Sweep frequency optical frequency comb generation system and generation method

Abstract

The invention relates to a sweep frequency optical frequency comb generation system and a generation method. Fourier mode locking is realized through a Fourier mode locking photoelectric oscillator system. The sweep frequency optical frequency comb generation system is a closed Fourier mode-locked laser loop which is composed of a first optical amplifier, an optical fiber isolator, a broadband filter, a polarization controller, a thin film lithium niobate optical chip, a signal generator, a dispersion compensation optical fiber and a first optical coupler; and a photoelectric oscillator loop is formed by a second optical coupler, a single-mode delay optical fiber, a second optical amplifier, a photoelectric detector, a narrow-band filter, a low-noise amplifier and an electric power divider. Time domain active mode locking and Fourier mode locking are carried out on the laser resonant cavity at the same time, synchronous modulation of multiple optical frequency comb modes is achieved, sweep frequency optical frequency comb signals with high repetition frequency, high modulation speed, high coherence length and high output power are generated, and tunable optical frequency comb and high-quality high-frequency microwave signal output can be provided at the same time.

Description

Technical Field

[0001] The present invention relates to a frequency-sweeping optical frequency comb generation system, in particular to a frequency-sweeping optical frequency comb generation system and generation method. Background Art

[0002] Frequency-modulated continuous wave (FMCW) lidar offers technical advantages such as high resolution, Doppler velocity measurement, and ease of on-chip integration. It holds broad application prospects in autonomous driving, intelligent transportation, robotics, and measurement. As a key component, the FMCW light source limits the overall performance of an FMCW lidar system. Its modulation bandwidth determines its range resolution, its linewidth determines its detection range and measurement sensitivity, and its repetition rate directly impacts the density of the lidar's point cloud.

[0003] The FMCW generation methods reported so far mainly include internal modulation and external modulation. For FMCW light sources with internal modulation, high tuning rate and narrow linewidth are a pair of indicators that cannot be met simultaneously. A longer resonant cavity means that a narrow linewidth can be achieved, but the tuning rate is lower. A shorter resonant cavity can increase the tuning rate, but it limits the linewidth level of the light source. The external modulation method can quickly change the instantaneous frequency of the light field while maintaining the excellent characteristics of the seed light through tuning mechanisms such as the electro-optic effect. However, due to the limited working bandwidth of the electro-optic effect itself, the increase in the tuning range of the light source is restricted, that is, the maximum resolution achievable by the system is restricted.

[0004] Swept optical frequency comb FMCW lidars (FMCW lidars) are a highly competitive technology approach for effectively improving detection accuracy and real-time imaging. The performance of FMCW lidars is directly determined by the characteristics of the swept optical frequency comb source, such as the linewidth of each comb tooth, sweep speed, sweep range, and number of comb teeth. Currently, swept optical frequency combs are primarily implemented using electro-optical modulation and optical microcavities. These technologies face technical challenges such as the need for a wide-bandwidth, high-frequency modulation signal source and low output power. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a swept optical frequency comb generation system to solve the technical difficulties of existing swept optical frequency comb generation systems in achieving large swept bandwidth, high repetition rate, and narrow comb linewidth.

[0006] A second object of the present invention is to provide a method for generating a swept optical frequency comb to solve the problems of low repetition frequency, small sweep bandwidth and large comb linewidth in existing swept optical frequency combs.

[0007] One of the purposes of the present invention is achieved in that: A swept optical frequency comb generation system has the following structure: the output end of a first optical amplifier is connected to the input end of a first optical fiber isolator via an optical fiber, the output end of the first optical fiber isolator is connected to the input end of a bandwidth filter via an optical fiber, the output end of the bandwidth filter is connected to the input end of a polarization controller via an optical fiber, the output end of the polarization controller is connected to a first chip end coupler via an optical fiber, the first chip end coupler is connected to the input end of an electrically tunable microring resonator in a thin-film lithium niobate optical chip, a signal generator is connected to the control end of the electrically tunable microring resonator, the output end of an intensity modulator in the thin-film lithium niobate optical chip is connected to a second chip end coupler, the second chip end coupler is connected to the input end of the first optical coupler via a dispersion compensation optical fiber, the first branch of the first optical coupler is connected to the input end of a second optical fiber isolator via an optical fiber, and the output of the second optical fiber isolator is connected to the first optical coupler. The end is connected back to the input end of the first optical amplifier via an optical fiber to form a closed Fourier mode-locked laser loop; the second branch of the first optical coupler is connected to the input end of the second optical coupler via an optical fiber, the first branch of the second optical coupler is used to output an optical frequency comb signal, the second branch of the second optical coupler is connected to the input end of the second optical amplifier via a single-mode delay optical fiber, the output end of the second optical amplifier is connected to the input end of the photodetector via an optical fiber, the output end of the photodetector is electrically connected to the input end of the narrowband filter, the output end of the narrowband filter is electrically connected to the input end of the low-noise amplifier, the output end of the low-noise amplifier is electrically connected to the input end of the electric power divider, one output end of the electric power divider is used as the output end of the radio frequency signal, and the other output end is connected to the radio frequency input end of the intensity modulator in the thin-film lithium niobate optical chip to form an optoelectronic oscillator loop.

[0008] The swept optical frequency comb generation system of the present invention comprises a first optical amplifier, an optical fiber isolator, a broadband filter, a polarization controller, a thin-film lithium niobate optical chip, a signal generator, a dispersion-compensating optical fiber, and a first optical coupler, forming a closed Fourier-mode-locked laser loop. Furthermore, a second optical coupler, a single-mode delay optical fiber, a second optical amplifier, a photodetector, a narrowband filter, a low-noise amplifier, and an electrical power divider form an optoelectronic oscillator loop. The system simultaneously performs time-domain active mode locking and Fourier mode locking on the laser resonator, achieving synchronous modulation of multiple optical frequency comb modes. This generates a swept optical frequency comb signal with high repetition rate, high modulation speed, high coherence length, and high output power, providing both a tunable optical frequency comb and high-quality high-frequency microwave signal output.

[0009] The swept optical frequency comb generation system of the present invention introduces an electrically tunable microring filter into the Fourier mode-locked laser loop to form a Fourier mode-locked optoelectronic oscillator system, thereby achieving Fourier mode locking and thus realizing high-speed swept frequency output with a narrow instantaneous linewidth. This swept optical frequency comb generation technology has the technical advantages of high repetition rate, high modulation rate, and large modulation bandwidth. At the same time, it integrates coupled optoelectronic oscillator technology and can simultaneously output high-frequency microwave signals with low time base jitter (low phase noise).

[0010] The second purpose of the present invention is achieved in this way: A method for generating a swept optical frequency comb comprises the following steps: S1. Set up the swept optical frequency comb generation system described in the present invention.

[0011] S2, using the spontaneous radiation of the first optical amplifier as a light source, after directionally transmitting through the first optical isolator and filtering through the broadband filter, entering the polarization controller to control the polarization state of the optical signal passing through; S3. The polarized light signal output by the polarization controller enters the electrically tunable microring resonator in the thin-film lithium niobate optical chip after being coupled by the first chip end face coupler. The electrically tunable microring resonator filters the light signal and filters out a series of light signals that are consistent with the free spectrum range of the electrically tunable microring resonator as the optical carrier signal; the intensity modulator in the thin-film lithium niobate optical chip modulates the optical carrier signal and loads the microwave modulation signal fed back by the optoelectronic oscillator loop onto the optical carrier signal; the modulated light signal is output after being coupled by the second chip end face coupler.

[0012] S4. The optical signal coupled out by the second chip end face coupler is compensated for the dispersion in the laser cavity by the dispersion compensation fiber, and a loop length matching the optoelectronic oscillator loop is provided. The optical signal is then input into the first optical coupler, which splits the optical signal into two. The first split beam passes through the first branch of the first optical coupler and returns to the first optical amplifier via the second optical isolator, forming a closed Fourier mode-locked laser loop.

[0013] S5. The second split light beam split by the first optical coupler is input into the second optical coupler through the second branch of the first optical coupler and then split into two. The first split light beam passes through the first branch of the second optical coupler and outputs an optical frequency comb signal. The second split light beam passes through the second branch of the second optical coupler and enters the single-mode delay fiber. After the single-mode delay fiber provides the optoelectronic oscillator loop with a loop length that matches the Fourier mode-locked laser loop, it is sent to the second optical amplifier. The second optical amplifier compensates for the coupling loss of the second chip end face coupler.

[0014] S6. The optical signal amplified by the second optical amplifier is converted into a microwave electrical signal through a photodetector and output. The microwave electrical signal is filtered and mode-selected by a narrowband filter, so that the radio frequency signal generated by the optoelectronic oscillator loop and the optical frequency comb generated by the Fourier mode-locked laser loop achieve single-mode oscillation.

[0015] S7. The low-noise amplifier amplifies the microwave electrical signal output by the narrowband filter to compensate for the loss of the optoelectronic oscillator loop; the microwave electrical signal output by the low-noise amplifier is split and output by the electric power divider, one of the outputs is used as the RF signal output end, and the other output is connected to the RF input end of the intensity modulator in the thin-film lithium niobate optical chip to form an optoelectronic oscillator loop.

[0016] S8. The signal generator sends out a sawtooth wave signal to control the linear scanning of the resonance peak of the electrically tunable microring resonator in the thin-film lithium niobate optical chip. When the scanning period matches the delay of the Fourier mode-locked laser loop, Fourier domain mode locking is achieved in the Fourier mode-locked laser loop, thereby generating a linearly swept optical frequency comb.

[0017] Furthermore, in step S8, when the delay of the Fourier mode-locked laser loop is an integer multiple of the oscillation period of the optoelectronic oscillator loop, the mode selection condition is met, the Fourier mode-locked laser loop starts to oscillate, generating a linearly swept optical frequency comb and a single-frequency radio frequency signal.

[0018] Furthermore, in step S8, the period T of the sawtooth wave signal emitted by the signal generator is equal to the delay T of the Fourier mode-locked laser loop. d The conditions met are: T=T d / N, where N is a positive integer.

[0019] The method for generating a swept optical frequency comb of the present invention combines a coupled optoelectronic oscillator based on active mode locking technology with Fourier mode-locked laser technology to simultaneously perform time-domain active mode locking and Fourier mode locking on the laser resonant cavity, thereby achieving synchronous modulation of multiple optical frequency comb modes, thereby generating swept optical frequency comb optical signals and high-quality microwave signals with high repetition frequency, high modulation speed, high coherence length and high output power. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a system structure block diagram of the swept optical frequency comb generation system of the present invention.

[0021] Figure 2 This is a schematic diagram of the working principle of the swept optical frequency comb generation system.

[0022] In the figure: 1. first optical amplifier, 2. first optical fiber isolator, 3. broadband filter, 4. polarization controller, 5. first chip end coupler, 6. thin-film lithium niobate optical chip, 7. signal generator, 8. second chip end coupler, 9. dispersion-compensating optical fiber, 10. first optical coupler, 11. second optical fiber isolator, 12. second optical coupler, 13. single-mode delay optical fiber, 14. second optical amplifier, 15. photodetector, 16. narrowband filter, 17. low-noise amplifier, 18. electrical power divider. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] like Figure 1 As shown, the system structure of the swept optical frequency comb generation system of the present invention is as follows: The output of the first optical amplifier 1 is connected to the input of a fiber isolator 2 via a first optical fiber. The spontaneous emission spectrum of the first optical amplifier serves as the initial light source for the system and also provides the gain required for laser oscillation as the laser cavity gain medium. The output of the first fiber isolator 2 is connected to the input of a bandwidth filter 3 via an optical fiber. The first fiber isolator 2 is used to ensure directional transmission of the optical signal output by the first optical amplifier to prevent damage. The output of the bandwidth filter 3 is connected to the input of a polarization controller 4 via an optical fiber. The broadband filter 3 is used to filter the spontaneous emission spectrum of the optical amplifier, and its bandwidth determines the range of optical frequency comb generation. The output of the polarization controller 4 is connected to a first chip end coupler 5 via an optical fiber. The polarization controller 4 is coupled to the end face of the input of the thin-film lithium niobate optical chip to control the polarization state of the optical carrier signal passing through it, ensuring that the input optical carrier signal enters the thin-film lithium niobate optical chip in the same polarization state, thereby improving optical coupling efficiency and transmission characteristics. The first chip end coupler 5 is connected to the input of an electrically tunable microring resonator 6-1 in the thin-film lithium niobate optical chip 6 to couple the polarization state of the optical carrier signal into the thin-film lithium niobate integrated optical chip.

[0025] The thin-film lithium niobate optical chip 6 is equipped with an electrically tunable microring resonator 6-1 and an intensity modulator 6-2. The electrically tunable microring resonator 6-1 is used to filter the input broadband signal. Its control end is connected to the signal generator 7, which is used to receive the sawtooth wave signal emitted by the signal generator and realize optical frequency comb sweeping by periodically controlling the position of the transmission resonance peak. The output end of the intensity modulator 6-2 in the thin-film lithium niobate optical chip 6 is connected to the second chip end coupler 8, which is used to modulate the filtered optical signal and load the microwave modulated signal onto the optical signal. The second chip end coupler 8 is connected to the input end of the first optical coupler 10 via the dispersion compensating fiber 9. The second chip end coupler 8 is used to couple the optical signal output by the thin-film lithium niobate integrated optical chip 6 to the dispersion compensating fiber 9. The dispersion compensating fiber 9 is used to compensate for the dispersion in the laser cavity and provide a loop length that matches the optoelectronic oscillator loop. The first branch of the first optical coupler 10 is connected via optical fiber to the input of the second optical fiber isolator 11. The first optical coupler 10 is used to split the signal generated by the Fourier-mode-locked laser loop. The light coupled and split by the first optical coupler 10 enters the optoelectronic oscillator loop. The second optical fiber isolator 11 ensures directional transmission of the optical signal entering the optoelectronic oscillator loop while suppressing double Rayleigh scattered light signals from long optical fibers. The output of the second optical fiber isolator 11 is connected back to the input of the first optical amplifier 1 via optical fiber, thus forming a closed Fourier-mode-locked laser loop.

[0026] The second branch of the first optical coupler 10 is connected to the input of a second optical coupler 12 via an optical fiber. The second optical coupler 12 is used to split the signal input to the optoelectronic oscillator loop. The first branch of the second optical coupler 12 is used to output an optical frequency comb signal. The second branch of the second optical coupler 12 is connected to the input of a second optical amplifier 14 via a single-mode delay fiber 13. The second optical amplifier 14 is used to amplify the input optical signal, compensate for the loss of the second chip end face coupler 8 and the single-mode delay fiber 13, and increase the signal power entering the photodetector 15. The single-mode delay fiber 13 provides the optoelectronic oscillator loop with a loop length that matches the Fourier mode-locked laser loop. The output of the second optical amplifier 14 is connected to the input of a photodetector 15 via an optical fiber. The photodetector 15 is used to convert the input optical signal into a microwave electrical signal. The output of photodetector 15 is electrically connected to the input of narrowband filter 16. Narrowband filter 16 is used to further filter and select the mode of the output microwave signal, so that the microwave signal generated by the OEO loop and the optical frequency comb generated by the Fourier-locked laser loop achieve single-mode oscillation. The output of narrowband filter 16 is electrically connected to the input of low-noise amplifier 17. Low-noise amplifier 17 is used to amplify the microwave electrical signal output by narrowband filter 16 and the feedback microwave electrical signal received by the system to compensate for losses in the OEO loop. The output of low-noise amplifier 17 is electrically connected to the input of electrical power divider 18. One output of electrical power divider 18 serves as the microwave signal output, while the other output is connected to the RF input of intensity modulator 6-2 in thin-film lithium niobate optical chip 6, forming an OEO loop.

[0027] Below through Figure 2 The working principle of the swept optical frequency comb generation system of the present invention is briefly described.

[0028] Figure 2 (1) represents all possible oscillating laser modes in a Fourier mode-locked laser loop, with the mode spacing determined by the cavity length. Without photoelectric feedback, the phases of the laser modes in the Fourier mode-locked laser loop are random, resulting in beat frequencies in the photodetector, generating microwave signals of various frequencies. Under the effects of Fourier mode-locking and active mode-locking, the laser modes in the Fourier mode-locked laser loop will be phase-locked in real time, forming an optical frequency comb.

[0029] Figure 2 (2) shows the microwave frequency distribution corresponding to the laser mode beat frequency. The fundamental frequency is the vector sum of the beat frequency signals of all adjacent modes, the second harmonic is the sum of the beat frequency components of the two adjacent modes, and so on. Due to the random phase of the modes, the resulting microwave signal has a small amplitude and a large noise.

[0030] Figure 2(3) represents all possible oscillation modes in the OEO loop. Since the cavity length of the OEO loop is much longer than that of the Fourier mode-locked laser loop, its mode spacing is smaller.

[0031] Figure 2 (4) A specific oscillation mode is selected by setting the center frequency of the radio frequency bandpass filter to be consistent with a beat frequency of the laser mode. When the gain of the optoelectronic oscillator loop is greater than 1, multiple modes will compete for oscillation within the filter bandwidth. By adjusting the optical delay line, only the optoelectronic oscillator mode that is consistent with the beat frequency of the Fourier mode-locked laser loop is allowed to obtain sufficient gain to achieve oscillation. The optoelectronic oscillator oscillation mode finally selected is used to drive the intensity modulator in the thin-film lithium niobate optical chip to modulate the gain of the Fourier mode-locked laser loop, so that all laser modes within the gain bandwidth are oscillated and have phase-locked characteristics, forming an optical frequency comb.

[0032] The method for generating a swept optical frequency comb of the present invention comprises the following steps: S1. Settings Figure 1 The swept optical frequency comb generation system shown.

[0033] S2. The spontaneous radiation light of the first optical amplifier 1 is used as a light source. After being directional-transmitted by the first optical isolator 2 and filtered by the broadband filter 3, the light enters the polarization controller 4 to control the polarization state of the optical signal passing through.

[0034] S3: The polarized optical signal output by the polarization controller 4 is coupled by the first chip end coupler 5 and then enters the electrically tunable microring resonator 6-1 in the thin-film lithium niobate optical chip 6. The electrically tunable microring resonator 6-1 filters the optical signal, filtering out a series of optical signals consistent with the free spectrum range of the electrically tunable microring resonator as the optical carrier signal. The intensity modulator 6-2 in the thin-film lithium niobate optical chip 6 modulates this optical carrier signal, adding the microwave modulation signal fed back by the optoelectronic oscillator loop to the optical carrier signal. The modulated optical signal is then coupled by the second chip end coupler 8 and then output.

[0035] S4. The optical signal coupled out by the second chip end face coupler 8 compensates for the dispersion in the laser cavity through the dispersion compensation fiber 9 and provides a loop length that matches the optoelectronic oscillator loop. The optical signal is then input into the first optical coupler 10, which splits the optical signal into two. The first split beam passes through the first branch of the first optical coupler 10 and returns to the first optical amplifier 1 via the second optical isolator 11, forming a closed Fourier mode-locked laser loop.

[0036] S5. The second split light beam split by the first optical coupler 10 is input into the second optical coupler 12 through the second branch of the first optical coupler 10 and then split into two. The first split light beam passes through the first branch of the second optical coupler 12 and outputs an optical frequency comb signal. The second split light beam passes through the second branch of the second optical coupler 12 and enters the single-mode delay fiber 13. The single-mode delay fiber 13 provides the optoelectronic oscillator loop with a loop length that matches the Fourier mode-locked laser loop. The second split light beam is then sent to the second optical amplifier 14, which compensates for the coupling loss of the second chip end face coupler 8.

[0037] S6. The optical signal amplified by the second optical amplifier 14 is converted into a microwave electrical signal and outputted via the photodetector 15. The microwave electrical signal is filtered and mode-selected by the narrowband filter 16, so that the radio frequency signal generated by the optoelectronic oscillator loop and the optical frequency comb generated by the laser cavity achieve single-mode oscillation.

[0038] S7. Low-noise amplifier 17 amplifies the microwave signal output from narrowband filter 16 to compensate for losses in the optoelectronic oscillator (OEO) loop. Electrical power divider 18 splits the microwave signal output from low-noise amplifier 17 into two output paths. One path serves as the RF signal output, while the other path is connected to the RF input of intensity modulator 6-2 in thin-film lithium niobate optical chip 6, completing the OEO loop.

[0039] S8. The signal generator 7 sends a sawtooth wave signal to control the resonance peak of the electrically tunable microring resonator 6-1 in the thin-film lithium niobate optical chip 6 to perform linear scanning. When the scanning period matches the delay of the Fourier mode-locked laser loop, Fourier domain mode locking is achieved in the Fourier mode-locked laser loop, thereby generating a linearly swept optical frequency comb.

[0040] The period T of the sawtooth wave signal emitted by the signal generator 7 and the delay T of the Fourier mode-locked laser loop d The conditions met are: T=T d / N, where N is a positive integer. When the delay of the Fourier mode-locked laser loop is an integer multiple of the oscillation period of the optoelectronic oscillator loop, the mode selection condition is met, the Fourier mode-locked laser loop starts to oscillate, generating a linearly swept optical frequency comb and a single-frequency RF signal.

Claims

1. A swept optical frequency comb generation system, characterized in that: The output end of the first optical amplifier is connected to the input end of the first optical fiber isolator via an optical fiber, the output end of the first optical fiber isolator is connected to the input end of the bandwidth filter via an optical fiber, the output end of the bandwidth filter is connected to the input end of the polarization controller via an optical fiber, the output end of the polarization controller is connected to the first chip end face coupler via an optical fiber, the first chip end face coupler is connected to the input end of the electrically tunable microring resonator in the thin film lithium niobate optical chip, the signal generator is connected to the control end of the electrically tunable microring resonator, the output end of the intensity modulator in the thin film lithium niobate optical chip is connected to the second chip end face coupler, the second chip end face coupler is connected to the input end of the first optical coupler via a dispersion compensation optical fiber, the first branch of the first optical coupler is connected to the input end of the second optical fiber isolator via an optical fiber, and the output end of the second optical fiber isolator is connected back to the first optical fiber via an optical fiber. The input end of an optical amplifier forms a closed Fourier mode-locked laser loop; the second branch of the first optical coupler is connected to the input end of a second optical coupler via an optical fiber, the first branch of the second optical coupler is used to output an optical frequency comb signal, the second branch of the second optical coupler is connected to the input end of a second optical amplifier via a single-mode delay optical fiber, the output end of the second optical amplifier is connected to the input end of a photodetector via an optical fiber, the output end of the photodetector is electrically connected to the input end of a narrowband filter, the output end of the narrowband filter is electrically connected to the input end of a low-noise amplifier, the output end of the low-noise amplifier is electrically connected to the input end of an electric power divider, one output end of the electric power divider serves as a radio frequency signal output end, and the other output end is connected to the radio frequency input end of an intensity modulator in a thin-film lithium niobate optical chip, so as to form an optoelectronic oscillator loop.

2. A method for generating a swept optical frequency comb, characterized in that: The following steps are involved: S1. Setting the swept optical frequency comb generation system according to claim 1; S2, using the spontaneous radiation of the first optical amplifier as a light source, after directionally transmitting through the first optical isolator and filtering through the broadband filter, entering the polarization controller to control the polarization state of the optical signal passing through; S3. The polarized light signal output by the polarization controller enters the electrically tunable microring resonator in the thin-film lithium niobate optical chip after being coupled by the first chip end face coupler. The electrically tunable microring resonator filters the light signal and filters out a series of light signals that are consistent with the free spectrum range of the electrically tunable microring resonator as the optical carrier signal. The intensity modulator in the thin-film lithium niobate optical chip modulates the optical carrier signal and loads the microwave modulation signal fed back by the optoelectronic oscillator loop onto the optical carrier signal. The modulated light signal is then coupled by the second chip end face coupler and output. S4. The optical signal coupled out by the second chip end face coupler is passed through a dispersion-compensating fiber to compensate for the dispersion in the laser cavity and provide a loop length that matches the optoelectronic oscillator loop. The optical signal is then input into the first optical coupler, which splits the optical signal into two. The first split light passes through the first branch of the first optical coupler and returns to the first optical amplifier via the second optical isolator, forming a closed Fourier mode-locked laser loop. S5. The second split light beam split by the first optical coupler is input into the second optical coupler through the second branch of the first optical coupler and then split into two. The first split light beam passes through the first branch of the second optical coupler and outputs an optical frequency comb signal. The second split light beam passes through the second branch of the second optical coupler and enters the single-mode delay fiber. The single-mode delay fiber provides the optoelectronic oscillator loop with a loop length that matches the Fourier mode-locked laser loop. The second split light beam is then sent to the second optical amplifier, which compensates for the coupling loss of the second chip end face coupler. S6. The optical signal amplified by the second optical amplifier is converted into a microwave electrical signal and outputted via a photodetector. The microwave electrical signal is filtered and mode-selected by a narrowband filter, so that the radio frequency signal generated by the optoelectronic oscillator loop and the optical frequency comb generated by the Fourier mode-locked laser loop achieve single-mode oscillation. S7. A low-noise amplifier amplifies the microwave electrical signal output by the narrowband filter to compensate for the loss of the optoelectronic oscillator loop. An electrical power divider is used to split the microwave electrical signal output by the low-noise amplifier into two output paths, one of which serves as a radio frequency signal output terminal, and the other output path is connected to the radio frequency input terminal of the intensity modulator in the thin-film lithium niobate optical chip to form an optoelectronic oscillator loop. S8. The signal generator sends out a sawtooth wave signal to control the linear scanning of the resonance peak of the electrically tunable microring resonator in the thin-film lithium niobate optical chip. When the scanning period matches the delay of the Fourier mode-locked laser loop, Fourier domain mode locking is achieved in the Fourier mode-locked laser loop, thereby generating a linearly swept optical frequency comb.

3. The method for generating a swept optical frequency comb according to claim 2, wherein: In step S8, when the delay of the Fourier mode-locked laser loop is an integer multiple of the oscillation period of the optoelectronic oscillator loop, the mode selection condition is met, the Fourier mode-locked laser loop starts to oscillate, generating a linearly swept optical frequency comb and a single-frequency RF signal.

4. The method for generating a swept optical frequency comb according to claim 2, wherein: In step S8, the period T of the sawtooth wave signal emitted by the signal generator is equal to the delay T of the Fourier mode-locked laser loop. d The conditions met are: T=T d / N, where N is a positive integer.

Images