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

Abstract

This invention discloses a narrow-linewidth fiber laser system based on a self-injection locked feedback mechanism, belonging to the field of fiber optic communication. The system includes a main cavity, a self-injection locked feedback module, and an erbium-doped fiber amplifier. The main cavity internally includes a composite ring cavity filter for selecting longitudinal modes. This composite ring cavity filter is sequentially connected to a polarization controller, a first erbium-doped fiber, a first wavelength division multiplexer, a second erbium-doped fiber, and a first uniform fiber grating via a first circulator. The output of the first uniform fiber grating is connected to the input of a first fiber coupler. One output of the first fiber coupler is sequentially connected to a fiber delay line and a Faraday rotator in the self-injection locked feedback module, with the Faraday rotator rotating at a 90° angle. The other output of the first fiber coupler is connected to the input of the erbium-doped fiber amplifier. Through this structure, the present invention improves the stability of the laser system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber communication and instrument technology, and more particularly to a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism. BACKGROUND

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

[0003] Single-longitudinal-mode fiber lasers are a prerequisite for achieving narrow linewidth laser output. Common implementation mechanisms include, but are not limited to, ultra-narrow band optical filters, temperature regulation, Fabry-Perot filters, etc. However, the above methods have problems such as complex manufacturing process, difficult parameter adjustment, and lack of practicality, and cannot be considered as the best mode selection scheme.

[0004] In addition, linewidth narrowing usually uses two methods: back Rayleigh scattering and stimulated Brillouin scattering. However, the above two methods require a long fiber extension line to enhance the intensity of the distributed feedback light, which not only introduces high 1 / f noise but also increases the instability of the fiber laser. SUMMARY

[0005] Therefore, the present application provides a narrow linewidth fiber laser system based on a self-injection locking feedback mechanism to at least solve some of the problems in the background art.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

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

[0008] The inside of the main cavity comprises a composite ring cavity filter for selecting a longitudinal mode. The composite ring cavity filter is connected in sequence with a polarization controller, a first erbium-doped fiber, a first wavelength division multiplexer, a second erbium-doped fiber and a first uniform fiber grating through a first circulator.

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

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

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

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

[0013] 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 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 connected to the 3 port of the first circulator; the output end of the fifth fiber coupler in the second sub-ring cavity is connected to the 1 port of the first circulator; and the 2 port 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 2x2 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 a 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] One signal input end of the second wavelength division multiplexer is connected to the other output end of the first fiber coupler as the input end of the erbium-doped fiber amplifier; 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 the 1 port of the second circulator; the 2 port of the second circulator is connected to the second uniform fiber grating, and the laser from the 3 port of the second circulator is output.

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

[0019] Preferably, the center 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] Compared with the prior art, the narrow linewidth fiber laser system based on a self-injection locking feedback mechanism has the following beneficial effects:

[0022] The narrow linewidth fiber laser system disclosed in the application introduces a self-injection locking feedback module, and is connected with a 90° Faraday rotating mirror through a fiber delay line, which not only prevents polarization fading, but also further increases 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 application, the output of single longitudinal mode laser is effectively ensured by the composite ring cavity filter and the saturable absorber arranged in the main cavity.

[0024] In the narrow linewidth fiber laser system disclosed in the application, the erbium-doped fiber amplifier optically amplifies the laser emitted by the main cavity, and the spontaneous emission optical amplification noise is effectively filtered out by arranging the second uniform fiber grating, thereby further improving the optical signal-to-noise ratio of the output laser. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0026] Figure 1 The narrow linewidth fiber laser system based on a self-injection locking feedback mechanism provided by the application is shown in the overall structure diagram.

[0027] Figure 2 The measured spectrum diagram of the first uniform fiber grating provided by the application is shown.

[0028] Figure 3 The measured spectrum diagram of the second uniform fiber grating provided by the application is shown.

[0029] Figure 4 The simulation transmission spectrum of the composite ring cavity filter and the reflection spectrum of the uniform grating provided by the application are shown, and the local enlarged view of the main resonance peak of the simulation transmission spectrum is shown in the inserted drawing.

[0030] Figure 5 The output laser spectrum diagram under different conditions provided by the application is shown.

[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 application is shown in the drawing, which is a scanning spectrum diagram of the output laser for one hour, and the scanning interval is 6 minutes.

[0032] Figure 7 The self-homodyne radio frequency spectrum of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present application without the composite ring cavity filter, saturable absorber and self-injection locking feedback module.

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

[0034] Figure 9 The homodyne radio frequency spectrum of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present application, and the drawing is a scanning homodyne radio frequency spectrum for one hour in the range of 0-100MHz, and the scanning time interval is 6 minutes.

[0035] Figure 10 The relationship curve of the output laser power of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present application with the pump power.

[0036] Figure 11 The frequency noise power spectral density and the linewidth value under different test times of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present application without the self-injection locking feedback module.

[0037] Figure 12 The frequency noise power spectral density and the linewidth value under different test times of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present application with the self-injection locking feedback module.

[0038] Figure 13 The comparison diagram of the relaxation oscillation of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism provided by the present application with and without the self-injection locking feedback module. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

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

[0041] The specific structure of the present application will be further described below. Figure 1 The specific structure of the present application will be further described below.

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

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

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

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

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

[0047] In the embodiment, the erbium-doped fiber amplifier comprises 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 one signal input end of the second wavelength division multiplexer 16 is connected with another output end of the first fiber coupler 12 as an input end of the erbium-doped fiber amplifier; a pump input end of the second wavelength division multiplexer 16 is connected with the second pump source 15; an output end of the second wavelength division multiplexer 16 is connected with one end of the third erbium-doped fiber 17, and another end of the third erbium-doped fiber 17 is connected with a 1 port of the second circulator 18; a 2 port of the second circulator 18 is connected with the second uniform fiber grating 19, and laser of the laser system is output from a 3 port of the second circulator 18 through a fiber pipe 182. In the embodiment, the 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 can further improve the optical signal-to-noise ratio 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, and the lengths thereof are 2.80 m and 3.00 m respectively, and the in-cavity stimulated radiation light amplification is realized by the pump source.

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

[0050] In the above embodiment, the first fiber coupler 12 is a 1x2 coupler, and the splitting ratio thereof is 50:50.

[0051] In the above embodiment, the polarization controller 06 is used for adjusting the in-cavity polarization state, and can be a straight-line polarization controller or a three-ring polarization controller.

[0052] In the embodiment, all the components are connected through fiber pipes, and the specific connection is as follows Figure 1As shown, the signal output end of the first wavelength division multiplexer 02 is connected with one end of the second erbium-doped fiber 03 through the first fiber pipeline 021, the other end of the second erbium-doped fiber 03 is connected with one end of the first uniform fiber grating 04 through the second fiber pipeline 031, the signal input end of the first wavelength division multiplexer 02 is connected with one end of the first erbium-doped fiber 05 through the third fiber pipeline 022, the other end of the first erbium-doped fiber 05 is connected with one end of the polarization controller 06 through the fourth fiber pipeline 051, the other end of the polarization controller 06 is connected with the 2 port of the first circulator 07 through the fifth fiber pipeline 061, the 3 port of the first circulator 07 is connected with one end of the input end of the second fiber coupler 08 through the sixth fiber pipeline 071, one end of the output end of the second fiber coupler 08 is connected with one end of the input end of the third fiber coupler 09 through the seventh fiber pipeline 081, the other end of the output end of the third fiber coupler 09 is connected with the other end of the input end of the second fiber coupler 08 through the eighth fiber pipeline 091, the other end of the output end of the third fiber coupler 09 is connected with one end of the input end of the fourth fiber coupler 10 through the ninth fiber pipeline 092, one end of the output end of the fourth fiber coupler 10 is connected with one end of the input end of the fifth fiber coupler 11 through the tenth fiber pipeline 101, the other end of the output end of the fifth fiber coupler 11 is connected with the other end of the input end of the fourth fiber coupler 10 through the eleventh fiber pipeline 111, the other end of the output end of the fifth fiber coupler 11 is connected with the 1 port of the first circulator 07 through the twelfth fiber pipeline 112, the other end of the first uniform fiber grating 04 is connected with the input end of the first fiber coupler 12 through the thirteenth fiber pipeline 041.

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

[0054] The other end of the output end of the first fiber coupler 12 is connected with the signal input end of the second wavelength division multiplexer 16 through the sixteenth fiber pipeline 122, the pump source two 15 is connected with the pump input end of the second wavelength division multiplexer 16, the signal output end of the second wavelength division multiplexer 16 is connected with one end of the third erbium-doped fiber 17 through the seventeenth fiber pipeline 161, the other end of the third erbium-doped fiber 17 is connected with the 1 port of the second circulator 18 through the eighteenth fiber pipeline 171, the 2 port of the second circulator 18 is connected with one end of the second uniform fiber grating 19 through the nineteenth fiber pipeline 181, the 3 port of the second circulator 18 outputs laser light through the twentieth fiber pipeline 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 length is 50 mm. Figure 2 As shown in the spectrum of the first uniform fiber grating 04, the center wavelength (λ), the reflection bandwidth (RB), and the reflectivity (R) are 1549.0753 nm, 0.0571 nm, and 80.95%, respectively. Figure 3 As shown in the spectrum of the second uniform fiber grating 19, the center wavelength (λ), the reflection bandwidth (RB), and the 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 pipeline 081, the eighth fiber pipeline 091, the ninth fiber pipeline 092, the tenth fiber pipeline 101, and the eleventh fiber pipeline 111, and the coupling ratio of the fiber coupler is 80:20. The cavity length difference of the composite ring cavity filter is 0.04 m, and the corresponding free spectral range is 5.18 GHz. As shown in the spectrum of the composite ring cavity filter, Figure 4 As shown in the spectrum of the composite ring cavity filter, the corresponding free spectral range is 0.04125 nm, which ensures that only one main resonance peak in the reflection bandwidth of the first uniform fiber grating 04 can obtain the maximum gain, and the full width at half maximum of the main resonance peak is 18.87 MHz, and the side mode suppression ratio is 3.81 dB, which ensures that only one main cavity longitudinal mode in the main cavity oscillates in the main resonance peak channel. After two mode selections and the use of a 0.8 m long saturable absorber, a stable single longitudinal mode laser output of the main cavity is ensured.

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

[0058] The application can narrow the laser linewidth at different test times through the self-injection locking feedback module.

[0059] The self-injection locking feedback module designed in the application not only uses a fiber delay line, but also uses a 90° Faraday rotator mirror, which not only prevents polarization fading, but also increases the optical path of the self-injection locking feedback light by one time based on the 100 m fiber delay line by reflecting the laser, thereby further narrowing the output laser linewidth.

[0060] As shown in the spectrum of the first uniform fiber grating 04, Figure 5As shown in FIG. 6, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the light path, 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 48.71 dB. When the erbium-doped fiber amplifier module is connected, due to the filtering of the second uniform fiber grating, the optical signal-to-noise ratio of the output laser is improved from the original > 48.71 dB to > 68.52 dB. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is improved from > 68.52 dB to > 75.04 dB. Figure 6 For the output laser spectrum of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism, the center wavelength of the output laser of the laser system is 1549.09 nm, and the maximum wavelength drift and peak power jitter of the output laser within 60 minutes are 0.0085 nm and 0.98 dB, respectively.

[0061] As shown in FIG. 6, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the light path, 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 48.71 dB. When the erbium-doped fiber amplifier module is connected, due to the filtering of the second uniform fiber grating, the optical signal-to-noise ratio of the output laser is improved from the original > 48.71 dB to > 68.52 dB. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is improved from > 68.52 dB to > 75.04 dB. Figure 7 Figure 8 Figure 9 As shown in FIG. 6, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the light path, 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 48.71 dB. When the erbium-doped fiber amplifier module is connected, due to the filtering of the second uniform fiber grating, the optical signal-to-noise ratio of the output laser is improved from the original > 48.71 dB to > 68.52 dB. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is improved from > 68.52 dB to > 75.04 dB.

[0062] As shown in FIG. 6, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the light path, 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 48.71 dB. When the erbium-doped fiber amplifier module is connected, due to the filtering of the second uniform fiber grating, the optical signal-to-noise ratio of the output laser is improved from the original > 48.71 dB to > 68.52 dB. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is improved from > 68.52 dB to > 75.04 dB. Figure 10 As shown in FIG. 6, due to the use of the erbium-doped fiber amplifier, the output laser power of the narrow linewidth fiber laser system based on the self-injection locking feedback mechanism can be as high as 157.20 mW.

[0063] As shown in FIG. 6, when the self-injection locking feedback module is not connected to the light path, the frequency noise spectrum line intersects with the beta dividing line at 4.745 kHz, and the linewidths under test times of 0.001 s, 0.002 s and 0.005 s are 36.167 kHz, 36.818 kHz and 40.802 kHz, respectively. As shown in FIG. 6, when the self-injection locking feedback loop is connected to the light path, the abscissa of the intersection point of the frequency noise spectrum line and the beta dividing line moves to the left to 2.090 kHz, and the linewidths under test times of 0.001 s, 0.002 s and 0.005 s are narrowed to 4.602 kHz, 9.449 kHz and 27.171 kHz, respectively. The use of the self-injection locking feedback module narrows the output laser linewidth under different test times. Figure 11 Figure 12 As shown in FIG. 6, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the light path, 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 48.71 dB. When the erbium-doped fiber amplifier module is connected, due to the filtering of the second uniform fiber grating, the optical signal-to-noise ratio of the output laser is improved from the original > 48.71 dB to > 68.52 dB. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is improved from > 68.52 dB to > 75.04 dB.

[0064] As shown in FIG. 6, when the self-injection locking feedback module and the erbium-doped fiber amplifier are not connected to the light path, 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 48.71 dB. When the erbium-doped fiber amplifier module is connected, due to the filtering of the second uniform fiber grating, the optical signal-to-noise ratio of the output laser is improved from the original > 48.71 dB to > 68.52 dB. When the self-injection locking feedback module is connected, the optical signal-to-noise ratio of the output laser is improved from > 68.52 dB to > 75.04 dB.​​​Figure 13 As shown, the frequency and intensity of the relaxation oscillation peak are 30.3 kHz and -72.90 dB / Hz, respectively, when the self-injection locking feedback module is not connected to the optical path. When the self-injection locking feedback module is connected to the optical path, the frequency of the relaxation oscillation peak shifts left to 18.7 kHz, and the intensity is -79.67 dB / Hz. The use of the self-injection locking feedback technology effectively improves the intracavity photon lifetime.

[0065] The various embodiments described in the specification are progressive in nature, and each embodiment highlights the differences from other embodiments. The same or similar parts between the embodiments can be mutually referred to. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, 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 a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform 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, The application relates to a laser system. The main cavity comprises a composite ring cavity filter for selecting a longitudinal mode; the composite ring cavity filter is 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 grating through a first circulator in sequence; the first erbium-doped fiber is used as a saturable absorber. An output end of the first uniform fiber grating is connected with an input end of a first fiber coupler; one output end of the first fiber coupler is connected with a fiber delay line and a Faraday rotator mirror in the self-injection locking feedback module in sequence; the Faraday rotator mirror has a rotation angle of 90 degrees; the other output end of the first fiber coupler is connected with an input end of the erbium-doped fiber amplifier. 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. One signal input end of the second wavelength division multiplexer is connected with the other output end of the first fiber coupler as an input end of the erbium-doped fiber amplifier; a pump input end of the second wavelength division multiplexer is connected with the second pump source; a signal output end of the second wavelength division multiplexer is connected with one end of the third erbium-doped fiber; the other end of the third erbium-doped fiber is connected with a 1 port of the second circulator; a 2 port of the second circulator is connected with the second uniform fiber grating; and laser light of the laser system is output from a 3 port of the second circulator. The length of the fiber delay line in the self-injection locking feedback module is 100 meters.

2. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, The composite ring cavity filter comprises a second fiber coupler, a third fiber coupler, a fourth fiber coupler and a fifth fiber coupler.

3. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, 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 connected with 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 connected with a 3 port of the first circulator; the output end of the fifth fiber coupler in the second sub-ring cavity is connected with a 1 port of the first circulator; and a 2 port of the first circulator is connected with one end of the polarization controller. 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.

4. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 3, wherein, The length of the first erbium-doped fiber is 0.8 m.

5. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, The pump input end of the first wavelength division multiplexer is connected with a first pump source.

6. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, The second pump source is a 980 nm semiconductor light source.

7. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, The center wavelength, reflection bandwidth and reflectivity of the second uniform fiber grating are 1549.0762 nm, 0.0832 nm and 92.41% respectively.

8. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, The polarization controller comprises an in-line polarization controller or a three-ring polarization controller.

9. The self-injection locking feedback mechanism based narrow linewidth fiber laser system of claim 1, wherein, ​

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