Fiber laser amplifier
By modulating the fiber seed laser with pseudo-random codes, the self-coherence of the seed laser is reduced, which solves the problems of Rayleigh scattering noise and nonlinear effects in high-power fiber laser amplifiers, and achieves more stable high-power narrow-linewidth laser output.
Patent Information
- Application Number
- CN202411034127.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-30
- Publication Date
- 2025-11-28
- Estimated Expiration
- 2044-07-30
AI Technical Summary
In existing high-power fiber laser amplifiers, the strong coherence of the seed light leads to severe Rayleigh scattering noise and nonlinear effects, affecting the output beam quality and power threshold.
A pseudo-random code modulated fiber seed laser is used to reduce the self-coherence of the seed laser through pseudo-random code phase modulation. A pseudo-random code generation unit and an arbitrary waveform generator are used to perform phase modulation on the narrow linewidth laser to generate randomly distributed high and low levels, thereby changing the phase distribution of the laser to suppress Rayleigh scattering noise.
It effectively suppresses Rayleigh scattering noise in fiber laser amplifiers, improves the stability of laser output and stimulated Raman scattering threshold, and maintains the output quality of high-power narrow-linewidth lasers.
Smart Images
Figure CN118943872B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application mainly relates to the technical field of fiber lasers, and particularly to a fiber laser amplifier. BACKGROUND
[0002] The fiber laser amplifier is an important means to realize high-quality and high-power directional output, and has important application value in the fields of industrial processing, laser cleaning, etc. There are four main methods to realize high-power narrow linewidth fiber laser output, including narrow linewidth semiconductor laser, high-power narrow linewidth fiber oscillator, narrow-band filtering based on wide-spectrum light source (super-fluorescent light source, random fiber laser), and single-frequency laser phase modulation technology based on master oscillator power amplifier (MOPA) structure. By comprehensively comparing the above four methods of generating narrow linewidth fiber laser, the seed source of single-frequency laser phase modulation has the advantages of more stable time domain and better spectral linewidth characteristics in the amplification process, and therefore is considered as the preferred solution to realize high-power narrow linewidth laser output.
[0003] The MOPA structure fiber laser amplifier mainly includes a seed laser, a high-power amplification module, and an output module. The seed laser source, as one of the core components of the high-power laser system, will have a significant impact on the final output performance of the fiber laser amplifier system due to its transmission characteristics. The main impacts include reducing the Brillouin scattering threshold of the high-power single-frequency fiber laser, and the stimulated Raman scattering threshold and the threshold of unstable output laser mode of the continuous high-power fiber laser amplifier.
[0004] In addition, the Rayleigh scattering noise in the high-power fiber laser amplifier also reduces the stability of the laser. The backward transmission of the Rayleigh scattering effect may cause coherent coupling effect of the seed laser, resulting in unstable transmission power of the seed light, thereby increasing the threshold of the nonlinear effect of the high-power fiber laser amplifier, and further causing the output beam quality of the entire laser system to decrease. In view of the above, it is necessary to optimize the seed light of the high-power fiber laser to improve the output performance of the overall system.
[0005] The optimization of the amplifier seed light usually includes two ways. The first way is to optimize the manufacturing and working process of the laser to reduce the factors that may cause scattering in the laser, that is, to reduce the impurities and defects in the laser by using high-quality materials and precise processes; and to take measures to control the working conditions of the laser, such as optimizing the pressure and temperature of the excitation gas, to minimize the occurrence of Rayleigh scattering. For the fiber laser amplifier, the longer the coherence length of the seed laser is, the better the output laser performance of the amplification stage is. However, the better the coherence performance of the seed light is, the stronger the Rayleigh scattering parasitic interference effect caused is, thereby causing the threshold of the nonlinear effect of the amplification stage to decrease. Based on this, the high-power narrow linewidth fiber laser amplifier often faces the contradiction between the output quality and the output power threshold. SUMMARY
[0006] In view of the deficiencies in the prior art, the present application provides a fiber laser amplifier.
[0007] To achieve the above object, the technical scheme adopted by the present application is as follows:
[0008] In one aspect, the present application provides a pseudo-random code modulated fiber seed laser, comprising a narrow linewidth laser, a phase modulation unit;
[0009] The narrow linewidth laser is configured to output continuous laser with narrow linewidth;
[0010] The phase modulation unit is configured to perform pseudo-random code phase modulation on the continuous laser output by the narrow linewidth laser, and modulate the laser phase into multiple pseudo-randomly distributed discrete phases, so as to reduce the self-coherence of the laser.
[0011] Further, the present application further comprises an amplification module to constitute a fiber laser amplifier, the amplification module is configured to amplify the power of the laser phase-modulated by the phase modulation unit and output, since the laser phase has been modulated into multiple pseudo-randomly distributed discrete phases, the self-coherence of the laser is reduced, and effective suppression of Rayleigh scattering noise in the fiber laser amplifier is achieved.
[0012] Further, the phase modulation unit comprises a fiber phase modulator, a pseudo-random code generation unit and an arbitrary waveform generator; the narrow linewidth laser is connected to the fiber phase modulator, the fiber phase modulator performs phase modulation on the continuous laser output by the narrow linewidth laser, the pseudo-random code generation unit generates a pseudo-random code and outputs it to the arbitrary waveform generator, the arbitrary waveform generator generates randomly distributed high and low levels according to the pseudo-random code and inputs the generated randomly distributed high and low levels to the fiber phase modulator to cause phase jump of the continuous laser, so that the phase of the continuous laser is modulated according to the high and low level distribution rule.
[0013] Further, the pseudo-random code is a series of 0, 1 randomly distributed number series or a series of -1, 1 randomly distributed number series.
[0014] Further, an attenuator is connected between the arbitrary waveform generator and the fiber phase modulator, and the randomly distributed high and low levels generated by the arbitrary waveform generator are input to the fiber phase modulator after being attenuated by the attenuator.
[0015] Further, the pseudo-random code is an m code sequence or a different order Gold code sequence.
[0016] The phase of the laser output by the narrow linewidth laser in the application is continuous before phase modulation, high and low levels distributed randomly are applied by the fiber phase modulator, the phase of the laser is modulated according to the distribution rule of the high and low levels, and the modulated phase is obtained, wherein the amplitude of the high and low levels input to the fiber phase modulator is exactly to make the laser phase change pi.
[0017] Further, the type of the narrow linewidth laser is not limited, and preferably the narrow linewidth laser is a laser of oscillator structure.
[0018] On the other hand, the application provides a pseudo-random code modulation fiber seed laser modulation method, which modulates the phase of the seed laser by a pseudo-random code to modulate the phase of the seed laser into many discrete phases distributed pseudo-randomly, so as to reduce the self-coherence of the seed laser.
[0019] Further, the pseudo-random code modulation fiber seed laser modulation method is applied to the pseudo-random code phase modulation of the seed laser in the fiber laser amplifier, and the laser after the pseudo-random code phase modulation is output after power amplification, since the phase of the seed laser is modulated into many discrete phases distributed pseudo-randomly, the self-coherence of the seed laser is reduced, and the Rayleigh scattering noise in the fiber laser amplifier is effectively suppressed.
[0020] The application changes the coherence between the seed laser and the Rayleigh scattering light without changing the linewidth of the seed laser, modulates the phase of the seed laser into many discrete phases distributed pseudo-randomly, reduces the self-coherence of the seed laser, effectively suppresses the Rayleigh scattering noise in the fiber laser amplifier, and further improves the stimulated Raman scattering threshold under the premise of maintaining the output quality of the fiber laser amplifier. BRIEF DESCRIPTION OF DRAWINGS
[0021] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained according to the structures shown in the drawings without creative labor.
[0022] Figure 1 is a structural schematic diagram of an embodiment;
[0023] Figure 2 is a structural schematic diagram of an embodiment;
[0024] Figure 3 is a structural schematic diagram of an embodiment;
[0025] Figure 4is a structural schematic diagram of an embodiment;
[0026] Figure 5 is a principle block diagram of m code sequence production;
[0027] Figure 6 is a principle block diagram of 7 order Gold code sequence generation;
[0028] Figure 7 is a comparison diagram of Rayleigh scattering suppression effect of the same fiber laser seed laser before and after pseudo-random code modulation in a comparison experiment;
[0029] Corresponding reference signs:
[0030] 1, narrow linewidth laser;
[0031] 2, phase modulation unit; 21, fiber phase modulator; 22, arbitrary waveform generator; 23, pseudo-random code generation unit;
[0032] 3, isolator;
[0033] 4, pump source;
[0034] 5, beam combiner; 51, first beam combiner; 52, second beam combiner; 53, third beam combiner;
[0035] 6, gain fiber;
[0036] 7, output end cap;
[0037] 8, cladding light filter;
[0038] 9, resonant cavity; 91, high reflectivity fiber grating; 92, gain fiber; 93, low reflectivity fiber grating. 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 part of the embodiments of the present application, not 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] Figure 1 is a structural schematic diagram of an embodiment. The present application provides a pseudo-random code modulated fiber seed laser, which comprises a narrow linewidth laser 1, a phase modulation unit 2;
[0041] The narrow linewidth laser 1 is used to output continuous laser with narrow linewidth;
[0042] The phase modulation unit 2 is used for pseudo-random code phase modulation of the continuous laser output by the narrow linewidth laser 1, and the laser phase is modulated into a plurality of pseudo-randomly distributed discrete phases to reduce the self-coherence of the laser.
[0043] The pseudo-random code modulated fiber seed laser further comprises an amplification module constituting a fiber laser amplifier, and the amplification module is used for power amplification and output of the laser phase modulated by the phase modulation unit.
[0044] Specifically, the fiber laser amplifier comprises an isolator 3, a pump source 4, a first beam combiner 51, a gain fiber 6, a second beam combiner 52, a cladding light filter 8 and an output end cap 7, wherein one side of each of the two beam combiners is provided with one signal arm and a plurality of pump arms, each of the pump arms is correspondingly connected with a pump source, and the other side of the beam combiner is a beam combining end.
[0045] The phase modulation unit comprises a fiber phase modulator 21, a pseudo-random code generation unit 23 and an arbitrary waveform generator 22; the narrow linewidth laser 1 is connected with the fiber phase modulator 21, the fiber phase modulator 21 performs phase modulation on the continuous laser output by the narrow linewidth laser 1, the pseudo-random code generation unit 23 generates a pseudo-random code and outputs the pseudo-random code to the arbitrary waveform generator 22, the arbitrary waveform generator 22 generates randomly distributed high and low levels according to the pseudo-random code and inputs the generated randomly distributed high and low levels to the fiber phase modulator 21 to cause phase jump of the continuous laser, so that the phase of the continuous laser is modulated according to the high and low level distribution law.
[0046] The pseudo-random code is a series of 0, 1 randomly distributed number series or a series of -1, 1 randomly distributed number series.
[0047] The pseudo-random code generation unit 23 generates a pseudo-random code and outputs the pseudo-random code to the arbitrary waveform generator 22, and the arbitrary waveform generator 22 generates randomly distributed high and low levels according to the pseudo-random code (a series of 0, 1 randomly distributed number series or a series of -1, 1 randomly distributed number series) and outputs the generated randomly distributed high and low levels.
[0048] The random distribution of high and low levels generated by the arbitrary waveform generator 22 is directly input to the fiber phase modulator 21, causing phase jump of the seed laser.
[0049] Preferably, an attenuator is connected between the arbitrary waveform generator 22 and the fiber phase modulator 21, and the random distribution of high and low levels generated by the arbitrary waveform generator 22 is attenuated by the attenuator and then input to the fiber phase modulator driver, which drives the fiber phase modulator 21, causing phase jump of the seed laser.
[0050] The pseudo-random code generation unit of the application generates pseudo-random codes of different orders or different types, and then modulates the seed laser into different types of discrete distribution through the phase modulator.
[0051] The pseudo-random code is an m code sequence or a Gold code sequence of different orders.
[0052] In the application, the phase of the laser output by the narrow linewidth laser 1 is continuous before phase modulation, and the random distribution of high and low levels is applied to the fiber phase modulator 21 to modulate the phase of the laser according to the distribution rule of high and low levels, obtaining the modulated phase, wherein the amplitude of the high and low levels input to the fiber phase modulator 21 is exactly π for the phase change of the laser.
[0053] Referring to Figure 2 , Figure 2 is a structural schematic diagram of an embodiment of the application, which provides a fiber laser amplifier, comprising a narrow linewidth laser 1, a phase modulation unit 2, and an amplification module.
[0054] Specifically, the fiber laser amplifier comprises an isolator 3, a pump source 4, a first beam combiner 51, a gain fiber 6, a cladding light filter 8, and an output end cap 7, wherein one side of the first beam combiner 51 is provided with a signal arm and a plurality of pump arms, each of which is connected with a corresponding pump source, and the other side of the beam combiner is a beam combining end. The narrow linewidth laser 1 is connected with one end of the fiber phase modulator 21, the other end of the fiber phase modulator 21 is connected with the input end of the isolator 3, the output end of the isolator 3 is connected with the signal arm of the first beam combiner 51, the beam combining end of the first beam combiner 51 is connected with the input end of the gain fiber 6, the output end of the gain fiber 6 is connected with the input end of the cladding light filter 8, and the output end of the cladding light filter 8 is connected with the input end of the output end cap 7.
[0055] The phase modulation unit comprises a fiber phase modulator 21, a pseudo-random code generation unit 23 and an arbitrary waveform generator 22; the narrow linewidth laser 1 is connected to the fiber phase modulator 21, the fiber phase modulator 21 performs phase modulation on the continuous laser output by the narrow linewidth laser 1, the pseudo-random code generation unit 23 generates a pseudo-random code and outputs the pseudo-random code to the arbitrary waveform generator 22, the arbitrary waveform generator 22 generates randomly distributed high and low levels according to the pseudo-random code and inputs the generated randomly distributed high and low levels to the fiber phase modulator 21 to cause phase jumps of the continuous laser, so that the phase of the continuous laser is modulated according to the high and low level distribution law. The other setting requirements of this embodiment are the same as those of embodiment 1 and will not be repeated here.
[0056] Referring to Figure 3 , Figure 3 is a structural schematic diagram of an embodiment of the present application, and the embodiment provides a fiber laser amplifier, which comprises a narrow linewidth laser 1, a phase modulation unit 2 and an amplification module;
[0057] Specifically, the fiber laser amplifier comprises an isolator 3, a gain fiber 6, a pump source 4, a second beam combiner 52, a cladding light filter 8 and an output end cap 7, wherein one side of the second beam combiner 52 is provided with one signal arm and a plurality of pump arms, each pump arm is correspondingly connected with a pump source, and the other side of the beam combiner is a beam combining end. The narrow linewidth laser 1 is connected to one end of the fiber phase modulator 21, the other end of the fiber phase modulator 21 is connected to the input end of the isolator 3, the output end of the isolator 3 is connected to the input end of the gain fiber 6, the output end of the gain fiber 6 is connected to the beam combining end of the second beam combiner 52, the signal arm of the second beam combiner 52 is connected to the input end of the cladding light filter 8, and the output end of the cladding light filter 8 is connected to the input end of the output end cap 7.
[0058] The phase modulation unit comprises a fiber phase modulator 21, a pseudo-random code generation unit 23 and an arbitrary waveform generator 22; the narrow linewidth laser 1 is connected to the fiber phase modulator 21, the fiber phase modulator 21 performs phase modulation on the continuous laser output by the narrow linewidth laser 1, the pseudo-random code generation unit 23 generates a pseudo-random code and outputs the pseudo-random code to the arbitrary waveform generator 22, the arbitrary waveform generator 22 generates randomly distributed high and low levels according to the pseudo-random code and inputs the generated randomly distributed high and low levels to the fiber phase modulator 21 to cause phase jumps of the continuous laser, so that the phase of the continuous laser is modulated according to the high and low level distribution law. The other setting requirements of this embodiment are the same as those of embodiment 1 and will not be repeated here.
[0059] Referring to Figure 4 , Figure 4 is a structural schematic diagram of an embodiment of the present application, and the embodiment provides a fiber laser amplifier, which comprises a narrow linewidth laser 1, a phase modulation unit 2 and an amplification module;
[0060] The narrow linewidth laser 1 is an oscillator structure laser, comprising a resonant cavity 9, the resonant cavity 9 comprising a high reflectivity fiber grating 91, a gain fiber 92, and a low reflectivity fiber grating 93.
[0061] Specifically, the third combiner 53 is provided with a plurality of pump arms on one side, and a pump source is correspondingly connected to each pump arm. The other side of the third combiner 53 is a combiner end. The fiber laser amplifier comprises an isolator 3, a pump source 4, a first combiner 51, a gain fiber 6, a second combiner 52, a cladding light filter 8, and an output end cap 7. One side of each of the two combiners is provided with a signal arm and a plurality of pump arms, and a pump source is correspondingly connected to each pump arm. The other side of the combiner is a combiner end. The combiner end of the third combiner 53 is connected to the input end of the high reflectivity fiber grating 91. The output end of the high reflectivity fiber grating 91 is connected to the input end of the gain fiber 92. The output end of the gain fiber 92 is connected to the input end of the low reflectivity fiber grating 93. The output end of the low reflectivity fiber grating 93 is connected to one end of the fiber phase modulator 21. The other end of the fiber phase modulator 21 is connected to the input end of the isolator 3. The output end of the isolator 3 is connected to the signal arm of the first combiner 51. The combiner end of the first combiner 51 is connected to the input end of the gain fiber 6. The output end of the gain fiber 6 is connected to the combiner end of the second combiner 52. The signal arm of the second combiner 52 is connected to the input end of the cladding light filter 8. The output end of the cladding light filter 8 is connected to the input end of the output end cap 7.
[0062] The phase modulation unit comprises a fiber phase modulator 21, a pseudo-random code generation unit 23, and an arbitrary waveform generator 22. The narrow linewidth laser 1 is connected to the fiber phase modulator 21. The fiber phase modulator 21 modulates the phase of the continuous laser output by the narrow linewidth laser 1. The pseudo-random code generation unit 23 generates a pseudo-random code and outputs it to the arbitrary waveform generator 22. The arbitrary waveform generator 22 generates randomly distributed high and low levels according to the pseudo-random code and inputs the generated randomly distributed high and low levels to the fiber phase modulator 21 to cause phase jumps of the continuous laser, so that the phase of the continuous laser is modulated according to the high and low level distribution law. The other setting requirements of this embodiment are the same as those of embodiment 1 and will not be described here.
[0063] Preferably, the pseudo-random code used in the present application is not an absolutely random sequence, the elements of which are determined and can be repeatedly generated and copied according to a specific algorithm, so that it has a better effect of reducing the self-coherence of the laser, and effectively suppresses the Rayleigh scattering noise in the fiber laser amplifier. Preferably, the m-code sequence and the Gold-code sequence are preferably used in the fiber laser amplifier to perform pseudo-random code phase modulation on the seed laser in the fiber laser amplifier. The Gold-code sequence is composed of two preferred sequences of the m-code sequence, so the suppression effect of the Rayleigh scattering based on the Gold-code sequence for the seed laser in the fiber laser amplifier is better than that of the m-code sequence for the seed laser in the fiber laser amplifier.
[0064] Not generally, the m-code sequence is generated by a linear shift register, as shown in Figure 5 , Figure 5 is the generation principle block diagram of the m-code sequence in an embodiment. Figure 5 In the formula, the input clock signal, the currently generated element can be given by the recursive relationship formula, that is:
[0065] ;
[0066] When the initial value of the register network is not all zero, the element distribution in a single period of the generated sequence is only related to the feedback coefficient , so a binary field {0, 1} polynomial is used to represent a specific shift register network, and
[0067] ;
[0068] In the formula, the polynomial is called the characteristic polynomial of the above-mentioned r order register network. Because the number of m-code sequences is relatively small, two groups of m-code sequences of the same order are often combined to form a new pseudo-random sequence in practical applications, and this sequence is called a Gold-code sequence.
[0069] Taking a 7-order Gold-code sequence as an example, referring to Figure 6 , Figure 6 is the generation principle block diagram of the 7-order Gold-code sequence. The m-code sequence can be simply expressed as: in a set of m-code sequences with a given order r , the two sequences with the maximum and minimum values of the absolute value of the cross-correlation function are closest. Figure 6 In the formula, the clock signal is input into the 7-order m-sequence generator 1 and the 7-order m-sequence generator 2, and the polynomials , The corresponding 7th order m sequence constitutes a preferred condition. If the m sequence is preferred to set different relative initial phases (or initial values), different Gold code sequences can be output, i.e. under the same topological structure, a large number of Gold code sequences can be generated, which is called a Gold code sequence cluster. The absolute value of the cross-correlation function of any two sequences in the Gold code sequence cluster is significantly smaller than that of the m code sequence, i.e. has better cross-correlation characteristics, so the suppression effect of Rayleigh scattering based on Gold code sequence for pseudo-random code phase modulation of seed laser in a fiber laser amplifier is better than that based on m code sequence for pseudo-random code phase modulation of seed laser in a fiber laser amplifier.
[0070] In a preferred embodiment, the distribution of the pseudo-random code is illustrated by taking a 9th order Gold code as an example, and the following {0, 1} sequence is as follows:
[0071] {0001001010001110000100101000111000010010100011100001001010001110000111010111000100011101011100010001110101110001000111010111000100011101011100010001110101110001000111010111000100011101011100010001110101110001000100101000111000010010100011100001001010001110000100101000111000010010100011100001001010001110000100101000111000010010100011100001001010001110000111010111000100011101011100010001110101110001000111010111000}
[0072] Referring to Figure 7 , Figure 7This is a comparative experiment showing the Rayleigh scattering suppression effect of the seed laser in the same fiber laser before and after pseudo-random code modulation based on the aforementioned 9th-order Gold code. The experiment verifies that, under a 10 km link transmission condition, due to the presence of Rayleigh scattering, the system's noise floor is close to -60 dB@1kHz (without random code modulation). After enabling pseudo-random code modulation, the system's noise floor is reduced to -85 dB@1kHz. The suppression of Rayleigh scattering exceeds 20 dB.
[0073] Matters not covered in this invention are common knowledge.
[0074] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0075] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, 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 concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.
[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A fiber laser amplifier, characterized by, The narrow linewidth laser, the phase modulation unit, and the amplification module are included. The narrow linewidth laser is configured to output continuous laser with narrow linewidth. The phase modulation unit is configured to perform pseudo-random code phase modulation on the continuous laser output by the narrow linewidth laser, and modulate the laser phase into multiple pseudo-randomly distributed discrete phases to reduce the self-coherence of the laser. The amplification module is configured to perform power amplification on the laser phase-modulated by the phase modulation unit and output the laser.
2. The fiber laser amplifier of claim 1, wherein, The phase modulation unit includes a fiber phase modulator, a pseudo-random code generation unit, and an arbitrary waveform generator.
3. The fiber laser amplifier of claim 2, wherein, The narrow linewidth laser is connected to the fiber phase modulator.
4. The fiber laser amplifier of claim 2 or 3, wherein, The fiber phase modulator performs phase modulation on the continuous laser output by the narrow linewidth laser.
5. The fiber laser amplifier of claim 2, wherein, The pseudo-random code generation unit generates a pseudo-random code and outputs the pseudo-random code to the arbitrary waveform generator.
6. The fiber laser amplifier of claim 5, wherein, The arbitrary waveform generator generates randomly distributed high and low levels according to the pseudo-random code and inputs the generated randomly distributed high and low levels to the fiber phase modulator to cause phase jumps of the continuous laser.
7. The fiber laser amplifier of claim 1, wherein, The pseudo-random code is a series of randomly distributed 0 and 1 or a series of randomly distributed -1 and 1. The arbitrary waveform generator is connected to the fiber phase modulator through an attenuator. The pseudo-random code is an m code sequence or a different order Gold code sequence. The high and low levels input to the fiber phase modulator change the laser phase by π. The narrow linewidth laser is an oscillator structure laser.