A fully locked optical frequency comb generation system and method based on cross-phase modulation effect

Abstract

This invention relates to a fully locked optical frequency comb generation system and method, specifically a fully locked optical frequency comb generation system and method based on cross-phase modulation effect. To address the inherent contradiction between large bandwidth and low repetition rate in traditional on-chip fully locked microcavity optical frequency combs, the fully locked optical frequency comb generation system of this invention based on cross-phase modulation effect includes a reference pump source unit, an auxiliary source unit, a micro-ring resonator unit for generating a broadband soliton optical frequency comb through nonlinear four-wave mixing, and a self-reference locking unit for achieving self-reference locking of the broadband soliton optical frequency comb. Simultaneously, the fully locked optical frequency comb generation method of this invention uses amplification or auxiliary laser replacement of the comb teeth of the broadband soliton optical frequency comb, utilizing the second or third harmonic effect to transfer them to a higher frequency band, and then feeds them back to the reference pump source unit to achieve self-reference locking.

Description

Technical Field

[0001] This invention relates to a fully locked optical frequency comb generation system and method, specifically to a fully locked optical frequency comb generation system and method based on cross-phase modulation effect. Background Technology

[0002] On-chip microcavity optical frequency combs (hereinafter referred to as microcavity optical frequency combs) have stable comb tooth spacing, which can coherently transfer optical frequencies to microwave frequencies and maintain pump optical frequency stability (referencing the optical frequency standard to the atomic transition peak). They are currently the ideal solution for optical frequency conversion in integrated optical atomic clocks.

[0003] Microcavity optical frequency combs are typically generated on-chip microring waveguide resonators with high quality factors. They are produced by nonlinear four-wave mixing of a narrow-linewidth continuous-wave laser to generate uniformly spaced comb teeth. This spacing is called the repetition frequency, and its magnitude depends on the size of the microring resonator, typically ranging from GHz to THz. Given current detector performance, achieving efficient optical-to-microwave conversion with repetition frequencies exceeding 200 GHz is difficult; therefore, the repetition frequency of the optical frequency comb cannot be too high. On the other hand, to achieve self-reference locking, the bandwidth of the optical frequency comb should be at least 2 / 3 octave (i.e., the ratio of the maximum to minimum comb tooth frequency is greater than 3 / 2). However, limited by the pump energy conversion efficiency of the optical frequency comb (less than 1%), when the repetition frequency is low, the bandwidth is narrow under the same pumping conditions, making it impossible to achieve the 2 / 3 octave requirement for self-reference locking. Currently reported microcavity optical frequency combs capable of self-reference locking typically have repetition frequencies in the hundreds of GHz range. Therefore, the contradiction between low repetition frequency and large bandwidth described above is the main challenge currently hindering self-reference locking of on-chip microcavity optical frequency combs. Recent research has employed vernier optical frequency combs or two interlocked optical frequency comb schemes, which can bypass the self-reference repetition frequency and bandwidth limitations. However, these schemes increase the number of locked loops, resulting in high system complexity, which is not conducive to the stable transmission of optical atomic clock signals and the future development of micro-miniaturization and integration. Summary of the Invention

[0004] The purpose of this invention is to solve the inherent contradiction between large bandwidth and low repetition rate in traditional on-chip microcavity optical frequency comb self-reference locking, and to provide a fully locked optical frequency comb generation system and method based on cross-phase modulation effect, so as to realize a self-reference locked optical frequency comb with directly detectable repetition rate, thus breaking through the existing technical bottleneck.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: A fully locked optical frequency comb generation system based on cross-phase modulation effect is characterized by comprising a reference pump source unit, an auxiliary source unit, a micro-ring resonator unit, and a self-reference locking unit. The reference pump source unit provides a pump laser whose frequency is locked to the atomic transition peak. The auxiliary source unit provides an auxiliary laser. The input of the micro-ring resonator unit is connected to the output of the reference pump source unit and the first output of the auxiliary source unit, respectively. It generates a primary soliton optical frequency comb based on nonlinear four-wave mixing of the pump laser and the auxiliary laser, and generates an XPM optical frequency comb under the cross-phase modulation effect, broadening the primary soliton optical frequency comb to a broadband soliton optical frequency comb with a bandwidth of more than 2 / 3 octaves. The self-reference locking unit includes an optical wavelength processing module, a first-band detection module, a second-band detection module, and a frequency doubling module. The input of the optical wavelength processing module is connected to the output of the micro-ring resonator unit, and it is used to split the received optical signal. The first-band detection module... The input terminal of the frequency doubling module is connected to the first output terminal of the optical wavelength processing module. It is used to detect the optical beat frequency signal between the XPM optical frequency comb and the original soliton optical frequency comb, and send it to the auxiliary light source unit. The auxiliary light source unit realizes frequency locking synchronization between the auxiliary laser and the comb teeth of the original soliton optical frequency comb. One input terminal of the frequency doubling module is connected to the third output terminal of the optical wavelength processing module, and the other input terminal is connected to the second output terminal of the auxiliary light source unit. The output terminal is connected to the reference pump light source unit. It is used to transfer the comb teeth of the broadband soliton optical frequency comb to the high frequency band by amplification or replacement by auxiliary laser, using the second harmonic or third harmonic effect, to obtain the slowly varying envelope signal of the broadband soliton optical frequency comb. It is fed back to the reference pump light source unit to achieve self-reference locking, thereby realizing full phase locking of the broadband soliton optical frequency comb. The input terminal of the second band detection module is connected to the second output terminal of the optical wavelength processing module. It is used to detect the full-locked soliton optical frequency comb repetition frequency microwave signal of the pump laser corresponding band after the full phase locking of the broadband soliton optical frequency comb.

[0006] Furthermore, the frequency doubling module includes an optical amplification module, a first beam combiner, an Fceo photodetector, a reference feedback module, and a frequency doubling selection module arranged sequentially. The input end of the optical amplification module is connected to the third output end of the optical wavelength processing module, and is used to amplify the high-frequency part of the comb teeth in the broadband soliton optical frequency comb at 2 / 3 or 1 / 2 of the auxiliary laser wavelength. The first input terminal of the frequency doubling module is connected to the output terminal of the optical amplification module, and the second input terminal is connected to the second output terminal of the auxiliary light source unit. It is used to double the frequency of the high-frequency portion of the comb teeth in the broadband soliton optical frequency comb at 2 / 3 of the auxiliary laser wavelength when the bandwidth of the broadband soliton optical frequency comb reaches 2 / 3 of the band, and triple the frequency of the auxiliary laser to obtain a first high-frequency signal and a second high-frequency signal, which are then combined and output. Alternatively, when the bandwidth of the optical frequency comb reaches 1 / 2 of the band, the frequency of the auxiliary laser is doubled to obtain a third high-frequency signal, which is then combined with the high-frequency portion of the comb teeth in the broadband soliton optical frequency comb at 1 / 2 of the auxiliary laser wavelength and output. The input terminal of the Fceo photodetector is connected to the output terminal of the frequency doubling module, which is used to detect the beam-combining signal, obtain the optical beat frequency signal, and convert it into an electrical signal for output to the reference feedback module. The reference feedback module outputs a servo signal to the reference pump light source unit based on the input electrical signal, so as to realize the self-reference locking of the broadband soliton optical frequency comb.

[0007] Furthermore, the frequency doubling module includes a first second frequency doubling module connected to the output of the optical amplification module, a third frequency doubling module connected to the second output of the auxiliary light source unit, and a first beam combiner whose input is connected to the output of the first second frequency doubling module and the output of the third frequency doubling module respectively. Alternatively, the frequency doubling module may include a second second frequency doubling module connected to the second output of the auxiliary light source unit, and a first beam combiner whose input is connected to the output of the second second frequency doubling module and the output of the optical amplification module, respectively.

[0008] Furthermore, the first band detection module includes a first optical filter, a first photodetector, and an auxiliary feedback module arranged sequentially. The first optical filter is used to filter out the overlapping portion of the XPM optical frequency comb and the original soliton optical frequency comb; The first photodetector is used to detect the optical beat frequency signal between the XPM optical frequency comb and the original soliton optical frequency comb based on the filtered signal, and convert it into an electrical signal and output it to the auxiliary feedback module; The auxiliary feedback module is used to convert the input electrical signal into a servo signal and output it to the auxiliary light source unit to achieve frequency locking synchronization between the auxiliary laser and the original soliton optical frequency comb teeth. The second band detection module includes a second optical filter and a second photodetector arranged sequentially. The second optical filter is used to filter out the spectrum of the pump laser band corresponding to the fully locked soliton optical frequency comb. The second photodetector is used to detect the optical beat frequency signal of the filtered fully locked soliton optical frequency comb repetition frequency and convert it into an electrical signal to obtain the fully locked soliton optical frequency comb repetition frequency microwave signal.

[0009] Furthermore, the microring resonator unit includes a wavelength division multiplexing module, a first input coupling fiber, a first on-chip microring resonator, a first output coupling fiber, and a first metal electrode corresponding to the first on-chip microring resonator, the first metal electrode being used to control the temperature of the first on-chip microring resonator. The two input terminals of the wavelength division multiplexing module are respectively connected to the output terminal of the reference pump light source unit and the first output terminal of the auxiliary light source unit, and are used to couple the pump laser and the auxiliary laser to the first input coupling fiber. The first input coupling fiber is used to match the fiber mode field of the pump laser and the auxiliary laser with the on-chip waveguide mode field with low loss and to couple into the first on-chip micro-ring resonator through evanescent field. The first on-chip micro-ring resonator is used to generate the original soliton optical frequency comb based on the auxiliary laser and the pump laser, and at the same time generate the XPM optical frequency comb to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb, which is output through the first output coupling optical fiber.

[0010] Furthermore, the microring resonator unit includes a first input coupling fiber, a first on-chip microring resonator, a first metal electrode, a first output coupling fiber, and a second input coupling fiber; The first input coupling fiber is connected to the output end of the reference pump source unit and is used to match the fiber mode field of the pump laser with the on-chip waveguide mode field and couple it into the first on-chip micro-ring resonator. The second input coupling fiber is connected to the first output end of the auxiliary light source unit and is used to match the fiber mode field of the auxiliary laser with the on-chip waveguide mode field and couple it into the first on-chip micro-ring resonator. The first on-chip micro-ring resonator is coupled with the first input coupling fiber and the second input coupling fiber respectively, which are used to generate the original soliton optical frequency comb based on the auxiliary laser and the pump laser, and at the same time generate the XPM optical frequency comb to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb, which is output through the first output coupling fiber. The first metal electrode is used to control the temperature of the micro-ring resonant cavity on the first chip.

[0011] Furthermore, the micro-ring resonant cavity unit includes a wavelength division multiplexing module, a first input coupling fiber, a first resonant module, a second resonant module, and a third output coupling fiber; The two input terminals of the wavelength division multiplexing module are respectively connected to the output terminals of the auxiliary light source unit and the reference pump light source unit, and are used to couple the auxiliary laser and the pump laser to the first input coupling fiber at the same time. The second resonant module is coupled to the first input coupling fiber and is used to resonate and enhance the auxiliary laser and pump laser; The first resonant module is coupled with the second resonant module to generate the original soliton optical frequency comb based on the resonant-enhanced auxiliary laser and pump laser. At the same time, an XPM optical frequency comb is generated to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb, which is output through the third output coupling optical fiber.

[0012] Furthermore, the reference pump light source unit includes a pump light source module, a first optical beam splitter, and an atomic reference module; The pump light source module is used to emit pump laser; The first optical beam splitter is connected to the output end of the pump light source module and is used to split the pump laser beam. One output end is connected to the micro-ring resonator unit and the other output end is connected to the atom reference module. The atomic reference module is used to provide an optical frequency standard that references the atomic transition peak, locks the pump laser to the optical frequency standard, and synchronizes the output frequency of the pump source module with the optical frequency standard. The auxiliary light source unit includes an auxiliary light source module, a second optical beam splitter, and an optical amplifier; The auxiliary light source module is used to emit auxiliary laser; The input end of the second optical beam splitter is connected to the output end of the auxiliary light source module, which is used to split the auxiliary laser into two paths. One path is sent to the input end of the optical amplifier, and the other path serves as the first output end of the auxiliary light source unit. The optical amplifier is used to amplify the laser power; the output of the optical amplifier serves as the second output of the auxiliary light source unit.

[0013] Furthermore, both the pump light source module and the auxiliary light source module are configured as narrow linewidth tunable continuous laser sources, with the pump laser having a wavelength of 1500-1620nm and the auxiliary laser having a wavelength of 1950-2050nm. The optical wavelength processing module is configured as a wavelength division multiplexer; The atomic reference module includes an optical reference source, a second beam combiner, a third photodetector, and a pump laser feedback locking module. The optical reference source is configured as an optical frequency standard referencing the atomic transition peak; The first input of the second beam combiner is connected to the other output of the first optical beam splitter, and the second input is connected to the output of the optical reference source, used to combine the pump laser and the optical frequency standard. The third photodetector is connected to the output of the second beam combiner and is used to detect the optical beat frequency signal and convert it into an electrical signal to be output to the pump laser feedback locking module. The pump laser feedback locking module is used to lock the laser frequency of the pump light source module to the optical reference source, ensuring that the pump laser frequency is synchronized with it.

[0014] Meanwhile, the present invention also provides a method for generating a fully locked optical frequency comb based on the cross-phase modulation effect, which is characterized by including the following steps: S1, Construct the fully locked optical frequency comb generation system based on the cross-phase modulation effect; S2 controls the pump laser emitted from the reference pump light source unit, locking the frequency of the pump laser to the atomic transition peak; Adjust the reference pump source unit so that the power of the pump laser satisfies the condition for nonlinear four-wave mixing in the micro-ring resonator unit; S3 controls the auxiliary light source unit to output auxiliary laser, and adjusts the center wavelength of the auxiliary laser to match the resonant wavelength of the micro-ring resonant cavity unit; S4, the micro-ring resonator unit receives the pump laser and the auxiliary laser, controls the blue shift of the resonant wavelength of the micro-ring resonator unit, and adjusts the auxiliary laser until the thermal equilibrium state of the auxiliary laser is reached, and nonlinear four-wave mixing is generated to produce the original soliton optical frequency comb. S5. Due to the cross-phase modulation effect, XPM optical frequency combs are generated at the auxiliary laser wavelength and at the high-frequency phase matching point of the original soliton optical frequency comb corresponding to the auxiliary laser wavelength, respectively. The spectra of the original soliton optical frequency comb and the generated XPM optical frequency comb are combined as a broadband soliton optical frequency comb. S6, adjust the auxiliary laser wavelength, move the XPM optical frequency comb generated at the high-frequency phase matching point to 2 / 3 or 1 / 2 of the auxiliary laser wavelength and overlap it with the original soliton optical frequency comb. The first band detection module feeds back the optical beat frequency signal of the optical frequency comb in this overlapping area to the auxiliary light source unit, so as to realize the frequency locking synchronization between the auxiliary laser and the original soliton optical frequency comb teeth, and the bandwidth of the broadband soliton optical frequency comb is widened to 2 / 3 octave or octave. S7, the frequency doubling module amplifies or replaces the comb teeth of the broadband soliton optical frequency comb with auxiliary lasers, and uses the second or third harmonic effect to transfer them to the high-frequency band. It obtains the slowly varying envelope signal of the broadband soliton optical frequency comb through self-reference technology, and feeds it back to the reference pump light source unit to achieve self-reference locking, thereby realizing full phase locking of the broadband soliton optical frequency comb. The second band detection module detects the repetition frequency microwave signal of the fully locked soliton optical frequency comb.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: 1. In the fully locked optical frequency comb generation system based on the cross-phase modulation effect of the present invention, a dual-pump injection optical microcavity method combining pump laser and auxiliary laser is used to generate self-referenced primary soliton optical frequency comb and broadband soliton optical frequency comb. This can ensure the stable excitation of the soliton optical frequency comb, and the auxiliary laser has high output energy. In the frequency doubling module, the auxiliary laser replaces the original lower comb energy to complete the frequency conversion in self-reference locking, without the need for additional optical amplification.

[0016] 2. In the fully locked optical frequency comb generation system based on the cross-phase modulation effect of the present invention, the long-wavelength auxiliary laser is locked and transferred to the short-wavelength band through the cross-phase modulation effect, which solves the problem of performance disadvantage of photodetectors in the long-wavelength band (e.g., around 2000nm). For the long-wavelength band far from the pump wavelength, there is no need to generate high-energy comb teeth, which greatly reduces the requirement for long-wavelength waveguide coupling efficiency.

[0017] 3. The fully locked optical frequency comb generation system based on the cross-phase modulation effect of this invention has the advantages of compact structure and simple system, easy integration, low cost, and features such as large bandwidth, low noise, and high reliability. It provides a simple and feasible approach for future on-chip integrated optical atomic clocks, and has significant research significance and practical application value.

[0018] 4. The present invention provides a fully locked optical frequency comb generation method based on the cross-phase modulation effect. The cross-phase modulation effect broadens the bandwidth of the original soliton optical frequency comb to more than 2 / 3 octaves. At the same time, the repetition rate is only 100 GHz, which can be directly detected in the corresponding band of the pump laser. This solves the problem of mutual constraint between the repetition frequency and bandwidth of the optical frequency comb, and breaks through the technical bottleneck that the dispersion reaches more than 2 / 3 octaves but the comb tooth energy is too low, which makes it impossible to meet the self-reference locking requirement. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the fully locked optical frequency comb generation system based on cross-phase modulation effect in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of the reference pump light source unit in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the auxiliary light source unit in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the micro-ring resonator unit in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the micro-ring resonant cavity unit in Embodiment 2 of the present invention; Figure 6 This is a schematic diagram of the micro-ring resonator unit in Embodiment 3 of the present invention; Figure 7 This is a schematic diagram of the self-reference locking unit in Embodiment 1 of the present invention; Figure 8 This is a spectral result diagram of the original soliton optical frequency comb under the assisted laser thermal equilibrium state in Embodiment 1 of the present invention; Figure 9 This is a spectral result diagram of the broadband soliton optical frequency comb in Embodiment 1 of the present invention.

[0020] Explanation of reference numerals in the attached figures: 10-Reference pump light source unit, 11-First optical beam splitter, 12-Second beam combiner, 13-Third photodetector, 14-Pump light source module; 20 - Pump laser feedback locking module; 21 - Optical reference source; 30-Microring resonator unit, 31-Wavelength division multiplexing module, 32-First input coupling fiber, 33-First on-chip microring resonator, 34-First metal electrode, 35-First output coupling fiber, 36-Second input coupling fiber, 37-Second output coupling fiber, 38-Third input coupling fiber, 39-Third output coupling fiber, 310-Second on-chip microring resonator, 311-Second metal electrode; 40-Self-reference locking unit, 41-First photodetector, 42-First optical filter, 43-Second optical filter, 44-Second photodetector, 45-Optical amplification module, 46-First second harmonic generation module, 47-Third harmonic generation module, 48-Fceo photodetector, 49-First beam combiner, 50-Auxiliary feedback module, 51-Wavelength division multiplexer, 60-Reference feedback module; 70-Auxiliary light source unit, 71-Second optical beam splitter, 72-Optical amplifier, 73-Auxiliary light source module. Detailed Implementation

[0021] Example 1

[0022] One of the keys to realizing a low-repetition-rate self-referenced optical frequency comb is dispersion design. By employing a highly nonlinear microring resonator, two dispersion zeros are generated in the long-wavelength and short-wavelength bands respectively through dispersion design. The spectrum of the optical frequency comb can then be extended using the dispersive waves generated by these dispersion zeros. However, due to limitations in material dispersion and fabrication capabilities, the extended energy of the dispersive waves is usually limited, and the position of the dispersive waves is not necessarily within the f-2f octave band or the 2f-3f octave band self-reference target wavelength. Therefore, the comb power at the self-reference target wavelength is often too low to achieve self-reference locking. Furthermore, achieving self-reference locking requires stable soliton optical frequency comb excitation. This invention employs a dual-injection scheme using a pump laser and an auxiliary laser. This not only balances the thermal equilibrium within the microcavity using the auxiliary laser, resulting in a stable broadband soliton optical frequency comb, but also generates an XPM optical frequency comb in the corresponding wavelength band of the auxiliary laser through cross-phase modulation (XPM) effect. When phase matching conditions are met, the XPM optical frequency comb is transferred to the short-wavelength or long-wavelength band via nonlinear four-wave mixing Bragg scattering, extending the broadband soliton optical frequency comb spectrum to more than 2 / 3 octaves. The XPM optical frequency comb frequency can be adjusted by regulating the auxiliary laser frequency, offering the advantage of flexible and tunable overall spectrum. In particular, the locking of the auxiliary laser and comb teeth in the long-wavelength band (2μm band) can be transferred to the mature short-wavelength band, avoiding the high noise floor and insufficient responsivity of long-wavelength detectors, while also reducing the efficiency requirements for the coupling waveguide of the long-wavelength microcavity.

[0023] Based on the above principles, the present invention provides a fully locked optical frequency comb generation system based on cross-phase modulation effect, as follows: Figure 1 As shown, it includes a reference pump source unit 10 for providing pump laser, an auxiliary source unit 70 for providing auxiliary laser, a micro-ring resonator unit 30 for receiving pump laser and auxiliary laser and generating nonlinear four-wave mixing, and a self-reference locking unit 40 for controlling the cross-phase modulation of auxiliary laser to achieve self-reference locking of optical frequency comb.

[0024] See Figure 2The reference pump source unit 10 includes a pump source module 14, a first optical beam splitter 11, and an atomic reference module. The atomic reference module includes a second beam combiner 12, a third photodetector 13, an optical reference source 21, and a pump laser feedback locking module 20. The pump source module 14 is configured as a narrow-linewidth tunable continuous laser source for emitting pump laser. In this embodiment, the pump laser wavelength is C-band (1530-1565nm); the first optical beam splitter 11 is connected to the output end of the pump light source module 14 and is used to split the pump laser beam. One output end outputs an optical signal b to deliver the pump laser to the micro-ring resonant cavity unit 30, and the other output end is connected to the second beam combiner 12. The optical reference source 21 is set as an atomic reference optical frequency standard to provide a highly stable laser that locks the frequency to the atomic transition peak. The first input end of the second beam combiner 12 is connected to the other output end of the first optical beam splitter 11, and the second input end is connected to the output end of the optical reference source 21 to combine the two beams and output them to the third photodetector 13; the third photodetector 13 is used to detect the optical beat frequency signal and convert it into an electrical signal to be output to the pump laser feedback locking module 20; the pump laser feedback locking module 20 is used to lock the laser frequency of the pump light source module 14 to the optical reference source 21, so that the pump laser frequency is synchronized with it.

[0025] See Figure 3 The auxiliary light source unit 70 includes an auxiliary light source module 73, a second optical beam splitter 71, and an optical amplifier 72. The auxiliary light source module 73 is configured as a narrow-linewidth tunable continuous laser source, used to emit auxiliary laser light into the second optical beam splitter 71. In this embodiment, the wavelength of the auxiliary laser is around 2000nm (1950-2050nm). The second optical beam splitter 71 splits the auxiliary laser light into two paths. One path outputs optical signal a through the first output terminal of the auxiliary light source unit 70 and sends optical signal a to the micro-ring resonant cavity unit 30. The other path outputs optical signal a through the second output terminal of the auxiliary light source unit 70 to the optical amplifier 72. The optical amplifier 72 is used to amplify the power of the auxiliary laser light to obtain optical signal d, and sends it to the self-reference locking unit 40.

[0026] In other embodiments of the present invention, the wavelength of the pump laser can be selected from any wavelength in the 1500-1620nm band, while the wavelength of the auxiliary laser does not need to be adjusted, only that the dispersion meets a broadband negative dispersion of more than 2 / 3 octave band.

[0027] See Figure 4In this embodiment, the micro-ring resonator unit 30 includes a wavelength division multiplexing module 31, a first input coupling fiber 32, a first on-chip micro-ring resonator 33, a first metal electrode 34, and a first output coupling fiber 35. The two input terminals of the wavelength division multiplexing module 31 receive optical signals a and b, respectively, and simultaneously couple them to the first input coupling fiber 32. The first input coupling fiber 32 performs low-loss matching between the fiber mode fields of the two-band optical signals a and b and the on-chip waveguide mode field, and couples them into the first on-chip micro-ring resonator 33 via an evanescent field. After receiving the input light, the first on-chip micro-ring resonator 33 generates a primary soliton optical frequency comb and simultaneously generates an XPM optical frequency comb to broaden the primary soliton optical frequency comb to obtain a broadband soliton optical frequency comb. Then, the first output coupling fiber 35 matches the on-chip waveguide and fiber mode fields, outputting optical signal e. The first metal electrode 34 is used to control the temperature of the first on-chip micro-ring resonator 33.

[0028] See Figure 1 The self-reference locking unit 40 receives optical signals e and d, and uses the output optical signals to adjust the frequency, power, and phase of the pump laser and auxiliary laser relative to the resonant peak of the micro-ring resonator 33 on the first chip, so that the micro-ring resonator unit 30 outputs a broadband soliton optical frequency comb that can be self-reference locked. At the same time, the comb teeth of the broadband soliton optical frequency comb are amplified or replaced by the auxiliary laser, and the second or third harmonic effect is used to transfer them to a high frequency band. The slowly varying envelope (Fceo) signal of the broadband soliton optical frequency comb is obtained by self-reference technology, and it is fed back to the reference pump light source unit 10 to achieve self-reference locking.

[0029] Figure 7 The self-reference locking unit 40 includes a wavelength division multiplexer 51 that receives the optical signal e. The wavelength division multiplexer 51 splits the optical signal e into optical signals h, which are then sent to the first band detection module, optical signal g, which is sent to the second band detection module, and optical signal k, which is sent to the frequency multiplication module.

[0030] The first band detection module includes a first optical filter 42, a first photodetector 41, and an auxiliary feedback module 50 arranged sequentially. The first optical filter 42 is a high-frequency optical filter. Its input end receives the optical signal h output by the wavelength division multiplexer 51 and is used to filter out the overlapping part of the XPM optical frequency comb and the original soliton optical frequency comb. The first photodetector 41 is used to detect the optical beat frequency signal of the XPM optical frequency comb and the original soliton optical frequency comb located in the high-frequency band according to the filtered signal and convert it into an electrical signal. The auxiliary feedback module 50 converts the electrical signal into a servo signal c and outputs it to the auxiliary light source module 73.

[0031] The second-band detection module includes a second optical filter 43 and a second photodetector 44 arranged sequentially. The input end of the second optical filter 43 receives the optical signal g output by the wavelength division multiplexer 51. In this embodiment, the second optical filter 43 is set as a C-band optical filter to filter out the fully locked soliton optical frequency comb of the corresponding band (C-band) of the pump laser. The second photodetector 44 is used to directly detect the optical beat frequency signal of the fully locked soliton optical frequency comb repetition frequency of the filtered C-band and convert it into an electrical signal to obtain the fully locked soliton optical frequency comb repetition frequency microwave signal.

[0032] The frequency doubling module includes an optical amplification module 45, a first beam combiner 49, an Fceo photodetector 48, a reference feedback module 60, and a selection frequency doubling module. The input of the optical amplification module 45 receives the optical signal k output by the wavelength division multiplexer 51, which is used to amplify the high-frequency part of the comb at 2 / 3 or 1 / 2 of the auxiliary laser wavelength.

[0033] In this embodiment, when the bandwidth of the broadband soliton optical frequency comb in the optical signal e received by the wavelength division multiplexer 51 reaches 2 / 3 octave, the frequency doubling module includes a first second frequency doubling module 46 connected to the output of the optical amplification module 45, a third frequency doubling module 47 connected to the second output of the auxiliary light source unit 70, and a first beam combiner 49 whose inputs are respectively connected to the outputs of the first second frequency doubling module 46 and the third frequency doubling module 47. The first frequency doubling module 46 is used to double the comb frequency of the high-frequency part corresponding to 2 / 3 of the wavelength of the received auxiliary laser. The third frequency doubling module 47 is used to triple the optical signal d, i.e., the auxiliary laser located in the low-frequency band. The two modules output the first high-frequency signal and the second high-frequency signal respectively, which are then combined by the first beam combiner 49. The Fceo photodetector 48 receives the combined signal, detects the optical beat frequency signal, and converts it into an electrical signal to be output to the reference feedback module 60. This optical beat frequency signal is a 2f-3f self-reference beat frequency signal. The reference feedback module 60 receives the electrical signal corresponding to the 2f-3f self-reference beat frequency signal and outputs the servo signal i to the pump light source module 14.

[0034] In other embodiments of the present invention, when the bandwidth of the broadband soliton optical frequency comb in the optical signal e received by the wavelength division multiplexer 51 reaches an octave, the selected frequency doubling module includes a second second frequency doubling module connected to the second output terminal of the auxiliary light source unit 70, and a first beam combiner 49 whose input terminals are respectively connected to the output terminal of the second second frequency doubling module and the output terminal of the optical amplification module 45. The second second frequency doubling module performs frequency doubling on the auxiliary laser to obtain a third high-frequency signal. The third high-frequency signal and the light output from the optical amplification module 45 are combined by the first beam combiner 49 and then input to the Fceo photodetector 48. The Fceo photodetector 48 is used to detect the signal after beam combining to obtain an optical beat frequency signal, and converts it into an electrical signal and outputs it to the reference feedback module 60. This optical beat frequency signal is an f-2f self-reference beat frequency signal. The reference feedback module 60 receives the electrical signal corresponding to the f-2f self-reference beat frequency signal and outputs a servo signal i to the pump light source module 14.

[0035] The working principle of this invention is as follows: First, the geometry of the on-chip microring resonator is rationally designed through dispersion engineering. Under the premise of direct detection within a free spectral range of approximately 100 GHz, the integrated dispersion of the on-chip microring resonator is designed to generate two dispersion zeros at long and short wavelengths with bandwidths exceeding 2 / 3 octaves, achieving broadband negative dispersion conditions exceeding 2 / 3 octaves. Then, the reference pump source unit 10 is referenced to an atomic reference optical frequency standard, ensuring the frequency stability of the pump laser output from the pump source module 14 is synchronized with the optical reference source 21. The auxiliary light source module 73, with its center wavelength in the long wavelength band, is combined with the pump laser through a wavelength division multiplexing module 31 and input into the on-chip microring resonator. The wavelength, power, and phase of the pump source module 14 and the auxiliary light source module 73, as well as the temperature of the microring resonator unit 30, are adjusted to achieve thermal equilibrium of the auxiliary laser within the first on-chip microring resonator 33, thereby generating the original soliton optical frequency comb (reference). Figure 8Then, the wavelength of the auxiliary laser is slowly adjusted. Through the cross-phase modulation effect, an XPM optical frequency comb is generated at the wavelength of the auxiliary laser. In the high-frequency part corresponding to 2 / 3 of the wavelength of the auxiliary laser, the XPM optical frequency comb is obtained by using the Bragg scattering effect of nonlinear four-wave mixing. The two XPM optical frequency combs have the same repetition frequency as the original soliton optical frequency comb, with only a phase difference. This phase difference is the same as the phase difference of the long-wavelength auxiliary laser frequency closest to the tooth of the original soliton optical frequency comb. Therefore, this phase difference is detected by the first photodetector 41, i.e., the optical beat frequency signal, and converted into an electrical signal, which is fed back to the auxiliary light source module 73 to achieve frequency locking synchronization between the auxiliary laser and the teeth of the original soliton optical frequency comb. At this time, the wavelength of the auxiliary laser is synchronized with the teeth of the original soliton optical frequency comb, and the XPM optical frequency comb is also synchronized with the original soliton optical frequency comb. The XPM optical frequency comb can be regarded as an additional part of the original soliton optical frequency comb. In this way, the bandwidth of the original soliton optical frequency comb is broadened, resulting in a broadband soliton optical frequency comb (see reference). Figure 9 ).

[0036] Next, when the bandwidth of the broadband soliton optical frequency comb reaches 2 / 3 octave, the high-frequency portion of the comb teeth at 2 / 3 of the auxiliary laser wavelength is amplified and passed through the first second harmonic module 46 to obtain the first high-frequency signal. The auxiliary laser passes through the third harmonic module 47 to obtain the second high-frequency signal. The two are combined and input into the Fceo photodetector 48 to obtain the 2f-3f self-reference beat frequency signal. The 2f-3f self-reference beat frequency signal is input into the reference feedback module 60 to generate a servo signal that is fed back to the reference pump source unit 10, realizing the self-reference locking of the broadband soliton optical frequency comb. At this time, since the pump laser has been referenced to the atomic reference optical frequency standard and the optical frequency comb has achieved self-reference locking, the broadband soliton optical frequency comb is in a fully phase-locked state. Its repetition frequency is output through the second optical filter 43 to the second photodetector 44 to obtain a fully locked soliton optical frequency comb repetition frequency microwave signal whose stability can be traced back to the optical frequency standard, realizing the stability transfer from optical frequency to microwave.

[0037] Based on the above system and working principle, the fully locked optical frequency comb generation method based on cross-phase modulation effect of the present invention can generate broadband soliton optical frequency combs and achieve self-reference locking, specifically including the following steps: Step 1: The narrow-linewidth tunable continuous laser source of the reference pump light source unit 10 emits pump laser, which is split into two paths after passing through the first optical beam splitter 11. One path is locked to the optical frequency standard of the atomic reference by the pump laser feedback locking module 20; the other path is input to the micro-ring resonator unit 30 after passing through the optical amplifier.

[0038] The narrow-linewidth tunable continuous laser source of the reference pump source unit 10 is adjusted so that the power of the pump laser satisfies the phase matching condition and intensity condition for the nonlinear four-wave mixing of the micro-ring resonator unit 30.

[0039] Step 2: Adjust the narrow linewidth tunable continuous laser source of the auxiliary light source unit 70 so that the center wavelength of the auxiliary laser matches the resonant wavelength of the adjacent micro-ring resonant cavity unit 30 before inputting it into the micro-ring resonant cavity unit 30.

[0040] Step 3: The light output from the reference pump light source unit 10 and the auxiliary light source unit 70 is combined through the wavelength division multiplexing module 31 and coupled into the first input coupling fiber 32. The first input coupling fiber 32 is then matched with the input port of the first on-chip micro-ring resonator 33 to achieve mode field matching. The first metal electrode 34 is adjusted to cause a blue shift in the resonant wavelength of the first on-chip micro-ring resonator 33, so that the center wavelengths of the pump laser and the auxiliary laser sweep across the resonant peak of the on-chip micro-ring resonator. At the same time, the narrow linewidth tunable continuous laser source of the auxiliary light source unit 70 is slowly adjusted so that the wavelength of the auxiliary laser is close to and greater than the resonant wavelength of the first on-chip micro-ring resonator 33 until the thermal equilibrium state of the auxiliary laser is reached, and nonlinear four-wave mixing occurs to generate a mode-locked primary soliton optical frequency comb.

[0041] When the auxiliary laser reaches thermal equilibrium, the pump laser and the auxiliary laser wavelengths are located at the red detuning and blue detuning of the micro-ring resonator 33 on the first chip, respectively.

[0042] Step 4: Simultaneously, the auxiliary laser and the pump laser enter the micro-ring resonator 33 on the first chip. Due to the cross-phase modulation effect, an XPM optical frequency comb is generated at the wavelength of the auxiliary laser. At the same time, a nonlinear four-wave mixing Bragg scattering effect occurs at the high-frequency phase matching point of the original soliton optical frequency comb corresponding to the wavelength of the auxiliary laser to generate an XPM optical frequency comb. The spectra of the original soliton optical frequency comb and the generated XPM optical frequency comb are combined to form a broadband soliton optical frequency comb.

[0043] Step 5: Fine-tune the auxiliary laser wavelength, moving the XPM optical frequency comb generated at the high-frequency phase matching point to 2 / 3 of the auxiliary laser wavelength, and overlapping it with the original soliton optical frequency comb. The first optical filter 42 filters and outputs the optical frequency comb from this overlapping area. The first photodetector 41 detects the phase difference (optical beat frequency signal) between the auxiliary laser and the optical frequency comb in this overlapping area, and feeds it back to the auxiliary light source unit 70 through the auxiliary feedback module 50 to achieve frequency locking synchronization between the auxiliary laser and the original soliton optical frequency comb teeth. At this point, the XPM optical frequency comb is synchronized with the original soliton optical frequency comb, and the XPM optical frequency comb can be considered an extension of the original soliton optical frequency comb. Therefore, the bandwidth of the obtained broadband soliton optical frequency comb can be widened to 2 / 3 octave bands.

[0044] Step 6: At this point, the bandwidth of the broadband soliton optical frequency comb reaches 2 / 3 octave. The high-frequency part of the comb teeth at 2 / 3 of the wavelength of the auxiliary laser is amplified and then passed through the first second-harmonic generation module 46. At the same time, the auxiliary laser output from the second optical beam splitter 71 passes through the third-harmonic generation module 47. The two are then combined and input into the Fceo photodetector 48 to detect the 2f-3f self-reference beat frequency signal.

[0045] Step 7: The 2f-3f self-reference beat frequency signal is input to the reference feedback module 60. The reference feedback module 60 outputs a servo signal, which is fed back to the reference pump light source unit 10 to achieve self-reference locking of the broadband soliton optical frequency comb. At this time, since the frequency of the pump laser has been locked to the atomic transition peak, full phase locking of the broadband soliton optical frequency comb is achieved. Subsequently, by adjusting the second optical filter 43, the comb teeth near the C-band are filtered out, and the second photodetector 44 detects the corresponding C-band fully locked soliton optical frequency comb repetition frequency microwave signal.

[0046] In other embodiments of the present invention, the XPM optical frequency comb generated at the high-frequency phase matching point in this step is moved to half the wavelength of the auxiliary laser, thus widening the bandwidth of the broadband soliton optical frequency comb to an octave. When the bandwidth of the broadband soliton optical frequency comb reaches an octave, the energy of the high-frequency portion of the comb teeth at half the wavelength of the auxiliary laser is amplified. Simultaneously, the auxiliary laser passes through a second second harmonic module to obtain a third high-frequency signal. The two are combined and input into the Fceo photodetector 48 to obtain an f-2f self-reference beat frequency signal. Then, through step 7 above, the self-reference locking of the broadband soliton optical frequency comb is achieved using the f-2f self-reference beat frequency signal.

[0047] This invention utilizes a pump laser combined with an auxiliary laser in thermal equilibrium to generate a stable broadband soliton optical frequency comb within an on-chip microcavity resonator that can be directly detected in the free spectral range (FSR). Due to the inherent repetition rate-bandwidth contradiction in on-chip optical frequency combs, soliton comb teeth cannot be generated at the self-reference target wavelength, or the soliton comb tooth energy is too low to achieve self-reference locking. Therefore, this invention generates an additional XPM optical frequency comb in the short-wavelength band through cross-phase modulation, broadening the bandwidth of the original soliton optical frequency comb. Furthermore, it transfers the long-wavelength auxiliary laser and comb tooth locking problem to the relatively mature short-wavelength band, achieving frequency locking synchronization between the auxiliary laser and the original soliton optical frequency comb teeth. Simultaneously, self-reference locking is achieved using 2f-3f or f-2f self-reference locking technology, with a repetition rate of approximately 100 GHz, which can be directly converted into a microwave signal output using a photodetector. This invention has a simple structure, is economical and practical, highly reliable, has few loops, and minimal stability loss. This invention is versatile and applicable to microcavity optical frequency combs made of various materials and in multiple near-infrared bands.

[0048] Example 2

[0049] The difference between this embodiment and Embodiment 1 lies in the arrangement of the micro-ring resonant cavity unit 30. Figure 5 In this embodiment, the microring resonator unit 30 is replaced by additional input and output coupling fibers instead of the wavelength division multiplexing module 31 in the first embodiment. The microring resonator unit 30 in this embodiment includes a first input coupling fiber 32, a first on-chip microring resonator 33, a first metal electrode 34, a first output coupling fiber 35, a second input coupling fiber 36, and a second output coupling fiber 37. The first input coupling fiber 32 performs low-loss matching between the fiber mode field of the optical signal b and the on-chip waveguide mode field and couples it into the first on-chip microring via evanescent field coupling. The first on-chip micro-ring resonator 33 consists of a resonant cavity 33 and a second input coupling fiber 36. The fiber mode field of the optical signal a is matched with the on-chip waveguide mode field with low loss and coupled into the first on-chip micro-ring resonator 33 via evanescent field coupling. Upon receiving the input light, the first on-chip micro-ring resonator 33 generates a primary soliton optical frequency comb and an XPM optical frequency comb to broaden the primary soliton optical frequency comb into a broadband soliton optical frequency comb. This is then matched to the on-chip waveguide mode field and the fiber mode field via the first output coupling fiber 35, outputting the optical signal e. A first metal electrode 34 is used to control the temperature of the first on-chip micro-ring resonator 33. The second output coupling fiber 37 serves as a backup output port or can be used to connect an external monitoring module to monitor the operating status of the first on-chip micro-ring resonator 33.

[0050] Correspondingly, in the fully locked optical frequency comb generation method based on cross-phase modulation effect of the present invention, step 3 specifically involves: the light from the reference pump light source unit 10 and the auxiliary light source unit 70 are simultaneously input into the first on-chip micro-ring resonator 33 through the first input coupling fiber 32 and the second input coupling fiber 36, respectively, and are respectively matched with the mode field of the first on-chip micro-ring resonator 33, so that the auxiliary laser and the pump light simultaneously enter the first on-chip micro-ring resonator 33 to undergo nonlinear four-wave mixing, generating the original soliton optical frequency comb and the XPM optical frequency comb, which are then coupled out.

[0051] Example 3

[0052] The difference between this embodiment and Embodiment 1 lies in the arrangement of the micro-ring resonant cavity unit 30, see [link to previous embodiment]. Figure 6 In addition to the wavelength division multiplexing module 31, the first input coupling fiber 32, and the first output coupling fiber 35 that are the same as in Embodiment 1, the micro-ring resonant cavity unit 30 also includes a first resonant module, a second resonant module, a third output coupling fiber 39, and a third input coupling fiber 38.

[0053] The second resonant module includes a second on-chip micro-ring resonant cavity 310 and a second metal electrode 311. The first input coupling fiber 32 couples two-band optical signals a and b into the second on-chip micro-ring resonant cavity 310 to enhance the resonance of the auxiliary laser and the pump laser.

[0054] The first resonant module consists of a first micro-ring resonant cavity 33 on a first chip and a first metal electrode 34. The first micro-ring resonant cavity 33 on the first chip is coupled to a second micro-ring resonant cavity 310 on a second chip to generate the original soliton optical frequency comb and at the same time generate the XPM optical frequency comb to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb.

[0055] The third output coupling fiber 39 is coupled to the first resonant module and is used to output a broadband soliton optical frequency comb and an XPM optical frequency comb.

[0056] The third input coupling fiber 38 and the first output coupling fiber 35 serve as backup input / output ports, which can be used as alternatives to the wavelength division multiplexing module 31, or to connect to an external monitoring module to monitor the operating status of the micro-ring resonator 33 on the first chip.

Claims

1. A fully locked optical frequency comb generation system based on cross-phase modulation effect, characterized in that: It includes a reference pump light source unit (10), an auxiliary light source unit (70), a micro-ring resonator unit (30), and a self-reference locking unit (40). The reference pump source unit (10) is used to provide pump laser with frequency locked to the atomic transition peak; The auxiliary light source unit (70) is used to provide auxiliary laser; The input end of the micro-ring resonator unit (30) is connected to the output end of the reference pump light source unit (10) and the first output end of the auxiliary light source unit (70), respectively. It is used to generate the original soliton optical frequency comb based on the nonlinear four-wave mixing of the pump laser and the auxiliary laser, and generate the XPM optical frequency comb under the cross phase modulation effect, thereby widening the original soliton optical frequency comb to a broadband soliton optical frequency comb with a bandwidth of more than 2 / 3 octave band. The self-reference locking unit (40) includes an optical wavelength processing module, a first band detection module, a second band detection module, and a frequency doubling module; the input end of the optical wavelength processing module is connected to the output end of the micro-ring resonant cavity unit (30) and is used to split the received optical signal. The input end of the first band detection module is connected to the first output end of the optical wavelength processing module, which is used to detect the optical beat frequency signal between the XPM optical frequency comb and the original soliton optical frequency comb, and send it to the auxiliary light source unit (70). The auxiliary light source unit (70) realizes frequency locking synchronization between the auxiliary laser and the comb teeth of the original soliton optical frequency comb. The frequency doubling module is used to transfer the comb teeth of the broadband soliton optical frequency comb to a high frequency band by amplification or auxiliary laser replacement, using the second or third harmonic effect, to obtain the slowly varying envelope signal of the broadband soliton optical frequency comb, and feed it back to the reference pump light source unit (10) to achieve self-reference locking, thereby realizing full phase locking of the broadband soliton optical frequency comb. The frequency doubling module includes, in sequence, an optical amplification module (45), a first beam combiner (49), an Fceo photodetector (48), a reference feedback module (60), and a frequency doubling selection module; The input end of the optical amplification module (45) is connected to the third output end of the optical wavelength processing module, and is used to amplify the high-frequency part of the comb teeth in the broadband soliton optical frequency comb at 2 / 3 or 1 / 2 of the auxiliary laser wavelength. The first input terminal of the frequency doubling module is connected to the output terminal of the optical amplification module (45), and the second input terminal is connected to the second output terminal of the auxiliary light source unit (70). It is used to double the frequency of the high-frequency part of the comb teeth in the broadband soliton optical frequency comb at 2 / 3 of the wavelength of the auxiliary laser when the bandwidth of the broadband soliton optical frequency comb reaches 2 / 3 of the band, and triple the frequency of the auxiliary laser to obtain the first high-frequency signal and the second high-frequency signal respectively, and output them after combining them; or, when the bandwidth of the optical frequency comb reaches 1 / 2 of the band, the frequency of the auxiliary laser is doubled to obtain the third high-frequency signal, and it is combined with the high-frequency part of the comb teeth in the broadband soliton optical frequency comb at 1 / 2 of the wavelength of the auxiliary laser and output. The input end of the Fceo photodetector (48) is connected to the output end of the frequency doubling module, which is used to detect the beam-combining signal, obtain the optical beat frequency signal, and convert it into an electrical signal to be output to the reference feedback module (60). The reference feedback module (60) outputs a servo signal to the reference pump light source unit (10) based on the input electrical signal to achieve self-reference locking of the broadband soliton optical frequency comb; The input of the second band detection module is connected to the second output of the optical wavelength processing module. It is used to detect the full-locked soliton frequency comb repetition frequency microwave signal of the pump laser corresponding band after the full phase locking of the broadband soliton frequency comb.

2. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to claim 1, characterized in that: The frequency doubling module includes a first second frequency doubling module (46) connected to the output of the optical amplification module (45), a third frequency doubling module (47) connected to the second output of the auxiliary light source unit (70), and a first beam combiner (49) whose input ends are respectively connected to the output ends of the first second frequency doubling module (46) and the third frequency doubling module (47). Alternatively, the frequency doubling module may include a second second frequency doubling module connected to the second output of the auxiliary light source unit (70), and a first beam combiner (49) whose input is connected to the output of the second second frequency doubling module and the output of the optical amplification module (45).

3. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to claim 2, characterized in that: The first band detection module includes a first optical filter (42), a first photodetector (41), and an auxiliary feedback module (50) arranged sequentially. The first optical filter (42) is used to filter out the overlapping portion of the XPM optical frequency comb and the original soliton optical frequency comb; The first photodetector (41) is used to detect the optical beat frequency signal of the XPM optical frequency comb and the original soliton optical frequency comb according to the filtered signal, and convert it into an electrical signal and output it to the auxiliary feedback module (50). The auxiliary feedback module (50) is used to convert the input electrical signal into a servo signal and output it to the auxiliary light source unit (70) to achieve frequency locking synchronization between the auxiliary laser and the original soliton optical frequency comb teeth; The second band detection module includes a second optical filter (43) and a second photodetector (44) arranged in sequence. The second optical filter (43) is used to filter out the spectrum of the pump laser band corresponding to the fully locked soliton optical frequency comb. The second photodetector (44) is used to detect the optical beat frequency signal of the filtered fully locked soliton optical frequency comb repetition frequency and convert it into an electrical signal to obtain the fully locked soliton optical frequency comb repetition frequency microwave signal.

4. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to claim 3, characterized in that: The microring resonator unit (30) includes a wavelength division multiplexing module (31), a first input coupling fiber (32), a first on-chip microring resonator (33), a first output coupling fiber (35) coupled in sequence, and a first metal electrode (34) corresponding to the first on-chip microring resonator (33). The first metal electrode (34) is used to control the temperature of the first on-chip microring resonator (33). The two input terminals of the wavelength division multiplexing module (31) are respectively connected to the output terminal of the reference pump light source unit (10) and the first output terminal of the auxiliary light source unit (70), and are used to couple the pump laser and the auxiliary laser to the first input coupling fiber (32). The first input coupling fiber (32) is used to match the fiber mode field of the pump laser and the auxiliary laser with the on-chip waveguide mode field with low loss and to enter the first on-chip micro-ring resonator (33) through evanescent field coupling. The first on-chip micro-ring resonator (33) is used to generate the original soliton optical frequency comb based on the auxiliary laser and the pump laser, and at the same time generate the XPM optical frequency comb to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb, which is output through the first output coupling fiber (35).

5. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to claim 3, characterized in that: The microring resonator unit (30) includes a first input coupling fiber (32), a first on-chip microring resonator (33), a first metal electrode (34), a first output coupling fiber (35), and a second input coupling fiber (36). The first input coupling fiber (32) is connected to the output end of the reference pump source unit (10) and is used to match the fiber mode field of the pump laser with the on-chip waveguide mode field and couple it into the first on-chip micro-ring resonator (33). The second input coupling fiber (36) is connected to the first output end of the auxiliary light source unit (70) and is used to match the fiber mode field of the auxiliary laser with the on-chip waveguide mode field and couple it into the first on-chip micro-ring resonator (33). The first on-chip micro-ring resonator (33) is coupled to the first input coupling fiber (32) and the second input coupling fiber (36) respectively, which are used to generate the original soliton optical frequency comb based on the auxiliary laser and the pump laser, and at the same time generate the XPM optical frequency comb to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb, which is output through the first output coupling fiber (35); The first metal electrode (34) is used to control the temperature of the first on-chip micro-ring resonant cavity (33).

6. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to claim 3, characterized in that: The micro-ring resonant cavity unit (30) includes a wavelength division multiplexing module (31), a first input coupling fiber (32), a first resonant module, a second resonant module, and a third output coupling fiber (39). The two input terminals of the wavelength division multiplexing module (31) are respectively connected to the output terminals of the auxiliary light source unit (70) and the reference pump light source unit (10), and are used to couple the auxiliary laser and the pump laser to the first input coupling fiber (32) at the same time. The second resonant module is coupled to the first input coupling fiber (32) and is used to resonate and enhance the auxiliary laser and the pump laser; The first resonant module is coupled with the second resonant module to generate the original soliton optical frequency comb based on the resonant-enhanced auxiliary laser and pump laser, and at the same time generate the XPM optical frequency comb to broaden the original soliton optical frequency comb to obtain a broadband soliton optical frequency comb, which is output through the third output coupling fiber (39).

7. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to any one of claims 1-6, characterized in that: The reference pump light source unit (10) includes a pump light source module (14), a first optical beam splitter (11), and an atomic reference module; The pump light source module (14) is used to emit pump laser; The first optical beam splitter (11) is connected to the output end of the pump light source module (14) and is used to split the pump laser beam. One output end is connected to the micro-ring resonator unit (30), and the other output end is connected to the atom reference module. The atomic reference module is used to provide an optical frequency standard that references the atomic transition peak, locks the pump laser to the optical frequency standard, and synchronizes the output frequency of the pump source module (14) with the optical frequency standard. The auxiliary light source unit (70) includes an auxiliary light source module (73), a second optical beam splitter (71), and an optical amplifier (72). The auxiliary light source module (73) is used to emit auxiliary laser; The input end of the second optical beam splitter (71) is connected to the output end of the auxiliary light source module (73) to split the auxiliary laser into two paths, one of which is sent to the input end of the optical amplifier (72), and the other is used as the first output end of the auxiliary light source unit (70). The optical amplifier (72) is used to amplify the laser power; the output of the optical amplifier (72) serves as the second output of the auxiliary light source unit (70).

8. The fully locked optical frequency comb generation system based on cross-phase modulation effect according to claim 7, characterized in that: Both the pump light source module (14) and the auxiliary light source module (73) are configured as narrow linewidth tunable continuous laser sources. The wavelength of the pump laser is 1500-1620nm, and the wavelength of the auxiliary laser is 1950-2050nm. The optical wavelength processing module is configured as a wavelength division multiplexer (51). The atomic reference module includes an optical reference source (21), a second beam combiner (12), a third photodetector (13), and a pump laser feedback locking module (20). The optical reference source (21) is set as an optical frequency standard referencing the atomic transition peak; The first input end of the second beam combiner (12) is connected to the other output end of the first optical beam splitter (11), and the second input end is connected to the output end of the optical reference source (21) for combining the pump laser and the optical frequency standard. The third photodetector (13) is connected to the output end of the second beam combiner (12) and is used to detect the optical beat frequency signal and convert it into an electrical signal to be output to the pump laser feedback locking module (20). The pump laser feedback locking module (20) is used to lock the laser frequency of the pump light source module (14) to the optical reference source (21) to ensure that the pump laser frequency is synchronized with it.

9. A method for generating a fully locked optical frequency comb based on cross-phase modulation effect, characterized in that, Includes the following steps: S1, Construct the fully locked optical frequency comb generation system based on cross-phase modulation effect as described in any one of claims 1-8; S2, control the reference pump light source unit (10) to emit pump laser, and lock the frequency of the pump laser to the atomic transition peak; Adjust the reference pump source unit (10) so that the power of the pump laser satisfies the condition for nonlinear four-wave mixing of the micro-ring resonator unit (30); S3, control the auxiliary light source unit (70) to output auxiliary laser, and adjust the center wavelength of the auxiliary laser to match the resonant wavelength of the micro-ring resonant cavity unit (30); S4, the micro-ring resonator unit (30) receives the pump laser and the auxiliary laser, controls the resonant wavelength of the micro-ring resonator unit (30) to blue shift, and adjusts the auxiliary laser until the auxiliary laser reaches thermal equilibrium, and generates the original soliton optical frequency comb through nonlinear four-wave mixing. S5. Due to the cross-phase modulation effect, XPM optical frequency combs are generated at the auxiliary laser wavelength and at the high-frequency phase matching point of the original soliton optical frequency comb corresponding to the auxiliary laser wavelength, respectively. The spectra of the original soliton optical frequency comb and the generated XPM optical frequency comb are combined as a broadband soliton optical frequency comb. S6, adjust the auxiliary laser wavelength, move the XPM optical frequency comb generated at the high-frequency phase matching point to 2 / 3 or 1 / 2 of the auxiliary laser wavelength and overlap it with the original soliton optical frequency comb. The first band detection module feeds back the optical beat frequency signal of the optical frequency comb in this overlapping area to the auxiliary light source unit (70), so as to realize the frequency locking synchronization between the auxiliary laser and the original soliton optical frequency comb teeth, and the bandwidth of the broadband soliton optical frequency comb is widened to 2 / 3 octave or octave. S7, the frequency doubling module amplifies or replaces the comb teeth of the broadband soliton optical frequency comb by means of auxiliary laser, and uses the second harmonic or third harmonic effect to transfer them to the high frequency band. The slow-varying envelope signal of the broadband soliton optical frequency comb is obtained by self-reference technology and fed back to the reference pump light source unit (10) to achieve self-reference locking, thereby realizing full phase locking of the broadband soliton optical frequency comb. The second band detection module detects the repetition frequency microwave signal of the fully locked soliton optical frequency comb.

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