2 [mu] m large-energy solid two-way amplifier based on single-frequency pulse optical fiber preceding stage

Abstract

A 2-micron large-energy solid two-way amplifier based on a single-frequency pulse optical fiber preceding stage can make full use of the small signal amplification capacity of optical fiber laser and the energy extraction capacity of solid laser, and meanwhile the problem that energy is difficult to improve due to the stimulated Brillouin scattering effect in an optical fiber is solved. And high-stability, high-repetition-frequency and large-energy single-frequency pulse laser output can be realized. The all-fiber cascade amplifier comprises an all-fiber cascade amplifier and a solid two-way amplifier, according to the all-fiber cascade amplifier, a continuous narrow-linewidth fiber laser is adopted as a seed source, continuous light is modulated into pulse light through an acousto-optic modulator, and the waveform, the pulse width and the repetition frequency of output pulse laser are adjusted; the modulated pulse light adopts a main oscillation power amplification structure and is preliminarily amplified by a polarization maintaining optical fiber amplifier; the solid-state amplifier adopts a two-way amplification structure, and further high-efficiency amplification is realized through solid-state two-way amplification. The whole laser system is compact in structure, stable, adjustable in parameter and capable of meeting application requirements of different scenes.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a 2μm high-energy solid double-pass amplifier based on a single-frequency pulse optical fiber front stage. Background Art

[0002] 2μm band single-frequency pulse laser has the characteristics of high atmospheric transmittance, good coherence, low background noise, strong CO2 absorption, etc. It has important applications in coherent laser radar, differential absorption radar, environmental monitoring and nonlinear frequency conversion. In recent years, 2μm coherent laser radar has been widely used in airport wind shear detection to ensure aviation safety. It can also be used in wind power generation, precision airdrop and other fields. CO2 differential absorption radar can monitor greenhouse gases such as CO2 in the atmosphere with high precision and high resolution, which is conducive to achieving global carbon balance and has important guiding significance for my country's "dual carbon" strategic plan. In 2μm laser radar, 2μm single-frequency light source is the core device. In order to improve the detection capability of the radar system, the light source should have the characteristics of high energy, high repetition rate, high frequency stability, hundred nanosecond pulse width, megahertz line width, etc.

[0003] Traditional 2μm single-frequency pulse lasers are mainly implemented with solid injection-locked lasers and amplifiers. Limited by the mechanical motion mechanism of PZT, the output laser repetition frequency is only in the hundreds of hertz range, making it difficult to achieve high repetition rate output. In addition, the change in cavity length of the injection-locked mechanism will deteriorate the stability of the laser frequency, affecting radar detection accuracy and increasing random errors. In contrast, the directly modulated multi-stage traveling wave amplifier does not need to control the cavity length, and the frequency stability depends only on the seed light, which greatly improves the frequency stability of the single-frequency pulse laser and makes it easier to obtain high-repetition-rate single-frequency pulse lasers, thereby improving the detection accuracy and detection capability of the radar system. The 2μm all-fiber directly modulated single-frequency pulse fiber amplifier has a compact structure and high stability, but due to the influence of nonlinear effects such as stimulated Brillouin scattering (SBS), the output energy is difficult to increase to the mJ level, making it difficult to meet the application requirements of special scenarios. Summary of the invention

[0004] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide a 2μm high-energy solid-state dual-pass amplifier based on a single-frequency pulse fiber front stage, which can fully utilize the small signal amplification capability of the fiber laser and the energy extraction capability of the solid laser, and can achieve high repetition rate and high-energy narrow-linewidth pulse laser output, avoiding the problem of difficulty in increasing energy due to the stimulated Brillouin scattering effect in the optical fiber, and can achieve high stability, high repetition rate, and high-energy single-frequency pulse laser.

[0005] The technical scheme of the present invention is: the 2μm high-energy solid two-way amplifier based on a single-frequency pulse fiber front stage comprises: an all-fiber cascade amplifier and a solid two-way amplifier; the all-fiber cascade amplifier adopts a low-power continuous narrow-linewidth fiber laser as a seed source, uses an acousto-optic modulator to modulate the continuous light into pulse light, and adjusts the waveform, pulse width and repetition frequency of the output pulse laser; the modulated pulse light adopts a main oscillation power amplification structure, and is preliminarily amplified by a polarization-maintaining fiber preamplifier and a fiber main amplifier respectively; the output wavelength of the solid pump source is at the strongest absorption peak of the solid, and is further amplified by the solid two-way amplifier.

[0006] The beneficial technical effects of the present invention are as follows:

[0007] 1. The present invention adopts the fiber-solid hybrid amplification method, which fully utilizes the small signal amplification capability of the fiber and the energy extraction capability of the solid. Large mode field, highly doped, short-length optical fiber is used to suppress the stimulated Brillouin scattering effect for preliminary amplification; the solid amplifier can avoid the introduction of stimulated Brillouin scattering effect. Finally, on the basis of high repetition rate, a high-energy 2μm single-frequency pulse laser is achieved.

[0008] 2. The present invention innovatively adopts a multi-stage traveling wave amplification scheme. The frequency stability of the output single-frequency pulse laser depends only on the narrow-linewidth fiber seed source. Compared with the injection locking method, this method does not require adjustment of the laser oscillator cavity length and can achieve 2μm single-frequency pulse laser with high frequency stability.

[0009] 3. The present invention innovatively adopts a solid double-pass amplification structure, which greatly improves the laser amplification efficiency and output energy. The solid part is composed only of the amplifier, which improves the efficiency while reducing the use of space components. The entire laser system has a compact structure and stable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the overall structure of the 2μm high-energy solid-state double-pass amplifier based on the single-frequency pulse fiber front stage of the present invention.

[0011] Figure 2 It is a schematic structural diagram of the all-fiber cascade amplifier of the present invention, which is a 2μm high-energy solid-state double-pass amplifier based on a single-frequency pulse fiber front stage.

[0012] Figure 3 It is a structural schematic diagram of a 2μm high-energy solid double-pass amplifier based on a single-frequency pulse fiber front stage of the present invention.

[0013] In the figure: 1—narrow linewidth fiber laser, 2—coupler, 3—acousto-optic modulator, 4—first fiber isolator, 5—fiber laser, 6—wavelength division multiplexer, 7—first gain fiber, 8—first bandpass filter, 9—second isolator, 10—first semiconductor laser, 11—first fiber combiner, 12—second gain fiber, 13—second bandpass filter, 14—third fiber isolator, 15—second fiber combiner, 16—second semiconductor laser, 17—third gain fiber, 18—third bandpass filter, 19—fourth fiber isolator, 20—third fiber combiner, 21—third Semiconductor laser, 22—fourth gain fiber, 23—fourth bandpass filter, 24—fifth fiber isolator, 25—output end cap, 26—single-frequency pulse fiber cascade amplifier, 27—first lens, 28—second lens, 29—third lens, 30—first half-wave plate, 31—spatial optical isolator, 32—second half-wave plate, 33—first reflector, 34—second reflector, 35—end-face pump gain crystal, 36—quarter wave plate, 37—0° reflector, 38—solid-state amplifier pump source, 39—fourth lens, 40—third reflector, 41—fourth reflector. DETAILED DESCRIPTION

[0014] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0015] It should be noted that the term "comprises" and any variations in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or equipment.

[0016] like Figure 1As shown in the figure, this 2μm high-energy solid-state dual-pass amplifier based on a single-frequency pulse fiber front stage includes: an all-fiber cascade amplifier and a solid-state dual-pass amplifier; the all-fiber cascade amplifier uses a low-power continuous narrow-linewidth fiber laser as a seed source, uses an acousto-optic modulator to modulate the continuous light into pulse light, and adjusts the waveform, pulse width and repetition frequency of the output pulse laser; the modulated pulse light adopts a master oscillator power amplification structure, and is preliminarily amplified by a polarization-maintaining fiber preamplifier and a fiber main amplifier respectively; the output wavelength of the solid pump source is at the strongest absorption peak of the solid, and is further amplified by the solid-state dual-pass amplifier. Finally, a 2μm high-repetition-rate, high-energy single-frequency pulse laser output is achieved. All modules of the front-stage fiber part adopt a full-fiber fusion method, which has a compact structure and stable performance; the back-stage solid amplification part is conducive to the generation of high-energy and high-peak-power pulse laser output. The entire laser has a compact structure, a stable system, and adjustable parameters.

[0017] The beneficial technical effects of the present invention are as follows:

[0018] 1. The present invention adopts the fiber-solid hybrid amplification method, which fully utilizes the small signal amplification capability of the fiber and the energy extraction capability of the solid. Large mode field, highly doped, short-length optical fiber is used to suppress the stimulated Brillouin scattering effect for preliminary amplification; the solid amplifier can avoid the introduction of stimulated Brillouin scattering effect. Finally, on the basis of high repetition rate, a high-energy 2μm single-frequency pulse laser is achieved.

[0019] 2. The present invention innovatively adopts a multi-stage traveling wave amplification scheme. The frequency stability of the output single-frequency pulse laser depends only on the narrow-linewidth fiber seed source. Compared with the injection locking method, this method does not require adjustment of the laser oscillator cavity length and can achieve 2μm single-frequency pulse laser with high frequency stability.

[0020] 3. The present invention innovatively adopts a solid double-pass amplification structure, which greatly improves the laser amplification efficiency and output energy. The solid part is composed only of the amplifier, which improves the efficiency while reducing the use of space components. The entire laser system has a compact structure and stable performance.

[0021] Preferably, the all-fiber cascade amplifier comprises a narrow linewidth continuous fiber seed source 1, a coupler 2, an acousto-optic modulator 3, and a first fiber isolator 4 are sequentially fused along the laser transmission direction; then a fiber cascade amplification structure is adopted: the first-stage preamplifier is sequentially fused to a wavelength division multiplexer 6 along the laser transmission direction, the output fiber of the fiber laser pump source 5 is fused to the pump fiber of the wavelength division multiplexer 6, and the output fiber of the wavelength division multiplexer 6 is sequentially fused to the first gain fiber 7, the first bandpass filter 8, and the second isolator 9; after entering the second-stage fiber preamplifier, the first fiber combiner 11 is fused, the output fiber of the first semiconductor laser 10 is fused to the pump fiber of the first fiber combiner 11, and the output fiber of the first fiber combiner 11 is sequentially fused to the second gain fiber 12, the second bandpass filter 1 3. The third optical fiber isolator 14; after entering the third-stage optical fiber pre-amplifier, the second optical fiber combiner 15 is fused, the output fiber of the second semiconductor laser 16 is fused with the pump fiber of the second optical fiber combiner 15, and the output fiber of the second optical fiber combiner 15 is sequentially fused with the third gain fiber 17, the third bandpass filter 18, and the fourth optical fiber isolator 19; entering the optical fiber main amplifier, the third optical fiber combiner 20 is fused, the output fiber of the third semiconductor laser 21 is fused with the pump fiber of the third optical fiber combiner 20, and the output fiber of the third optical fiber combiner 20 is sequentially fused with the fourth gain fiber 22, the fourth bandpass filter 23, and the fifth optical fiber isolator 24, and finally the output end cap 25 with pigtail is fused; this optical fiber cascade amplifier has an output energy of hundreds of μJ at a repetition frequency of kHz;

[0022] The solid double-pass amplifier is provided with a first lens 27, a second lens 28, a third lens 29, a first half-wave plate 30, a second half-wave plate 32, a first reflector 33 placed at an angle of 45° to the optical path, a second reflector 34, an end-face pump gain crystal 35, a quarter-wave plate 36, and a 0° reflector 37 in sequence along the laser transmission direction of the single-frequency pulse fiber cascade amplifier 26. The output laser of the solid amplifier pump source 38 passes through a fourth lens 39, a third reflector 40 placed at an angle of 45° to the optical path, a fourth reflector 41, a first reflector 33, and a second reflector 34, and then enters the end-face pump gain crystal 35 from the end face. The combination of the two realizes high-efficiency amplification.

[0023] The first bandpass filter, the second bandpass filter, the third bandpass filter, and the fourth bandpass filter are used to filter out the pump light and amplify the spontaneous radiation, while narrowing the laser pulse line width. The first fiber isolator, the second isolator, the third fiber isolator, the fourth fiber isolator, and the fifth fiber isolator are used to prevent the laser feedback from damaging the front-stage device during the laser amplification process. The first lens, the second lens, the third lens, and the fourth lens perform beam transformation on the signal light and the pump light respectively to ensure that the waist size and position of the two beams in the crystal are consistent, so as to achieve high-efficiency amplification.

[0024] Preferably, the narrow-linewidth continuous optical fiber seed source is a laser that outputs high-quality narrow-linewidth linearly polarized low-power continuous optical fiber.

[0025] Preferably, the first gain fiber 7, the second gain fiber 12, the third gain fiber 17, and the fourth gain fiber 22 are thulium-doped, holmium-doped, or thulium-holmium co-doped gain fibers.

[0026] Preferably, the output end cap 25 is a quartz end cap with a pigtail, which can ensure that the light spot has high quality and can withstand high-power laser output.

[0027] Preferably, a spatial optical isolator 31 is provided between the first half wave plate 30 and the second half wave plate. The spatial optical isolator ensures that during the solid state amplification process, feedback light is prevented from entering the optical fiber amplifier, damaging the device and affecting the stability of the optical fiber amplifier.

[0028] Preferably, the first lens 27, the second lens 28, the third lens 29 and the fourth lens 39 respectively perform beam transformation on the signal light and the pump light so that the waist sizes and positions of the two beams in the crystal are consistent.

[0029] Preferably, the end-pump gain crystal 35 is a thulium-doped, holmium-doped, or thulium-holmium co-doped gain crystal, and a double-pass amplification structure is adopted for the end-pump gain crystal.

[0030] Preferably, the 0° reflector is used to reflect the signal light, so that the signal light passes through the gain crystal again; the 0° reflector is placed at the focus of the thermal lens generated by the gain crystal, so that the first emitted laser returns to the gain crystal with the same light distribution, thereby achieving double-pass efficient amplification. At a repetition frequency of kHz, the output energy reaches the order of 10mJ.

[0031] Preferably, the all-fiber cascade amplifier uses fully polarization-maintaining optical fibers and devices, and the output is linearly polarized laser after solid double-pass amplification.

[0032] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A 2μm high energy solid double-pass amplifier based on a single-frequency pulse fiber front stage, characterized by: It includes: All-fiber cascade amplifier and solid-state two-way amplifier; the all-fiber cascade amplifier uses a low-power continuous narrow-linewidth fiber laser as a seed source, and uses an acousto-optic modulator to modulate the continuous light into pulsed light, and adjusts the waveform, pulse width and repetition frequency of the output pulsed laser; the modulated pulsed light adopts a master oscillator power amplification structure, and is initially amplified by a polarization-maintaining fiber pre-amplifier and a fiber main amplifier respectively; the output wavelength of the solid pump source is at the strongest absorption peak of the solid, and is further amplified by a solid-state two-way amplifier.

2. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 1, characterized in that: The all-fiber cascade amplifier comprises a narrow linewidth continuous fiber seed source (1), a coupler (2), an acousto-optic modulator (3), and a first fiber isolator (4) which are sequentially fused along the laser transmission direction; then a fiber cascade amplification structure is adopted: a first-stage preamplifier is sequentially fused to a wavelength division multiplexer (6) along the laser transmission direction, an output fiber of a fiber laser pump source (5) is fused to a pump fiber of the wavelength division multiplexer (6), and the output fiber of the wavelength division multiplexer (6) is sequentially fused to a first gain fiber (7), a first bandpass filter (8), and a second isolator (9); after entering a second-stage fiber preamplifier, a first fiber combiner (11) is fused, an output fiber of a first semiconductor laser (10) is fused to a pump fiber of the first fiber combiner (11), and the output fiber of the first fiber combiner (11) is sequentially fused to a second gain fiber ( 12), a second bandpass filter (13), and a third optical fiber isolator (14); after entering the third-stage optical fiber pre-amplifier, the second optical fiber combiner (15) is fused, the output fiber of the second semiconductor laser (16) is fused with the pump fiber of the second optical fiber combiner (15), and the output fiber of the second optical fiber combiner (15) is sequentially fused with the third gain fiber (17), the third bandpass filter (18), and the fourth optical fiber isolator (19); after entering the optical fiber main amplifier, the third optical fiber combiner (20) is fused, the output fiber of the third semiconductor laser (21) is fused with the pump fiber of the third optical fiber combiner (20), and the output fiber of the third optical fiber combiner (20) is sequentially fused with the fourth gain fiber (22), the fourth bandpass filter (23), and the fifth optical fiber isolator (24), and finally the output end cap (25) with pigtail is fused; The solid double-pass amplifier comprises a first lens (27), a second lens (28), a third lens (29), a first half-wave plate (30), a second half-wave plate (32), a first reflector (33) placed at an angle of 45° to the optical path, a second reflector (34), an end-face pumping gain crystal (35), a quarter-wave plate (36), and a 0° reflector (37) arranged in sequence along the laser transmission direction of the single-frequency pulse fiber cascade amplifier (26); the output laser of the solid amplifier pump source (38) respectively passes through a fourth lens (39), a third reflector (40) placed at an angle of 45° to the optical path, a fourth reflector (41), the first reflector (33), and the second reflector (34) and then enters the end-face pumping gain crystal (35) from the end face.

3. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The narrow line width continuous optical fiber seed source is a laser that outputs high-quality narrow line width linear polarization low power continuous optical fiber.

4. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The first gain optical fiber (7), the second gain optical fiber (12), the third gain optical fiber (17), and the fourth gain optical fiber (22) are gain optical fibers doped with thulium, doped with holmium, or co-doped with thulium and holmium.

5. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The output end cap (25) is a quartz end cap with a pigtail.

6. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: A spatial optical isolator (31) is arranged between the first half-wave plate (30) and the second half-wave plate.

7. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The first lens (27), the second lens (28), the third lens (29) and the fourth lens (39) respectively perform beam transformation on the signal light and the pump light, so that the waist sizes and positions of the two beams in the crystal are consistent.

8. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The end-pump gain crystal (35) is a thulium-doped, holmium-doped, or thulium-holmium co-doped gain crystal, and a double-pass amplification structure is adopted for the end-pump gain crystal.

9. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The 0° reflector is used to reflect the signal light so that the signal light passes through the gain crystal again; the 0° reflector is placed at the focus of the thermal lens generated by the gain crystal, so that the laser emitted for the first time returns to the gain crystal with the same light distribution, thereby realizing double-pass efficient amplification.

10. The 2μm high energy solid double-pass amplifier based on single-frequency pulse fiber front stage according to claim 2, characterized in that: The all-fiber cascade amplifier uses full polarization-maintaining optical fiber and devices, and the output is linearly polarized laser after solid double-pass amplification.

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