Optical resonator, optical modulator and method for manufacturing the same, optical frequency comb generator, optical oscillator

Abstract

By suppressing the defects and rounded corners when processing the corners of the optical waveguide end face, each reflective film can be stably covered without peeling off at the corner portion of the uppermost part of the end face, thereby improving the reflectivity of the reflective film and the fineness of the resonator. The incident side reflective film (93) and the exit side reflective film (94) are used to form a resonant component, so that light incident through the incident side reflective film (93) resonates. The optical waveguide (12) is formed in a manner that passes through the incident side reflective film (93) to the exit side reflective film (94), and the resonated light is transmitted. The optical waveguide (12) is formed from the upper surface of the substrate (11), and a first protective member (86) and a second protective member (86) corresponding to the material of the substrate (11) are provided. The component (87) is arranged on the upper part of the waveguide path (12) in such a manner that at least one of its end faces forms the same plane (91, 92) with the first end face (84) and the second end face (85) of the substrate (11) including the light incident end or the light exit end of the optical waveguide (12), and the incident side reflection film (93) and the exit side reflection film (94) are respectively covered as single-layer or multi-layer vapor-deposited films on the plane (91, 92) perpendicular to the formed optical waveguide (12).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an optical resonator and an optical modulator, which are used in fields such as optical communications, optical CT, and optical frequency standards, which require a standard light source with multiple wavelengths and high coherence, or a light source that can also utilize the coherence between the wavelengths, as well as an optical resonator, an optical modulator, an optical frequency comb generator, and an optical oscillator. This application claims priority based on Japanese Patent Application No. 2019-227630 filed on December 17, 2019 in Japan and Japanese Patent Application No. 2020-099226 filed on June 8, 2020, and is cited in this application by reference to the above applications. Background Art

[0002] With the recent development of optoelectronics, waveguide optical resonators that resonate light confined in an optical waveguide are widely used to respond to requests for laser control for frequency multiplexing and frequency measurement of absorption lines distributed over a wide range.

[0003] When measuring optical frequency with high precision, heterodyne detection is performed to detect the electrical signal of the optical beat frequency generated by interfering the measured light with other light. The frequency band of light that can be measured in this heterodyne detection is limited to the frequency band of the light receiving element used in the detection system, which is approximately tens of GHz.

[0004] On the other hand, with the recent development of optoelectronics, light control for frequency multiplexing and frequency measurement of absorption lines distributed over a wide range have been performed, and therefore, it has been required to further expand the measurable frequency band of light.

[0005] In response to the request for expansion of the measurable frequency band, a wide-band heterodyne detection system using an optical frequency comb generator (e.g., see Patent Document 1) has been proposed. The optical frequency comb generator generates comb-shaped sidebands arranged at equal intervals on the frequency axis within a wide frequency band, and the frequency stability of the sidebands is roughly equivalent to the frequency stability of the incident light. By performing heterodyne detection on the generated sidebands and the measured light, a wide-band heterodyne detection system spanning several THz can be constructed.

[0006] Figure 1 The principle structure of the conventional optical frequency comb generator 1003 is shown.

[0007] The optical frequency comb generator 1003 uses an optical resonator 1000 including an optical phase modulator 1031 and reflection mirrors 1032 and 1033 disposed opposite to each other with the optical phase modulator 1031 interposed therebetween.

[0008] The optical resonator 1000 allows light L incident with a small transmittance via the reflector 1032 to inResonance occurs between the reflectors 1032 and 1033, and a portion of the light L out The optical phase modulator 1031 is composed of an electro-optical crystal for optical phase modulation whose refractive index changes when an electric field is applied, and the frequency f applied to the electrode 1036 is m The electrical signal accordingly applies phase modulation to the light passing through the optical resonator 1000 .

[0009] In the optical frequency comb generator 1003, by driving the optical phase modulator 1031 with an electrical signal synchronized with the time when the light reciprocates in the optical resonator 1000, a phase modulation several tens of times deeper can be applied compared to the case where the light passes through the optical phase modulator 1031 only once. As a result, hundreds of high-order sidebands can be generated, and the frequency interval f between adjacent sidebands can be 1 / 4. m All related to the frequency f of the input electrical signal m Equivalent.

[0010] In addition, conventional optical frequency comb generators are not limited to the bulk type described above. Figure 2 The application shown is a waveguide type optical frequency comb generator 1020 using an optical waveguide.

[0011] The waveguide type optical frequency comb generator 1020 is constituted by 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 reflection film 1204, an exit side reflection film 1205, and an oscillator 1206.

[0012] The substrate 1201 is obtained by slicing a large crystal of LiNbO3, GaAs or the like with a diameter of 3 to 4 inches grown by the Czochralski method into a wafer shape. The sliced ​​substrate 1201 is subjected to mechanical polishing, chemical polishing or the like.

[0013] The optical waveguide 1202 is configured to propagate light, and the refractive index of the layer constituting the optical waveguide 1202 is set higher than the refractive index of other layers such as the substrate 1201. Light incident on the optical waveguide 1202 propagates by total reflection 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 epitaxial growth on the substrate 1201.

[0014] In addition, a LiNbO3 crystal optical waveguide can also be applied as the optical waveguide 1202. The LiNbO3 crystal optical waveguide can be formed by diffusing Ti on the surface of the substrate 1201 formed of LiNbO3 or the like. In the case of actually manufacturing the LiNbO3 crystal optical waveguide, a photoresist pattern is firstly made on the surface of the substrate 1201, Ti is evaporated on the pattern, and then the photoresist is removed to manufacture a thin line of Ti having a width of micrometer size. Then, the thin line of Ti is heated to be thermally diffused into the substrate 1201.

[0015] Furthermore, when the Ti is thermally diffused into the substrate 1201 formed of LiNbO3, the refractive index of the region where the Ti is diffused becomes higher than the refractive index of other regions, so that light can be confined. That is, the region where the Ti is diffused forms an optical waveguide 1202 capable of propagating light. Since the LiNbO3 crystal-type optical waveguide 1202 manufactured by such a method has an electro-optical effect, the refractive index can be changed by applying an electric field thereto.

[0016] The electrode 1203 is formed of a metal material such as Al, Cu, Pt, Au, etc., and transmits a frequency f supplied from the outside. m The electrical signal is driven to the optical waveguide 1202. In addition, the propagation direction of the light in the optical waveguide 1202 is the same as the traveling direction of the modulated electric field. The speed of the light propagating in the optical waveguide 1202 and the speed of the electrical signal propagating on the electrode 1203 can also be made consistent by adjusting the width and thickness of the electrode 1203. In this way, the phase of the electrical signal sensed by the light propagating in the optical waveguide 1202 can be kept constant.

[0017] The incident side reflection film 1204 and the outgoing side reflection film 1205 are provided to resonate the light incident on the optical waveguide 1202, and the light passing through the optical waveguide 1202 is reciprocally reflected to resonate. The oscillator 1206 is connected to the electrode 1203 and supplies a frequency f m The electrical signal.

[0018] The incident side reflective film 1204 is arranged on the light incident side of the waveguide type optical modulator 1200, and light of frequency ν1 is incident on the incident side reflective film 1204 from a light source not shown. The incident side reflective film 1204 also reflects the light reflected by the emitting side reflective film 1205 and passing through the optical waveguide 1202.

[0019] The output-side reflective film 1205 is disposed on the light output side of the waveguide type optical modulator 1200, and reflects the light that has passed through the optical waveguide 1202. The output-side reflective film 1205 allows the light that has passed through the optical waveguide 1202 to be emitted to the outside at a certain ratio.

[0020] In the waveguide type optical frequency comb generator 1020 having the above structure, by driving the input of an electrical signal synchronized with the time when the light reciprocates in the optical waveguide 1202 from the electrode 1203 to the waveguide type optical modulator 1200, a phase modulation several tens of times deeper can be applied compared to the case where the light passes through the optical phase modulator only once. Thus, similarly to the bulk type optical frequency comb generator 1003, an optical frequency comb having sidebands across a wide frequency band can be generated, and the frequency intervals of adjacent sidebands are all the same as the frequency f of the input electrical signal. m Equivalent.

[0021] The waveguide type optical frequency comb generator 1020 is characterized in that the interaction area between light and electric signals is smaller. Since light is propagated in a closed manner in the micrometer-level optical waveguide 1202 having a higher refractive index than the surroundings, the electric field intensity in the optical waveguide 1202 can be locally increased by installing the electrode 1203 at a very close position to the optical waveguide 1202. Therefore, the electro-optical effect generated in the optical waveguide 1202 becomes larger compared to the bulk type optical frequency comb generator 1003, and a large modulation can be obtained with less power.

[0022] However, in the structure of the optical waveguide 1202, the conventional waveguide type optical frequency comb generator 1020 is difficult to coat the incident side reflection film 1204 and the exit side reflection film 1205, and polish the end surface coated with these reflection films, and it is difficult to manufacture a high-fineness resonator with good reproducibility. In order to improve the performance of the waveguide type optical frequency comb generator 1020, it is indispensable to improve the fineness of the resonator composed of the incident side reflection film 1204 and the exit side reflection film 1205. The reason is that even if the modulation index in the forward direction or the return direction of the optical waveguide 1202 is high, the number of reciprocating times of light cannot be increased if the fineness itself is low, and therefore, high-intensity sidebands cannot be generated within a wide bandwidth.

[0023] Furthermore, an optical comb generator and an optical modulator have been proposed that perform phase modulation not only on light propagating in the forward direction but also on light propagating in the return direction in an optical waveguide (see, for example, Patent Document 2).

[0024] also, Figure 3 1 shows the end surface of the waveguide type optical frequency comb generator 1020 on which the incident side reflection film 1204 is formed. Figure 3 , an optical waveguide 1202 is formed on the upper end of the substrate 1201, a relatively thin buffer layer is stacked thereon, and an electrode 1203 is formed thereon. 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, it is difficult to polish the optical waveguide 1202. Figure 3 If a defect occurs at the uppermost portion of the end face, the light that should be resonated will be scattered and become lost.

[0025] Furthermore, depending on the state of end face polishing, even if the corner at the top of the end face is not damaged, the corner may be rounded. If the corner is rounded, part of the reflected light will be separated from the waveguide mode of the optical waveguide 1202 and become lost.

[0026] In addition, in rare cases, it is possible to grind without causing a defect in the corner of the uppermost portion of the end face and without causing the corner to become rounded, but in this case, a problem will also occur when forming the incident side reflection film 1204 on the end face. High reflection films such as the incident side reflection film 1204 are generally produced by alternately stacking films with a higher refractive index and films with a lower refractive index, but at the corner of the uppermost portion of the end face, the film itself is easily peeled off and the material of the high reflection film spreads from the end face to the side surface, causing the film thickness to change, resulting in a problem that the film thickness cannot be controlled to be as designed.

[0027] That is, in an optical waveguide in which a core is formed in a substrate by diffusion or the like, since the core is formed on the surface of the substrate, at least one edge of the outer periphery of the core is located at the outer periphery of the substrate at the end face. If an optical thin film such as a reflective film is formed on the end face of such an optical waveguide by evaporation, sputtering, chemical vapor growth, or the like, film-forming particles on the outer periphery of the end face of the substrate spread to the side, and film-forming particles flying from the side spread to the end face, so it is difficult to obtain a uniform film thickness on the outer periphery of the end face of the substrate. Therefore, it is very difficult to form a film that is thin enough to function as a reflective film or the like and has a small film thickness distribution on the end face of the core located at the outer periphery of the end face of the substrate.

[0028] Here, the applicant of this case first proposed the following optical resonator, optical modulator, optical comb generator, and optical oscillator: by suppressing the damage and rounding of the corners of the optical waveguide end face during processing and making each reflective film stably cover without peeling off at the corner of the uppermost part of the end face, the reflectivity of the reflective film and the fineness of the optical resonator are improved, and the function of the device itself is improved. (For example, refer to Patent Document 3).

[0029] That is, a member having the same hardness as a substrate for forming an optical waveguide from the upper surface is disposed on the upper portion of the optical waveguide in such a manner that at least one end face thereof forms the same plane as an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, and an incident-side reflecting film and an emitting-side reflecting film constituting a resonance component are coated on the above-mentioned plane formed by grinding the end face of the member and the end face of the substrate, thereby suppressing chipping and rounding when processing the corners of the end face of the optical waveguide, and making each reflecting film stably coated without peeling off at the corner portion of the uppermost end face, thereby improving the reflectivity of the reflecting film and the fineness of the optical resonator, and improving the function of the device itself.

[0030] Prior art literature

[0031] Patent Literature

[0032] Patent Document 1: Japanese Patent Application Publication No. 2003-202609

[0033] Patent Document 2: Japanese Patent No. 3891977

[0034] Patent Document 3: Japanese Patent No. 4781648 Summary of the invention

[0035] Problem that the invention aims to solve

[0036] In addition, 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, if a single-layer or multi-layer vapor-deposited film is formed on the end face as an optical thin film such as a reflective film by vapor deposition, sputtering, chemical vapor growth, etc., there is a problem that film-forming particles on the periphery of the end face of the substrate spread toward the side, and film-forming particles flying from the side spread toward the end face, so it is difficult to obtain a uniform film thickness on the periphery of the end face of the substrate. It is very difficult to form a film that is thin enough to function as a reflective film and has a small film thickness distribution on the end face of the core located on the periphery of the end face of the substrate.

[0037] In addition, when grinding the end face of the optical waveguide 1202, there is a problem that the corner of the end face of the optical waveguide 1202 is easily damaged during processing. In addition, the corner of the end face of the optical waveguide 1202 becomes rounded during processing, and the reflective film formed on the end face of the optical waveguide 1202 is easily peeled off at the corner portion of the uppermost part of the end face.

[0038] These problems will lead to a decrease in the reflectivity of the reflection film covering the end face of the optical waveguide 1202, a decrease in the fineness of the resonator composed of the incident side reflection film 204 and the exit side reflection film 1205, and a decrease in the function of the waveguide type optical frequency comb generator 1020 itself. In addition, since it depends on the production environment, the reproducibility of the performance of the waveguide type optical frequency comb generator 1020 and the waveguide type Fabry-Perot resonator using the waveguide type optical frequency comb generator 20 cannot be guaranteed, which will lead to a decrease in the yield.

[0039] Furthermore, conventionally, in a waveguide type optical resonator that resonates light confined in an optical waveguide, an optical waveguide that transmits polarized light components of orthogonal mode mixing is used, and when an optical modulator or optical frequency comb generator is constructed, the optical output obtained also includes polarized light components of orthogonal mode mixing.

[0040] In conventional optical frequency comb generators, when an optical frequency comb is used for measurement, in order to obtain a stable output, a part of the light emitted from an optical resonator is detected by a photodetector, and the resonance length of the optical resonator is feedback-controlled so as to become a predetermined resonance length. However, since an optical waveguide is used that transmits polarized light components mixed in orthogonal modes, Figure 4 As indicated by the circle in the middle, the transmission mode waveform is deformed by the orthogonal polarization component. Moreover, the locations (relative positions relative to the main mode) where the transmission mode waveform is deformed by the orthogonal polarization component are scattered and there are multiple extremely small parts, which leads to instability in controlling the resonance length.

[0041] That is, when an optical frequency comb is generated by an optical comb generator using a waveguide-type optical resonator that resonates light enclosed in an optical waveguide, orthogonal polarized light components sometimes cause the control for making the resonant frequency of the optical frequency comb generator consistent with the laser frequency to become unstable, which becomes a cause of control point deviation, control oscillation, etc. In the case where the optical frequency comb is used in a measuring device for measuring the distance or height to a measurement object, for example, the orthogonal polarized light components can lead to measurement errors.

[0042] Furthermore, as described above, by disposing a protective member having the same hardness as that of a substrate for forming an optical waveguide from the upper surface on the upper portion 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 of the optical waveguide, the incident side reflection film and the emitting side reflection film constituting the resonance part are coated on the above-mentioned plane formed by grinding the end surface of the protective member and the end surface of the substrate, thereby suppressing chipping and rounding when processing the corners of the end surface of the optical waveguide, and making each reflection film stably coated without causing damage to the end surface of the optical waveguide. Partial peeling of the corner at the uppermost part of the end face can improve the reflectivity of the reflective film, the fineness of the optical resonator, and the function of the device itself. However, there is a problem that the thermosetting optical adhesive or photocuring optical adhesive such as epoxy and acrylic series used to bond and fix the protective member to the upper part of the above-mentioned optical waveguide will also emit gas components when heated after curing. When the incident side reflective film and the exit side reflective film are formed as a vapor-deposited film, the amount of emitted gas increases as the vapor deposition temperature rises, and the emitted gas deteriorates the optical properties of the vapor-deposited film.

[0043] Furthermore, optical adhesives have problems such as the deterioration of the adhesive itself due to exceeding the glass transition temperature, a decrease in the strength of the bonded portion, and physical deformation of the deposited film due to deformation.

[0044] Therefore, the present invention is proposed in view of the above-mentioned conventional problems, and its object is to provide the following optical resonator, optical modulator, optical frequency comb generator, optical oscillator, and a method for manufacturing an optical resonator and an optical modulator having the above-mentioned functions, namely: by suppressing defects and rounded corners when processing the corners of the end face of an optical waveguide, a multilayer vapor-deposited film with a reflectivity of 95% to 99% is stably applied as each reflective film without peeling off at the corner portion of the uppermost part of the end face, thereby improving the reflectivity of the reflective film, the fineness of the resonator, and improving the function of the device itself.

[0045] Another object of the present invention is to stabilize the resonator control without causing deformation of the transmission mode waveform of the optical waveguide.

[0046] In addition, another object of the present invention is to suppress the output of orthogonal polarization components that do not contribute to the generation of an optical frequency comb, seek to improve the polarization extinction ratio, and obtain an optical frequency comb output with improved single polarization degree.

[0047] Furthermore, another object of the present invention is to achieve stabilization of an optical frequency comb generator, improvement of the accuracy of a measurement device including an optical frequency comb, reduction of errors, and the like.

[0048] In addition, another object of the present invention is to provide the following optical resonator, optical modulator, optical frequency comb generator, optical oscillator, and a method for manufacturing an optical resonator and an optical modulator having the above functions, namely: without suffering from adverse effects such as degradation of the optical properties of the vapor-deposited film caused by the emitted gas generated by the optical adhesive due to heating, and physical deformation of the vapor-deposited film caused by the decrease in the strength of the bonding part, the multilayer vapor-deposited film with a reflectivity of 95% to 99% is stably covered as each reflective film without peeling off at the corner part of the uppermost part of the end face, thereby being able to improve the reflectivity of the reflective film, the fineness of the resonator, and the function of the device itself. The above-mentioned optical adhesive is used to bond and fix the protective component for suppressing defects and rounding the corners when processing the end face of the optical waveguide to the upper part of the optical waveguide.

[0049] Other objects of the present invention and specific advantages obtainable by the present invention will become more apparent from the description of the embodiments described below.

[0050] Solutions for solving problems

[0051] The present invention is a method for manufacturing an optical resonator, which uses an optical waveguide formed in a manner of penetrating from an incident side reflection film to an exit side reflection film to propagate light incident through the incident side reflection film and cause it to resonate, and is characterized in that the manufacturing method comprises: an optical waveguide forming step, in which the optical waveguide is formed from the upper surface of a substrate; an arranging step, in which a protective member having the same hardness as the substrate is arranged on the upper part of the optical waveguide in a manner that at least one end face thereof forms the same plane as the end face of the substrate including the light incident end or the light exit end of the optical waveguide; and a grinding step, in which the end face of the protective member arranged in the arranging step and the end face of the substrate are ground to form a flat surface including the light incident end or the light exit end of the optical waveguide. The invention relates to a process for forming a plane perpendicular to the optical waveguide by grinding the surface thereof; and a reflective film coating process, in which a single-layer or multi-layer vapor-deposited film is coated on the plane formed in the grinding process as the incident side reflective film or the exit side reflective film. In the arrangement process, the protective member is attached to the upper part of the optical waveguide by using an adhesive. In the reflective film coating process, a multi-layer vapor-deposited film having a reflectivity of 95% to 99% is coated over the entire range of the plane formed by the end face of the protective member attached by using the adhesive and the end face of the substrate under the condition of a temperature lower than the heat resistance temperature of the adhesive and without emitting gas components from the cured adhesive, thereby forming the incident side reflective film or the exit side reflective film on the plane perpendicular to the optical waveguide.

[0052] The present invention is a method for manufacturing an optical modulator, which uses an optical waveguide formed with an incident side reflection film and an exit side reflection film to propagate and modulate light incident through the incident side reflection film, and is characterized in that the manufacturing method comprises: an optical waveguide forming step, in which the optical waveguide is formed from the upper surface of a substrate; a laminating step, in which a buffer layer is laminated on the substrate in a manner that at least covers the optical waveguide formed in the optical waveguide forming step; an electrode forming step, in which an electrode for applying an electric field to the optical waveguide is formed on the buffer layer laminated in the laminating step; an arranging step, in which a protective member having the same hardness as the substrate is arranged on the upper part of the optical waveguide in a manner that at least one end face thereof forms the same plane as the end face of the substrate including the light incident end or the light exit end of the optical waveguide; and a grinding step, in which the protective member arranged in the arranging step is polished by grinding. The end face of the protective member and the end face of the substrate are disposed so as to form a plane perpendicular to the optical waveguide as a flat polished surface including the light incident end or the light exit end of the optical waveguide; and a reflective film coating step, in which a single layer or a multilayer vapor-deposited film is coated on the plane formed in the polishing step as the incident side reflective film or the exit side reflective film. In the arranging step, the protective member is attached to the upper part of the optical waveguide by using an adhesive. In the reflective film coating step, a multilayer vapor-deposited film having a reflectivity of 95% to 99% is coated over the entire range of the plane formed by the end face of the protective member and the end face of the substrate attached by using the adhesive under the condition of a temperature lower than the heat resistance temperature of the adhesive and no gas component is emitted from the cured adhesive, thereby forming the incident side reflective film or the exit side reflective film on the plane perpendicular to the optical waveguide.

[0053] Furthermore, in the method for manufacturing an optical modulator of the present invention, it can be arranged that, in the optical waveguide forming step, the optical waveguide is formed from the upper surface of the substrate having at least an electro-optical effect by proton exchange as a region where a waveguide mode exists only with respect to a single polarization wave component.

[0054] Furthermore, in the manufacturing method of the optical modulator of the present invention, it can be set that the manufacturing method has a ridge structure forming step of forming a ridge structure on the above-mentioned substrate, and in the above-mentioned electrode forming step, an electrode with a ridge structure is formed on the buffer layer stacked on the above-mentioned substrate on which the ridge structure is formed in the above-mentioned stacking step, as an electrode for applying an electric field to the above-mentioned optical waveguide.

[0055] The present invention is an optical resonator, characterized in that the optical resonator includes: a resonance component, which is composed of an incident side reflection film and an exit side reflection film, and causes light incident through the incident side reflection film to resonate; an optical waveguide, which is formed in a manner of penetrating from the incident side reflection film to the exit side reflection film, and propagates the light resonated by the resonance component; a substrate, on the upper surface of which the optical waveguide is formed; and an end face protection component, which is composed of a protection member having the same hardness as the substrate, and at least one end face of the protection member is in contact with a portion of the substrate including a light incident end or a light exit end of the optical waveguide. The protective member is attached to the upper part of the optical waveguide by an adhesive so that the end faces thereof are formed into the same plane. The incident-side reflective film and the exit-side reflective film are multilayer vapor-deposited films having a reflectivity of 95% to 99% and covering a plane perpendicular to the optical waveguide under a temperature condition lower than the heat-resistant temperature of the adhesive and without emitting gas components from the adhesive after curing. The plane is formed by grinding the entire range of the plane formed by the end face of the protective member attached by the adhesive and the end face of the substrate, thereby forming a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

[0056] Furthermore, in the optical resonator of the present invention, it can be configured that the protection member constituting the end face protection member is formed of the same material as the substrate, and further, the end face of the protection member and the end face of the substrate forming the plane have the same crystal orientation as each other, and the end face protection member is arranged on the upper part of the optical waveguide in such a manner that one end face of the protection member and the end face of the substrate including the light incident end of the optical waveguide form the same plane, and the other end face of the protection member and the end face of the substrate including the light emitting end of the optical waveguide form the same plane.

[0057] The present invention is an optical modulator, characterized in that the optical modulator includes: an oscillating component that oscillates a modulation signal of a predetermined frequency; a resonating component that is composed of an incident-side reflection film and an exit-side reflection film and causes light incident through the incident-side reflection film to resonate; an optical waveguide that is formed in a manner of penetrating from the incident-side reflection film to the exit-side reflection film and modulates the phase of the light resonated by the resonating component in accordance with the modulation signal supplied from the oscillating component; a substrate on which the optical waveguide is formed on the upper surface of the substrate; and an end face protection component that is composed of a protection member having the same hardness as the substrate and with at least one end face of the protection member being in contact with the upper surface. The protective member is attached to the upper part of the optical waveguide by using an adhesive so that the end faces of the substrate including the light incident end or the light emitting end of the optical waveguide form the same plane, the incident side reflection film and the emitting side reflection film are multi-layer vapor-deposited films with a reflectivity of 95% to 99% and are attached to a plane perpendicular to the optical waveguide under a temperature condition lower than the heat resistance temperature of the adhesive and without emitting gas components from the adhesive after curing, and the plane is formed by grinding the entire range of the plane formed by the end face of the protective member attached by using the adhesive and the end face of the substrate, thereby serving as a flat grinding surface including the light incident end or the light emitting end of the optical waveguide.

[0058] In addition, the present invention is an optical modulator, characterized in that the optical modulator includes: a resonance component, which is composed of an incident side reflection film and an exit side reflection film, and causes light incident through the incident side reflection film to resonate; an optical waveguide, which is formed in a manner of penetrating from the above-mentioned incident side reflection film to the above-mentioned exit side reflection film; a substrate, on the upper surface of which the above-mentioned optical waveguide is formed; an optical modulation component, which is formed on the above-mentioned substrate and is composed of electrodes for propagating a modulation signal in a forward direction or a backward direction, and modulates the phase of light propagating in the above-mentioned optical waveguide according to the wavelength of the electrical signal supplied to the above-mentioned electrode; and an end face protection component, which is composed of a protection member having the same hardness as the above-mentioned substrate, and the above-mentioned protection member is formed on the upper surface of the substrate. The protective member is attached to the upper part of the optical waveguide by using an adhesive in such a manner that at least one end face of the protective member forms the same plane with the end face of the substrate including the light incident end or the light exit end of the optical waveguide, the incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are attached to a plane perpendicular to the optical waveguide under a temperature condition lower than the heat resistance temperature of the adhesive and without emitting gas components from the adhesive after curing, the plane being formed by grinding the entire range of the plane formed by the end face of the protective member attached by using the adhesive and the end face of the substrate, thereby serving as a flat ground surface including the light incident end or the light exit end of the optical waveguide.

[0059] Furthermore, in the optical modulator of the present invention, the optical waveguide may be formed on the substrate having at least an electro-optical effect as a region where a waveguide mode exists only for a single polarization component.

[0060] Furthermore, in the optical modulator of the present invention, the electrode of the optical modulation element may have a ridge structure.

[0061] The present invention is an optical frequency comb generator, characterized in that the optical frequency comb generator includes: an oscillating component that oscillates a modulation signal of a predetermined frequency; a resonating component that is composed of an incident side reflection film and an exit side reflection film, and causes light incident through the incident side reflection film to resonate; an optical waveguide that is formed in a manner of penetrating from the incident side reflection film to the exit side reflection film, and modulates the phase of the light resonated by the resonating component in accordance with the modulation signal supplied from the oscillating component, and generates sidebands centered on the frequency of the incident light at intervals of the frequency of the modulation signal; a substrate, on the upper surface of which the optical waveguide is formed; and an optical modulation component that is formed on the substrate, and is composed of electrodes for propagating the modulation signal in a forward direction or a return direction, and modulates the phase of the light resonated by the resonating component in accordance with the wavelength of the electrical signal supplied to the electrodes. The phase of light propagating inside the optical waveguide; and an end face protection component, which is composed of a protection member having the same hardness as the above-mentioned substrate, and the above-mentioned protection member is attached to the upper part of the above-mentioned optical waveguide by using an adhesive in such a way that at least one end face of the above-mentioned protection member forms the same plane with the end face of the above-mentioned substrate including the light incident end or the light exit end of the above-mentioned optical waveguide, and the above-mentioned incident side reflection film and the exit side reflection film are multi-layer vapor-deposited films with a reflectivity of 95% to 99% and are covered on a plane perpendicular to the above-mentioned optical waveguide under a temperature condition lower than the heat resistance temperature of the above-mentioned adhesive and without emitting gas components from the above-mentioned adhesive after curing, and the plane is formed by grinding the entire range of the plane formed by the end face of the above-mentioned protection member attached by using the above-mentioned adhesive and the end face of the above-mentioned substrate, thereby serving as a flat grinding surface including the light incident end or the light exit end of the above-mentioned optical waveguide.

[0062] Furthermore, in the optical frequency comb generator of the present invention, it can be set that the optical frequency comb generator further includes a reflection mirror that reflects light that is transmitted to the outside through the incident-side reflection film, among the light resonated by the resonance member.

[0063] The present invention is an optical oscillator, characterized in that the optical oscillator includes: a resonance component, which is composed of an incident side reflection film and an exit side reflection film, and resonates light incident through the incident side reflection film or light generated by laser amplification; an optical waveguide, which is formed in a manner of penetrating from the incident side reflection film to the exit side reflection film, and amplifies the light resonated by the resonance component and emits the light to the outside through the exit side reflection film; a substrate, on the upper surface of which the optical waveguide is formed; an optical modulation component, which is formed on the substrate and is composed of electrodes for propagating a modulated signal in a forward direction or a backward direction, and modulates the phase of light propagating in the optical waveguide according to the wavelength of an electrical signal supplied to the electrodes; and an end face protection component, which is composed of a component having a phase with The protective member is formed of a protective member having the same hardness as the substrate, and the protective member is attached to the upper part of the optical waveguide by using an adhesive in such a way that at least one end face of the protective member forms the same plane as the end face of the substrate including the light incident end or the light exit end of the optical waveguide, and the incident side reflection film and the exit side reflection film are multi-layer vapor-deposited films having a reflectivity of 95% to 99% and covering a plane perpendicular to the optical waveguide under a temperature condition lower than the heat resistance temperature of the adhesive and without emitting gas components from the cured adhesive, and the plane is formed by grinding the entire range of the plane formed by the end face of the protective member attached by using the adhesive and the end face of the substrate, thereby serving as a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

[0064] Furthermore, in the optical oscillator of the present invention, the optical waveguide may be formed by absorbing the light incident through the incident-side reflective film and diffusing the light through a medium having an amplification characteristic with respect to a wavelength of light inherent to the medium.

[0065] Furthermore, in the optical oscillator of the present invention, the optical waveguide may be formed of a nonlinear optical crystal.

[0066] The present invention is an optical oscillator, characterized in that the optical oscillator includes: an oscillating component that oscillates a modulation signal of a predetermined frequency; a resonating component that is composed of an incident-side reflection film and an exit-side reflection film, and resonates light incident through the incident-side reflection film or light generated by laser amplification; an optical waveguide that is formed in a manner of penetrating from the incident-side reflection film to the exit-side reflection film, and amplifies the light resonated by the resonating component in accordance with the modulation signal supplied from the oscillating component, and emits the light to the outside through the exit-side reflection film; a substrate, on the upper surface of which the optical waveguide is formed; an optical modulating component that is formed on the substrate, and is composed of electrodes for propagating the modulation signal in a forward direction or a backward direction, and modulates the phase of the light propagating in the optical waveguide in accordance with the wavelength of the electrical signal supplied to the electrodes; and an end face protecting component that The protective member is formed by a protective member having the same hardness as the substrate, and the protective member is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protective member forms the same plane with the end face of the substrate including the light incident end or the light exit end of the optical waveguide, and the incident side reflection film and the exit side reflection film are multi-layer vapor-deposited films having a reflectivity of 95% to 99% and covering a plane perpendicular to the optical waveguide under a temperature condition lower than the heat resistance temperature of the adhesive and without emitting gas components from the cured adhesive, and the plane is formed by grinding the entire range of the plane formed by the end face of the protective member attached by the adhesive and the end face of the substrate, thereby serving as a flat grinding surface including the light incident end or the light exit end of the optical waveguide, and the incident side reflection film and the exit side reflection film obtain phase synchronization between multiple modes of laser oscillation.

[0067] Effects of the Invention

[0068] In the present invention, a protective member having the same hardness as a substrate for forming an optical waveguide from the upper surface is bonded and arranged on the upper part of the optical waveguide by an adhesive so that at least one end face thereof forms the same plane as the end face of the substrate including the light incident end or the light emitting end of the optical waveguide. On a plane perpendicular to the optical waveguide formed by grinding the end face of the protective member and the end face of the substrate to form a flat ground surface including the light incident end or the light emitting end of the optical waveguide, a multilayer vapor-deposited film having a reflectivity of 95% to 99% is applied as an incident-side reflective film and an exit-side reflective film constituting a resonance part to the entire range of the plane formed by the end face of the protective member and the end face of the substrate. Therefore, it is possible to suppress chipping and rounding when processing the corner of the end face of the optical waveguide, and each reflective film is stably applied without peeling off at the corner portion of the uppermost end face, thereby improving the reflectivity of the reflective film and the fineness of the resonator, thereby improving the function of the device itself. By covering the entire range of the plane formed by the end face of the above-mentioned protective component and the end face of the above-mentioned substrate pasted by the above-mentioned adhesive at a temperature lower than the heat resistance temperature of the above-mentioned adhesive and without emitting gas components from the above-mentioned adhesive after curing, the multilayer vapor-deposited film with a reflectivity of 95% to 99% will not suffer from adverse effects such as degradation of the optical properties of the vapor-deposited film due to emitted gas generated by heating of the above-mentioned adhesive and physical deformation of the vapor-deposited film due to reduced strength of the bonding part. The above-mentioned multilayer vapor-deposited film with a reflectivity of 95% to 99% can be stably covered as each reflective film without peeling off at the corner portion of the uppermost part of the end face.

[0069] In addition, in the present invention, since the optical waveguide is formed as a region where a waveguide mode exists only for a single polarization wave component in a substrate having at least an electro-optical effect so as to penetrate from the incident end to the exit end, only the single polarization wave component of the light incident through the incident side reflection film propagates in the optical waveguide and is phase modulated and emitted from the exit end. By including the incident side reflection film and the exit side reflection film constituting the resonance part, a light comb can be generated as a light modulated output of only a single polarization wave component through the exit side reflection film.

[0070] Furthermore, in the present invention, by including an optical modulation component that is formed on an optical waveguide formed in a substrate having at least an electro-optical effect, and modulating the phase of light propagating in the above-mentioned optical waveguide in accordance with a modulation signal supplied to an electrode having a ridge structure for propagating the modulation signal in a forward direction or a return direction, the power of microwaves used as the modulation signal required for driving can be reduced.

[0071] That is, according to the present invention, the optical waveguide has a multilayer vapor-deposited film with a reflectivity of 95% to 99% as a light incident end face and a light emitting end face formed on a plane perpendicular to the optical waveguide under a temperature condition that is lower than the heat resistance temperature of the above-mentioned adhesive and does not emit gas components from the above-mentioned adhesive after curing, and includes an electrode with a ridge structure, and the plane is obtained by grinding the end face of a protective member having the same hardness as the substrate used to form the optical waveguide and the end face of the above-mentioned substrate, thereby suppressing defects and rounded corners when processing the corners of the optical waveguide end face. By using the above-mentioned optical waveguide, it is possible to provide an optical modulator and an optical comb generator that can achieve low-power drive and can achieve energy saving, low heat generation, miniaturization and light weight, improved reliability, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 This is a diagram showing the principle structure of a conventional optical frequency comb generator.

[0073] Figure 2 This is a diagram showing the principle structure of a conventional waveguide type optical frequency comb generator.

[0074] Figure 3 This is a diagram showing an end surface of a conventional waveguide type optical frequency comb generator on which an incident side reflection film is formed.

[0075] Figure 4 This is a characteristic diagram showing deformation of a transmission mode waveform caused by orthogonal polarization components, which occurs when the resonance length of an optical resonator is feedback-controlled in a conventional optical comb generator using an optical waveguide that transmits polarization components mixed in orthogonal modes.

[0076] Figure 5 It is a diagram showing the structure of an optical modulator to which the present invention is applied.

[0077] Figure 6 is a side view of an optical modulator to which the present invention is applied.

[0078] Figure 7 This is a diagram showing a plane on which a reflection film on the incident side of the light modulator to which the present invention is applied is formed.

[0079] Figure 8 In Figure 8 (A) Figure 8 (B) Figure 8 (C) Figure 8 (D) Figure 8 (E) Figure 8 (F) is a longitudinal cross-sectional view of a main part for explaining each step of a method for producing a light modulator to which the present invention is applied.

[0080] Fig. 9 It is a diagram for explaining the experimental results of the loss characteristics of the optical modulator to which the present invention is applied.

[0081] Fig.10 The diagram shows the structure of a light modulator having a wafer that serves as both a protective member and a buffer layer.

[0082] Fig.11 In Fig.11 (A) Fig.11 (B) Fig.11 (C) is a diagram showing a configuration example of a reciprocating modulation type optical modulator to which the present invention is applied.

[0083] Fig.12 This is a diagram showing the intensity distribution of each frequency (wavelength) of the sideband when the present invention is applied to an optical frequency comb generator.

[0084] Fig.13 This is a diagram showing the structure of an optical waveguide type laser oscillator to which the present invention is applied.

[0085] Fig.14 In Fig.14 (A) Fig.14 (B) is a diagram showing the structure of a laser oscillator to which the present invention is applied.

[0086] Fig.15 It is a diagram showing a structural example of a modified FP electro-optical modulator to which the present invention is applied.

[0087] Fig.16 In Fig.16 (A) Fig.16 (B) is a diagram for explaining an example of a communication system in which the optical modulator to which the present invention is applied is mounted in a base station.

[0088] Fig.17 In Fig.17 (A) Fig.17 (B) is a diagram for explaining a case where the length of the optical modulator to which the present invention is applied is limited.

[0089] Fig.18 This is another diagram for explaining a case where the length of the optical modulator to which the present invention is applied is limited.

[0090] Fig.19 It is a perspective view showing another structural example of the light modulator to which the present invention is applied.

[0091] Fig. 20 is a side view of the above-mentioned light modulator.

[0092] Fig.21 In Fig.21 (A) Fig.21 (B) Fig.21 (C) Fig.21 (D) Fig.21(E) Fig.21 (F) is a longitudinal sectional view of a main part for explaining each step of the method for manufacturing the above-mentioned light modulator.

[0093] Fig. 22 This is a perspective view of a substrate provided with three optical waveguides produced for measuring the end face reflectivity of the optical modulator to which the present invention is applied.

[0094] Fig.23 It is a front view showing the incident side end surface of the above-mentioned substrate.

[0095] Fig.24 is a top view of the above-mentioned substrate.

[0096] Fig.25 It is a perspective view showing the structure of an optical modulator (optical comb generator) including an electrode having a ridge structure to which the present invention is applied.

[0097] Fig.26 In Fig.26 (A) Fig.26 (B) Fig.26 (C) Fig.26 (D) Fig.26 (E) Fig.26 (F) Fig.26 (G) is a longitudinal cross-sectional view of the main parts for explaining each step of the method for manufacturing the above-mentioned light modulator (optical comb generator).

[0098] Fig. 27 It is a perspective view showing a substrate on which an electrode having a ridge structure is formed in the above-mentioned optical modulator (optical comb generator).

[0099] Fig.28 It is a longitudinal sectional front view of the main part showing an electrode having a ridge structure of the above-mentioned optical modulator (optical comb generator).

[0100] Fig.29 This is a diagram for explaining the results of actually measuring changes in the driving voltage (AC Vpi) at 25 GHz due to the presence or absence of the ridge structure of the electrode for the optical modulator to which the present invention is applied.

[0101] Fig.30 This is a diagram for explaining the results of actually measuring changes in direct current driving voltage (DC Vpi) due to the presence or absence of a ridge structure of an electrode for an optical modulator to which the present invention is applied.

[0102] Fig.31 This is a block diagram showing a configuration example of an optical comb generator using a low-power optical comb unit to which the present invention is applied.

[0103] Fig.32This is a block diagram showing another configuration example of an optical comb generator using a low-power optical comb unit to which the present invention is applied.

[0104] Fig.33 This is a block diagram showing a configuration example of an optical comb light source constructed using a low-power optical comb unit to which the present invention is applied.

[0105] Fig.34 This is a block diagram showing the structure of an optical comb distance meter formed using the above-mentioned optical comb light source.

[0106] Fig.35 This is a characteristic diagram showing a transmission mode waveform without deformation obtained when the resonance length of an optical resonator is feedback-controlled in an optical comb generator using an optical waveguide that transmits only a single polarization component to which the present invention is applied. DETAILED DESCRIPTION

[0107] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, common components are labeled with common reference numerals in the drawings for description. In addition, the present invention is not limited to the following examples, and it is self-evident that it can be arbitrarily changed within the scope of the gist of the present invention.

[0108] The present invention is applied to Figure 5 , Figure 6 The optical modulator 8 shown in FIG. 8 includes: a substrate 11; an optical waveguide 12 formed on the substrate 11 and used to modulate the phase of propagating light; a buffer layer 14 stacked on the substrate 11 in a manner covering the optical waveguide 12; an electrode 83 provided on the upper surface of the optical waveguide 12 in a manner that the direction of the modulated electric field is substantially perpendicular to the propagation direction of the light; a first end face 84 and a second end face 85 provided in a manner opposite to each other with the optical waveguide 12 interposed therebetween; and a first protective member 86 provided on the upper surface of the optical waveguide 12 in a manner that forms the same plane as the first end face 84. a second protective member 87 disposed on the upper portion of the optical waveguide 12 in such a manner as to form the same plane as the second end face 85; an incident side reflective film 93 consisting of a single layer or a multilayer evaporated film covering a plane 91 formed between the first end face 84 and the end face 86a of the first protective member 86; an emitting side reflective film 94 consisting of a single layer or a multilayer evaporated film covering a plane 92 formed between the second end face 85 and the end face 87a of the second protective member 87; an oscillator 16 disposed on one end side of the electrode 83 for causing the frequency f m and a terminal resistor 18 disposed on the other end side of the electrode 83.

[0109] The substrate 11 is obtained by slicing a large crystal of LiNbO3, GaAs or the like with a diameter of 3 to 4 inches grown by the Czochralski method into a wafer shape. The sliced ​​substrate 11 is subjected to mechanical polishing, chemical polishing or the like.

[0110] The optical waveguide 12 is formed so as to penetrate from the incident side reflection film 93 to the exit side reflection film 94, and is formed so as to propagate the resonated light. The refractive index of the layer constituting the optical waveguide 12 is set higher than the refractive index of other layers such as the substrate 11. The light incident on the optical waveguide 12 propagates by total reflection 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 epitaxial growth on the substrate 11.

[0111] In addition, a LiNbO3 crystal optical waveguide can also be used as the optical waveguide 12. The LiNbO3 crystal optical waveguide can be formed by diffusing Ti on the surface of a substrate 11 formed of LiNbO3 or the like. Since light can be confined when the refractive index of the area where the Ti is diffused becomes higher than the refractive index of other areas, an optical waveguide 12 capable of propagating light can be formed. The LiNbO3 crystal type optical waveguide 12 manufactured based on such a method has electro-optical effects 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, and thus it is possible to modulate light using this physical phenomenon.

[0112] The buffer layer 14 covers the optical waveguide 12 to suppress the propagation loss of light in the optical waveguide 12. If the buffer layer 14 is too thick, the electric field intensity decreases and the modulation efficiency decreases. Therefore, the thickness may be set as thin as possible within a range that does not increase the propagation loss of light.

[0113] The electrode 83 is formed of a metal material such as Ti, Pt, Au, etc., and is provided with a frequency f m The modulation signal is driven input to the optical waveguide 12 to apply phase modulation to the light propagating in the optical waveguide 12.

[0114] The first protective member 86 and the second protective member 87 are respectively made of a member corresponding to the material of the substrate 11. The first protective member 86 and the second protective member 87 may also be made of the same material as the substrate 11. In addition, the end face 86a and the first end face 84 of the first protective member 86 forming the above-mentioned plane 91 may be processed to have the same crystal orientation as each other, and the end face 87a and the second end face 85 of the second protective member 87 forming the above-mentioned plane 92 may also be processed to have the same crystal orientation as each other.

[0115] The incident-side reflective film 93 and the outgoing-side reflective film 94 are provided in parallel with each other so as to resonate the light incident on the optical waveguide 12 , and constitute the optical resonator 5 which resonates the light passing through the optical waveguide 12 by reciprocating reflections.

[0116] Light of frequency ν1 is incident on the incident side reflection film 93 from a light source not shown. In addition, the incident side reflection film 93 reflects the light that has been reflected by the exit side reflection film 94 and has passed through the optical waveguide 12. The exit side reflection film 94 reflects the light that has passed through the optical waveguide 12. In addition, the exit side reflection film 94 emits the light that has passed through the optical waveguide 12 to the outside at a certain ratio.

[0117] Furthermore, the incident-side reflective film 93 and / or the outgoing-side reflective film 94 may be formed on the entire surface of the flat surfaces 91 and 92 , respectively, but may be formed to cover only the end portion of the optical waveguide 12 at a minimum.

[0118] The terminal resistor 18 is a resistor mounted at the terminal of the electrode 83, and prevents the reflection of the electric signal at the terminal to prevent the waveform from being disturbed.

[0119] Figure 7 from Figure 6 The A direction in φ indicates the plane 91 on which the incident-side reflecting film 93 is formed.

[0120] The first end face 84 including the light incident end of the optical waveguide 12 and the end face 86a of the protective member 86 form a common plane 91. The slope of the formed plane 91 is 0.05° or less. For the plane 91 with a slope of 0.05°, when calculating 1 / e 2 When a beam of light with a diameter of 10 μm is reflected by an end face with a slope of 0.05°, the loss is 4×10 －4 , which is so small as to be almost negligible compared to the reflectivity of the incident-side reflective film 93 .

[0121] By forming the first end face 91 and the second end face 92 substantially perpendicular to the optical waveguide 12 in this manner, light can be efficiently resonated by the incident side reflection film 93 and the emission side reflection film 94 coated on these end faces as single-layer or multi-layer vapor-deposited films.

[0122] In the optical modulator 8 having the above-described structure, light incident from the outside via the incident-side reflective film 93 propagates in the forward direction in the optical waveguide 12, is reflected by the output-side reflective film 94, and partially transmits to the outside. Light reflected by the output-side reflective film 94 propagates in the return direction in the optical waveguide 12, and is reflected by the incident-side reflective film 93. By repeating this process, light resonates in the optical waveguide 12.

[0123] Furthermore, by driving the input of an electrical signal synchronized with the time of the light reciprocating in the optical waveguide 12 via the electrode 83, a phase modulation several tens of times deeper can be applied compared to the case where the light passes through the optical modulator 8 only once. In addition, hundreds of sidebands can be generated in a wide bandwidth with the frequency ν1 of the incident light as the center. In addition, the frequency intervals of the generated sidebands are all consistent with the frequency f of the input electrical signal. m Therefore, the optical modulator 8 can also be used as an optical frequency comb generator composed of multiple sidebands.

[0124] Next, use Figure 8 A method for manufacturing the optical modulator 8 to which the present invention is applied will be described.

[0125] First, in step S11, Figure 8 As shown in (A), a photoresist pattern is formed on the surface of a substrate 11 composed of LiNbO3 crystals, and Ti is vapor-deposited thereon. Then, the photoresist is removed to form a thin line of Ti with a width of micrometer size.

[0126] Then move to step S12, as Figure 8 As shown in (B), by heating the substrate 11 on which the Ti thin wires are formed, Ti atoms are thermally diffused into the substrate 11 to form the optical waveguide 12 .

[0127] Then move to step S13, as Figure 8 As shown in (C), a SiO2 thin film is vapor-deposited on the surface of the substrate 11 as a buffer layer 14. In this step S13, the buffer layer 14 can also be formed by attaching a SiO2 wafer to the surface of the substrate 11. In this case, considering the mounting area of ​​the electrode in the later-described step S14, the vapor-deposited buffer layer 14 can also be controlled to an appropriate film thickness by grinding.

[0128] Then move to step S14, as Figure 8 As shown in (D), an electrode 83 is formed on the buffer layer 14. Then, the process proceeds to step S15. Figure 8 As shown in (E), protective members 86 and 87 are bonded to the upper part of the optical waveguide 12. As for the bonding method of the protective members 86 and 87, they can be bonded by adhesive or directly bonded by other methods. In the case where the substrate 11 is composed of LiNbO3 crystals, the protective members 86 and 87 can be composed of LiNbO3 as the same material. In this step S15, the bonded protective members 86 and 87 are cut to form a plane 91 between the end face 86a and the first end face 84, and a plane 92 between the end face 87a and the second end face 85.

[0129] As the adhesive used when bonding the protective members 86 and 87 to the upper portion of the optical waveguide 12, a thermosetting optical adhesive such as an epoxy-based adhesive or an acrylic-based adhesive or a photocuring optical adhesive is used.

[0130] Finally, move to step S16, such as Figure 8 As shown in (F), the planes 91 and 92 thus obtained are polished to be planes perpendicular to the optical waveguide 12. Then, an incident side reflection film 93 and an outgoing side reflection film 94 are formed on the polished planes 91 and 92 perpendicular to the optical waveguide 12 over the entire surface.

[0131] Here, the incident side reflection film 93 and the outgoing side reflection film 94 are formed by depositing a single layer or a multilayer of vapor-deposited films on the flat surfaces 91 and 92 by vapor deposition, sputtering, chemical vapor growth, or the like.

[0132] When forming the incident side reflection film 93 and the exit side reflection film 94 as vapor-deposited films, the vapor deposition process is performed under temperature conditions lower than the heat resistance temperature, for example, the glass transition temperature Tg, of the optical adhesive used when bonding the protective members 86 and 87 to the upper part of the optical waveguide 12 .

[0133] Thus, in the optical modulator 8 to which the present invention is applied, since the protective members 86 and 87 are attached to the respective ends, the end face of the conventional optical waveguide 12 at the uppermost corner of the end face is Figure 7 As shown in FIG. 1 , the flat surface 91 (92) is moved to the approximate center of the flat surface 91 (92). As a result, even if the corner of the flat surface 91 (92) is damaged during the polishing in step S16, the end face of the optical waveguide 12 will not be damaged. In other words, the end face of the optical waveguide 12 itself can be configured to be difficult to be damaged. As a result, the light loss from each end face of the optical waveguide 12 can be minimized.

[0134] Furthermore, by forming the material of the protective members 86 and 87 with the best material corresponding to the material of the substrate 11, the polishing speed in step S16 can be made uniform in the range from the first end face 84 and the second end face 85 to the end faces 86a and 87a of the substrate 11. As a result, the end face of the optical waveguide 12 does not become rounded during processing, and the planes 91 and 92 perpendicular to the optical waveguide 12 formed of the flat polished surface can be obtained, and the reflection loss of the end face of the optical waveguide 12 can be suppressed to the minimum. In addition, the reflection loss can be further suppressed by making the crystal orientation of the end faces constituting the respective planes 91 and 92 the same.

[0135] Furthermore, by intentionally providing the protection members 86 and 87, the polishing accuracy in step S16 is improved, and the perpendicularity of the obtained flat surface 91 (92) to the optical waveguide 12 is also improved. As a result, the light loss caused by the loss of perpendicularity can be minimized.

[0136] Furthermore, by providing the protective members 86 and 87, it is possible to suppress the change in the film thickness of the incident side reflection film 93 and the emission side reflection film 94 to be coated as a single layer or a multilayer vapor-deposited film, which is caused by the spread of film-forming particles from the planes 91 and 92 to other side surfaces and the spread of film-forming particles flying from the side surfaces to the end surfaces. Therefore, the film thickness near the end surface of the optical waveguide 12, which is important in ensuring the reflectivity, can be optimized, and the reflectivity can be further improved.

[0137] Furthermore, since the incident side reflection film 93 and the exit side reflection film 94 are formed in a wide range from the first end face 84 and the second end face 85 of the substrate 11 to the end faces 86a and 87a, they are very stable and difficult to peel off, and the reproducibility of film formation can be further improved.

[0138] In fact, when the plane 91 (92) was polished after the protective components 86 and 87 were attached in order to experimentally verify the effect of setting the protective components 86 and 87, it was confirmed that there was no defect or bending in the end face portion of the optical waveguide 12, and a flat optical polishing suitable for covering the incident side reflection film 93 and the exit side reflection film 94 composed of a single layer or a multi-layer vapor-deposited film was implemented.

[0139] In particular, the first protective member 86 and the second protective member 87 are made of the same material as the substrate 11, and the end faces 86a, 87a of the protective members 86, 87 that are processed to form planes 91, 92 and the first end face 84, the second end face 85 have the same crystal orientation as each other, so that the hardness of the crystal is the same between the two, and therefore the planes 91, 92 will not be tilted due to the difference in grinding speed.

[0140] Thus, 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 to the respective ends, thereby achieving the reduction of the end face damage and rounding of the optical waveguide 12, ensuring the perpendicularity between the optical waveguide 12 and the planes 91 and 92, improving the grinding accuracy of the planes 91 and 92, reducing the peeling and spreading of the incident side reflection film 93 and the exit side reflection film 94, improving the reflectivity of the incident side reflection film 93 and the exit side reflection film 94, achieving the designed reflection characteristics, and improving the performance reproducibility of the reflection film. As a result, the fineness of the optical resonator 5 composed of the incident side reflection film 93 and the exit side reflection film 94 can be improved, and an optical modulator and an optical frequency comb generator with better performance can be manufactured with better reproducibility, and the yield rate can also be improved.

[0141] The optical modulator 8 having the above structure was fabricated by coating the polished flat surfaces 91 and 92 with reflective films 93 and 94 having a reflectivity of 97% as single-layer or multi-layer vapor-deposited films. As a result, when the crystal length of the optical waveguide 12 was set to 27.4 mm (hereinafter referred to as a short resonator), a maximum fineness of 61 was obtained. When the crystal length of the optical waveguide 12 was set to 54.7 mm (hereinafter referred to as a long resonator), a maximum fineness of 38 was obtained. Since the maximum fineness of the conventional waveguide type optical resonator (IEEE Photonics Technology Letters, Vol. 8, No. 10, 1996) was 30, it was found that the optical modulator 8 with improved end surface polishing and coating accuracy could significantly improve fineness. In particular, all six samples of the fabricated optical modulator 8 were able to obtain fineness of more than 30, which also indicates that the reproducibility of the fabrication process is high.

[0142] That is, by using an optical adhesive to adhere protective members 86, 87 having the same hardness as that of the substrate 11 for forming the optical waveguide 12 from the upper surface to the upper portion of the optical waveguide 12 in such a manner that at least one end face thereof forms the same plane 91, 92 as the end face of the substrate 11 including the light incident end or the light emitting end of the optical waveguide 12, the end faces of the protective members 86, 87 and the end faces of the substrate 11 are polished, thereby forming planes 91, 92 perpendicular to the optical waveguide 12 as flat polished surfaces including the light incident end or the light emitting end of the optical waveguide 12. Furthermore, by applying the reflective film as a single-layer or multi-layer vapor-deposited film to the entire range of the planes 91 and 92 formed by the end faces of the protective members 86 and 87 and the end face of the substrate 11 attached by the adhesive under a temperature condition lower than the heat resistance temperature of the adhesive, the optical properties of the vapor-deposited film are not deteriorated due to the gas emitted by the adhesive when heated, the physical deformation of the vapor-deposited film is not affected by the strength reduction of the bonding portion, and the single-layer or multi-layer vapor-deposited film can be stably applied as each reflective film 93 and 94 without peeling off at the corner of the uppermost part of the end face. As a result, it is possible to suppress the defect and rounded corner when processing the corner of the end face of the optical waveguide 12, and to apply the reflective film 93 and 94 stably without peeling off at the corner of the uppermost part of the end face, so that the reflectivity of the reflective film 93 and 94 and the fineness of the resonator can be improved, thereby improving the function of the device itself.

[0143] Fig. 9 ∝ represents the internal loss of the optical resonator 5 in each propagation direction of the optical waveguide 12 in either the forward direction or the return direction. Fig. 9In the figure, the loss in each propagation direction of the optical modulator 8 composed of the above-mentioned long resonator is measured for three samples and plotted (indicated by ● in the figure), and the loss in each propagation direction of the optical modulator 8 composed of the short resonator is measured for three samples and plotted (indicated by ■ in the figure), and the plots are approximated by straight lines.

[0144] Based on the obtained straight line, when the reflectivity of the reflection films 93 and 94 is defined as R and the loss per unit length of the optical waveguide 12 is defined as α, when the loss itself is small, Ls=α is used. l -lnR represents the internal loss Ls in each propagation direction of the optical waveguide 12 of the optical resonator 5 of length l. When the measured fineness is set to F, the loss Ls in each propagation direction is obtained by Ls = π / F. When the internal loss Ls is obtained from the measured fineness F and converted into coordinates, Fig. 9 As shown, it can be seen that as the crystal length of the optical waveguide 12 increases, the internal loss caused by the optical waveguide 12 increases.

[0145] In addition, in this Fig. 9 In the case where the length of the optical resonator 5 is 0, the internal loss is based on the loss generated at the crystal end face. That is, since the reflective films 93 and 94 with a reflectivity of 97% (transmittance of 3%) are coated, a minimum loss of 3% is generated. Fig. 9 It can be seen that there is no significant loss except for the transmission through the reflective films 93 and 94 on the planes 91 and 92 .

[0146] The waveguide loss rate of the optical waveguide is made consistent with the transmittance of the mirror, which increases the fineness and transmittance of the resonator and improves 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 single pass, when the reflective film 93, 94 with a reflectivity in the range of 95% to 99% is applied, an optical resonator with better performance can be manufactured.

[0147] Similarly, when the optical modulator 8 is applied to an optical frequency comb generator, the flat surfaces 91 and 92 are polished and the incident side reflection film 93 and the exit side reflection film 94 are applied with the protective members 86 and 87 attached, so that the reflectivity of these reflection films 93 and 94 can be increased. As a result, the fineness of the optical resonator 5 can be increased, and the frequency band of the sideband generation can be expanded.

[0148] Furthermore, when the optical modulator 8 is applied to an optical frequency comb generator, the incident side reflective film 93 may be replaced with a narrowband filter that transmits only the light incident into the optical waveguide 12 and reflects the sideband generated in the optical waveguide 12. By replacing with such a narrowband filter, the conversion efficiency from the incident light to the sideband can be improved.

[0149] Similarly, the exit-side reflective film 94 can also be replaced with a filter for flattening the output spectrum. In a conventional optical frequency comb generator, the light intensity of the obtained sideband decreases exponentially as the order increases. Therefore, by replacing the exit-side reflective film 94 with a filter having a characteristic of offsetting the decrease in light intensity corresponding to the order, the light intensity of each obtained sideband can be flattened.

[0150] In addition, both the incident-side reflection film 93 and the outgoing-side reflection film 94 may be replaced with the above-mentioned filters, or either one of the reflection films 93 and 94 may be replaced with the above-mentioned filters.

[0151] In addition, the optical modulator 8 and the optical frequency comb generator using the optical modulator 8 of the present invention are monolithic in which the incident side reflection film 93 and the emission side reflection film 94 are directly formed on the planes 91 and 92. In other words, since the optical modulator 8 is not structured in which the reflection films 93 and 94 are provided at positions spatially separated from the planes 91 and 92, the FSR (Free Spectral Range) of the optical resonator 5 is controlled by the crystal length from the plane 91 to the plane 92 of the crystal constituting the optical waveguide 12 after polishing in step S16. Therefore, the optical modulator 8 requires extremely precise control of the crystal length so that an integral multiple of the FSR of the optical resonator 5 becomes a desired modulation frequency.

[0152] For example, when the FSR of the optical resonator 5 is adjusted to the frequency f FSR When the group refractive index n of the optical waveguide 12 is consistent with g and the average value τ of the group delay time of the incident side reflection film 93 and the exit side reflection film 94 g , so that the crystal length L of the optical waveguide 12 (the distance from the first end face 84 to the second end face 85 of the substrate 11) satisfies the following formula (1):

[0153] L=c / 2n g f FSR -cτ g / n g ……(1)

[0154] (c is the speed of light in a vacuum), so that the FSR of the optical resonator 5 can be FSR Consistent, can greatly improve the modulation efficiency.

[0155] In addition, the present invention is not limited to the above-mentioned embodiment. Fig.10 The optical modulator 9 shown in FIG. 1 is the same as the optical modulator 8 in the optical modulator 9. Figure 5 , Figure 6 The instructions in , omit the instructions here.

[0156] The optical modulator 9 includes: a substrate 11; an optical waveguide 12, which is formed on the substrate 11 and is used to modulate the phase of propagating light; a wafer 95, which is arranged on the upper surface of the optical waveguide 12; an electrode 83, which is arranged on the upper surface of the wafer 95 in a manner that the direction of the modulated electric field is approximately perpendicular to the propagation direction of the light; a first end face 84 and a second end face 85, which are arranged in a manner opposite to each other across the optical waveguide 12; an incident side reflection film 93, which is covered on a plane 101 formed between the first end face 84 and the end face 96a of the wafer 95 and is composed of a single layer or a multi-layer vapor-deposited film; and an exit side reflection film 94, which is covered on a plane 102 formed between the second end face 85 and the end face 97a of the wafer 95 and is composed of a single layer or a multi-layer vapor-deposited film.

[0157] Similar to the above-mentioned optical modulator 8, the optical modulator 9 is also connected to a frequency f m The modulated signal oscillates an oscillator (not shown) and a terminal resistor (not shown).

[0158] The wafer 95 is made of SiO2 or the like, and is formed in a Japanese U-shape with a length substantially the same as that of the optical waveguide 12. The wafer 95 is formed thick only at the end, and is formed thin only at the center where the electrode 83 is disposed. Thus, the electrode 83 can efficiently apply a modulated electric field to the light propagating in the optical waveguide 12.

[0159] The wafer 95 serves as the buffer layer 14 described above, and suppresses light loss by covering the optical waveguide 12 formed just below the surface of the substrate 11. In addition, the wafer 95 also serves as the first protective member 86 and the second protective member 87 of the optical modulator 8 described above, and is cut so that a plane 101 is formed between the end face 96a and the first end face 84, and a plane 102 is formed between the end face 97a and the second end face 85.

[0160] When the wafer 95 is provided, a SiO2 wafer having the same thickness as the end portion is attached to the substrate 11, and then the portion where the electrode 83 is provided is cut out, so that the wafer 95 can be finished into Fig.10 The Japanese U-shaped character shown.

[0161] That is, the optical modulator 9 has the advantage that the same effect as that of the optical modulator 8 can be obtained and the labor of mounting the protective member can be saved.

[0162] In addition, the present invention is not limited to the above-mentioned embodiment. Fig.11 The reciprocating modulation type optical modulator 51 shown in FIG. The same configuration and elements as those of the above-mentioned optical modulator 8 in the optical modulator 51 are referred to as Figure 5 , Figure 6 The instructions in , omit the instructions here.

[0163] In addition, the light modulator 51 is provided with an exit-side reflection film 94 composed of a single-layer or multi-layer vapor-deposited film as a high reflection film at one end of the optical waveguide 12, and an anti-reflection film 63 composed of a single-layer or multi-layer vapor-deposited film is provided at the other end, so that Fig.11 The optical modulator 51 shown in the figure can also operate as a so-called reciprocating modulation type.

[0164] like Fig.11 As shown in (A), the optical modulator 51 includes: a substrate 11; an optical waveguide 12, which is formed on the substrate 11 and is used to modulate the phase of the propagating light; a buffer layer 14, which is stacked on the substrate 11 in a manner covering the optical waveguide 12; an electrode 83, which is arranged on the upper surface of the optical waveguide 12 in a manner that the direction of the modulated electric field is approximately perpendicular to the propagation direction of the light; a first protective member 86 and a second protective member 87, which are arranged on the upper part of the optical waveguide 12; an anti-reflection film 63, which is covered on the plane 91 and is composed of a single layer or a multi-layer vapor-deposited film; and an output side reflection film 94, which is covered on the plane 92 and is composed of a single layer or a multi-layer vapor-deposited film.

[0165] In addition, if Fig.11 As shown in (B), when the optical modulator 51 is actually used, an optical system is also installed, which includes: an optical transmission path 23, which is composed of an optical fiber for transmitting input light from a light source not shown in the figure or output light output from the optical modulator 51 to the outside; an optical circulator 21, which is used to separate the above-mentioned input light and output light; and a focusing device 22, which is optically connected to the optical circulator 21. When the optical modulator 51 is actually used, a focusing device 22 is also provided on one end side of the electrode 83 and used to make the frequency f m The oscillator 16 that oscillates the modulated signal and the phase shifter 19a and reflector 19b located on the other end side of the electrode 83.

[0166] The antireflection film 63 is applied to the flat surface 91 formed between the first end surface 84 and the end surface 86a of the first protective member 86. The antireflection film 63 may be a low-reflection film or may be uncoated to obtain the same effect as that of a low-reflection film.

[0167] The focusing device 22 focuses the input light that has passed through the optical circulator 21 toward the end of the optical waveguide 12, and collects the output light that has passed through the anti-reflection film 63 from the end of the optical waveguide 12, and transmits the light to the optical circulator 21. The focusing device 22 may be composed of a lens or the like for optically coupling the input light so that the spot diameter corresponds to the diameter of the optical waveguide 12.

[0168] The optical modulator 51 having such a structure operates as a so-called reciprocating modulation type optical modulator by providing an exit-side reflection film 94 as a high reflection film at one end of the optical waveguide 12 and providing an anti-reflection film 63 at the other end. The input light incident on the optical waveguide 12 is modulated while propagating in the optical waveguide 12, and after being reflected by the exit-side reflection film 94 at the end face, propagates in the optical waveguide 12 again, passes through the anti-reflection film 63, and is emitted to the focuser 22 side, thereby becoming output light. At the same time, the frequency f supplied from the oscillator 16 is modulated. m The electrical signal propagates on the electrode 83 while modulating the input light and is then reflected by the reflector 19b.

[0169] In the optical modulator 51, the frequency f oscillated by the oscillator 16 is supplied to the electrode 83. m When a modulated signal is transmitted to the electrode 83, the modulated signal will propagate in the forward direction in the electrode 83, and the phase of the light propagating in the forward direction in the optical waveguide 12 can be modulated. The modulated signal propagating in the forward direction on the electrode 83 is directly reflected by the reflector 19b, and after the phase is adjusted by the phase shifter 19a, it propagates in the return direction in the electrode 83 the next time. Thus, the phase of the light propagating in the return direction in the optical waveguide 12 can be modulated. In addition, the phase adjusted by the phase shifter 19a may be such that the phase modulation performed on the light propagating in the return direction in the optical waveguide 12 is the same as the phase shift modulation performed on the light propagating in the forward direction.

[0170] In the optical modulator 51 , phase modulation is performed not only on the light propagating in the forward direction but also on the light propagating in the return direction in the optical waveguide 12 , so that the modulation efficiency can be increased.

[0171] Furthermore, in the optical modulator 51, by driving the input of an electrical signal synchronized with the time when the light reciprocates in the optical waveguide 12 from the electrode 83, a phase modulation several tens of times deeper can be applied compared to the case where the light passes through the optical waveguide 12 only once. In this way, an optical frequency comb having sidebands across a wide frequency band can be generated, and the frequency intervals of adjacent sidebands are all the same as the frequency f of the input electrical signal. m Equivalent.

[0172] Furthermore, since the optical modulator 51 can push light into a narrow optical waveguide 12 for modulation, the modulation index can be increased, and it can function as an optical frequency comb generator 1, and can increase the number of generated sidebands and the amount of sideband light compared to a bulk-type optical frequency comb generator.

[0173] In the optical frequency comb generator 1 using the optical modulator 51, the shape of the electrode 83 and the frequency f of the modulation signal are adjusted. m and the group refractive index n of the optical waveguide 12 gThe phase of the modulation signal reflected by the reflector 19b and adjusted by the phase shifter 19a is adjusted accordingly to align the phase of the light with high precision, so that phase modulation can be efficiently performed not only on the light propagating in the forward direction in the optical waveguide 12 but also on the light propagating in the return direction, and the modulation efficiency can be increased to nearly twice at most. In addition, since the modulation efficiency can be effectively improved without increasing the voltage applied to the electrode 83, the power consumption can be reduced, the heterodyne detection system equipped with the optical frequency comb generator 1 can be slimmed down, and the cost can be greatly reduced.

[0174] In addition, the optical modulator 51 may also be Fig.11 As shown in (C), an oscillator 25 and a terminal resistor 27 are provided on one end side of the electrode 83, so that the electric signal supplied from the oscillator 25 is propagated on the electrode 83 and then reflected on the other end side of the electrode 83. At this time, an isolator 26 for separating the electric signal supplied from the oscillator 25 and the electric signal reflected on the other end side of the electrode 83 may also be provided. In addition, in the optical modulator 51, an incident side reflection film 93 composed of a single layer or a multilayer vapor-deposited film with a high reflectivity is covered. Thus, light can be resonated inside the optical waveguide 12. In addition, as an alternative to the incident side reflection film 93, the above-mentioned anti-reflection film 63 with a low reflectivity may also be covered. Thus, phase modulation can also be implemented while making the light reciprocate only once in the optical waveguide 12.

[0175] In the optical modulator 51, the reflected phase of the electric signal is adjusted to match the phase of the light reflected by the emission-side reflective film 94, so that the phase of the light can be modulated by the electric signal reciprocating in the electrode 83, respectively, and thus the modulation efficiency can be increased. In particular, in the optical modulator 51 in which the peeling, defect, etc. of the films 63, 93, 94 are suppressed as described above by attaching the protective members 86 and 87 and the fineness is further improved, the light modulation efficiency can be further increased.

[0176] Furthermore, when the optical modulator 51 is applied to an optical frequency comb generator, the light resonating in the optical waveguide 12 can be reciprocally modulated by the electrical signal reciprocating in the electrodes. In this case, the intensity distribution of each frequency (wavelength) of the generated sideband is as follows: Fig.12 As shown in FIG. 1 , when the modulation frequency of the electric signal applied to the electrode 83 is set to 25 GHz and the power thereof is set to 0.5 W, the modulation index expressed as the magnitude of the modulation applied to the optical waveguide 12 is π radians in each propagation direction. From the result, it can be seen that the half-wavelength voltage Vπ defined as the voltage required to shift the phase by half a wavelength is 7.1 V.

[0177] The optical modulator 8 composed of a short resonator has a sideband generation efficiency higher than that of the optical modulator 8 composed of a long resonator by an amount corresponding to the higher fineness as described above, and the sideband generation frequency bandwidth Δf reaches 11 THz. In addition, the length of the electrode 83 of the optical modulator 8 composed of a short resonator is only 20 mm, but it can obtain a modulation efficiency that is comparable to that of the optical modulator 8 composed of a long resonator. In other words, it can be seen that reciprocating modulation works effectively.

[0178] In addition, instead of reflecting the electrical signal, the optical modulator 51 can also drive the input electrical signal from both ends of the electrode 83 by dividing the output of the oscillator 16 as the signal source, or by connecting independent oscillators 16 at both ends of the electrode 83 to perform this operation.

[0179] In addition, the present invention can also be applied to Fig.13 The optical waveguide type laser oscillator 52 shown in FIG. In the laser oscillator 52, the same components as those of the above-mentioned optical modulator 8 are referred to as Figure 5 , Figure 6 The instructions in , omit the instructions here.

[0180] like Fig.13 As shown, the laser oscillator 52 includes: a substrate 11; an optical waveguide 12 formed on the substrate 11; a buffer layer 14 stacked on the substrate 11 so as to cover the optical waveguide 12; a first protective member 86 and a second protective member 87 disposed on the upper portion of the optical waveguide 12; an incident side reflection film 93 covering the plane 91 and consisting of a single layer or a multi-layer vapor-deposited film; and an emission side reflection film 94 covering the plane 92 and consisting of a single layer or a multi-layer vapor-deposited film, and an optical resonator 5 is formed between the incident side reflection film 93 and the emission side reflection film 94. In addition, when the laser oscillator 52 is actually used, an excitation light source 28 emitting light of wavelength λ0 is installed.

[0181] For example, an amplifying medium such as erbium ions that absorbs light incident through the incident side reflection film 93 and has amplifying characteristics for the wavelength of light inherent to the medium is diffused into the optical waveguide 12 of the laser oscillator 52. In this way, the optical waveguide 12 can function as an amplifying medium for light. In addition, when light of an appropriate wavelength is incident on the optical waveguide 12 as such an amplifying medium, it functions as an amplifier of light for the inherent wavelength determined by the energy level. In addition, it also functions as an oscillator that amplifies the light generated by the natural emission transition and makes it oscillate. Since laser oscillation is a case where the amplification factor in the optical resonator 5 is greater than the loss factor, by pasting the protective members 86 and 87 to prevent the reflection films 93 and 94 from peeling off, being damaged, etc., and improving the reflection characteristics of the end face of the optical waveguide 12, the loss factor in the optical resonator 5 is also reduced, so that the threshold of laser oscillation can be lowered.

[0182] Even without introducing a special amplifying medium into the optical waveguide 12, by forming the optical waveguide 12 from a nonlinear optical crystal such as a LiNbO3 crystal, it is possible to amplify wavelengths different from the incident light by nonlinear polarization caused by the light incident into the optical waveguide 12. For example, the optical waveguide 12 may be formed using a nonlinear optical crystal having a periodic polarization inversion structure.

[0183] The incident-side reflection film 93 constituting the optical resonator 5 of the laser oscillator 52 may be a film having a low reflectivity with respect to the light from the excitation light source 28 and a high reflectivity with respect to the wavelength of the light oscillated by the optical waveguide 12. Furthermore, the output-side reflection film 94 constituting the optical resonator 5 may be a film having a reflectivity that enables optimal output coupling of the wavelength of the light oscillated by the optical waveguide 12.

[0184] In addition, the laser oscillator 52 can also be used as an optical parametric oscillator. In this case, since oscillation occurs when the amplification factor in the optical resonator 5 is greater than the loss factor, the oscillation threshold can be lowered by forming a high-fineness optical resonator 5 in which the reflective films 93 and 94 to which the protective members 86 and 87 are attached are not peeled off or damaged.

[0185] The advantage of using the optical waveguide 12 in the laser oscillator 52 and the optical parametric oscillator using the laser oscillator 52 is that the amplification factor can be increased by confining the light in a narrow area and increasing the electric field intensity. In particular, the laser oscillator 52 and the like can achieve higher fineness than conventional oscillators, which further enhances the advantage of using the optical waveguide 12.

[0186] In addition, the present invention can also be applied to Fig.14 The laser oscillator 53 shown in the figure is a laser oscillator that oscillates mode-synchronized light. The mode-synchronized light refers to aligning the phases of multiple modes oscillating at equal frequency intervals. In the laser oscillator 53, the same configuration and elements as those of the above-mentioned optical modulator 8 and laser oscillator 52 are referenced. Figure 5 , Figure 6 , Fig.13 The instructions in , omit the instructions here.

[0187] like Fig.14 (A) Fig.14As shown in (B), the laser oscillator 53 includes: a substrate 11; an optical waveguide 12 formed on the substrate 11 and used to modulate the phase of the propagating light; a buffer layer 14 stacked on the substrate 11 in a manner covering the optical waveguide 12; an electrode 83 provided on the upper surface of the optical waveguide 12 in a manner that the direction of the modulated electric field is substantially perpendicular to the propagation direction of the light; a first protective member 86 and a second protective member 87 provided on the upper portion of the optical waveguide 12; an incident side reflection film 93, which is coated on the plane 91 and is composed of a single layer or a multi-layer vapor-deposited film; and an exit side reflection film 94, which is coated on the plane 92 and is composed of a single layer or a multi-layer vapor-deposited film, and an optical resonator 5 is formed between the incident side reflection film 93 and the exit side reflection film 94. In addition, when the laser oscillator 53 is actually used, an excitation light source 28 emitting light of wavelength λ0 is installed, and a light source 28 is provided at one end of the electrode 83 and is used to make the frequency f m The oscillator 16 oscillating the modulated signal and the terminal resistor 18 located at the other end side of the electrode 83. The incident side reflection film 93 and the emission side reflection film 94 both have the function of obtaining phase synchronization between multiple modes of laser oscillation.

[0188] In the laser oscillator 53 having such a structure, the electrode 83 is disposed on the upper part of the optical waveguide 12 in the above-mentioned laser oscillator 52, so that the oscillation of the mode-synchronized laser beam that is synchronized with each mode can be performed. Here, by driving and inputting a modulation signal having a frequency that matches an integral multiple of the FSR of the optical resonator 5 from the oscillator 16, the phase synchronization of each mode is performed based on the electro-optical effect of the optical waveguide 12 that oscillates light in multiple modes, and as a result, the laser oscillator operates as a mode-synchronized laser beam.

[0189] When the mode synchronization is implemented, the time waveform of the light oscillated by the laser oscillator 53 becomes a short pulse having a time width of the reciprocal degree of the amplified frequency bandwidth. In addition, the waveform of the frequency axis becomes an optical frequency comb in which the sidebands are arranged at certain frequency intervals. Therefore, by optimizing the control of the laser oscillator 53, it can also be applied to the frequency measurement of light and to a multi-wavelength light source. In addition, it goes without saying that the laser oscillator 53 can also be used as an optical parameter oscillator in the same way as the laser oscillator 52 described above. In particular, since the laser oscillator 53 is attached with protective components 86 and 87, the reflective films 93 and 94 will not be peeled off or damaged, and the overall fineness of the optical resonator 5 can be improved, and the mode-synchronized laser oscillation can be efficiently achieved.

[0190] The mode synchronization of the laser oscillator 53 is not limited to the above-mentioned electro-optical effect, but may be based on any phenomenon as long as it utilizes the nonlinear effect of the optical element in the optical resonator 5. For example, the effect can be made more significant by using LiNbO3 crystal for the optical waveguide 12.

[0191] In addition, the present invention can also be applied to Fig.15 The modified Fabry-Perot (FP) electro-optical modulator 54 is shown. In the modified FP electro-optical modulator 54, the same configuration and elements as those of the optical modulator 8 and the laser oscillator 52 are referred to. Figure 5 , Figure 6 , Fig.13 The instructions in , omit the instructions here.

[0192] like Fig.15 As shown, the modified FP electro-optic modulator 54 includes: a substrate 11; an optical waveguide 12 formed on the substrate 11 and used to modulate the phase of propagating light; a buffer layer 14 stacked on the substrate 11 in a manner covering the optical waveguide 12; an electrode 83 provided on the upper surface of the optical waveguide 12 in a manner that the direction of the modulated electric field is substantially perpendicular to the propagation direction of the light; a first protective member 86 and a second protective member 87 provided on the upper portion of the optical waveguide 12; an incident side reflective film 93 covering the plane 91 and composed of a single layer or a multi-layer vapor-deposited film; and an exit side reflective film 94 covering the plane 92 and composed of a single layer or a multi-layer vapor-deposited film, and an optical resonator 5 is formed between the incident side reflective film 93 and the exit side reflective film 94. In addition, when the modified FP electro-optic modulator 54 is actually used, a reflective mirror 31 is installed, and if necessary, a reflective film 31 is provided on one end side of the electrode and used to make the frequency f m The modulation signal is oscillated by an oscillator (not shown) and a terminal resistor (not shown) located on the other end side of the electrode.

[0193] The reflector 31 transmits light supplied from the outside and guides it to the end of the optical waveguide 12 on the side of the deformed FP electro-optical modulator 54, and reflects the light emitted from the end of the optical waveguide 12. That is, by providing the reflector 31, only the light incident into the optical waveguide 12 can be transmitted, and the sideband generated in the optical waveguide 12 can be reflected, so that the conversion efficiency from the incident light to the sideband can be improved. That is, in the deformed FP electro-optical modulator 54 composed of such a structure, it is possible to obtain the same effect as the case where the incident side reflection film 93 is replaced with a narrow band filter that only transmits the light incident into the optical waveguide 12 and reflects the generated sideband. In particular, in the deformed FP electro-optical modulator 54, since the protective members 86 and 87 are attached, the reflection films 93 and 94 will not be peeled off or damaged, and the overall fineness of the optical resonator 5 can be improved, so the conversion efficiency to the sideband can be further improved.

[0194] Furthermore, the optical modulator 8 to which the present invention is applied can also be applied to a communication system 55 described below.

[0195] The communication system 55 is, for example, a system that uses a symbol division multiplexing connection based on a WDM communication method, such as Fig.16As shown in (A), it includes a portable communication device 57 which is a mobile terminal that can be carried by pedestrians, a plurality of base stations 58 for relaying communications by sending and receiving wireless signals between the portable communication device 57, and a host control device 59 for controlling the communication of the entire network including the base stations 58 by means of the connected optical fiber communication networks 35, 38.

[0196] The portable communication device 57 is configured to be mounted on a vehicle or carried in order to transmit and receive wireless signals with base stations 58 installed in various regions. That is, the portable communication device 57 includes, for example, a device for carrying data communication on a fax communication or a personal computer, but generally is a mobile phone, a PHS (Personal Handyphone System), etc. for making voice calls, and is particularly configured to be small, lightweight, and specialized in portability.

[0197] like Fig.16 As shown in FIG. 1A , each base station 58 is equipped with an optical modulator 8. An antenna 33 for transmitting and receiving microwaves between the optical modulator 8 and the portable communication device 57 is connected to the electrode 83 of the optical modulator 8. In addition, the optical modulator 8 allows a part of the light transmitted from the host control device 59 via the optical fiber communication network 35 to be incident on the optical waveguide 12 via the incident side reflection film 93. The light incident on the optical waveguide 12 resonates by the incident side reflection film 93 and the output side reflection film 94 arranged substantially in parallel. In addition, in the optical modulator 8, since the microwave supplied from the portable communication device 57 can be received by the antenna 33, a modulation signal corresponding to the microwave is applied to the light propagating in the optical waveguide 12 via the electrode 83, so that the light can be phase-modulated according to the transmission information from the portable communication device 57. In addition, the optical modulator 8 causes the phase-modulated light to be emitted via the output side reflection film 94. The emitted light is transmitted to the host control device 59 via the optical fiber communication network 38.

[0198] The host control device 59 generates light for transmission to the base station 58, and obtains a detection output by photoelectrically converting the light modulated in the base station 58. That is, the host control device 59 can collectively manage the detection outputs from various base stations.

[0199] In such a communication system 55, 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 causes the transmitted light to propagate in the optical waveguide 12 of the optical modulator 8 and further performs phase modulation corresponding to microwaves, and then transmits the light to the host control device 59 via the optical fiber communication network 38.

[0200] That is, when a call is made from a portable communication device 57 located in the vicinity of the base station 58, phase modulation corresponding to the content of the call contained in the microwave is applied to the light transmitted to the base station 58. On the other hand, when a call is not made from a portable communication device 57 located in the vicinity of the base station 58, the above-mentioned phase modulation is not applied to the light transmitted to the base station 58. In the host control device 59, when phase modulation is applied to the light transmitted from the base station 58 via the optical fiber communication network 38, the light is photoelectrically converted, thereby obtaining a detection output corresponding to the content of the call.

[0201] In the communication system 55 , since the optical modulator 8 having a high-fineness resonator to which the protective members 86 and 87 are attached is mounted in the base station 58 , the number of reciprocating times of light propagating in the optical waveguide 12 can be increased, and the sensitivity of the optical modulator 8 itself can be improved.

[0202] In addition, in the communication system 55, it is also possible to Fig.16 It is self-evident that light transmission is performed in a bidirectional manner using one core as shown in (B).

[0203] Furthermore, in the optical modulator 8 to which the present invention is applied, Figure 5 As shown, the crystal length LC1 of the forward direction (return direction) of the optical waveguide 12 is adjusted to about 27 mm (or 54 mm). The effects achieved by setting the crystal length to this value will be described below.

[0204] When the loss rate of light propagating in the forward direction (return direction) of the optical waveguide 12 is represented by Lo1, the relationship between the loss rate Lo1 and the crystal length LC1 of the optical waveguide 12 is represented by Fig.17 (A) shows that the loss of propagating light gradually increases as the crystal length LC1 increases. In addition, Fig.17 (B) shows the relationship between fineness and the crystal length LC1. Fig.17 As shown in (B), fineness is generally expressed by π / Lo1. It can be seen that the smaller the crystal length LC1, the higher the fineness.

[0205] The performance index of the optical modulator 8 can be expressed as Vπ / (fineness) (Vπ is the voltage required to modulate the optical phase by π radians). The smaller the performance index, the better the performance of the optical modulator 8 and the optical frequency comb generator using the optical modulator 8.

[0206] Fig.18 The performance index calculated based on the above-mentioned fineness and loss rate Lo1 is expressed in terms of the relationship with the crystal length LC1. Fig.18In the figure, 1 mm represents the difference between the length of the electrode 83 and the crystal length LC1. Generally, since electrodes cannot be provided several mm away from both ends of the optical waveguide 12, calculations are performed using the case where 1 mm is set to 6 mm and the case where 1 mm is set to 1 mm as examples.

[0207] If the Fig.18 As shown in the figure, when lm=6mm, the performance index decreases when the crystal length LC1 is 15mm to 30mm. It can also be seen that when the FSR corresponding to the crystal length LC1 of the performance index is plotted, the best performance is achieved near 2.5GHz. Fig.18 In the case of the trend in , the modulation frequency is set to 25 GHz, the transmission loss of microwaves caused by the electrode 83 is assumed to be -10 dB / 50 mm @ 25 GHz, and in terms of modulation efficiency, the modulation index is π radians when Pin = 0.43 W and the crystal length LC1 = 27 mm (when the length of the electrode 83 is 21 mm) during reciprocating modulation, and the transmission loss α of light is assumed to be -0.0106 / cm. In addition, the reflectivity of the reflector is optimized with respect to the loss rate corresponding to the crystal length.

[0208] Therefore, in the case of 1 m = 6 mm, by setting the crystal length LC1 of the optical waveguide 12 to about 27 mm, the performance as the optical modulator 8 can be further improved. In addition, the crystal length LC1 is not limited to the case of 27 mm, and can be any length as long as it is in the range of 24 ± 6 mm. In addition, the practical crystal length LC1 is preferably an integer fraction of 5 GHz, which is the greatest common divisor of 10 GHz of time division multiplex (TDM) optical communication and 25 GHz of wavelength division multiplex (WDM) optical communication in the field of optical communication, and 27 mm is equivalent to 2.5 GHz.

[0209] In addition, when the FSR plot corresponding to the crystal length LC1 is 1.25 GHz, excellent performance is also shown. Therefore, the crystal length LC1 corresponding to this can also be configured at about 54 mm.

[0210] In the case of 1 m=1 mm, excellent performance is shown at around 10 GHz in a similar simulation, and therefore, by adjusting the crystal length LC1 to correspond to this, the performance as the optical modulator 8 can be further improved.

[0211] In addition, in the above Figure 8In the method for manufacturing the optical modulator 8 to which the present invention is applied, in the process of manufacturing the optical waveguide 12 in steps S11 and S12, the optical waveguide 12 is formed by thermally diffusing Ti atoms into the substrate 11. However, this may be replaced by immersing LiNbO3 crystals in benzoic acid to replace Li with H. + Proton exchange method.

[0212] Here, in the optical comb generation process of an optical comb generator using a waveguide type optical resonator that resonates light enclosed in an optical waveguide, orthogonal polarized light components may cause the control for making the resonant frequency of the optical comb generator consistent with the laser frequency to become unstable, resulting in a shift in the control point, oscillation of the control, etc. When the optical comb is used in a measuring device for measuring the distance or height to a measurement object, for example, the orthogonal polarized light components may cause measurement errors. However, by using, for example, Figure 5 The waveguide type optical modulator 8A having the structure shown has an optical waveguide 12A formed as a region where a waveguide mode exists only with respect to a single polarization wave component, suppresses the output of orthogonal polarization light components that do not contribute to the generation of an optical comb, seeks to improve the polarization extinction ratio, and obtains an optical comb output with improved single polarization degree, so that the transmission mode waveform of the optical waveguide will not be deformed, and the resonator control can be stabilized, which can achieve stabilization as an optical comb generator, improvement of the accuracy of a measuring device including the optical comb, reduction of errors, etc.

[0213] Fig.19 The structure of the waveguide type optical modulator 8A shown is similar to that of the optical waveguide 12A except that the optical waveguide 12A is formed as a region where a waveguide mode exists only for a single polarization wave component. Figure 5 The waveguide type optical modulator 8 shown is the same, and therefore the same components are denoted by the same reference numerals, and detailed description thereof is omitted.

[0214] Fig. 20 It is a side view of the waveguide type optical modulator 8A.

[0215] In the waveguide optical modulator 8A, the optical waveguide 12A is formed in the substrate 11 having at least an electro-optical effect as a region where a waveguide mode exists only for a single polarization component so as to penetrate from the incident-side antireflection film 63 to the emission-side antireflection film 64 .

[0216] The light incident on the optical waveguide 12A via the incident-side anti-reflection film 63 propagates while only a single polarization component is totally reflected at the boundary surface of the optical waveguide 12A.

[0217] Here, the optical waveguide 12A that only allows a single polarized light component to pass can be formed as a region with a higher refractive index only for a single polarized light component in the substrate 11 having an electro-optical effect by an optical waveguide formation method that causes a change in the refractive index only for a specific polarized light component, such as a proton exchange method.

[0218] The optical waveguide 12A can be formed, for example, by a proton exchange method in a substrate 11 made of LiNbO 3 or the like as a region where a waveguide mode exists only for a single polarization component.

[0219] In addition, when the optical waveguide 12A is produced by diffusing Ti atoms in the substrate 11 or by epitaxial growth on the substrate 11, it can be formed as a region where the waveguide mode is limited to a single polarized light by designing the refractive index distribution. The optical waveguide 12A can be formed by diffusing Ti on the surface of the substrate 11 formed of LiNbO3 or the like, using, for example, a LiNbO3 crystal optical waveguide. Since the refractive index of the region where the Ti is diffused is higher than the refractive index of other regions, light of a single polarized wave component can be confined, and thus the optical waveguide 12A that can propagate light of a single polarized wave component can be formed. Although the refractive index becomes higher with respect to two orthogonal polarized wave components, there are also conditions under which the waveguide mode is established only with respect to a single polarized wave component.

[0220] The LiNbO3 crystal-type optical waveguide 12A manufactured based on such a method has electro-optical effects 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. Therefore, this physical phenomenon can be used to modulate light of a single polarization component.

[0221] The buffer layer 14 covers the optical waveguide 12A in order to suppress the propagation loss of the light of the single polarization component in the optical waveguide 12A. In addition, if the film thickness of the buffer layer 14 is too thick, the electric field intensity decreases and the modulation efficiency decreases. Therefore, the film thickness can be set as thin as possible within the range in which the propagation loss of the light of the single polarization component does not increase.

[0222] The electrode 83 is formed of a metal material such as Ti, Pt, Au, etc., and is provided with a frequency f m The modulation signal is driven input to the optical waveguide 12A to apply phase modulation to the light propagating in the optical waveguide 12A.

[0223] The first protective member 86 and the second protective member 87 are respectively made of a member corresponding to the material of the substrate 11. The first protective member 86 and the second protective member 87 may also be made of the same material as the substrate 11. In addition, the end face 86a and the first end face 84 of the first protective member 86 forming the above-mentioned plane 91 may be processed to have the same crystal orientation as each other, and the end face 87a and the second end face 85 of the second protective member 87 forming the above-mentioned plane 92 may also be processed to have the same crystal orientation as each other.

[0224] The incident-side anti-reflection film 63 is formed as a single-layer or multi-layer vapor-deposited film on a plane 91 perpendicular to the optical waveguide 12A formed between the first end face 84 and the end face 86a of the first protective member 86. The emission-side anti-reflection film 64 is formed as a single-layer or multi-layer vapor-deposited film on a plane 92 perpendicular to the optical waveguide 12A formed between the second end face 85 and the end face 87a of the second protective member 87. These anti-reflection films 63 and 64 may be formed of a low-reflection film, or may be formed of a non-coated film to obtain an effect equivalent to that of a method of coating with a low-reflection film.

[0225] The terminal resistor 18 is a resistor mounted at the terminal of the electrode 83, and prevents the reflection of the electric signal at the terminal to prevent the waveform from being disturbed.

[0226] Next, use Fig.21 A method for manufacturing the optical modulator 8A to which the present invention is applied will be described.

[0227] First, in step S21, Fig.21 As shown in (A), a photoresist pattern 13 is formed on the surface of a substrate 11 formed of LiNbO3 crystals.

[0228] Then move to step S22, as Fig.21 As shown in FIG. 2A , an optical waveguide 12A is formed as a region where a waveguide mode exists only for a single polarization wave component by a proton exchange method. The proton exchange method is to heat a substrate 11 of a LiNbO3 crystal having a photoresist pattern 13 formed on the surface while being immersed in a proton exchange liquid such as benzoic acid, so that Li in the surface layer of the substrate 11 is replaced by H + .

[0229] In addition, the production process of the optical waveguide 12A in steps S21 and S22 is not limited to the proton exchange method, and it can also be replaced by a Ti diffusion method, for example. In the Ti diffusion method, in step S21, a photoresist pattern 13 is produced on the surface of a substrate 11 formed of LiNbO3 crystals, Ti is vapor-deposited on the surface of the substrate 11 formed of LiNbO3 crystals, and the photoresist is removed, thereby producing a Ti fine wire having a width of micrometer size, and in the next step S22, the substrate 11 on which the Ti fine wire is formed is heated, so that Ti atoms are thermally diffused into the substrate 11, and the optical waveguide 12A is formed as a region where a waveguide mode exists only with respect to a single polarization wave component.

[0230] Then move to step S23, as Fig.21 As shown in (C), the resist pattern 13 is removed, and a SiO2 thin film as a buffer layer 14 is vapor-deposited on the surface of the substrate 11. In this step S23, the buffer layer 14 can also be formed by a method of pasting a SiO2 wafer on the surface of the substrate 11. In this case, considering the mounting area of ​​the electrode in the next step S24, the vapor-deposited buffer layer 14 can also be controlled to an appropriate film thickness by grinding.

[0231] Then, if Fig.21 As shown in (D), the process proceeds to step S24 , where an electrode 83 is formed on the buffer layer 14 .

[0232] Then move to step S25, as Fig.21 As shown in (E), protective members 86 and 87 are bonded to the upper part of the optical waveguide 12A. As for the bonding method of the protective members 86 and 87, they can be bonded by adhesive or directly bonded by other methods. In the case where the substrate 11 is composed of LiNbO3 crystals, the protective members 86 and 87 can also be composed of LiNbO3 as the same material. In this step S25, the bonded protective members 86 and 87 are cut to form a plane 91 between the end face 86a and the first end face 84, and a plane 92 between the end face 87a and the second end face 85.

[0233] Finally, move to step S26, such as Fig.21 As shown in FIG. 5 , the obtained planes 91 and 92 are polished to be planes perpendicular to the optical waveguide 12A. Then, the incident side anti-reflection film 63 and the emission side anti-reflection film 64 are formed on the polished planes 91 and 92 perpendicular to the optical waveguide 12A over the entire surface.

[0234] Thus, in the optical modulator 8A to which the present invention is applied, since the protective members 86 and 87 are attached to each end, the end face of the optical waveguide 12A, which is located at the corner of the uppermost end face in the past, is moved to the substantially central part of the plane 91 (92). As a result, even if the corner of the plane 91 (92) is damaged during the grinding in step S26, the end face of the optical waveguide 12A will not be damaged. That is, the end face of the optical waveguide 12A itself can be configured to be difficult to be damaged. Thus, the light loss from each end face of the optical waveguide 12A can be suppressed as much as possible.

[0235] Furthermore, by making the material of the protective members 86 and 87 of the best material corresponding to the material of the substrate 11, the polishing speed in step S26 can be made uniform in the range from the first end face 84 and the second end face 85 to the end faces 86a and 87a of the substrate 11. As a result, the end face of the optical waveguide 12A does not become rounded during processing, and the planes 91 and 92 composed of flat polished surfaces can be obtained, and the reflection loss of the end face of the optical waveguide 12A can be suppressed to the minimum. In addition, the reflection loss can be further suppressed by making the crystal orientation of the end faces constituting the respective planes 91 and 92 the same.

[0236] Furthermore, by intentionally providing the protection members 86 and 87, the polishing accuracy in step S26 is improved, and the perpendicularity of the obtained plane 91 (92) with respect to the optical waveguide 12 is also improved. As a result, the light loss caused by the loss of the perpendicularity can be minimized.

[0237] Furthermore, since the incident side reflection film 63 and the exit side reflection film 64 are formed in a wide range from the first end face 84 and the second end face 85 of the substrate 11 to the end faces 86a and 87a, they are very stable and difficult to peel off, and the reproducibility of film formation can be further improved.

[0238] In fact, when the plane 91 (92) was polished after the protective components 86 and 87 were attached in order to experimentally verify the effect of setting the protective components 86 and 87, it was confirmed that there was no defect or bending in the end face portion of the optical waveguide 12A, and a flat optical polishing suitable for covering the incident side reflection film 63 and the exit side reflection film 64 composed of a single layer or a multi-layer vapor-deposited film was implemented.

[0239] In particular, the first protective member 86 and the second protective member 87 are made of the same material as the substrate 11, and the end faces 86a, 87a of the protective members 86, 87 that are processed to form planes 91, 92 and the first end face 84, the second end face 85 have the same crystal orientation as each other, so that the hardness of the crystal is the same between the two, and therefore the planes 91, 92 will not be tilted due to the difference in grinding speed.

[0240] In the optical modulator 8A having such a structure, the frequency f supplied from the oscillator 16 is used. m The modulation signal phase-modulates the light of only a single polarization component that enters through the incident-side anti-reflection film 63 and propagates in the optical waveguide 12A, and emits it through the emission-side anti-reflection film 64. In addition, in the optical modulator 8A to which the present invention is applied, by attaching protective members 86 and 87 to each end, the end face of the optical waveguide 12A can be moved to the approximate center of the plane 91 (92), thereby achieving the reduction of the end face defect and rounded corners of the optical waveguide 12A, ensuring the perpendicularity between the optical waveguide 12A and the planes 91 and 92, and improving the grinding accuracy of the planes 91 and 92, and thus improving the yield rate.

[0241] Here, regarding a single polarization type optical waveguide produced by a proton exchange method that propagates only a single polarization component of incident light and an orthogonal polarization type optical waveguide produced by a Ti diffusion method that propagates only an orthogonal polarization component of incident light, as shown in FIG. Fig. 22 , Fig.23 , Fig.24 As shown, as the LiNbO3 crystal substrate module described later, 10 samples of 6 types of optical path widths W3 of 3 optical waveguides 112A, 112B, and 112C were prepared, respectively, and the reflectivities of the incident surfaces A1, B1, and C1 and the exit surfaces A2, B2, and C2 of the 3 optical waveguides 112A, 112B, and 112C were measured, and the fineness and transmittance of each sample were calculated. In this case, the following results were obtained: the aforementioned LiNbO3 crystal substrate module is prepared by [mm], length L1 = 27.4 [mm], thickness T1 = 0.5 [mm], three optical waveguides 112A, 112B, 112C are formed on a LiNbO3 crystal substrate 11, and protective components 86, 87 with a width W2 = 1.9 [mm], a length L2 = 1.5 [mm], and a thickness T2 = 0.5 [mm] are bonded to the upper parts of the optical waveguides 112A, 112B, 112C, and the end faces of the protective components 86, 87 and the end faces of the LiNbO3 crystal substrate 11 are polished, so that the incident surfaces and the exit surfaces of the three optical waveguides 112A, 112B, 112C are finely processed into planes.

[0242] That is, the fineness of the cross-polarization type waveguide is about 30 to 45, while the fineness of the single polarization type waveguide is about 50 to 65. In addition, the transmittance of the cross-polarization type waveguide is about 12.5 [%] to 25 [%], while the transmittance of the single polarization type waveguide is about 20 [%] to 32.5 [%].

[0243] In addition, the optical modulator 8A can also be used as the above-mentioned optical modulator 8 in the same manner as the above-mentioned optical modulator 8 by providing an exit-side reflection film 94 as a high reflection film at one end of the optical waveguide 12A formed as a region where a waveguide mode exists only with respect to a single polarization wave component, and providing an anti-reflection film 63 at the other end. Fig.11 (A) Fig.11 (B) Fig.11 A so-called reciprocating modulation type optical modulator having the structure shown in (C) operates.

[0244] Furthermore, in the above-mentioned step S26, by grinding the planes 91 and 92 to be parallel to each other, an incident side reflection film 93 and an exit side reflection film 94 are formed on the entire surface of the ground planes 91 and 92 to replace the above-mentioned incident side anti-reflection film 63 and the exit side anti-reflection film 64, so that the above-mentioned optical modulator 8A functions as an optical comb generator 1A.

[0245] That is, in the optical comb generator 1A, the incident side reflection film 93 and the output side reflection film 94 are arranged parallel to each other to resonate the light incident on the optical waveguide 12A, and the optical resonator 5 is configured to resonate by reciprocating reflection of the light passing through the optical waveguide 12A.

[0246] By forming the first end face 84 and the second end face 85 substantially perpendicular to the optical waveguide 12A, light of a single polarization component can be efficiently resonated using the incident side reflection film 93 and the output side reflection film 94 composed of a single layer or a multilayer vapor-deposited film covering these end faces.

[0247] In the optical comb generator 1A having the above-described structure, light incident from the outside through the incident-side reflective film 93 propagates in the forward direction in the optical waveguide 12A and is reflected by the output-side reflective film 94, while a portion of the light is transmitted to the outside. The light of the single polarized wave component reflected by the output-side reflective film 94 propagates in the return direction in the optical waveguide 12A and is reflected by the incident-side reflective film 93. By repeating this process, resonance is performed in the optical waveguide 12A using the light of the single polarized wave component.

[0248] Furthermore, by driving the input of an electrical signal synchronized with the time when the light of a single polarized wave component reciprocates in the optical waveguide 12A via the electrode 83, a phase modulation several tens of times deeper can be applied compared to the case where the light of a single polarized wave component passes through the optical modulator 8A only once. In addition, hundreds of sidebands can be generated in a wide bandwidth with the frequency v1 of the incident light as the center. In addition, the frequency intervals of the generated sidebands are all consistent with the frequency f of the input electrical signal. mTherefore, the light modulator 8A functions as an optical comb generator 1A that generates an optical comb of a single polarization wave component composed of a plurality of sidebands by replacing the incident-side anti-reflection film 63 and the exit-side anti-reflection film 64 with the incident-side reflection film 93 and the exit-side reflection film 94 .

[0249] That is, since the optical comb generator 1A includes an optical waveguide 12A formed as a region where a waveguide mode exists only with respect to a single polarization wave component in a substrate 11 having at least an electro-optical effect in a manner penetrating from the incident-side reflection film 93 constituting a resonance component to the exit-side reflection film 94, only the single polarization wave component of the light incident through the incident-side reflection film 93 propagates in the optical waveguide 12A, and an optical comb can be generated as a light modulation output of only the single polarization wave component through the exit-side reflection film 94.

[0250] Here, in the optical modulator 8, 8A, 51 of the present invention, the electrode 83 provided on the upper surface of the optical waveguide 12A supplying the modulation signal is formed by, for example, Fig.25 By having a ridge structure like the waveguide type optical modulator 8B (optical comb generator 1B) having the structure shown, the optical modulation efficiency can be further improved.

[0251] The waveguide optical modulator 8B (optical comb generator 1B) is Fig.19 , Fig. 20 The electrode 83 of the waveguide type optical modulator 8A (optical comb generator 1A) shown in the figure has a ridge structure, and the same components as those of the optical modulator 8A (optical comb generator 1A) as described above are referred to. Fig.19 , Fig. 20 The instructions in , omit the instructions here.

[0252] In the waveguide type optical modulator 8B (optical comb generator 1B), the substrate 11 is obtained by slicing a large crystal of LiNbO3, GaAs, etc., grown by the Czochralski method, with a diameter of 3 inches to 4 inches, into a wafer shape. The cut substrate 11 is subjected to mechanical polishing, chemical polishing, etc. to form the convex stripe portion 20 for forming the electrode 83A having a ridge structure.

[0253] The optical waveguide 12A is formed by a proton exchange method or a Ti diffusion method so as to penetrate from the incident end to the output end, and is formed as a region where a waveguide mode exists only for a single polarization component in order to propagate light of a single polarization component.

[0254] 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. Light incident on the optical waveguide 12A propagates with only a single polarization component being totally reflected at the boundary surface of the optical waveguide 12A.

[0255] The LiNbO3 crystal-type optical waveguide 12A manufactured based on this method has electro-optical effects 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. Therefore, this physical phenomenon can be used to modulate light of a single polarization component.

[0256] The electrode 83A having a ridge structure has a main electrode formed on the convex stripe 20, and is formed of a metal material such as Ti, Pt, Au, etc. The electrode 83A having a ridge structure having a main electrode formed on the convex stripe 20 generates a frequency f supplied from the oscillator 16. m The modulation signal is driven into the optical waveguide 12A, thereby applying phase modulation to the light propagating in the optical waveguide 12A.

[0257] use Fig.26 A method for manufacturing the waveguide type optical modulator 8B (optical comb generator 1B) having such a structure will be described.

[0258] That is, first in step S31, Fig.26 As shown in (A), a photoresist pattern 13 is formed on the surface of a substrate 11 formed of LiNbO3 crystals.

[0259] Then move to step S32, as Fig.26 As shown in FIG. 2A , an optical waveguide 12A is formed as a region where a waveguide mode exists only for a single polarization wave component by a proton exchange method. The proton exchange method is to heat a substrate 11 of a LiNbO3 crystal having a photoresist pattern 13 formed on the surface while being immersed in a proton exchange liquid such as benzoic acid, so that Li in the surface layer of the substrate 11 is replaced by H + .

[0260] In addition, the production process of the optical waveguide 12A in steps S31 and S32 is not limited to the proton exchange method, and it can also be replaced by a Ti diffusion method, for example. In the Ti diffusion method, in step S31, a photoresist pattern 13 is produced on the surface of a substrate 11 formed of LiNbO3 crystals, Ti is vapor-deposited on the surface of the substrate 11 formed of LiNbO3 crystals, and the photoresist is removed, thereby producing a Ti fine wire having a width of micrometer size, and in the next step S32, the substrate 11 on which the Ti fine wire is formed is heated, so that Ti atoms are thermally diffused into the substrate 11, and the optical waveguide 12A is formed as a region where a waveguide mode exists only with respect to a single polarization wave component.

[0261] Then move to step S33, as Fig.26 As shown in (C), the resist pattern 13 of the substrate 11 on which the optical waveguide 12A is formed is removed, and then the substrate 11 is subjected to mechanical polishing, chemical polishing or the like. Fig. 27The convex stripe portion 20 is provided to form an electrode 83A having a ridge structure.

[0262] Then move to step S34, as Fig.26 As shown in (D), a SiO2 thin film as a buffer layer 14 is deposited on the surface of the substrate 11. In this step S34, the buffer layer 14 can also be formed by a method of attaching a SiO2 wafer to the surface of the substrate 11. In this case, considering the mounting area of ​​the electrode in the later-described step S35, the deposited buffer layer 14 can also be controlled to an appropriate film thickness by grinding.

[0263] Then move to step S35, as Fig.26 As shown in (E), an electrode 83A having a ridge structure is formed on the buffer layer 14 of the substrate 11. The electrode having a ridge structure is shown in FIG. Fig.28 The main part of the longitudinal section.

[0264] Then move to step S36, as Fig.26 As shown in (F), protective members 86 and 87 are bonded to the upper part of the optical waveguide 12A. As for the bonding method of the protective members 86 and 87, they can be bonded by adhesive or directly bonded by other methods. In the case where the substrate 11 is composed of LiNbO3 crystals, the protective members 86 and 87 can also be composed of LiNbO3 as the same material. In this step S36, the bonded protective members 86 and 87 are cut to form a plane 91 between the end face 86a and the first end face 84, and a plane 92 between the end face 87a and the second end face 85.

[0265] In the optical modulator 8B to which the present invention is applied, in the final step S37, as Fig.26 As shown in (G), the obtained flat surfaces 91 and 92 are polished to be flat surfaces perpendicular to the optical waveguide 12A, and the incident side anti-reflection film 63 and the outgoing side anti-reflection film 64 are formed on the entire surface of the polished flat surfaces 91 and 92, respectively.

[0266] Furthermore, in the optical comb generator 1B to which the present invention is applied, in the above-mentioned step S37, the planes 91 and 92 are ground to be parallel to each other, and an incident side reflection film 93 and an exit side reflection film 94 are respectively formed on the entire surface of the ground planes 91 and 92 perpendicular to the optical waveguide 12A, replacing the above-mentioned incident side anti-reflection film 63 and the exit side anti-reflection film 64.

[0267] In the optical modulator 8B and the optical comb generator 1B having such a structure, light having only a single polarization component incident from the incident end and propagating through the optical waveguide 12A can be polarized by using the frequency f supplied from the oscillator 16 to the electrode 83A having a ridge structure. m The modulation signal efficiently applies phase modulation.

[0268] Moreover, in the optical modulator 8B and the optical comb generator 1B to which the present invention is applied, by pasting protective components 86 and 87 on each end, the end face of the optical waveguide 12A can be moved to the approximate center of the plane 91 (92), thereby achieving the defects of the end face of the optical waveguide 12A, suppressing the rounded corners, ensuring the perpendicularity between the optical waveguide 12A and the planes 91 and 92, improving the grinding accuracy of the planes 91 and 92, and also improving the yield rate.

[0269] In the optical comb generator 1B, light incident from the outside through the incident-side reflective film 93 propagates in the optical waveguide 12A in the forward direction as a single polarized wave component and is reflected by the emitting-side reflective film 94, while a portion of the light is transmitted to the outside. The light of the single polarized wave component reflected by the emitting-side reflective film 94 propagates in the return direction in the optical waveguide 12A and is reflected by the incident-side reflective film 93. By repeating this process, the light of the single polarized wave component resonates in the optical waveguide 12A.

[0270] Furthermore, by driving the input of an electrical signal synchronized with the time when the light of a single polarized wave component reciprocates in the optical waveguide 12A via the electrode 83A, a phase modulation several tens of times deeper can be applied compared to the case where the light of a single polarized wave component passes through the optical modulator 8B only once. In addition, hundreds of sidebands can be generated in a wide bandwidth with the frequency v1 of the incident light as the center. In addition, the frequency intervals of the generated sidebands are all consistent with the frequency f of the input electrical signal. m Therefore, the optical modulator 8B functions as an optical comb generator 1B that generates an optical comb of a single polarization wave component composed of a plurality of sidebands.

[0271] Thus, in the optical comb generator 1B to which the present invention is applied, the optical waveguide 12A is formed as a region where a waveguide mode exists only for a single polarization component in a substrate having at least an electro-optical effect so as to penetrate from the incident-side reflection film 93 constituting the resonance part to the emission-side reflection film 94. Therefore, only the single polarization component of the light incident through the incident-side reflection film 93 propagates in the optical waveguide 12A, and can be output as a light modulation of only the single polarization component through the emission-side reflection film 94 to generate an optical comb. In addition, since the optical waveguide 12A is configured by attaching the protective members 86 and 87 to each end, the end face of the optical waveguide 12A, which is located at the corner of the uppermost end face, is moved to the substantially central portion of the plane 91 (92). As a result, even if the corner of the plane 91 (92) is damaged during the polishing in step S37, the end face of the optical waveguide 12A is not damaged. That is, a structure in which the end face of the optical waveguide 12A itself is difficult to be damaged can be set. This makes it possible to minimize light loss from each end face of the optical waveguide 12A.

[0272] Moreover, if Fig.28 As shown in the longitudinal section of the main part of FIG. 8B , since the optical modulator 8B includes the electrode 83A having a ridge structure formed on the buffer layer 14 of the substrate 11 , the modulation efficiency can be further improved.

[0273] Here, in the optical modulator 8B, samples of the optical modulator 8A were prepared in which the ridge width RW of the electrode 83A having a ridge structure formed on the buffer layer 14 of the substrate 11 was set to 10, 12, 14, 16 and 18 [μm], and the average depth AVD (Average depths) of the ridge groove was set to 3.3, 2.96, 4.79 and 4.72 [μm]. The driving voltage (AC Vpi) and the direct current driving voltage (DC Vpi) at 25 GHz were actually measured, and the results are shown in FIG. Fig.29 , Fig.30 Vpi is the voltage required to modulate the phase by π radians.

[0274] That is, compared to the previous optical modulator with an electrode structure without a ridge structure, the driving voltage (AC Vpi) at 25 GHz is about 8V to 10V, and the DC driving voltage (DC Vpi) is about 6V to 6.5V, while in the optical modulator 8B having an electrode 83A with a ridge structure, the driving voltage (AC Vpi) at 25 GHz is about 3.5V to 7.5V, and the DC driving voltage (DCVpi) is about 5V to 6V.

[0275] By setting the ridge structure in this way, the average driving voltage (AC Vpi) at 25GHz is reduced to about 70% of the original voltage compared to the case without the ridge structure, which is equivalent to a reduction of about 50% in terms of power. In addition, the average DC driving voltage (DC Vpi) is reduced to about 80% of the original voltage compared to the case without the ridge structure, which is equivalent to a reduction of about 50% in terms of power.

[0276] That is, the optical modulator 8B and the optical comb generator 1B are provided with a first protective member 86 and a second protective member 87, the first protective member 86 and the second protective member 87 being composed of members having the same hardness as the substrate 11 of the optical waveguide 12A, and being arranged on the upper part of the optical waveguide 12A in such a manner that at least one end face of the members forms the same plane as the end face of the substrate 11 including the light incident end or the light emitting end of the optical waveguide 12A, and the end faces of the members and the substrate 11 are ground to form a uniform plane. The planes perpendicular to the optical waveguide 12A formed by the end faces of the substrate are covered with the incident side anti-reflection film 63 or the incident side reflection film 93, and the output side anti-reflection film 64 or the output side reflection film 94 as single-layer or multi-layer vapor-deposited films, thereby preventing defects from being generated on the end faces of the optical waveguide, stabilizing the mounting of the high reflection film, improving the fineness of the optical resonator 5 composed of the incident side reflection film 93 and the output side reflection film 94, and reducing the driving power by providing the electrode 83A with a ridge structure.

[0277] Therefore, in the optical modulator 8A, 8B, and optical modulator 51 having the above-mentioned structure, members 86, 87 having the same hardness as the substrate 11 for forming the optical waveguide 12A from the upper surface are arranged on the upper part of the optical waveguide 12A in such a manner that at least one end face thereof forms the same plane as the end face of the substrate 11 including the light incident end or the light emitting end of the optical waveguide 12A, and an incident side reflection film 93 and an exit side reflection film 94 composed of a single-layer or multi-layer vapor-deposited film constituting a resonance part are coated on a plane perpendicular to the optical waveguide 12A formed by grinding the end faces of the members 86, 87 and the end face of the substrate 11, thereby suppressing damage and rounding of the corners of the optical waveguide end face when processing the corners. By stably covering each reflection film without peeling off at the corner portion of the uppermost part of the end face, the reflectivity of the reflection film and the fineness of the optical resonator can be improved, and the function of the device itself can be improved. By having an optical waveguide 12A formed as a region where a waveguide mode exists only for a single polarization wave component in a substrate 11 having at least an electro-optical effect in a manner that penetrates from the incident side reflection film 93 constituting the resonance component to the exit side reflection film 94, the optical comb generator 1, 1A functions as an optical comb that can generate a stable optical comb as a single polarization wave component of light incident through the incident side reflection film 93 propagates in the optical waveguide 12A and can be output as a light modulation of only a single polarization wave component through the exit side reflection film 94.

[0278] The optical waveguide 12A of the optical modulator 8B and the optical modulator 51 as described above is formed as a region in which a waveguide mode only exists with respect to a single polarization wave component in a substrate 11 having at least an electro-optical effect in a manner penetrating from the incident side reflection film 93 to the exit side reflection film 94, and an electrode 83A having a ridge structure is provided, thereby constructing a low-power laser source and optical comb generator that can output a laser or an optical comb with only a single polarization wave component.

[0279] In addition, in the optical modulators 8A and 8B (optical comb generators 1A and 1B), by covering with reflective films 93 and 94 having a reflectivity in the range of 95% to 99%, the waveguide loss rate of the optical waveguide 12A can be made consistent with the transmittance of the reflective films 93 and 94, thereby improving the fineness and transmittance of the resonator and improving the performance of the resonator.

[0280] Next, the structure of the optical comb generator 210 using the low power optical comb unit of the present invention is shown in FIG. Fig.31 Block diagram of the .

[0281] The optical comb generator 210 includes an optical coupler 211 that branches a portion of the optical comb output from the low-power optical comb assembly 200A to which the present invention is applied, a light detector 212 for detecting the light branched by the optical coupler 211, and a control circuit 213 to which a light detection signal obtained by the light detector 212 is supplied.

[0282] The optical comb assembly 200A generates an optical comb and outputs it by inputting laser light from a laser source (not shown) and inputting an RF modulation signal via the bias device 214, applying phase modulation to a single polarization wave component of the incident laser light by the RF modulation signal. The optical comb assembly 200A controls the resonance length of the resonance component realized by the incident side reflection film and the emission side reflection film provided on the optical waveguide under the temperature control of the temperature control circuit 219.

[0283] The control circuit 213 obtains an error with respect to a control target from the light detection signal, generates a control signal for making the error zero, and supplies the control signal to the bias device 214 .

[0284] By applying a control signal to the DC bias of the optical comb assembly 200A, the resonance frequency of the optical comb assembly 200A can be made to follow the input laser frequency.

[0285] The control circuit 213 may be a printed circuit board alone or a combination of an RF mixer, an isolator and a printed circuit board. The light detection signal of the photodetector 212 is mixed with a synchronization signal to generate a control signal corresponding to the error amount relative to the control target.

[0286] A part of the output of the RF modulation signal source can be used as a synchronization signal. In this case, the operating frequency band of the photodetector 212 needs to be higher than the RF driving frequency.

[0287] In the control circuit 213, the low frequency component of the signal obtained by inputting the light detection signal and the synchronization signal to the mixer via the phase adjuster is obtained as an error signal. Alternatively, the RF drive signal can use another modulation signal (dither signal) as a synchronization signal. The laser frequency or the resonant frequency of the optical comb assembly 200A is modulated with an amplitude smaller than the FSR of the resonant mode, and the output signal of the light detector 212 and the synchronization signal are mixed. If the dither signal frequency is low, the error signal can also be generated by converting the light detection signal into a digital signal by an analog-digital converter and performing a product-sum operation of digital signal processing.

[0288] The signal obtained by adjusting the frequency characteristics of the error signal is applied as a control signal to the DC bias of the optical comb assembly 200A via the bias device 214. Generally speaking, the error signal is input to a circuit having proportional, integral, and differential functions, and the frequency characteristics of the control loop are determined by adjusting the amplitudes of these components, so that the resonant frequency of the optical comb assembly 200A follows the oscillation frequency of the input laser.

[0289] In addition, the structure of the optical comb generator 220 using the low-power optical comb assembly of the present invention is shown in FIG. Fig.32 Block diagram of the .

[0290] The optical comb generator 220 performs resonator control using reflected light from the low-power optical comb unit 200A to which the present invention is applied. Part of the reflected light from the low-power optical comb unit 200A is branched by the optical coupler 211 and enters the photodetector 212 .

[0291] The components of the optical comb generator 220 are Fig.31 The optical comb generator 210 shown in FIG. Fig.32 In the drawings, the same reference numerals are given to corresponding components and detailed descriptions thereof are omitted.

[0292] The control circuit 213 obtains an error relative to a control target based on the light detection signal obtained by the light detector 212, and outputs a control signal for making the error zero. By applying the control signal to the DC bias of the optical comb assembly, the resonance frequency of the optical comb assembly 200A can be made to follow the input laser frequency.

[0293] Furthermore, the low-power optical comb assembly of the present invention can be used to construct, for example, Fig.33 A light comb light source 300 of the structure shown.

[0294] The optical comb light source 300 includes a laser source 301 oscillating at a single frequency, a separation optical system 302 such as an optical coupler and an optical beam splitter for separating the laser light of a single frequency emitted from the laser source 301 into two lasers, a frequency shifter 305 for shifting the frequency of a laser light separated by the separation optical system 302, and two optical comb generators (OFCG1, OFCG2) 320A, 320B respectively using low-power optical comb components.

[0295] In the optical comb light source 300 , laser light emitted from a single-frequency oscillating laser source 301 is split into two laser lights by a splitting optical system 302 and input to two optical comb generators (OFCG1 , OFCG2 ) 320A, 320B.

[0296] The two optical comb generators 320A and 320B use different frequencies f m and frequency f m +Δf m The oscillators 303A and 303B are driven to oscillate. The oscillators 303A and 303B are phase-synchronized by using a common reference oscillator 304, so that m With f m +Δf m The relative frequency becomes stable. A frequency shifter 305 such as an acousto-optic frequency shifter (AOFS) is provided before the optical comb generator (OFCG2) 320B, and the frequency shifter 305 is used to shift the optical frequency of the input laser light by the frequency fa. As a result, the beat frequency between the carrier frequencies is not a DC signal but an AC signal of the frequency fa. As a result, since the beat signal of the high-frequency sideband of the carrier frequency and the beat signal of the low-frequency sideband are generated in the frequency region relative to each other with the beat frequency fa between the carrier frequencies of the beat signal, it is convenient for phase comparison.

[0297] The two optical comb generators (OFCG1, OFCG2) 320A, 320B are respectively constituted by low-power optical comb modules to which the present invention is applied, and can output an optical comb of a single polarization component by phase-modulating only a single polarization component of input laser light.

[0298] The optical comb light source 300 shares a single-frequency oscillating laser source 301 to generate two optical combs having different center frequencies and frequency intervals for two optical comb generators (OFCG1, OFCG2) 320A, 320B. For example, by using the optical comb light source 300 as the first light source and the second light source of the distance meter and the optical three-dimensional shape measuring machine in Japanese Patent No. 5231883 previously proposed by the inventor of the present case, that is, the first light source and the second light source that respectively emit interfering reference light and measurement light whose intensity or phase is periodically modulated and whose modulation periods are different from each other, it is possible to construct a measuring system of the distance meter and the optical three-dimensional shape measuring machine as follows: by irradiating the surface of the measured object with the optical comb output for measuring the polarized wave components of the two optical comb generators (OFCG1, OFCG2) 320A, 320B while scanning, the reflected light from the surface is detected little by little for the irradiated point and the distance (height) is calculated, thereby performing a stable measurement operation.

[0299] Fig.34 1 is a block diagram showing the structure of an optical comb distance meter 400 formed using the optical comb light source 300 described above.

[0300] Fig.34 The optical comb distance meter 400 shown in the block diagram uses an optical frequency comb interferometer to measure the distance. The intensity or phase of two optical frequency combs with different center frequencies and frequency intervals emitted from the first optical comb light source 401 and the second optical comb light source 402 are periodically modulated respectively, and the interfering reference light S1 and the measuring light S2 with different modulation periods are irradiated to the reference plane 404 and the measuring plane 405 via the interfering optical system 410. The interfering light of the reference light S1 and the measuring light S2 irradiated to the above-mentioned reference plane 404 and the measuring plane 405 is detected by the reference light detector 403. S3, and the interference light S4 of the reference light S1' reflected by the reference surface 404 and the measurement light S2' reflected by the measurement surface 405 is detected by the measurement light detector 406, and the difference between the distance L1 from the reference surface 404 and the distance L2 from the measurement surface 405 can be obtained by the signal processing unit 407 based on the time difference between the interference signal obtained by the reference light detector 403 detecting the interference light S3 and the interference signal obtained by the measurement light detector 406 detecting the interference light S4, according to the speed of light and the refractive index in the measurement wavelength. In addition, there are multiple forms of interferometers and detectors.

[0301] The optical comb distance meter 400 can be combined with an optical scanning device to form an optical comb shape measuring device as follows: the measuring light S2 is irradiated onto the surface of the measured object while scanning, the reflected light from the surface is detected point by point at the irradiation point, and the distance (height) is calculated, and the surface shape of the object is obtained based on the distribution of the scanned coordinates and the distance (height). There are various forms of scanner optical systems. When a telecentric optical system is used, light can be incident on the object approximately vertically within the measurement range.

[0302] In addition, for example, by using the above-mentioned optical comb light source 300 as the light source of the vibration measuring device in Japanese Patent No. 5336921 and Japanese Patent No. 5363231 previously proposed by the inventor of the present case, that is, a light source unit that emits a spectrum of predetermined frequency intervals, and has reference light and measurement light whose modulation frequencies and center frequencies are different from each other and whose phases are synchronized with each other and have interfering properties, it is possible to construct a measurement system for the vibration measuring device as follows: an optical comb of a single polarization wave component emitted from two optical comb generators (OFCG1, OFCG2) 320A, 320B is irradiated to different places according to the wavelength via an element assigned to each wavelength, thereby performing a stable multi-point vibration measurement operation.

[0303] Here, the measuring device uses a light comb obtained by a light comb generator using an optical waveguide that transmits polarized light components of orthogonal mode mixing. In the measuring device, Figure 4 As shown in the ○ mark in the figure, the transmission mode waveform formed by the orthogonal polarization component is sometimes deformed, and the location of generation (relative position with respect to the main mode) is scattered, and the extremely small parts become multiple, which leads to unstable control. However, by using an optical waveguide that only allows a single polarization component to pass, such as Fig.35 As shown, the transmission mode waveform does not deform, and the stabilization of the optical comb generator, the improvement of the accuracy of the measurement device including the optical comb, the reduction of errors, etc. can be achieved.

[0304] That is, when the optical comb is used for measurement, the polarized light component orthogonal to the generation of the optical comb will cause measurement errors of the distance and height. In addition, the polarized light component orthogonal to the generation of the optical comb sometimes makes the control for making the resonance frequency of the optical comb generator consistent with the laser frequency unstable, which will cause the displacement of the control point and the oscillation of the control. In addition, when the optical comb is used for measurement, it will cause measurement errors of the distance and height. However, by using an optical waveguide that only allows a single polarized light component to pass through to generate the optical comb, it is possible to suppress the output of the orthogonal polarized light component that does not contribute to the generation of the optical comb, improve the polarization extinction ratio of the optical comb output, improve the single polarization degree, stabilize the resonator control, remove useless interference signals, and eliminate measurement errors in distance measurement and shape measurement using the optical comb, thereby achieving improved measurement accuracy and improved reliability of the entire system.

[0305] Description of Reference Numerals

[0306] 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, terminal resistor; 19a, phase shifter; 19b, reflector; 20, convex strip; 21, optical circulator; 22, focusing device; 63, anti-reflection film; 83, 83A, electrode; 84, first end face; 85, second end face; 86, first protective member; 86a, 87a, end face; 87, second protective member; 91, 92, plane; 93, incident side reflection film; 94, exit side reflection film; 200A, low-power optical comb assembly; 210, 220, optical comb generator; 211, optical coupler; 212, photodetector; 213, control circuit; 214, bias device; 130, 300, optical comb light source; 301, laser 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 photodetector; 404, reference plane; 405, measurement plane; 406, measurement photodetector; 407, signal processing unit.

Claims

1. A method for manufacturing an optical resonator, wherein light incident through an incident side reflection film is propagated and resonated by using an optical waveguide formed so as to penetrate from an incident side reflection film to an exit side reflection film, wherein: The production method has the following features: an optical waveguide forming step, in which the optical waveguide is formed from the upper surface of the substrate; a disposing step of disposing a protective member having the same hardness as the substrate on an upper portion of the optical waveguide so that at least one end surface thereof forms a flush plane with an end surface of the substrate including a light incident end or a light emitting end of the optical waveguide; a grinding step of grinding the end face of the protection member and the end face of the substrate arranged in the arranging step to form a plane perpendicular to the optical waveguide as a flat ground surface including the light incident end or the light emitting end of the optical waveguide; and a reflective film coating step, in which a single layer or a multi-layer vapor-deposited film is coated on the plane formed in the polishing step as the incident side reflective film or the exit side reflective film, In the above-mentioned disposing step, the above-mentioned protection member is adhered and disposed on the upper part of the above-mentioned optical waveguide by using an adhesive. In the reflective film coating step, a multilayer vapor-deposited film having a reflectivity of 95% to 99% is coated over the entire range of a plane formed by the end faces of the protective member and the end faces of the substrate bonded by the adhesive, under temperature conditions that are lower than the glass transition temperature of the adhesive and do not emit gas components from the cured adhesive, thereby forming the incident side reflective film or the exit side reflective film in a plane perpendicular to the optical waveguide.

2. A method for manufacturing an optical modulator, which uses an optical waveguide formed with an incident side reflection film and an exit side reflection film to propagate and modulate light incident through the incident side reflection film, characterized in that: The production method has the following features: an optical waveguide forming step, in which the optical waveguide is formed from the upper surface of the substrate; a lamination 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; an electrode forming step of forming an electrode for applying an electric field to the optical waveguide on the buffer layer stacked in the stacking step; a disposing step of disposing a protective member having the same hardness as the substrate on an upper portion of the optical waveguide so that at least one end surface thereof forms a flush plane with an end surface of the substrate including a light incident end or a light emitting end of the optical waveguide; a grinding step of grinding the end face of the protection member and the end face of the substrate arranged in the arranging step to form a plane perpendicular to the optical waveguide as a flat ground surface including the light incident end or the light emitting end of the optical waveguide; and a reflective film coating step, in which a single layer or a multi-layer vapor-deposited film is coated on the plane formed in the polishing step as the incident side reflective film or the exit side reflective film, In the above-mentioned disposing step, the above-mentioned protection member is adhered and disposed on the upper part of the above-mentioned optical waveguide by using an adhesive. In the reflective film coating step, a multilayer vapor-deposited film having a reflectivity of 95% to 99% is coated over the entire range of a plane formed by the end faces of the protective member and the end faces of the substrate bonded by the adhesive, under temperature conditions that are lower than the glass transition temperature of the adhesive and do not emit gas components from the cured adhesive, thereby forming the incident side reflective film or the exit side reflective film in a plane perpendicular to the optical waveguide.

3. The method for manufacturing an optical modulator according to claim 2, characterized in that: In the optical waveguide forming step, the optical waveguide is formed as a region where a waveguide mode exists only for a single polarization component from the upper surface of the substrate having at least an electro-optical effect by proton exchange.

4. The method for manufacturing an optical modulator according to claim 2, characterized in that: The manufacturing method comprises a ridge structure forming step of forming a ridge structure on the substrate. In the electrode forming step, an electrode having a ridge structure is formed on the buffer layer stacked on the substrate having the ridge structure in the stacking step as an electrode for applying an electric field to the optical waveguide.

5. An optical resonator, characterized in that: The optical resonator comprises: a resonance component, which is composed of an incident-side reflection film and an exit-side reflection film, and causes light incident through the incident-side reflection film to resonate; an optical waveguide formed so as to penetrate from the incident-side reflective film to the exit-side reflective film and propagate the light resonated by the resonant member; a substrate having the optical waveguide formed on its upper surface; and an end face protection member, which is composed of a protection component having the same hardness as the substrate, and the protection component is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protection component forms a same plane with an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, The incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are applied to a plane perpendicular to the optical waveguide at a temperature lower than the glass transition temperature of the adhesive and without emitting gas components from the cured adhesive. The plane is formed by grinding the entire range of the plane formed by the end face of the protective member and the end face of the substrate bonded with the adhesive to form a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

6. The optical resonator according to claim 5, characterized in that The protection member constituting the end face protection component is formed of the same material as the substrate, and the end face of the protection member forming the plane and the end face of the substrate have the same crystal orientation as each other. The end face protection component is arranged on the upper part of the optical waveguide in such a manner that one end face of the protection component forms the same plane with the end face of the substrate including the light incident end of the optical waveguide, and in such a manner that the other end face of the protection component forms the same plane with the end face of the substrate including the light emitting end of the optical waveguide.

7. An optical modulator, characterized in that: The optical modulator comprises: an oscillating member that oscillates a modulation signal of a predetermined frequency; a resonance component, which is composed of an incident-side reflection film and an exit-side reflection film, and causes light incident through the incident-side reflection film to resonate; an optical waveguide formed so as to penetrate from the incident-side reflective film to the exit-side reflective film, and modulating the phase of the light resonated by the resonance member in accordance with the modulation signal supplied from the oscillation member; a substrate having the optical waveguide formed on its upper surface; and an end face protection member, which is composed of a protection component having the same hardness as the substrate, and the protection component is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protection component forms a same plane with an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, The incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are applied to a plane perpendicular to the optical waveguide at a temperature lower than the glass transition temperature of the adhesive and without emitting gas components from the cured adhesive. The plane is formed by grinding the entire range of the plane formed by the end face of the protective member and the end face of the substrate bonded with the adhesive to form a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

8. An optical modulator, characterized in that: The optical modulator comprises: a resonance component, which is composed of an incident-side reflection film and an exit-side reflection film, and causes light incident through the incident-side reflection film to resonate; an optical waveguide formed so as to penetrate from the incident-side reflective film to the exit-side reflective film; a substrate, the optical waveguide being formed on the upper surface of the substrate; an optical modulation component formed on the substrate, comprising electrodes for propagating a modulated signal in a forward direction or a backward direction, and modulating a phase of light propagating in the optical waveguide in accordance with a wavelength of an electrical signal supplied to the electrodes; and an end face protection member, which is composed of a protection component having the same hardness as the substrate, and the protection component is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protection component forms a same plane with an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, The incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are applied to a plane perpendicular to the optical waveguide at a temperature lower than the glass transition temperature of the adhesive and without emitting gas components from the cured adhesive. The plane is formed by grinding the entire range of the plane formed by the end face of the protective member and the end face of the substrate bonded with the adhesive to form a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

9. The optical modulator according to claim 8, characterized in that The optical waveguide is formed on the substrate having at least an electro-optical effect as a region where a waveguide mode exists only for a single polarization component.

10. The optical modulator according to claim 8 or 9, characterized in that: A ridge structure is formed on the substrate, and the electrode of the light modulation element has the ridge structure.

11. An optical frequency comb generator, characterized in that: The optical frequency comb generator comprises: an oscillating member that oscillates a modulation signal of a predetermined frequency; a resonance component, which is composed of an incident-side reflection film and an exit-side reflection film, and causes light incident through the incident-side reflection film to resonate; an optical waveguide formed so as to penetrate from the incident-side reflective film to the exit-side reflective film, modulate the phase of the light resonated by the resonance member in accordance with the modulation signal supplied from the oscillation member, and generate sidebands centered on the frequency of the incident light at intervals of the frequency of the modulation signal; a substrate, the optical waveguide being formed on the upper surface of the substrate; an optical modulation component formed on the substrate, comprising electrodes for propagating a modulated signal in a forward direction or a backward direction, and modulating a phase of light propagating in the optical waveguide in accordance with a wavelength of an electrical signal supplied to the electrodes; and an end face protection member, which is composed of a protection component having the same hardness as the substrate, and the protection component is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protection component forms a same plane with an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, The incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are applied to a plane perpendicular to the optical waveguide at a temperature lower than the glass transition temperature of the adhesive and without emitting gas components from the cured adhesive. The plane is formed by grinding the entire range of the plane formed by the end face of the protective member and the end face of the substrate bonded with the adhesive to form a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

12. An optical oscillator, characterized in that: The optical oscillator comprises: A resonant component, which is composed of an incident side reflection film and an exit side reflection film, and resonates light incident through the incident side reflection film or light generated by laser amplification; an optical waveguide formed so as to penetrate from the incident-side reflective film to the emitting-side reflective film, amplifies the light resonated by the resonance member, and emits the light to the outside through the emitting-side reflective film; a substrate, the optical waveguide being formed on the upper surface of the substrate; an optical modulation component formed on the substrate, comprising electrodes for propagating a modulated signal in a forward direction or a backward direction, and modulating a phase of light propagating in the optical waveguide in accordance with a wavelength of an electrical signal supplied to the electrodes; and an end face protection member, which is composed of a protection component having the same hardness as the substrate, and the protection component is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protection component forms a same plane with an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, The incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are applied to a plane perpendicular to the optical waveguide at a temperature lower than the glass transition temperature of the adhesive and without emitting gas components from the cured adhesive. The plane is formed by grinding the entire range of the plane formed by the end face of the protective member and the end face of the substrate bonded with the adhesive to form a flat grinding surface including the light incident end or the light exit end of the optical waveguide.

13. The optical oscillator according to claim 12, wherein: The optical waveguide is formed by absorbing the light incident through the incident side reflection film and diffusing the medium having a characteristic of amplifying the wavelength of the light inherent in the medium.

14. The optical oscillator according to claim 12 or 13, characterized in that: The optical waveguide is composed of a nonlinear optical crystal.

15. An optical oscillator, characterized in that: The optical oscillator comprises: an oscillating member that oscillates a modulation signal of a predetermined frequency; A resonant component, which is composed of an incident side reflection film and an exit side reflection film, and resonates light incident through the incident side reflection film or light generated by laser amplification; an optical waveguide formed so as to penetrate from the incident side reflection film to the exit side reflection film, amplifying the light resonated by the resonance member in accordance with the modulation signal supplied from the oscillation member, and emitting the light to the outside through the exit side reflection film; a substrate, the optical waveguide being formed on the upper surface of the substrate; an optical modulation component formed on the substrate, comprising electrodes for propagating a modulated signal in a forward direction or a backward direction, and modulating a phase of light propagating in the optical waveguide in accordance with a wavelength of an electrical signal supplied to the electrodes; and an end face protection member, which is composed of a protection component having the same hardness as the substrate, and the protection component is attached to the upper part of the optical waveguide by an adhesive in such a manner that at least one end face of the protection component forms a same plane with an end face of the substrate including a light incident end or a light emitting end of the optical waveguide, The incident side reflection film and the exit side reflection film are multilayer vapor-deposited films with a reflectivity of 95% to 99% and are applied to a plane perpendicular to the optical waveguide at a temperature lower than the glass transition temperature of the adhesive and without emitting gas components from the cured adhesive. The plane is formed by grinding the entire range of a plane formed by the end face of the protective component and the end face of the substrate bonded with the adhesive to form a flat polished surface including the light incident end or the light exit end of the optical waveguide. The incident side reflection film and the exit side reflection film obtain phase synchronization between multiple modes of laser oscillation.

Images