JP2003098497A - Optical waveguide type light frequency comb generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide type light frequency comb generator which has the efficiency of conversion to light frequency comb improved by increasing the efficiency of incidence on an optical resonator. SOLUTION: The optical resonator 130 is constituted by providing reflecting films 131 and 132 on two opposite end surfaces of both end parts of an optical waveguide 120 which is formed on an optical material substrate 110 having electrooptic effect such that the refractive index varies through the application of an electric field and passes a light beam causing optical resonance. An incident light waveguide 125 is provided to the optical waveguide 120 across a Y-branch part 121. While an end part of the incident light waveguide 125 serves as an incident end 128, the light which causes the optical resonance is made incident on the optical waveguide 120 of the optical resonator 130 from the incidence end 128 through the Y-branch part 121.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type optical frequency comb generator used for optical frequency standard, high precision optical frequency measurement, spectroscopic analysis, light source for optical measurement and the like.

[0002]

2. Description of the Related Art Conventionally, an optical frequency comb generator (Optical Frequency Comb
Comb Generator) is used. That is, when two laser lights are heterodyne-detected and the difference frequency is measured, the band is limited by the band of the light receiving element and is about several tens of GHz, so a wideband heterodyne is used by using an optical frequency comb generator. I am trying to build a detection system. The optical frequency comb generator generates several hundred sidebands of the incident laser light at equal frequency intervals, and the frequency stability of the generated sidebands is almost the same as that of the original laser light. Therefore, by heterodyne-detecting this sideband wave and the laser light to be measured, a wide-band heterodyne detection system over several THz can be constructed.

The bulk type optical frequency comb generator is composed of, for example, an optical phase modulator and an optical resonator composed of a pair of reflecting mirrors arranged so as to face each other via the optical phase modulator. There is.

In the optical frequency comb generator, the optical phase modulator is made of an optical material for optical phase modulation in which the refractive index changes by applying an electric field, and the phase modulation is performed on the light passing through the optical resonator. multiply. Light incident on the optical resonator with a slight transmittance through the incident side reflecting mirror resonates between the pair of reflecting mirrors, undergoes phase modulation by the optical phase modulator, and passes through the emitting side reflecting mirror. It is emitted as frequency comb output light.

Further, the optical waveguide type optical frequency comb generator is
It is equipped with an optical resonator with reflecting mirrors formed on both end faces of a broadband optical waveguide type optical phase modulator, and drives the optical waveguide type optical phase modulator at an integral multiple of the free spectral range of the optical resonator to generate laser light. An optical frequency comb is generated by the modulation.

[0006]

By the way, an optical resonator is generally constituted by a reflection boundary having a high reflectance, and in a conventional optical frequency comb generator, one of the reflection boundaries forming the optical resonator is used. Since the light beam that causes the optical resonance is made incident on the optical resonator, most of the light beam that is made to enter the optical resonator is reflected, and the incident efficiency on the optical resonator is extremely low. However, there was a problem that the conversion efficiency to the optical frequency comb was low.

Therefore, in view of such conventional problems, an object of the present invention is to provide an optical waveguide type optical frequency comb generator in which the efficiency of incidence on the optical resonator is increased and the efficiency of conversion into an optical frequency comb is improved. To provide.

[0008]

An optical waveguide type optical frequency comb generator according to the present invention causes optical resonance formed on an optical material substrate having an electro-optical effect in which a refractive index is changed by applying an electric field. An optical waveguide for passing a light beam,
An optical resonator formed by providing reflecting films on two opposite end faces of the optical waveguide, an incident optical waveguide provided on the optical waveguide through a Y branch, and an optical resonator parallel to the optical waveguide. And an optical phase modulator consisting of electrodes formed by
It is characterized in that an end portion of the incident optical waveguide is used as an incident end, and a light beam which causes optical resonance is incident on the optical resonator from the incident end through the Y branch portion.

In the optical waveguide type optical frequency comb generator according to the present invention, a comb-shaped electrode for surface acoustic wave is provided at an intermediate portion between the Y-branch portion of the optical waveguide and the optical phase modulator, and the light is incident from the incident end. The first guided mode is excited by the generated light beam, and the surface acoustic wave generated from the comb-shaped electrode for the surface acoustic wave is acted on the guided mode. It is possible to adopt a structure in which mode conversion is performed between the optical waveguide and the optical waveguide of the second waveguide mode to optically resonate the optical beam of the second waveguide mode.

The optical waveguide type optical frequency comb generator according to the present invention may have a structure in which a proton exchange section is provided on one of the optical waveguide branched by the Y branch section and the incident optical waveguide.

In the optical waveguide type optical frequency comb generator according to the present invention, a proton exchange section is provided in the optical waveguide branched by the Y branch section, and the TM mode is excited by the light beam incident from the incident end. However, it is possible to have a structure in which the TE mode light is optically resonated in the optical resonator.

In the optical waveguide type optical frequency comb generator according to the present invention, a proton exchange section is provided in the incident optical waveguide branched by the Y branch section, and a TE mode is generated by the light beam incident from the incident end. A structure in which the TM mode light is excited to cause optical resonance in the optical resonator can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The optical waveguide type optical frequency comb generator according to the present invention is constructed, for example, as shown in FIGS.

FIG. 1 is a plan view schematically showing the main structure of an optical waveguide type optical frequency comb generator 100 according to the present invention, and FIG. 2 is a plan view of the optical waveguide type optical frequency comb generator 100. 3 is a schematic perspective view of FIG.

This optical waveguide type optical frequency comb generator 100
Includes an optical waveguide 120 for passing a light beam that causes optical resonance on an electro-optic crystal substrate 110 whose refractive index changes by applying an electric field, and a Y branch portion 121 is provided in the optical waveguide 120. Then, an incident optical waveguide 125 continuous with the optical waveguide 120 is formed via the Y branch portion 121.

Specifically, the electro-optic crystal substrate 110 described above is used.
As X-cut lithium niobate (LiNbO ₃ )
Using a dielectric substrate, the optical waveguide 120 is manufactured in a direction perpendicular to the Z axis by Ti diffusion, and a Y-shaped branch portion 121 is provided in the middle thereof.
An incident optical waveguide 125 continuous with the optical waveguide 120 via 21 is formed.

The optical resonator 130 is constructed by providing the reflecting films 131 and 132 on the two opposite end faces of the both ends of the optical waveguide 120. One reflection film 131 is a total reflection mirror, and the other reflection film 132 is a reflection mirror with high reflectance.

This optical waveguide type optical frequency comb generator 100
Then, with the end of the incident optical waveguide 125 as the incident end 128, a light beam that causes optical resonance is incident on the optical resonator 130 from the incident end 128 via the Y branch portion 121.

The optical waveguide type optical frequency comb generator 100 further includes a pair of electrodes 141 and 142 formed in parallel so as to sandwich the optical waveguide 120.
The refractive index of the optical waveguide 120 between the electrodes 141 and 142 is changed by the electro-optical effect according to a high frequency signal applied to the optical waveguides 41 and 142 from the high frequency power source 145 to change the phase of the light beam passing through the optical waveguide 120. An optical phase modulator 140 for changing is configured. The electrodes 141, 14
2, the high frequency power source 145 is connected to one end in the longitudinal direction,
The other end is terminated by a terminating resistor 148. And
The optical phase modulator 140 supplies a high-frequency signal from the high-frequency power source 145 to the pair of electrodes 141 and 142 formed in parallel so as to sandwich the optical waveguide 120, so that the width direction of the optical waveguide 120 is increased. In response to the change in the electric field due to the applied high frequency signal, the optical waveguide 12
The refractive index of 0 is changed by the electro-optical effect, and the phase of the light beam passing through the optical waveguide 120 is changed.

Further, in this optical waveguide type optical frequency comb generator 100, a comb-shaped electrode 150 for surface acoustic wave is provided at an intermediate portion between the Y branch portion 121 of the optical waveguide 120 and the optical phase modulator 140. There is. The comb-shaped electrode 150 for surface acoustic wave generates a surface acoustic wave (SAW) when a high frequency signal is applied from a high frequency power source (not shown). This surface acoustic wave is propagated along the optical waveguide 120. In this optical waveguide type optical frequency comb generator 100,
By causing the surface acoustic wave generated from the comb-shaped electrode 150 for the surface acoustic wave to act on the guided mode of the light beam propagating in the optical waveguide 120, the mode conversion between the TM guided mode and the TE guided mode is performed. I do.

Further, the Y branch portion 1 of the optical waveguide 120.
21 is a proton exchange part 160 in which a proton exchange is carried out in the vicinity of 21.
Is provided. Here, the optical waveguide 120 and the incident optical waveguide 125 formed by Ti diffusion propagate light of each mode of TM mode light and TE mode light as they are, whereas the proton exchange unit 160 propagates only TE mode light. To do.

Therefore, the Y of the incident optical waveguide 125 is
By providing the proton exchange part 160 near the branch part 121, in the Y branch part 121, TE of the light reflected by the reflection film 132 of the optical resonator 130 and returned is TE.
The mode light passes through the optical waveguide 120 provided with the proton exchange unit 160, and the reflection film 131 of the optical resonator 130.
The TM mode light propagated toward the optical path is returned to the incident end 128 through the incident optical waveguide 125. That is,
The Y branch section 121 provided with the proton exchange section 160 is
It functions as a TE-TM mode splitter that separates TE mode light and TM mode light.

As described above, in the optical waveguide type optical frequency comb generator 100 according to the present invention, the optical material substrate 1 having an electro-optical effect in which the refractive index is changed by applying an electric field.
The reflection film 1 is formed on the two opposite end faces of the optical waveguide 120 through which the light beam that causes optical resonance formed in FIG.
31 and 132 are provided to configure the optical resonator 130, and the optical waveguide 1 is incident on the optical waveguide 120 via the Y branch portion 121.
25, and the end portion of the incident optical waveguide 125 is set to the incident end 1
Reference numeral 28 denotes a light beam that causes optical resonance from the incident end 128 via the Y branch portion 121.
By making the light incident on the optical waveguide 120 of 30, the incidence efficiency on the optical resonator 130 can be improved.
That is, the optical resonator 130 includes the reflective films 131 and 132.
Therefore, the incident end 128 can be made to have a high transmittance, and thus the optical resonator 130 can be made.
The efficiency of incidence on light can be improved.

In this optical waveguide type optical frequency comb generator 100, the incident end 128 of the incident optical waveguide 125 is
Laser light is incident from a laser light source (not shown), and the TM mode is excited by this laser light.

From the incident end 128 to the incident optical waveguide 125
The TM mode light incident on the optical path is incident on the optical resonator 130 through the Y branch section 121.

When the TM mode light incident on the optical resonator 130 passes through the surface of the comb-shaped electrode 150 for surface acoustic waves, the SAW generated by the comb-shaped electrode 150 is generated.
And the interaction with the guided mode in the optical waveguide 120,
The TM mode light is converted to the TE mode light. This TE
The mode light is reflected by the reflection film 132 having a high reflectance at the end of the optical resonator 130, is converted into the TM mode again in the area where the SAW exists, and enters the optical waveguide 120 through the Y branch portion 121. It will be distributed to the optical waveguide 125.

However, for the TE mode light reflected by the reflection film 132 having a high reflectance at the end of the optical resonator 130 and returning to the SAW existing region again, the optical phase modulator 14 is used.
Since the phase modulation is applied when passing through the optical waveguide 120 sandwiched by the 0 electrodes 141 and 142, sidebands having different wavelengths are generated around the light source wavelength due to the modulation frequency. Since this sideband light has a wavelength different from that of the light source, the interaction with the SAW is small and TE-TM mode conversion does not occur. Therefore, the sideband light is
In the TE mode, the light is distributed to the optical waveguide 120 and the incident optical waveguide 125 through the Y branch portion 121.

The TE-mode light propagated along the optical waveguide 120 without returning to the incident optical waveguide 125 is
The light is totally reflected by the reflection film 131 of the optical resonator 130 and again subjected to phase modulation when passing through the optical waveguide 120 sandwiched between the electrodes 141 and 142 of the optical phase modulator 140,
Furthermore, the sideband increases. By repeating this operation, an optical frequency comb is generated in a wide frequency range.

The optical frequency comb thus generated is taken out through the high reflectance reflective film 132 of the optical resonator 130.

This optical waveguide type optical frequency comb generator 100
Then, the comb-shaped electrode 1 for surface acoustic wave is provided at an intermediate portion between the Y branch portion 121 of the optical waveguide 120 and the optical phase modulator 140.
50 is provided, the TM mode is excited by the light beam incident from the incident end 128, and the surface acoustic wave generated from the comb-shaped electrode 150 for the surface acoustic wave is caused to act on the guided mode. Is converted into a TE mode, and the TE mode light beam is optically resonated in the optical resonator 130, whereby the light beam incident from the incident end 128 can be efficiently converted into an optical frequency comb. .

Further, in this optical waveguide type optical frequency comb generator 100, the Y branch section 121 provided with the proton exchange section 160 separates the TE mode light and the TM mode light from each other.
Since it functions as an E-TM mode splitter,
E-mode light can be efficiently confined in the optical resonator 130, and the light beam incident from the incident end 128 can be efficiently converted into an optical frequency comb.

The optical waveguide type optical frequency comb generator according to the present invention is constructed as shown in FIGS. 3 and 4, for example.

FIG. 3 is a plan view schematically showing the main structure of an optical waveguide type optical frequency comb generator 200 according to the present invention, and FIG. 4 is a plan view of the optical waveguide type optical frequency comb generator 200. 3 is a schematic perspective view of FIG.

This optical waveguide type optical frequency comb generator 200
Is a Z-cut lithium niobate (LiNbO ₃ ) dielectric substrate is used as the electro-optic crystal substrate 210 whose refractive index changes by applying an electric field. Optical resonance occurs on the electro-optic crystal substrate 210. The optical waveguide 220 that allows the light beam to pass therethrough is formed by Ti diffusion, and the optical waveguide 220 is provided with a Y branch portion 221. The incident optical waveguide 225 that is continuous with the optical waveguide 220 via the Y branch portion 221. Are formed.

An optical resonator 230 is constructed by providing a total reflection film 231 and a high-reflectance reflection film 232 on the two opposite end faces of the optical waveguide 220.

This optical waveguide type optical frequency comb generator 200
Then, with the end of the incident optical waveguide 225 as the incident end 228, a TE mode light beam that causes optical resonance is incident on the optical resonator 230 from the incident end 228 via the Y branch portion 221.

Further, the optical waveguide type optical frequency comb generator 200 comprises a pair of electrodes 241 formed in parallel so as to sandwich the optical waveguide 220, and an electrode 242 provided on the optical waveguide 220. In response to a high frequency signal applied from the high frequency power supply 245 to the electrodes 241 and 242,
An optical phase modulator 240 that changes the refractive index of the optical waveguide 220 below the electrode 242 by an electro-optical effect and changes the phase of the light beam passing through the optical waveguide 220 is configured. A high frequency power supply 245 is connected to one end of each of the electrodes 241 and 242 in the longitudinal direction, and the other end is a terminating resistor 24.
Terminated by 8. Then, the optical phase modulator 2
40 is a pair of electrodes 241 formed in parallel to sandwich the optical waveguide 220 and an electrode 242 provided on the optical waveguide 220, and a high frequency signal is supplied from a high frequency power supply 245 to the optical waveguide 40. The refractive index of the optical waveguide 220 is changed by the electro-optical effect according to the change of the electric field due to the high frequency signal applied in the thickness direction of the 220, and the phase of the light beam passing through the optical waveguide 220 is changed.

Further, in this optical waveguide type optical frequency comb generator 200, a comb-shaped electrode 250 for surface acoustic wave is provided at an intermediate portion between the Y branch portion 221 of the optical waveguide 220 and the optical phase modulator 240. Therefore, a surface acoustic wave (SAW) generated by applying a high frequency signal from a high frequency power source (not shown) is applied to the waveguide mode of the light beam propagating in the optical waveguide 220, whereby
Mode conversion between M guided modes is performed.

In the optical waveguide type optical frequency comb generator 200, the SAW absorption layer is arranged so that the SAW generated from the surface acoustic wave comb-shaped electrode 250 is not propagated to the Y branch portion 221 side. 290 is the Y branch section 2
21 and the comb-shaped electrode 250.

Further, the Y branch portion 2 of the optical waveguide 220.
A proton exchange section 260 is provided in the vicinity of 21. Here, the optical waveguide 220 and the incident optical waveguide 225 formed by Ti diffusion propagate light of each mode of TM mode light and TE mode light as they are, whereas the proton exchange unit 260 propagates only TE mode light. To do.

Therefore, by providing the proton exchange section 260 in the vicinity of the Y branch section 221 of the optical waveguide 220, in the Y branch section 221, of the light reflected by the reflection film 232 of the optical resonator 230 and returned. , TM mode light is propagated toward the reflection film 231 of the optical resonator 230 through the optical waveguide 220 provided with the proton exchange section 260, and TE mode light is transmitted in the incident optical waveguide 2
25, and is returned to the entrance end 228. That is, the Y branch portion 221 provided with the proton exchange portion 260 is
It functions as a TE-TM mode splitter that separates mode light and TM mode light.

As described above, in the optical waveguide type optical frequency comb generator 200 according to the present invention, the optical material substrate 2 having an electro-optical effect in which the refractive index is changed by applying an electric field.
The reflection film 2 is formed on the two opposite end faces of the optical waveguide 220 through which the light beam that causes optical resonance is formed.
31 and 232 are provided to configure an optical resonator 230, an incident optical waveguide 225 that is continuous to the optical waveguide 220 via a Y branch portion 221 is provided, and an end portion of the incident optical waveguide 225 serves as an incident end 228. By making a light beam that causes resonance enter the optical waveguide 220 of the optical resonator 230 from the incident end 228 through the Y branch portion 221, the incidence efficiency of the optical resonator 230 can be improved. . That is, the optical resonator 230 includes the reflective film 23.
1, 232, the incident end 22
8 can have a high transmittance, which can improve the efficiency of incidence on the optical resonator 230.

Then, in the optical waveguide type optical frequency comb generator 200, the incident end 228 of the incident optical waveguide 225 is used.
Laser light is incident from a laser light source (not shown), and the TE mode is excited by this laser light.

From the incident end 228 to the incident optical waveguide 225
The TE-mode light incident on is incident on the optical resonator 230 through the Y branch portion 221.

The TE-mode light incident on the optical resonator 230 passes through the comb-shaped electrode 250 portion for the surface acoustic wave, and the SAW generated by the comb-shaped electrode 250.
And the guided mode in the optical waveguide 220,
The TE mode light is converted into the TM mode light. This TM
The mode light is reflected by the reflection film 232 having a high reflectance at the end of the optical resonator 230, is converted into the TE mode again in the area where the SAW exists, and enters the optical waveguide 220 through the Y branch portion 221. It is distributed to the optical waveguide 225.

However, for the TM mode light reflected by the reflection film 232 having a high reflectance at the end of the optical resonator 230 and returning to the area where the SAW exists, the optical phase modulator 24 is used.
Since the phase modulation is applied when passing through the optical waveguide 220 below the 0 electrode 242, sidebands having different wavelengths are generated around the light source wavelength due to the modulation frequency. Since this sideband light has a wavelength different from that of the light source, the interaction with the SAW is small and the TM-TE mode conversion does not occur. Therefore, the sideband light remains in the TM mode, passes through the Y branch portion 221, and enters the incident optical waveguide 22.
5 is propagated.

The TM-mode light propagated along the optical waveguide 220 without returning to the incident optical waveguide 225 through the Y-branching portion 221 is totally reflected by the total reflection film 231 of the optical resonator 230. Then, again, the optical phase modulator 240
When passing through the optical waveguide 220 below the electrode 242, the phase modulation is applied, and the side band further increases. By repeating this operation, an optical frequency comb is generated in a wide frequency range.

The optical frequency comb thus generated is taken out through the reflection film 232 having a high reflectance of the optical resonator 230.

This optical waveguide type optical frequency comb generator 200
Then, the comb-shaped electrode 2 for surface acoustic wave is provided at an intermediate portion between the Y branch portion 221 of the optical waveguide 220 and the optical phase modulator 240.
50 is provided, the TM mode is excited by the light beam incident from the incident end 228, and the surface acoustic wave generated from the comb-shaped electrode 250 for the surface acoustic wave is applied to the guided mode to cause the TE mode. Is converted into the TM mode and the TM mode light beam is optically resonated in the optical resonator 230, whereby the light beam incident from the incident end 228 can be efficiently converted into an optical frequency comb. .

Furthermore, in this optical waveguide type optical frequency comb generator 200, the Y branching section 221 provided with the proton exchange section 260 separates the TE mode light and the TM mode light from each other.
Since it functions as an E-TM mode splitter,
By confining the M-mode light in the optical resonator 230, the light beam incident from the incident end 228 can be efficiently converted into an optical frequency comb.

[0052]

As described in detail above, in the optical waveguide type optical frequency comb generator according to the present invention, the light formed on the optical material substrate having the electro-optical effect in which the refractive index is changed by applying the electric field. An optical resonator is configured by providing reflecting films on two opposite end faces of an optical waveguide through which a light beam that causes resonance is passed, and an incident optical waveguide that is continuous through the Y branch portion is provided in the optical waveguide. A light beam for causing optical resonance is incident on the optical waveguide of the optical resonator from the incident end through the Y branch portion to the optical resonator by using the end portion of the incident optical waveguide as the incident end. The incidence efficiency can be improved.

Further, in the optical waveguide type optical frequency comb generator according to the present invention, a comb-shaped electrode for surface acoustic wave is provided at an intermediate portion between the Y-branch portion of the optical waveguide and the optical phase modulator, and the incident end is provided. The first guided mode is excited by the light beam incident from the first surface, and the surface acoustic wave generated from the comb-shaped electrode for surface acoustic waves acts on the guided mode.
By performing mode conversion between the waveguide mode of the second waveguide mode and the second waveguide mode and optically resonating the light beam of the second waveguide mode in the optical resonator. The optical beam can be efficiently converted into an optical frequency comb.

Further, in this optical waveguide type optical frequency comb generator, the Y branch portion provided with the proton exchange portion serves as a waveguide mode splitter for separating the first guided mode light and the second guided mode light. Since it functions, the second guided mode light can be confined in the optical resonator and the light beam incident from the incident end can be efficiently converted into an optical frequency comb.

Therefore, according to the present invention, it is possible to provide an optical waveguide type optical frequency comb generator in which the incidence efficiency on the optical resonator is improved and the conversion efficiency to the optical frequency comb is improved.

[0056]

[Brief description of drawings]

FIG. 1 is a plan view schematically showing a configuration example of a main part of an optical waveguide type optical frequency comb generator according to the present invention.

FIG. 2 is a schematic perspective view of the optical waveguide type optical frequency comb generator.

FIG. 3 is a plan view schematically showing another configuration example of the main part of the optical waveguide type optical frequency comb generator according to the present invention.

FIG. 4 is a schematic perspective view of the optical waveguide type optical frequency comb generator.

[Explanation of symbols]

100,200 Optical waveguide type optical frequency comb generator, 11
0,210 electro-optic crystal substrate, 120,220 optical waveguide, 121,221 Y branch, 125,225 incident optical waveguide, 130,230 optical resonator, 131,13
2, 231, 232 reflective film, 128, 228 incident end, 140, 240 optical phase modulator, 141, 142,
241,242 electrodes, 145,245 high frequency power supply,
148,248 Termination resistance, 150,250 Comb type electrode, 160,260 Proton exchange part, 290 Absorption layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Osamu Nakamoto             3-3-4 Kamata, Ota-ku, Tokyo (72) Inventor Bang Bang Widy Tomoko             3034-3 Nagatsuta-cho, Midori-ku, Yokohama-shi, Kanagawa (72) Inventor Yoshinori Nakayama             3-43-9 Okusawa, Setagaya-ku, Tokyo F-term (reference) 2H079 AA02 AA04 AA12 BA03 CA04                       CA11 CA24 DA03 EA03 EA05                       EA28 EB05 EB23 HA08 KA18

Claims (5)

[Claims] 1. An optical waveguide formed on an electro-optic crystal substrate having an electro-optic effect, the refractive index of which changes when an electric field is applied, for passing a light beam for causing optical resonance, and opposite ends of the optical waveguide facing each other. An optical resonator including an optical resonator formed by providing a reflection film on two end surfaces thereof, an incident optical waveguide provided in the optical waveguide via a Y branch portion, and an electrode formed in parallel with the optical waveguide. A modulator, wherein a light beam for causing optical resonance is incident on the optical resonator from the incident end through the Y branch portion with the end of the incident optical waveguide as the incident end. Waveguide optical frequency comb generator. 2. A comb-shaped electrode for a surface acoustic wave is provided in an intermediate portion between the Y branch portion of the optical waveguide and the optical phase modulator, and a first waveguide mode is generated by a light beam incident from the incident end. Excitation is performed, and the surface acoustic wave generated from the above-mentioned surface acoustic wave comb-shaped electrode is caused to act on the guided mode, thereby performing mode conversion between the first guided mode and the second guided mode. 2. The optical waveguide type optical frequency comb generator according to claim 1, wherein the optical beam of the second guided mode is optically resonated in the optical resonator. 3. The optical waveguide type optical frequency comb generator according to claim 2, wherein a proton exchange portion is provided on one of the optical waveguide branched by the Y branch portion and the incident optical waveguide. 4. A proton exchange section is provided in the optical waveguide branched by the Y branch section, the TM mode is excited by the light beam incident from the incident end, and the TE mode light is optically resonated in the optical resonator. The optical waveguide type optical frequency comb generator according to claim 3, wherein 5. A proton exchange section is provided in the incident optical waveguide branched by the Y branch section, a TE mode is excited by a light beam incident from the incident end, and TM mode light is optically resonated in the optical resonator. The optical waveguide type optical frequency comb generator according to claim 3, wherein