebands can be generated over a wide band around the frequency ν ₁ of the incident light. Incidentally, the frequency interval of each of the generated side bands is equivalent to the frequency _fm of the input electric signal. Therefore, the light modulator 8 can also be applied as an optical frequency comb generator composed of a large number of side bands.

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 is formed on the surface of the substrate 11 made of LiNbO3 crystals _, and Ti is vapor-deposited therein. Next, by removing this photoresist, a thin line of Ti composed of a micron-sized width is produced.

Next, the process proceeds to step S12, and the substrate 11 on which the fine wires of Ti are formed is heated to thermally diffuse the Ti atoms into the substrate 11 to form the optical waveguide 12.

Next, the process proceeds to step S13, and the SiO ₂ thin film as the buffer layer 14 is vapor-deposited on the surface of the substrate 11. In this step S13, the buffer layer 14 may be formed by a method of attaching the SiO ₂ wafer to the surface of the substrate 11. In such a case, the film thickness may be controlled to an appropriate level by polishing the vapor-deposited buffer layer 14 in consideration of the electrode mounting area in step S14 described later.

Next, the process proceeds to step S14, and the electrode 83 is formed on the buffer layer 14. Next, the process proceeds to step S15, and the protective members 86 and 87 are adhered to the upper part of the optical waveguide 12. As for the method of adhering the protective members 86 and 87, they may be attached with an adhesive or may be directly bonded based on another method. When the substrate 11 is made of LiNbO ₃ crystals, the protective members 86, 87 may be made of LiNbO ₃ as the same material. In this step S15, the end faces 86a and 87a of the attached protective members 86 and 87 can form planes 91 and 92 between the first end face 84 and the second end face 85, respectively. And trim it.

As the adhesive used when adhering the protective members 86 and 87 on the upper part of the optical waveguide 12, a thermosetting optical adhesive such as an epoxy or acrylic adhesive or a photocurable optical adhesive is used.

Finally, the process proceeds to step S16, and the obtained planes 91 and 92 are polished to a plane perpendicular to the optical waveguide 12. Then, the incident side reflective film 93 and the outgoing side reflective film 94 are formed over one surface on the planes 91 and 92 perpendicular to the polished optical waveguide 12.

Here, the incident side reflective film 93 and the outgoing side reflective film 94 are adhered and formed on the planes 91 and 92 as a single-layer or multi-layered vapor phase growth film by a vapor deposition method, a sputtering method, a chemical vapor deposition method, or the like. Ru.

When forming the incident side reflective film 93 and the outgoing side reflective film 94 as the gas phase growth film, the temperature should be below the heat resistant temperature of the optical adhesive used to bond the protective members 86 and 87 on the upper part of the optical waveguide 12. The temperature condition for the vapor deposition treatment is, for example, when an epoxy metacrate-based ultraviolet curable optical adhesive having a relatively high glass transition temperature Tg is used, the chip surface temperature is 200 ° C. or less. When an epoxy-based or acrylic-based ultraviolet curable optical adhesive having a glass transition temperature Tg lower than that of the epoxy metacrate-based adhesive is used, it is necessary to set the temperature condition of the vapor deposition treatment low. The temperature condition of the vapor deposition process can be set high by using an optical adhesive having a glass transition temperature Tg higher than that of the optical adhesive.

As described above, in the optical modulator 8 to which the present invention is applied, since the protective members 86 and 87 are attached to each end portion, the end surface of the optical waveguide 12 which has been conventionally located at the uppermost corner of the end surface is configured. Moves to a substantially central portion of the plane 91 (92) as shown in FIG. As a result, even when the corner of the plane 91 (92) is chipped during polishing in step S16, the end face of the optical waveguide 12 is not chipped. That is, it is possible to configure the optical waveguide 12 so that the end face itself is less likely to be chipped. This makes it possible to suppress the light loss from each end face of the optical waveguide 12 as much as possible.

Further, by configuring the material of the protective members 86 and 87 with the optimum material corresponding to the material of the substrate 11, the polishing speed in step S16 is set to the first end surface 84 and the second end surface 85 to the end surface 86a of the substrate 11. It can be made uniform over 87a. As a result, the end face of the optical waveguide 12 does not become rounded during processing, and planes 91 and 92 perpendicular to the optical waveguide 12 made of a flat polished surface can be obtained, and the reflection loss at the end face of the optical waveguide 12 can be minimized. It is possible to limit it to the limit. Further, by making the crystal orientations of the end faces constituting the planes 91 and 92 the same, it is possible to further suppress the reflection loss.

Further, by intentionally providing the protective members 86 and 87, the polishing accuracy in step S16 is improved, and the verticality of the obtained flat surface 91 (92) with respect 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, by providing the protective members 86 and 87, the incident side reflective film 93 and the outgoing side reflective film 94 to be adhered as a single-layer or multi-layer gas phase growth film are formed on the other side surfaces from the planes 91 and 92. It is possible to suppress the change in film thickness due to the wraparound of the particles to the side surface and the wraparound of the film-formed particles flying from the side surface direction to the end face. Therefore, the film thickness in the vicinity of 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 reflective film 93 and the outgoing side reflective film 94 are very stable because they 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 on the substrate 11. It is difficult to peel off, and it is possible to improve the reproducibility of film formation.

When the flat surface 91 (92) was actually polished after the protective members 86, 87 were attached in order to experimentally verify the effect of providing the protective members 86, 87, the end face of the optical waveguide 12 was actually polished. No chipping or bending occurs in the portion, and flat optical polishing suitable for adhesion of the incident side reflective film 93 and the outgoing side reflective film 94 made of a single-layer or multi-layer gas phase growth film is applied. Can be confirmed.

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 and the first end face 84 of the protective members 86, 87 forming the planes 91, 92 are formed. By processing the second end face 85 so as to have the same crystal orientation as each other, the hardness of the crystals becomes the same between the two, so that the planes 91 and 92 do not tilt due to the difference in polishing speed.

As described above, in the optical modulator 8 to which the present invention is applied, the end face of the optical waveguide 12 can be moved to the substantially central portion of the plane 91 (92) by attaching the protective members 86 and 87 at each end portion. Therefore, the end face of the optical waveguide 12 is chipped or rounded, the verticality between the optical waveguide 12 and the planes 91 and 92 is ensured, the polishing accuracy on the planes 91 and 92 is improved, and the incident side reflective film 93 and the outgoing side reflective film 94 are formed. It is possible to suppress peeling and wraparound, improve the reflectance of the incident side reflective film 93 and the outgoing side reflective film 94, realize the designed reflection characteristics, and improve the performance reproducibility of the reflective film. As a result, the finesse of the optical resonator 5 composed of the incident side reflecting film 93 and the emitting side reflecting film 94 can be improved, and a high-performance optical modulator and optical frequency comb generator can be manufactured with good reproducibility. It is also possible to improve the yield.

An optical modulator 8 having the above configuration is actually mounted on a polished flat surface 91, 92 with a reflective film 93,94 having a reflectance of 97% as a single layer or under a temperature condition lower than the heat resistant temperature of the adhesive. As a result of forming the optical waveguide 12 as a multi-layered gas phase growth film, a maximum of 61 finesse can be obtained when the crystal length of the optical waveguide 12 is 27.4 mm (hereinafter referred to as a short resonator). Further, when the crystal length of the optical waveguide 12 was 54.7 mm (hereinafter referred to as a long resonator), a maximum of 38 finesse could be obtained. Since the finesse of the conventional waveguide type optical resonator (IEEE Photonics Technology Letters, Vol.8, No. 10, 1996) was the highest at 30, this light with improved end face polishing and coating accuracy. It can be seen that the modulator 8 can significantly improve the finesse. In particular, it has been shown that finesse of 30 or more can be obtained for all six samples of the light modulator 8 produced, and the reproducibility of the production process is high.

That is, the substrate 11 having the same hardness as the substrate 11 for forming the optical waveguide 12 from the upper surface, the substrate 11 having at least one end surface including a light incident end or a light emitting end in the optical waveguide 12. The end face of the protective member 86, 87 and the end face of the substrate 11 are polished by being attached and arranged on the upper part of the optical waveguide 12 with an optical adhesive so as to form the same flat surface 91, 92 as the end face of the above. Thereby, as a flat polished surface including the light incident end or the light emitting end of the optical waveguide 12, planes 91 and 92 perpendicular to the optical waveguide 12 can be formed. Further, under temperature conditions lower than the heat resistant temperature of the adhesive over all of the flat surfaces 91 and 92 formed by the end faces of the protective members 86 and 87 attached with the adhesive and the end faces of the substrate 11. Since the reflective film is adhered as a single-layer or multi-layered gas phase growth film, the physics of the gas phase growth film due to deterioration of the optical characteristics of the XTIA gas phase growth film due to the gas emitted by the heating of the adhesive and the decrease in the strength of the adhesive portion. As each of the reflective films 93 and 94, a single-layer or multi-layered gas phase growth film can be stably adhered without being peeled off at the uppermost corner of the end face without suffering an adverse effect such as deformation. As a result, chipping and rounding during processing of the corners of the optical waveguide 12 end face can be suppressed, and each reflective film 93,94 can be stably adhered without peeling at the uppermost corner portion of the end face. It is possible to improve the reflectance of the 94 and the finesse of the resonator to enhance the function of the device itself.

FIG. 5 shows the internal loss of the optical resonator 5 in the propagation direction of either the outward path direction or the return path direction in the optical waveguide 12. In FIG. 5, the loss per propagation direction of the optical modulator 8 composed of the above-mentioned long resonator is measured and plotted over three samples (indicated by ● in the figure), and the short resonator is used. The loss per propagation direction for the configured light modulator 8 is measured and plotted over three samples (indicated by ■ in the figure), and each obtained plot is approximated by a straight line.

From this obtained straight line, the internal loss Ls per propagation direction in the optical waveguide 12 of the optical cavity 5 having a length l is the reflectance R in the reflective films 93 and 94, and the loss per unit length in the optical waveguide 12. When α is, it is expressed by Ls = α _l −lnR when the loss itself is small. When the measured finesse is F, the loss Ls per propagation direction is calculated as Ls = π / F. When the internal loss Ls is obtained from the measured finesse F and graphed, it can be seen that the internal loss due to the optical waveguide 12 increases as the crystal length of the optical waveguide 12 increases as shown in FIG.

Incidentally, in FIG. 5, the internal loss when the length of the optical resonator 5 is 0 is based on the loss generated at the crystal end face. That is, since the reflective films 93,94 having a reflectance of 97% (transmittance of 3%) are coated, a loss of at least 3% will occur. However, from FIG. 5, it can be seen that there is no noticeable loss other than the transmission to the reflective films 93 and 94 on the planes 91 and 92.

Matching the waveguide loss rate of the optical waveguide with the transmittance of the mirror leads to an increase in the finesse and transmittance of the resonator and an improvement in the performance of the resonator. Since the loss rate of the optical waveguide that can be used as an optical comb generator is generally in the range of 1% to 5% per one way, a reflective film 93,94 having a reflectance in the range of 95% to 99% is adhered. Then, a high-performance optical resonator can be manufactured.

Similarly, when this light modulator 8 is applied to an optical frequency comb generator, the temperature conditions are lower than the heat resistant temperature of the polishing of the flat surfaces 91 and 92 and the adhesive with the protective members 86 and 87 attached. Since the incident side reflective film 93 and the outgoing side reflective film 94 are adhered as the gas phase growth film, the reflectance of these reflective films 93 and 94 can be improved. As a result, the finesse of the optical resonator 5 can be improved, and the generation frequency band of the side band can be expanded.

By the way, when this light modulator 8 is applied to an optical frequency comb generator, the incident side reflecting film 93 transmits only the light incident on the optical waveguide 12, and the side band generated in the optical waveguide 12 is generated. It may be replaced with a reflecting narrow band filter. By substituting with such a narrow band filter, it is possible to improve the conversion efficiency from the incident light to the sideband.

Similarly, the emission side reflective film 94 may be replaced with a filter for flattening the output spectrum. In a normal optical frequency comb generator, the resulting sideband light intensity decreases exponentially with increasing order. Therefore, by substituting the light emitting side reflective film 94 with a filter having a characteristic of canceling the decrease in light intensity according to the order, it is possible to flatten the light intensity of each obtained side band.

The incident side reflective film 93 and the outgoing side reflective film 94 may be replaced with the above-mentioned filters, or any one of the reflective films 93 and 94 may be replaced with the above-mentioned filters.

The light modulator 8 to which the present invention is applied and the optical frequency comb generator to which the present invention is applied are monolithic type in which the incident side reflective film 93 and the outgoing side reflective film 94 are directly formed on the planes 91 and 92. It is configured. In other words, since the optical modulator 8 is not configured to provide the reflective films 93 and 94 at positions spatially separated from the planes 91 and 92, the FSR (Free Spectral Range) of the optical resonator 5 is a step. It is dominated by the crystal length from the plane 91 to the plane 92 of the crystal constituting the optical waveguide 12 after polishing in S16. Therefore, the optical modulator 8 is required to control the crystal length extremely precisely so that an integral multiple of the FSR of the optical resonator 5 becomes a desired modulation frequency.

For example, when the FSR of the optical cavity 5 is matched with the frequency f _FSR , the group refractive index _ng of the optical waveguide 12 and the average value τ _g of the group delay times of the incident side reflective film 93 and the outgoing side reflective film 94 are taken into consideration. Then, the crystal length (distance from the first end face 84 to the second end face 85 on the substrate 11) L of the optical waveguide 12 is set to the following equation (1).
L = c / 2n _g f _FSR -cτ _g / _ng ... (1)
(C is the speed of light in vacuum)
By adjusting to, the FSR of the optical resonator 5 can be matched with the f _FSR , and the modulation efficiency can be significantly improved.

The present invention is not limited to the above-described embodiment. For example, it can be applied to the light modulator 9 as shown in FIG. Regarding the same configuration and elements as the above-mentioned optical modulator 8 in this optical modulator 9, the explanations in FIGS. 1 and 2 will be quoted, and the description thereof will be omitted here.

The optical modulator 9 includes a substrate 11, an optical waveguide 12 formed on the substrate 11 that modulates the phase of propagating light, a wafer 95 provided on the upper surface of the optical waveguide 12, and the direction of the modulation electric field is light. An electrode 83 provided on the upper surface of the wafer 95 so as to be substantially perpendicular to the propagation direction of the wafer, a first end surface 84 provided so as to face each other via an optical waveguide 12, and a second end surface 85. , A single-layer or multi-layer gas phase growth film adhered on a plane 101 formed between the first end face 84 and the end face 96a of the wafer 95 under a temperature condition lower than the heat resistant temperature of the adhesive. A single layer or a multilayer coated on a plane 102 formed between the incident side reflective film 93 and the second end surface 85 and the end surface 97a of the wafer 95 under temperature conditions lower than the heat resistant temperature of the adhesive. It is provided with an emission side reflective film 94 made of a gas phase growth film.

Also in this light modulator 9, similarly to the above-mentioned optical modulator 8, an oscillator (not shown) that oscillates a modulation signal having a frequency _fm and a terminating resistor (not shown) are connected.

The wafer 95 is made of SiO ₂ or the like, and is configured to have a length substantially the same as that of the optical waveguide 12 and to have a U-shape. The wafer 95 is configured to be thick only at the end portion and thin only at the central portion where the electrode 83 is arranged. As a result, a modulated electric field can be efficiently applied from the electrode 83 to the light propagating in the optical waveguide 12.

The wafer 95 plays a role as the buffer layer 14 described above, and suppresses light loss by covering the optical waveguide 12 formed directly under the surface of the substrate 11. The wafer 95 also serves as a first protective member 86 and a second protective member 87 in the above-mentioned light modulator 8, and the end faces 96a and 97a are the first end face 84 and the second end face 85, respectively. It is trimmed so that planes 101 and 102 can be formed between them, respectively.

When arranging the wafer 95, a wafer of SiO ₂ corresponding to the thickness of the end portion is attached on the substrate 11, and then the portion where the electrode 83 is provided is cut, as shown in FIG. It is possible to finish it in a U-shape.

That is, the light modulator 9 has an advantage that the same effect as that of the light modulator 8 can be obtained and the trouble of attaching the protective member can be saved.

The present invention is not limited to the above-described embodiment. For example, it can be applied to the reciprocating modulation type optical modulator 51 as shown in FIG. Regarding the optical modulator 51 having the same configuration and elements as the optical modulator 8 described above, the explanations in FIGS. 1 and 2 will be quoted, and the description thereof will be omitted here.

Further, the light modulator 51 is provided with an exit-side reflective film 94 made of a single-layer or multi-layer gas phase growth film as a high-reflection film at one end of the optical waveguide 12, and is provided with a single layer or a single layer at the other end. By providing the antireflection film 63 made of a multi-layered gas phase growth film, it can be operated as a so-called reciprocating modulation type optical modulator 51 as shown in FIG. 7.

As shown in FIG. 7A, the light modulator 51 covers the substrate 11, the optical waveguide 12 formed on the substrate 11 and modulating the phase of the propagating light, and the optical waveguide 12 on the substrate 11. The buffer layer 14 is laminated so as to be laminated, an 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 an arrangement on the upper portion of the optical waveguide 12. Antireflection composed of a first protective member 86 and a second protective member 87, and a single-layer or multi-layer gas phase growth film adhered on a flat surface 91 under a temperature condition lower than the heat-resistant temperature of the adhesive. A film 63 and an exit-side reflective film 94 made of a single-layer or multi-layer gas phase growth film adhered on a flat surface 92 under a temperature condition lower than the heat-resistant temperature of the adhesive are provided.

Further, when the optical modulator 51 is actually used, 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 externally transmitted. An optical system including an optical transmission path 23 composed of an optical fiber or the like for transmission to, an optical circulator 21 for separating the input light and the output light, and a focuser 22 optically connected to the optical circulator 21. An oscillator 16 which is mounted and arranged on one end side of the electrode 83 to oscillate a modulated signal having a frequency _fm , and a phase shifter 19a and a reflector 19b are further arranged on the other end side of the electrode 83.

The antireflection film 63 is adhered on a flat surface 91 formed between the first end surface 84 and the end surface 86a of the first protective member 86 under temperature conditions lower than the heat resistant temperature of the adhesive. The antireflection film 63 may be made of a low-reflection film, or may be made of an uncoated film so as to obtain the same effect as that of a low-reflection film.

The focuser 22 focuses the input light that has passed through the optical circulator 21 to the end of the optical waveguide 12, and also collects the output light that has passed through the antireflection film 63 from the end of the optical waveguide 12 and collects the output light, which is collected by the optical circulator 21. Send to. The focuser 22 may be configured by a lens or the like for optical coupling of input light so as to have a spot diameter corresponding to the diameter of the optical waveguide 12.

The light modulator 51 having such a configuration is provided with an emission-side reflective film 94 as a high-reflection film at one end of the optical waveguide 12, and a so-called reciprocating film by providing an antireflection film 63 at the other end. It operates as a modulation type optical modulator. The input light incident on the optical waveguide 12 is modulated while propagating through the optical waveguide 12, reflected by the exit-side reflective film 94 on the end face, then propagates again through the optical waveguide 12 and passes through the antireflection film 63. It is emitted to the focuser 22 side and becomes output light. At the same time, the electric signal having a frequency of _fm supplied from the oscillator 16 propagates on the electrode 83 while modulating the input light, and then is reflected by the reflector 19b.

In the optical modulator 51, when a modulation signal having a frequency _fm oscillated by the oscillator 16 is supplied to the electrode 83, the modulation signal propagates through the electrode 83 in the outward path direction, and the modulation signal propagates in the optical waveguide 12. The phase can be modulated by the light propagating in the outward direction. The modulated signal propagating on the electrode 83 in the outward path direction is reflected by the antireflector 19b as it is, is phase-adjusted by the phase shifter 19a, and then propagates on the electrode 83 in the return path direction. As a result, the light propagating in the optical waveguide 12 in the return direction can be phase-modulated. Incidentally, the phase adjusted by the phase shifter 19a is such that the phase modulation applied to the light propagating in the optical waveguide 12 in the return direction is the same as the phase modulation for the light propagating in the outward direction. May be good.

In this light modulator 51, not only the light propagating in the optical waveguide 12 in the outward path direction but also the light propagating in the return path direction can be phase-modulated, so that the modulation efficiency can be increased.

Further, in this light modulator 51, by using an electric signal synchronized with the time when light reciprocates in the optical waveguide 12 as a drive input from the electrode 83, several tens of times as compared with the case where the light passes through the optical waveguide 12 only once. It is possible to apply more than double the deep phase modulation. This makes it possible to generate an optical frequency comb having sidebands over a wide band, and the frequency intervals of adjacent sidebands are all equal to the frequency _fm of the input electrical signal.

Further, since the light modulator 51 can push light into a narrow optical waveguide 12 to modulate it, the modulation index can be increased, and it functions as an optical frequency comb generator 1 to be a bulk type light. The number of sidebands generated and the amount of light in the sidebands can be increased as compared with the frequency comb generator.

In the optical frequency comb generator 1 using the optical modulator 51, the phase of the modulated signal reflected by the reflector 19b and adjusted by the phase shifter 19a is set to the shape of the electrode 83 and the frequency _fm of the modulated signal. By adjusting according to the group refractive index _ng of the optical waveguide 12, the light propagates in the optical waveguide 12 not only in the outward direction but also in the return direction by adjusting to the phase of the light with high accuracy. Phase modulation can be applied to light with high efficiency, and the modulation efficiency can be increased up to nearly twice. Further, since the modulation efficiency can be effectively improved without increasing the voltage applied to the electrode 83, the power consumption can be reduced and the heterodyne detection system itself in which the optical frequency comb generator 1 is arranged is slimmed down. It can be done and the cost can be significantly reduced.

Further, in this light modulator 51, as shown in FIG. 7 (c), an oscillator 25 and a terminating resistor 27 are provided on one end side of the electrode 83, and an electric signal supplied from the oscillator 25 is propagated on the electrode 83. Above, 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 by the other end side of the electrode 83 may be provided. Further, in the light modulator 51, the incident side reflective film 93 made of a single-layer or multi-layered gas phase growth film having high reflectance is adhered under a temperature condition lower than the heat resistant temperature of the adhesive. As a result, light can be resonated inside the optical waveguide 12. Further, as an alternative to the incident side reflective film 93, the above-mentioned low reflectance antireflection film 63 may be adhered under a temperature condition lower than the heat resistant temperature of the adhesive. This makes it possible to perform phase modulation while reciprocating light only once in the optical waveguide 12.

In this light modulator 51, the phase of light can be modulated by each of the electric signals reciprocating in the electrode 83 by adjusting the reflection phase of the electric signal according to the phase of the light reflected by the light emitting side reflecting film 94. Therefore, the modulation efficiency can be increased. In particular, in the optical modulator 51 in which the films 63, 93, 94 are suppressed from peeling or chipping and the finesse is further improved by attaching the protective members 86, 87, the optical modulation efficiency is further increased. Is possible.

Further, when these light modulators 51 are applied to an optical frequency comb generator, it is possible to perform reciprocating modulation on the light resonating in the optical waveguide 12 by the electric signal reciprocating between the electrodes. In such a case, the intensity distribution at each frequency (wavelength) of the generated sideband is when the modulation frequency of the electric signal applied to the electrode 83 is 25 GHz and the power is 0.5 W, as shown in FIG. 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-wavelength voltage Vπ defined as the voltage required to move the phase by half a wavelength is 7.1V.

The light modulator 8 composed of the short resonator has a higher finesse as described above, and the efficiency of sideband generation is higher than that of the optical modulator 8 composed of the long resonator. The generated frequency bandwidth Δf reaches 11 THz. Further, although the length of the electrode 83 of the optical modulator 8 composed of the short resonator is only 20 mm, the modulation efficiency comparable to that of the optical modulator 8 composed of the long resonator can be obtained. .. That is, it can be seen that the reciprocating modulation works effectively.

Instead of reflecting the electric signal, the light modulator 51 may divide the output of the oscillator 16 as a signal source so that the electric signal is separately driven and input from both ends of the electrode 83. , This may be done by connecting different oscillators 16 to both ends of the electrode 83.

The present invention can also be applied to, for example, an optical waveguide type laser oscillator 52 as shown in FIG. Regarding the same components as the above-mentioned optical modulator 8 in the laser oscillator 52, the description in FIGS. 1 and 2 will be quoted, and the description thereof will be omitted here.

As shown in FIG. 9, the laser oscillator 52 includes a substrate 11, an optical waveguide 12 formed on the substrate 11, a buffer layer 14 laminated so as to cover the optical waveguide 12 on the substrate 11, and an optical beam. The first protective member 86 and the second protective member 87 arranged on the upper part of the waveguide 12 and the single-layer or multi-layered air adhered on the flat surface 91 under a temperature condition lower than the heat-resistant temperature of the adhesive. An incident-side reflective film 93 made of a phase-growth film and an outgoing-side reflective film 94 made of a single-layer or multi-layered gas-phase growth film adhered on a flat surface 92 under a temperature condition lower than the heat-resistant temperature of the adhesive. An optical resonator 5 is formed between the incident side reflecting film 93 and the emitting side reflecting film 94. Further, when the laser oscillator 52 is actually used, an excitation light source 28 that emits light having a wavelength λ ₀ is mounted.

In the optical waveguide 12 of the laser oscillator 52, an amplification medium such as an erbium ion that absorbs light incident through the incident side reflection film 93 and has amplification characteristics with respect to the wavelength of light peculiar to the medium. To spread. This makes it possible to make the optical waveguide 12 work as a light amplification medium. Further, when light having an appropriate wavelength is incident on the optical waveguide 12 as such an amplification medium, it acts as an amplifier of light for a specific wavelength determined by an energy level. It also acts as an oscillator that amplifies and oscillates the light generated by the spontaneous emission transition. Laser oscillation occurs when the amplification factor in the optical resonator 5 exceeds the loss factor. Therefore, protective members 86,87 are attached to prevent peeling or chipping of the reflective films 93,94 and the optical waveguide. By enhancing the reflection characteristic at the end face of 12, the loss rate in the optical resonator 5 is also lowered, so that the threshold value of laser oscillation can be lowered.

Non-linearity induced by light incident in the optical waveguide 12 by forming the optical waveguide ₁₂ with a nonlinear optical crystal such as a LiNbO3 crystal without introducing a special amplification medium into the optical waveguide 12. Polarization makes it possible to have an amplification gain at a wavelength different from the incident light. For example, the optical waveguide 12 may be configured by using a nonlinear optical crystal having a periodic polarization inversion structure.

The incident side reflecting film 93 constituting the optical resonator 5 in the laser oscillator 52 has a low reflectance with respect to the light from the excitation light source 28 and has a high reflection with respect to the wavelength of the light oscillated by the optical waveguide 12. A rate film may be used. Further, as the emission side reflecting film 94 constituting the optical resonator 5, a film having a reflectance capable of optimal output coupling with respect to the wavelength of the light oscillated by the optical waveguide 12 may be used.

Incidentally, this laser oscillator 52 may be applied as an optical parametric oscillator. In such a case, oscillation occurs when the amplification factor in the optical resonator 5 exceeds the loss rate, so that the reflective film 93,94 to which the protective members 86, 87 are attached is not peeled off or chipped. By configuring the finesse optical resonator 5, the oscillation threshold can be lowered.

As described above, the advantages of using the optical waveguide 12 in the laser oscillator 52 and the optical parametric oscillator to which the optical parametric oscillator is applied are that the light can be confined in a narrow region and the electric field strength can be increased to improve the amplification factor. In particular, since the laser oscillator 52 and the like can obtain high finesse as compared with the conventional oscillator, the advantage of using the optical waveguide 12 is further promoted.

The present invention can also be applied to, for example, a laser oscillator 53 that oscillates light whose modes are synchronized as shown in FIG. Light synchronized with this mode is one in which the phases of many modes oscillating at equal frequency intervals are aligned. Regarding the laser oscillator 53, the same configurations and elements as those of the light modulator 8 and the laser oscillator 52 described above are referred to in FIGS. 1, 2 and 9, and the description thereof will be omitted here.

As shown in FIGS. 10A and 10B, the laser oscillator 53 includes a substrate 11, an optical waveguide 12 formed on the substrate 11 and modulating the phase of propagating light, and an optical waveguide on the substrate 11. A buffer layer 14 laminated so as to cover the light 12, an 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 an upper portion of the optical waveguide 12. From the single-layer or multi-layer vapor-phase growth film adhered to the first protective member 86 and the second protective member 87 arranged on the flat surface 91 under a temperature condition lower than the heat-resistant temperature of the adhesive. The incident side reflecting film 93 and the emitting side reflecting film 94 made of a single-layer or multi-layered gas phase growth film adhered on a flat surface 92 under a temperature condition lower than the heat resistant temperature of the adhesive are provided. An optical resonator 5 is formed between the reflecting film 93 and the emitting side reflecting film 94. Further, when the laser oscillator 53 is actually used, an excitation light source 28 that emits light having a wavelength λ ₀ is mounted, and an oscillator that is further arranged on one end side of the electrode 83 and oscillates a modulated signal having a frequency _fm . 16 and a terminal resistor 18 disposed on the other end side of the electrode 83 are arranged. The incident side reflecting film 93 and the emitting side reflecting film 94 each have a function of achieving phase synchronization between multiple modes of laser oscillation.

In the laser oscillator 53 having such a configuration, by disposing the electrode 83 on the upper part of the optical waveguide 12 in the above-mentioned laser oscillator 52, it is possible to oscillate a mode-synchronized laser in which synchronization is performed for each mode. Here, the phase of each mode is based on the electro-optical effect of the optical waveguide 12 that oscillates multi-mode light by driving and inputting a modulation signal having a frequency corresponding to an integral multiple of the FSR of the optical resonator 5 from the oscillator 16. As a result of synchronization, it operates as a laser oscillator that oscillates a mode-synchronized laser.

When this mode synchronization is performed, the time waveform of the light oscillated from the laser oscillator 53 becomes a short pulse having a time width of about the reciprocal of the amplified frequency bandwidth. Further, the waveform of the frequency axis is an optical frequency comb in which side bands are arranged at regular frequency intervals. Therefore, by optimizing the control for the laser oscillator 53, it can be applied to the frequency measurement of light and the multi-wavelength light source. Of course, the laser oscillator 53 may be applied as an optical parametric oscillator in the same manner as the laser oscillator 52 described above. In particular, since the protective members 86 and 87 are attached to the laser oscillator 53, the reflective films 93 and 94 are not peeled off or chipped, the finesse of the entire optical resonator 5 can be improved, and the mode-synchronized laser is made efficient. It is possible to oscillate well.

By the way, the mode synchronization in the laser oscillator 53 is not limited to the one utilizing the above-mentioned electro-optical effect, but is based on any phenomenon as long as it utilizes the nonlinear effect of the optical element in the optical resonator 5. It may be. For example, by using the LiNbO ₃ crystal for the optical waveguide 12, it is possible to further emphasize the effect.

The present invention can also be applied to, for example, the modified Fabry-Perot (FP) electro-optical modulator 54 as shown in FIG. In this modified FP electro-optical modulator 54, the same configurations and elements as those of the light modulator 8 and the laser oscillator 52 described above are referred to in FIGS. 1, 2 and 9, and the description thereof will be omitted here.

As shown in FIG. 11, the modified FP electro-optical modulator 54 covers the substrate 11, the optical waveguide 12 formed on the substrate 11 and modulating the phase of propagating light, and the optical waveguide 12 on the substrate 11. The buffer layer 14 is laminated so as to be laminated, an electrode 83 provided on the upper surface of the optical waveguide 12 so that the direction of the modulated electric field is substantially perpendicular to the light propagation direction, and an arrangement on the upper part of the optical waveguide 12. The incident side composed of the first protective member 86 and the second protective member 87, and a single-layer or multi-layer gas phase growth film adhered on the flat surface 91 under a temperature condition lower than the heat-resistant temperature of the adhesive. An incident side reflective film 93 is provided with a reflective film 93 and an outgoing side reflective film 94 made of a single-layer or multi-layer gas phase growth film adhered on a flat surface 92 under a temperature condition lower than the heat resistant temperature of the adhesive. The optical resonator 5 is formed between the light resonator and the light emitting side reflecting film 94. Further, when the modified FP electro-optical modulator 54 is actually used, a reflecting mirror 31 is mounted, and if necessary, it is further arranged on one end side of the electrode to oscillate a modulated signal having a frequency _fm . An oscillator (not shown) and a terminating resistor (not shown) arranged on the other end side of the electrode are arranged.

The reflector 31 transmits light supplied from the outside and guides it to the end of the optical waveguide 12 on the modified FP electro-optical modulator 54 side, and reflects the light emitted from the end of the optical waveguide 12. That is, by providing the reflector 31, only the light incident on the optical waveguide 12 can be transmitted and the sideband generated in the optical waveguide 12 can be reflected, so that the incident light is converted into a sideband. Efficiency can be improved. That is, in the modified FP electro-optical modulator 54 having such a configuration, when the incident side reflecting film 93 is replaced with a narrow band filter that transmits only the light incident on the optical waveguide 12 and reflects the generated side band. The same effect as can be obtained. In particular, in this modified FP electro-optical modulator 54, since the protective members 86 and 87 are attached, the reflective films 93 and 94 are not peeled off or chipped, and the finesse of the entire optical resonator 5 can be improved. It is possible to further improve the conversion efficiency to the side band.

The light modulator 8 to which the present invention is applied can also be further applied to the communication system 55 described below.

As the communication system 55, for example, a system that performs code division multiplex connection based on the WDM communication method is applied, and as shown in FIG. 12A, the communication device 55 and the portable communication device 57 as a mobile terminal that can be carried by a pedestrian. A network including a plurality of base stations 58 for relaying communication by transmitting and receiving wireless signals to and from the mobile communication device 57, and the base stations 58 via connected optical fiber communication networks 35 and 38. It is provided with a host control device 59 that controls communication as a whole.

The portable communication device 57 is configured to be in-vehicle or portable so as to transmit and receive a wireless signal to and from a base station 58 provided in each district. That is, the mobile communication device 57 includes, for example, a device mounted on a facsimile communication, a personal computer, or the like for performing data communication, but generally, a mobile phone or a PHS (personal handy phone system) for performing a voice call is used. ) Etc., and is configured as a device that is particularly compact and lightweight and specialized in portability.

Each base station 58 is equipped with an optical modulator 8 as shown in FIG. 12 (a). An antenna 33 for transmitting and receiving microwaves to and from the portable communication device 57 is connected to the electrode 83 of the light modulator 8. Further, in the light modulator 8, a part of the light transmitted from the host control device 59 via the optical fiber communication network 35 is incident on the optical waveguide 12 via the incident side reflection film 93. The light incident on the optical waveguide 12 is resonated by the incident side reflecting film 93 and the emitting side reflecting film 94 arranged substantially in parallel. Further, in this optical modulator 8, the microwave supplied from the portable communication device 57 is received via the antenna 33, and the modulation signal corresponding to the microwave is converted into light propagating in the optical waveguide 12 via the electrode 83. Since it can be applied, it is possible to perform phase modulation according to the transmission information from the portable communication device 57. The light modulator 8 emits phase-modulated light via the light emitting side reflective film 94. The emitted light will be transmitted to the host control device 59 via the optical fiber communication network 38.

The host control device 59 generates light for transmission to the base station 58, and photoelectrically converts the light modulated in the base station 58 to obtain a detection output. That is, the host control device 59 can collectively manage the detection outputs from various base stations.

In such a communication system 55, the light output from the host control device 59 is transmitted to the base station 58 via the optical fiber communication network 35. The base station 58 propagates the transmitted light in the optical waveguide 12 in the optical modulator 8, further performs phase modulation according to the microwave, and then hosts the transmitted light via the optical fiber communication network 38. It is transmitted to the control device 59.

That is, when the light transmitted to the base station 58 is called from the portable communication device 57 around the base station 58, the light is phase-modulated according to the content of the call included in the microwave described above. become. On the other hand, when the light transmitted to the base station 58 is not called from the portable communication device 57 around the base station 58, the above-mentioned phase modulation is not performed. In the host control device 59, when the light transmitted from the base station 58 via the optical fiber communication network 38 is phase-modulated, it is photoelectrically converted to generate a detection output according to the content of the call. It becomes possible to acquire.

In this communication system 55, since the optical modulator 8 having a high finesse resonator to which the protective members 86 and 87 are attached is mounted on the base station 58, the number of round trips of light propagating in the optical waveguide 12 can be increased. This makes it possible to improve the sensitivity of the optical modulator 8 itself.

Of course, in this communication system 55, as shown in FIG. 12B, optical transmission may be performed in a single core bidirectional manner.

Further, in the light modulator 8 to which the present invention is applied, even if the crystal length LC ₁ in the outward direction (return direction) of the optical waveguide 12 is adjusted to be about 27 mm (or 54 mm) as shown in FIG. good. The effect of having such a crystal length will be described below.

FIG. 13A shows the relationship between the loss rate Lo ₁ and the crystal length LC ₁ of the optical waveguide 12, when the loss rate of light propagating in the outward direction (return direction) in the optical waveguide 12 is Lo ₁ . It has been shown that as the crystal length LC ₁ increases, the loss of propagating light gradually increases. Further, FIG. 13 (b) shows the relationship of finesse with respect to the crystal length LC ₁ . As shown in FIG. 13 (b), the finesse is generally represented by π / Lo ₁ , but it can be seen that the smaller the crystal length LC ₁ , the higher the finesse.

The figure of merit of the light modulator 8 can be expressed as Vπ / (finesse) (Vπ is the voltage required to π-radian the optical phase). The smaller the figure of merit, the better the performance as the optical modulator 8 and as the optical frequency comb generator using the optical modulator 8.

FIG. 14 shows the figure of merit calculated based on these finesse and loss rate Lo ₁ in relation to the crystal length LC ₁ . In FIG. 14, lm represents the difference in length of the electrode 83 with respect to the crystal length LC ₁ . In general, electrodes cannot be provided several mm from both ends of the optical waveguide 12, so the calculation is performed by taking the case where the lm is 6 mm and the case where the lm is 1 mm as an example.

As shown in FIG. 14, when lm = 6 mm, it can be seen that the figure of merit becomes smaller when the crystal length LC ₁ is 15 to 30 mm. Moreover, when the FSR corresponding to the crystal length LC ₁ of the figure of merit is plotted, it can be seen that the best performance is obtained in the vicinity of 2.5 GHz. Incidentally, in simulating the tendency in FIG. 14, it is assumed that the modulation frequency is 25 GHz, the transmission loss of the microwave by the electrode 83 is -10 dB / 50 mm @ 25 GHz, and the modulation efficiency is Pin = 0 at the time of reciprocating modulation. Considering that the modulation index is π radian when .43 W and crystal length LC ₁ = 27 mm (when the length of the electrode 83 is 21 mm), the light transmission loss α is -0.0106 / cm. It is assumed that there is a case. Further, the reflectance of the mirror is optimized for the loss rate according to the crystal length.

Therefore, when the lm = 6 mm, the crystal length LC ₁ of the optical waveguide 12 is set to about 27 mm, so that the performance as the optical modulator 8 can be further improved. Incidentally, the crystal length LC ₁ is not limited to the case where it is 27 mm, and may be configured with any length as long as it is in the range of 24 ± 6 mm. The practical crystal length LC ₁ is the greatest common divisor of 10 GHz in time division multiplexing (TDM) optical communication in the optical communication field and 25 GHz in WDM: Wavelenth Division Multiplex (WDM) optical communication. It is preferable to set it to 1 / integer of 5 GHz, and 27 mm corresponds to 2.5 GHz.

Further, even when the plot of the FSR corresponding to the crystal length LC ₁ is 1.25 GHz, the crystal length LC ₁ corresponding to this may be configured to be about 54 mm because the excellent performance is similarly shown. ..

Further, even when lm = 1 mm, excellent performance is shown at about 10 GHz by the same simulation. Therefore, by making the crystal length LC ₁ correspond to this, the performance as the optical modulator 8 can be further improved. Is possible.

In the method for manufacturing the optical modulator 8 to which the present invention is applied as shown in FIG. 4, in the step of manufacturing the optical waveguide 12 in steps S11 and S12, Ti atoms are thermally diffused in the substrate 11 to obtain the optical waveguide 12. Although formed, this may be replaced by a proton exchange method in which Li is replaced with H ⁺ by immersing _LiNbO3 crystals in benzoic acid.

Here, 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, the orthogonal polarization components make the resonance frequency of the optical comb generator match the laser frequency. This may make the control unstable, which may cause the control point to shift, control oscillation, etc., and when the optical comb is used as a measuring device that measures the distance or height to the measurement target, for example, it is orthogonal. Although the polarization component is a factor of measurement error, it has an optical waveguide 12A formed as a region in which a waveguide mode exists only for a single polarization component having a configuration as shown in FIG. 1, for example. By adopting a waveguide type optical modulator 8A, the output of the orthogonally polarized light component that does not contribute to the generation of optical combs is suppressed to improve the polarization extinction ratio, and the optical comb output with an increased single polarization degree can be obtained. By setting the setting to, the transmission mode waveform of the optical waveguide is not deformed, the resonator control can be stabilized, the stabilization as an optical comb generator, the accuracy improvement of the measuring device including the optical comb, and the error. Can be reduced.

The waveguide type optical modulator 8A shown in FIG. 15 has a configuration other than the optical waveguide 12A formed as a region in which a waveguide mode exists only for a single polarization component. Since it is the same as the type optical modulator 8, the same components are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 16 is a side view of the waveguide type optical modulator 8A.

In this waveguide type optical modulator 8A, the optical waveguide 12A has a single polarization component on 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 a region where the waveguide mode exists only with respect to it.

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

Here, the optical waveguide 12A that allows only a single polarizing component to pass through is single on the substrate 11 having an electro-optical effect by an optical waveguide forming method that causes a change in the refractive index only for a specific polarizing component, for example, a proton exchange method. It can be formed as a region having a high refractive index only with respect to the polarization component of.

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

Further, when the optical waveguide 12A 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 single polarization by devising the refractive index distribution. It can be formed as a limited area. For this optical waveguide 12A, for example, a LiNbO ₃ crystal optical waveguide can be used, and it can be formed by diffusing Ti on the surface of a substrate 11 made of LiNbO ₃ or the like. This Ti-diffused region has a higher refractive index than the other regions and can confine the light of a single polarization component, so that the light of a single polarization component can be propagated. Waveguide 12A can be formed. The refractive index is high for both orthogonal polarization components, but there is also a condition that the waveguide mode is established only for a single polarization component.

The LiNbO ₃ crystal type optical waveguide 12A produced based on such a method has electricity 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, it is possible to modulate the light of a single polarization component by utilizing such a physical phenomenon.

The buffer layer 14 covers the optical waveguide 12A in order to suppress the light propagation loss of a single polarization component. By the way, if the film thickness of 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 the range where the light propagation loss of a single polarization component does not increase. You may try to do it.

The electrode 83 is made of a metal material such as Ti, Pt, or Au, and is phased with light propagating in the optical waveguide 12A by driving and inputting a modulation signal having a frequency _fm supplied from the oscillator 16 to the optical waveguide 12A. Modulate.

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

The antireflection film 63 on the incident side is a single-layer or multi-layer vapor phase growth on a plane 91 perpendicular to the optical waveguide 12A formed between the first end surface 84 and the end surface 86a of the first protective member 86. It is adherently formed as a film. The emission side antireflection film 64 is lower than the heat resistant temperature of the adhesive on the plane 92 perpendicular to the optical waveguide 12A formed between the second end surface 85 and the end surface 87a of the second protective member 87. It is adherently formed as a single-layer or multi-layer vapor phase growth film under temperature conditions. These antireflection films 63 and 64 may be made of a low-reflection film, or may be made of an uncoated film so as to obtain the same effect as that of a low-reflection film. ..

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

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

First, in step S21, a photoresist pattern 13 is produced on the surface of a substrate ₁₁ made of LiNbO3 crystals.

Next, the process proceeds to step S22, and the substrate 11 of the LiNbO ₃ crystal having the photoresist pattern 13 formed on the surface is heated in a state of being immersed in a proton exchange solution such as benzoic acid to heat Li on the surface layer portion of the substrate 11. The optical waveguide 12A is formed as a region in which the waveguide mode exists only for a single polarization component by the proton exchange method of substituting with H ⁺ .

The process of manufacturing the optical waveguide 12A 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 LiNbO3 crystals. Ti is vapor-deposited on the surface of the substrate 11 made of LiNbO ₃ crystals, and the photoresist is removed to prepare a thin wire of Ti having a width of a micron size. In the next step S22, this is prepared. By heating the substrate 11 on which the thin wire of Ti is formed, the Ti atom is thermally diffused in the substrate 11, and the optical waveguide 12A is used as a region in which 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 is removed, and a SiO ₂ thin film as the buffer layer 14 is vapor-deposited on the surface of the substrate 11. In this step S23, the buffer layer 14 may be formed by a method of attaching the SiO ₂ wafer to the surface of the substrate 11. In such a case, the film thickness may be controlled to an appropriate level by polishing the vapor-deposited buffer layer 24 in consideration of the electrode mounting area in the next step S24.

Next, the process proceeds to step S24, and the electrode 83 is formed on the buffer layer 14.

Next, the process proceeds to step S25, and the protective members 86 and 87 are adhered to the upper part of the optical waveguide 12A. As for the method of adhering the protective members 86 and 87, they may be attached with an adhesive or may be directly bonded based on another method. When the substrate 11 is made of LiNbO ₃ crystals, the protective members 86, 87 may be made of LiNbO ₃ as the same material. In this step S25, the end faces 86a and 87a of the attached protective members 86 and 87 can form planes 91 and 92 between the first end face 84 and the second end face 85, respectively. And trim it.

Finally, the process proceeds to step S26, and the obtained planes 91 and 92 are polished to a plane perpendicular to the optical waveguide 12A. Then, the antireflection film 63 on the incident side and the antireflection film 64 on the exit side are spread over one surface on the flat surfaces 91 and 92 perpendicular to the polished optical waveguide 12A under temperature conditions lower than the heat resistant temperature of the adhesive. It is formed as a gas phase growth film.

As described above, in the optical modulator 8A to which the present invention is applied, since the protective members 86 and 87 are attached to each end portion, the end surface of the optical waveguide 12A which has been conventionally located at the uppermost corner of the end surface is formed. Moves to a substantially central portion of the plane 91 (92). As a result, even when the corner of the plane 91 (92) is chipped during polishing in step S26, the end face of the optical waveguide 12A is not chipped. That is, it is possible to configure the optical waveguide 12A so that the end face itself is less likely to be chipped. This makes it possible to suppress the light loss from each end face of the optical waveguide 12A as much as possible.

Further, by configuring the material of the protective members 86 and 87 with the optimum material corresponding to the material of the substrate 11, the polishing speed in step S26 is set to the first end surface 84 and the second end surface 85 to the end surface 86a of the substrate 11. It can be made uniform over 87a. As a result, the end face of the optical waveguide 12A is not rounded during processing, flat surfaces 91 and 92 made of a flat polished surface can be obtained, and the reflection loss at the end face of the optical waveguide 12A can be minimized. Become. Further, by making the crystal orientations of the end faces constituting the planes 91 and 92 the same, it is possible to further suppress the reflection loss.

Further, by intentionally providing the protective members 86 and 87, the polishing accuracy in step S26 is improved, and the verticality of the obtained flat surface 91 (92) with respect to the optical waveguide 12A 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 exit side antireflection film 64 have a temperature lower than the heat resistant temperature of the adhesive over a wide range from the first end face 84 and the second end face 85 to the end faces 86a and 87a in the substrate 11. Since it is formed as a vapor phase growth film under conditions, it is extremely stable, does not easily peel off, and can improve the reproducibility of film formation.

When the flat surface 91 (92) was actually polished after the protective members 86, 87 were attached in order to experimentally verify the effect of providing the protective members 86, 87, the end face of the optical waveguide 12A was actually polished. No chipping or bending occurs in the portion, and flat optical polishing suitable for adhesion of the incident side antireflection film 63 and the emission antireflection film 64 made of a single-layer or multi-layer gas phase growth film is performed. I was able to confirm that.

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 and the first end face 84 of the protective members 86, 87 forming the planes 91, 92 are formed. By processing the second end face 85 so as to have the same crystal orientation as each other, the hardness of the crystals becomes the same between the two, so that the planes 91 and 92 do not tilt due to the difference in polishing speed.

In the light modulator 8A having such a configuration, only a single polarization component incident through the incident side antireflection film 63 and propagated through the optical waveguide 12A is modulated at a frequency _fm supplied from the oscillator 16. It is phase-modulated by the signal and is emitted via the emission-side antireflection film 64. Moreover, in the optical modulator 8A to which the present invention is applied, the end face of the optical waveguide 12A can be moved to a substantially central portion of the plane 91 (92) by attaching the protective members 86 and 87 at each end portion. , The end face of the optical waveguide 12A is chipped or rounded, the verticality between the optical waveguide 12A and the planes 91 and 92 can be ensured, the polishing accuracy on the planes 91 and 92 can be improved, and the yield can be improved.

Here, both the single-polarized optical waveguide produced by the proton exchange method in which only a single polarization component of the incident light is propagated and only the orthogonal polarization component of the incident light are propagated. As shown in FIGS. 18, 19, and 20, the width W ₁ = 1.9 [mm] and the length L ₁ = 27.4 [mm] of the orthogonally polarized optical waveguide produced by the Ti diffusion method. Three optical waveguides 112A, 112B, 112C are formed on a LiNbO ₃ crystal substrate 11 having a thickness T ₁ = 0.5 [mm], and a width W ₂ = 1.9 [mm] is formed above the optical waveguides 112A, 112B, 112C. ], Length L ₂ = 1.5 [mm], thickness T ₂ = 0.5 [mm], the protective members 86,87 are bonded, and the end face of the protective member 86,87 and the end face of the LiNbO ₃ crystal substrate 11 As a LiNbO ₃ crystal substrate block in which the entrance surface and the exit surface of the three optical waveguides 112A, 112B, 112C are finished to be flat by polishing, the optical path widths W3 of the three optical waveguides 112A, 112B, 112C, respectively, are formed. Prepared 10 samples of 6 types of 6.0 [μm], 6.3 [μm], 6.6 [μm], 6.9 [μm], 7.2 [μm], and 7.5 [μm]. Then, the reflectances of the _three optical waveguides 112A, 112B, 112C at the entrance surfaces A1, _B1 , C1 and the exit surfaces _A2 , B2, and _{C2 are} measured, and the finesse and transmission of _each sample are measured. When asked, the following results were obtained.

That is, the finesse of the orthogonally polarized optical waveguide was about 30 to 45, whereas the finesse of the single-polarized optical waveguide was about 50 to 65. Further, the transmittance of the orthogonally polarized optical waveguide was about 12.5 to 25 [%], whereas the transmittance of the single-polarized optical waveguide was about 20 to 32.5 [%]. Has been done.

The light modulator 8A has an emission side reflective film as a high reflection film at one end of the optical waveguide 12A formed as a region in which a waveguide mode exists only for a single polarization component. By providing the 94 and providing the antireflection film 63 at the other end, the so-called reciprocating modulation type optical modulator having the configuration shown in FIGS. 7a, 7b, and 7c described above is similarly provided with the optical modulator 8. It can also be operated as.

Further, in step S26, the optical modulator 8A polishes the planes 91 and 92 in parallel with each other, and on the polished planes 91 and 92, the incident side antireflection film 63 and the exit side antireflection film 64. Instead, the incident side reflective film 93 and the outgoing side reflective film 94 are formed over one surface thereof, thereby functioning as the optical comb generator 1A.

That is, in the optical comb generator 1A, the incident side reflecting film 93 and the emitting 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 12A, and the optical waveguide 12A. It constitutes an optical resonator 5 that resonates by reciprocating the light passing through the above.

By forming the first end face 84 and the second end face 85 substantially perpendicular to the optical waveguide 12A, the incident side reflective film 93 and the exit side reflective film 93 made of a single-layer or multi-layer gas phase growth film adhered thereto. The side reflective film 94 can efficiently resonate the light of a single polarization component.

In the optical comb generator 1A having the above-described configuration, the light incident from the outside through the reflecting film 93 on the incident side is such that the light of a single polarization component propagates in the optical waveguide 12A in the outward direction and is emitted on the outgoing side. It is reflected by the reflective film 94 and partially penetrates to the outside. The light of the single polarization component reflected from the emission side reflection film 94 propagates in the optical waveguide 12A in the return direction and is reflected by the incident side reflection film 93. By repeating this, the light of a single polarization component resonates in the optical waveguide 12A.

Further, by using an electric signal synchronized with the time when the light of a single polarization component reciprocates in the optical waveguide 12A as a drive input via the electrode 83, the light of a single polarization component becomes this light modulator. Compared with the case of passing through 8A only once, it is possible to apply a deep phase modulation several tens of times or more. In addition, hundreds of sidebands can be generated over a wide band around the frequency ν ₁ of the incident light. Incidentally, the frequency interval of each of the generated side bands is equivalent to the frequency _fm of the input electric signal. Therefore, the optical modulator 8A has a single bias composed of a large number of side bands by replacing the incident side antireflection film 63 and the emitting side antireflection film 64 with the incident side reflective film 93 and the emitting side reflective film 94. It functions as an optical comb generator 1A that generates optical combs of wave components.

That is, the optical comb generator 1A is applied only to a single polarization component on the substrate 11 having at least an electro-optical effect so as to penetrate from the incident-side reflecting film 93 constituting the resonance means to the emitting-side reflecting film 94. Since the optical waveguide 12A formed as a region where the waveguide mode exists, only a single polarization component of the light incident through the incident side reflection film 93 is propagated through the optical waveguide 12A. Therefore, an optical comb can be generated as an optical modulation output of only a single polarization component via the light emitting side reflective film 94.

Here, in the light modulators 8, 8A, 51 according to the present invention, the electrode 83 provided on the upper surface of the optical waveguide 12A to which the modulation signal is supplied is, for example, a waveguide type optical modulation having a configuration as shown in FIG. The light modulation efficiency can be further improved by having a ridge structure as in the device 8B (optical comb generator 1B).

In this waveguide type optical modulator 8B (optical comb generator 1B), the electrodes 83 in the waveguide type optical modulator 8A (optical comb generator 1A) shown in FIGS. 15 and 16 have a ridge structure. Therefore, the same components as the above-mentioned optical modulator 8A (optical comb generator 1A) are referred to in FIGS. 15 and 16, and the description thereof will be omitted here.

In this waveguide type optical modulator 8B (optical comb generator 1B), the substrate 11 is formed by cutting out 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. be. A ridge portion 20 for forming an electrode 83A having a ridge structure is provided on the cut-out substrate 11 by subjecting it to a treatment such as mechanical polishing or chemical polishing.

The optical waveguide 12A is formed by a proton exchange method or a Ti diffusion method so as to penetrate from an incident end to an emitted end, and is guided only to a single polarized component in order to propagate light of a single polarized component. It is formed as a region where the wave mode exists.

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

The LiNbO ₃ crystal type optical waveguide 12A produced based on such a method has electricity 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, it is possible to modulate the light of a single polarization component by utilizing such a physical phenomenon.

The electrode 83A having a ridge structure has a main electrode formed on the convex 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 12A by using a modulation signal having a frequency _fm supplied from the oscillator 16 as a drive input to the optical waveguide 12A. Phase modulation is applied to the light.

A method of manufacturing the waveguide type optical modulator 8B (optical comb generator 1B) having such a structure will be described with reference to FIG. 22.

That is, first, in step S31, a photoresist pattern 13 is produced on the surface of the substrate ₁₁ made of LiNbO3 crystals.

Next, the process proceeds to step S32, and the substrate 11 of the LiNbO3 crystal having the photoresist pattern 13 formed on the surface is heated in a state of being immersed in a proton exchange solution, for example, benzoic acid, to heat Li in the surface layer portion of the substrate 11. The optical waveguide 12A is formed as a region in which the waveguide mode exists only for a single polarization component by the proton exchange method of substituting with ⁺ .

The process of manufacturing the optical waveguide 12A in steps S31 and S32 is not limited to the proton exchange method. For example, in step S31, the photoresist pattern 13 is formed on the surface of the substrate ₁₁ made of LiNbO3 crystals. Ti is vapor-deposited on the surface of the substrate 11 made of LiNbO ₃ crystals, and the photoresist is removed to prepare a thin wire of Ti having a width of a micron size. In the next step S32, this is prepared. By heating the substrate 11 on which the thin wire of Ti is formed, the Ti atom is thermally diffused in the substrate 11, and the optical waveguide 12A is used as a region in which 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 S33, the resist pattern 13 of the substrate 11 on which the optical waveguide 12A is formed is removed, and further, by processing such as mechanical polishing and chemical polishing, as shown in FIG. 23, the electrode 83A having a ridge structure is formed. The ridge portion 20 for forming the above is provided.

Next, the process proceeds to step S34, and the SiO ₂ thin film as the buffer layer 14 is vapor-deposited on the surface of the substrate 11. In this step S34, the buffer layer 14 may be formed by a method of attaching the SiO ₂ wafer to the surface of the substrate 11. In such a case, the film thickness may be controlled to an appropriate level by polishing the vapor-deposited buffer layer 14 in consideration of the electrode mounting area in step S35 described later.

Next, the process proceeds to step S35, and as shown in the vertical cross section of the main part of FIG. 24, the electrode 83A having a ridge structure is formed on the buffer layer 14 of the substrate 11.

Next, the process proceeds to step S36, and the protective members 86 and 87 are adhered to the upper part of the optical waveguide 12A. As for the method of adhering the protective members 86 and 87, they may be attached with an adhesive or may be directly bonded based on another method. When the substrate 11 is made of LiNbO ₃ crystals, the protective members 86, 87 may be made of LiNbO ₃ as the same material. In this step S36, the end faces 86a and 87a of the attached protective members 86 and 87 can form planes 91 and 92 between the first end face 84 and the second end face 85, respectively. And trim it.

In the optical modulator 8B to which the present invention is applied, in the final step S37, the obtained planes 91 and 92 are polished to a plane perpendicular to the optical waveguide 12A, and the obtained planes 91 and 92 are polished on the polished planes 91 and 92. An antireflection film 63 on the incident side and an antireflection film 64 on the exit side are formed over one surface as a gas phase growth film under a temperature condition lower than the heat resistant temperature of the adhesive.

Further, in the optical comb generator 1B to which the present invention is applied, in the step S37, the planes 91 and 92 are polished in parallel with each other, and on the planes 91 and 92 perpendicular to the polished optical waveguide 12A. Instead of the incident-side antireflection film 63 and the emission-side antireflection film 64, the incident-side reflection film 93 and the emission-side reflection film 94 are each covered with gas phase growth under temperature conditions lower than the heat-resistant temperature of the adhesive. Formed as a film.

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

Moreover, in the optical modulator 8B and the optical comb generator 1B to which the present invention is applied, the end face of the optical waveguide 12A is placed in the substantially central portion of the plane 91 (92) by attaching the protective members 86 and 87 at each end. Since it can be moved, the end face of the optical waveguide 12A can be chipped or rounded, the verticality between the optical waveguide 12A and the planes 91 and 92 can be ensured, and the polishing accuracy on the planes 91 and 92 can be improved, thereby improving the yield. Is also possible.

Further, in the optical comb generator 1B, the light incident from the outside through the incident side reflecting film 93 propagates only a single polarization component in the outward path direction in the optical waveguide 12A and is reflected by the emitting side reflecting film 94. At the same time, it partially penetrates to the outside. The light of the single polarization component reflected from the emission side reflection film 94 propagates in the optical waveguide 12A in the return direction and is reflected by the incident side reflection film 93. By repeating this, the light of a single polarization component resonates in the optical waveguide 12A.

Further, by using an electric signal synchronized with the time when the light of a single polarization component reciprocates in the optical waveguide 12A as a drive input via the electrode 83A, the light of a single polarization component becomes this light modulator. Compared with the case of passing through 8B only once, it is possible to apply a deep phase modulation several tens of times or more. In addition, hundreds of sidebands can be generated over a wide band around the frequency ν ₁ of the incident light. Incidentally, the frequency interval of each of the generated side bands is equivalent to the frequency _fm of the input electric signal. Therefore, the light modulator 8B functions as an optical comb generator 1B that generates an optical comb having a single polarization component composed of a large number of side bands.

As described above, in the optical comb generator 1B to which the present invention is applied, a single bias is provided on a substrate having at least an electro-optical effect so as to penetrate from the incident side reflecting film 93 constituting the resonance means to the emitting side reflecting film 94. Since the optical waveguide 12A formed as a region where the waveguide mode exists only for the wave component, only a single polarization component of the light incident through the incident side reflection film 93 is provided. An optical comb can be generated as an optical modulation output of only a single polarization component by propagating through the optical waveguide 12A and passing through the light emitting side reflective film 94, and protective members 86 and 87 are attached at each end. Since it is attached and configured, the end surface of the optical waveguide 12A, which has been conventionally located at the uppermost corner of the end surface, moves to the substantially central portion of the plane 91 (92). As a result, even when the corner of the plane 91 (92) is chipped during polishing in step S37, the end face of the optical waveguide 12A is not chipped. That is, it is possible to configure the optical waveguide 12A so that the end face itself is less likely to be chipped. This makes it possible to suppress the light loss from each end face of the optical waveguide 12A as much as possible.

Moreover, since the optical modulator 8B includes an electrode 83A having a ridge structure formed on the buffer layer 14 of the substrate 11, as shown in the vertical cross section of the main part of FIG. 24, the modulation efficiency is further improved. Can be made to.

Here, in this light modulator 8B, 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. Samples of the light modulator 8A with depths AVD (Average depths) of 3.3, 2.96, 4.79, and 4.72 [μm] were prepared, and the drive voltage (AC Vpi) and direct current at 25 GHz were prepared. The driving voltage (DC Vpi) is actually measured and the results are shown in FIGS. 25 and 26. Vpi is the voltage required to π-radian the phase.

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 8B provided with the electrode 83A having a 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 average voltage of the drive voltage (AC Vpi) at 25 GHz is reduced to about 70% of the original voltage as compared with the case without the ridge structure, and the electric power is about 50%. Corresponds to the decrease in. Further, in the direct current drive voltage (DC Vpi), the average voltage is reduced to about 80% of the original voltage as compared with the case without the ridge structure, which corresponds to a decrease of about 50% in electric power.

That is, the optical modulator 8B and the optical comb generator 1B are composed of a protective member having the same hardness as the substrate 11 of the optical waveguide 12A, and at least one end surface of the protective member is a light incident end in the optical waveguide 12A. Alternatively, the protective member 86 includes a first protective member 86 and a second protective member 87 arranged on the upper portion of the optical waveguide 12A so as to form the same plane as the end surface of the substrate 11 including the light emitting end. The incident side antireflection film 63 or the incident side reflective film 93 and the exit side antireflection film 64 or the emission side on a plane perpendicular to the optical waveguide 12A formed by polishing the end faces of 86 and 87 and the end face of the substrate 11. Since the side reflective film 94 is adhered as a single-layer or multi-layered gas phase growth film under temperature conditions lower than the heat-resistant temperature of the adhesive, it is possible to prevent chipping of the end face of the optical waveguide and to have high reflection. It is possible to stabilize the film attachment, improve the finesse of the optical resonator 5 composed of the incident side reflective film 93 and the outgoing side reflective film 94, and further, by providing the electrode 83A having a ridge structure, the driving power is provided. Can be reduced.

Therefore, the optical modulators 8A and 8B and the optical modulator 51 having the above-described configuration have at least one end face of the protective members 86 and 87 having the same hardness as the substrate 11 for forming the optical waveguide 12A from the upper surface. Is arranged on the upper part of the optical waveguide 12A so as to form the same plane as the end surface of the substrate 11 including the light incident end or the light emitting end in the optical waveguide 12A, and the end faces of the protective members 86, 87 and the above. An incident side reflective film 93 and an outgoing side reflective film made of a single-layer or multi-layered gas phase growth film constituting the resonance means on a plane perpendicular to the optical waveguide 12A formed by polishing the end surface of the substrate 11. Since 94 is adhered, chipping and rounding during processing of the corners of the end face of the optical waveguide can be suppressed, and each reflective film can be stably adhered without peeling at the uppermost corner of the end face. A substrate that can improve the reflectance and finesse of the optical resonator, enhance the function of the device itself, and have at least an electro-optical effect so as to penetrate from the incident-side reflecting film 93 constituting the resonance means to the emitting-side reflecting film 94. By providing the optical waveguide 12A formed as a region in which the waveguide mode exists only for a single polarization component in 11, a single light incident through the incident side reflection film 93 is provided. Only the polarization component is propagated through the optical waveguide 12A, and an optical comb capable of generating a stable optical comb as an optical modulation output of only a single polarization component via the light emitting side reflective film 94 is generated. Functions as 1A.

The optical waveguide 12A in the light modulator 8B and the light modulator 51 as described above has a single polarization component on 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. A low-power type that can output laser light or optical comb with only a single polarization component by providing an electrode 83A having a ridge structure, which is formed as a region where a waveguide mode exists only for. Laser light sources and optical com generators can be constructed.

Further, also in the optical modulators 8A and 8B (optical comb generators 1A and 1B), the waveguide of the optical waveguide 12A is made by adhering the reflective films 93 and 94 having the transmittance in the range of 95% to 99%. The loss rate and the transmittance of the reflective films 93 and 94 can be matched to increase the finesse and transmittance of the resonator and improve the performance of the resonator.

Next, the block diagram of FIG. 27 shows the configuration of the optical comb generator 210 using the low power type optical comb module to which the present invention is applied.

The optical comb generator 210 has an optical coupler 211 that branches a part of the optical comb output from the low power optical comb module 200A to which the present invention is applied, and a photodetector that detects light branched by the optical coupler 211. It includes a device 212 and a control circuit 213 to which a light detection signal obtained by the photodetector 212 is supplied.

In the optical comb module 200A, a laser beam is incident from a laser light source (not shown) and an RF modulation signal is input via a bias tee 214, so that the incident laser beam has a single polarization component. By applying phase modulation with the RF modulation signal, an optical comb is generated and output. In the optical comb module 200A, the resonance length of the resonance means by the incident side reflecting film and the emitting side reflecting film provided in the optical waveguide is controlled by the temperature control by the temperature control circuit 219.

The control circuit 213 obtains an error with respect to the control target from the light detection signal, generates a control signal such that the error becomes zero, and supplies the control signal to the bias tee 214.

By applying it to the DC bias of the optical comb module 200A, the resonance frequency of the optical comb module 200A can be made to follow the input laser frequency.

The control circuit 213 may be a single printed circuit board or a combination of an RF mixer or an isolator and a printed circuit board. By mixing the photodetector signal of the photodetector 212 and the synchronization signal, a control signal corresponding to the amount of error from the control target is created.

A portion of the output of the RF modulated signal source can be used as the sync signal. In that case, the operating band of the photodetector 212 needs to be equal to or higher than the RF drive frequency.

In the control circuit 213, the low frequency component of the signal obtained by inputting the photodetection signal and the synchronization signal to the mixer via the phase adjuster is taken and used as an error signal. Alternatively, another modulated 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 200A is modulated with a smaller amplitude than that of the FSR in the resonance mode, and the output signal of the photodetector 212 and the synchronization signal are mixed. If the dither signal frequency is low, it is also possible to generate an error signal by the product-sum operation of digital signal processing after converting the optical detection signal into a digital signal by an analog-digital converter.

The frequency characteristic of the error signal is adjusted and added to the DC bias of the optical comb module 200A as a control signal via the bias tee 214. Generally, the error signal is input to a circuit having proportional, integral, and differential functions, the frequency characteristics of the control loop are determined by adjusting the amplitude of those components, and the resonance frequency of the optical comb module 200A is the input laser. It is controlled to follow the oscillation frequency.

Further, the block diagram of FIG. 28 shows the configuration of the optical comb generator 220 using the low power type optical comb module to which the present invention is applied.

The optical comb generator 220 controls the resonator by using the reflected light of the low power optical comb module 200A to which the present invention is applied, and a part of the reflected light of the low power optical comb module 100A is light. It is branched by the coupler 211 so that it is incident on the light detector 212.

Each component of the optical comb generator 220 is the same as the component of the optical comb generator 210 shown in FIG. 27, and the corresponding components are designated by the same reference numerals in FIG. 28 and detailed description thereof is omitted. do.

The control circuit 213 obtains an error with respect to the control target from the photodetection signal obtained by the photodetector 212, 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 200A 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, an optical comb light source 300 having a configuration as shown in FIG. 29 can be constructed.

The optical comb light source 300 includes a laser light source 301 that oscillates at a single frequency, and a separation optical system 302 such as an optical coupler or an optical beam splitter that separates a single frequency laser light emitted from the laser light source 301 into two laser lights. It is equipped with a frequency shifter 305 that shifts the frequency of one of the laser beams separated by the separation optical system 302, two optical comb generators (OFCG1, OFCG2) 320A, 320B, etc. using low-power optical comb modules, respectively.

In this optical comb light source 300, the laser light emitted from one single frequency oscillation laser light source 301 is separated into two laser lights by the separation optical system 302, and two optical comb generators (OFCG1 and OFCG2) are used. It is designed to be input to 320A and 320B.

The two optical comb generators 320A and 320B are driven by oscillators 303A and 303B that oscillate _at different frequencies fm and frequency _fm + _Δfm . The respective oscillators 303A and 303B are phase-locked by a common reference oscillator 304, so that the relative frequencies of _fm and _fm + _Δfm become stable. In front of the optical comb generator (OFCG2) 320B, a frequency shifter 305 such as an acoustic optical frequency shifter (AOFS) is provided so that the input laser light is given an optical frequency shift of frequency fa by this frequency shifter 305. It has become. As a result, the beat frequency between the carrier frequencies becomes an AC signal having a frequency fa instead of a DC signal. As a result, the beat signal of the high frequency side band of the carrier frequency and the beat signal of the low frequency side side band are generated in the opposite frequency regions with the beat frequency fa between the carrier frequencies of the beat signal, which is convenient for phase comparison. ..

The two optical comb generators (OFCG1 and OFCG2) 320A and 320B 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 beam. By modulation, it is possible to output an optical comb with a single polarization component.

This optical comb light source 300 shares one single frequency oscillation laser light source 301, and two optical combs having different center frequencies and frequency intervals of two optical comb generators (OFCG1 and OFCG2) 320A and 320B. It is generated, for example, the first and second light sources in the distance meter and the optical three-dimensional shape measuring machine according to the patent No. 5231883 previously proposed by the present inventor, that is, the intensity or the phase, respectively. Two optical comb generators (OFCG1 and OFCG2) by using the optical comb light source 300 as the first and second light sources that are modulated and emit interfering reference light and measurement light having different modulation periods from each other. The optical comb output for measuring the polarization component of 320A and 320B is irradiated while scanning the surface of the measurement target, and the reflected light from the surface is detected for each irradiation point to calculate the distance (height). By doing so, it is possible to construct a measurement system of a distance meter or an optical three-dimensional shape measuring machine that performs stable measurement operation.

FIG. 30 is a block diagram showing a configuration of an optical comb distance meter 400 configured by using the optical comb light source 300.

The optical comb distance meter 400 shown in the block diagram of FIG. 30 measures the distance using an optical frequency comb interferometer, and has a center frequency emitted from the first and second optical comb light sources 401 and 402. Two optical frequency combs with different frequency intervals are periodically modulated in intensity or phase, and are measured with the reference plane 404 via the interference optical system 410 as the reference light S1 and the measurement light S2 having coherence with different modulation periods. The reference light detector 403 detects the interference light S3 between the reference light S1 and the measurement light S2 that irradiates the surface 405 and irradiates the reference surface 404 and the measurement surface 405, and the reference light reflected by the reference surface 404. Interference light S4 between S1'and the measurement light S2'reflected by the measurement surface 305 is detected by the measurement light detector 406, and interference light S3 is detected by the signal processing unit 407 by the reference light detector 403. From the time difference between the signal and the interference signal obtained by detecting the interference light S4 by the measurement light detector 406, the difference between the distance L1 from the light speed and the refractive index at the measurement wavelength to the reference surface 404 and the distance L2 to the measurement surface 405 is obtained. be able to. There are multiple forms of interferometers and detectors.

By combining this optical comb distance meter 400 with an optical scanning device, the measurement light S2 is irradiated while scanning the surface of the measurement target, and the reflected light from the surface is detected for each irradiation point and the distance ( It is possible to construct an optical comb shape measuring instrument that can obtain the surface shape of an object from the distribution of scan coordinates and distance (height) by performing a height) calculation. Scanner optical systems come in many forms. Telecentric optics can be used to ensure that light is incident almost perpendicular to the object within the measurement range.

Further, for example, it is a light source in the vibration measuring device according to Patent No. 5336921 and Patent No. 5363231 proposed by the present inventor, that is, a spectrum having a predetermined frequency interval, and the modulation frequencies and center frequencies are different from each other. By using the optical comb light source 300 as a light source unit that emits phase-synchronized and interfering reference light and measurement light, a single light comb generator (OFCG1, OFCG2) 320A, 320B is emitted. It is possible to construct a measurement system of a vibration measuring device that performs stable multipoint vibration measurement operation by irradiating different places depending on the wavelength through an element that divides the optical comb of the polarization component 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 the circle in FIG. 35, the orthogonal polarization component is used. The transmission mode waveform may be deformed, and the place where it occurs (relative to the main mode) is different, and it becomes an unstable factor of control because there are multiple minimum parts, but only a single polarization component. By using the optical waveguide through which the light is passed, as shown in FIG. 31, the transmission mode waveform is not deformed, the stabilization as an optical comb generator, the accuracy improvement of the measuring device including the optical comb, the reduction of error, and the like. Can be planned.

That is, the polarization component orthogonal to the generation of the optical comb causes measurement errors in distance and height when the optical comb is used for measurement, and the polarization component orthogonal to the generation of the optical comb is the cause of the optical comb generator. The control for matching the resonance frequency to the laser frequency may become unstable, causing the control point to shift and the control to oscillate. Also, when using the optical comb for measurement, the distance and height are measured. Although it was a factor of error, by generating optical combs using an optical waveguide that allows only a single polarizing component to pass through, the output of orthogonally polarized light components that do not contribute to the generation of optical combs is suppressed, and the polarization of the optical comb output is suppressed. The extinction ratio can be improved, the degree of single polarization can be increased, the resonator control is stabilized, unnecessary interference signals are eliminated, and measurement errors in distance measurement and shape measurement using optical combs are eliminated. It is possible to improve the measurement accuracy and the reliability of the entire system.

1,1A, 1B, 210,220,320A, 320B optical comb generator, 5 optical resonator, 8,8A, 8B, 51 optical modulator, 11 substrate, 12, 12A optical waveguide, 14 buffer layer, 16 oscillator, 18 Termination resistor, 19a phase controller, 19b reflector, 20 ridges, 21 optical circulator, 22 focuser, 63 antireflection film, 83,83A electrodes, 84 first end face, 85 second end face, 86 first Protective member, 86a, 87a end face, 87 second protective member, 91,92 flat surface, 93 incident side reflective film, 94 outgoing side reflective film, 200A low power type optical comb module, 210, 220 optical comb generator, 211 optical Coupler, 212 optical detector, 213 control circuit, 214 bias tee, 130,300 optical comb light source, 301 laser light source, 302 separation optical system, 303A, 303B oscillator, 304 reference oscillator, 305 frequency shifter, 320A, 320B optical comb. Generator (OFCG1, OFCG2), 400 optical comb distance meter, 401, 402 optical comb light source, 403 reference light detector, 404 reference plane, 405 measurement surface, 406 measurement light detector, 407 signal processing unit

Claims (6)

In a method for manufacturing an optical resonator in which light incident on the incident side is propagated and resonated by an optical waveguide formed so as to penetrate from the incident side reflective film to the outgoing side reflective film.
The optical waveguide forming step of forming the above optical waveguide from the upper surface of the substrate,
A protective member having the same hardness as the substrate is placed on the upper part of the optical waveguide so that at least one end surface thereof forms the same plane as the end surface of the substrate including the light incident end or the light emitting end in the optical waveguide. Distributing process and disposing
By polishing the end face of the protective member and the end face of the substrate arranged in the arrangement step, a flat polishing surface including the light incident end or the light emitting end of the optical waveguide is perpendicular to the optical waveguide. The polishing process to form a flat surface and
It has a reflective film attachment step of adhering a single-layer or multi-layer gas phase growth film as the incident-side reflective film or the outgoing-side reflective film on the plane formed in the polishing step.
In the arrangement step, the protective member is attached to the upper part of the optical waveguide with an adhesive and arranged.
In the reflective film adhesion step, the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate is simply under a temperature condition lower than the heat resistant temperature of the adhesive. A method for producing an optical resonator, which comprises forming the incident side reflecting film or the emitting side reflecting film on a plane perpendicular to the optical waveguide by adhering a layer or a multilayer vapor growth film. .. In the reflective film adhesion step, the film thickness in the end face region including the light incident end or the light emitting end of the optical waveguide is optimized for the loss rate according to the crystal length in the light propagation direction of the optical waveguide. The method for manufacturing an optical resonator according to claim 1, wherein a single-layer or multi-layered gas phase growth film is adhered. In a method for manufacturing an optical modulator that propagates and modulates light incident on the incident side through the incident side reflective film by an optical waveguide on which an incident side reflective film and an outgoing side reflective film are formed.
The optical waveguide forming step of forming the above optical waveguide from the upper surface of the substrate,
At least, a laminating step of laminating a buffer layer on the substrate so as to cover the optical waveguide formed in the optical waveguide forming step.
An electrode forming step of forming an electrode for applying an electric field to the optical waveguide on the buffer layer laminated in the laminating step, and an electrode forming step.
A protective member having the same hardness as the substrate is placed on the upper part of the optical waveguide so that at least one end surface thereof forms the same plane as the end surface of the substrate including the light incident end or the light emitting end in the optical waveguide. Distributing process and disposing
By polishing the end face of the protective member and the end face of the substrate arranged in the arrangement step, a flat polishing surface including the light incident end or the light emitting end of the optical waveguide is perpendicular to the optical waveguide. The polishing process to form a flat surface and
It has a reflective film attachment step of adhering a single-layer or multi-layer gas phase growth film as the incident-side reflective film or the outgoing-side reflective film on the plane formed in the polishing step.
In the arrangement step, the protective member is attached to the upper part of the optical waveguide with an adhesive and arranged.
In the reflective film adhesion step, the entire plane formed by the end face of the protective member attached with the adhesive and the end face of the substrate is simply under a temperature condition lower than the heat resistant temperature of the adhesive. A method for producing an optical modulator, which comprises forming the incident side reflecting film or the emitting side reflecting film on a plane perpendicular to the optical waveguide by adhering a layer or a multilayer vapor growth film. .. In the reflective film adhesion step, the film thickness in the end face region including the light incident end or the light emitting end of the optical waveguide is optimized for the loss rate according to the crystal length in the light propagation direction of the optical waveguide. The method for producing an optical modulator according to claim 3, wherein the vapor phase growth film having a single layer or a plurality of layers is adhered. The optical waveguide forming step is characterized in that the optical waveguide is formed as a region in which a waveguide mode exists only for a single polarization component by proton exchange from the upper surface of the substrate having at least an electro-optical effect. The method for manufacturing an optical modulator according to claim 3 or 4. It has a ridge structure forming step of forming a ridge structure on the above substrate, and has a ridge structure forming step.
In the electrode forming step, an electrode having a ridge structure is formed as an electrode for applying an electric field to the optical waveguide on the buffer layer laminated in the laminating step on the substrate on which the ridge structure is formed. The method for manufacturing an optical modulator according to any one of claims 3 to 5, wherein the optical modulator is characterized.

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