Optical force optical frequency comb generation device and generation method

Abstract

The application discloses a kind of optical force optical frequency comb generation device and generation method.The device includes wavelength tunable light source, polarization controller, coupling structure and spoke micro-disk cavity;Spoke micro-disk cavity includes central region, edge region and multiple hollow areas, central region and edge region are connected by spoke structure, spoke micro-disk cavity contains optical mode and mechanical mode;Wavelength tunable light source provides pump light, pump light is coupled into spoke micro-disk cavity, excites optical mode;Optical mode excites mechanical mode;The periodic change optical structure shape of spoke micro-disk cavity in the force field in mechanical mode, generates dynamic reaction, periodically modulates the light field in optical mode, generates optical sideband, outputs optical frequency comb.The technical scheme of the embodiment of the application solves the problem that the spectral range of optical force optical frequency comb is narrow, and the spectral range of MHz-level repetition frequency can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, in particular to a light force optical frequency comb generating device and method. BACKGROUND

[0002] The conventional optical frequency comb generating device has high precision and frequency stability, but due to its large size and high cost, it is difficult to realize commercial production in the civil field, and as a space equipment load, it also lacks economy, so integration is a major issue in the field of optical frequency combs at present. At present, there are still many challenges in the research of on-chip low repetition rate optical frequency combs. The scheme using mode-locked laser and electro-optic modulator either has a large size or produces a limited number of comb teeth. The Kerr optical frequency comb is suitable for miniaturization and can obtain a broadband spectrum of an octave, but due to the limitation of the free spectral range of the cavity mode, the repetition frequency is generally in the GHz range, which cannot produce a low repetition rate optical frequency comb.

[0003] In addition, the existing optical frequency comb has not yet reached the practical level in terms of comb tooth number and spectral width, and has problems such as large phase noise and is not conducive to integration. Existing work focuses on the physical mechanism, and the number of comb teeth is generally in the tens. SUMMARY

[0004] The embodiment of the present application provides an optical force optical frequency comb generating device and method, which utilizes an on-chip spoke micro-disk cavity to generate an optical frequency comb based on optical force nonlinearity. In this scheme, multiple sidebands are generated on both sides of the incident light frequency, the frequency interval between the sidebands is a mechanical oscillation frequency of tens of MHz, and the number of comb teeth can reach several hundred. By using this method, the embodiment of the present application solves the problem of narrow spectral range of optical force optical frequency comb, and can obtain a MHz-level repetition frequency spectrum. This is ideal for a series of precision applications such as single-comb atomic spectrum, double-comb molecular spectrum, and quantum optics integrated pulse source. The present application aims to optimize the design of high-quality factor microcavities in order to achieve higher frequency precision and wider frequency coverage, thereby meeting the needs of future precision science and optoelectronic technology.

[0005] According to one aspect of the present application, an optical force optical frequency comb generating device is provided, 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 with the input end of the polarization controller, the output end of the polarization controller is connected with the first end of the coupling structure, and the coupling structure is coupled with the spoke micro-disk cavity.

[0007] The spoke micro-disk cavity comprises a central region, an edge region, and a plurality of hollowed-out areas between the central region and the edge region, the central region and the edge region are connected by a spoke structure between adjacent two hollowed-out areas, 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, which is coupled into the spoke micro-disk cavity after passing through the polarization controller and the coupling structure, and excites the optical mode;

[0009] The light field in the optical mode makes the spoke micro-disk cavity bear force through radiation light pressure, and excites 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 an optical sideband, and outputs an optical frequency comb;

[0011] 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.

[0012] Optionally, it also includes an optical amplifier, the input end of the optical amplifier is connected with the output end of the wavelength tunable light source, and the output end of the optical amplifier is connected with the input end of the polarization controller.

[0013] Optionally, it also includes a first attenuator, the input end of the first attenuator is connected with the output end of the optical amplifier, and the output end of the first attenuator is connected with the 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 with the output end of the polarization controller, the first output end of the first beam splitter is connected with the input end of the second beam splitter, the second output end of the first beam splitter is connected with the first end of the coupling structure, the first output end of the second beam splitter is connected with the first optical power meter, and the second output end of the second beam splitter is connected with the Mach-Zehnder interferometer;

[0016] The second end of the coupling structure is connected with an input end of the third beam splitter, a first output end of the third beam splitter is connected with the second optical power meter, a second output end of the third beam splitter is connected with an input end of the fourth beam splitter, a first output end of the fourth beam splitter is connected with an input end of the fifth beam splitter, a second output end of the fourth beam splitter is connected with the optical spectrum analyzer, a first output end of the fifth beam splitter is connected with the first photodetector, the first photodetector is connected with the frequency spectrum analyzer, a second output end of the fifth beam splitter is connected with an input end of the sixth beam splitter, a first output end of the sixth beam splitter is connected with the second photodetector, and a second output end of the sixth beam splitter is connected with the third photodetector.

[0017] Optionally, the coupling structure further comprises a second attenuator, an input end of the second attenuator is connected with the second end of the coupling structure, and an output end of the second attenuator is connected with the input end of the third beam splitter.

[0018] Optionally, the spoke micro-disk cavity is made of 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 di-deuterium phosphate.

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

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

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

[0022] According to another aspect of the present application, a method for generating an optical force optical frequency comb is provided, which is performed by using the optical force optical frequency comb generation device described above, and comprises the following steps:

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

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

[0025] The optical field in the optical mode is forced by the radiation light pressure to excite the mechanical mode, and the force field in the mechanical mode periodically changes the optical structure shape of the spoke micro-disk cavity to generate a dynamic reaction, periodically modulate the optical field in the optical mode, generate an optical sideband, and output an optical frequency comb.

[0026] The optical force optical frequency comb generating device provided by the embodiment of the present application comprises 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 with the input end of the polarization controller, the output end of the polarization controller is connected with the first end of the coupling structure, and the coupling structure is coupled with the spoke micro-disk cavity. The spoke micro-disk cavity comprises a central region, an edge region, and a plurality of hollow areas between the central region and the edge region. The central region and the edge region are connected through spoke structures between adjacent two hollow areas. The spoke micro-disk cavity comprises an optical mode and a mechanical mode. Pump light is provided through the wavelength tunable light source, the pump light is coupled into the spoke micro-disk cavity after passing through the polarization controller and the coupling structure, and the optical mode is excited. The optical field in the optical mode is forced by the radiation light pressure to excite 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 to generate a dynamic reaction, periodically modulate the optical field in the optical mode, generate an optical sideband, and output an optical frequency comb. 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. The technical solution of the embodiment of the present application solves the problem of narrow spectrum 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 precise applications such as single comb atomic spectrum, double comb molecular spectrum, quantum optical integrated pulse source, etc. The present application aims to optimize the design of high-quality factor microcavities to achieve higher frequency accuracy and wider frequency coverage, thereby meeting the needs of future precision science and optoelectronic technology.

[0027] It should be understood that the content described in this part is not intended to identify key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0029] Figure 1 A structural schematic diagram of an optical force optical frequency comb generating device provided by an embodiment of the present application is shown in FIG. 1.

[0030] Figure 2 A structural schematic diagram of a spoke micro-disk cavity provided by an embodiment of the present application is shown in FIG. 2.

[0031] Figure 3 A schematic diagram of the generation principle of an optical mechanical frequency comb provided by an embodiment of the present application is shown in FIG. 3.

[0032] Figure 4 A structural schematic diagram of another optical force optical frequency comb generating device provided by an embodiment of the present application is shown in FIG. 4.

[0033] Figure 5 A structural schematic diagram of still another optical force optical frequency comb generating device provided by an embodiment of the present application is shown in FIG. 5.

[0034] Figure 6 A structural schematic diagram of still another optical force optical frequency comb generating device provided by an embodiment of the present application is shown in FIG. 6.

[0035] Figure 7 A result schematic diagram of an optical force optical frequency comb generating device provided by an embodiment of the present application is shown in FIG. 7.

[0036] Figure 8 A flow schematic diagram of an optical force optical frequency comb generating method provided by an embodiment of the present application is shown in FIG. 8. DETAILED DESCRIPTION

[0037] In order to make the person skilled in the art better understand the present application scheme, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the scope of protection of the present application.

[0038] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" 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 does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0039] Figure 1 This is a schematic diagram of a photoelectric frequency comb generating device provided in an embodiment of the present invention, with reference to... Figure 1 The optical power 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] 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 practical implementation, the wavelength-tunable light source can be a wavelength-tunable laser, such as a 1550nm wavelength-tunable fiber laser. The polarization controller 20 is used to adjust the polarization state of the pump light. In practical implementation, the wavelength-tunable light source and the coupling structure 30 can be connected via optical fiber. The polarization controller 20 is fixed to the optical fiber, and the change of the pump light polarization state is achieved by twisting the optical fiber. The coupling structure 30 can include tapered optical fiber, micro / nano optical fiber, or other optical waveguides, etc., as an illustration. Figure 1 The coupling structure 30 shown is an optical fiber including a tapered structure. The pump light generates an evanescent field in the tapered structure, achieving coupling with the spoke microdisc cavity 40. The coupling efficiency can be adjusted by regulating the distance between the tapered structure and the spoke microdisc cavity 40. The tapered structure can be obtained by fused fiber tapering. The fiber tapered 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 the actual experimental conditions, and the embodiments of the present invention are not limited thereto. In another embodiment, the coupling structure 30 can be a structure that can be integrated on a substrate, such as micro-nano optical fiber. By integrating the coupling structure 30 and the spoke microdisc cavity 40 on the same substrate, the integration level of the optical power and frequency comb generation device can be further improved.

[0041] Figure 2 This is a schematic diagram of a spoke microdisc cavity provided in an embodiment of the present invention, wherein (a) is a simulation model diagram and (b) is a scanning electron microscope image. Reference Figure 2 In Figure (a), the spoke micro disk cavity 40 includes a central region 41, an edge region 42, and a plurality of hollowed-out areas 43 located between the central region 41 and the edge region. The central region 41 and the edge region 42 are connected by spoke structures 44 located between two adjacent hollowed-out areas 43.

[0042] Optionally, the material of the spoke micro disk cavity 40 includes silicon oxide, amorphous silicon, silicon carbide, silicon germanide, silicon nitride, gallium phosphide, indium arsenide, gallium arsenide, lithium niobate, potassium titanate phosphate, barium metaborate, lithium triborate, potassium dihydrogen phosphate, or potassium dideuterium phosphate. The material can be selected according to the actual situation in specific implementation. In the embodiments of this invention, silicon oxide is used as an example.

[0043] The applicant's research found that existing optical-mechanical frequency combs have not yet reached practical application levels in terms of the number of comb teeth and spectral width, and suffer from problems such as high phase noise and difficulties in integration. Existing work mainly focuses on the underlying physical mechanisms, with the number of comb teeth typically in the tens. A major challenge in generating broadband optical frequency combs in optically coupled microcavities stems from the emergence of chaos under high pump power. Furthermore, the design and fabrication of high-quality microcavities still face challenges. The process for magnesium fluoride crystal cavities is incompatible with wafer fabrication processes, hindering mass production and integration; silicon nitride microcavities have a lower quality factor and face the problem of coupling loss in integrated waveguides. As an insulating material for fiber cores and electronic integrated circuits, silicon dioxide waveguides have long been used in integrated nonlinear optics research. Their nonlinear coefficient is not high, and their extremely low loss and mature processes compensate for the disadvantage of weak nonlinear effects.

[0044] In previous research, the applicant had already been able to generate optical frequency combs with a relatively wide range using micro-ring cavities. However, the laser reflow process suffers from drawbacks such as difficulty in controlling dimensions and complex manufacturing processes, and the laser melting process also restricts the fabrication of internal microstructures. Furthermore, due to its larger cross-sectional area, the micro-ring cavity has a larger effective mass compared to a microdisk (31 ng at 61.3 μm, compared to 19 ng for a microdisk cavity of the same size). This significantly reduces the amplitude of optical oscillations, leading to a narrower optical frequency comb spectral width (proportional to the mechanical amplitude). However, in terms of manufacturing processes, it is difficult to achieve the same high optical quality factor as the micro-ring cavity. Overall, the broadening of the optical oscillation frequency comb generated by a microdisk cavity is not significantly different from that generated by a micro-ring cavity for the same size.

[0045] To further enable the optical system to generate a wider optical frequency comb spectrum, a spoked microdisk cavity structure is designed in this invention, as shown in the figure below. Figure 2 As shown in (a). In Figure 2(b) shows an electron microscope picture of a spoke micro-disk cavity structure made by the applicant, which has a diameter of 60 μm, compared with a micro-disk structure, the middle part of which is hollowed out, and a spoke structure is used to support the outer silicon oxide micro-disk. The experimental measurement shows that the mechanical vibration frequencies of the spoke structure and the micro-disk structure with a diameter of 60 μm are 84.1 MHz and 35.2 MHz, respectively, which has a significant decrease. According to the finite element simulation results, the effective mass decreases from 18.23 ng to 3.28 ng. In the ideal case of consistent optical loss and input light power, the number of comb teeth of the optical force optical frequency comb generated by the spoke micro-disk cavity is ten times that of the micro-disk cavity and the micro-ring core cavity structure, which is obviously superior to the micro-ring core cavity and the ordinary micro-disk cavity. It reaches the threshold of the optical force optical frequency comb for manufacturing high-resolution spectrum.

[0046] The spoke micro-disk cavity 40 comprises an optical mode and a mechanical mode; the wavelength tunable light source 10 is used to provide pump light, the pump light is coupled into the spoke micro-disk cavity 40 after passing through the polarization controller 20 and the coupling structure 30, and the optical mode is excited; the light field in the optical mode makes the spoke micro-disk cavity 40 bear force through the radiation light pressure, and the mechanical mode is excited; 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 40, generates a dynamic reaction, periodically modulates the light field in the optical mode, generates an optical sideband, 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] In the present embodiment, the principle of generating the optical force optical frequency comb is as follows:

[0048] The cavity wall is pushed by the radiation pressure, and the optical microcavity and the microcavity generating the Kerr optical frequency comb have similar characteristics, both of which will cause the coupling between the optical path and the optical intensity, one through the cavity strain and the other through the refractive index. The optical pressure can cause the mechanical deformation of the microcavity structure, and make the cavity mode deviate from the resonance with the continuous pump light, thereby reducing the radiation pressure. After the microcavity deformation recovers, the process starts again, resulting in the periodic motion of the cavity. For a ring (or disc) microcavity, when the laser power is greater than the optical force oscillation threshold, the resonant cavity oscillates in the radial direction, and since it is similar to the chest rising and shrinking regularly when breathing, it is called "breathing mode" figuratively.

[0049] The optical force system can be regarded as a composite system of an optical device and a mechanical oscillator, and the essence of the mechanical oscillator is phonon vibration, so the optical force nonlinear process can also be regarded as a phonon scattering process. The phonon scattering process is a non-elastic scattering, and the frequency of the scattered photons will change. When the optical force nonlinearity is very strong, the mechanical oscillator will oscillate and produce high-order harmonics through the "transfer function". Figure 3 The generation principle of the optical mechanical frequency comb provided in the present embodiment is shown in the schematic diagram of Figure 3The mechanical oscillation and the generation of high-order harmonics will produce multiple sidebands around the incident light frequency, with the frequency spacing between the sidebands being the mechanical oscillation frequency.

[0050] The evolution master equation of the optical force optical comb is as follows:

[0051]

[0052] In the formula, a is the amplitude of the optical 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 optical force coupling coefficient, which represents the change of the microcavity frequency caused by the oscillation displacement, Δω L = ω L - ω0 is the frequency mismatch of the pump light frequency ω L relative to the microcavity resonance frequency ω0. The total loss of the optical resonator is k = k0+ k e , where k0 is the optical intrinsic loss of the cavity, k e is the coupling loss of the microcavity and the optical fiber, S in is the amplitude of the input pump light field in the optical fiber. Γ m , m, Ω m are the attenuation rate, mass and oscillation frequency of the mechanical oscillation, respectively. is the rate of change of the resonance frequency caused by temperature.

[0053] The generation of the optical force can be written in the form of superposition of the pump frequency component and a series of high-order sidebands, and the amplitude of the kth-order sideband is:

[0054]

[0055] When the mechanical vibration is a stable sinusoidal function, the solution of the sideband expression can be analogized to the tight-binding model of the uniformly accelerated electron passing through the periodic potential well in the electrostatic field, i.e., the Bloch theory, by observing the form of the dynamic equation. The discrete frequency spectrum is similar to the Wannier-Stark localization model. After a series of mathematical derivation processes, the following formula is obtained:

[0056]

[0057] x1 = F eff / Γ m Ω0m0

[0058] Δω p = ± Gx1;

[0059] where F eff is the effective radiation pressure, m0 is the effective mass of the microcavity (reduced mass at the maximum amplitude), and x1 is the amplitude of the mechanical oscillation.

[0060] From the above equation, it is not difficult to see that when the micro-disk radius and the comb total power are fixed, the spectral width only depends on the acoustic Q, the effective mass and the mechanical frequency. In order to expand the spectral range, on the one hand, the mechanical mode decay rate needs to be reduced, and on the other hand, the effective mass and the mechanical frequency of the light force oscillation need to be lower. Compared with the micro-ring core cavity, the product of the effective mass and the mechanical frequency of the micro-disk structure with a spoke is reduced to less than one tenth of the original, which indicates a spectral range expansion potential of about 10 times of the optical frequency comb.

[0061] Assuming that the mechanical decay rate is independent of the radius (i.e., the acoustic Q is proportional to the radius), if the spoke and the outer ring width are taken as a fixed fine value (such as 3 μm / 8 μm, respectively) when designing micro-cavities of different diameters, so as to maximize the mechanical amplitude while maintaining stable optical and mechanical modes, then from the above equation combined with the mechanical vibration formula, it can be deduced that the spectral width is generally proportional to r -2 , and 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 rise in the thermal effect in the cavity, which cannot increase the comb power, so a compromise needs to be made. The sample diameter used in the embodiment of the present application is 60 μm.

[0062] The technical scheme of the embodiment of the present application solves the problem of narrow spectral range of the light force optical frequency comb, and can obtain a MHz-level repetition frequency spectrum. This is ideal for a series of precise applications such as single-comb atomic spectroscopy, double-comb molecular spectroscopy, quantum optics integrated pulse source, etc. The present application aims to optimize the design of high-quality factor micro-cavities in order to achieve higher frequency accuracy and wider frequency coverage, thereby meeting the needs of future precise science and optoelectronic technology.

[0063] Figure 4 Another structure schematic diagram of the light force optical frequency comb generating device provided by the embodiment of the present application is shown in FIG. 3. Figure 4 Optionally, the light force optical frequency comb generating device further comprises an optical amplifier 50, an input end of the optical amplifier 50 is connected with an output end of the wavelength tunable light source 10, and an output end of the optical amplifier 50 is connected with an input end of the polarization controller 20.

[0064] The optical amplifier 50 is used to amplify the power of the pump light. In a specific implementation, the optical amplifier 50 can be an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA), and the embodiment of the present application does not limit this.

[0065] Figure 5 Another structure schematic diagram of the light force optical frequency comb generating device provided by the embodiment of the present application is shown in FIG. 3. Figure 5Optionally, the optical force optical frequency comb generating device further comprises a first attenuator 60, an input end of the first attenuator 60 is connected with an output end of the optical amplifier 50, and an output end of the first attenuator 60 is connected with the first end of the coupling structure 30, and the attenuator 60 is used for adjusting the output power of the amplified pump light.

[0066] Figure 6 Another structure schematic diagram of the optical force optical frequency comb generating device provided by the embodiment of the present application is shown in FIG. 6. Figure 5 Optionally, the optical force optical frequency comb generating device further comprises 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 frequency spectrometer 84 and a spectrometer 85.

[0067] The output ratio of the first output end and the second output end 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 with the output end of the polarization controller 20, the first output end of the first beam splitter 71 is connected with the input end of the second beam splitter 72, the second output end of the first beam splitter 71 is connected with the first end of the coupling structure 30, the first output end of the second beam splitter 72 is connected with the first optical power meter 77, and the second output end of the second beam splitter 72 is connected with the Mach-Zehnder interferometer 79; the second end of the coupling structure 30 is connected with the input end of the third beam splitter 73, the first output end of the third beam splitter 73 is connected with the second optical power meter 78, the second output end of the third beam splitter 73 is connected with the input end of the fourth beam splitter 74, the first output end of the fourth beam splitter 74 is connected with the input end of the fifth beam splitter 75, the second output end of the fourth beam splitter 74 is connected with the spectrometer 85, the first output end of the fifth beam splitter 75 is connected with the first photodetector 80, the first photodetector 80 is connected with the frequency spectrometer 84, the second output end of the fifth beam splitter 75 is connected with the input end of the sixth beam splitter 76, the first output end of the sixth beam splitter 76 is connected with the second photodetector 81, the second output end of the sixth beam splitter 76 is connected with the third photodetector 82, and the second photodetector 81 and the third photodetector 82 are connected with the oscilloscope 83.

[0069] Continuing to refer to Figure 6Optionally, the optical force optical frequency comb generating device further comprises a second attenuator 86, an input end of the second attenuator 86 is connected with the second end of the coupling structure 30, and an output end of the second attenuator 86 is connected with an input end of the third beam splitter 73.

[0070] In order to realize the generation of the optical force optical frequency comb, the following steps need to be performed in the experiment:

[0071] 1. Design and manufacture of the optomechanical microcavity

[0072] The sample adopted in the embodiment of the present application is a hollow silicon oxide microcavity, with a diameter of about 60 μm and a thickness of 2 μm, and an inclination angle of about 30°. Affected by the photoresist shrinkage and non-selective etching, the outer ring width of the edge area is slightly less than 8 μm, and the spoke width is slightly less than 4 μm (the numerical values are the designed sizes, as shown in FIG. 8b). The dimensions of each structure are determined by software simulation modeling to solve the expected effective mass and characteristic frequency, and then combined with experimental results. The sample is manufactured through standard photolithography process and hydrofluoric acid wet etching, and can be mass-produced. Figure 2

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

[0074] Reference Figure 6 The wavelength tunable light source 10 (in this embodiment, an external cavity diode laser ECDL is selected) emits a pump laser with a wavelength of about 1550 nm, which is amplified by the optical amplifier 50 (in this embodiment, an erbium-doped fiber amplifier EDFA is selected), and then passes through the first attenuator 60 (VOA1), the polarization controller 20 (FPC), and then passes through the first beam splitter 71 (1:99 beam splitter). The lower power one is used to measure the frequency detuning by the fiber Mach-Zehnder interferometer 79 (MZ) through the oscilloscope signal, and the first optical power meter 77 is used to monitor the input cavity power (the indication is about 1:200, and the proportion is calibrated in advance). The higher power one is coupled into the silicon oxide spoke microcavity 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) is used to monitor the absorption peak and mechanical vibration change of the transmission spectrum respectively. The microwave converted by the first photodetector 80 (high-speed detector PD1) is detected by the frequency spectrometer 84 (ESA), and the spectrum of the generated microwave signal is detected. The optical spectrum 85 (OSA) is used to record the spectrum of the generated optical frequency comb.

[0075] ​To select the proper sample, the optical quality factor (Q) and the mechanical quality factor of the sample need to be measured. To measure the optical Q, an arbitrary waveform generator (AWG) is used to generate a 10 Hz triangle wave signal with a peak-to-peak value of 5 V as the external piezoelectric source and the oscilloscope trigger source. The laser wavelength is tuned to the absorption peak of the target mode. The coupling position between the fiber taper and the microcavity is adjusted using a piezoelectric displacement stage until the absorption peak shows a Lorentzian line shape and the transmission valley reaches the minimum. The polarization controller is adjusted to reduce the central wavelength transmission to a minimum, and then the distance between the fiber and the sample is slightly increased to a weak coupling state (peak transmission of 80-90%). A calibrated Mach-Zehnder fiber interferometer (MZ) with a known optical path length is inserted into the optical path, which outputs a sinusoidal signal corresponding to the sweep speed to determine the frequency detuning of each point on the oscilloscope time-domain graph. The half-peak width of the absorption peak is fitted to calculate the optical Q of the sample.

[0076] To measure the mechanical Q, the pump power is adjusted to a higher level to exceed the optical force oscillation threshold, at which the third photodetector 82 can detect a high-frequency vibration waveform. The pump power is continuously increased while adjusting the pump detuning to ensure that the pump frequency does not exceed the spectral range after the mode broadening, until a flickering spectral line appears at the microcavity mechanical oscillation frequency on the spectrum analyzer 84. The spectral line is moved to the center of the display, and the spectrum analyzer range is reduced to just enough to display the mechanical mode peak completely. The spectral line resolution is increased and the noise floor is reduced. In practice, the resolution bandwidth (RBW) of the intermediate frequency filter is reduced to the point where the mechanical mode half-peak width no longer narrows, and then the VBW is reduced to 1 Hz to smooth the waveform. The half-peak width of the radio frequency spectral line is fitted to calculate the mechanical Q of the sample.

[0077] 3. Enhancement of optomechanical coupling

[0078] Overcoupling of the optical mode is achieved by reducing the gap between the fiber taper and the microcavity. Specifically, the coupling is adjusted using a piezoelectric displacement stage so that the widest optical frequency comb spectrum is generated when the in-cavity light attenuation rate is substantially equal to the mechanical vibration frequency, which is consistent with the simulation results of the kinetic equation. The researchers explain the effect of light attenuation rate on the number of excited optical force optical comb teeth through the concept of energy flow: when the light attenuation rate κ e <Ω0, the in-cavity light energy maintained during the microcavity expansion provides a larger effect during the contraction, resulting in a decrease in the ratio of the net energy absorbed by the resonant cavity to the total in-cavity energy during the optical force oscillation period, which means a decrease in pump efficiency. On the other hand, κ e >>Ω0 will result in faster dissipation of light energy during the 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 power, thereby enhancing the optomechanical coupling effect and facilitating the generation of more frequency comb lines.

[0079] The large amplitude of mechanical oscillation makes the pump not maintain the match with the cavity mode, which can effectively lead the light energy out of 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, has good mode selection characteristics, and helps to maintain the stability of the system.

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

[0082] 4. Use of thermal-optical nonlinearity

[0083] As Figure 3 As shown in the left column, the thermal-optical effect causes the red shift of the microcavity resonance frequency, increases the effective pump detuning Δω L , and thus amplifies the amplitude of mechanical oscillation, further expanding the span of the frequency comb. From the energy point of view, in the process of generating the optical force optical frequency comb, the Stokes process dominates, and the increase of the effective pump detuning is conducive to the generation of a low-frequency photon and a same-frequency phonon under the action of mechanical vibration, which actually forms a sound generator, which has a positive feedback effect on the cascade of the optical frequency comb.

[0084] 5. Operation process of generating optical force optical frequency comb

[0085] (1) Select a suitable pump mode with high optical and mechanical quality factors. Scan the pump laser to monitor the absorption spectrum on the oscilloscope, and the scanning speed is about 10 Hz. Adjust the polarization state of the in-cavity laser and the coupling state of the tapered optical fiber and the micro-disk to the case of κ e = Ω0 as described above;

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

[0087] (3) Turn off the frequency sweep 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, and in this case, the input cavity power is increased to 60 mW. At this time, the wavelength of the laser is set and the internal piezoelectric is adjusted in the long wave direction to continue to increase the number of frequency lines displayed on the spectrum analyzer until the maximum. At this time, if the pump continues to red shift, the pump will be out of the cavity mode expansion interval, and the optical frequency comb will disappear. The pump is adjusted back significantly, and after the microcavity is started and heated, it can be recovered by slowly red shifting. Carefully adjust the coupling between the microcavity and the optical fiber to make the spectrum as wide as possible.

[0088] (4) Record the optical frequency comb spectrum under the condition that the input power is 60 mW using the spectrum analyzer, and by the comprehensive application of the above technical solutions, an optical frequency comb with 530 comb lines is successfully generated in the micro-disk cavity resonator with a spoke structure. Figure 7 The result schematic diagram of the optical force optical frequency comb generation device provided by the embodiment of the present application, wherein (a) is a microscope picture of the sample, (b) is a representation of the optical quality factor (Q0) of the sample, (c) is a mechanical quality factor Q of the sample m (measured at low power), (d) is an optical spectrum of the sample, and the pump light power P pump = 60 W. As can be seen from (d), the comb line spacing is 35.34 MHz. Although the process is not optimized, the optical Q and acoustic Q are much lower than those of the micro-ring core cavity structure sample. Similarly, with a pump power of 60 mW, the number of comb lines has increased to nearly twice that of the micro-ring core cavity structure (the number of comb lines output by the micro-ring core cavity structure is slightly higher than 300). Figure 7 (d) can be seen, the comb line spacing is 35.34 MHz. Although the process is not optimized, the optical Q and acoustic Q are much lower than those of the micro-ring core cavity structure sample. Similarly, with a pump power of 60 mW, the number of comb lines has increased to nearly twice that of the micro-ring core cavity structure (the number of comb lines output by the micro-ring core cavity structure is slightly higher than 300).

[0089] In other embodiments, different spoke shapes can be designed, for example, Figure 8 The structure schematic diagram of several spoke micro-disk cavities provided by the embodiment of the present application, wherein (a) adds a circular arc transition design; (b) uses stable 7 equal parts, and the holes are all circular to reduce the influence of the rough inner wall on the optical mode as much as possible; (c) extends the spoke to increase the mechanical amplitude; (d) uses stable 5 spokes and bends them; (e) is actually 3 spokes, each composed of two cantilevers, and imitates the automobile wheel in the 5 spoke design to reduce the moment of inertia; (f) is the initial design used in the foregoing embodiment.

[0090] When designing different spoke shapes, the following conditions can be met:

[0091] (1) The hole area can be divided into several congruent areas distributed around the center to make the micro-disk produce stable breathing mode vibration. According to the idea of structural mechanics, under the condition of balancing the effective mass and the thickness of the spoke, 5 / 7 equal parts can increase the structural strength.

[0092] (2) No hole in the outermost certain area (such as 6 μm) to avoid interference with the laser mode.

[0093] (3) A maximum radius circle is made with the center as the center, and there is no hole in the range of the circle. Any two points at a distance of the diameter of the circle will pass through the hole area. At this time, if the material edge is eroded inward at the same speed, the outer silicon will be completely separated from the silicon oxide disc, and the center will still have a silicon support column.

[0094] (4) The thinnest part of any structure is not less than a certain minimum value (such as 3 μm), so as not to break.

[0095] The optimization of the specific hole shape may be introduced into computer reverse design, such as the following brief assumption:

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

[0097] Method one: fixed radius, the product of effective mass and characteristic frequency as the objective function. Randomly reduce / increase a certain amount of area unit at the boundary (even inside) of the hole area, according to the trend of the objective function, use the idea of genetic algorithm / simulated annealing to optimize the next iteration, and make the design that does not meet the constraint condition tend to disappear, and finally get the optimal hole shape.

[0098] Method two: train a neural network, the input parameters are various different designs of parameter abstraction (it is said that the introduction of density and level set topology optimization can also widen the universality and calculation efficiency of reverse design), and the corresponding effective mass and frequency, after training, the output optimization design, so that the product of effective mass and frequency is minimum.

[0099] The technical scheme of the embodiment of the application realizes a large mechanical oscillation amplitude by using a large blue detuning pump light and a thermal-optical nonlinear interaction. The large oscillation amplitude is a key to generating a broadband optical frequency comb, and the spectral width and the number of comb teeth are much better than the experimental results of the prior art. The optical fiber overcoupling and high mechanical quality factor successfully suppress the optical mechanical chaos phenomenon that is prone to occur at high pump power. The ability to suppress chaos is crucial to realize a stable optical mechanical frequency comb, and provides a new stability guarantee for the practical application of the optical mechanical system. The silicon oxide microcavity is used, which has a super-high optical quality factor and a lower effective mass, is compatible with integrated circuit processing technology, and is suitable for mass production. The microcavity supported by the spoke structure is designed, which can significantly reduce the vibration frequency and effective mass of the cavity breathing mode, and further greatly increase the spectral width and the number of comb teeth of the optical frequency comb.

[0100] Based on the same inventive concept, the embodiment of the present application also provides a method for generating an optical force optical frequency comb, using any one of the optical force optical frequency comb generation devices provided by the above-mentioned embodiments, Figure 8 A flowchart of a method for generating an optical force optical frequency comb is provided for the embodiment of the present application, referring to Figure 8 The method for generating an optical force optical frequency comb comprises:

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

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

[0103] S120, adjust 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 to make the spoke micro-disk cavity output an optical frequency comb.

[0104] The optical field in the optical mode makes the spoke micro-disk cavity bear force through radiation pressure, excites the mechanical mode, and 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 optical field in the optical mode, generates an optical sideband, outputs an optical frequency comb, 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.

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

[0106] The above specific embodiments do not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An optical force optical frequency comb generating device, characterized by, The wavelength tunable light source, the polarization controller, the coupling structure and the spoke micro-disk cavity are included. The output end of the wavelength tunable light source is connected with the input end of the polarization controller, the output end of the polarization controller is connected with the first end of the coupling structure, and the coupling structure is coupled with the spoke micro-disk cavity. The spoke micro-disk cavity includes a central region, an edge region and a plurality of hollow areas between the central region and the edge region, the central region and the edge region are connected through spoke structures between adjacent two hollow areas, and the spoke micro-disk cavity contains an optical mode and a mechanical mode. The wavelength tunable light source is used to provide pump light, the pump light is coupled into the spoke micro-disk cavity after passing through the polarization controller and the coupling structure, and the optical mode is excited. The light field in the optical mode makes the spoke micro-disk cavity bear force through radiation light pressure, and the mechanical mode is excited. 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 an optical sideband, 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.

2. The optical force optical frequency comb generating device of claim 1, wherein, Further comprising an optical amplifier, the input end of the optical amplifier is connected with the output end of the wavelength tunable light source, and the output end of the optical amplifier is connected with the input end of the polarization controller.

3. The optical force optical frequency comb generating device of claim 2, wherein, Further comprising a first attenuator, the input end of the first attenuator is connected with the output end of the optical amplifier, and the output end of the first attenuator is connected with the first end of the coupling structure.

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

5. The optical force optical frequency comb generating device of claim 4, wherein, A second attenuator is further included, an input end of the second attenuator is connected with the second end of the coupling structure, and an output end of the second attenuator is connected with the input end of the third beam splitter.

6. The optical force optical frequency comb generating device of claim 1, wherein, The material of the spoke micro-disk cavity includes silicon oxide, amorphous silicon, silicon carbide, germanium silicon, silicon nitride, gallium phosphide, indium arsenide, gallium arsenide, lithium niobate, potassium titanium oxide phosphate, barium metaborate, lithium triborate, potassium dihydrogen phosphate, or potassium di-deuterium phosphate.

7. The optical force optical frequency comb generating device of claim 1, wherein, The coupling structure includes a tapered fiber or a micro-nano fiber.

8. The optical force optical frequency comb generating device of claim 1, wherein, The coupling structure and the spoke micro-disk cavity are integrated on the same substrate.

9. The optical force optical frequency comb generating device of claim 1, wherein, The wavelength-tunable light source is a wavelength-tunable laser.

10. A method for generating an optical frequency comb, characterized in that, The optical force optical comb generator device is executed by using the optical force optical comb generator device in any one of claims 1-9. The wavelength-tunable light source outputs pump light, the pump light is coupled into the spoke micro-disk cavity through the polarization controller and the coupling structure; The pump light, the polarization controller and the coupling structure are adjusted, so that the pump light excites the optical mode of the spoke micro-disk cavity, the optical mode and the mechanical mode of the spoke micro-disk cavity interact, so that the spoke micro-disk cavity outputs an optical frequency comb; The optical field in the optical mode is forced by the radiation light pressure, so that the spoke micro-disk cavity is excited to excite 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 optical field in the optical mode, generates an optical sideband, outputs an optical frequency comb, 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.

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