A dual optical frequency comb generation system and method based on mode multiplexed resonator

Abstract

The application discloses a kind of based on mode multiplexing resonator's dual optical frequency comb generation system and method, system includes continuous light laser, first optical coupler, second optical coupler, third optical coupler, acoustooptic frequency shifter, first mode coupler, second mode coupler, third mode coupler, fiber ring resonator;Fiber ring resonator is by first mode coupler, second mode coupler, third mode coupler and few-mode fiber constitute;By above system, single base mode transmission is changed into the coupling transmission of high-order mode and base mode in cavity, to generate optical frequency comb respectively, and merge into dual optical frequency comb.The system uses the exchange of mode to avoid the excessive accumulation of the speed difference of two modes of fiber ring of fiber ring resonator, so that the light of two paths has different loop time, and by controlling the length difference of two optical fibers of fiber ring resonator, the dual optical frequency comb with the required repetition frequency difference is obtained.The scheme of the application has simple structure, is easy to manufacture, low in cost and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of fiber lasers and optical frequency comb generation systems, and particularly to a dual optical frequency comb generation system and method based on a mode-multiplexed resonant cavity. Background Technology

[0002] An optical frequency comb is a spectrum composed of a series of uniformly spaced frequency components with coherent and stable phase relationships, which manifests as an ultrashort laser pulse sequence in the time domain. Human exploration and research into optical frequency combs has led to their increasingly wide range of applications, from initial spectral detection to current applications in high-precision optical frequency comb ranging, optical atomic clocks, atomic and molecular absorption spectroscopy, radar, and a range of other scientific research fields. Microring resonators can generate high-repetition-rate optical frequency combs, but the complexity of the manufacturing process leads to a sharp increase in production costs. While optical frequency combs based on mode-locked lasers can perform basic sensing and detection, the required fiber amplifiers, gain fibers, and other equipment complicate the system and increase costs significantly. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a dual-optical frequency comb generation system and method based on a mode-multiplexed resonant cavity, wherein the system includes:

[0004] Continuous optical laser, first optical coupler, second optical coupler, third optical coupler, acousto-optic frequency shifter, first mode coupler, second mode coupler, third mode coupler, fiber optic ring resonator;

[0005] The fiber optic ring resonator is composed of a first-mode coupler, a second-mode coupler, and a third-mode coupler; the first-mode coupler is connected to the second-mode coupler, and the second-mode coupler is also connected to the third-mode coupler.

[0006] The continuous light laser is connected to a first optical coupler, and the output of the first optical coupler has two branches.

[0007] The first branch of the first optical coupler is connected to the acousto-optic frequency shifter, and then to the first input of the second optical coupler. The output of the second optical coupler has two branches. The first branch of the second optical coupler outputs the first optical frequency comb. The second branch of the second optical coupler is connected to the first mode coupler.

[0008] The second branch of the first optical coupler is connected to the first input of the third optical coupler. The output of the third optical coupler has two branches. The first branch of the third optical coupler outputs the second optical frequency comb. The second branch of the third optical coupler is connected to the first mode coupler.

[0009] The third-mode coupler has two output ports. The first output port of the third-mode coupler is connected to the second input of the second optocoupler and outputs from the first output port of the second optocoupler. The second output port of the third-mode coupler is connected to the second input of the third optocoupler and outputs from the first output port of the third optocoupler.

[0010] Furthermore, the coupling coefficient of the first optical coupler is 50%, the coupling coefficient of the second optical coupler is 5%, the coupling coefficient of the third optical coupler is 5%, the allocation ratio of the first branch of the first optical coupler is 50%, the allocation ratio of the second branch is 50%, the allocation ratio of the first branch of the second optical coupler is 5%, the allocation ratio of the second branch is 95%, and the allocation ratio of the first branch of the third optical coupler is 5%, and the allocation ratio of the second branch is 95%.

[0011] Furthermore, the continuous light laser outputs continuous light with a wavelength of 1550nm.

[0012] Furthermore, the first mode coupler and the second mode coupler in the fiber optic ring of the fiber optic resonator are connected by few-mode fiber, as are the second mode coupler and the third mode coupler, while all other parts of the system are connected by single-mode fiber.

[0013] The first mode coupler is connected to the second mode coupler via the first few-mode fiber, and the second mode coupler is also connected to the third mode coupler via the second few-mode fiber.

[0014] The continuous-wave laser is connected to the first optical coupler via a first single-mode fiber. The first branch of the first optical coupler is connected to the acousto-optic frequency shifter via a second single-mode fiber, and then to the first input of the second optical coupler via a fourth single-mode fiber. The output of the second optical coupler has two branches. The first branch of the second optical coupler outputs the first optical frequency comb via a fifth single-mode fiber. The second branch of the second optical coupler is connected to the first mode coupler via an eighth single-mode fiber.

[0015] The second branch of the first optical coupler is connected to the first input of the third optical coupler through the third single-mode fiber. The output of the third optical coupler has two branches. The first branch of the third optical coupler outputs the second optical frequency comb through the seventh single-mode fiber. The second branch of the third optical coupler is connected to the first mode coupler through the ninth single-mode fiber.

[0016] The first branch of the third-mode coupler is connected to the second input of the second optical coupler via the eleventh single-mode fiber and outputs from the first branch of the second optical coupler. The second branch of the third-mode coupler is connected to the second input of the third optical coupler via the tenth single-mode fiber and outputs from the first branch of the third optical coupler.

[0017] Furthermore, the first few-mode fiber and the second few-mode fiber are panda fibers, and the fundamental mode dispersion of the first few-mode fiber and the second few-mode fiber is 0.8943 ps / (nm·km), and the third-order dispersion is 0.0034 ps. 3 / km; the dispersion value of the higher-order mode is 0.6508ps / (nm·km), and the third-order dispersion is 0.0022ps. 3 / km; the self-phase modulation coefficient of the fundamental mode of the first few-mode fiber and the second few-mode fiber is 0.0031W. -1 / m, the self-phase modulation coefficient of the higher-order mode is 0.002W. -1 / m, the cross-phase modulation coefficients for both modes are 0.0019W -1 / m; The dimensions of the first few-mode fiber and the second few-mode fiber are as follows: distance from the center of the ring core to the center of the inner core is 32μm, inner core radius is 4μm, ring core diameter is 45μm, and fiber diameter is 25μm.

[0018] Furthermore, the fiber loop of the fiber resonator is 85m long, and the length difference between the first mode coupler and the second mode coupler and the second mode coupler is selected according to the required repetition frequency difference.

[0019] A dual-optical frequency comb generation method based on a mode-multiplexed resonant cavity is also proposed. Based on the above system implementation, the specific implementation process is as follows:

[0020] A continuous-wave laser is turned on to generate a continuous-wave signal. This continuous-wave signal is split into two paths by a first optical coupler. The first path of the first optical coupler passes through an acousto-optic modulator to a second optical coupler. The output of the second optical coupler is also split into two paths. The first path of the second optical coupler outputs a first optical frequency comb, and the second path of the second optical coupler outputs into a resonant cavity. The signal is then converted from the fundamental mode to a higher-order mode by a first mode coupler. Inside the cavity, the signal is converted from the higher-order mode to the fundamental mode by a second mode coupler, forming a higher-order mode-to-fundamental mode conversion within the cavity. Finally, the signal is output as the fundamental mode from the first path of the second optical coupler as the first optical frequency comb by a third mode coupler.

[0021] The second branch of the first optical coupler passes through the third optical coupler. The output of the third optical coupler is split into two branches. The first branch of the third optical coupler outputs the second optical frequency comb. The second branch of the third optical coupler outputs into the resonant cavity and passes through the first mode coupler. When it enters the cavity, it is in the fundamental mode. In the cavity, it is converted from the fundamental mode to a higher-order mode through the second mode coupler. A fundamental-to-higher-order mode conversion is formed in the cavity. Finally, the output passes through the third mode coupler and is converted from the higher-order mode to the fundamental mode. The fundamental mode is then output from the first branch of the third optical coupler as the second optical frequency comb.

[0022] The beneficial effects of the technical solution provided by this invention are:

[0023] Compared with existing technologies, this invention successfully realizes a dual optical frequency comb generation system and method based on a mode-multiplexed resonant cavity. The resonant cavity is composed of two modes, fundamental mode-higher-order mode and higher-order mode-fundamental mode, to generate a stable dual optical frequency comb with wide application fields. The first half of the few-mode fiber from the first mode coupler (OSDM1) to the second mode coupler (OSDM2) in the resonant cavity, and the second half of the few-mode fiber from the second mode coupler (OSDM2) to the third mode coupler (OSDM3), can be used to obtain dual optical frequency combs with different repetition frequency differences by flexibly controlling the length difference. The repetition frequency difference can be flexibly controlled. At the same time, the use of mode couplers to form mode exchange between the fundamental mode and higher-order mode and between higher-order mode and fundamental mode in the cavity makes the loop time difference between the two optical frequency combs small, that is, the difference in the free spectral range (repetition frequency) of the generated dual optical frequency combs is small. The system of this invention does not require the experimental equipment such as fiber amplifiers and gain fibers used in the mode-locked laser dual optical comb generation method, and the system structure is simple and the cost is low. Attached Figure Description

[0024] Figure 1 This is a structural block diagram of a dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity according to the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the few-mode optical fiber designed in the embodiments of the present invention;

[0026] Figure 3 This is the time-domain waveform of two optical paths undergoing 300 loops in the fiber optic ring in this embodiment of the invention. Figure 3 (a) is the time-domain waveform of the two optical paths, fundamental mode-higher-order mode and higher-order mode-fundamental mode, after 300 loops in the fiber optic ring; Figure 3 (b) is the number of loops traversed within the fiber optic loop;

[0027] Figure 4 This is a spectrum diagram of optical frequency comb 1 and optical frequency comb 2 after polarized light undergoes 300 loops in an embodiment of the present invention. Figure 4 (a) is the spectrum of optical frequency comb 1 after the two optical paths of fundamental mode-higher-order mode and higher-order mode-fundamental mode have undergone 300 loops; Figure 4 (b) is the spectrum of the optical frequency comb 2 after the two optical paths of fundamental mode-higher-order mode and higher-order mode-fundamental mode have undergone 300 loops. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0029] The structural block diagram of the dual optical frequency comb generation system based on a mode-multiplexing resonant cavity implemented in this embodiment of the present invention is as follows: Figure 1Specifically, it includes:

[0030] Continuous Wave Laser (CW Laser), First Optical Coupler OC1, Second Optical Coupler OC2, Third Optical Coupler OC3, Acousto-Optical Shifter (AOFS), First Mode Coupler OSDM1, Second Mode Coupler OSDM2, Third Mode Coupler OSDM3, and Fiber Ring Resonator.

[0031] The continuous light laser outputs continuous light with a wavelength of 1550nm and has an output power of 5W.

[0032] The coupling coefficient of the first optical coupler is 50%, the coupling coefficient of the second optical coupler is 5%, and the coupling coefficient of the third optical coupler is 5%.

[0033] The fiber optic ring resonator is composed of a first mode coupler OSDM1, a second mode coupler OSDM2, a third mode coupler OSDM3, and a first few-mode fiber FMF1 and a second few-mode fiber FMF2. The first mode coupler OSDM1 is connected to the second mode coupler OSDM2 through the first few-mode fiber FMF1, and the second mode coupler OSDM2 is also connected to the third mode coupler OSDM3 through the second few-mode fiber FMF2.

[0034] The continuous light laser (CW Laser) is connected to the first optical coupler (OC1) via the first single-mode fiber (SMF1). The output of the first optical coupler (OC1) has two branches with a 50%:50% ratio.

[0035] The first branch of the first optical coupler OC1 is connected to the acousto-optic frequency shifter AOFS through the second single-mode fiber SMF2, and then connected to the first input of the second optical coupler OC2 through the fourth single-mode fiber SMF4. The output of the second optical coupler OC2 has two branches, with the first branch having a 5% allocation ratio and the second branch having a 95% allocation ratio.

[0036] The first branch of the second optical coupler OC2 outputs the first optical frequency comb through the fifth single-mode fiber SMF5; the second branch of the second optical coupler OC2 is connected to the first mode coupler OSDM1 through the eighth single-mode fiber SMF8.

[0037] The second branch of the first optical coupler OC1 is connected to the first input of the third optical coupler OC3 through the third single-mode fiber SMF3. The output of the third optical coupler OC3 has two branches, with the first branch having a 5% allocation ratio and the second branch having a 95% allocation ratio.

[0038] The first branch of the third optical coupler OC3 outputs the second optical frequency comb through the seventh single-mode fiber SMF7, and the second branch of the third optical coupler OC3 is connected to the first mode coupler OSDM1 through the ninth single-mode fiber SMF9.

[0039] The third-mode coupler OSDM3 has two output ports. The first output port of OSDM3 is connected to the second input of the second optical coupler through the eleventh single-mode fiber SMF11, and outputs as optical frequency comb 1 from the first output port of the second optical coupler OC2. The second output port of OSDM3 is connected to the second input of the third optical coupler through the tenth single-mode fiber SMF10, and outputs as optical frequency comb 2 from the first output port of the third optical coupler OC3.

[0040] The fiber optic ring resonator is 85m long. The length difference between the first-mode coupler OSDM1 and the second-mode coupler OSDM2, and between the second-mode coupler OSDM2 and the third-mode coupler OSDM3, is flexibly selected according to the required repetition frequency difference. Adjusting the length difference between the two fiber segments within the cavity, from OSDM1 to OSDM2 and from OSDM2 to OSDM3, allows for completely symmetrical time-domain characteristics (equal peak value and pulse width) in the two modes when the detuning is large. To achieve balanced output power in symmetrical transmission, the detuning needs to be kept within the range where the cavity soliton characteristics are identical. For asymmetrical transmission, fine-tuning the length difference between the two few-mode fiber segments is considered to introduce a certain group velocity mismatch between the cavity solitons in the two modes, allowing them to operate independently with a repetition frequency difference, thus obtaining a mode-multiplexed dual-frequency comb.

[0041] The structural schematic diagram of the few-mode optical fiber designed in this embodiment of the invention is shown below. Figure 2 As shown, the first few-mode fiber FMF1 and the second few-mode fiber FMF2 are panda fibers. The fundamental mode (LP01) dispersion value of the first few-mode fiber FMF1 and the second few-mode fiber FMF2 is 0.8943 ps / (nm·km), and the third-order dispersion is 0.0034 ps. 3 / km; the dispersion value of the higher-order mode (LP11) is 0.6508ps / (nm·km), and the third-order dispersion is 0.0022ps. 3 / km; the self-phase modulation coefficient of the fundamental mode of the first few-mode fiber FMF1 and the second few-mode fiber FMF2 is 0.0031W. -1 / m, the self-phase modulation coefficient of the higher-order mode is 0.002W. -1 / m, the cross-phase modulation coefficients for both modes are 0.0019W -1 / m; The dimensions of the first and second few-mode fibers are as follows: distance from the center of the ring core to the center of the inner core d1 = 32 μm, inner core radius r1 = 4 μm, ring core diameter d2 = 45 μm, and fiber diameter D = 25 μm. The stress bar is composed of boron-doped quartz, while the core is composed of germanium-doped quartz. The core material of the stress bar is SiO2 with a boron doping concentration of 25%. The germanium doping concentration of the core is 12%.

[0042] This embodiment also includes a dual-optical frequency comb generation method based on a mode-multiplexed resonant cavity. Based on the above system implementation, the specific implementation process is as follows:

[0043] The CW Laser is activated to generate a continuous light signal. This continuous light signal is split into two paths by the first optical coupler OC1. The first path of the first optical coupler OC1 passes through the acousto-optic modulator AOFS to the second optical coupler OC2. The output of the second optical coupler OC2 is also split into two paths. The first path of the second optical coupler OC2 outputs the first optical frequency comb (optical frequency comb 1), and the second path of the second optical coupler OC2 outputs into the resonant cavity. The signal is then converted from the fundamental mode (LP01) to a higher-order mode (LP11) by the first mode coupler OSDM1. Inside the cavity, the signal is converted from the higher-order mode (LP11) back to the fundamental mode (LP01) by the second mode coupler OSDM2, forming a higher-order mode (LP11) to fundamental mode (LP01) mode conversion within the cavity. Finally, the signal is output from the first path of the second optical coupler OC2 as the fundamental mode (LP01) by the third mode coupler OSDM3.

[0044] The second branch of the first optical coupler OC1 passes through the third optical coupler OC3. The output of the third optical coupler OC3 is split into two branches. The first branch of the third optical coupler OC3 outputs the second optical frequency comb (optical frequency comb 2). The second branch of the third optical coupler OC3 outputs into the resonant cavity and passes through the first mode coupler OSDM1. When it enters the cavity, it is the fundamental mode (LP01). In the cavity, it passes through the second mode coupler OSDM2 and is converted from the fundamental mode (LP01) to a higher-order mode (LP11). A mode conversion from the fundamental mode (LP01) to the higher-order mode (LP11) is formed in the cavity. Finally, the output passes through the third mode coupler OSDM3 and is converted from the higher-order mode (LP11) back to the fundamental mode (LP01). The fundamental mode (LP01) is output from the first branch of the third optical coupler OSDM3 as the second optical frequency comb (optical frequency comb 2). By transforming the intracavity mode and the length difference between the two segments, the repetition frequency difference between the fundamental mode and the higher-order mode and the higher-order mode and the fundamental mode can be flexibly adjusted, thus obtaining a dual optical frequency comb based on a mode-reused resonant cavity.

[0045] In the Matlab simulation software, relevant parameters are set to simulate the evolution of the optical signal in the fiber optic ring resonator. The center wavelength of the continuous wave is set to around 1550nm, the power is set to 5W, and the splitting ratio is set to divide the energy into two equal parts and input two optical fields. At the same time, Gaussian pulses are superimposed on the fundamental mode-higher-order mode and higher-order mode-fundamental mode paths in the cavity, and then enter the fiber optic ring resonator with the above parameters. Taking the optical field of the fundamental mode-higher-order mode path as a reference, a certain length difference is set (in this example, the length difference is set to 0.2m and the repetition frequency difference is 2.56Hz).

[0046] The pulses in the other optical field undergo "drift" in the time domain, as shown in the simulation results. Figure 3 and Figure 4 As shown. Figure 3 (a) is a time-domain waveform diagram of the two optical paths, fundamental mode-higher-order mode and higher-order mode-fundamental mode, after 300 loops in the fiber optic ring. The vertical axis |E1,2| represents the power of the two optical paths in the cavity, in W. The horizontal axis is a fast time coordinate with reference to the group velocity of the higher-order mode-fundamental mode optical signal, in ps. Figure 3 (b) is the number of loops traversed within the fiber optic ring. Based on the time-domain drift of 2.2 ps per loop (i.e., the loop time difference between the two optical signals per loop), and given that the free spectral range of the fiber optic ring is 2.39 MHz, the repetition frequency difference between the two optical frequency combs can be calculated to be 2.56 Hz.

[0047] Figure 4 (a) is the spectrum of optical frequency comb 1 after the fundamental mode-higher-order mode and higher-order mode-fundamental mode optical paths have undergone 300 loops. Figure 4 (b) is the spectrum diagram of optical frequency comb 2 after the fundamental-higher-order mode and higher-order mode-fundamental mode optical signals have undergone 300 loops. The horizontal axis represents the wavelength range of the optical signal in the frequency domain, in nm, and the vertical axis represents the intensity of the optical signal at different wavelengths, in dBm. Figure 4 (a) and Figure 4 As can be seen in (b), two optical frequency combs were generated.

[0048] In summary, the dual-optical frequency comb generation system and method based on a mode-multiplexed resonant cavity proposed in this invention can transform the transmission of a single fundamental mode into the coupled transmission of optical fields of higher-order modes and the fundamental mode within the cavity, thereby generating optical frequency combs separately and merging them into a dual-optical frequency comb. This system uses self-made few-mode fiber, and mode switching avoids excessive accumulation of the velocity difference between the two modes in the fiber ring, allowing the two optical paths to have different loop times. Furthermore, the desired repetition rate difference can be obtained by controlling the length difference between the two fiber segments. The fiber ring resonant cavity, composed of a coupler and few-mode fiber, has a simple structure, is easy to manufacture, and has low cost. The dual-optical frequency comb generated by this scheme has broad prospects in the fields of precision ranging and sensing.

[0049] It should be noted that any content not described in detail in this specification is common knowledge to those skilled in the art. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity, characterized in that, include: Continuous optical laser, first optical coupler, second optical coupler, third optical coupler, acousto-optic frequency shifter, first mode coupler, second mode coupler, third mode coupler, fiber optic ring resonator; The fiber optic ring resonator is composed of a first-mode coupler, a second-mode coupler, and a third-mode coupler; the first-mode coupler is connected to the second-mode coupler, and the second-mode coupler is also connected to the third-mode coupler. The continuous light laser is connected to a first optical coupler, and the output of the first optical coupler has two branches. The first branch of the first optical coupler is connected to the acousto-optic frequency shifter, and then to the first input of the second optical coupler. The output of the second optical coupler has two branches. The first branch of the second optical coupler outputs the first optical frequency comb. The second branch of the second optical coupler is connected to the first mode coupler. The second branch of the first optical coupler is connected to the first input of the third optical coupler. The output of the third optical coupler has two branches. The first branch of the third optical coupler outputs the second optical frequency comb. The second branch of the third optical coupler is connected to the first mode coupler. The third-mode coupler has two output ports. The first output port of the third-mode coupler is connected to the second input of the second optocoupler and outputs from the first output port of the second optocoupler. The second output port of the third-mode coupler is connected to the second input of the third optocoupler and outputs from the first output port of the third optocoupler.

2. The dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity according to claim 1, characterized in that, The coupling coefficient of the first optical coupler is 50%, the coupling coefficient of the second optical coupler is 5%, the coupling coefficient of the third optical coupler is 5%, the allocation ratio of the first branch of the first optical coupler is 50%, the allocation ratio of the second branch is 50%, the allocation ratio of the first branch of the second optical coupler is 5%, the allocation ratio of the second branch is 95%, and the allocation ratio of the first branch of the third optical coupler is 5%, and the allocation ratio of the second branch is 95%.

3. The dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity according to claim 1, characterized in that, The continuous light laser outputs continuous light with a wavelength of 1550nm.

4. The dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity according to claim 1, characterized in that, In the fiber optic ring resonator, the first mode coupler and the second mode coupler, as well as the second mode coupler and the third mode coupler, are connected by few-mode fiber, while all other parts of the system are connected by single-mode fiber. The first mode coupler is connected to the second mode coupler via the first few-mode fiber, and the second mode coupler is also connected to the third mode coupler via the second few-mode fiber. The continuous-wave laser is connected to the first optical coupler via a first single-mode fiber. The first branch of the first optical coupler is connected to the acousto-optic frequency shifter via a second single-mode fiber, and then to the first input of the second optical coupler via a fourth single-mode fiber. The output of the second optical coupler has two branches. The first branch of the second optical coupler outputs the first optical frequency comb via a fifth single-mode fiber. The second branch of the second optical coupler is connected to the first mode coupler via an eighth single-mode fiber. The second branch of the first optical coupler is connected to the first input of the third optical coupler through the third single-mode fiber. The output of the third optical coupler has two branches. The first branch of the third optical coupler outputs the second optical frequency comb through the seventh single-mode fiber. The second branch of the third optical coupler is connected to the first mode coupler through the ninth single-mode fiber. The first branch of the third-mode coupler is connected to the second input of the second optical coupler via the eleventh single-mode fiber and outputs from the first branch of the second optical coupler. The second branch of the third-mode coupler is connected to the second input of the third optical coupler via the tenth single-mode fiber and outputs from the first branch of the third optical coupler.

5. A dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity according to claim 4, characterized in that, The first and second few-mode fibers are panda fibers. The fundamental mode dispersion of the first and second few-mode fibers is 0.8943 ps / (nm·km), and the third-order dispersion is 0.0034 ps. 3 / km; the dispersion value of the higher-order mode is 0.6508ps / (nm·km), and the third-order dispersion is 0.0022ps. 3 / km; the self-phase modulation coefficient of the fundamental mode of the first few-mode fiber and the second few-mode fiber is 0.0031W. -1 / m, the self-phase modulation coefficient of the higher-order mode is 0.002W. -1 / m, the cross-phase modulation coefficients for both modes are 0.0019W -1 / m; The dimensions of the first few-mode fiber and the second few-mode fiber are as follows: distance from the center of the ring core to the center of the inner core is 32μm, inner core radius is 4μm, ring core diameter is 45μm, and fiber diameter is 25μm.

6. The dual-optical frequency comb generation system based on a mode-multiplexed resonant cavity according to claim 1, characterized in that, The fiber optic resonator has a fiber loop length of 85m. The length difference between the first-mode coupler and the second-mode coupler and the third-mode coupler is selected according to the required repetition frequency difference.

7. A method for generating dual optical frequency combs based on a mode-multiplexed resonant cavity, implemented based on the system described in any one of claims 1-6, characterized in that, The specific implementation process is as follows: A continuous-wave laser is turned on to generate a continuous-wave signal. This continuous-wave signal is split into two paths by a first optical coupler. The first path of the first optical coupler passes through an acousto-optic modulator to a second optical coupler. The output of the second optical coupler is also split into two paths. The first path of the second optical coupler outputs a first optical frequency comb, and the second path of the second optical coupler outputs into a resonant cavity. The signal is then converted from the fundamental mode to a higher-order mode by a first mode coupler. Inside the cavity, the signal is converted from the higher-order mode to the fundamental mode by a second mode coupler, forming a higher-order mode-to-fundamental mode conversion within the cavity. Finally, the signal is output as the fundamental mode from the first path of the second optical coupler as the first optical frequency comb by a third mode coupler. The second branch of the first optical coupler passes through the third optical coupler. The output of the third optical coupler is split into two branches. The first branch of the third optical coupler outputs the second optical frequency comb. The second branch of the third optical coupler outputs into the resonant cavity and passes through the first mode coupler. When it enters the cavity, it is in the fundamental mode. In the cavity, it is converted from the fundamental mode to a higher-order mode through the second mode coupler. A fundamental-to-higher-order mode conversion is formed in the cavity. Finally, the output passes through the third mode coupler and is converted from the higher-order mode to the fundamental mode. The fundamental mode is then output from the first branch of the third optical coupler as the second optical frequency comb.

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