A repetition rate wideband tuning system and method for a coupled microcavity optical comb

Abstract

The application discloses a kind of coupling microcavity optical comb's repetition frequency broadband tuning system and method, tunable pump light source module outputs pump light in the system;Coupling microcavity soliton generation module divides microcavity soliton optical frequency comb into two ways;Repetition frequency monitoring module extracts the repetition frequency information in electrical signal, generates feedback signal;Feedback control module calculates the difference between current repetition frequency value and preset target frequency value, generates control instruction according to difference;Tunable pump light source module adjusts the output frequency of pump light according to control instruction, to switch the cavity mode position of pump light;Heater changes the detuning amount of pump light relative to resonant cavity, and locks the repetition frequency to target frequency value.The application switches pump light between different longitudinal resonance modes, makes microcavity soliton optical frequency comb work at different pump wavelengths, and realizes wideband, high-precision continuous tuning of repetition frequency by using the change of local free spectral range with wavelength.

Description

Technical Field

[0001] This solution relates to the field of microcavity optical frequency comb technology, and in particular to a repetition rate broadband tuning system and method for coupling a microcavity optical comb. Background Technology

[0002] With the development of quantum communication technology, quantum key distribution (QKD), based on the quantum no-cloning and measurement perturbation properties, can achieve highly secure key distribution and has become an important technological direction for future information security. Among them, measurement-device-independent quantum key distribution (MDI-QKD) and twin-field quantum key distribution (TF-QKD) can effectively improve system security, transmission distance, and network scalability. To further improve the key generation rate and system capacity, multi-wavelength parallel quantum key distribution systems based on wavelength division multiplexing have attracted widespread attention. These systems require different user ends or remote nodes to provide multi-wavelength light sources with stable frequencies, good coherence, and consistent channel spacing, and to achieve high-visibility two-photon interference at the intermediate measurement end.

[0003] Microcavity soliton optical frequency combs possess advantages such as a large number of comb teeth, uniform frequency spacing, good phase coherence, chip-level integration, and repetition frequency matching with wavelength division multiplexing (WDM) channels, making them ideal light sources for realizing massively parallel MDI-QKD and TF-QKD. However, in practical applications, different user terminals typically employ independent soliton microcomb light sources. To meet the requirement of photon frequency indistinguishability at intermediate nodes, not only is it necessary to keep the pump light frequency locked, but also to ensure strict alignment of the comb tooth frequencies between independent soliton microcombs, i.e., highly consistent repetition frequencies.

[0004] Due to fabrication errors in micro and nanometers, different microcavities inevitably differ in cavity length, waveguide cross-section, effective refractive index, and dispersion parameters, leading to deviations in their free spectral range and soliton microcomb repetition frequency. These deviations typically range from hundreds of kHz (kilohertz) to several MHz (megahertz). Furthermore, existing methods such as thermal tuning and pump-cavity detuning have limited repetition frequency adjustment ranges, making it difficult to compensate for these deviations under pump-locked conditions.

[0005] Therefore, there is an urgent need for a technical solution that can achieve continuous and controllable adjustment of the soliton microcomb repetition frequency in the MHz range, so as to achieve strict alignment of the frequency of the independent microcomb teeth and provide a stable integrated light source for large-scale parallel quantum communication and quantum networks. Summary of the Invention

[0006] This solution aims to at least address the technical problems existing in the prior art. To this end, the first aspect of this invention proposes a broadband repetition rate tuning system for a coupled microcavity optical comb, the system comprising: a tunable pump source module, a coupled microcavity soliton generation module, a repetition rate monitoring module, and a feedback control module; wherein: The tunable pump light source module is used to output pump light; The coupled microcavity soliton generation module is used to receive the pump light, enhance the power of the pump light and excite Kerr solitons to generate a microcavity soliton optical frequency comb; the coupled microcavity soliton generation module is also used to split the microcavity soliton optical frequency comb into a first optical signal and a second optical signal, the first optical signal is used as the system output terminal, and the second optical signal is input to the repetition frequency monitoring module; The repetition frequency monitoring module is used to convert the second optical signal into an electrical signal, extract the repetition frequency information from the electrical signal, and generate a feedback signal characterizing the current repetition frequency value. The feedback control module is used to receive the feedback signal, calculate the difference between the current repetition frequency value and the preset target frequency value, generate a control command based on the difference, and output the control command to the tunable pump light source module. The tunable pump light source module is also used to adjust the output frequency of the pump light according to the control command, so as to switch the cavity mode position of the pump light; The coupled microcavity soliton generator module heater changes the detuning of the pump light of the coupled microcavity soliton generator module relative to the resonant cavity by changing the microcavity mode frequency, thereby locking the repetition frequency of the microcavity soliton optical frequency comb to the preset target frequency value.

[0007] Optionally, the coupled microcavity soliton generation module includes an optical amplifier for amplifying the pump light, a nonlinear cavity for exciting dissipative Kerr solitons with strong light, and an auxiliary cavity coupled to the nonlinear cavity via an evanescent field. The auxiliary cavity is coupled to the nonlinear cavity via an evanescent field; the auxiliary cavity is used to perform mode hybridization with at least some of the resonant modes of the nonlinear cavity and introduce a mode frequency shift related to the number of modes into the modes of the nonlinear cavity; The coupled microcavity soliton generation module also includes a heater, which is used to adjust the detuning of the pump light relative to the resonant cavity by means of temperature.

[0008] Optionally, the nonlinear cavity and the auxiliary cavity are any one or two of the following: microring resonant cavity, microdisk resonant cavity, microsphere cavity, microrod cavity, and other resonant cavities that support Kerr nonlinear processes; The nonlinear cavity and the auxiliary cavity are made of one or more of the following materials: silicon nitride, silicon dioxide, doped glass, magnesium fluoride, and silicon-based.

[0009] Optionally, the tunable pump source module is a narrow linewidth laser with tunable wavelength or frequency; the tuning range of the narrow linewidth laser covers multiple resonant modes that can be used to generate microcavity soliton optical frequency combs, so that the pump light can switch between different pump modes.

[0010] Optionally, the repetition frequency monitoring module includes a photodetector and a repetition frequency detector connected in sequence; the photodetector is used to convert the optical signal of the soliton microcomb input to the repetition frequency detection module into an electrical signal, and the repetition frequency detector is used to read and monitor the repetition frequency data of the electrical signal; The photodetector is a high-speed photodetector; the repetition frequency detector is one or more of a frequency counter, a spectrum analyzer, or an oscilloscope.

[0011] Optionally, the feedback control module includes a first negative feedback module and a second negative feedback module; the first negative feedback module and the second negative feedback module are either FPGA control circuits or computer programs. The first negative feedback module is used to control the tunable pump light source module to change the output frequency when the difference is greater than a preset first threshold, so that the pump light switches to the pump resonance mode, and to perform discrete step coarse tuning of the repetition frequency of the soliton microcomb by utilizing the difference in the local free spectral range at different pump wavelengths. The second negative feedback module is used to adjust the detuning of the pump light relative to the resonant cavity by a heater in the same pump mode when the difference is greater than a preset second threshold and less than or equal to the first threshold, so that the number of modes of the soliton spectral center or equivalent center is shifted, and the repetition frequency is continuously fine-tuned by utilizing the change in the equivalent mode interval caused by microcavity dispersion. When the difference is less than or equal to the second threshold, the feedback control module maintains the current tuning state and stably outputs the microcavity soliton optical frequency comb.

[0012] A second aspect of this invention provides a repetition rate broadband tuning method for coupled microcavity optical combs, the method comprising: The tunable pump light source module outputs pump light of a specific wavelength; The coupled microcavity soliton generation module receives the pump light, enhances the power of the pump light, and uses strong light to excite dissipative Kerr solitons to generate a microcavity soliton optical frequency comb; the microcavity soliton optical frequency comb is also split into two paths, one of which is output through a polarization-maintaining fiber for use, and the other is input to the repetition frequency monitoring module. The repetition frequency monitoring module converts the optical signal of the microcavity soliton optical frequency comb into an electrical signal and obtains the repetition frequency value of a single microcavity soliton optical frequency comb, and inputs the repetition frequency value into the negative feedback module. The feedback control module determines the adjustment range of the repetition frequency of the microcavity soliton optical frequency comb based on the difference between the repetition frequency value and the preset target value, and performs broadband tuning of the repetition frequency based on the adjustment range.

[0013] Optionally, the feedback control module determines the adjustment range of the repetition frequency of the microcavity soliton optical frequency comb based on the difference between the repetition frequency value and the preset target value, and performs broadband tuning of the repetition frequency based on the adjustment range, including: When the difference is greater than a preset first threshold, the first negative feedback module controls the tunable pump light source module to change the output frequency, so that the pump light switches to the pump resonance mode, and uses the difference in the local free spectral range at different pump wavelengths to perform discrete step coarse tuning of the repetition frequency of the soliton microcomb. When the difference is greater than a preset second threshold and less than or equal to the first threshold, the second negative feedback module adjusts the detuning of the pump light relative to the resonant cavity through the heater in the same pumping mode, so that the number of modes of the soliton spectral center or equivalent center shifts, and the equivalent mode interval change caused by microcavity dispersion is used to achieve continuous fine adjustment of the repetition frequency of the soliton microcomb. When the difference is less than or equal to the second threshold, the feedback control module maintains the current tuning state and stably outputs the microcavity soliton optical frequency comb.

[0014] Optionally, when performing discrete step coarse tuning on the repetition frequency of the soliton microcomb, the adjustment amount of the pump light frequency is an integer multiple of the target repetition frequency; after the pump light switches to the pump resonant mode, the pump light frequency is kept fixed, and the frequency of the resonant mode is changed by the heater, and the pump-cavity mode detuning is adjusted at the fixed pump frequency to establish the soliton state. When continuously fine-tuning the repetition frequency, the pump light frequency is kept constant, and the detuning of the pump light relative to the resonant cavity is changed by adjusting the microcavity resonant mode frequency, so as to achieve continuous fine-tuning of the repetition frequency of the microcavity soliton optical frequency comb.

[0015] The embodiments of the present invention have the following beneficial effects: The present invention provides a broadband tuning system for a coupled microcavity optical comb, comprising: a tunable pump source module, a coupled microcavity soliton generation module, a repetition frequency monitoring module, and a feedback control module; wherein: the tunable pump source module is used to output pump light; the coupled microcavity soliton generation module is used to receive the pump light, enhance the power of the pump light, and excite Kerr solitons to generate a microcavity soliton optical frequency comb; the coupled microcavity soliton generation module is further used to split the microcavity soliton optical frequency comb into a first optical signal and a second optical signal, the first optical signal serving as the system output, and the second optical signal being input to the repetition frequency monitoring module; the repetition frequency monitoring module is used to convert the second optical signal into an electrical signal. The system receives the signal and extracts the repetition frequency information from the electrical signal to generate a feedback signal characterizing the current repetition frequency value. The feedback control module receives the feedback signal, calculates the difference between the current repetition frequency value and the preset target frequency value, generates a control command based on the difference, and outputs the control command to the tunable pump light source module. The tunable pump light source module is also used to adjust the output frequency of the pump light according to the control command to switch the cavity mode position of the pump light. The coupled microcavity soliton generator module heater changes the cavity mode frequency of the microcavity to change the detuning of the pump light of the coupled microcavity soliton generator module relative to the resonant cavity, thereby locking the repetition frequency of the microcavity soliton optical frequency comb to the preset target frequency value. This invention achieves broadband, high-precision continuous tuning of the repetition frequency by switching the pump light between different longitudinal resonant modes, enabling the microcavity soliton optical frequency comb to operate at different pump wavelengths, and utilizing the local free spectral range caused by material dispersion and waveguide dispersion to vary with wavelength. Attached Figure Description

[0016] Figure 1 This is a structural block diagram of a frequency repetition rate broadband tuning system coupled with a microcavity optical comb, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of a high-repetition-rate broadband tuning system coupled with a microcavity optical comb, provided in an embodiment of the present invention. Figure 3 This is a flowchart illustrating the steps of a frequency repetition rate broadband tuning method for a coupled microcavity optical comb provided in an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present solution, and not all embodiments. Based on the embodiments of the present solution, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present solution.

[0018] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0019] The purpose of this invention is to address the limitation in the repetition frequency adjustment range of existing microcavity soliton optical frequency combs based on thermal effects and pump-cavity mistuning. This invention provides a broadband repetition frequency tuning system and method based on a mode-shift coupled microcavity optical frequency comb. This system and method enable broadband, precise, and flexible tuning of the microcavity optical frequency comb's repetition frequency, which is of great significance for promoting the application of microcavity soliton optical frequency combs in precision measurement, dual-comb spectroscopy, and large-scale parallel quantum communication.

[0020] Figure 1 This is a structural block diagram of a frequency repetition rate broadband tuning system coupled with a microcavity optical comb, provided in an embodiment of the present invention.

[0021] like Figure 1 As shown, the system includes a tunable pump light source module 1, a coupled microcavity soliton generation module 2, a feedback control module 3, and a repetition frequency monitoring module 4; wherein: The tunable pump light source module 1 is used to output pump light; The coupled microcavity soliton generation module 2 is used to receive the pump light, enhance the power of the pump light and excite Kerr solitons to generate a microcavity soliton optical frequency comb; the coupled microcavity soliton generation module 2 is also used to split the microcavity soliton optical frequency comb into a first optical signal and a second optical signal, the first optical signal is used as the system output terminal, and the second optical signal is input to the repetition frequency monitoring module 4; The repetition frequency monitoring module 4 is used to convert the second optical signal into an electrical signal, extract the repetition frequency information in the electrical signal, and generate a feedback signal characterizing the current repetition frequency value. The feedback control module 3 is used to receive the feedback signal, calculate the difference between the current repetition frequency value and the preset target frequency value, generate a control command based on the difference, and output the control command to the heater of the tunable pump light source module 1 or the coupled microcavity soliton generator module 2. The tunable pump light source module 1 is also used to adjust the output frequency of the pump light according to the control command, so as to change the microcavity mode pumped by the pump light. The coupled microcavity soliton generator module heater changes the detuning of the pump light of the coupled microcavity soliton generator module relative to the resonant cavity by changing the microcavity mode frequency, thereby locking the repetition frequency of the microcavity soliton optical frequency comb to the preset target frequency value.

[0022] In this embodiment of the invention, pump light refers to continuous laser light of a specific wavelength. The tunable pump light source module 1 is a tunable pump light source laser, and the output frequency of the laser can be controlled by an external electrical signal.

[0023] After the pump light is amplified by the EDFA and enters the coupled microcavity soliton generation module 2, it accumulates cyclically in the nonlinear cavity under the effect of resonance enhancement, forming a high intracavity optical power and exciting Kerr nonlinearity and four-wave mixing effects. Under appropriate group velocity dispersion and pump-cavity mode detuning, the Kerr nonlinearity and dispersion, microcavity loss and external pump reach a dynamic balance, generating a microcavity soliton optical frequency comb. The coupled microcavity soliton generation module 2 includes an optical beamsplitter, which splits the microcavity soliton optical frequency comb into a first signal and a second signal. The first signal is output through polarization-maintaining fiber for practical applications, and the second signal is output to the input of the repetition frequency monitoring module 4.

[0024] The repetition frequency monitoring module 4 uses a high-speed photodetector to convert the optical pulse sequence into a radio frequency sine wave, that is, to convert the second optical signal into an electrical signal. The repetition frequency monitoring module 4 extracts the repetition frequency information from the electrical signal; it extracts the fundamental frequency. frep .

[0025] Feedback control module 3 calculates the repetition frequency difference of the soliton microcomb based on the set repetition frequency:

[0026] in, This indicates the current repetition frequency value. This indicates the preset target frequency value. e This represents the difference.

[0027] The feedback control module 3 converts the calculated difference into control commands and transmits them to the tunable pump light source or the heater of the coupled microcavity soliton generation module. The tunable pump light source finely adjusts the frequency of its output laser according to the control commands to switch different pump modes, or the heater changes the cavity mode frequency of the microcavity. This frequency change alters the frequency difference between the pump light and the intrinsic resonance of the microcavity, i.e., the detuning.

[0028] Within the soliton operating range, the change in this detuning amount precisely alters the group velocity of the optical soliton within the microcavity, i.e., the repetition frequency, thus forming a complete physical causal chain. Ultimately, this stabilizes the actual repetition frequency of the microcavity soliton optical frequency comb at the preset target frequency, achieving fine and flexible tuning of the output frequency.

[0029] As an optional embodiment, the coupled microcavity soliton generation module includes an optical amplifier for amplifying the pump light, a nonlinear cavity for exciting dissipative Kerr solitons, and an auxiliary cavity coupled to the nonlinear cavity via an evanescent field; the auxiliary cavity is coupled to the nonlinear cavity via the evanescent field; the auxiliary cavity is used to generate mode hybridization with at least some of the resonant modes of the nonlinear cavity and introduce a mode frequency shift related to the mode number in the modes of the nonlinear cavity; the coupled microcavity soliton generation module also includes a heater, which is used to adjust the detuning of the pump light relative to the resonant cavity by temperature.

[0030] In this embodiment of the invention, the optical amplifier serves to provide sufficiently high peak power for the subsequent nonlinear process, since exciting solitons requires extremely high instantaneous light intensity.

[0031] The pump light is amplified by an EDFA and coupled into the nonlinear cavity. Due to the resonant enhancement effect of the microcavity, the pump light accumulates cyclically within the cavity. When the optical power within the cavity exceeds the parametric oscillation threshold, a four-wave mixing effect occurs, generating new frequency components. Ultimately, a dissipative Kerr soliton is generated under the balance between dispersion and nonlinearity, and loss and pumping. In the time domain, this manifests as a periodically cyclical ultrashort pulse sequence within the microcavity; in the frequency domain, it appears as a microcavity soliton frequency comb composed of equally spaced, phase-coherent comb teeth. To more effectively generate and control solitons, an auxiliary cavity is introduced. The auxiliary cavity does not directly participate in soliton excitation but is coupled to the nonlinear cavity in the near field through an evanescent field. This coupling triggers a key effect: mode hybridization. Mode hybridization refers to the interaction between a resonant mode of the nonlinear cavity and a resonant mode of the auxiliary cavity, thereby forming two new supermodes that combine the characteristics of both.

[0032] This hybridization introduces a mode frequency shift related to the number of modes into the original modes of the nonlinear cavity. This means that light of different frequencies experiences different resonant frequency shifts within the cavity, and this additional, controllable frequency shift is equivalent to artificially altering the cavity's dispersion curve.

[0033] The module also integrates a heater, which is responsible for precise tuning at the microscopic level.

[0034] The heater plays two main roles here: (1) When generating soliton microcomb, it controls the cavity mode position of the nonlinear cavity to change the detuning amount to generate soliton microcomb; (2) When fine-tuning, it controls the cavity mode position to change the detuning amount to control the Raman frequency shift, which is equivalent to changing the soliton spectrum center or the number of equivalent center modes to achieve fine-tuning of the repetition frequency.

[0035] Because the generation of solitons is extremely sensitive to the relative relationship between the cavity resonant frequency and the pump light frequency, any fluctuation in ambient temperature or change in cavity length caused by thermal effects will disrupt the soliton state. The heater precisely adjusts the temperature to change the refractive index and physical length of the nonlinear cavity, thereby fine-tuning the cavity's resonant frequency.

[0036] As an optional embodiment, the nonlinear cavity and the auxiliary cavity are any one or two of the following: microring resonant cavity, microdisk resonant cavity, microsphere cavity, microrod cavity, and other resonant cavities that support Kerr nonlinear processes; the nonlinear cavity and the auxiliary cavity are made based on one or more of the following materials: silicon nitride, silicon dioxide, doped glass, magnesium fluoride, and silicon-based.

[0037] In the embodiments of the present invention, microring resonators (shaped like a racetrack or ring), microdisk resonators (flat disk-shaped), microspheres (spheres), microrods (slender columnar shapes), etc., are all "sounding-gallery mode" resonators.

[0038] Their common physical principle is that light circulates continuously within the cavity wall through total internal reflection, thus accumulating an extremely high light intensity density within a very small volume. They all support Kerr nonlinear processes, that is, having a sufficiently long light-matter interaction time and a sufficiently small mode volume, so that the pump light can effectively excite nonlinear effects such as four-wave mixing, which is the physical premise for the generation of dissipative Kerr solitons.

[0039] In practical implementation, the nonlinear cavity and auxiliary cavity can be arbitrarily combined; for example, both can be microrings, or one can be a microdisk and the other a microrod. The configuration can be selected based on the target soliton characteristics and integration requirements, as long as the evanescent field coupling between them can be effectively established.

[0040] As an optional embodiment, the tunable pump source module is a narrow linewidth laser with tunable wavelength or frequency; the tuning range of the narrow linewidth laser covers multiple resonant modes that can be used to generate microcavity soliton optical frequency combs, so that the pump light can switch between different pump modes.

[0041] In this embodiment of the invention, the generation of dissipative Kerr solitons places extremely stringent requirements on the purity of the pump light. A narrower linewidth indicates a more stable phase and better coherence of the light. If the laser linewidth is too wide, it's equivalent to the pump light itself carrying random noise. This noise is amplified drastically by the nonlinear cavity, thereby disrupting the precise phase-matching conditions for soliton formation, leading to unstable soliton generation or rapid disintegration after generation. Therefore, a narrow linewidth laser is chosen.

[0042] A microcavity has countless resonant modes, each corresponding to a different resonant frequency. When the pump light locks onto a specific resonant mode and generates a soliton, the output optical frequency comb (i.e., a series of equally spaced frequency teeth) centers on that mode. "Covering multiple resonant modes" means that by adjusting the laser's output wavelength, the pump light can be switched between different resonant modes.

[0043] As an optional embodiment, the repetition frequency monitoring module includes a photodetector and a repetition frequency detector connected in sequence; the photodetector is used to convert the optical signal of the soliton microcomb input to the repetition frequency detection module into an electrical signal, and the repetition frequency detector is used to read and monitor the repetition frequency data of the electrical signal; the photodetector is a high-speed photodetector; the repetition frequency detector is one or more of a frequency counter, a spectrum analyzer, or an oscilloscope.

[0044] In this embodiment of the invention, the photodetector is specifically a high-speed photodetector, which can convert such a high-speed optical pulse sequence into a radio frequency (RF) electrical pulse signal of the same frequency.

[0045] The function of a repetition frequency detector is to read and monitor electrical signals, that is, to accurately extract the repetition frequency (fundamental frequency) and harmonics of a pulse sequence.

[0046] The repetition frequency detector is one or more of a frequency counter, a spectrum analyzer, or an oscilloscope.

[0047] A frequency counter directly reads the fundamental frequency value of an electrical signal, providing a highly accurate repetition frequency. A spectrum analyzer not only displays the fundamental frequency but also reveals the fine structure of the entire radio frequency spectrum, including harmonic components, noise sidebands, and spurious signals. An oscilloscope directly displays the waveform of an electrical pulse in the time domain, allowing observation of the pulse's periodicity, amplitude stability, and the presence of time-domain anomalies such as "missing pulses."

[0048] As an optional embodiment, the feedback control module includes a first negative feedback module and a second negative feedback module; the first negative feedback module and the second negative feedback module are either FPGA control circuits or computer programs. The first negative feedback module is used to control the tunable pump light source module to change the output frequency when the difference is greater than a preset first threshold, so that the pump light switches to the pump resonance mode, and to perform discrete step coarse tuning of the repetition frequency of the soliton microcomb by utilizing the difference in the local free spectral range at different pump wavelengths. The second negative feedback module is used to adjust the detuning of the pump light relative to the resonant cavity by a heater in the same pump mode when the difference is greater than a preset second threshold and less than or equal to the first threshold, so that the number of modes of the soliton spectral center or equivalent center is shifted, and the repetition frequency is continuously fine-tuned by utilizing the change in the equivalent mode interval caused by microcavity dispersion. When the difference is less than or equal to the second threshold, the feedback control module maintains the current tuning state and stably outputs the microcavity soliton optical frequency comb.

[0049] In this embodiment of the invention, the feedback control module consists of a first negative feedback module and a second negative feedback module, which can be implemented based on FPGA (Field Programmable Gate Array) hardware circuits or computer programs.

[0050] FPGAs offer advantages in low latency and parallel processing, making them suitable for real-time control; while computer programs are more flexible and easier to implement complex algorithms. They both receive repetition frequency data from the repetition frequency monitoring module. and the preset target repetition frequency value Compare and calculate the difference. e Difference e The size of the value directly determines which tuning strategy the system adopts.

[0051] When this difference is greater than the preset first threshold ( , (The threshold value is set at 1), meaning the current repetition frequency deviates significantly from the target value and falls within a large error range. At this point, the first negative feedback module initiates discrete step coarse tuning. The negative feedback control module shifts the frequency of the tunable pump laser module by an integer multiple of the repetition frequency, switching between different pump modes. Because the group refractive index of the microcavity guided mode varies with wavelength, the local free spectral range differs at different pump wavelengths. Consequently, the microcavity soliton optical frequency comb has different repetition frequencies under different pump modes, thus achieving discrete step coarse tuning of the repetition frequency.

[0052] When the difference is within the range that is greater than the second threshold but less than or equal to the first threshold ( , Once the second threshold is reached, the system enters the fine-tuning stage, where the second negative feedback module performs continuous fine-tuning. By finely adjusting the heater temperature, the system can slowly change the refractive index of the microcavity, thereby fine-tuning the detuning of the pump light relative to the resonant cavity. This change in detuning directly affects the state of the solitons within the cavity, specifically manifested as a shift in the number of central or equivalent central modes in the soliton spectrum. Due to the inherent dispersion effect of the microcavity (i.e., the spacing between different modes varies with frequency), when the spectral envelope of the soliton shifts laterally within the cavity, its corresponding equivalent mode spacing (i.e., repetition frequency) also undergoes continuous and smooth minute changes. This achieves "fine-tuning" of the repetition frequency, with a resolution far exceeding that of the coarse-tuning step, enabling precise locking of the repetition frequency to the target value.

[0053] Finally, when the system's feedback control successfully compresses the difference to less than or equal to the second threshold ( When the frequency is within the tolerance range of the target value, it means that the current repetition frequency is close enough to meet the accuracy requirements for stable system operation. At this time, the feedback control module will maintain all current tuning states (including the wavelength of the pump laser and the temperature of the heater) and will no longer actively intervene, thereby achieving long-term, stable output of the microcavity soliton optical frequency comb.

[0054] Figure 2 This is a schematic diagram of a high-repetition-rate broadband tuning system coupled with a microcavity optical comb, provided as an embodiment of the present invention.

[0055] like Figure 2 As shown, the optical amplifier 21 is located at the front end of the system, receives weak seed light from the tunable pump laser module, and amplifies its power to a level sufficient to excite Kerr solitons.

[0056] Nonlinear cavity 22 and auxiliary cavity 23 are coupled via evanescent field (represented by adjacent or connecting lines in the diagram). Amplified pump light is injected into nonlinear cavity 22, generating dissipative Kerr solitons under strong light excitation, thus forming an optical frequency comb. Auxiliary cavity 23 introduces a mode-number-related frequency shift into the nonlinear cavity through mode hybridization, used for dispersion modulation. The generated soliton optical frequency comb is output from the nonlinear cavity and split into two paths: one as the system output, and the other sent to the monitoring module.

[0057] Heater 24 is arranged around the nonlinear cavity and the auxiliary cavity to finely control the amount of detuning of the pump light relative to the resonant cavity by adjusting the refractive index of the cavity through temperature.

[0058] The photodetector 41 receives the second optical signal (i.e., soliton optical frequency comb) split from the nonlinear cavity and converts its high-speed optical pulse sequence into an radio frequency electrical signal of the same frequency.

[0059] The repetition frequency detector 42 processes the electrical signal output by the photodetector, accurately reads and extracts the value of the repetition frequency, generates a feedback signal representing the current repetition frequency value, and sends it to the control module.

[0060] The first negative feedback module 31 and the second negative feedback module 32 together constitute the feedback control module. They receive the current repetition frequency value from the repetition frequency detector and compare it with the preset target value to obtain the difference.

[0061] When the difference is greater than the first threshold, the first negative feedback module 31 issues an instruction to control the tunable pump laser module to change the output frequency, switch the pump light to other resonant modes, and realize the discrete step coarse tuning of the repetition frequency.

[0062] When the difference is between the first and second thresholds, the negative feedback module 32 issues a command to control the heater 24, which changes the detuning amount by fine-tuning the temperature, thereby achieving continuous fine-tuning of the repetition frequency.

[0063] When the difference is less than or equal to the second threshold, the system maintains the current state and achieves stable output locking.

[0064] In summary, the broadband tuning system based on a mode-shift coupled microcavity optical comb provided by this invention includes: a tunable pump source module, a coupled microcavity soliton generation module, a repetition frequency monitoring module, and a feedback control module; wherein: the tunable pump source module is used to output pump light; the coupled microcavity soliton generation module is used to receive the pump light, enhance the power of the pump light, and excite Kerr solitons to generate a microcavity soliton optical frequency comb; the coupled microcavity soliton generation module is also used to split the microcavity soliton optical frequency comb into a first optical signal and a second optical signal, the first optical signal serving as the system output, and the second optical signal being input to the repetition frequency monitoring module; the repetition frequency monitoring module is used to... The optical signal is converted into an electrical signal, and the repetition frequency information in the electrical signal is extracted to generate a feedback signal characterizing the current repetition frequency value. The feedback control module is used to receive the feedback signal, calculate the difference between the current repetition frequency value and the preset target frequency value, generate a control command based on the difference, and output the control command to the tunable pump light source module. The tunable pump light source module is also used to adjust the output frequency of the pump light according to the control command to switch the cavity mode position of the pump light. The heater is used to change the detuning of the pump light of the coupled microcavity soliton generation module relative to the resonant cavity by changing the cavity mode frequency of the microcavity, thereby locking the repetition frequency of the microcavity soliton optical frequency comb to the preset target frequency value. This invention achieves broadband, high-precision continuous tuning of the repetition frequency by switching the pump light between different longitudinal resonant modes, making the microcavity soliton optical frequency comb work at different pump wavelengths, and utilizing the local free spectral range caused by material dispersion and waveguide dispersion to vary with wavelength.

[0065] Figure 3 This is a flowchart illustrating the steps of a frequency repetition rate broadband tuning method for a coupled microcavity optical comb provided in an embodiment of the present invention.

[0066] like Figure 3 As shown, the method includes: Step 101: The tunable pump light source module outputs pump light of a specific wavelength; Step 102: The coupled microcavity soliton generation module receives the pump light, enhances the power of the pump light, and uses strong light to excite dissipative Kerr solitons to generate a microcavity soliton optical frequency comb; the microcavity soliton optical frequency comb is also divided into two paths, one of which is output through a polarization-maintaining fiber for use, and the other is input to the repetition frequency monitoring module. Step 103: The repetition frequency monitoring module converts the optical signal of the microcavity soliton optical frequency comb into an electrical signal and obtains the repetition frequency value of a single microcavity soliton optical frequency comb, and inputs the repetition frequency value into the negative feedback module. Step 104: The feedback control module determines the adjustment range of the repetition frequency of the microcavity soliton optical frequency comb based on the difference between the repetition frequency value and the preset target value, and performs broadband tuning of the repetition frequency based on the adjustment range.

[0067] In steps 101-104, the pump light refers to a continuous laser of a specific wavelength. The tunable pump source module is a tunable pump source laser, whose output frequency can be controlled by an external electrical signal.

[0068] After the pump light is amplified by the EDFA and enters the coupled microcavity soliton generation module 2, it accumulates cyclically in the nonlinear cavity under the effect of resonance enhancement, forming a high intracavity optical power and exciting Kerr nonlinearity and four-wave mixing effects. Under appropriate group velocity dispersion and pump-cavity mode detuning, the Kerr nonlinearity and dispersion, microcavity loss and external pump reach a dynamic balance, generating a microcavity soliton optical frequency comb. The coupled microcavity soliton generation module includes an optical beamsplitter, which splits the soliton optical frequency comb into a first signal and a second signal. The first signal is output through polarization-maintaining fiber for practical applications, and the second signal is output to the input of the repetition frequency monitoring module.

[0069] The repetition frequency monitoring module uses a high-speed photodetector to convert the optical pulse sequence into a radio frequency sine wave, that is, to convert the second optical signal into an electrical signal. The repetition frequency monitoring module then extracts the repetition frequency information from the electrical signal; specifically, it extracts the fundamental frequency. frep .

[0070] The feedback control module calculates the repetition frequency difference of the soliton microcomb based on the set repetition frequency:

[0071] in, This indicates the current repetition frequency value. This indicates the preset target frequency value. e This represents the difference.

[0072] The feedback control module 3 converts the calculated difference into control commands and transmits them to the tunable pump light source or the heater of the coupled microcavity soliton generation module. The tunable pump light source finely adjusts the frequency of its output laser according to the control commands to switch different pump modes, or the heater changes the cavity mode frequency of the microcavity. This frequency change alters the frequency difference between the pump light and the intrinsic resonance of the microcavity, i.e., the detuning.

[0073] Within the soliton operating range, the change in this detuning amount precisely alters the group velocity of the optical soliton within the microcavity, i.e., the repetition frequency, thus forming a complete physical causal chain. Ultimately, this stabilizes the actual repetition frequency of the soliton optical frequency comb at the preset target frequency, enabling precise and flexible tuning of the output frequency.

[0074] As an optional embodiment, step 104 includes: Step 1041: When the difference is greater than the preset first threshold, the first negative feedback module controls the tunable pump light source module to change the output frequency, so that the pump light switches to the pump resonance mode, and uses the difference in the local free spectral range at different pump wavelengths to perform discrete step coarse tuning of the repetition frequency of the soliton microcomb. Step 1042: When the difference is greater than the preset second threshold and less than or equal to the first threshold, the second negative feedback module adjusts the detuning of the pump light relative to the resonant cavity through the heater in the same pumping mode, so that the number of modes of the soliton spectral center or equivalent center is shifted, and the repetition frequency of the soliton microcomb is continuously fine-tuned by utilizing the change in the equivalent mode interval caused by the microcavity dispersion. Step 1043: When the difference is less than or equal to the second threshold, the feedback control module maintains the current tuning state and stably outputs the microcavity soliton optical frequency comb.

[0075] In steps 1041-1043, the feedback control module consists of a first negative feedback module and a second negative feedback module, which together receive repetition frequency data from the repetition frequency monitoring module. and the preset target repetition frequency value Compare and calculate the difference. e Difference e The size of the value directly determines which tuning strategy the system adopts.

[0076] When this difference is greater than the preset first threshold ( , (The threshold value is set at 1), meaning the current repetition frequency deviates significantly from the target value and falls within a large error range. At this point, the first negative feedback module initiates discrete step coarse tuning. The negative feedback control module shifts the frequency of the tunable pump laser module by an integer multiple of the repetition frequency, switching between different pump modes. Because the group refractive index of the microcavity guided mode varies with wavelength, the local free spectral range differs at different pump wavelengths. Consequently, the microcavity soliton optical frequency comb has different repetition frequencies under different pump modes, thus achieving discrete step coarse tuning of the repetition frequency.

[0077] When the difference is within the range that is greater than the second threshold but less than or equal to the first threshold ( , Once the second threshold is reached, the system enters the fine-tuning stage, where the second negative feedback module performs continuous fine-tuning. By finely adjusting the heater temperature, the system can slowly change the refractive index of the microcavity, thereby fine-tuning the detuning of the pump light relative to the resonant cavity. This change in detuning directly affects the state of the solitons within the cavity, specifically manifested as a shift in the number of central or equivalent central modes in the soliton spectrum. Due to the inherent dispersion effect of the microcavity (i.e., the spacing between different modes varies with frequency), when the spectral envelope of the soliton shifts laterally within the cavity, its corresponding equivalent mode spacing (i.e., repetition frequency) also undergoes continuous and smooth minute changes. This achieves "fine-tuning" of the repetition frequency, with a resolution far exceeding that of the coarse-tuning step, enabling precise locking of the repetition frequency to the target value.

[0078] Finally, when the system's feedback control successfully compresses the difference to less than or equal to the second threshold ( When the frequency is within the tolerance range of the target value, it means that the current repetition frequency is close enough to meet the accuracy requirements for stable system operation. At this time, the feedback control module will maintain all current tuning states (including the wavelength of the pump laser and the temperature of the heater) and will no longer actively intervene, thereby achieving long-term, stable output of the microcavity soliton optical frequency comb.

[0079] As an optional embodiment, when performing discrete step coarse tuning of the repetition frequency of the soliton microcomb, the adjustment amount of the pump light frequency is an integer multiple of the target repetition frequency; after the pump light switches to the pump resonant mode, the pump light frequency is kept fixed, and the frequency of the resonant mode is changed by the heater, and the pump-cavity mode detuning is adjusted at the fixed pump frequency to establish the soliton state. When continuously fine-tuning the repetition frequency, the pump light frequency is kept constant, and the detuning of the pump light relative to the resonant cavity is changed by adjusting the microcavity resonant mode frequency, so as to achieve continuous fine-tuning of the repetition frequency of the microcavity soliton optical frequency comb.

[0080] In this embodiment of the invention, when the system determines that a significant change in the repetition frequency is needed, a coarse adjustment process is initiated. At this time, the adjustment amount of the pump light frequency is set to an integer multiple of the target repetition frequency. The physical meaning here is that the frequency interval (i.e., the free spectral range) between the various resonant modes of the microcavity is approximately equal to the current repetition frequency. Therefore, shifting the laser frequency to an integer multiple of one or more repetition frequencies means precisely switching the pump light to another integer-order resonant mode.

[0081] After the switch, the pump light frequency remains fixed and is no longer actively changed. The system then uses a heater to slowly change the temperature of the microcavity, causing a thermal drift across the entire resonant mode spectrum. In this way, the frequencies of the resonant modes are scanned relative to the fixed pump light. When the resonant peak of a new mode happens to sweep across the pump light frequency and enter the red detuning region required for soliton generation, the soliton is re-established in the new mode.

[0082] When the system enters the fine-tuning stage, its operating logic is the opposite of coarse-tuning. At this stage, the pump light frequency remains constant, and the system uses a heater to perform extremely slow and smooth fine-tuning of the microcavity temperature. This causes a continuous and minute drift in the frequency of the entire resonant mode. Essentially, it continuously changes the detuning of the pump light relative to the current resonant mode.

[0083] By employing the aforementioned method to combine coarse and fine adjustments, the system can span a wide bandwidth while achieving extremely high frequency resolution, ultimately locking the repetition frequency precisely to the target value. This combined strategy is a key design element in ensuring the stability, reliability, and soliton state retention of the entire closed-loop control system.

[0084] In summary, the broadband repetition rate tuning method based on a frequency-shifting soliton microcomb provided by this invention includes: a tunable pump light source module outputting pump light of a specific wavelength; a coupled microcavity soliton generation module receiving the pump light, enhancing the power of the pump light, and using strong light to excite dissipative Kerr solitons to generate a microcavity soliton optical frequency comb; the microcavity soliton optical frequency comb being divided into two paths, one of which is output through a polarization-maintaining fiber for use, and the other is input to a repetition rate monitoring module; the repetition rate monitoring module converting the optical signal of the microcavity soliton optical frequency comb into an electrical signal and obtaining the repetition rate value of a single set of microcavity soliton optical frequency combs, and inputting the repetition rate value into a negative feedback module; the feedback control module determining the adjustment range of the repetition rate of the microcavity soliton optical frequency comb based on the difference between the repetition rate value and a preset target value, and performing broadband tuning of the repetition rate based on the adjustment range. This invention enables the microcavity soliton optical frequency comb to operate at different pump wavelengths by switching the pump light between different longitudinal resonant modes, and achieves broadband, high-precision continuous tuning of the repetition frequency by utilizing the local free spectral range caused by material dispersion and waveguide dispersion that varies with wavelength.

[0085] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0086] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0087] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A high-repetition-rate broadband tuning system coupled with a microcavity optical comb, characterized in that, The system includes: a tunable pump source module, a coupled microcavity soliton generation module, a repetition frequency monitoring module, and a feedback control module; wherein: The tunable pump light source module is used to output pump light; The coupled microcavity soliton generation module is used to receive the pump light, enhance the power of the pump light and excite Kerr solitons to generate a microcavity soliton optical frequency comb; the coupled microcavity soliton generation module is also used to split the microcavity soliton optical frequency comb into a first optical signal and a second optical signal, the first optical signal is used as the system output terminal, and the second optical signal is input to the repetition frequency monitoring module; The repetition frequency monitoring module is used to convert the second optical signal into an electrical signal, extract the repetition frequency information from the electrical signal, and generate a feedback signal characterizing the current repetition frequency value. The feedback control module is used to receive the feedback signal, calculate the difference between the current repetition frequency value and the preset target frequency value, generate a control command based on the difference, and output the control command to the heater of the tunable pump light source module or the coupled microcavity soliton generator module. The tunable pump light source module is also used to adjust the output frequency of the pump light according to the control command, so as to switch the cavity mode position of the pump light; The coupled microcavity soliton generator module heater changes the detuning of the pump light of the coupled microcavity soliton generator module relative to the resonant cavity by changing the microcavity mode frequency, thereby locking the repetition frequency of the microcavity soliton optical frequency comb to the preset target frequency value.

2. The system according to claim 1, characterized in that: The coupled microcavity soliton generation module includes an optical amplifier for amplifying the pump light, a nonlinear cavity for exciting dissipative Kerr solitons, and an auxiliary cavity coupled to the nonlinear cavity via an evanescent field. The auxiliary cavity is coupled to the nonlinear cavity via an evanescent field; the auxiliary cavity is used to perform mode hybridization with at least some of the resonant modes of the nonlinear cavity and introduce a mode frequency shift related to the number of modes into the modes of the nonlinear cavity; The coupled microcavity soliton generation module also includes a heater, which is used to adjust the detuning of the pump light relative to the resonant cavity by means of temperature.

3. The system according to claim 2, characterized in that: The nonlinear cavity and the auxiliary cavity are any one or two of the following: microring resonant cavity, microdisk resonant cavity, microsphere cavity, microrod cavity, and other resonant cavities that support Kerr nonlinear processes. The nonlinear cavity and the auxiliary cavity are made of one or more of the following materials: silicon nitride, silicon dioxide, doped glass, magnesium fluoride, and silicon-based.

4. The system according to claim 1, characterized in that, The tunable pump source module is a narrow linewidth laser with tunable wavelength or frequency; the tuning range of the narrow linewidth laser covers multiple resonant modes that can be used to generate microcavity soliton optical frequency combs, so that the pump light can switch between different pump modes.

5. The system according to claim 1, characterized in that, The repetition frequency monitoring module includes a photodetector and a repetition frequency detector connected in sequence; the photodetector is used to convert the optical signal of the soliton microcomb input to the repetition frequency detection module into an electrical signal, and the repetition frequency detector is used to read and monitor the repetition frequency data of the electrical signal; The photodetector is a high-speed photodetector; the repetition frequency detector is one or more of a frequency counter, a spectrum analyzer, or an oscilloscope.

6. The system according to claim 1, characterized in that, The feedback control module includes a first negative feedback module and a second negative feedback module; the first negative feedback module and the second negative feedback module are either FPGA control circuits or computer programs. The first negative feedback module is used to control the tunable pump light source module to change the output frequency when the difference is greater than a preset first threshold, so that the pump light switches to the pump resonance mode, and to perform discrete step coarse tuning of the repetition frequency of the soliton microcomb by utilizing the difference in the local free spectral range at different pump wavelengths. The second negative feedback module is used to adjust the detuning of the pump light relative to the resonant cavity by a heater in the same pump mode when the difference is greater than a preset second threshold and less than or equal to the first threshold, so that the number of modes of the soliton spectral center or equivalent center is shifted, and the repetition frequency is continuously fine-tuned by utilizing the change in the equivalent mode interval caused by microcavity dispersion. When the difference is less than or equal to the second threshold, the feedback control module maintains the current tuning state and stably outputs the microcavity soliton optical frequency comb.

7. A repetition rate broadband tuning method for coupled microcavity optical combs, applied to the system described in any one of claims 1-6, characterized in that, The method includes: The tunable pump light source module outputs pump light of a specific wavelength; The coupled microcavity soliton generation module receives the pump light, enhances the power of the pump light, and uses strong light to excite dissipative Kerr solitons to generate a microcavity soliton optical frequency comb; the microcavity soliton optical frequency comb is also split into two paths, one of which is output through a polarization-maintaining fiber for use, and the other is input to the repetition frequency monitoring module. The repetition frequency monitoring module converts the optical signal of the microcavity soliton optical frequency comb into an electrical signal and obtains the repetition frequency value of a single microcavity soliton optical frequency comb, and inputs the repetition frequency value into the negative feedback module. The feedback control module determines the adjustment range of the repetition frequency of the microcavity soliton optical frequency comb based on the difference between the repetition frequency value and the preset target value, and performs broadband tuning of the repetition frequency based on the adjustment range.

8. The method according to claim 7, characterized in that, The feedback control module determines the adjustment range of the repetition frequency of the microcavity soliton optical frequency comb based on the difference between the repetition frequency value and the preset target value, and performs broadband tuning of the repetition frequency based on the adjustment range, including: When the difference is greater than the preset first threshold, the first negative feedback module controls the tunable pump light source module to change the output frequency, so that the pump light switches to the pump resonance mode, and uses the difference in the local free spectral range at different pump wavelengths to perform discrete step coarse tuning of the repetition frequency of the soliton microcomb. When the difference is greater than a preset second threshold and less than or equal to the first threshold, the second negative feedback module adjusts the detuning of the pump light relative to the resonant cavity through the heater in the same pumping mode, so that the number of modes of the soliton spectral center or equivalent center shifts, and the equivalent mode interval change caused by microcavity dispersion is used to achieve continuous fine adjustment of the repetition frequency of the soliton microcomb. When the difference is less than or equal to the second threshold, the feedback control module maintains the current tuning state and stably outputs the microcavity soliton optical frequency comb.

9. The method according to claim 8, characterized in that: When performing discrete step coarse tuning of the repetition frequency of the soliton microcomb, the adjustment amount of the pump light frequency is an integer multiple of the target repetition frequency; after the pump light switches to the pump resonant mode, the pump light frequency is kept fixed, and the frequency of the resonant mode is changed by the heater, and the pump-cavity mode detuning is adjusted under the fixed pump frequency to establish the soliton state. When continuously fine-tuning the repetition frequency, the pump light frequency is kept constant, and the detuning of the pump light relative to the resonant cavity is changed by adjusting the microcavity resonant mode frequency, so as to achieve continuous fine-tuning of the repetition frequency of the microcavity soliton optical frequency comb.

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