A high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering

Abstract

The present invention discloses a high-repetition-rate single-cavity dual-optical comb based on multimode interference spectral filtering, comprising a semiconductor saturable absorber mirror, a dielectric film, a single-mode passive optical fiber, a few-mode gain optical fiber, a pump source, an isolator, a wavelength division multiplexer, and the like. The semiconductor saturable absorber mirror is connected to the single-mode passive optical fiber, the dielectric film is connected to the few-mode gain optical fiber, and the single-mode passive optical fiber and the few-mode gain optical fiber are fused in an ultrashort linear cavity to construct a multimode interference spectral filtering structure equivalent to a single-mode passive optical fiber-few-mode gain optical fiber-single-mode passive optical fiber, which excites and generates high-repetition-rate asynchronous dual-wavelength mode-locked pulses. Two wavelength components are separated by a filter-type wavelength division multiplexer, the short wavelength component is amplified by a first amplifier and spectrally broadened by a first high-nonlinear optical fiber, the long wavelength component is amplified by a second amplifier and spectrally broadened by a second high-nonlinear optical fiber, and finally the two wavelength components are combined and beat by an optical coupler to obtain a single-cavity dual-optical comb.

Description

Technical Field

[0001] The present invention belongs to the technical field of dual optical frequency combs, and in particular relates to a high repetition rate single-cavity dual optical comb based on multi-mode interference spectral filtering. Background Art

[0002] As a revolutionary frequency metrology tool, the optical frequency comb offers unparalleled measurement accuracy. By using two optical frequency combs with slightly different repetition frequencies to generate multi-longitudinal mode heterodyne interference, a dual optical frequency comb can be formed. This not only allows for rapid spectrum measurement without mechanical scanning, but also utilizes heterodyne detection to further improve measurement accuracy. By down-converting the optical frequency component to the radio frequency region, it can be directly detected by a photodetector. The actual optical frequency signal can be obtained with the aid of Fourier transform, greatly reducing the reliance on detector bandwidth. The advantages of dual optical combs, such as high sensitivity, high resolution, and high accuracy, hold great promise for application in high-speed spectroscopy, precision metrology, hyperspectral optical imaging, and high-sensitivity optical sensing.

[0003] Traditional dual optical frequency combs contain two independent mode-locked lasers with different repetition rates. This requires additional complex and bulky optical and electrical locking devices to achieve high stability and high mutual coherence between the two optical frequency combs, which undoubtedly increases the complexity of the system and greatly limits the practical application of dual optical combs. To solve this problem, researchers have gradually focused on single-cavity dual optical comb technology in recent years. This is to output two sets of asynchronous pulse trains with slightly different repetition rates in a single mode-locked laser through multiplexing. This greatly reduces the complexity of the dual optical comb system. Because the two asynchronous mode-locked pulse trains are homologous, they share the same environmental interference and passively maintain extremely high mutual coherence. Therefore, they have outstanding advantages such as good stability and low common-mode noise, which greatly facilitates the practical application of dual optical frequency combs. Commonly used multiplexing methods include wavelength multiplexing achieved by using dual-wavelength lasers (Picometer-resolution dual-combspectroscopy with a free-running fiber laser), polarization multiplexing achieved by using the birefringence effect of optical fiber (Polarization-multiplexed, single-cavity dual-comb fiber laser based on abirefringent crystal and a saturable absorber), directional multiplexing achieved by different working directions of laser propagation (Bidirectional mode-locked all-normal dispersion fiber laser), cavity space multiplexing achieved by using non-common-path cavity structure (A Multidimensional Multiplexing Mode-Locked LaserBased on a Dual-Ring Integrative Structure for Tri-Comb Generation), etc. However, most of the multiplexing structures currently use a ring cavity method, which means that the repetition frequency can only be limited to the kHz-MHz level. In order to obtain a faster acquisition speed and improve measurement efficiency, it is necessary to have a larger repetition frequency difference (refresh time) between the dual combs. Δf rep =( ... Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a wavelength-multiplexed high-repetition-rate single-cavity dual-optical comb based on a multimode interference spectral filtering mechanism. By using a single-mode passive fiber and a few-mode gain fiber fused together in a linear cavity to construct a spectral filtering structure based on multimode interference, high-repetition-rate asynchronous dual-wavelength mode-locked pulse output is achieved. The two wavelength components are amplified and spectrally broadened separately, and then combined and beat to obtain a high-repetition-rate single-cavity dual-optical comb.

[0005] The present invention is achieved through at least one of the following technical solutions.

[0006] A high repetition rate single-cavity dual optical comb based on multimode interference spectral filtering, comprising a semiconductor saturable absorber mirror, a dielectric film, a single-mode passive optical fiber, a few-mode gain optical fiber, a wavelength division multiplexer, a pump source, an isolator, a filter-type wavelength division multiplexer, a first amplifier, a second amplifier, a first highly nonlinear optical fiber, a second highly nonlinear optical fiber, and an optical coupler;

[0007] The semiconductor saturable absorber mirror is connected to a single-mode passive optical fiber, which is connected to a dielectric film via a few-mode gain optical fiber. The fusion structure of the single-mode passive optical fiber and the few-mode gain optical fiber in an ultrashort linear cavity is equivalent to a multi-mode interference spectral filtering structure of "single-mode passive optical fiber-few-mode gain optical fiber-single-mode passive optical fiber". The high-order mode and the fundamental mode undergo time domain walk-off due to the inter-mode group velocity difference, and are excited to generate high-repetition-rate asynchronous dual-wavelength mode-locked pulses when the multi-mode light field is coupled back to the single-mode passive optical fiber. The common end, pump end and signal end of the wavelength division multiplexer are respectively connected to the dielectric film, pump source and isolator. The filter-type wavelength division multiplexer divides the signal light output by the isolator into two wavelength components. The short wavelength component is amplified by the first amplifier and spectrally broadened by the first high nonlinear optical fiber. The long wavelength component is amplified by the second amplifier and spectrally broadened by the second high nonlinear optical fiber. Finally, the two wavelength components are combined and beat by an optical coupler to obtain a single-cavity dual-light comb.

[0008] Furthermore, the few-mode gain fiber is an optical fiber supporting multi-mode operation, and its normalized frequency is greater than 2.405.

[0009] Furthermore, the single-mode passive optical fiber has a smaller mode field diameter than the few-mode gain optical fiber, so as to reduce the contact area between the light and the semiconductor saturable absorber mirror, thereby increasing the energy density of the light on the semiconductor saturable absorber mirror and preventing damage to the semiconductor saturable absorber mirror.

[0010] Furthermore, the modulation depth of the semiconductor saturable absorption mirror is 1% to 30%.

[0011] Furthermore, the reflectivity of the dielectric film to signal light is greater than 70%.

[0012] Furthermore, the transmittance of the dielectric film to pump light is greater than 70%.

[0013] Furthermore, the sum of the lengths of the single-mode passive optical fiber and the few-mode gain optical fiber is less than 10 cm, so as to achieve high repetition rate mode-locked pulse output greater than 1 GHz.

[0014] Furthermore, the few-mode gain fiber is a rare earth ion-doped fiber, and the doped rare earth ions include one or more of erbium, ytterbium, thulium and holmium.

[0015] Furthermore, the cutoff wavelength of the filter-type wavelength division multiplexer is between the center of the dual-wavelength laser, that is, it can just completely separate the two wavelength components.

[0016] Furthermore, the nonlinear coefficients of the first highly nonlinear optical fiber and the second highly nonlinear optical fiber are both greater than 10W. - 1 km -1 .

[0017] Compared with the existing technology, the beneficial effects of the present invention are:

[0018] The present invention provides a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering. By using a fusion of a few-mode gain fiber supporting multimode operation and a single-mode passive fiber as the laser cavity gain medium, a multimode interference-based spectral filtering structure is constructed to achieve high-repetition-rate asynchronous dual-wavelength mode locking. The two wavelength components are amplified and spectrally broadened separately before being combined to obtain a single-cavity dual-comb. Compared with traditional dual-combs that require two mode-locked lasers, it has a more compact structure and superior performance, further reducing costs and system complexity. In addition, because the high-repetition-rate asynchronous dual-wavelength pulses are generated in the same laser cavity, they share environmental interference, resulting in high relative frequency stability, good coherence, and low common-mode noise between pulse sequences, which has significant advantages in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly describes the drawings required for use in the embodiments. It should be understood that the following drawings illustrate only certain embodiments of the present invention and should not be construed as limiting the scope of the present invention. Those skilled in the art can, without inventive effort, derive other relevant drawings from these drawings.

[0020] Figure 1 A schematic diagram of a high-repetition-rate single-cavity dual-comb structure based on multimode interference spectral filtering provided by an embodiment of the present invention;

[0021] Figure 2 This is a seed source output spectrum diagram of a high repetition rate single-cavity dual-comb based on multimode interference spectral filtering provided by an embodiment of the present invention;

[0022] Figure 3 This is a diagram showing the output spectrum of a seed source of a high-repetition-rate single-cavity dual-optical comb based on multimode interference spectral filtering provided by an embodiment of the present invention;

[0023] Figure 4 A spectrum broadening diagram of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering provided by an embodiment of the present invention;

[0024] Figure 5 A time-domain interferogram of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering provided by an embodiment of the present invention;

[0025] Figure 6 This is a Fourier transform spectrum diagram of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering provided by an embodiment of the present invention.

[0026] Among them, 1-semiconductor saturable absorber mirror; 2-single-mode passive optical fiber; 3-few-mode gain optical fiber; 4-dielectric film; 5-wavelength division multiplexer; 6-pump source; 7-isolator; 8-filter-type wavelength division multiplexer; 9-first amplifier; 10-second amplifier; 11-first highly nonlinear optical fiber; 12-second highly nonlinear optical fiber; 13-optical coupler. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation examples. It should be noted that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0029] Example 1

[0030] like Figure 1 As shown, a schematic diagram of a high repetition rate single-cavity dual-comb structure based on multimode interference spectral filtering provided by this embodiment includes: a semiconductor saturable absorber mirror 1, a dielectric film 4, a single-mode passive fiber 2, a few-mode gain fiber 3, a wavelength division multiplexer 5, a pump source 6, an isolator 7, a filter-type wavelength division multiplexer 8, a first amplifier 9, a second amplifier 10, a first highly nonlinear fiber 11, a second highly nonlinear fiber 12, and an optical coupler 13;

[0031] The semiconductor saturable absorber mirror 1 is connected to the single-mode passive optical fiber 2, and the single-mode passive optical fiber 2 is connected to the dielectric film 4 through the few-mode gain optical fiber 3, and the dielectric film 4 is connected to the few-mode gain optical fiber 3. The fusion structure of the single-mode passive optical fiber 2 and the few-mode gain optical fiber 3 in the ultrashort linear cavity is equivalent to the multi-mode interference spectrum filtering structure of "single-mode passive optical fiber 2-few-mode gain optical fiber 3-single-mode passive optical fiber 2". The high-order mode and the fundamental mode are separated in the time domain due to the group velocity difference between the modes, and are excited to generate high-repetition-rate asynchronous dual-wavelength mode-locked pulses when the multi-mode light field is coupled back to the single-mode passive optical fiber 2; the common end, pump end and signal end of the wavelength division multiplexer 5 are respectively connected to the dielectric film 4, the pump source 6 and the isolator 7; Figure 1 As shown, the output end of the isolator 7 is connected to the input end of the filter-type wavelength division multiplexer 8, the output end of the filter-type wavelength division multiplexer 8 is connected to the input ends of the first amplifier 9 and the second amplifier 10, the output ends of the first amplifier 9 and the second amplifier 10 are connected to the first high nonlinear optical fiber 11 and the second high nonlinear optical fiber 12 respectively, and the output ends of the first high nonlinear optical fiber 11 and the second high nonlinear optical fiber 12 are connected to the optical coupler 13; the filter-type wavelength division multiplexer 8 divides the signal light into two wavelength components, the short wavelength component is amplified by the first amplifier 9 and the spectrum is broadened by the first high nonlinear optical fiber 11, the long wavelength component is amplified by the second amplifier 10 and the spectrum is broadened by the second high nonlinear optical fiber 12, and finally the two wavelength components are combined and beat by the optical coupler 13 to obtain a single-cavity dual-light comb.

[0032] In practical applications, the few-mode gain fiber 3 is a fiber supporting multi-mode operation, and its normalized frequency is 2.809; the single-mode passive fiber 2 is a fiber supporting only single-mode operation, and its normalized frequency is 2.198.

[0033] The single-mode passive fiber 2 is 0.8 cm long, with a core diameter of 5.3 μm and a cladding diameter of 125 μm. The few-mode gain fiber 3 is an 8.5 cm long ytterbium-doped fiber with a core diameter of 6 μm and a cladding diameter of 125 μm. The single-mode passive fiber 2 and the few-mode gain fiber 3 are fused together using a fusion splicer to achieve low-loss connection.

[0034] The single-mode passive optical fiber 2 has a smaller mode field diameter than the few-mode gain optical fiber 3 to reduce the contact area between light and the semiconductor saturable absorber mirror 1, thereby increasing the energy density of light on the semiconductor saturable absorber mirror 1 and preventing damage to the semiconductor saturable absorber mirror 1.

[0035] The semiconductor saturable absorber mirror 1 is a reflector with saturable absorption performance formed by growing a special semiconductor material directly on a semiconductor Bragg reflector and growing another reflector on the top layer. The upper and lower reflectors form a Fabry-Perot cavity, which has a central wavelength of 1040nm, a reflection bandwidth of 1020-1100nm, and an area of ​​1×1mm. 2 , thickness 450μm, non-saturated absorption 8%, modulation depth 5%, non-saturated loss 3%, saturation flux 40μJ / cm 2 , relaxation time is 1ps, damage threshold is 3mJ / cm 2 .

[0036] The dielectric film 4 is a dichroic dielectric film plated on the end face of the ferrule by plasma sputtering. The film thickness is 13 μm, the reflection center wavelength is 1064 nm, the reflection bandwidth is 1010-1080 nm, the reflectivity is greater than 85%, the transmission center wavelength is 976 nm, and the transmittance is greater than 90%.

[0037] The pump source 6 is a single-mode semiconductor laser with a central wavelength of 976 nm and a maximum output power of 500 mW.

[0038] The wavelength division multiplexer 5 is used to couple the pump light generated by the pump source 6 into the resonant cavity and output the generated signal light out of the resonant cavity.

[0039] The isolator 7 is connected to the wavelength division multiplexer 5 and is used to prevent the return light from affecting the output of the high repetition rate asynchronous dual-wavelength mode-locked pulse.

[0040] The cutoff wavelength of the filter-type wavelength division multiplexer 8 is 1059 nm, which is used to completely separate the two wavelength components of the generated asynchronous dual-wavelength mode-locked pulse, wherein the center wavelength of the short wavelength component is 1056 nm and the center wavelength of the long wavelength component is 1062 nm.

[0041] The first amplifier 9 and the second amplifier 10 are both optical amplifiers, which amplify the signal light to about 40 mW.

[0042] The first highly nonlinear optical fiber 11 and the second highly nonlinear optical fiber 12 are both photonic crystal fibers, and their nonlinear coefficients are 34W. -1 km -1 .

[0043] The optical coupler 13 combines the two amplified and spectrum-broadened wavelength components to obtain a single-cavity dual-optical comb.

[0044] like Figure 2The figure shows the output spectrum of the seed source of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering. The center wavelengths of the two wavelength components are 1056nm and 1062nm, respectively, and the corresponding 3dB spectral bandwidths are 2.12nm and 1.54nm, respectively.

[0045] like Figure 3 The figure shows the output spectrum of the seed source of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering. The fundamental frequency repetition frequencies of the two wavelength components are 1.092258 GHz and 1.092406 GHz, respectively, corresponding to a laser cavity length of 9.3 cm, and the repetition frequency difference is 148 kHz.

[0046] like Figure 4 The figure shows the spectrum broadening diagram of the high repetition rate single-cavity dual-comb based on multimode interference spectral filtering, that is, the spectrum of the seed source spectrum is divided into two wavelength components by the filter-type wavelength division multiplexer 8 and then amplified by the amplifier and spectrally broadened by the high nonlinear fiber.

[0047] like Figure 5 The figure shows the time-domain interferogram of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering, which is acquired by a high-speed real-time oscilloscope after passing through a 550MHz low-pass filter.

[0048] like Figure 6 Shown is the Fourier spectrum of a high-repetition-rate single-cavity dual-comb based on multimode interference spectral filtering, which is obtained by Fourier transforming the time-domain interferogram, where the optical-to-RF mapping factor is 7386.

[0049] Example 2

[0050] like Figure 1 As shown, the high repetition rate single-cavity dual-comb based on multimode interference spectral filtering provided in this embodiment has the same structure as that of Example 1, but the material parameters such as the few-mode gain fiber 3, the dielectric film 4, and the semiconductor saturable absorber mirror 1 used are different, and the central spectrum, spectral bandwidth and repetition frequency of the obtained high repetition rate asynchronous dual-wavelength mode-locked pulse output are also different.

[0051] The dielectric film 4 is a dichroic dielectric film plated on the end face of the ceramic ferrule by plasma sputtering. The film thickness is 16 μm, the reflection center wavelength is 1550 nm, the reflection bandwidth is 1480-1700 nm, the reflectivity is greater than 90%, the transmission center wavelength is 976 nm, and the transmittance is greater than 90%.

[0052] The semiconductor saturable absorption mirror 1 has a central wavelength of 1550 nm, a reflection bandwidth of 1450-1580 nm, and an area of ​​1×1 mm. 2, thickness is 450μm, non-saturated absorption is 7%, modulation depth is 3%, non-saturated loss is 4%, and saturation flux is 15μJ / cm 2 , relaxation time is 10ps, and damage threshold is 800μJ / cm 2 .

[0053] The few-mode gain fiber 3 is an erbium-ytterbium co-doped fiber with a length of 7 cm, a core diameter of 6 μm and a cladding diameter of 125 μm, and a normalized frequency of 2.903.

[0054] The cutoff wavelength of the filter-type wavelength division multiplexer 8 is 1550 nm, which is used to completely separate the two wavelength components of the generated asynchronous dual-wavelength mode-locked pulse, wherein the center wavelength of the short wavelength component is 1545 nm and the center wavelength of the long wavelength component is 1555 nm.

[0055] Example 3

[0056] like Figure 1 As shown, the high repetition rate single-cavity dual-comb based on multimode interference spectral filtering provided in this embodiment has the same structure as that of Example 1, but the material parameters such as the few-mode gain fiber 3, the dielectric film 4, and the semiconductor saturable absorber mirror 1 used are different, and the central spectrum, spectral bandwidth and repetition frequency of the obtained high repetition rate asynchronous dual-wavelength mode-locked pulse output are also different.

[0057] The dielectric film 4 is a dichroic dielectric film plated on the end face of the ceramic ferrule by plasma sputtering. The film thickness is 18 μm, the reflection center wavelength is 1950 nm, the reflection bandwidth is 1850-2050 nm, the reflectivity is greater than 90%, the transmission center wavelength is 1570 nm, and the transmittance is greater than 95%.

[0058] The semiconductor saturable absorber mirror 1 has a central wavelength of 2000 nm, a reflection bandwidth of 1890-2060 nm, and an area of ​​1×1 mm. 2 , thickness 450μm, non-saturated absorption 20%, modulation depth 12%, non-saturated loss 8%, saturation flux 65μJ / cm 2 , relaxation time is 10ps, damage threshold is 2mJ / cm 2 .

[0059] The few-mode gain fiber 3 is thulium-doped silica fiber with a length of 6 cm, a core diameter of 7 μm and a cladding diameter of 125 μm, and a normalized frequency of 2.876.

[0060] The cutoff wavelength of the filter-type wavelength division multiplexer 8 is 1950 nm, which is used to completely separate the two wavelength components of the generated asynchronous dual-wavelength mode-locked pulse, wherein the center wavelength of the short wavelength component is 1946 nm and the center wavelength of the long wavelength component is 1954 nm.

[0061] The pump source 6 is a 1570nm single-mode semiconductor laser.

[0062] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0063] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering, characterized in that: The invention comprises a semiconductor saturable absorber mirror (1), a dielectric film (4), a single-mode passive optical fiber (2), a few-mode gain optical fiber (3), a wavelength division multiplexer (5), a pump source (6), an isolator (7), a filter-type wavelength division multiplexer (8), a first amplifier (9), a second amplifier (10), a first highly nonlinear optical fiber (11), a second highly nonlinear optical fiber (12), and an optical coupler (13); The semiconductor saturable absorber mirror (1) is connected to a single-mode passive optical fiber (2), and the single-mode passive optical fiber (2) is connected to a dielectric film (4) via a few-mode gain optical fiber (3). The fusion structure of the single-mode passive optical fiber (2) and the few-mode gain optical fiber (3) in an ultrashort linear cavity is equivalent to a multi-mode interference spectrum filtering structure of a single-mode passive optical fiber (2)-few-mode gain optical fiber (3)-single-mode passive optical fiber (2). The high-order mode and the fundamental mode undergo time domain walk-off due to the inter-mode group velocity difference, and are excited to generate high repetition rate asynchronous dual-wavelength locking when the multi-mode light field is coupled back to the single-mode passive optical fiber (2). mode pulse; the common end, pump end and signal end of the wavelength division multiplexer (5) are respectively connected to the dielectric film (4), the pump source (6) and the isolator (7); the filter-type wavelength division multiplexer (8) divides the signal light output by the isolator (7) into two wavelength components, the short wavelength component is amplified by the first amplifier (9) and spectrally broadened by the first high nonlinear optical fiber (11), the long wavelength component is amplified by the second amplifier (10) and spectrally broadened by the second high nonlinear optical fiber (12), and finally the two wavelength components are combined and beat by the optical coupler (13) to obtain a single-cavity dual-light comb.

2. The high repetition rate single-cavity dual optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The few-mode gain optical fiber (3) is an optical fiber supporting multi-mode operation, and its normalized frequency is greater than 2.

405.

3. The high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The single-mode passive optical fiber (2) has a smaller mode field diameter than the few-mode gain optical fiber (3), so as to reduce the contact area between light and the semiconductor saturable absorber mirror (1), thereby increasing the energy density of light on the semiconductor saturable absorber mirror (1) and preventing damage to the semiconductor saturable absorber mirror (1).

4. The high repetition rate single-cavity dual optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The modulation depth of the semiconductor saturable absorption mirror (1) is 1% to 30%.

5. The high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The reflectivity of the dielectric film (4) to signal light is greater than 70%.

6. The high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The dielectric film (4) has a transmittance of greater than 70% for pump light.

7. The high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The sum of the lengths of the single-mode passive optical fiber (2) and the few-mode gain optical fiber (3) is less than 10 cm, so as to achieve high repetition rate mode-locked pulse output greater than 1 GHz.

8. The high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The few-mode gain optical fiber (3) is a rare earth ion-doped optical fiber, and the doped rare earth ions include one or more of erbium, ytterbium, thulium and holmium.

9. The high repetition rate single-cavity dual-optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The cut-off wavelength of the filter-type wavelength division multiplexer (8) is between the center of the dual-wavelength laser, that is, it can completely separate the two wavelength components.

10. The high repetition rate single-cavity dual optical comb based on multimode interference spectral filtering according to claim 1, characterized in that: The nonlinear coefficients of the first highly nonlinear optical fiber (11) and the second highly nonlinear optical fiber (12) are both greater than 10W. -1 km -1 .

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