Light power and light frequency comb generating device and generating method

Abstract

The invention discloses a light power and light frequency comb generation device and a light power and light frequency comb generation method. The device comprises a wavelength-adjustable light source, a polarization controller, a coupling structure and a spoke micro-disk cavity, the spoke micro-disk cavity comprises a central area, an edge area and a plurality of hollow areas, the central area and the edge area are connected through a spoke structure, and the spoke micro-disk cavity comprises an optical mode and a mechanical mode; the wavelength-adjustable light source provides pump light, and the pump light is coupled into the spoke micro disc cavity to excite an optical mode; the optical mode excites the mechanical mode; the force field in the mechanical mode periodically changes the shape of the optical structure of the spoke micro-disk cavity, generates dynamic reaction, periodically modulates the light field in the optical mode, generates an optical sideband, and outputs an optical frequency comb. According to the technical scheme of the embodiment of the invention, the problem that the spectral range of the optical power optical frequency comb is narrow is solved, and the spectrum with MHz-level repetition frequency can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a photomechanical optical frequency comb generating device and a generating method. Background Art

[0002] Traditional optical frequency comb generators have high precision and frequency stability, but due to their large size and high cost, they are difficult to achieve commercial mass production in the civilian field. They are also not economical as a payload for aerospace equipment. Therefore, integration is a major issue in the field of optical frequency combs. At present, there are still many challenges in the research of on-chip low-repetition-rate optical frequency combs. Solutions using mode-locked lasers and electro-optic modulators are either large in size or have a limited number of comb teeth. Kerr optical frequency combs are suitable for miniaturization and can obtain broadband spectra of octaves, but are limited by the free spectral range of the cavity mode, and the repetition frequency is generally in the GHz range, making it impossible to produce low-repetition-rate optical frequency combs.

[0003] In addition, the existing optical frequency combs have not yet reached the practical level in terms of the number of teeth and spectral width, and there are problems such as large phase noise and difficulty in integration. Existing work is mostly aimed at the physical mechanism, and the number of teeth is generally in the dozens. Summary of the invention

[0004] The embodiment of the present invention provides a photomechanical optical frequency comb generating device and method, which utilizes an on-chip spoke microdisk cavity to generate an optical frequency comb based on photomechanical nonlinearity. In this scheme, multiple sidebands are generated on both sides of the incident light frequency, and the frequency interval between the sidebands is a mechanical oscillation frequency of tens of MHz, and the number of comb teeth can reach hundreds. Using this method, the embodiment of the present invention solves the problem of the narrow spectral range of the photomechanical optical frequency comb, and can obtain a spectrum with a MHz-level repetition frequency. This is ideal for a series of precision applications such as single-comb atomic spectroscopy, dual-comb molecular spectroscopy, and quantum optical integrated pulse sources. The present invention aims to achieve higher frequency accuracy and wider frequency coverage through the optimized design of a high-quality factor microcavity, thereby meeting the needs of future precision science and optoelectronic technology.

[0005] According to one aspect of the present invention, there is provided a photomechanical optical frequency comb generating device, comprising a wavelength tunable light source, a polarization controller, a coupling structure and a spoke micro-disk cavity;

[0006] The output end of the wavelength tunable light source is connected to the input end of the polarization controller, the output end of the polarization controller is connected to the first end of the coupling structure, and the coupling structure is coupled to the spoke micro-disk cavity;

[0007] The spoke micro-disk cavity comprises a central region, an edge region, and a plurality of hollow regions between the central region and the edge region, wherein the central region and the edge region are connected via a spoke structure between two adjacent hollow regions, and the spoke micro-disk cavity comprises an optical mode and a mechanical mode;

[0008] The wavelength tunable light source is used to provide pump light, and the pump light is coupled into the spoke micro-disk cavity after passing through the polarization controller and the coupling structure to excite the optical mode;

[0009] The light field in the optical mode causes the spoke micro-disk cavity to be stressed by radiating light pressure, thereby exciting the mechanical mode;

[0010] After the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke micro-disk cavity, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates optical sidebands, and outputs an optical frequency comb;

[0011] The tooth spacing of the optical frequency comb is in the order of megahertz, and the number of teeth of the optical frequency comb is greater than 100.

[0012] Optionally, an optical amplifier is further included, wherein the input end of the optical amplifier is connected to the output end of the wavelength tunable light source, and the output end of the optical amplifier is connected to the input end of the polarization controller.

[0013] Optionally, a first attenuator is further included, wherein an input end of the first attenuator is connected to an output end of the optical amplifier, and an output end of the first attenuator is connected to a first end of the coupling structure.

[0014] Optionally, it also includes a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a sixth beam splitter, a first optical power meter, a second optical power meter, a Mach-Zehnder interferometer, a first photodetector, a second photodetector, a third photodetector, an oscilloscope, a spectrum analyzer and a spectrometer;

[0015] The input end of the first beam splitter is connected to the output end of the polarization controller, the first output end of the first beam splitter is connected to the input end of the second beam splitter, the second output end of the first beam splitter is connected to the first end of the coupling structure, the first output end of the second beam splitter is connected to the first optical power meter, and the second output end of the second beam splitter is connected to the Mach-Zehnder interferometer;

[0016] The second end of the coupling structure is connected to the input end of the third beam splitter, the first output end of the third beam splitter is connected to the second optical power meter, the second output end of the third beam splitter is connected to the input end of the fourth beam splitter, the first output end of the fourth beam splitter is connected to the input end of the fifth beam splitter, the second output end of the fourth beam splitter is connected to the spectrometer, the first output end of the fifth beam splitter is connected to the first photodetector, the first photodetector is connected to the spectrometer, the second output end of the fifth beam splitter is connected to the input end of the sixth beam splitter, the first output end of the sixth beam splitter is connected to the second photodetector, the second output end of the sixth beam splitter is connected to the third photodetector, and the second photodetector and the third photodetector are both connected to the oscilloscope.

[0017] Optionally, a second attenuator is further included, wherein the input end of the second attenuator is connected to the second end of the coupling structure, and the output end of the second attenuator is connected to the input end of the third beam splitter.

[0018] Optionally, the material of the spoke microdisk cavity includes silicon oxide, amorphous silicon, silicon carbide, silicon germanium, silicon nitride, gallium phosphide, indium arsenide, gallium arsenide, lithium niobate, potassium titanyl phosphate, barium metaborate, lithium triborate, potassium dihydrogen phosphate or potassium dideuterium phosphate.

[0019] Optionally, the coupling structure includes a tapered optical fiber or a micro-nano optical fiber.

[0020] Optionally, the coupling structure and the spoke micro-disk cavity are integrated on the same base substrate.

[0021] Optionally, the wavelength tunable light source is a wavelength tunable laser.

[0022] According to another aspect of the present invention, a method for generating a photomechanical optical frequency comb is provided, which is performed using the above-mentioned photomechanical optical frequency comb generating device, comprising:

[0023] The wavelength-tunable light source outputs pump light, and the pump light is coupled into the spoke micro-disk cavity after passing through a polarization controller and a coupling structure;

[0024] Adjusting the pump light, the polarization controller and the coupling structure, so that the pump light excites the optical mode of the spoke micro-disk cavity, and the optical mode and the mechanical mode of the spoke micro-disk cavity interact with each other, so that the spoke micro-disk cavity outputs an optical frequency comb;

[0025] The light field in the optical mode causes the spoke micro-disk cavity to be subjected to force through radiation light pressure, thereby exciting the mechanical mode. After the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke micro-disk cavity, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates optical sidebands, and outputs an optical frequency comb. The tooth spacing of the optical frequency comb is in the order of megahertz, and the number of teeth of the optical frequency comb is greater than 100.

[0026] The photomechanical optical frequency comb generating device provided by the embodiment of the present invention includes a wavelength tunable light source, a polarization controller, a coupling structure and a spoke micro-disk cavity; the output end of the wavelength tunable light source is connected to the input end of the polarization controller, the output end of the polarization controller is connected to the first end of the coupling structure, and the coupling structure is coupled to the spoke micro-disk cavity; the spoke micro-disk cavity includes a central area, an edge area and a plurality of hollow areas located between the central area and the edge area, the central area and the edge area are connected by a spoke structure located between two adjacent hollow areas, and the spoke micro-disk cavity contains an optical mode and a mechanical mode. Pump light is provided by a wavelength-tunable light source, and the pump light is coupled into the spoke microdisk cavity after passing through a polarization controller and a coupling structure to excite an optical mode; the light field in the optical mode causes the spoke microdisk cavity to be subjected to force through radiation light pressure, thereby exciting a mechanical mode; after the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke microdisk cavity, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates optical sidebands, and outputs an optical frequency comb; wherein the comb tooth spacing of the optical frequency comb is of the order of megahertz, and the number of comb teeth of the optical frequency comb is greater than 100. The technical solution of the embodiment of the present invention solves the problem of the narrow spectral range of the optical force optical frequency comb, and can obtain a spectrum with a MHz-level repetition frequency. This is ideal for a series of precision applications such as single-comb atomic spectroscopy, dual-comb molecular spectroscopy, and quantum optical integrated pulse source. The present invention aims to achieve higher frequency accuracy and wider frequency coverage through the optimized design of a high-quality factor microcavity, thereby meeting the needs of future precision science and optoelectronic technology.

[0027] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 Schematic structural diagram of an optomechanical optical frequency comb generation device provided by an embodiment of the present invention;

[0030] Figure 2 Schematic structural diagram of a spoke microdisk cavity provided by an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the generation principle of an optomechanical frequency comb provided by an embodiment of the present invention;

[0032] Figure 4 Schematic structural diagram of another optomechanical optical frequency comb generation device provided by an embodiment of the present invention;

[0033] Figure 5 Schematic structural diagram of yet another optomechanical optical frequency comb generation device provided by an embodiment of the present invention;

[0034] Figure 6 Schematic structural diagram of yet another optomechanical optical frequency comb generation device provided by an embodiment of the present invention;

[0035] Figure 7 Schematic diagram of the result of an optomechanical optical frequency comb generation device provided by an embodiment of the present invention;

[0036] Figure 8 Schematic flowchart of an optomechanical optical frequency comb generation method provided by an embodiment of the present invention. Detailed implementation manners

[0037] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such used data may be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order different from those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units is not necessarily limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0039] Figure 1 A schematic diagram of a structure of a photodynamic optical frequency comb generating device provided by an embodiment of the present invention, referring to Figure 1 The photodynamic optical frequency comb generating device includes a wavelength tunable light source 10, a polarization controller 20, a coupling structure 30 and a spoke micro-disk cavity 40; the output end of the wavelength tunable light source 10 is connected to the input end of the polarization controller 20, the output end of the polarization controller 20 is connected to the first end of the coupling structure 30, and the coupling structure 30 is coupled to the spoke micro-disk cavity 40.

[0040] Among them, the wavelength tunable light source 10 can be a wavelength tunable laser. Since lasers have many advantages such as high brightness, good directionality, and good monochromaticity, in a specific implementation, the wavelength tunable light source can be a wavelength tunable laser, for example, a wavelength tunable fiber laser in the 1550nm band. The polarization controller 20 is used to adjust the polarization state of the pump light. In a specific implementation, the wavelength tunable light source and the coupling structure 30 can be connected by an optical fiber, and the polarization controller 20 is fixed on the optical fiber. The change of the polarization state of the pump light is achieved by twisting the optical fiber. The coupling structure 30 can include a tapered optical fiber, a micro-nano optical fiber, or other optical waveguides, schematically, Figure 1 The coupling structure 30 shown in the figure is an optical fiber including a tapered structure. The pump light generates an evanescent field in the tapered structure to achieve coupling with the spoke micro-disk cavity 40. The coupling efficiency can be adjusted by adjusting the distance between the tapered structure and the spoke micro-disk cavity 40. The tapered structure can be obtained by melting and tapering the optical fiber. The optical fiber taper coupling method has the advantages of high coupling efficiency, strong controllability, and convenient adjustment. In specific implementation, the type of coupling structure 30 can be selected according to actual experimental conditions, and the embodiment of the present invention is not limited. In another embodiment, the coupling structure 30 can be a structure such as a micro-nano optical fiber that can be integrated on a substrate. By integrating the coupling structure 30 and the spoke micro-disk cavity 40 on the same substrate, the integration of the optical force optical frequency comb generating device can be further improved.

[0041] Figure 2 A schematic diagram of the structure of a spoke microdisk cavity provided by an embodiment of the present invention, wherein (a) is a simulation modeling diagram and (b) is a scanning electron microscope photograph. Figure 2 In the middle figure (a), the spoke micro-disk cavity 40 includes a central region 41, an edge region 42, and a plurality of hollow regions 43 located between the central region 41 and the edge region. The central region 41 and the edge region 42 are connected by a spoke structure 44 located between two adjacent hollow regions 43.

[0042] Optionally, the material of the spoke micro-disk cavity 40 includes silicon oxide, amorphous silicon, silicon carbide, silicon germanium, silicon nitride, gallium phosphide, indium arsenide, gallium arsenide, lithium niobate, potassium titanyl phosphate, barium metaborate, lithium triborate, potassium dihydrogen phosphate or potassium dideuterium phosphate. The material can be selected according to actual conditions during implementation. In the embodiments of the present invention, silicon oxide material is taken as an example.

[0043] The applicant's research found that the existing photomechanical frequency combs have not yet reached the practical level in terms of the number of comb teeth and spectral width, and there are problems such as large phase noise and inconvenience in integration. Existing work is mostly aimed at the physical mechanism, and the number of comb teeth is generally dozens. A major challenge in generating a wide-spectrum optical frequency comb in a photomechanically coupled microcavity stems from the emergence of chaos under high pump power. In addition, there are still challenges in the design and preparation of high-quality factor microcavities. The process of magnesium fluoride crystal cavities is incompatible with the wafer production process, which is not conducive to mass manufacturing and integration; the quality factor of silicon nitride microcavities is low, and there is a problem of integrated waveguide coupling loss. As a material for optical fiber cores and electronic integrated circuit insulation layers, silica waveguides have long been used in integrated nonlinear optics research. Its nonlinear coefficient is not high, and it makes up for the disadvantage of weak nonlinear effects with extremely low losses and mature processes.

[0044] In previous research, the applicant has been able to produce a wider range of optical frequency combs using a micro-ring core cavity, but the laser reflow process has the disadvantages of difficult size control and complex process, and the laser melting process also restricts the manufacture of internal microstructures. In addition, due to the larger cross-sectional area, the micro-ring core cavity has a larger effective mass than the micro-disk (31 ng at 61.3 μm, and 19 ng for a micro-disk cavity of the same size), which will significantly reduce the amplitude of the photoforce oscillation, thereby causing the optical frequency comb spectrum to narrow (proportional to the mechanical amplitude). However, in terms of technology, it is difficult to make the optical quality factor of the micro-disk cavity as high as that of the micro-ring core cavity. In general, the broadening of the photoforce optical frequency comb generated by the micro-disk cavity and the micro-ring core cavity of the same size is not much different.

[0045] In order to further enable the optical system to generate a wider optical frequency comb spectrum, the present invention designs a spoke micro-disk cavity structure, the style of which is as follows: Figure 2 (a) is shown. Figure 2(b) shows an electron microscope image of a spoke microdisk cavity structure made by the applicant, which has a diameter of 60μm. Compared with the microdisk structure, the middle part is hollowed out and the spoke structure is used to support the external silicon oxide microdisk. The experimental measurement shows that the mechanical vibration frequencies of the spoke structure and microdisk structure with a diameter of 60μm are 84.1MHz and 35.2MHz respectively, which is a significant decrease. And according to the finite element simulation results, the effective mass is reduced from 18.23ng to 3.28ng. Under the ideal condition of consistent optical loss and input light power, the number of teeth of the photomechanical frequency comb generated by the spoke microdisk cavity is ten times that of the microdisk cavity and microring core cavity structure, which is significantly better than the microring core cavity and ordinary microdisk cavity. The threshold for photomechanical frequency combs to be used to produce high-resolution spectra has been reached.

[0046] The spoke microdisk cavity 40 includes an optical mode and a mechanical mode; the wavelength tunable light source 10 is used to provide pump light, which is coupled into the spoke microdisk cavity 40 after passing through the polarization controller 20 and the coupling structure 30 to excite the optical mode; the light field in the optical mode causes the spoke microdisk cavity 40 to be subjected to force through the radiation light pressure, thereby exciting the mechanical mode; after the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke microdisk cavity 40, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates optical sidebands, and outputs an optical frequency comb; wherein the comb tooth spacing of the optical frequency comb is in the order of megahertz, and the number of comb teeth of the optical frequency comb is greater than 100.

[0047] The principle of generating the optical frequency comb according to the embodiment of the present invention is as follows:

[0048] Optical microcavities whose walls are driven by radiation pressure have similar properties to microcavities that produce Kerr optical frequency combs. Both cause coupling between optical path and light intensity, one through cavity strain and the other through refractive index. Optical pressure can cause mechanical deformation of the microcavity structure and cause the cavity mode to break away from the resonance with the continuous pump light, thereby reducing the radiation pressure. After the microcavity deformation is restored, the process restarts, resulting in periodic motion of the cavity. For annular (or disk) microcavities, when the laser power is greater than the optical force oscillation threshold, the resonant cavity oscillates radially in a stretching and relaxing manner. Because it is similar to the regular expansion and contraction of the chest during breathing, it is figuratively called the "breathing mode."

[0049] The photomechanical system can be regarded as a composite system of optical devices and mechanical oscillators. The essence of mechanical oscillators is phonon vibration. Therefore, the nonlinear process of photomechanical force can also be regarded as a phonon scattering process. The phonon scattering process is an inelastic scattering, and the frequency of scattered photons will change. When the nonlinearity of photomechanical force is very strong, the mechanical oscillator will oscillate and generate high-order harmonics through the "transfer function". Figure 3 Schematic diagram of the generation principle of the optomechanical frequency comb provided by the embodiment of the present invention, refer to Figure 3, the generation of mechanical oscillation and high-order harmonics will produce multiple sidebands on both sides of the incident light frequency, and the frequency interval between the sidebands is the mechanical oscillation frequency.

[0050] The main equation for the evolution of the photomechanical optical frequency comb is as follows:

[0051]

[0052] Where a is the amplitude of the light field in the cavity, x is the displacement of the mechanical oscillation, ΔT is the temperature difference between the position of the optical mode in the microcavity and the surrounding environment, is the photomechanical coupling coefficient, which characterizes the change of the microcavity frequency caused by the oscillation displacement, Δω L =ω L -ω 0 is the pump light frequency ω L Relative microcavity resonance frequency ω 0 The total loss of the optical resonant cavity is k = κ 0 +k e , where k 0 is the optical intrinsic loss of the cavity, k e is the coupling loss between the microcavity and the optical fiber, S in is the amplitude of the pump light field input into the optical fiber. m , m, Ω m are the decay rate, mass and oscillation frequency of the mechanical oscillation respectively. is the rate of change of the resonant frequency caused by temperature.

[0053] The generated optical force can be written as the superposition of the pump frequency component and a series of high-order sidebands. The amplitude of the k-th order sideband is:

[0054]

[0055] When the mechanical vibration is a stable sinusoidal function, the solution of the sideband expression can be compared to the tight binding model of uniformly accelerated electrons passing through a periodic potential well under an electrostatic field, namely the Bloch theory. The discrete spectrum is similar to the Wannier-Stark localization simulation. After a series of mathematical derivations, we get:

[0056]

[0057] x 1 =F eff / Γ m Ω 0 m 0

[0058] Δω p = ±Gx 1 ;

[0059] where Feff is the effective radiation pressure, m 0 is the effective mass of the microcavity (the reduced mass at the maximum amplitude), x 1 is the amplitude of the mechanical oscillation.

[0060] According to the above equations, it is not difficult to see that when the radius of the microdisk and the total power of the comb teeth are fixed, the spectral width depends only on the acoustic Q, the effective mass and the mechanical frequency. In order to broaden the spectral range, on the one hand, the attenuation rate of the mechanical mode must be reduced, and on the other hand, a lower effective mass and mechanical frequency of the optical force oscillation are required. Compared with the microring core cavity, the product of the effective mass and the mechanical frequency of the spoked microdisk structure is reduced to less than one-tenth of the original, which indicates a potential for broadening the spectral range of the optical frequency comb by about 10 times.

[0061] Assuming that the mechanical attenuation rate is independent of the radius (i.e., the acoustic Q is proportional to the radius), if the spoke and outer ring widths are fixed to a relatively thin value (e.g., 3 μm / 8 μm, respectively) when designing microcavities with different diameters, so as to maximize the mechanical amplitude while maintaining stable optical and mechanical modes, then the above equation can be deduced in combination with the mechanical vibration formula to obtain that the spectral width is roughly proportional to r -2 The number of comb teeth is proportional to the product of the spectral width and the radius. However, reducing the radius will lead to a decrease in optical Q and a sharp increase in the thermal effect in the cavity, and the comb power cannot be increased. Therefore, a compromise must be made. The sample diameter used in the embodiment of the present invention is set to 60 μm.

[0062] The technical solution of the embodiment of the present invention solves the problem of the narrow spectral range of the optical frequency comb, and can obtain a spectrum with a MHz-level repetition frequency. This is ideal for a series of precision applications such as single-comb atomic spectroscopy, dual-comb molecular spectroscopy, and quantum optical integrated pulse sources. The present invention aims to achieve higher frequency accuracy and wider frequency coverage through the optimized design of high-quality factor microcavities, thereby meeting the needs of future precision science and optoelectronic technology.

[0063] Figure 4 A schematic diagram of another optical frequency comb generating device provided by an embodiment of the present invention, referring to Figure 4 Optionally, the photodynamic optical frequency comb generating device also includes an optical amplifier 50, the input end of the optical amplifier 50 is connected to the output end of the wavelength tunable light source 10, and the output end of the optical amplifier 50 is connected to the input end of the polarization controller 20.

[0064] The optical amplifier 50 is used to amplify the power of the pump light. In specific implementation, the optical amplifier 50 may be an erbium-doped fiber amplifier EDFA or a semiconductor optical amplifier SOA, which is not limited in the embodiment of the present invention.

[0065] Figure 5A schematic diagram of the structure of another optical frequency comb generating device provided by an embodiment of the present invention, referring to Figure 5 Optionally, the photodynamic optical frequency comb generating device also includes a first attenuator 60, the input end of the first attenuator 60 is connected to the output end of the optical amplifier 50, and the output end of the first attenuator 60 is connected to the first end of the coupling structure 30, and the attenuator 60 is used to adjust the output power of the amplified pump light.

[0066] Figure 6 A schematic diagram of the structure of another optical frequency comb generating device provided by an embodiment of the present invention, referring to Figure 5 Optionally, the photodynamic optical frequency comb generating device also includes a first beam splitter 71, a second beam splitter 72, a third beam splitter 73, a fourth beam splitter 74, a fifth beam splitter 75, a sixth beam splitter 76, a first optical power meter 77, a second optical power meter 78, a Mach-Zehnder interferometer 79, a first photodetector 80, a second photodetector 81, a third photodetector 82, an oscilloscope 83, a spectrometer 84 and a spectrometer 85.

[0067] Among them, the output ratios of the first output ends and the second output ends of the first beam splitter 71, the second beam splitter 72, the third beam splitter 73, the fourth beam splitter 74, the fifth beam splitter 75 and the sixth beam splitter 76 can be 1:99, 50:50, 1:99, 50:50, 90:10 and 50:50 respectively.

[0068] The input end of the first beam splitter 71 is connected to the output end of the polarization controller 20, the first output end of the first beam splitter 71 is connected to the input end of the second beam splitter 72, the second output end of the first beam splitter 71 is connected to the first end of the coupling structure 30, the first output end of the second beam splitter 72 is connected to the first optical power meter 77, and the second output end of the second beam splitter 72 is connected to the Mach-Zehnder interferometer 79; the second end of the coupling structure 30 is connected to the input end of the third beam splitter 73, the first output end of the third beam splitter 73 is connected to the second optical power meter 78, and the second output end of the third beam splitter 73 is connected to the input end of the fourth beam splitter 74. The first output end of the fourth beam splitter 74 is connected to the input end of the fifth beam splitter 75, the second output end of the fourth beam splitter 74 is connected to the spectrometer 85, the first output end of the fifth beam splitter 75 is connected to the first photodetector 80, the first photodetector 80 is connected to the spectrometer 84, the second output end of the fifth beam splitter 75 is connected to the input end of the sixth beam splitter 76, the first output end of the sixth beam splitter 76 is connected to the second photodetector 81, the second output end of the sixth beam splitter 76 is connected to the third photodetector 82, and the second photodetector 81 and the third photodetector 82 are connected to the oscilloscope 83.

[0069] Continue to refer Figure 6, Optionally, the optomechanical optical frequency comb generation device further includes a second attenuator 86. The input end of the second attenuator 86 is connected to the second end of the coupling structure 30, and the output end of the second attenuator 86 is connected to the input end of the third beam splitter 73.

[0070] To generate an optomechanical optical frequency comb, the following steps are required in the experiment:

[0071] 1. Design and fabrication of the optomechanical microdisk cavity

[0072] The sample used in the embodiment of the present invention is a hollowed-out silica microdisk cavity with a diameter of about 60 μm, a thickness of 2 μm, and an inclination angle of about 30°. Affected by photoresist shrinkage and non-selective etching, the outer ring width of the edge region is slightly less than 8 μm, and the spoke width is slightly less than 4 μm (the values are design dimensions, Figure 2 as shown in Fig. b). Before production, software simulation modeling has been carried out to solve the expected effective mass and characteristic frequency, and the dimensions of each structure have been determined in combination with the experimental results. The sample is fabricated by standard photolithography process and hydrofluoric acid wet etching, and can be mass-produced.

[0073] 2. Construction of the optical frequency comb generation system

[0074] Refer to Figure 6 , the pump laser with a wavelength near 1550 nm emitted by the wavelength-tunable light source 10 (the external cavity diode laser ECDL is selected in this embodiment) is amplified by the optical amplifier 50 (the erbium-doped fiber amplifier EDFA is selected in this embodiment), and then passes through the first attenuator 60 (VOA1), the polarization controller 20 (FPC), and then through the first beam splitter 71 (1:99 beam splitter). The lower-power path uses the fiber Mach-Zehnder interferometer 79 (MZ) to measure the frequency detuning through the oscilloscope signal, and the first optical power meter 77 monitors the input cavity power (the indication is about 1:200, and the ratio is calibrated in advance). The higher-power path is coupled into the silica spoke microdisk cavity through the fiber taper. The transmitted pump light is detected by the second photodetector 81 (PD2) and the third photodetector 82 (high-frequency detector PD3), and the oscilloscope 83 (OSC) monitors the absorption peak of the transmission spectrum and the mechanical vibration change respectively. After being converted into microwaves by the first photodetector 80 (high-speed detector PD1), the spectrum of the generated microwave signal is detected by the spectrum analyzer 84 (ESA), and the spectrum of the generated optical frequency comb is recorded by the spectrometer 85 (OSA).

[0075] In order to select suitable samples, it is necessary to measure the optical quality factor (Q) and mechanical quality factor of the sample. When measuring the optical Q, an arbitrary waveform generator (AWG) is used to generate a triangular wave signal with a frequency of 10Hz and a peak-to-peak value of 5V as the external piezoelectric and oscilloscope trigger source for the laser. The laser wavelength is tuned to observe the absorption peak of the target mode. The piezoelectric displacement stage is used to adjust the coupling position of the fiber cone relative to the microcavity so that the absorption peak is Lorentz linear and the transmittance valley reaches the minimum. The polarization controller is adjusted to reduce the central wavelength transmittance to 0, and then the distance between the fiber and the sample is slightly increased to weak coupling (peak transmittance 80-90%). A Mach-Zehnder fiber interferometer (MZ) calibrated through the optical path of the interference arm is connected in the optical path. It will output a sine signal corresponding to the sweep speed to determine the frequency detuning of each point relative to the pump on the oscilloscope time domain diagram. The optical Q of the sample can be calculated by fitting the half-height width of the absorption peak.

[0076] When measuring mechanical Q, adjust the pump power to a higher level to exceed the photomechanical oscillation threshold, at which point the third photodetector 82 can detect a high-frequency vibration waveform. Continue to increase the pump power, while adjusting the pump detuning so that the pump frequency does not exceed the spectral range after mode broadening, until a flickering spectral line appears on the spectrometer 84 at the microcavity mechanical oscillation frequency. Move the spectral line to the center of the display screen, and reduce the spectrum analyzer range to just allow the mechanical mode peak to be displayed completely. Improve the spectral line resolution and reduce the background noise. In actual operation, reduce the resolution bandwidth (RBW) of the intermediate frequency filter until the half-width at half-height of the mechanical mode is no longer narrowed, and then reduce the VBW to 1 Hz to make the waveform smooth. The half-width at half-height of the fitted RF spectrum line can calculate the mechanical Q of the sample.

[0077] 3. Enhancement of optomechanical coupling

[0078] The overcoupling of the optical mode is achieved by reducing the gap between the fiber taper and the microcavity. The specific method is to use a piezoelectric displacement stage to adjust the coupling so that the light decay rate in the cavity is basically equal to the mechanical vibration frequency to produce the widest optical frequency comb spectrum, which is consistent with the simulation results of the dynamic equation. The researchers explained the influence of the light decay rate on the number of teeth of the excited optical frequency comb through the concept of energy flow: when the light decay rate κ e <Ω 0 When κ is , the light energy in the cavity maintained during the expansion of the microcavity provides a greater effect during the contraction period, resulting in a decrease in the ratio of the net energy absorbed by the resonant cavity to the total energy entering the cavity during the optical force oscillation period, which means a decrease in the pumping efficiency. e >>Ω 0 This results in faster light energy dissipation during microcavity expansion, thereby weakening its push on the cavity wall. Overcoupling increases the optical attenuation rate of the system, allowing the system to operate at higher pump powers, thereby enhancing the optomechanical coupling effect and facilitating the generation of more frequency comb lines.

[0079] The greatly oscillating cavity wall prevents the pump from maintaining a match with the cavity mode, which can effectively extract the light energy from the microcavity, reduce the accumulation of light energy inside the microcavity, and thus reduce the possibility of chaos.

[0080] The sample has a high mechanical quality factor, which means that the energy loss of mechanical vibration in the breathing mode is low, and has good mode selection characteristics, which helps to maintain the stability of the system.

[0081] The experiment used large blue detuned pump light, which helps to enhance the amplitude of mechanical oscillations. Under this condition, the system is more inclined to produce deterministic nonlinear dynamic behavior rather than chaos.

[0082] 4. Utilization of thermo-optical nonlinearity

[0083] like Figure 3 As shown in the left column, the thermo-optic effect causes the microcavity resonance frequency to redshift, increasing the effective pump detuning Δω L , thereby amplifying the mechanical oscillation amplitude and further expanding the span of the frequency comb. From an energy perspective, the Stokes process is dominant in the generation of the optical frequency comb. The increase in effective pump detuning is conducive to the generation of a low-frequency photon and a phonon of the same frequency by the photon under the action of mechanical vibration. This actually forms an exciter, which has a positive feedback effect on the cascade of the optical frequency comb.

[0084] 5. Operational process of generating optical frequency comb

[0085] (1) Select a suitable pump mode with high optical quality factor and mechanical quality factor, scan the pump laser to monitor the absorption spectrum on an oscilloscope, and the scanning speed is about 10 Hz. Adjust the polarization state of the laser entering the cavity and adjust the coupling state between the tapered fiber and the microdisk to the κ mentioned above. e =Ω 0 the situation;

[0086] (2) Adjust the pump power to a higher level to exceed the photomechanical oscillation threshold, and adjust the pump detuning to ensure that the pump frequency does not exceed the spectral range after mode broadening, until a flashing spectrum line appears on the spectrum analyzer at the microcavity mechanical oscillation frequency. Move the spectrum line to the center of the display, reduce the display range of the spectrum analyzer, and increase the spectrum line resolution (increase RBW and VBW) to measure the RF spectrum of the mechanical vibration.

[0087] (3) Turn off the frequency scanning of the pump laser, increase the display range of the spectrum analyzer to about 10 GHz, and appropriately change the RBW and VBW so that the spectrum analyzer has a usable refresh rate. Continue to increase the pump power. In this case, the power into the cavity is increased to 60 mW. At this time, the laser wavelength setting and the internal piezoelectric continue to adjust in the long-wave direction until the number of frequency lines displayed on the spectrum analyzer increases to the maximum. At this time, if the pump is continued to be red-shifted, the pump will be out of the cavity mode broadening range and the optical frequency comb will disappear. The pump can be significantly adjusted back, and the microcavity can be restored by slowly red-shifting after oscillation and heating. Carefully fine-tune the coupling between the microcavity and the optical fiber to make the spectrum as broad as possible.

[0088] (4) The optical frequency comb spectrum was recorded using a spectrometer at an input power of 60 mW. Through the comprehensive application of the above technical solutions, an optical frequency comb with 530 comb lines was successfully generated in a micro-disk cavity resonator with a spoke structure. Figure 7 Schematic diagram of the results of the optical frequency comb generation device provided by the embodiment of the present invention, wherein (a) is a microscope image of the sample, and (b) is the optical quality factor characterization (Q 0 ), (c) is the mechanical quality factor Q of the sample m (measured at low power), (d) is the optical spectrum of the sample, the pump light power P pump =60W. Figure 7 (d) It can be seen that the spectral line comb spacing is 35.34MHz. Although the process is not optimized, the optical Q and acoustic Q are much lower than those of the micro-ring core structure sample. At the same 60mW pump power, the number of comb teeth has increased to nearly twice that of the micro-ring core structure (the number of comb teeth output using the micro-ring core is slightly more than 300).

[0089] In other embodiments, different spoke shapes can be designed. For example, Figure 8 Schematic diagrams of the structures of several spoke micro-disk cavities provided in embodiments of the present invention, wherein (a) incorporates an arc transition design; (b) uses a stable 7-partition, and the holes are all circular, minimizing the effect of the rough inner wall on the optical mode; (c) extends the spokes to increase the mechanical amplitude; (d) uses a stable 5-spoke and bends it; (e) actually has 3 spokes, each consisting of two cantilevers, imitating the car wheel with holes in the 5-spoke design to reduce the moment of inertia; (f) is the initial design adopted in the aforementioned embodiments.

[0090] When designing different spoke shapes, the following conditions are sufficient:

[0091] (1) The hole area can be divided into several congruent areas distributed around the center of the circle, so that the microdisk can generate stable breathing mode vibration. According to the idea of ​​structural mechanics, under the condition of balancing the effective mass and the thickness of the spokes, the 5 / 7 equal division can increase the structural strength.

[0092] (2) There are no holes within a certain outermost area (e.g. 6 μm) to avoid interfering with the laser mode.

[0093] (3) Draw a circle with the maximum radius with the center of the circle as the center, so that there is no hole area within its range, and it is required that the line connecting two points at any distance outside the center of the circle that is the diameter of the circle will pass through the hole area. At this time, if the material is eroded from the edge to the inside at the same speed, there will still be silicon support columns in the center when the outer silicon and the silicon oxide disk are completely separated.

[0094] (4) The thinnest part of any structure is not narrower than a certain minimum value (such as 3μm) to prevent it from breaking.

[0095] The optimization of the specific hole shape may introduce computer reverse design, such as the following brief idea:

[0096] A mechanical vibration simulation model is established to solve the effective mass, and only the radial vibration of the xoy plane is considered to simplify the calculation.

[0097] Method 1: Fixed radius, taking the product of effective mass and characteristic frequency as the objective function. Randomly reduce / increase a certain amount of area units at the boundary (or even inside) of the hole-digging area, and according to the trend of the objective function, use the genetic algorithm / simulated annealing idea to perform weighted optimization for the next round of iteration, and make the design that does not meet the constraints tend to die, and finally get the optimal hole-digging shape.

[0098] Method 2: Train a neural network, with the input parameters being various different designs of parameter abstraction (it is said that the introduction of technologies such as density and level set topology optimization can also broaden the versatility and computational efficiency of inverse design) and the corresponding effective mass and frequency. After training, output the optimized design to minimize the product of effective mass and frequency.

[0099] The technical solution of the embodiment of the present invention achieves a huge optomechanical oscillation amplitude by using the interaction of large blue detuned pump light and thermo-optical nonlinearity. This huge oscillation amplitude is the key to generating a broadband optical frequency comb, and its spectral width and comb teeth number are far better than the experimental results of predecessors; the optomechanical chaos phenomenon that is prone to occur under high pump power is successfully suppressed through fiber overcoupling and high mechanical quality factor. This ability to suppress chaos is crucial for achieving a stable optomechanical frequency comb and provides a new stability guarantee for the practical application of optomechanical systems; a silicon oxide microdisk cavity is used, which has an ultra-high optical quality factor and a lower effective mass, is compatible with integrated circuit processing technology, and is suitable for mass production; a microdisk cavity supported by a spoke structure is designed, which can significantly reduce the vibration frequency and effective mass of the cavity breathing mode, thereby greatly increasing the spectral width and comb teeth number of the optical frequency comb.

[0100] Based on the same inventive concept, an embodiment of the present invention further provides a method for generating a photomechanical optical frequency comb, which is performed using any of the photomechanical optical frequency comb generating devices provided in the above embodiments. Figure 8 A schematic diagram of a method for generating a light frequency comb according to an embodiment of the present invention is provided. Figure 8 , the photodynamic optical frequency comb generation method comprises:

[0101] S110, the wavelength tunable light source outputs pump light, and the pump light is coupled into the spoke micro-disk cavity after passing through the polarization controller and the coupling structure.

[0102] Among them, the wavelength-tunable light source may include a wavelength-tunable laser, and the coupling structure may include a tapered optical fiber, a micro-nano optical fiber or other optical waveguides, etc., which can be flexibly selected according to actual conditions during specific implementation.

[0103] S120, adjusting the pump light, polarization controller and coupling structure, so that the pump light excites the optical mode of the spoke micro-disk cavity, and the optical mode and mechanical mode of the spoke micro-disk cavity interact with each other, so that the spoke micro-disk cavity outputs an optical frequency comb.

[0104] Among them, the light field in the optical mode causes the spoke micro-disk cavity to be subjected to force through the radiation light pressure, thereby exciting the mechanical mode. After the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke micro-disk cavity, generates a dynamic reaction, and periodically modulates the light field in the optical mode to generate optical sidebands and output an optical frequency comb. The tooth spacing of the optical frequency comb is in the megahertz range, and the number of teeth of the optical frequency comb is greater than 100.

[0105] The photodynamic optical frequency comb generation method provided in an embodiment of the present invention is executed by the photodynamic optical frequency comb generation device provided in the above embodiment, and has the same or corresponding technical effects, which will not be described in detail this time.

[0106] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A photodynamic optical frequency comb generating device, characterized in that: It includes a wavelength tunable light source, a polarization controller, a coupling structure, and a spoke micro-disk cavity; The output end of the wavelength tunable light source is connected to the input end of the polarization controller, the output end of the polarization controller is connected to the first end of the coupling structure, and the coupling structure is coupled to the spoke micro-disk cavity; The spoke micro-disk cavity comprises a central region, an edge region, and a plurality of hollow regions between the central region and the edge region, wherein the central region and the edge region are connected via a spoke structure between two adjacent hollow regions, and the spoke micro-disk cavity comprises an optical mode and a mechanical mode; The wavelength tunable light source is used to provide pump light, and the pump light is coupled into the spoke micro-disk cavity after passing through the polarization controller and the coupling structure to excite the optical mode; The light field in the optical mode causes the spoke micro-disk cavity to be stressed by radiating light pressure, thereby exciting the mechanical mode; After the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke micro-disk cavity, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates optical sidebands, and outputs an optical frequency comb; The tooth spacing of the optical frequency comb is in the order of megahertz, and the number of teeth of the optical frequency comb is greater than 100.

2. The optical frequency comb generating device according to claim 1, characterized in that: It also includes an optical amplifier, the input end of the optical amplifier is connected to the output end of the wavelength tunable light source, and the output end of the optical amplifier is connected to the input end of the polarization controller.

3. The optical frequency comb generating device according to claim 2, characterized in that: It also includes a first attenuator, wherein the input end of the first attenuator is connected to the output end of the optical amplifier, and the output end of the first attenuator is connected to the first end of the coupling structure.

4. The optical frequency comb generating device according to any one of claims 1 to 3, characterized in that: Also includes a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a sixth beam splitter, a first optical power meter, a second optical power meter, a Mach-Zehnder interferometer, a first photodetector, a second photodetector, a third photodetector, an oscilloscope, a spectrum analyzer and a spectrometer; The input end of the first beam splitter is connected to the output end of the polarization controller, the first output end of the first beam splitter is connected to the input end of the second beam splitter, the second output end of the first beam splitter is connected to the first end of the coupling structure, the first output end of the second beam splitter is connected to the first optical power meter, and the second output end of the second beam splitter is connected to the Mach-Zehnder interferometer; The second end of the coupling structure is connected to the input end of the third beam splitter, the first output end of the third beam splitter is connected to the second optical power meter, the second output end of the third beam splitter is connected to the input end of the fourth beam splitter, the first output end of the fourth beam splitter is connected to the input end of the fifth beam splitter, the second output end of the fourth beam splitter is connected to the spectrometer, the first output end of the fifth beam splitter is connected to the first photodetector, the first photodetector is connected to the spectrometer, the second output end of the fifth beam splitter is connected to the input end of the sixth beam splitter, the first output end of the sixth beam splitter is connected to the second photodetector, the second output end of the sixth beam splitter is connected to the third photodetector, and the second photodetector and the third photodetector are both connected to the oscilloscope.

5. The optical frequency comb generating device according to claim 4, characterized in that: It also includes a second attenuator, wherein the input end of the second attenuator is connected to the second end of the coupling structure, and the output end of the second attenuator is connected to the input end of the third beam splitter.

6. The optical frequency comb generating device according to claim 1, characterized in that: The material of the spoke microdisk cavity includes silicon oxide, amorphous silicon, silicon carbide, silicon germanium, silicon nitride, gallium phosphide, indium arsenide, gallium arsenide, lithium niobate, potassium titanyl phosphate, barium metaborate, lithium triborate, potassium dihydrogen phosphate or potassium dideuterium phosphate.

7. The optical frequency comb generating device according to claim 1, characterized in that: The coupling structure includes a tapered optical fiber or a micro-nano optical fiber.

8. The optical frequency comb generating device according to claim 1, characterized in that: The coupling structure and the spoke micro-disk cavity are integrated on the same base substrate.

9. The optical frequency comb generating device according to claim 1, characterized in that: The wavelength tunable light source is a wavelength tunable laser.

10. A method for generating a photodynamic optical frequency comb, characterized in that: The method is performed by using the optical force optical frequency comb generating device according to any one of claims 1 to 9, comprising: The wavelength-tunable light source outputs pump light, and the pump light is coupled into the spoke micro-disk cavity after passing through a polarization controller and a coupling structure; Adjusting the pump light, the polarization controller and the coupling structure, so that the pump light excites the optical mode of the spoke micro-disk cavity, and the optical mode and the mechanical mode of the spoke micro-disk cavity interact with each other, so that the spoke micro-disk cavity outputs an optical frequency comb; The light field in the optical mode causes the spoke micro-disk cavity to be subjected to force through radiation light pressure, thereby exciting the mechanical mode. After the mechanical mode is excited, the force field in the mechanical mode periodically changes the optical structure shape of the spoke micro-disk cavity, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates optical sidebands, and outputs an optical frequency comb. The tooth spacing of the optical frequency comb is in the order of megahertz, and the number of teeth of the optical frequency comb is greater than 100.

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