A microwave frequency comb generation system and generation method

Abstract

The embodiment of the present invention discloses a microwave frequency comb generation system and generation method. The microwave frequency comb generation system includes a pump source, a coupling structure, a photomechanical microcavity and a first photodetector; the pump source is used to provide pump light, and the pump light is coupled into the coupling structure; the coupling structure is used to couple the pump light into the photomechanical microcavity; the photomechanical microcavity includes an optical mode and a mechanical mode; the pump light excites the optical mode in the photomechanical microcavity; the optical mode is coupled with the mechanical mode to generate a dynamic reaction; the dynamic reaction drives the mechanical mode to generate an optical sideband and output an optical frequency comb; the first photodetector is located at the output end of the photomechanical microcavity, and is used to receive the optical frequency comb, and the beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb. The technical solution of the embodiment of the present invention can generate a high-performance, wide-bandwidth, low-repetition-rate microwave frequency comb for chip integration.

Description

Technical Field

[0001] The embodiments of the present invention relate to micro-nano microwave device technology, and more particularly to a microwave frequency comb generation system and generation method. Background Art

[0002] Microwave frequency combs have important applications in modern microwave signal detection, microwave communications, electrical pulse signal generators, quantum optical devices, modulators and other fields.

[0003] Generally, microwave frequency combs can be generated using electrical nonlinear circuits, ultrafast mode-locked pulsed lasers, or frequency-locked semiconductor lasers. The electrical method generates microwave frequency combs, and the coherence of the comb teeth is limited by the noise of electronic devices, making it difficult to narrow the line width of the comb teeth at high frequencies. Optical methods can achieve high coherence and extremely narrow line width of microwave comb teeth, but the ultrafast mode-locked femtosecond laser and mode-locked semiconductor laser are difficult to achieve miniaturization or even chip integration due to the complexity of the device. In addition, the idea of ​​using microcavity Kerr nonlinearity to generate optical frequency combs and then beat the optical frequency comb to generate microwave frequency combs can achieve the miniaturization and chip integration of microwave frequency combs generated by optical methods, but it is limited by its high repetition frequency (GHz to THz) and it is difficult to generate microwave frequency combs with repetition frequencies below MHz, so it has not been used in the research of microwave frequency comb generation. So far, there is no suitable optical method for generating microcavity microwave frequency combs with repetition bandwidth of less than GHz, high efficiency, narrow line width, flat microwave frequency comb, and suitable for miniaturization and chip integration. Summary of the invention

[0004] The embodiments of the present invention provide a microwave frequency comb generation system and generation method to generate a high-performance, wide-bandwidth, low-repetition-rate (<GHz) microwave frequency comb that can be used for chip integration.

[0005] In a first aspect, an embodiment of the present invention provides a microwave frequency comb generation system, including a pump source, a coupling structure, a photomechanical microcavity, and a first photodetector;

[0006] The pump source is used to provide pump light, and the pump light is coupled into the coupling structure;

[0007] The coupling structure is used to couple the pump light into the optical force microcavity;

[0008] The optical force microcavity is integrated on a base substrate, and the optical force microcavity includes an optical mode and a mechanical mode;

[0009] The pump light excites the optical mode in the optical force microcavity;

[0010] The optical mode is coupled with the mechanical mode to generate a dynamic reaction;

[0011] The dynamic reaction drives the mechanical mode to generate optical sidebands and output an optical frequency comb;

[0012] The first photodetector is located at the output end of the optical force microcavity, and is used to receive the optical frequency comb, and the beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb;

[0013] Among them, the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state. The large blue detuned state means that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the over-coupled state means that the optical mode loss rate is at the same order of magnitude as the mechanical mode resonance frequency.

[0014] Optionally, a polarization controller is further included, wherein the polarization controller is located between the pump source and the coupling structure, and the polarization controller is used to adjust the polarization direction of the pump light.

[0015] Optionally, it also includes a beam splitter, a second photodetector, an oscilloscope and a spectrum analyzer;

[0016] The output end of the coupling structure extending from the optical force microcavity is connected to the input end of the beam splitter, the first output end of the beam splitter is connected to the first photodetector, the first photodetector is connected to the oscilloscope, the second output end of the beam splitter is connected to the second photodetector, and the second photodetector is connected to the spectrometer;

[0017] The oscilloscope is used to output the time domain waveform detected by the first photodetector, and the spectrum analyzer is used to measure the spectrum of the microwave frequency comb.

[0018] Optionally, the pump source includes a wavelength-tunable laser.

[0019] Optionally, the pump source includes a laser with a fixed wavelength.

[0020] Optionally, the optical force microcavity includes a whispering gallery mode optical force microcavity, and the optical mode is coupled with the mechanical mode of the optical force microcavity itself.

[0021] Optionally, the optical force microcavity includes a standing wave mode optical force microcavity, and a micro-nano structure, a membrane structure, a photonic crystal, a phononic crystal or a vibrating atomic cloud is arranged in the standing wave mode optical force microcavity;

[0022] The optical mode is coupled with the mechanical mode of the object in the optical force microcavity.

[0023] Optionally, the comb line width of the microwave frequency comb is in the sub-Hz to 10 Hz range.

[0024] Optionally, the coupling structure and the optical force microcavity are integrated on the same base substrate.

[0025] In a second aspect, an embodiment of the present invention further provides a microwave frequency comb generation method, which is performed using any of the above-mentioned microwave frequency comb generation systems, comprising:

[0026] The pump source outputs pump light, and the pump light is coupled into the optical force microcavity through the coupling structure;

[0027] Adjusting the pump light and the coupling structure so that the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state, so that the optical force microcavity outputs an optical frequency comb;

[0028] A first photodetector receives the optical frequency comb, and a beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb;

[0029] Among them, the pump light excites an optical mode in the photomechanical microcavity; the optical mode is coupled with the mechanical mode to generate a dynamic reaction; the dynamic reaction drives the mechanical mode to generate optical sidebands and output an optical frequency comb; the large blue detuned state is that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the overcoupled state is that the optical mode loss rate is at the same order of magnitude as the mechanical mode resonance frequency.

[0030] The microwave frequency comb generation system provided by the embodiment of the present invention includes a pump source, a coupling structure, an optical force microcavity and a first photodetector; the pump source is used to provide pump light, and the pump light is coupled into the coupling structure; the coupling structure is used to couple the pump light into the optical force microcavity; the optical force microcavity is integrated on a substrate, and the optical force microcavity includes an optical mode and a mechanical mode; the pump light excites the optical mode in the optical force microcavity; the optical mode is coupled with the mechanical mode to generate a dynamic reaction; the dynamic reaction drives the mechanical mode to generate an optical sideband and output an optical frequency comb; the first photodetector is located at the output end of the optical force microcavity, and is used to receive the optical frequency comb, and the beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb; wherein the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state, the large blue detuned state is that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the over-coupled state is that the optical mode loss rate and the mechanical mode resonance frequency are at the same order of magnitude. A pump light is provided by a pump source, and the pump light is coupled into an optical force microcavity through a coupling structure. The optical force microcavity includes an optical mode and a mechanical mode. When the pump light is transmitted in the optical force microcavity, it is coupled with the mechanical mode. When the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state, the optical mode and the mechanical mode are coupled to produce a dynamic reaction; the dynamic reaction drives the mechanical mode to produce an optical sideband, thereby outputting an optical frequency comb; the optical frequency comb is received by a first photodetector, and the beat frequency between the teeth of the optical frequency comb produces a microwave frequency comb; by utilizing an optical force microcavity integrated on a substrate, chip integration can be achieved; the large blue detuned state and the over-coupled state can improve the bandwidth, efficiency and spectral flatness of the microwave frequency comb, and can suppress the optical force chaos phenomenon, thereby suppressing the optical force chaos from causing the coherence of the microwave comb to decrease; the microwave frequency comb generation system provided in this embodiment can generate a high-performance, wide-bandwidth, low-repetition-rate (<GHz) microwave frequency comb that can be used for chip integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic structural diagram of a microwave frequency comb generation system provided by an embodiment of the present invention;

[0032] Figure 2 is a schematic structural diagram of another microwave frequency comb generation system provided by an embodiment of the present invention;

[0033] Figure 3 is a schematic structural diagram of another microwave frequency comb generation system provided by an embodiment of the present invention;

[0034] Figure 4 is a schematic structural diagram of another microwave frequency comb generation system provided by an embodiment of the present invention;

[0035] Figures 5 to 10They are schematic diagrams of the structure of an optical force microcavity provided by an embodiment of the present invention;

[0036] Fig.11 is a schematic flow chart of a microwave frequency comb generation method provided by an embodiment of the present invention;

[0037] Fig.12 is a schematic diagram of a microwave spectrum of a microwave frequency comb generated by an embodiment of the present invention;

[0038] Fig.13 is a schematic diagram of the first comb tooth line width of a microwave frequency comb generated by an embodiment of the present invention;

[0039] Fig.14 Schematic diagram of the line widths of the 10th, 30th, 50th and 70th comb teeth of a microwave frequency comb generated by an embodiment of the present invention;

[0040] Fig.15 is a schematic diagram of an oscilloscope waveform of a microwave frequency comb generated by an embodiment of the present invention;

[0041] Fig.16 Schematic diagram of the relationship between the number of comb teeth and pump power in an embodiment of the present invention;

[0042] Fig.17 is a schematic diagram of a microwave spectrum of another microwave frequency comb generated by an embodiment of the present invention;

[0043] Fig.18 is a schematic diagram of the first comb tooth line width of another microwave frequency comb generated by an embodiment of the present invention;

[0044] Fig.19 Schematic diagram of the line widths of the 30th, 50th and 70th comb teeth of a microwave frequency comb generated by an embodiment of the present invention;

[0045] Fig. 20 is a schematic diagram of an oscilloscope waveform of another microwave frequency comb generated by an embodiment of the present invention;

[0046] Fig.21 is a schematic diagram of a microwave spectrum of another microwave frequency comb generated by an embodiment of the present invention;

[0047] Fig. 22 is a schematic diagram of a microwave spectrum of another microwave frequency comb generated by an embodiment of the present invention;

[0048] Fig.23 It is a schematic diagram of the principle of a microwave frequency comb generation system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0050] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. It should be noted that the directional words such as "upper", "lower", "left", "right" and the like described in the embodiments of the present invention are described at the angles shown in the accompanying drawings and should not be understood as limitations on the embodiments of the present invention. In addition, in the context, it is also necessary to understand that when it is mentioned that an element is formed "on" or "under" another element, it can not only be directly formed "on" or "under" another element, but also indirectly formed "on" or "under" another element through an intermediate element. The terms "first", "second" and the like are only used for descriptive purposes and do not indicate any order, quantity or importance, but are only used to distinguish different components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0051] Figure 1 FIG. 1 is a schematic diagram of the structure of a microwave frequency comb generation system provided by an embodiment of the present invention. Figure 1 The microwave frequency comb generation system provided in this embodiment includes a pump source 10, a coupling structure 20, an optical force microcavity 30 and a first photodetector 40; the pump source 10 is used to provide pump light, and the pump light is coupled into the coupling structure 20; the coupling structure 20 is used to couple the pump light into the optical force microcavity 30; the optical force microcavity 30 is integrated on a substrate, and the optical force microcavity 30 includes an optical mode and a mechanical mode; the pump light excites the optical mode in the optical force microcavity 30; the optical mode is coupled with the mechanical mode to generate a dynamic reaction; the dynamic reaction drives the mechanical mode, generates optical sidebands, and outputs an optical frequency comb; the first photodetector 40 is located at the output end of the optical force microcavity 30, and is used to receive the optical frequency comb, and the beat frequency between the comb teeth of the optical frequency comb generates a microwave frequency comb; wherein, the pump light and the optical force microcavity 30 are in a large blue detuned state, and the coupling structure 20 and the optical force microcavity 30 are in an over-coupled state. The large blue detuned state means that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the over-coupled state means that the optical mode loss rate is at the same order of magnitude as the mechanical mode resonance frequency.

[0052] Wherein, the pump source 10 is used to generate pump light for exciting the optical frequency comb, and the beat signal when the optical frequency comb is received by the first photodetector 40 generates a microwave frequency comb. In a certain embodiment, optionally, the pump source 10 includes a wavelength-tunable laser, such as a wavelength-tunable fiber laser, a wavelength-tunable semiconductor laser, etc., and the pump light is adjusted to a pump frequency that is detuned from the large blue state of the optical force microcavity 30 by adjusting the output wavelength of the pump light. In another embodiment, optionally, the pump source 10 includes a laser with a fixed wavelength, and the pump source 10 outputs a pump light of a fixed frequency, and utilizes the nonlinear effect of the optical force microcavity 30 (such as thermo-optical nonlinearity, the thermal effect generated by the optical force microcavity causes the optical mode resonance frequency to undergo a nonlinear frequency shift, which is equivalent to a change in the pump light frequency) so that the large blue detuned state condition is directly achieved when the pump light wavelength remains unchanged. In specific implementation, the pump source 10 can be selected according to actual conditions, and the embodiment of the present invention is not limited to this. The coupling structure 20 is used to receive the pump light emitted by the pump source 10 and couple the pump light into the optical microcavity 30. In specific implementation, the coupling structure 20 may include a tapered optical fiber, a micro-nano optical fiber or other optical waveguides. Schematically, Figure 1 The coupling structure 20 shown in the figure is an optical fiber including a conical structure. The pump light generates an evanescent field in the conical structure to achieve coupling with the optical force microcavity 30. The coupling efficiency can be adjusted by adjusting the distance between the conical structure and the optical force microcavity 30. The conical 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. During specific implementation, the type of coupling structure 20 can be selected according to actual experimental conditions, and the embodiment of the present invention is not limited thereto.

[0053] The optical microcavity 30 is a monolithically integrated optical microcavity with a high optical mode quality factor and a mechanical mode quality factor. It can be understood that in order to make the pump light in an over-coupled state, the total optical mode loss rate in the optical microcavity 30 needs to be equivalent to the mechanical mode resonance frequency (maintained within an order of magnitude), and the unit is Hz, and the total loss rate is obtained by adding the intrinsic loss rate to the coupling loss rate. The intrinsic loss rate is fixed after the microcavity is selected, so the total loss rate can only be adjusted by adjusting the coupling loss rate. The over-coupled state means that because the optical microcavity quality factor is very high and the intrinsic loss rate is very small, the efficiency of the optical frequency comb generation can be greatly improved. At this time, if the total optical mode loss rate is to be equivalent to the mechanical mode resonance frequency, the loss rate caused by the coupling must be increased. At this time, the coupling loss rate is much greater than the cavity intrinsic loss rate, which is the so-called over-coupled state. In this state, the bandwidth, efficiency and spectral flatness of the optical frequency comb can be improved, and the optical force chaos phenomenon can also be effectively suppressed. The large blue detuned state requires the pump detuning to be at least ten times greater than the mechanical mode resonance frequency. The pump detuning is the difference between the pump light frequency and the mechanical mode resonance frequency. The pump detuning determines the spectral width of the optical frequency comb. The larger the pump detuning, the wider the spectral width, thereby enhancing the spectral width of the microwave optical frequency comb. In specific implementation, it is often greater than thirty times the mechanical mode resonance frequency. By adjusting the pump frequency to a suitable large blue detuned pump, the amplification and optimal pumping of the mechanical mode amplitude of the optical force microcavity 30 are achieved, generating a wide bandwidth, high efficiency, spectrally flat, and highly coherent optical frequency comb, and then realizing a microwave frequency comb through the optical frequency comb beat frequency. In this way, the embodiment of the present invention can achieve a microwave frequency comb with high efficiency, high coherence, and a flat microwave spectrum.

[0054] In addition, by adjusting different pump powers, optical frequency combs of different bandwidths can be generated, and then microwave frequency combs of different bandwidths can be generated. The bandwidth of the microwave frequency comb can be expanded by increasing the pump power. Optionally, the repetition frequency of the microwave frequency comb is determined by the mechanical mode resonance frequency, which is in the kHz, MHz or GHz order. By selecting optical force microcavities with different mechanical modes, microwave frequency combs of different repetition frequencies can be achieved. In this embodiment, the comb tooth line width of the microwave frequency comb is extremely narrow. Optionally, the comb tooth line width of the microwave frequency comb is in the sub-Hz to 10Hz order.

[0055] The technical solution of this embodiment is to provide pump light through a pump source, and couple the pump light into the photomechanical microcavity through a coupling structure. The photomechanical microcavity includes an optical mode and a mechanical mode. When the pump light is transmitted in the photomechanical microcavity, it couples with the mechanical mode. When the pump light and the photomechanical microcavity are in a large blue detuned state, and the coupling structure and the photomechanical microcavity are in an over-coupled state, the optical mode and the mechanical mode are coupled to produce a dynamic reaction; the dynamic reaction drives the mechanical mode to produce an optical sideband, thereby outputting an optical frequency comb; the optical frequency comb is received by a first photodetector, and the beat frequency between the teeth of the optical frequency comb produces a microwave frequency comb; by utilizing the photomechanical microcavity integrated on a substrate, chip integration can be achieved; the large blue detuned state and the over-coupled state can improve the bandwidth, efficiency and spectral flatness of the microwave frequency comb, and can suppress the photomechanical chaos phenomenon, thereby suppressing the photomechanical chaos that causes the coherence of the microwave comb to decrease; the microwave frequency comb generation system provided in this embodiment can generate a high-performance, wide-bandwidth, low-repetition-rate (<GHz) microwave frequency comb that can be used for chip integration.

[0056] Based on the above technical solutions, Figure 2 FIG. 2 is a schematic diagram of the structure of another microwave frequency comb generation system provided by an embodiment of the present invention. Figure 2 Optionally, the microwave frequency comb provided in this embodiment further includes a polarization controller 50, and the polarization controller 50 is located between the pump source 10 and the coupling structure 20, and the polarization controller 50 is used to adjust the polarization direction of the pump light.

[0057] Exemplarily, in a specific implementation, the coupling structure 20 includes an optical fiber, and the polarization direction of the pump light is adjusted by adjusting the polarization controller 50 to be in different states, thereby adjusting the coupling efficiency between the pump light and the optical force microcavity 30. The polarization controller 50 can be a three-ring or embedded polarization controller, which is not limited to the embodiments of the present invention.

[0058] Figure 3 FIG. 2 is a schematic diagram of the structure of another microwave frequency comb generation system provided by an embodiment of the present invention. Figure 3 Optionally, the microwave frequency comb generation system provided in this embodiment further includes a beam splitter 60, a second photodetector 70, an oscilloscope 80 and a spectrometer 90; the output end of the coupling structure 20 extending from the optical force microcavity 30 is connected to the input end of the beam splitter 60, the first output end of the beam splitter 60 is connected to the first photodetector 40, the first photodetector 40 is connected to the oscilloscope 80, the second output end of the beam splitter 60 is connected to the second photodetector 70, and the second photodetector 70 is connected to the spectrometer 90; the oscilloscope 80 is used to output the time domain waveform detected by the first photodetector 40, and the spectrometer 90 is used to measure the spectrum of the microwave frequency comb.

[0059] It is understandable that in order to verify whether the microwave frequency comb generation system provided by the embodiment of the present invention generates a microwave frequency comb, a test needs to be performed. By observing the time domain waveform of the oscilloscope 80 and the spectrum measured by the spectrometer 90, it can be determined whether a microwave frequency comb is generated. In specific implementation, a spectrometer can also be used to observe whether an optical frequency comb is generated. The beam splitter 60 can use a fiber coupler with a splitting ratio of 90:10 (any ratio is acceptable, not limited here) between the first output end and the second output end. In other embodiments, optical amplifiers, filters, polarization controllers and other structures can also be set at the output end of the pump source 10, and can be selected according to actual conditions in specific implementation.

[0060] In other embodiments, in order to maintain the consistency of the frequency domain signal and the time domain signal, the same photodetector can be used. Figure 4 FIG. 2 is a schematic diagram of the structure of another microwave frequency comb generation system provided by an embodiment of the present invention. Figure 4 ,and Figure 3 The difference is that in this embodiment, the beam splitter and the second photodetector are not provided, and the oscilloscope 80 and the spectrometer 90 are connected to the first photodetector 40 at the same time.

[0061] Optionally, the optical force microcavity 30 includes a whispering gallery mode optical force microcavity, and the optical mode is coupled with the mechanical mode of the optical force microcavity itself. Optionally, the optical force microcavity 30 includes a standing wave mode optical force microcavity, and a micro-nano structure, a membrane structure, a photonic crystal, a phononic crystal or a vibrating atomic cloud is arranged in the standing wave mode optical force microcavity; the optical mode is coupled with the mechanical mode of the object in the optical force microcavity.

[0062] For example, Figures 5 to 10 The following are schematic diagrams of the structure of a light force microcavity provided by an embodiment of the present invention. Figures 5 to 10 , the shaded part is the light field distribution, the black line is the vibration contour of the cavity boundary, and the optical microcavity can be a microring core cavity, a microsphere cavity, or a microdisk cavity in the whispering gallery mode ( Figure 5 ), or it can be an optical microcavity in a standing wave mode, where Figure 6 Shown is a standing wave mode cantilever mirror. Figure 7 It is a membrane structure placed inside the cantilever mirror. Figure 8 is the localized mode in the photonic crystal / phononic crystal, Fig. 9 Place a cloud of trapped / vibrating atoms or other suspended objects in the cavity. Fig.10 A vibrating capacitor is coupled to the microwave field.

[0063] Optionally, the coupling structure 20 and the optical force microcavity 30 are integrated on the same substrate. In a specific implementation, the coupling structure 20 can be a structure such as a micro-nano optical fiber that can be integrated on a substrate. By integrating the coupling structure 20 and the optical force microcavity 30 on the same substrate, the integration of the microwave frequency comb generation system can be further improved.

[0064] Fig.11 The figure is a flow chart of a microwave frequency comb generation method provided by an embodiment of the present invention. The method can be performed by any microwave frequency comb generation system provided by the above embodiments, and specifically comprises the following steps:

[0065] Step S110: The pump source outputs pump light, and the pump light is coupled into the optical force microcavity through the coupling structure.

[0066] The pump source may include a wavelength-tunable laser or a fixed-wavelength laser, and the coupling structure may include a tapered optical fiber, a micro-nano optical fiber or other optical waveguides, etc., which may be flexibly selected according to actual conditions during implementation.

[0067] Step S120, adjust the pump light and the coupling structure so that the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state, so that the optical force microcavity outputs an optical frequency comb.

[0068] Among them, the pump light excites the optical mode in the photomechanical microcavity; the optical mode is coupled with the mechanical mode to produce a dynamic reaction; the dynamic reaction drives the mechanical mode to produce optical sidebands and output an optical frequency comb; the large blue detuned state is that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the overcoupled state is that the optical mode loss rate is at the same order of magnitude as the mechanical mode resonance frequency.

[0069] Step S130: The first photodetector receives the optical frequency comb, and the beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb.

[0070] The first photodetector is arranged at the output end of the optical force microcavity to receive an optical frequency comb, and the beat frequency signal of the optical frequency comb generates a microwave frequency comb.

[0071] The technical solution of this embodiment is to provide pump light through a pump source, and couple the pump light into the photomechanical microcavity through a coupling structure. The photomechanical microcavity includes an optical mode and a mechanical mode. When the pump light is transmitted in the photomechanical microcavity, it couples with the mechanical mode. When the pump light and the photomechanical microcavity are in a large blue detuned state, and the coupling structure and the photomechanical microcavity are in an over-coupled state, the optical mode and the mechanical mode are coupled to produce a dynamic reaction; the dynamic reaction drives the mechanical mode to produce an optical sideband, thereby outputting an optical frequency comb; the optical frequency comb is received by a first photodetector, and the beat frequency between the teeth of the optical frequency comb produces a microwave frequency comb; by utilizing the photomechanical microcavity integrated on a substrate, chip integration can be achieved; the large blue detuned state and the over-coupled state can improve the bandwidth, efficiency and spectral flatness of the microwave frequency comb, and can suppress the photomechanical chaos phenomenon, thereby suppressing the photomechanical chaos that causes the coherence of the microwave comb to decrease; the microwave frequency comb generation system provided in this embodiment can generate a high-performance, wide-bandwidth, low-repetition-rate (<GHz) microwave frequency comb that can be used for chip integration.

[0072] Specifically, Figure 3 or Figure 4 Taking the microwave frequency comb generation system structure shown in the figure as an example, in a certain embodiment, the pump source 10 adopts a wavelength tunable laser of about 1550nm, the coupling structure 20 adopts an optical fiber with a tapered structure, the optical fiber is bendable and has good compatibility and integration characteristics with existing optical fiber output and input port devices, and the optical force microcavity 30 adopts a silicon oxide material on-chip whispering gallery mode microring core cavity structure, and the substrate adopts a silicon structure. Here, the silicon oxide microring core cavity has the advantages of low cost, ultra-high optical and mechanical mode quality factors, and chip integration. The silicon oxide microring core cavity used has a diameter of 50μm and an optical mode quality factor of >10 7 , mechanical mode quality factor>3000, mechanical mode resonance frequency 28.5MHz, optical-mechanical coupling coefficient 20GHz / nm, Fig.12 FIG. 1 is a schematic diagram of a microwave spectrum of a microwave frequency comb generated by an embodiment of the present invention. Fig.13 FIG. 1 is a schematic diagram of the first comb line width of a microwave frequency comb generated by an embodiment of the present invention, Fig.13 It can be seen that the comb tooth frequency interval is the mechanical mode resonance frequency of 28.5MHz. Fig.14 The figure shows the line width of the 10th, 30th, 50th and 70th comb teeth of a microwave frequency comb generated by an embodiment of the present invention. Figure 12 to Figure 14 Obtained from a spectrum analyzer. Fig.15 Shown is a schematic diagram of an oscilloscope waveform of a microwave frequency comb generated by an embodiment of the present invention. Fig.16 FIG. 1 is a schematic diagram showing the relationship between the number of comb teeth and pump power in an embodiment of the present invention, referring to FIG. Fig.16By gradually increasing the pump power and adjusting the pump source 10 to a suitable large blue detuning frequency, it can be obtained that the number of microwave frequency comb teeth (bandwidth) increases with increasing power.

[0073] In another embodiment, the optical force microcavity 30 is a silicon oxide microsphere cavity with a diameter of 30 μm and an optical mode quality factor of >10. 7 , the mechanical mode quality factor is >3000, the mechanical mode resonance frequency is 136.5MHz, and the photomechanical coupling coefficient is 20GHz / nm. Fig.17 FIG. 1 is a schematic diagram of a microwave spectrum of another microwave frequency comb generated by an embodiment of the present invention. Fig.18 FIG. 1 is a schematic diagram of the first comb line width of another microwave frequency comb generated by an embodiment of the present invention, Fig.18 It can be seen that the comb tooth frequency interval is the mechanical mode resonance frequency of 136.5MHz. Fig.19 The figure shows the line width of the 30th, 50th and 70th comb teeth of a microwave frequency comb generated by an embodiment of the present invention. Figure 17 to Figure 19 Obtained from a spectrum analyzer. Fig. 20 FIG. 1 is a schematic diagram of an oscilloscope waveform of another microwave frequency comb generated by an embodiment of the present invention. The mechanical mode resonance frequency of 105.3 MHz is selected. Fig.21 The figure shows a microwave spectrum diagram of another microwave frequency comb generated by an embodiment of the present invention, which generates a microwave frequency comb with a comb tooth spacing of 105.3MHz. In addition, a mechanical mode resonance frequency of 436.7MHz is selected. Fig. 22 Shown is a schematic diagram of a microwave spectrum of another microwave frequency comb generated by an embodiment of the present invention, which generates a microwave frequency comb with a comb tooth spacing of 436.7 MHz.

[0074] In other embodiments, the optical microcavity may also be a standing wave mode microwave microcavity. Fig.23 The figure shows a schematic diagram of the principle of a microwave frequency comb generation system provided by an embodiment of the present invention, in which one cavity mirror is a movable cavity mirror, and the cavity mirror is driven to move by the microwave mode light pressure in the microwave microcavity, so that the microwave mode in the standing wave mode microwave microcavity is coupled with the cavity mirror mechanical mode, and a microwave frequency comb is generated through dynamic reaction. Microwave sidebands are generated by optical waveguides and standing wave mode microwave microcavities. The pump light source is continuously adjusted to a suitable large blue detuned pump frequency to widen a small amount of microwave sidebands to a wide bandwidth microwave frequency comb, and the frequency interval of the microwave frequency comb teeth is realized to be the resonance frequency of the cavity mirror mechanical mode.

[0075] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A microwave frequency comb generation system, characterized in that: It includes a pump source, a coupling structure, a photomechanical microcavity and a first photodetector; The pump source is used to provide pump light, and the pump light is coupled into the coupling structure; The coupling structure comprises a tapered optical fiber or a micro-nano optical fiber, and the coupling structure is used to couple the pump light into the optical force microcavity; The optical force microcavity is integrated on a base substrate, and the optical force microcavity includes an optical mode and a mechanical mode; The pump light excites the optical mode in the optical force microcavity; The optical mode is coupled with the mechanical mode to generate a dynamic reaction; The dynamic reaction drives the mechanical mode to generate optical sidebands and output an optical frequency comb; The first photodetector is located at the output end of the optical force microcavity, and is used to receive the optical frequency comb, and the beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb; Among them, the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state. The large blue detuned state means that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the over-coupled state means that the optical mode loss rate is at the same order of magnitude as the mechanical mode resonance frequency.

2. The microwave frequency comb generation system according to claim 1, characterized in that: It also includes a polarization controller, which is located between the pump source and the coupling structure, and is used to adjust the polarization direction of the pump light.

3. The microwave frequency comb generation system according to claim 1, characterized in that: Also includes a beam splitter, a second photodetector, an oscilloscope and a spectrum analyzer; The output end of the coupling structure extending from the optical force microcavity is connected to the input end of the beam splitter, the first output end of the beam splitter is connected to the first photodetector, the first photodetector is connected to the oscilloscope, the second output end of the beam splitter is connected to the second photodetector, and the second photodetector is connected to the spectrometer; The oscilloscope is used to output the time domain waveform detected by the first photodetector, and the spectrum analyzer is used to measure the spectrum of the microwave frequency comb.

4. The microwave frequency comb generation system according to any one of claims 1 to 3, characterized in that: The pump source includes a wavelength-tunable laser.

5. The microwave frequency comb generation system according to any one of claims 1 to 3, characterized in that: The pump source includes a fixed wavelength laser.

6. The microwave frequency comb generation system according to any one of claims 1 to 3, characterized in that: The optical force microcavity includes a whispering gallery mode optical force microcavity, and the optical mode is coupled with the mechanical mode of the optical force microcavity itself.

7. The microwave frequency comb generation system according to any one of claims 1 to 3, characterized in that: The optical force microcavity includes a standing wave mode optical force microcavity, in which a micro-nano structure, a membrane structure, a photonic crystal, a phononic crystal or a vibrating atomic cloud is arranged; The optical mode is coupled with the mechanical mode of the object in the optical force microcavity.

8. The microwave frequency comb generation system according to any one of claims 1 to 3, characterized in that: The comb tooth line width of the microwave frequency comb is in the sub-Hz to 10 Hz range.

9. The microwave frequency comb generation system according to any one of claims 1 to 3, characterized in that: The coupling structure and the optical force microcavity are integrated on the same base substrate.

10. A method for generating a microwave frequency comb, characterized in that: The method is performed using the microwave frequency comb generation system according to any one of claims 1 to 9, comprising: The pump source outputs pump light, and the pump light is coupled into the optical force microcavity through the coupling structure; Adjusting the pump light and the coupling structure so that the pump light and the optical force microcavity are in a large blue detuned state, and the coupling structure and the optical force microcavity are in an over-coupled state, so that the optical force microcavity outputs an optical frequency comb; A first photodetector receives the optical frequency comb, and a beat frequency between the teeth of the optical frequency comb generates a microwave frequency comb; Among them, the pump light excites an optical mode in the photomechanical microcavity; the optical mode is coupled with the mechanical mode to generate a dynamic reaction; the dynamic reaction drives the mechanical mode to generate optical sidebands and output an optical frequency comb; the large blue detuned state is that the difference between the pump light frequency and the optical mode resonance frequency is greater than ten times the mechanical mode resonance frequency, and the overcoupled state is that the optical mode loss rate is at the same order of magnitude as the mechanical mode resonance frequency.

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