L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping

Abstract

The invention discloses an in-band pumping-based nanosecond pulse fiber laser with switchable L-band wavelength, which relates to the technical field of lasers and comprises an ECL narrow linewidth semiconductor seed source, a 2 * 1 magneto-optical switch, a coupler, an MEMS (micro-electromechanical system) variable optical attenuator, a first fiber isolator, a first signal pumping combiner, an acoustic optical modulator and a circulator. According to the in-band pumping-based nanosecond pulse fiber laser with the switchable L-waveband wavelength, an in-band pumping structure is adopted, so that the L-waveband laser gain is effectively improved, the ASE noise generated by a C-waveband is reduced, and the utilization rate of the in-band pumping-based nanosecond pulse fiber laser is improved. High-beam-quality laser output is realized by designing a fiber core pumping mode, reasonably optimizing an optical fiber welding program, optimizing a gain optical fiber coiling diameter and optimizing a main amplification stage optical path, and high-signal-to-noise-ratio output of a main amplifier is realized by reasonably planning gain distribution of each stage and designing a filtering isolation device. By designing a Bragg grating resonance structure, 1535nm in-band pump light is generated, the space utilization rate of the amplification module is improved, and the total cost of the laser is saved.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to an L-band wavelength switchable nanosecond pulse fiber laser based on same-band pumping. Background Art

[0002] Nanosecond pulse fiber lasers have a long transmission distance, good anti-interference performance, good beam quality, high single pulse energy and eye safety characteristics, so they have broad application prospects in the fields of atmospheric detection, aerospace remote sensing, laser processing, space optical communication and laser medical treatment. For example, wind field parameter measurement in the field of atmospheric remote sensing includes three-dimensional wind speed, shear prediction, etc. In addition, they are also used in the fields of medical precision endoscopy sensor detection light source, underwater disturbance detection, and micro-component three-dimensional molding. At the same time, 1572nm is on the absorption spectrum of CO2 gas, so the 1572nm laser also has important application prospects in the field of CO2 gas concentration measurement.

[0003] At present, the commonly used 1572nm pulse laser is a solid semiconductor laser as a pump source, and 1572nm high-energy pulse light is generated through Q-switching technology. The disadvantage of this method is that the wavelength accuracy and pulse width are difficult to control. At the same time, the system beam quality is restricted by the working material. The output spot usually presents a mixture of multiple modes, and the spot shape is highly distorted, which increases the difficulty of subsequent system alignment. When the traditional MOPA mode is used to design a 1572nm pulse fiber laser, the L-band gain is lower than the conventional C-band gain due to the influence of the erbium ion energy level structure, and the ASE noise generated during the amplification process is high. The fiber laser based on the same-band pump structure has a higher quantum efficiency according to quantum theory because the stimulated radiation occurs in the same energy band. At the same time, it has a better suppression effect on the ASE noise in the C band.

[0004] To this end, we propose an L-band wavelength-switchable nanosecond pulse fiber laser based on in-band pumping. Summary of the invention

[0005] The main purpose of the present invention is to provide an L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping, which can effectively solve the problems in the background technology.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: an L-band wavelength switchable nanosecond pulse fiber laser based on same-band pumping, including an ECL narrow-linewidth semiconductor seed source, a 2*1 magneto-optical switch, a coupler, a MEMS adjustable optical attenuator, a No. 1 optical fiber isolator, a No. 1 signal pump combiner, an acousto-optic modulator, a circulator, a No. 2 signal pump combiner, a No. 1 polarization-maintaining bandpass filter isolator, a No. 2 optical fiber isolator, a No. 3 signal pump combiner, a No. 2 polarization-maintaining bandpass filter isolator, a mode field adapter, a large mode field four-port circulator, a No. 4 signal pump combiner, a cladding light stripper, a No. 1 photodetector, a No. 2 photodetector, a No. 3 photodetector and a No. 4 photodetector;

[0007] The coupler is at least used to split the signal light;

[0008] The first optical fiber isolator and the second optical fiber isolator are at least used to isolate the return light in the amplifier stage and protect the key components in the optical path;

[0009] One end of the MEMS adjustable optical attenuator is provided with a local oscillator light output port, one end of the No. 1 optical fiber isolator is provided with a photodetector, one end of the No. 1 signal pump combiner is provided with a first multi-mode semiconductor pump laser, a first-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber is provided between the No. 1 signal pump combiner and the acousto-optic modulator, a second-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber is provided between the circulator and the No. 2 signal pump combiner, one end of the No. 2 signal pump combiner is provided with a second multi-mode semiconductor multi-mode pump laser, one end of the No. 2 signal pump combiner is provided with a fiber total reflection mirror, one end of the No. 1 polarization-maintaining bandpass filter isolator is provided with a seed module laser output port, one end of the No. 1 polarization-maintaining bandpass filter isolator is provided with a No. 2 photodetector, and one end of the No. 2 optical fiber isolator is provided with an amplifier module laser input port. A third multimode semiconductor pump laser is arranged at one end of the signal No. 3 pump combiner, a third polarization-maintaining erbium-yttrium co-doped double-clad optical fiber is arranged between the signal No. 3 pump combiner and the second polarization-maintaining bandpass filter isolator, a fourth large-mode-field erbium-yttrium co-doped double-clad optical fiber is arranged between the mode field adapter and the large-mode-field four-port circulator, a low-reflectivity FBG is arranged between the large-mode-field four-port circulator and the signal No. 4 pump combiner, a high-power multimode semiconductor multimode pump laser is arranged at one end of the signal No. 4 pump combiner, a polarization-maintaining erbium-yttrium co-doped double-clad optical fiber is arranged between the signal No. 4 pump combiner and the signal No. 4 pump combiner, a high-reflectivity FBG is arranged at one end of the cladding light stripper, and a laser return light input port, a No. 4 photodetector and an amplifier module laser output port are arranged at one end of the large-mode-field four-port circulator.

[0010] Preferably, the power amplifier of the L-band wavelength switchable nanosecond pulse fiber laser based on same-band pumping includes a first-stage multimode amplifier, a second-stage double-pass multimode amplifier, a third-stage multimode amplifier, a fourth-stage same-band pumped multimode amplifier and a 1535nm pump light multimode amplifier.

[0011] Preferably, the first-stage single-mode amplifier is a 10 / 128 first polarization-maintaining erbium-yttrium co-doped fiber that is forward pumped or backward pumped; the second-stage multimode amplifier is a 10 / 128 second polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; the third-stage multimode amplifier is a 10 / 128 third polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; the main-stage multimode amplifier is a 25 / 300 fourth polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; and the 1535nm pump light multimode amplifier is a 10 / 128 polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped.

[0012] Preferably, the main-stage multimode amplifier can achieve fundamental frequency light output with high beam quality by adopting a core pumping method, selecting a four-channel circulator, and optimizing the winding diameter of the fourth polarization-maintaining ytterbium-doped optical fiber and the passive optical fiber length.

[0013] Preferably, the third-stage and main-stage multi-mode amplifiers achieve high single-pulse energy output by reasonably allocating gain and optimizing the passive optical fiber length to increase the stimulated Brillouin scattering threshold.

[0014] Preferably, the large mode field four-port circulator has a mode field adaptation function, and the optical fiber of port 1 is PM-GDF-10 / 125, the optical fiber of port 2 is PLMA-GDF-25 / 300, the optical fiber of port 3 is PLMA-GDF-25 / 300, the optical fiber of port 4 is PM-GDF-10 / 125, and the 1% tap optical fiber of port is PM-GDF-10 / 125.

[0015] Preferably, the ultra-stable seed laser source of the ECL narrow linewidth semiconductor seed source has an output wavelength of 1572.018nm and 1572.480nm, a wavelength drift of less than 2pm after 12 hours of continuous operation, and a power stability RMS value of less than 1%; the temperature drift of the working environment of the ultra-stable seed laser source of the ECL narrow linewidth semiconductor seed source is less than 0.1°C per hour.

[0016] Preferably, the MEMS adjustable optical attenuator can change the local oscillator output power attenuation coefficient by adjusting the current, so as to achieve adjustable local oscillator light within the range of 0 to 2.3 mW.

[0017] Preferably, the operating center wavelength of the polarization-maintaining bandpass filter isolator is 1572 nm, the 0.5 dB filtering bandwidth is 2 nm, and the 25 dB suppression bandwidth is 20 nm.

[0018] Preferably, the low-reflectivity FBG has a working center wavelength of 1535 nm, a reflectivity of 10%, a 3dB bandwidth of 0.2 nm, an optical fiber model of PM1550-XP, and a working mode of slow axis operation; the high-reflectivity FBG has a working center wavelength of 1535 nm, a reflectivity of 99%, a 3dB bandwidth of 1 nm, an optical fiber model of PM1550-XP, and a working mode of slow axis operation.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] By designing the core pumping method, optimizing the winding of the gain fiber, and screening the four-port circulator, the beam quality of the pulsed light is optimized. At the same time, the same-band pumping structure is adopted and the filter isolator is selected to effectively improve the L-band laser gain, reduce the ASE noise generated by the C-band, and achieve high signal-to-noise ratio pulse light output; at the same time, the pump distribution in the multi-stage amplification is optimized to achieve a high Brillouin scattering threshold, thereby achieving high single pulse energy output. Compared with traditional solid L-band lasers, the optical path of the present invention adopts an all-fiber body, so the present invention has the advantages of simple and compact structure and high conversion efficiency, and can be used in fields such as CO2 gas differential radar detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0022] Figure 2 It is a first split schematic diagram of the overall structure of the present invention;

[0023] Figure 3 This is a second split schematic diagram of the overall structure of the present invention.

[0024] In the figure: 1. ECL narrow linewidth semiconductor seed source; 2. 2*1 magneto-optic switch; 3. Coupler; 4. MEMS adjustable optical attenuator; 5. Local oscillator light output port; 6. No. 1 optical fiber isolator; 7. No. 1 photodetector; 8. First multi-mode semiconductor pump laser; 9. No. 1 signal pump combiner; 10. First polarization-maintaining erbium-yttrium co-doped double-clad fiber; 11. Acousto-optic modulator; 12. Circulator; 13. Second polarization-maintaining erbium-yttrium co-doped double-clad fiber; 14. No. 2 signal pump combiner; 15. Second multi-mode semiconductor multi-mode pump laser; 16. Optical fiber total reflection mirror; 17. No. 1 polarization-maintaining bandpass filter isolator; 18. Seed module laser output port; 19. No. 2 photodetector; 20. Amplifier module laser output port Entrance; 21. No. 2 optical fiber isolator; 22. No. 3 signal pump combiner; 23. No. 3 multi-mode semiconductor pump laser; 24. No. 3 polarization-maintaining erbium-yttrium co-doped double-clad optical fiber; 25. No. 2 polarization-maintaining bandpass filter isolator; 26. No. 3 photodetector; 27. Mode field adapter; 28. No. 4 large mode field erbium-yttrium co-doped double-clad optical fiber; 29. ​​Large mode field four-port circulator; 30. Low reflectivity FBG; 31. High power multi-mode semiconductor multi-mode pump laser; 32. No. 4 signal pump combiner; 33. Polarization-maintaining erbium-yttrium co-doped double-clad optical fiber; 34. Cladding light stripper; 35. High reflectivity FBG; 36. Laser return light input port; 37. No. 4 photodetector; 38. Amplifier module laser output port. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] like Figure 1-3 As shown, the L-band wavelength switchable nanosecond pulse fiber laser based on same-band pumping provided by the embodiment of the present invention includes an ECL narrow-linewidth semiconductor seed source 1, a 2*1 magneto-optical switch 2, a coupler 3, a MEMS adjustable optical attenuator 4, a No. 1 optical fiber isolator 6, a No. 1 signal pump combiner 9, an acousto-optic modulator 11, a circulator 12, a No. 2 signal pump combiner 14, a No. 1 polarization-maintaining bandpass filter isolator 17, a No. 2 optical fiber isolator 21, a No. 3 signal pump combiner 22, a No. 2 polarization-maintaining bandpass filter isolator 25, a mode field adapter 27, a large mode field four-port circulator 29, a No. 4 signal pump combiner 32, a cladding light stripper 34, a No. 1 photodetector 7, a No. 2 photodetector 19, a No. 3 photodetector 26 and a No. 4 photodetector 37;

[0027] The coupler 3 is at least used to split the signal light;

[0028] The first optical fiber isolator 6 and the second optical fiber isolator 21 are used at least to isolate the return light in the amplifier stage and protect the key components in the optical path;

[0029] A local oscillator light output port 5 is provided at one end of the MEMS variable optical attenuator 4, a photodetector 7 is provided at one end of the No. 1 optical fiber isolator 6, a first multimode semiconductor pump laser 8 is provided at one end of the No. 1 signal pump combiner 9, a first polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 10 is provided between the No. 1 signal pump combiner 9 and the acousto-optic modulator 11, and a second polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 10 is provided between the circulator 12 and the No. 2 signal pump combiner 14. 3. A second multimode semiconductor multimode pump laser 15 is disposed at one end of the second signal pump combiner 14. A fiber total reflection mirror 16 is disposed at one end of the second signal pump combiner 14. A seed module laser output port 18 is disposed at one end of the first polarization-maintaining bandpass filter isolator 17. A second photodetector 19 is disposed at one end of the first polarization-maintaining bandpass filter isolator 17. An amplifier module laser input port 20 is disposed at one end of the second fiber isolator 21. The third signal pump A third multimode semiconductor pump laser 23 is arranged at one end of the pump combiner 22, a third polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 24 is arranged between the third signal pump combiner 22 and the second polarization-maintaining bandpass filter isolator 25, a fourth large-mode-field erbium-yttrium co-doped double-clad optical fiber 28 is arranged between the mode field adapter 27 and the large-mode-field four-port circulator 29, and a low-reflectivity FBG 30 is arranged between the large-mode-field four-port circulator 29 and the fourth signal pump combiner 32. A high-power multimode semiconductor multimode pump laser 31 is arranged at one end of the No. 4 signal pump combiner 32, a polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 33 is arranged between the No. 4 signal pump combiner 32 and the No. 4 signal pump combiner 32, a high-reflectivity FBG35 is arranged at one end of the cladding light stripper 34, and a laser return light input port 36, a No. 4 photodetector 37 and an amplifier module laser output port 38 are arranged at one end of the large mode field four-port circulator 29.

[0030] In one embodiment provided by the present invention, a power amplifier of an L-band wavelength switchable nanosecond pulse fiber laser based on co-band pumping includes a first-stage multi-mode amplifier, a second-stage dual-pass multi-mode amplifier, a third-stage multi-mode amplifier, a fourth-stage co-band pumping multi-mode amplifier and a 1535nm pump light multi-mode amplifier, and adopts a co-band pumping structure to effectively improve the L-band laser gain and reduce the ASE noise generated in the C-band.

[0031] In another embodiment provided by the present invention, the first-stage single-mode amplifier is a 10 / 128 first polarization-maintaining erbium-yttrium co-doped fiber that is forward pumped or backward pumped; the second-stage multimode amplifier is a 10 / 128 second polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; the third-stage multimode amplifier is a 10 / 128 third polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; the main-stage multimode amplifier is a 25 / 300 fourth polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; and the 1535nm pump light multimode amplifier is a 10 / 128 polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped. By reasonably planning the gain distribution of each stage and designing filtering and isolation devices, a high signal-to-noise ratio output of the main amplifier is achieved.

[0032] In another embodiment provided by the present invention, the main-stage multimode amplifier can achieve high-beam-quality fundamental frequency light output by adopting a core pumping method, selecting a four-channel circulator, optimizing the winding diameter of the fourth polarization-maintaining ytterbium-doped fiber and the passive fiber length; and achieve high-beam-quality laser output by designing a core pumping method, reasonably optimizing the fiber fusion procedure, optimizing the gain fiber winding diameter, and optimizing the main amplifier stage optical path.

[0033] In one embodiment provided by the present invention, the third-stage and main-stage multimode amplifiers achieve high single-pulse energy output by reasonably allocating gain and optimizing the passive optical fiber length to increase the stimulated Brillouin scattering threshold, and generate 1535nm co-band pump light by designing a Bragg grating resonant structure, thereby improving the space utilization of the amplification module and saving the total cost of the laser.

[0034] In another embodiment provided by the present invention, the large mode field four-port circulator 29 has a mode field adaptation function, wherein the optical fiber at port 1 is PM-GDF-10 / 125, the optical fiber at port 2 is PLMA-GDF-25 / 300, the optical fiber at port 3 is PLMA-GDF-25 / 300, the optical fiber at port 4 is PM-GDF-10 / 125, and the tap optical fiber at port 1% is PM-GDF-10 / 125. The large mode field four-port circulator 29 is convenient for adapting the mode field and can improve the effect of stable output.

[0035] In another embodiment provided by the present invention, the ultra-stable seed laser source of the ECL narrow linewidth semiconductor seed source 1 has an output wavelength of 1572.018nm and 1572.480nm, a wavelength drift of less than 2pm after continuous operation for 12 hours, and a power stability RMS value of less than 1%; the temperature drift of the ultra-stable seed laser source of the ECL narrow linewidth semiconductor seed source 1 in the working environment per hour is less than 0.1°C, and the output power of the ECL narrow linewidth semiconductor seed source 1 is 5mW, and the output is a PM1550 fiber optic jumper.

[0036] In an embodiment provided by the present invention, the MEMS adjustable optical attenuator 4 can change the attenuation coefficient of the local oscillator output power by adjusting the current, so as to achieve adjustable local oscillator light within the range of 0 to 2.3 mW.

[0037] In another embodiment provided by the present invention, the operating center wavelength of the polarization-maintaining bandpass filter isolator 17 is 1572 nm, the 0.5 dB filtering bandwidth is 2 nm, and the 25 dB suppression bandwidth is 20 nm. The polarization-maintaining bandpass filter isolator 17 can achieve a better filtering effect when in use.

[0038] In another embodiment provided by the present invention, the working center wavelength of the low-reflectivity FBG30 is 1535nm, the reflectivity is 10%, the 3dB bandwidth is 0.2nm, the optical fiber model is PM1550-XP, and the working mode is slow axis operation; the working center wavelength of the high-reflectivity FBG35 is 1535nm, the reflectivity is 99%, the 3dB bandwidth is 1nm, the optical fiber model is PM1550-XP, and the working mode is slow axis operation.

[0039] It should be noted that the present invention is an L-band wavelength switchable nanosecond pulse fiber laser based on the same-band pump. When in use, each fiber optic device is connected by a matching passive transmission fiber. The fiber optic devices are all selected to have a working center wavelength of 1572nm, and the 1.5um band contains both C-band and L-band low-loss devices. The ECL narrow linewidth semiconductor seed source 1 power supply is fused with the 2*1 magneto-optical switch 2 through optical fiber, and the dual seed wavelength switchability is achieved by giving the 2*1 magneto-optical switch 2 high and low level signals;

[0040] The coupler 3 divides the seed output light into two paths, one path is output as the local oscillator through the MEMS adjustable optical attenuator 4 from the local oscillator light output port 5, and the other path enters the optical path amplification stage. The above optical paths are connected by optical fiber fusion. One path of the output light from the coupler 3 enters the No. 1 optical fiber isolator 6, and the monitoring signal is collected by the No. 1 photodetector 7. The signal pump combiner 9 is responsible for combining the laser beams of the first multi-mode semiconductor pump laser 8 and the No. 1 optical fiber isolator 6, and enters the first-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 10 to realize the first-stage laser pre-amplification. The amplified laser is modulated into a pulse light by the acousto-optic modulator 11 and enters Enter the second stage amplification, the above optical paths are connected by fiber fusion splicing; the type of the No. 1 signal pump combiner 9 is 1+1×1, and its signal end and common end pigtails are passive double-clad optical fibers with a core diameter of 10μm and an inner cladding diameter of 125μm; its pump end pigtail is a multimode optical fiber with a core diameter of 105μm, a cladding diameter of 125μm, and a core numerical aperture of 0.22; the second polarization-maintaining double-clad erbium-yttrium co-doped optical fiber 13 is an active double-clad EYDF with a core diameter of 10μm, an inner cladding diameter of 128μm, a core numerical aperture of 0.2, and an optical fiber length of 5m;

[0041] The pulse light output by the acousto-optic modulator 11 enters port 1 of the circulator device 12, and is output from port 2 of the circulator device 12, and enters the second-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 13. The second multimode semiconductor pump laser 15 is combined into the gain optical fiber through the signal pump combiner 14. The output laser is reflected by the optical fiber total reflection mirror 16 and amplified again by the second stage, enters port 2 of the circulator device 12 and is connected to the first polarization-maintaining bandpass filter optical fiber isolator 17 through port 3, and finally emits from the seed module laser output port 18. The second signal pump combiner 14 is of type (1+1)×1, and its signal end and common end pigtails are passive double-clad optical fibers with a core diameter of 10μm and an inner cladding diameter of 125μm; its pump end pigtail is a multimode optical fiber with a core diameter of 105μm and an inner cladding diameter of 125μm. The core diameter of the optical fiber is 125μm, and the core numerical aperture is 0.22; the polarization-maintaining double-clad erbium-yttrium co-doped optical fiber 13 is an active double-clad EYDF, with a core diameter of 10μm, an inner cladding diameter of 128μm, a core numerical aperture of 0.2, and a fiber length of 4.5m. The second photodetector 19 is used to monitor the second-stage amplification, and from 1 to 19 can be used as independent modules to achieve low-energy laser output; the polarization-maintaining double-clad erbium-yttrium co-doped optical fiber 13 is an active double-clad EYDF, with a core diameter of 10μm, an inner cladding diameter of 128μm, a core numerical aperture of 0.2, and a fiber length of 4.5m; the optical fiber of the polarization-maintaining bandpass filter optical fiber isolator is PM1550 optical fiber, the filtering center wavelength is 1572nm, and the filtering width is 2nm; the above devices are all connected by optical fiber fusion splicing;

[0042] The laser input port 20 of the amplifier module can be connected to the laser output port 18 of the seed module through a flange. After passing through the No. 2 optical fiber isolator 21, the laser is injected into the third-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber 24 through the signal pump combiner 22 and the pumping light beam of the third multimode semiconductor pump laser 23, and then enters the main amplifier stage through the No. 2 polarization-maintaining bandpass filter optical fiber isolator 25. The No. 3 photodetector 26 is used to monitor the third-stage amplification; the No. 3 signal pump combiner 22 is of type (1+1)×1, and its signal end and common end pigtails are passive double-clad optical fibers with a core diameter of 10μ m, the inner cladding diameter is 125μm; its pump end pigtail is a multimode optical fiber, its core diameter is 105μm, its cladding diameter is 125μm, and its core numerical aperture is 0.22; the polarization-maintaining double-clad erbium-yttrium co-doped optical fiber 24 is an active double-clad EYDF, its core diameter is 10μm, its inner cladding diameter is 128μm, its core numerical aperture is 0.2, and its optical fiber length is 3.5m; the optical fiber of the polarization-maintaining bandpass filter optical fiber isolator is PM1550 optical fiber, the filtering center wavelength is 1572nm, and the filtering width is 2nm; the above devices are all connected by optical fiber fusion splicing;

[0043] The main amplifier stage is composed of a mode field adapter 27, a fourth-stage large mode field erbium-yttrium co-doped double-clad fiber 28, a second large mode field four-port circulator 29, a low reflectivity FBG 30, a high-power multi-mode semiconductor pump laser 31, a signal pump combiner 32, a polarization-maintaining erbium-yttrium co-doped double-clad fiber 33, a CPS 34, a high reflectivity FBG 35, and a photodetector 37; in addition, the circulator port 3 is used as the amplification module laser output port 38, and the circulator port 4 is used as the laser return light input port 36. In the main amplifier stage, the mode field adapter 2 7 is drawn from PLMA-GDF-10 / 125 and PLMA-GDF-25 / 300 optical fibers; TCIR port 1 is connected to low-reflectivity FBG30, port 2 is connected to the fourth-level large-mode-field erbium-yttrium co-doped double-clad optical fiber 28, port 3 is the large-mode-field 25 / 300GDF output port 38 packaged in a 3mm sleeve, and port 4 is the 10 / 125GDF return light output port 36 packaged in a 3mm sleeve; the reflectivity of the low-reflectivity FBG30 is 10%, and the central wavelength of the grating is 1535nm; high-power multi- The semiconductor pump laser 31 uses a semiconductor laser with an operating wavelength of 940nm and a maximum pump power of 30W; the type of the signal pump combiner 32 is (2+1)×1, and its signal end and common end pigtails are passive double-clad optical fibers with a core diameter of 10μm and an inner cladding diameter of 125μm; its pump end pigtail is a multimode optical fiber with a core diameter of 105μm, a cladding diameter of 125μm, and a core numerical aperture of 0.22; the polarization-maintaining double-clad ytterbium-doped optical fiber 33 is an active double-clad EYDF, and its fiber The core diameter is 25μm, the inner cladding diameter is 300μm, the core numerical aperture is 0.09, and the fiber length is 3.18m; the pigtail of CPS34 is a passive double-clad fiber with a core diameter of 10μm and an inner cladding diameter of 125μm; the high-reflectivity FBG35 has a reflectivity of 99% and a grating center wavelength of 1535nm; the photodetector 37 is used to monitor the main amplifier stage, and the above periods are all connected by fiber fusion splicing; the winding method of the polarization-maintaining erbium-yttrium co-doped fiber 33 needs to be optimized by output beam quality and power.

[0044] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. L-band wavelength switchable nanosecond pulse fiber laser based on co-band pumping, characterized by: It includes an ECL narrow linewidth semiconductor seed source (1), a 2*1 magneto-optical switch (2), a coupler (3), a MEMS adjustable optical attenuator (4), a No. 1 optical fiber isolator (6), a No. 1 signal pump combiner (9), an acousto-optic modulator (11), a circulator (12), a No. 2 signal pump combiner (14), a No. 1 polarization-maintaining bandpass filter isolator (17), a No. 2 optical fiber isolator (21), a No. 3 signal pump combiner (22), a No. 2 polarization-maintaining bandpass filter isolator (25), a mode field adapter (27), a large mode field four-port circulator (29), a No. 4 signal pump combiner (32), a cladding light stripper (34), a No. 1 photodetector (7), a No. 2 photodetector (19), a No. 3 photodetector (26) and a No. 4 photodetector (37); The coupler (3) is at least used to split the signal light; The first optical fiber isolator (6) and the second optical fiber isolator (21) are at least used to isolate the return light in the amplifier stage and protect key components in the optical path; One end of the MEMS adjustable optical attenuator (4) is provided with a local oscillator light output port (5), one end of the first optical fiber isolator (6) is provided with a photodetector (7), one end of the first signal pump combiner (9) is provided with a first multi-mode semiconductor pump laser (8), a first-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber (10) is provided between the first signal pump combiner (9) and the acousto-optic modulator (11), and a second-stage polarization-maintaining erbium-yttrium co-doped double-clad optical fiber is provided between the circulator (12) and the second signal pump combiner (14). (13), a second multimode semiconductor multimode pump laser (15) is disposed at one end of the second signal pump combiner (14), a fiber total reflection mirror (16) is disposed at one end of the second signal pump combiner (14), a seed module laser output port (18) is disposed at one end of the first polarization-maintaining bandpass filter isolator (17), a second photodetector (19) is disposed at one end of the first polarization-maintaining bandpass filter isolator (17), an amplifier module laser input port (20) is disposed at one end of the second fiber isolator (21), and the three A third multimode semiconductor pump laser (23) is arranged at one end of the No. 3 signal pump combiner (22); a third polarization-maintaining erbium-yttrium co-doped double-clad optical fiber (24) is arranged between the No. 3 signal pump combiner (22) and the No. 2 polarization-maintaining bandpass filter isolator (25); a fourth large-mode-field erbium-yttrium co-doped double-clad optical fiber (28) is arranged between the mode field adapter (27) and the large-mode-field four-port circulator (29); a low-reflectivity FBG (30) is arranged between the large-mode-field four-port circulator (29) and the No. 4 signal pump combiner (32); ), a high-power multi-mode semiconductor multi-mode pump laser (31) is arranged at one end of the No. 4 signal pump combiner (32), a polarization-maintaining erbium-yttrium co-doped double-clad optical fiber (33) is arranged between the No. 4 signal pump combiner (32) and the No. 4 signal pump combiner (32), a high-reflectivity FBG (35) is arranged at one end of the cladding light stripper (34), and a laser return light input port (36), a No. 4 photodetector (37) and an amplifier module laser output port (38) are arranged at one end of the large mode field four-port circulator (29).

2. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The power amplifier of the L-band wavelength switchable nanosecond pulse fiber laser based on same-band pumping includes a first-stage multimode amplifier, a second-stage double-pass multimode amplifier, a third-stage multimode amplifier, a fourth-stage same-band pumping multimode amplifier and a 1535nm pump light multimode amplifier.

3. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The first-stage single-mode amplifier is a 10 / 128 first polarization-maintaining erbium-yttrium co-doped fiber that is forward pumped or backward pumped; the second-stage multi-mode amplifier is a 10 / 128 second polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; the third-stage multi-mode amplifier is a 10 / 128 third polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; the main-stage multi-mode amplifier is a 25 / 300 fourth polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped; and the 1535nm pump light multi-mode amplifier is a 10 / 128 polarization-maintaining erbium-yttrium co-doped fiber that is unidirectionally pumped or bidirectionally pumped.

4. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The main-stage multimode amplifier can achieve fundamental frequency light output with high beam quality by adopting a core pumping method, selecting a four-channel circulator, and optimizing the winding diameter of the fourth polarization-maintaining ytterbium-doped optical fiber and the length of the passive optical fiber.

5. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The third-stage and main-stage multi-mode amplifiers achieve high single-pulse energy output by reasonably allocating gain and optimizing the passive optical fiber length to increase the stimulated Brillouin scattering threshold.

6. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The large mode field four-port circulator (29) has a mode field adaptation function, wherein the optical fiber of port 1 is PM-GDF-10 / 125, the optical fiber of port 2 is PLMA-GDF-25 / 300, the optical fiber of port 3 is PLMA-GDF-25 / 300, the optical fiber of port 4 is PM-GDF-10 / 125, and the tap optical fiber of port 1% is PM-GDF-10 / 125.

7. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The ultra-stable seed laser source of the ECL narrow linewidth semiconductor seed source (1) has an output wavelength of 1572.018 nm and 1572.480 nm, a wavelength drift of less than 2 pm after continuous operation for 12 hours, and a power stability RMS value of less than 1%; the temperature drift of the working environment of the ultra-stable seed laser source of the ECL narrow linewidth semiconductor seed source (1) is less than 0.1°C per hour.

8. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The MEMS adjustable optical attenuator (4) can change the local oscillator output power attenuation coefficient by adjusting the current, thereby achieving adjustable local oscillator light within the range of 0 to 2.3 mW.

9. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The polarization-maintaining bandpass filter isolator (17) has an operating center wavelength of 1572 nm, a 0.5 dB filtering bandwidth of 2 nm, and a 25 dB suppression bandwidth of 20 nm.

10. The L-band wavelength switchable nanosecond pulse fiber laser based on in-band pumping according to claim 1, characterized in that: The low reflectivity FBG (30) has an operating center wavelength of 1535 nm, a reflectivity of 10%, a 3dB bandwidth of 0.2 nm, an optical fiber model of PM1550-XP, and an operating mode of slow axis operation. The high reflectivity FBG (35) has an operating center wavelength of 1535 nm, a reflectivity of 99%, a 3dB bandwidth of 1 nm, an optical fiber model of PM1550-XP, and an operating mode of slow axis operation.

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