Micro optical resonator, and light frequency comb generation device

Abstract

To solve the problem that, in starting a light frequency comb, the resonance wavelength and the refractive index change due to thermal deformation of a resonator, so that it has been difficult to shift a wavelength λ1 of excitation light 33 to a region to form soliton accurately, the serious problem in terms of size reduction and cost because the function of sweeping the excitation light to a soliton region of the resonator requires to change the wavelength of the excitation light, and moreover the problem that the continuous generation of soliton light comb has been unstable due to ambient temperature change.SOLUTION: An optical comb device includes a thermal deformation actuator 13 in which the diameter of a first waveguide 12 is variable, a first heater that heats the thermal deformation actuator 13, and a substrate that cools the thermal deformation actuator 13. When the comb of the first waveguide is started, a first end thermal deformation actuator is heated and then the soliton light comb is started by the subsequent cooling process; thus, the optical comb device with a simpler and smaller structure can be achieved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for controlling the frequency of an optical frequency comb, and more particularly to an apparatus and method for controlling the frequency of an optical frequency comb that reliably starts a soliton optical comb and continuously generates and maintains a soliton optical comb. [Background technology]

[0002] An optical frequency comb is an optical signal with a comb-shaped spectrum consisting of components (modes) arranged at equal intervals on the frequency axis.

[0003] To activate an optical frequency comb, it is not enough to simply create an anomalous dispersion state within the cavity; a special procedure is required. In 2014, a method was discovered in which the wavelength of a continuous-wave (CW) laser light source introduced into a circular optical waveguide is continuously swept around its resonant frequency, and many techniques based on this method have been researched.

[0004] However, activation using the above method is extremely complicated because it is necessary to consider two factors in the resonant frequency shift in the circular optical waveguide: the optical shift due to the Kerr nonlinear effect, and the thermal shift due to the change in the refractive index of the material itself due to temperature rise and thermal expansion.

[0005] A conventional optical frequency comb generator will now be described. This micro-optical resonator is shown in Figure 11. Figure 11(a) is a plan view of the waveguide, and Figure 11(b) shows a cross-sectional view along the x-axis. 29a is a first cladding layer made of silicon dioxide (SiO2) deposited on a substrate 28. A portion of this first cladding layer 29a is etched away to embed a resonator 31, which is a circular optical resonator, and a waveguide 30, on top of which a second cladding layer 29b is formed. The resonator 31 is ring-shaped, and the waveguide 30 is linear. The resonator 31 and the waveguide 30 are arranged with a small gap d between them. The z-direction side of the gap d is formed by a surface processed by dry etching. The resonator 31 and the waveguide 30 are made of silicon nitride.

[0006] The operation of the conventional optical frequency comb generator configured as above will now be described.

[0007] An input unit 32 is connected to the waveguide 30, which receives input of excitation light irradiated from a continuous wave (CW) laser light source device not shown, and excitation light 33, which is CW laser light, is incident on the waveguide 30 from the CW laser light source device.

[0008] The incident pumping light 33 is a continuous wave having a wavelength λ1. Figure 12(a) shows the wavelength spectrum of the incident pumping light 33. When the resonant wavelength λ1 of the pumping light 33 overlaps with the resonant wavelength of the resonator 31, the pumping light 33 leaks out of the waveguide 30 and is taken into the resonator 31 as a so-called evanescent wave.

[0009] When the modes with different wavelengths inside the resonator are aligned, their peaks overlap and constructively interfere with each other, generating a pulse 36. This state is called mode locking. This pulse is also called an optical comb. Figure 13 shows the concept of modes.

[0010] The mode spacing is expressed as the repetition frequency frep, frep =c / (2nL) where n is the effective refractive index of the waveguide material, L is the perimeter of the resonator, and c is the speed of light. When viewed on the frequency axis, the optical comb has a spectrum in which modes are arranged at equal intervals like a comb, as shown in Figure 12(b).

[0011] Here, wavelength sweeping of a micro optical resonator will be explained with reference to FIG. The optical comb is generated by sweeping the wavelength of the pump light 33 from short to long wavelengths relative to the resonant wavelength λ2 of the resonant waveform 35 of the micro-optical resonator. Here, the distance between the wavelength λ1 of the pump light 33 and the resonant wavelength λ2 of the micro-optical comb is referred to as the detuning amount. The position of the resonant wavelength λ2 is called zero detune. The wavelength shorter than zero detune is called blue detune, and the wavelength longer than zero detune is called red detune. As the detuning amount decreases from the blue detune side, the pump light 33 resonates as an evanescent wave from the waveguide 30, and coupling power is guided into the resonator 31. This gradually increases the optical power within the resonator 31. When the coupling power of the pump light 33 exceeds the threshold of the nonlinear optical effect, a comb mode is generated by four-wave mixing (FWM). What is generated at this time is a chaotic optical comb.

[0012] Comb-like spectra generated using a micro-optical resonator can be broadly divided into chaotic optical combs and soliton optical combs. An optical comb that is not mode-locked is called a chaotic optical comb. On the other hand, an optical comb that is mode-locked and is the most stable in terms of phase, frequency, pulse waveform, etc. is called a soliton optical comb.

[0013] In order to generate a soliton optical comb, it is necessary to capture a soliton region 37 where the wavelength λ1 of the pump light 33 has shifted to red detune, exceeding the zero-tuned wavelength λ2.

[0014] Figure 15 shows the process by which pump light 33 reaches the red-detuned soliton region. In Figure 15(1), the wavelength λ1 of pump light 33 shifts toward the longer wavelength side. In Figure 15(2), when the pump light 33 is applied to the resonant waveform, optical energy gradually flows into the resonator 31.

[0015] This optical energy heats the resonator 31. This heat causes the ring diameter of the resonator 31 to expand, shifting the resonant wavelength λ2 to the longer wavelength side. 34 is the change in the resonant wavelength of the resonator due to heat. The refractive index also increases. Furthermore, if the optical intensity inside the ring becomes high, the Kerr effect will appear. To avoid this, it is necessary to pass through the resonance peak at a high speed. Then, in Figure 15 (3), the pump light 33 overtakes the resonance peak and reaches the soliton region, where it stops. In this way, the pump light 33 must pass the peak of the resonance waveform 35, inject high optical intensity into the resonator 31, and then reach the soliton region where it stops. These operations result in a soliton optical comb. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent No. 10,268,100 [Non-patent literature]

[0017] [Non-Patent Document 1] Jacob S.Levy,et al.,Nature Photonics,4,pp.37-40(2010) [Non-patent document 2] T. Herr,et al.,Nature Photonics,8,pp.145-152(2014) Summary of the Invention [Problem to be solved by the invention]

[0018] In the above-described conventional configuration, when generating an optical frequency comb, the wavelength of the pump light must be shifted from a wavelength smaller than the resonant wavelength of the resonator to a wavelength larger than the resonant wavelength of the resonator, and a comb mode must be generated by four-wave mixing.

[0019] However, as the wavelength of the pump light approaches the wavelength of the resonator, the resonant wavelength of the resonator becomes longer due to expansion caused by heat generated by optical energy, and the region where the optical comb solitonizes shifts toward longer wavelengths. Furthermore, as the refractive index increases due to heat, the wavelength of the pump light becomes shorter, and it becomes necessary to increase the wavelength to be swept to compensate for this. This has posed a problem: it is difficult to accurately shift the wavelength λ1 of the pump light 33 into the region where solitonization occurs.

[0020] The present invention is intended to solve the above-mentioned conventional problems, and has as its object to provide a micro optical resonator that uses changes in the resonant wavelength of the resonator due to heat to reliably convert an optical comb into a soliton with a simple configuration. [Means for solving the problem]

[0021] To achieve this goal, the optical frequency comb generator of the present invention fixes the wavelength of the pump light without sweeping its wavelength. Meanwhile, a first heater heats a cylindrical thermally deformable actuator located inside the first waveguide and coaxially with the center of the first waveguide. After a first temperature sensor detects that the first heater has reached a predetermined temperature, the voltage is controlled to cool the thermally deformable actuator. As a result, the ring diameter of the first waveguide decreases, shifting its resonant wavelength toward shorter wavelengths, and the pump light relatively reaches the soliton region of the resonant waveform. [Effects of the Invention]

[0022] As described above, the present invention allows the launch of a soliton optical comb by fixing the wavelength of the pump light 23 during the launch process of the micro optical comb. This eliminates the need to control the pump light and sweep the wavelength during the launch process. This eliminates the need for a laser light source control device for wavelength sweeping operations, allowing for significant cost reductions and device miniaturization.

[0023] Furthermore, by maintaining a constant temperature of the substrate, it is possible to stabilize the continuous generation of soliton optical combs even when the external environmental temperature changes. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a plan view of a micro optical resonator according to a first embodiment of the present invention. [Figure 2] 1 is a cross-sectional view of a micro optical resonator according to a first embodiment of the present invention. [Figure 3] FIG. 2 is a plan view of a first heater of the micro optical resonator according to the first embodiment of the present invention. [Figure 4] 3 shows material characteristics of the micro optical resonator according to the first embodiment of the present invention. [Figure 5] 4 is an operation diagram of the thermal deformation actuator of the micro optical resonator according to the first embodiment of the present invention. FIG. [Figure 6] 6(a) is a timing chart for explaining the operation of the micro optical resonator according to the first embodiment of the present invention, and (b) is a diagram showing the temperature of the first heater corresponding to FIG. [Figure 7] 10A and 10B are diagrams showing the movement process of a resonance waveform with a fixed excitation light for explaining the operation of the micro optical resonator according to the first embodiment of the present invention. [Figure 8] 3A to 3C are diagrams illustrating a manufacturing process of the micro optical comb according to the first embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view of a micro optical resonator according to a second embodiment of the present invention. [Figure 10] FIG. 10 is an explanatory diagram of the operation of the temperature control device according to the second embodiment of the present invention. [Figure 11] 1A and 1B are plan and cross-sectional views of a conventional micro-optical resonator. [Figure 12] FIG. 1 is an explanatory diagram illustrating the concept of mode locking of a micro optical resonator. [Figure 13] FIG. 1 is an explanatory diagram of a comb-shaped spectrum generated by a micro optical comb. [Figure 14] 1 is an explanatory diagram showing the relationship between pump light and the resonant waveform of a resonator when a soliton optical comb is generated using a micro optical comb. FIG. [Figure 15] 1A and 1B are diagrams illustrating the sweep process of excitation light for explaining the operation of a conventional micro optical resonator. DETAILED DESCRIPTION OF THE INVENTION

[0025] The invention described in claim 1 of the present invention comprises an input section that accepts input of excitation light having a predetermined frequency irradiated from a laser light source device; a ring-shaped first waveguide made of a material having a third-order nonlinear optical effect; a second waveguide that receives the excitation light from the input section, inputs at least a portion of the excitation light into the first waveguide, and extracts from the first waveguide an optical frequency comb having a plurality of comb-like spectra with equal frequency intervals; a cladding that surrounds the first waveguide and the second waveguide and is formed with a refractive index lower than that of the first waveguide and the second waveguide; a cylindrical thermal deformation actuator that is formed inside the ring of the first waveguide and is coaxial with the center of the first waveguide; a first heater that heats the thermal deformation actuator; and cooling means that cools the thermal deformation actuator, wherein the thermal deformation actuator heated by the first heater increases the diameter of the first waveguide, thereby changing the resonant wavelength of the resonator.

[0026] This configuration makes it possible to eliminate the conventional sweeping operation of continuously changing the wavelength of the pump light when starting a soliton optical comb, thereby enabling a more reliable soliton optical comb startup process and eliminating the need for a conventional system that sweeps the pump light.

[0027] The invention described in claim 2 of the present invention has a first temperature sensor that detects the temperature of the thermal deformation actuator in order to control the voltage applied to the first heater, which makes it possible to accurately manage the temperature of the first thermal deformation actuator and realize optimal soliton optical comb activation.

[0028] In the third aspect of the present invention, the thermal deformation actuator and the first heater are in contact with each other. This improves the response speed of the thermal actuator, thereby enabling the soliton optical comb startup process to be carried out more reliably.

[0029] In the fourth aspect of the present invention, the thermal deformation actuator is in contact with the substrate, which is the cooling means. This allows the temperature of the thermal deformation actuator to be cooled quickly, improving the response speed of the thermal deformation actuator. This makes it possible to more reliably perform the soliton optical comb startup process.

[0030] The invention described in claim 5 of the present invention includes an input unit that receives an input of excitation light having a predetermined frequency irradiated from a laser light source device; a ring-shaped first waveguide made of a material having a third-order nonlinear optical effect; a second waveguide that receives the excitation light from the input unit and optically couples it with the first waveguide to input at least a portion of the excitation light into the first waveguide and extract an optical frequency comb having a plurality of comb-like spectra with equal frequency intervals from the first waveguide; and a second waveguide that surrounds the first and second waveguides and couples the first and second waveguides to the first and second waveguides. The device includes a cladding formed with a refractive index lower than that of the waveguide, a thermal deformation actuator formed inside the ring of the first waveguide, a first heater for heating the thermal deformation actuator, a first temperature sensor for detecting the temperature of the thermal deformation actuator, a cooling means for cooling the thermal deformation actuator, a second heater for heating the substrate, a second temperature sensor for detecting the temperature of the cooling means, and a temperature control device for controlling the second heater by feeding back a signal detected by the second temperature sensor, thereby controlling the temperature of the substrate to a predetermined value, thereby controlling the substrate to a constant temperature at all times.

[0031] This configuration makes it possible to eliminate the conventional sweeping operation of continuously changing the wavelength of the pump light when starting up a soliton optical comb, and also makes it possible to more reliably perform the soliton optical comb startup process even if the ambient temperature changes.Furthermore, it is possible to provide an optical frequency comb generator that is highly reliable when continuously generating soliton optical combs over long periods of time, even if the external ambient temperature changes.

[0032] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. (Embodiment 1) FIG. 1 is a plan view of a micro-optical resonator 10 of the present invention. The micro-optical resonator 10 is configured with a ring-shaped first waveguide 12 and a linear second waveguide 11, surrounded by a cladding 16 having a refractive index lower than that of the waveguide. Furthermore, the ring-shaped first waveguide 12 is provided on the same plane as the linear second waveguide 11 with a small gap d provided. The radius r of the ring is determined by the repetition frequency of the mode period. Frep=c / (2nL) L=2πr where n is the effective refractive index of the first waveguide, L is the perimeter of the resonator, and c is the speed of light. An input section 20 is provided at one end of the second waveguide to receive pumping light 23 from the laser light source. An output section 21 is provided at the other end of the second waveguide 11 to output the generated soliton optical comb 22.

[0033] FIG. 2 is a cross-sectional view of a micro-optical resonator 10 of the present invention. The micro-optical resonator 10 is formed on a silicon substrate 15, which serves as a cooling means with excellent thermal conductivity. The cylindrical bottom surface 13a of the thermally deformable actuator 13 is provided directly on the substrate 15. The cylindrical thermally deformable actuator 13 is disposed inside the first waveguide 12 at a distance g, and the doughnut-shaped gap is filled with a cladding portion 16x. The width g of the cladding portion 16x is set as small as possible without affecting the light inside the waveguide. A first heater 14 is provided directly on the top surface 13b of the cylindrical thermally deformable actuator 13, and 14a and 14b are electrode pads of the first heater.

[0034] Figure 3 shows a plan view of the first heater 14 and electrode pads 14a and 14b. The first heater 14 is formed from a platinum thin film and has a curved path that increases electrical resistance. The electrode pads 14a and 14b are partially exposed for external wiring. A first temperature sensor 19 is attached to the first heater 14 to detect the temperature of the first heater 14. The first temperature sensor 19 is provided with electrode pads 19a and 19b, partially exposed for external wiring. The first temperature sensor 19 is a thermocouple that detects the temperature difference between the substrate 15 and the first heater 14. In this example, the second waveguide 11 and the first waveguide are made of silicon nitride (Si3N4). Silicon oxide (SiO2) is used as the cladding material. The material characteristics are shown in Figure 4.

[0035] The soliton optical comb startup operation of the micro optical resonator configured as above will now be described. First, the function of adjusting the resonant frequency of the first waveguide using the thermally deformable actuator 13, a feature of the present application, will be described with reference to FIG. 5. In FIG. 5(a), the thermally deformable actuator 13 is heated by the first heater 14 and displaced in the direction (arrow direction) in which the radius of its cylindrical surface increases. This thermal deformation mechanically deforms the inner surface of the first waveguide 12 in the circumferential direction, increasing the circumferential length L of the resonator. On the other hand, in FIG. 5(b), when the heating by the first heater 14 is stopped and the thermally deformable actuator 13 is cooled, the thermally deformable actuator contracts and the circumferential length L decreases. In this way, by heating or cooling the thermally deformable actuator 13, the circumferential length of the first waveguide 12 is changed, and its resonant wavelength is adjusted.

[0036] 6(a) is a timing chart showing the startup operation when starting a frequency soliton optical comb, and FIG. 6(b) is a diagram showing the wavelength shift amount Δλ2 of the corresponding resonant waveform 24.

[0037] 7 is a diagram showing the correlation between the wavelength λ1 of the pump light 23 and the zero tune λ2 of the resonant waveform 24 at each position in the timing chart of FIG. 6. Each position will be described as step (1) to step (5).

[0038] When the frequency soliton optical comb start command is turned on, At (1), the first heater 14 is turned on and heated by an external power source. This causes the thermally deformable actuator 13 to thermally expand and reach a predetermined diameter. This deformation increases the diameter of the first waveguide 12, and the resonant wavelength λ2 shifts toward the longer wavelength side by Δλ2. The resonant waveform before heating is shown by a solid line, and the resonant wavelength after heating is shown by a dashed line. In (2), when the first temperature sensor 19 attached to the first heater 14 detects a predetermined temperature T1, the first heater 14 is turned off. When the first heater 14 is turned off, the thermal deformation actuator 13 is cooled to the second temperature T2 of the substrate 15, and the resonant waveform shifts to the shorter wavelength side (to the left in the figure). The excitation light 23 is activated at this timing. Note that the wavelength is fixed to a constant value. (3) is the position where the pump light 23 overlaps the base of the resonant waveform 24. From this point on, the optical intensity is injected into the first waveguide 12. (4) is the position where the pump light 23 overlaps the peak (zero tune) of the resonance waveform 24. At this time, a large optical intensity is injected into the first waveguide 12, and four-wave mixing is excited. (5) is the position where the pump light 23 is applied to the soliton region in the red tune of the resonant waveform 24. The wavelength λ2 of the pump light reaches the soliton region.

[0039] FIG. 8 shows the manufacturing process of the micro optical comb. In step (1), a silicon oxide film is formed on a substrate 15 to form a cladding 16a. In step (2), a groove 12a for forming the first waveguide 12 and a groove 11a for forming the second waveguide 11 are processed in the cladding 16a. In step (3), a recess 13x for providing the thermally deformable actuator 13 directly on the substrate 15 is machined in the cladding 16a. In step (4), a silicon nitride film is formed. In step (5), excess silicon nitride is removed by chemical mechanical polishing. In step (6), a cladding layer 16b of silicon oxide is formed. In step (7), a recess 13y for the thermal deformation actuator 13 is formed. In step (8), a silicon nitride film is formed. In step (9), excess silicon nitride is removed by chemical mechanical polishing. In step (10), the first heater 14 and the temperature sensor 19 are formed on the thermally deformable actuator 13. In step (11), a silicon oxide film is formed on the first heater 14. 16c is a cladding that covers the first heater 14 and the temperature sensor 19. The material of the thermally deformable actuator 13 may be silicon, which has a higher thermal conductivity and thermal expansion coefficient than silicon nitride. In this case, the process shown in Figure 8 must be modified.

[0040] As described above, according to this embodiment, the wavelength of the excitation light 23 is fixed, and the resonant wavelength of the first waveguide 12 is mechanically changed by the thermal deformation actuator 13. Alternatively, it is possible to change the resonant wavelength by heating the first waveguide. However, in this case, it is not possible to directly install a heater on the first waveguide, and heating is performed via the cladding 16. If silicon oxide is used as the cladding material, its low thermal conductivity poses a problem in response in terms of cooling speed.

[0041] In this embodiment, the strain caused by the deformation of the thermally deformable actuator 13 is transmitted to the first ring waveguide via the cladding portion 16x, thereby ensuring high responsiveness. Furthermore, the refractive index of the waveguide material increases with increasing temperature. Therefore, when heating the waveguide, the material is simultaneously affected by thermal expansion and refractive index changes, meaning that two parameters act on the input heater heat amount. This leaves issues with regard to variation and stability. In this embodiment, only mechanical thermal deformation is applied, resulting in excellent reliability.

[0042] The material for the thermally deformable actuator 13 may be silicon, which has a higher thermal conductivity and thermal expansion coefficient than silicon nitride. In this case, the process shown in Figure 8 must be modified. Also, in step (2) of Figure 5, the first heater is turned off to allow the thermally deformable actuator 13 to cool naturally, but the input voltage of the first heater 14 may be controlled to reduce the voltage and allow cooling.

[0043] (Embodiment 2) FIG. 9 is a cross-sectional view of the x-axis (the same as the x-axis in FIG. 1) of a micro-optical resonator 26 according to a second embodiment of the present invention. The plan view is the same as that of FIG. 1, so a description thereof will be omitted. A cylindrical thermal deformation actuator 13 is disposed inside the first waveguide 12 at a distance g, with the gap filled with a cladding portion 16x. The width g of the cladding portion 16x is set as small as possible without affecting the light inside the waveguide. A first heater 14 is provided on the top surface 13b of the cylindrical thermal deformation actuator 13, with 14a and 14b being electrode pads of the first heater.

[0044] The first heater 14 is made of a thin platinum film and has a curved path that increases electrical resistance, and electrode pads 14a and 14b are partially exposed for external wiring. A first temperature sensor 19 is attached to the first heater 14 so that the temperature of the first heater 14 can be detected. The first temperature sensor 19 is a thermocouple that detects the temperature difference between the substrate 15 and the first heater 14.

[0045] The first temperature sensor 19 is provided with electrode pads 19a and 519b, which are partially exposed for external wiring. The micro optical resonator 26 is formed on a substrate 15 with excellent thermal conductivity. The thermal deformation actuator 13 has its cylindrical bottom surface 13a directly mounted on the substrate 15.

[0046] 10 is a block diagram of a temperature control device 25 that constantly maintains a constant temperature of the substrate 15. The difference from the configuration of the first embodiment in FIG. In the temperature control device 25, a second heater 17 and a second temperature sensor 18 are provided on the substrate 15. The second heater 17 is provided over a wide area so as to uniformly heat the entire substrate 15. The second temperature sensor 18 is an NTC thermistor.

[0047] The environmental temperature in which the micro optical resonator 26 is used naturally changes, so the environmental temperature for use is preset in the product specifications. If the product specification allows temperatures up to 85°C, the reference temperature T2 of the board is: T2 = 85°C Let's say.

[0048] The operation of the micro optical resonator 26 configured as above will now be described. If the measured temperature T3 of the substrate 15 is lower than the reference temperature T2, i.e., T2>T3 At this time, the temperature control unit 27 applies power proportional to the temperature difference (T2-T3) to the second heater 17 so as to raise the temperature of the substrate 15 to T2.

[0049] At startup, the second temperature sensor detects the temperature T3 of the substrate 15 and transmits this information to the temperature control unit 27. The temperature obtained by subtracting the detected temperature T3 from the reference temperature T2 is fed back to the second heater 17. After the substrate temperature has stabilized at the reference temperature T2, the operation proceeds to start up the soliton optical comb using the same operations as in the first embodiment.

[0050] As described above, according to this embodiment, there is provided an input section that receives an input of excitation light having a predetermined frequency irradiated from a laser light source device, a ring-shaped first waveguide made of a material having a third-order nonlinear optical effect, a second waveguide that receives the excitation light from the input section and optically couples it with the first waveguide to input at least a portion of the excitation light into the first waveguide and extract from the first waveguide an optical frequency comb having a plurality of comb-like spectra with equal frequency intervals, a cladding that surrounds the first waveguide and the second waveguide and has a refractive index lower than that of the first waveguide and the second waveguide, and a cladding formed inside the ring of the first waveguide. By providing a thermal deformation actuator, a first heater that heats the thermal deformation actuator, a first temperature sensor that detects the temperature of the thermal deformation actuator, a cooling means that cools the thermal deformation actuator, a second heater that heats the cooling means, a second temperature sensor that detects the temperature of the cooling means, and a temperature control device that controls the second heater by feeding back the signal detected by the second temperature sensor, thereby controlling the temperature of the substrate to a predetermined value, it is possible to suppress expansion of the waveguide due to heat and changes in the resonant wavelength of the first waveguide due to changes in the refractive index of the waveguide, even if the environmental temperature changes, and it becomes possible to stably start up and continuously generate soliton optical combs. [Explanation of symbols]

[0051] 10 Micro-optical resonators 11 Second waveguide 12 First waveguide 13 Thermal deformation actuator 13a Bottom of the thermal deformation actuator 13b Top surface of the thermal deformation actuator 13x 13y recess 14 First Heater 14a, b Electrode pads 15 PCB 16 Clad 16x clad section 17 Second Heater 18 Second temperature sensor 19 First temperature sensor 19a Electrode pad of first temperature sensor 20 Input section 21 Output section 22 Soliton optical comb 23 Excitation light 24 Resonant waveform 25 Temperature control device 26 Micro-optical resonators 27 Temperature control unit 28 PCB 29(a) First cladding section 29(b) Second cladding section 30 Waveguide 31 Resonator 32 Input section 33 Excitation light 34 Thermal change in resonant wavelength of resonator 35 Resonant waveform 36 Pulse 37 Soliton region

Claims

1. a first ring-shaped waveguide made of a material having a third-order nonlinear optical effect; a second waveguide configured to receive the excitation light from the input section, input at least a portion of the excitation light into the first waveguide, and extract from the first waveguide an optical frequency comb having a plurality of comb-like spectra with equal frequency intervals; a cladding surrounding the first waveguide and the second waveguide and formed with a refractive index lower than that of the first waveguide and the second waveguide; a cylindrical thermal deformation actuator formed inside the ring of the first waveguide and coaxial with the center of the first waveguide; a first heater for heating the thermal deformation actuator; and a cooling means for cooling the thermal deformation actuator, wherein the thermal deformation actuator heated by the first heater increases the diameter of the first waveguide and changes the optical resonant frequency of the first waveguide.

2. 2. The micro optical resonator according to claim 1, further comprising a first temperature sensor for detecting the temperature of said thermal deformation actuator in order to control the voltage applied to said first heater.

3. 3. The micro optical resonator according to claim 1, wherein the thermal deformation actuator and the first heater are in contact with each other.

4. 3. The micro optical resonator according to claim 1, wherein the thermal deformation actuator and the substrate serving as the cooling means are in contact with each other.

5. an input section that receives an input of excitation light having a predetermined frequency irradiated from a laser light source device; a ring-shaped first waveguide made of a material having a third-order nonlinear optical effect; a second waveguide that receives the excitation light from the input section and optically couples it with the first waveguide to input at least a portion of the excitation light into the first waveguide and extract an optical frequency comb having a plurality of comb-like spectra with equal frequency intervals from the first waveguide; and a second waveguide that surrounds the first and second waveguides and has a refractive index determined by the refractive indexes of the first and second waveguides. An optical frequency comb generator comprising: a cladding formed with a low refractive index; a thermal deformation actuator formed inside the ring of the first waveguide; a first heater for heating the thermal deformation actuator; a first temperature sensor for detecting the temperature of the thermal deformation actuator; a cooling means for cooling the thermal deformation actuator; a second heater for heating the cooling means; a second temperature sensor for detecting the temperature of the cooling means; and a temperature control device for controlling the second heater by feeding back a signal detected by the second temperature sensor, thereby controlling the temperature of the substrate to a predetermined value.

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