Narrow linewidth fiber laser system based on self-injection locking feedback mechanism

Abstract

The invention discloses a narrow linewidth optical fiber laser system based on a self-injection locking feedback mechanism, which belongs to the field of optical fiber communication and comprises a main cavity, a self-injection locking feedback module and an erbium-doped optical fiber amplifier. Wherein the main cavity internally comprises a composite ring cavity filter for selecting a longitudinal mode; the composite ring cavity filter is sequentially connected with a polarization controller, a first erbium-doped fiber, a first wavelength division multiplexer, a second erbium-doped fiber and a first uniform fiber bragg grating through a first circulator; the output end of the first uniform fiber bragg grating is connected with the input end of a first optical fiber coupler, one output end of the first optical fiber coupler is sequentially connected with an optical fiber delay line and a Faraday rotating mirror in the self-injection locking feedback module, and the rotating angle of the Faraday rotating mirror is 90 degrees; and the other output end of the first optical fiber coupler is connected with the input end of the erbium-doped optical fiber amplifier. Through the above structure, the stability of the laser system is improved.

Description

Technical Field

[0001] The invention relates to the field of optical fiber communication and instrumentation technology, and more particularly to a narrow linewidth optical fiber laser system based on a self-injection locking feedback mechanism. Background Art

[0002] Narrow linewidth erbium-doped fiber lasers are widely used in optical metrology, fiber sensing, fiber communication and other fields due to their advantages such as high stability, low transmission loss, low dispersion, low noise, and long coherence distance. However, the linewidth of the output lasers of many erbium-doped fiber lasers is still relatively wide, remaining at the order of tens of kHz, so narrow linewidth fiber lasers and their linewidth narrowing technology have become the main research direction at present.

[0003] Single longitudinal mode fiber laser is a major prerequisite for achieving narrow linewidth laser output. Commonly used implementation mechanisms include but are not limited to ultra-narrowband optical filters, temperature control, Fabry-Perot filters, etc. However, the above methods have problems such as complex manufacturing process, difficult parameter control, and impracticality, and cannot be regarded as the best mode selection solution.

[0004] In addition, line width narrowing usually uses two methods: backward Rayleigh scattering and stimulated Brillouin scattering. However, the above two methods require a longer distance of optical fiber extension line to enhance the intensity of distributed feedback light, which will not only introduce higher 1 / f noise but also increase the instability of the fiber laser. Summary of the invention

[0005] In view of this, the present invention provides a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism, which is used to at least solve some of the technical problems in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A narrow linewidth fiber laser system based on a self-injection locking feedback mechanism, comprising a main cavity, a self-injection locking feedback module and an erbium-doped fiber amplifier;

[0008] The main cavity includes a composite ring cavity filter for selecting the longitudinal mode; the composite ring cavity filter is sequentially connected to the polarization controller, the first erbium-doped fiber, the first wavelength division multiplexer, the second erbium-doped fiber and the first uniform fiber grating through the first circulator;

[0009] The output end of the first uniform fiber grating is connected to the input end of the first fiber coupler, one output end of the first fiber coupler is connected to the fiber delay line and the Faraday rotator in the self-injection locking feedback module in sequence, and the rotation angle of the Faraday rotator is 90°; the other output end of the first fiber coupler is connected to the input end of the erbium-doped fiber amplifier.

[0010] Preferably, in the self-injection locking feedback module, the length of the optical fiber delay line is 100 meters.

[0011] Preferably, the first erbium-doped optical fiber is an unpumped gain optical fiber used as a saturable absorber, and has a length of 0.8 m.

[0012] Preferably, the composite ring cavity filter comprises a second optical fiber coupler, a third optical fiber coupler, a fourth optical fiber coupler and a fifth optical fiber coupler;

[0013] Among them, the second fiber coupler and the third fiber coupler are connected to form a first sub-ring cavity; the fourth fiber coupler and the fifth fiber coupler are connected to form a second sub-ring cavity; the output end of the third fiber coupler in the first sub-ring cavity is simultaneously connected to the input end of the fourth fiber coupler in the second sub-ring cavity; the input end of the second fiber coupler in the first sub-ring cavity is simultaneously connected to port 3 of the first circulator; the output end of the fifth fiber coupler in the second sub-ring cavity is simultaneously connected to port 1 of the first circulator; and port 2 of the first circulator is connected to one end of the polarization controller.

[0014] Preferably, the second fiber coupler, the third fiber coupler, the fourth fiber coupler and the fifth fiber coupler in the composite ring cavity filter are all 2×2 fiber couplers with a splitting ratio of 80:20.

[0015] Preferably, the pump input end of the first wavelength division multiplexer is directly connected to the first pump source.

[0016] Preferably, the erbium-doped fiber amplifier comprises a second wavelength division multiplexer, a third erbium-doped fiber, a second circulator, a second uniform fiber grating and a second pump source;

[0017] Among them, one signal input end of the second wavelength division multiplexer serves as the input end of the erbium-doped fiber amplifier and is connected to the other output end of the first fiber coupler; the pump input end of the second wavelength division multiplexer is connected to the second pump source; the signal output end of the second wavelength division multiplexer is connected to one end of the third erbium-doped fiber, and the other end of the third erbium-doped fiber is connected to port 1 of the second circulator; port 2 of the second circulator is connected to the second uniform fiber grating, and the laser of the laser system is output from port 3 of the second circulator.

[0018] Preferably, the second pump source is a 980nm semiconductor light source.

[0019] Preferably, the central wavelength, reflection bandwidth and reflectivity of the second uniform fiber grating are 1549.0762 nm, 0.0832 nm and 92.41% respectively.

[0020] Preferably, the polarization controller comprises an in-line polarization controller or a three-ring polarization controller.

[0021] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism, which has the following beneficial effects:

[0022] The narrow-linewidth fiber laser system disclosed in the present invention introduces a self-injection locking feedback module, and is connected to a 90° Faraday rotation mirror through an optical fiber delay line, which can not only prevent polarization fading, but also further increase the feedback laser photon lifetime, thereby improving the stability of the narrow-linewidth fiber laser system.

[0023] In the narrow linewidth fiber laser system disclosed in the present invention, the output of single longitudinal mode laser is effectively ensured by a composite ring cavity filter and a saturable absorber arranged in a main cavity.

[0024] In the narrow linewidth fiber laser system disclosed in the present invention, an erbium-doped fiber amplifier amplifies the laser emitted from the main cavity, and at the same time, a second uniform fiber grating is provided to effectively filter out the spontaneous radiation light amplification noise, thereby further improving the optical signal-to-noise ratio of the output laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 This is a schematic diagram of the overall structure of a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism provided by the present invention.

[0027] Figure 2 This is a measured spectrum diagram of the first uniform fiber grating provided by the present invention.

[0028] Figure 3 This is a measured spectrum diagram of the second uniform fiber grating provided by the present invention.

[0029] Figure 4 The simulated transmission spectrum of the composite ring cavity filter and the reflection spectrum of the uniform grating provided by the present invention; the inset is a local magnified view of the main resonance peak of the simulated transmission spectrum.

[0030] Figure 5 Schematic diagram of output laser spectrum under different conditions provided by the present invention.

[0031] Figure 6 The output laser spectrum of the narrow-linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present invention, and the inset is a scanning spectrum diagram of the output laser for one hour, with a scanning interval of 6 minutes.

[0032] Figure 7 The invention discloses a self-homodyne spectrum of a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism without a composite ring cavity filter, a saturable absorber and a self-injection locking feedback module.

[0033] Figure 8 The homodyne spectrum of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present invention without the self-injection locking feedback module, the illustration is the one-hour scanned self-homodyne spectrum in the range of 0-100 MHz, and the scanning time interval is 6 minutes.

[0034] Fig. 9 The self-homodyne spectrum of the narrow-linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present invention, the inset is the one-hour scanned self-homodyne spectrum in the range of 0-100 MHz, and the scanning time interval is 6 minutes.

[0035] Fig.10 The invention provides a curve showing the relationship between the output laser power of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism and the change of the pump power.

[0036] Fig.11 The frequency noise power spectrum density and line width values ​​at different test times when there is no self-injection locking feedback module provided by the present invention.

[0037] Fig.12 The present invention provides the frequency noise power spectrum density when a self-injection locking feedback module is provided and the line width values ​​under different test times.

[0038] Fig.13 A comparison diagram of relaxation oscillations with and without the self-injection locking feedback module provided by the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The embodiment of the present invention discloses a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism, which mainly comprises three parts: a main cavity, a self-injection locking feedback module, and an erbium-doped fiber amplifier.

[0041] Combine the following Figure 1 The specific structure of the present invention is further described.

[0042] In this embodiment, the main cavity includes a composite ring cavity filter for selecting the longitudinal mode; in addition, the composite ring cavity filter in the main cavity is connected to the polarization controller 06, the first erbium-doped fiber 05, the first wavelength division multiplexer 02, the second erbium-doped fiber 03 and the first uniform fiber grating 04 in sequence through the first circulator 07. In this embodiment, the total cavity length of the main cavity is 12.46m, corresponding to the main cavity longitudinal mode interval of 16.45MHz.

[0043] The output end of the first uniform fiber grating 04 is connected to the input end of the first fiber coupler 12, and one output end of the first fiber coupler 12 is connected to the fiber delay line 13 and the Faraday rotator 14 in the self-injection locking feedback module in sequence, and the rotation angle of the Faraday rotator is 90°; the other output end of the first fiber coupler 12 is connected to the input end of the erbium-doped fiber amplifier.

[0044] In this embodiment, the first erbium-doped optical fiber 05 is not pumped by a pump source, has a length of 0.8 m, and is used as a saturable absorber to improve the stability of the single longitudinal mode output of the laser system.

[0045] In this embodiment, one input end of the first wavelength division multiplexer 02 is directly connected to the first pump source 01 .

[0046] In this embodiment, the composite ring cavity filter includes a second fiber coupler 08, a third fiber coupler 09, a fourth fiber coupler 10 and a fifth fiber coupler 11; wherein, the second fiber coupler 08 and the third fiber coupler 09 are first connected to form a first sub-ring cavity; the fourth fiber coupler 10 and the fifth fiber coupler 11 are connected to form a second sub-ring cavity; the output end of the third fiber coupler 09 in the first sub-ring cavity is simultaneously connected to the input end of the fourth fiber coupler 10 in the second sub-ring cavity; the input end of the second fiber coupler 08 in the first sub-ring cavity is simultaneously connected to the 3-port of the first circulator 07; the output end of the fifth fiber coupler 11 in the second sub-ring cavity is simultaneously connected to the 1-port of the first circulator 07; and the 2-port of the first circulator is connected to the input end of the polarization controller 06.

[0047] In this embodiment, the erbium fiber amplifier includes a second wavelength division multiplexer 16, a third erbium-doped fiber 17, a second circulator 18, a second uniform fiber grating 19 and a second pump source 15; wherein, a signal input end of the second wavelength division multiplexer 16 serves as an input end of the erbium-doped fiber amplifier and is connected to the other output end of the first fiber coupler 12; the pump input end of the second wavelength division multiplexer 16 is connected to the second pump source 15; the output end of the second wavelength division multiplexer 16 is connected to one end of the third erbium-doped fiber 17, and the other end of the third erbium-doped fiber 17 is connected to port 1 of the second circulator 18; port 2 of the second circulator 18 is connected to the second uniform fiber grating 19, and the laser of the laser system is output from port 3 of the second circulator 18 through the optical fiber pipe 182. In the embodiment of the present invention, a second uniform fiber grating 19 is additionally introduced into the erbium-doped fiber amplifier. The introduction of the grating can not only filter out the spontaneous emission noise in the output laser, but also further improve the optical signal-to-noise ratio of the output laser of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism.

[0048] In the above embodiment, the second erbium-doped fiber 03 and the third erbium-doped fiber 17 are gain fibers, the lengths of which are 2.80 m and 3.00 m respectively, and the stimulated emission light amplification in the cavity is achieved through a pump source.

[0049] In the above embodiment, the first pump source 01 and the second pump source 15 can both be 980nm semiconductor light sources with high stability.

[0050] In the above embodiment, the first optical fiber coupler 12 is a 1×2 coupler with a splitting ratio of 50:50.

[0051] In the above embodiment, the polarization controller 06 is used to adjust the polarization state in the main cavity, and may be an in-line polarization controller or a three-ring polarization controller.

[0052] In the embodiment of the present invention, each component is connected through an optical fiber tube, as shown in the following example. Figure 1As shown, the signal output end of the first wavelength division multiplexer 02 is connected to one end of the second erbium-doped fiber 03 through the first optical fiber pipe 021, the other end of the second erbium-doped fiber 03 is connected to one end of the first uniform fiber grating 04 through the second optical fiber pipe 031, the signal input end of the first wavelength division multiplexer 02 is connected to one end of the first erbium-doped fiber 05 through the third optical fiber pipe 022, the other end of the first erbium-doped fiber 05 is connected to one end of the polarization controller 06 through the fourth optical fiber pipe 051, the other end of the polarization controller 06 is connected to the 2nd port of the first circulator 07 through the fifth optical fiber pipe 061, the 3rd port of the first circulator 07 is connected to one end of the input end of the second optical fiber coupler 08 through the sixth optical fiber pipe 071, and one end of the output end of the second optical fiber coupler 08 is connected to the input end of the third optical fiber coupler 09 through the seventh optical fiber pipe 081. One end of the output end of the third fiber coupler 09 is connected to the other end of the input end of the second fiber coupler 08 through an eighth fiber optic pipe 091, the other end of the output end of the third fiber coupler 09 is connected to one end of the input end of the fourth fiber coupler 10 through a ninth fiber optic pipe 092, one end of the output end of the fourth fiber coupler 10 is connected to one end of the input end of the fifth fiber coupler 11 through a tenth fiber optic pipe 101, one end of the output end of the fifth fiber coupler 11 is connected to the other end of the input end of the fourth fiber coupler 10 through an eleventh fiber optic pipe 111, the other end of the output end of the fifth fiber coupler 11 is connected to port 1 of the first circulator 07 through a twelfth fiber optic pipe 112, and the other end of the first uniform fiber grating 04 is connected to the input end of the first fiber coupler 12 through a thirteenth fiber optic pipe 041.

[0053] One end of the output end of the first fiber coupler 12 is connected to one end of the fiber delay line 13 through the fourteenth fiber duct 121 , and the other end of the fiber delay line 13 is connected to the Faraday rotation mirror 14 through the fifteenth fiber duct 131 .

[0054] The other end of the output end of the first optical fiber coupler 12 is connected to the signal input end of the second wavelength division multiplexer 12 through the sixteenth optical fiber pipe 122, the pump source 2 15 is connected to the pump input end of the second wavelength division multiplexer 12, the signal output end of the second wavelength division multiplexer 12 is connected to one end of the erbium-doped optical fiber 3 17 through the seventeenth optical fiber pipe 161, the other end of the erbium-doped optical fiber 3 17 is connected to the 1st port of the second circulator 18 through the eighteenth optical fiber pipe 171, the 2nd port of the second circulator 18 is connected to one end of the second uniform optical fiber grating 19 through the nineteenth optical fiber pipe 181, and the 3rd port of the second circulator 18 outputs laser through the twentieth optical fiber pipe 182.

[0055] In addition to the above connection relationship, in the above embodiment, the first uniform fiber grating 04 and the second uniform fiber grating 19 are written using a phase mask method, wherein the phase mask period is 1071.1 mm and the grating region length is 50 mm. The spectral characteristics of the first uniform fiber grating 04 are as follows: Figure 2 As shown in FIG. 1 , the central wavelength (λ), reflection bandwidth (RB) and reflectivity (R) are 1549.0753 nm, 0.0571 nm and 80.95% respectively. The spectral characteristics of the second uniform fiber grating 19 are shown in FIG. Figure 3 As shown, the central wavelength (λ), reflection bandwidth (RB) and reflectivity (R) are 1549.0762 nm, 0.0832 nm and 92.41% respectively.

[0056] The composite ring cavity filter in the main cavity is composed of the second fiber coupler 08, the third fiber coupler 09, the fourth fiber coupler 10 and the fifth fiber coupler 11, the seventh fiber duct 081, the eighth fiber duct 091, the ninth fiber duct 092, the tenth fiber duct 101 and the eleventh fiber duct 111. The coupling ratio of the fiber couplers is 80:20. The cavity length difference of the composite ring cavity filter is 0.04m, and the corresponding free spectrum range is 5.18GHz. Figure 4 As shown, the corresponding free spectrum range of the composite ring cavity filter is 0.04125nm, which ensures that only one main resonance peak in the reflection bandwidth of the first uniform fiber grating 04 can obtain the maximum gain. At the same time, the half-width of the main resonance peak is 18.87MHz, and the side mode suppression ratio is 3.81dB, which ensures that there is only one main cavity longitudinal mode oscillating in the main resonance peak channel in the main cavity. After two mode selections and the use of a 0.8m long saturable absorber, the main cavity outputs stable single longitudinal mode lasing.

[0057] The length of the optical delay line 13 of the self-injection locking feedback loop is 100 m, and a 90° Faraday rotation mirror 14 is used to reflect the output laser to increase the optical path, thereby increasing the photon lifetime.

[0058] The present invention can narrow the laser line width at different test times through a self-injection locking feedback module.

[0059] The self-injection locking feedback module mainly designed in the present invention not only uses an optical fiber delay line, but also uses a 90° Faraday rotation mirror, which not only prevents polarization fading, but also doubles the optical path of the self-injection locking feedback light on the basis of a 100m optical fiber delay line by reflecting laser, further narrowing the output laser line width.

[0060] like Figure 5As shown in the figure, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the optical path, a high spontaneous emission noise appears in the output laser spectrum, and the optical signal-to-noise ratio of the output laser is only greater than 48.71dB. When the erbium-doped fiber amplifier module is connected, the optical signal-to-noise ratio of the output laser is increased from the original >48.71dB to >68.52dB due to the filtering of the second uniform fiber grating. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is increased from >68.52dB to >75.04dB. Figure 6 This is the output laser spectrum of the narrow-linewidth fiber laser system based on the self-injection locking feedback mechanism. The central wavelength of the output laser of this laser system is 1549.09nm. The maximum wavelength drift and peak power jitter of the output laser within 60 minutes are 0.0085nm and 0.98dB respectively.

[0061] like Figure 7 , Figure 8 , Fig. 9 As shown, when the composite ring cavity filter and the saturable absorber are not connected to the optical path, dense non-zero frequency beat signals appear in the self-homodyne RF spectrum of the output laser, and the laser system operates in a multi-longitudinal mode state; when the composite ring cavity filter and the saturable absorber are connected to the optical path, the polarization controller is adjusted, and no non-zero frequency beat signals appear in the RF spectrum, and the laser maintains single longitudinal mode lasing; due to the external cavity injection structure, when the self-injection locking feedback module is connected to the optical path, no non-zero frequency beat signals appear in the self-homodyne RF spectrum in the frequency range of 0-100MHz and the one-hour self-homodyne RF spectrum. In summary, the laser system can still maintain stable single longitudinal mode lasing for 60 minutes.

[0062] like Fig.10 As shown, due to the use of erbium-doped fiber amplifier, the output laser power of the narrow-linewidth fiber laser system based on the self-injection locking feedback mechanism can reach up to 157.20mW.

[0063] like Fig.11 As shown in Figure 1, when the self-injection locking feedback module is not connected to the optical path, the frequency noise spectrum intersects with the β-division line at 4.745kHz, and the line widths at 0.001s, 0.002s, and 0.005s test times are 36.167kHz, 36.818kHz, and 40.802kHz, respectively. When the self-injection locking feedback loop is connected to the optical path, as shown in Figure 1 Fig.12 As shown in the figure, the horizontal coordinate of the intersection of the frequency noise spectrum line and the β dividing line moves to the left to 2.090kHz, and the line width at the test time of 0.001s, 0.002s, and 0.005s is narrowed to 4.602kHz, 9.449kHz, and 27.171kHz. The use of the self-injection locking feedback module narrows the output laser line width at different test times.

[0064] like Fig.13 As shown in the figure, when the self-injection locking feedback module is not connected, the frequency and intensity of the relaxation oscillation peak are 30.3kHz and -72.90dB / Hz respectively. When the self-injection locking feedback module is connected to the optical path, the frequency of the relaxation oscillation peak shifts left to 18.7kHz and the intensity is -79.67dB / Hz. The use of self-injection locking feedback technology effectively improves the photon lifetime in the cavity.

[0065] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0066] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A narrow linewidth fiber laser system based on self-injection locking feedback mechanism, characterized in that: It includes a main cavity, a self-injection locking feedback module and an erbium-doped fiber amplifier; The main cavity includes a composite ring cavity filter for selecting the longitudinal mode; the composite ring cavity filter is sequentially connected to the polarization controller, the first erbium-doped fiber, the first wavelength division multiplexer, the second erbium-doped fiber and the first uniform fiber grating through the first circulator; The output end of the first uniform fiber grating is connected to the input end of the first fiber coupler, one output end of the first fiber coupler is connected to the fiber delay line and the Faraday rotator in the self-injection locking feedback module in sequence, and the rotation angle of the Faraday rotator is 90°; the other output end of the first fiber coupler is connected to the input end of the erbium-doped fiber amplifier.

2. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 1, characterized in that: In the self-injection locking feedback module, the length of the optical fiber delay line is 100 meters.

3. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 1, characterized in that: The composite ring cavity filter comprises a second optical fiber coupler, a third optical fiber coupler, a fourth optical fiber coupler and a fifth optical fiber coupler; Among them, the second fiber coupler and the third fiber coupler are connected to form a first sub-ring cavity; the fourth fiber coupler and the fifth fiber coupler are connected to form a second sub-ring cavity; the output end of the third fiber coupler in the first sub-ring cavity is simultaneously connected to the input end of the fourth fiber coupler in the second sub-ring cavity; the input end of the second fiber coupler in the first sub-ring cavity is simultaneously connected to port 3 of the first circulator; the output end of the fifth fiber coupler in the second sub-ring cavity is simultaneously connected to port 1 of the first circulator; and port 2 of the first circulator is connected to one end of the polarization controller.

4. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 3, characterized in that: The second optical fiber coupler, the third optical fiber coupler, the fourth optical fiber coupler and the fifth optical fiber coupler in the composite ring cavity filter are all 2×2 optical fiber couplers with a splitting ratio of 80:

20.

5. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 1, characterized in that: The first erbium-doped optical fiber is used as a saturable absorber and has a length of 0.8 m.

6. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 1, characterized in that: The pump input end of the first wavelength division multiplexer is connected to a first pump source.

7. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 1, characterized in that: The erbium-doped fiber amplifier includes a second wavelength division multiplexer, a third erbium-doped fiber, a second circulator, a second uniform fiber grating and a second pump source; Among them, one signal input end of the second wavelength division multiplexer serves as the input end of the erbium-doped fiber amplifier and is connected to the other output end of the first fiber coupler; the pump input end of the second wavelength division multiplexer is connected to the second pump source; the signal output end of the second wavelength division multiplexer is connected to one end of the third erbium-doped fiber, and the other end of the third erbium-doped fiber is connected to port 1 of the second circulator; port 2 of the second circulator is connected to the second uniform fiber grating, and the laser of the laser system is output from port 3 of the second circulator.

8. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 7, characterized in that: The second pump source is a 980nm semiconductor light source.

9. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 7, characterized in that: The central wavelength, reflection bandwidth and reflectivity of the second uniform fiber grating are 1549.0762 nm, 0.0832 nm and 92.41% respectively.

10. The narrow linewidth fiber laser system based on self-injection locking feedback mechanism according to claim 1, characterized in that: The polarization controller includes an in-line polarization controller or a three-ring polarization controller.

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