A SBS suppression module, a fiber master amplifier and a high-power narrow linewidth laser

Abstract

This invention belongs to the field of fiber lasers, specifically relating to an SBS suppression module, a fiber main amplifier, and a high-power narrow-linewidth laser. The SBS suppression module includes a polarization beam combiner and a 1×2 optical switch; the fiber main amplifier consists of a double-clad gain fiber, the SBS suppression module, and accompanying passive fiber devices; the high-power narrow-linewidth laser is composed of a narrow-linewidth laser seed source, a fiber preamplifier, and a fiber main amplifier connected sequentially, with the fiber preamplifier consisting of three stages of single-clad fiber amplifiers. The SBS suppression module effectively suppresses SBS, and its simple structure facilitates packaging. This invention enables narrow-linewidth fiber laser output with high beam quality at the 5kW level and above, and employs all-fiber fusion splicing technology to construct an all-fiber system, offering advantages such as compact and simple structure, good stability, increased power, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of fiber lasers, specifically relating to an SBS suppression module, a fiber main amplifier, and a high-power narrow-linewidth laser. Background Technology

[0002] High-power narrow-linewidth fiber lasers have significant application value in fields such as high-power laser beamforming, advanced laser manufacturing, high-performance light sources for ultra-wideband optical communication, frequency conversion, strong-field laser physics, and gravitational wave detection, thanks to their advantages of compact structure, low noise, good beam quality, and good coherence.

[0003] In high-power narrow-linewidth fiber lasers, the fiber transmits high power, has a small core cross-sectional area, and the interaction distance of the transmitted light in the fiber is very long. During laser amplification, nonlinear effects such as SBS, self-phase modulation (SPM), and four-wave mixing (FWM) are easily generated.

[0004] In narrow-linewidth fiber amplifiers, the low threshold of SBS (Short-Side Stokes Beam) and the resulting strong destructive power of the back-stokes light easily damage optical components, making it a major factor limiting the output power improvement of narrow-linewidth fiber amplifiers. The SBS process is a nonlinear interaction between the pump wave and the Stokes wave via acoustic waves. The pump wave generates acoustic waves through electrostriction, which in turn modulate the refractive index of the medium. The pump wave-induced refractive index grating scatters the pump wave through Bragg diffraction. Due to the Doppler displacement of the grating, which moves at the speed of sound, the scattered light experiences a frequency downshift. Scholars both domestically and internationally have proposed various methods to suppress the SBS effect, such as increasing the mode field area of ​​the fiber to reduce the power density of the signal light, reducing the length of the gain fiber, applying temperature or stress gradients to broaden the Brillouin gain spectrum, and phase modulation to broaden the seed source spectral linewidth. However, these methods also have some drawbacks. Large mode field fibers and short gain length fibers increase the mode instability (MI) threshold. Applying temperature or stress gradients and phase modulation methods are complex in practice, introduce radio frequency signals, and complicate the entire fiber laser system.

[0005] Chinese patent CN111541138A utilizes the cross-phase modulation effect between the introduced back-pulsed laser and the back-stokes scattered light to broaden the gain spectrum and reduce the peak gain of the Stokes scattered light, thereby suppressing the back-stokes scattered light. However, it also introduces a nonlinear effect of cross-phase modulation, making the system unstable and preventing further power increases.

[0006] Chinese patent CN113097850A uses a long-distance passive optical fiber to broaden the spectrum of the seed light used in a narrow-linewidth high-power fiber laser amplifier in order to suppress the SBS effect. However, the system of this patent introduces a self-phase modulation nonlinear effect, and the system power cannot be further increased.

[0007] Chinese patent CN102087452A achieves the suppression of the SBS effect by dividing the laser beam into multiple segments with different polarization states using a glass slide, but the signal light power loss is large and the system is unstable.

[0008] Chinese patent CN109378687B utilizes the high loss of tilted fiber gratings in the Brillouin section to filter lasers by connecting the tilted fiber gratings into an optical fiber amplifier, thereby achieving the purpose of suppressing SBS. However, it suffers from problems such as complex structure and instability, and the gratings are easily damaged under high power when filtering. Summary of the Invention

[0009] This invention aims to propose an SBS suppression module, an optical fiber main amplifier, and a high-power narrow-linewidth laser. The SBS suppression module can reduce the Brillouin gain, thereby achieving the purpose of suppressing SBS. At the same time, the optical fiber main amplifier and the high-power narrow-linewidth laser have a compact and simple structure, good stability, high power output, and low cost, which can effectively solve the problems and shortcomings of the above methods.

[0010] This invention is achieved through the following technical solution:

[0011] An SBS suppression module includes a polarizing beam splitter and a 1×2 optical switch. The horizontal polarization output of the polarizing beam splitter is connected to one input of the 1×2 optical switch, and the vertical polarization output of the polarizing beam splitter is connected to the other input of the 1×2 optical switch.

[0012] The input laser of the polarization beam splitter in the SBS suppression module is circularly polarized light, 45° linearly polarized light, or unpolarized light, with an insertion loss of less than 1.0 dB.

[0013] The 1×2 optical switch in the SBS suppression module is either a mechanical or non-mechanical optical switch, with a switching time of 1ms to 5ms and an insertion loss of less than 1.0dB.

[0014] The laser is injected into the SBS suppression module, where a polarization beam splitter separates the input laser into two linearly polarized beams with mutually perpendicular polarization directions, and injects them into a 1×2 optical switch. The 1×2 optical switch alternately outputs the two linearly polarized beams with mutually perpendicular polarization directions at a switching time of 1ms to 5ms.

[0015] An optical fiber main amplifier includes an SBS suppression module, which consists of a double-clad gain fiber, the SBS suppression module, and passive optical fiber devices used in conjunction with it. The output of a circulator is connected to the input of a backward monitor. The inverting input of the circulator is connected to the input of a third mode field adapter. The output of the third mode field adapter is connected to the signal fiber end of a third fiber combiner. The output of a fourth semiconductor laser is connected to the pump fiber end of the third fiber combiner. The output of the third fiber combiner is connected to the input of the SBS suppression module. The output of the SBS suppression module is connected to the input of a fourth gain fiber. The output of the fourth gain fiber is connected to the input of a cladding optical filter. An output cap is fused to the output of the cladding optical filter.

[0016] Four to eight fourth semiconductor lasers with output power of 600mW to 800mW are used as pump sources; the fourth gain fiber in the fiber main amplifier is a double-clad ytterbium-doped fiber with a fiber core diameter of 35μm and an inner cladding diameter of 240μm, and an absorption coefficient of 1.20dB / m to 2.70dB / m for pump light at 976nm.

[0017] A high-power narrow-linewidth laser includes an optical fiber amplifier, which is a high-power narrow-linewidth laser consisting of a narrow-linewidth laser seed source, an optical fiber preamplifier, and an optical fiber main amplifier connected in sequence. The optical fiber preamplifier consists of three single-clad optical fiber amplifiers.

[0018] The first-stage single-clad fiber amplifier I uses a first semiconductor laser with a maximum output power of 500mW as the pump source; the second-stage single-clad fiber amplifier II uses 2 to 4 second semiconductor lasers with an output power of 10W as the pump source; and the third-stage single-clad fiber amplifier III uses 2 to 4 third semiconductor lasers with an output power of 100W as the pump source.

[0019] Each fiber preamplifier stage consists of a semiconductor laser, a wavelength division multiplexer, a gain fiber, a fiber isolator, and a mode field adapter. The output of the fiber isolator is connected to the signal fiber end of the wavelength division multiplexer, the output of the semiconductor laser is connected to the pump fiber end of the wavelength division multiplexer, the output of the wavelength division multiplexer is connected to the input of the gain fiber, the output of the gain fiber is connected to the input of the fiber isolator, and the output of the fiber isolator is connected to the input of the mode field adapter.

[0020] The narrow linewidth laser seed source includes a narrow linewidth laser and a first fiber optic isolator; the signal output fiber of the narrow linewidth laser is connected to the input end of the first fiber optic isolator.

[0021] The first gain fiber, second gain fiber, and third gain fiber in the optical fiber preamplifier are single-clad ytterbium-doped fibers with a cladding diameter of 100μm to 150μm and a core diameter ratio of 1:2:3. The absorption coefficient of pump light at 976nm is 0.80dB / m to 1.80dB / m.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] 1. The SBS suppression module proposed in this invention utilizes a polarization beam combiner and a 1×2 optical switch to achieve alternating output of linearly polarized light with mutually perpendicular polarization directions, preventing stimulated Brillouin scattering light from being amplified subsequently, thereby suppressing SBS. The entire SBS suppression module has a simple structure and is easy to package.

[0024] 2. The SBS suppression module, fiber optic main amplifier, and high-power narrow-linewidth laser proposed in this invention do not require an additional radio frequency signal source or a complex phase modulation device. They can suppress the subsequent amplification of Brillouin scattered light, reduce Brillouin gain, and have a simple structure that can balance power improvement and linewidth narrowing.

[0025] 3. The fiber preamplifier of this invention is a three-stage single-clad fiber amplifier. By adjusting the core size of each gain fiber, the core ratio of the three-stage gain fibers is made to be 1:2:3, which can effectively suppress amplified spontaneous emission (ASE) and improve the output power of the preamplifier.

[0026] 4. Based on this invention, narrow-linewidth fiber laser output with high beam quality at the 5kW level or above can be achieved. Furthermore, the all-fiber system constructed using all-fiber fusion splicing technology offers advantages such as compact structure, low cost, and stable performance. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the high-power narrow-linewidth laser structure described in this invention;

[0029] Figure 2 This is a schematic diagram of the SBS suppression module described in this invention;

[0030] Reference numerals: 1-Narrow linewidth laser; 2-First fiber optic isolator; 3-First semiconductor laser; 4-First wavelength division multiplexer; 5-First gain fiber; 6-Second fiber isolator; 7-First mode field adapter; 8-Second semiconductor laser; 9-First fiber combiner; 10-Second gain fiber; 11-Third fiber isolator; 12-Second mode field adapter; 13-Third semiconductor laser; 14-Second fiber combiner; 15-Third gain fiber; 16-Fourth fiber isolator; 17-Circulator; 18-Backward monitor; 19-Third mode field adapter; 20-Fourth semiconductor laser; 21-Third fiber combiner; 22-SBS suppression module; 23-Fourth gain fiber; 24-Clad optical filter; 25-Output cap; 26-Polarization beam combiner; 27-1×2 optical switch. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and conventional means in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0032] Example 1: As Figure 2 As shown, an SBS suppression module includes a polarization beam combiner 26 and a 1×2 optical switch 27. The horizontal polarization output of the polarization beam combiner 26 is connected to one input of the 1×2 optical switch 27, and the vertical polarization output of the polarization beam combiner 26 is connected to the other input of the 1×2 optical switch 27.

[0033] The input laser of the polarization beam splitter 26 in the SBS suppression module 22 is circularly polarized light, 45° linearly polarized light, or unpolarized light, with an insertion loss of less than 1.0 dB.

[0034] The 1×2 optical switch 27 in the SBS suppression module 23 is either a mechanical optical switch or a non-mechanical optical switch. The switching time of the optical switch is 1ms to 5ms, and the insertion loss is less than 1.0dB.

[0035] The process of suppressing SBS is as follows: the laser is injected into the SBS suppression module 23, and the input laser is split into two linearly polarized beams with mutually perpendicular polarization directions by the polarization beam splitter 26, and injected into the 1×2 optical switch 27; the 1×2 optical switch 27 alternately outputs the two linearly polarized beams with mutually perpendicular polarization directions at a switching time of 1ms to 5ms.

[0036] Example 2: Figure 1As shown, an optical fiber main amplifier consists of a double-clad gain fiber, an SBS suppression module, and passive optical fiber devices used in conjunction with it. The output of a circulator 17 is connected to the input of a backward monitor 18. The inverting input of the circulator 17 is connected to the input of a third mode field adapter 19. The output of the third mode field adapter 19 is connected to the signal fiber end of a third fiber combiner 21. The output of a fourth semiconductor laser 20 is connected to the pump fiber end of the third fiber combiner 21. The output of the third fiber combiner 21 is connected to the input of an SBS suppression module 22. The output of the SBS suppression module 22 is connected to the input of a fourth gain fiber 23. The output of the fourth gain fiber 23 is connected to the input of a cladding optical filter 24. An output cap 25 is fused to the output of the cladding optical filter 24.

[0037] The fiber optic main amplifier uses six fourth semiconductor lasers 20 with a maximum output power of 800mW as pump sources; the fourth gain fiber 23 in the fiber optic main amplifier is a double-clad ytterbium-doped fiber with a fiber core diameter of 35μm and an inner cladding diameter of 240μm, and an absorption coefficient of 2.70dB / m for pump light at 976nm.

[0038] Example 3: Figure 1 or Figure 2 As shown: A high-power narrow-linewidth laser is composed of a narrow-linewidth laser seed source, an optical fiber preamplifier, and an optical fiber main amplifier connected in sequence. The optical fiber preamplifier is composed of three single-clad optical fiber amplifiers.

[0039] The three-stage single-clad fiber amplifier includes a first semiconductor laser 3, a first wavelength division multiplexer 4, a first gain fiber 5, a second fiber isolator 6, a first mode field adapter 7, a second semiconductor laser 8, a first fiber combiner 9, a second gain fiber 10, a third fiber isolator 11, a second mode field adapter 12, a third semiconductor laser 13, a second fiber combiner 14, a third gain fiber 15, and a fourth fiber isolator 16.

[0040] The output of the first fiber isolator 2 is connected to the signal fiber end of the first wavelength division multiplexer 4; the output of the first semiconductor laser 3 is connected to the pump fiber end of the first wavelength division multiplexer 4; the output of the first wavelength division multiplexer 4 is connected to the input of the first gain fiber 5; the output of the first gain fiber 5 is connected to the input of the second fiber isolator 6; the output of the second fiber isolator 6 is connected to the input of the first mode field adapter 7; the output of the first mode field adapter 7 is connected to the signal fiber end of the first fiber combiner 9; the output of the second semiconductor laser 8 is connected to the pump fiber end of the first fiber combiner 9; the first fiber... The output of the fiber combiner 9 is connected to the input of the second gain fiber 10. The output of the second gain fiber 10 is connected to the input of the third fiber isolator 11. The output of the third fiber isolator 11 is connected to the input of the second mode field adapter 12. The output of the second mode field adapter 12 is connected to the signal fiber end of the second fiber combiner 14. The output of the third semiconductor laser 13 is connected to the pump fiber end of the second fiber combiner 14. The output of the second fiber combiner 14 is connected to the input of the third gain fiber 15. The output of the third gain fiber 15 is connected to the input of the fourth fiber isolator 16.

[0041] The first-stage single-clad fiber amplifier I uses a first semiconductor laser 3 with a maximum output power of 500mW as the pump source; the second-stage single-clad fiber amplifier II uses two second semiconductor lasers 8 with an output power of 10W as the pump source; and the third-stage single-clad fiber amplifier III uses three third semiconductor lasers 13 with an output power of 100W as the pump source.

[0042] The narrow linewidth laser seed source includes a narrow linewidth laser 1 and a first fiber optic isolator 2; the signal output fiber of the narrow linewidth laser 1 is connected to the input end of the first fiber optic isolator 2.

[0043] The first gain fiber 5, the second gain fiber 10, and the third gain fiber 15 in the optical fiber preamplifier are single-clad ytterbium-doped fibers with a cladding diameter of 125 μm and a core diameter ratio of 1:2:3. Their absorption coefficients for pump light at 976 nm are 0.80 dB / m, 1.20 dB / m, and 1.80 dB / m, respectively.

[0044] This invention enables narrow-linewidth fiber laser output with high beam quality at the 5kW level and above. Furthermore, it employs all-fiber fusion splicing technology to construct an all-fiber system, offering advantages such as compact and simple structure, good stability, increased power output, and low cost.

[0045] The above descriptions are merely embodiments of the present invention, and while they are detailed and specific, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. An SBS suppression module, characterized in that: It includes a polarization beam splitter (26) and a 1×2 optical switch (27). The horizontal polarization output end of the polarization beam splitter (26) is connected to one input end of the 1×2 optical switch (27), and the vertical polarization output end of the polarization beam splitter (26) is connected to the other input end of the 1×2 optical switch (27). The process of suppressing SBS is as follows: the laser is injected into the SBS suppression module (22), and the input laser is split into two beams of linearly polarized light with mutually perpendicular polarization directions by the polarization beam splitter (26), and injected into the 1×2 optical switch (27). The 1×2 optical switch (27) alternately outputs the two beams of linearly polarized light with mutually perpendicular polarization directions at a switching time of 1ms to 5ms.

2. The SBS suppression module according to claim 1, characterized in that: The input laser of the polarized beam splitter (26) in the SBS suppression module (22) is circularly polarized light, 45° linearly polarized light or unpolarized light, and the insertion loss is less than 1.0dB.

3. The SBS suppression module according to claim 1, characterized in that: The 1×2 optical switch (27) in the SBS suppression module (22) is a mechanical optical switch or a non-mechanical optical switch. The switching time of the optical switch is 1ms to 5ms and the insertion loss is less than 1.0dB.

4. An optical fiber main amplifier, comprising the SBS suppression module according to any one of claims 1-3, characterized in that: It consists of a double-clad gain fiber, an SBS suppression module, and passive fiber optic devices used in conjunction with it. The output of the circulator (17) is connected to the input of the backward monitor (18). The reverse input of the circulator (17) is connected to the input of the third mode field adapter (19). The output of the third mode field adapter (19) is connected to the signal fiber end of the third fiber combiner (21). The output of the fourth semiconductor laser (20) is connected to the pump fiber end of the third fiber combiner (21). The output of the third fiber combiner (21) is connected to the input of the SBS suppression module (22). The output of the SBS suppression module (22) is connected to the input of the fourth gain fiber (23). The output of the fourth gain fiber (23) is connected to the input of the cladding optical filter (24). The output of the cladding optical filter (24) is fused with an output cap (25).

5. The fiber optic main amplifier according to claim 4, characterized in that: Four to eight fourth semiconductor lasers (20) with output power of 600mW to 800mW are used as pump sources; the fourth gain fiber (23) in the fiber main amplifier is a double-clad ytterbium-doped fiber with a fiber core diameter of 35μm and an inner cladding diameter of 240μm, and an absorption coefficient of 1.20dB / m to 2.70dB / m for pump light at 976nm.

6. A high-power narrow-linewidth laser, comprising the fiber optic main amplifier as described in claim 4, characterized in that: A high-power narrow-linewidth laser is composed of a narrow-linewidth laser seed source, an optical fiber preamplifier, and an optical fiber main amplifier connected in sequence. The optical fiber preamplifier consists of three single-clad optical fiber amplifiers.

7. The high-power narrow-linewidth laser according to claim 6, characterized in that: The first-stage single-clad fiber amplifier (I) uses a first semiconductor laser (3) with a maximum output power of 500mW as the pump source, the second-stage single-clad fiber amplifier (II) uses 2 to 4 second semiconductor lasers (8) with an output power of 10W as the pump source, and the third-stage single-clad fiber amplifier (III) uses 2 to 4 third semiconductor lasers (13) with an output power of 100W as the pump source.

8. The high-power narrow-linewidth laser according to claim 6, characterized in that: Each fiber preamplifier stage consists of a semiconductor laser, a wavelength division multiplexer, a gain fiber, a fiber isolator, and a mode field adapter. The output of the fiber isolator is connected to the signal fiber end of the wavelength division multiplexer, the output of the semiconductor laser is connected to the pump fiber end of the wavelength division multiplexer, the output of the wavelength division multiplexer is connected to the input of the gain fiber, the output of the gain fiber is connected to the input of the fiber isolator, and the output of the fiber isolator is connected to the input of the mode field adapter.

9. The high-power narrow-linewidth laser according to claim 6, characterized in that: The narrow linewidth laser seed source includes a narrow linewidth laser (1) and a first fiber isolator (2); the signal output fiber of the narrow linewidth laser (1) is connected to the input end of the first fiber isolator (2); the first gain fiber (5), the second gain fiber (10) and the third gain fiber (15) in the fiber preamplifier are single-clad ytterbium-doped fibers with a cladding diameter of 100μm to 150μm and a core diameter ratio of 1:2:

3. The absorption coefficient of pump light at 976nm is 0.80dB / m to 1.80dB / m.

Images