Semi-open cavity type multiband random Raman fiber laser

Abstract

The invention provides a semi-open cavity type multiband random Raman fiber laser, which relates to the technical field of fiber lasers and comprises a pumping module used for matching the wavelength emitted by a laser diode with the absorption wavelength of a pumping ytterbium-doped fiber and providing a pumping light source; the total reflection module is composed of a high-reflectivity fiber Bragg grating and a fiber reflector and is used for intelligently controlling total reflection paths of pump light, emitted light generated by excitation of a pump ytterbium-doped fiber and multi-order Stokes light generated by an excited Raman scattering effect through a grid search algorithm to form a semi-open cavity structure; and the pump beam combining module is used for coupling the multiple beams of pump light to generate one beam of pump light. By integrating a plurality of functional modules, efficient utilization of pump light and intelligent generation and accurate regulation and control of multiband Raman laser are realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, in particular to a semi-open cavity multi-band random Raman optical fiber laser. Background Art

[0002] Traditional fiber lasers rely on rare-earth doped fibers (such as erbium-doped and ytterbium-doped fibers) as gain media, and their output wavelength range is limited by the energy level structure of the doped ions.

[0003] For example, the typical output wavelength is around 1550 nm. Although the wavelength range can be expanded through nonlinear effects or external tuning technology, the tuning range is still limited, and the output wavelength is mainly concentrated in the 1030-1080 nm band, making it difficult to cover a wider spectral range. This limitation in the wavelength tuning range requires additional optical components or system design for traditional fiber lasers in multi-band applications, increasing costs.

[0004] Random lasers are based on multiple scattering and random feedback mechanisms. Although they can achieve wide-spectrum output, their output stability is usually poor.

[0005] For example, due to the uncontrollability of the random feedback mechanism, the output spectrum and power may fluctuate with slight changes in ambient temperature, fiber bending, or pump power. Although multi-band output can be achieved, the inhomogeneity of the distribution of nanoparticles may lead to a decrease in the uniformity and stability of the output spectrum. This instability limits the use of random lasers in high-precision applications such as spectroscopy or optical sensing. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a semi-open cavity multi-band random Raman fiber laser, which can achieve efficient gain within a specific wavelength range.

[0007] In order to solve the above technical problems, the technical solution of the present invention is as follows: First, a semi-open cavity multi-band random Raman fiber laser, comprising: A pump module is used to match the wavelength emitted by the laser diode with the absorption wavelength of the pump ytterbium-doped optical fiber to provide a pump light source; The total reflection module is composed of a high-reflection fiber Bragg grating and a fiber reflector, and is used to intelligently control the total reflection path of the pump light, the emission light generated by the pump ytterbium-doped fiber, and the multi-order Stokes light generated by the stimulated Raman scattering effect through a grid search algorithm to form a semi-open cavity structure; A pump beam combining module is used to couple multiple pump beams to generate one pump beam; The Raman gain module is used to generate multi-order Stokes light by stimulated Raman scattering under the action of pump light, and the multi-order Stokes light is subjected to spectrum analysis by Fourier transform method to obtain the frequency components and power distribution of each order of Stokes light, and finally form a multi-band random Raman fiber laser signal; A mode control module, used to adjust the laser mode in the laser to perform single-mode or multi-mode laser output; The polarization control module is used to adjust the polarization state within the laser and optimize the polarization characteristics of the laser output.

[0008] Furthermore, the total reflection paths of the pump light, the emission light generated by the pumped Yb-doped fiber, and the multi-order Stokes light generated by the stimulated Raman scattering effect are intelligently controlled by a grid search algorithm to form a semi-open cavity structure, including: Determine the value range of the total reflection path parameters of the pump light, the emission light and each order of Stokes light, including the reflection angle and the position of the reflection surface, and combine the total reflection path parameters into a multi-dimensional grid search space; According to the multi-dimensional grid search space, an initial grid point set is generated, each grid point represents a set of optical path parameters; Set the step size and iteration number parameters of the grid search, and for each grid point, simulate the propagation process of the pump light, emission light and each order of Stokes light in the fiber laser, calculate the reflection, refraction and scattering effects of each light in the optical path, and obtain the output characteristics of the optical path; According to the preset performance indicators, including reflection efficiency, optical path stability, and multi-band output uniformity, the optical path performance corresponding to each grid point is evaluated through a comprehensive evaluation function to obtain the final grid point and the corresponding optical path parameters; According to the step size and iteration number of the grid search, the grid point set is adjusted to generate a new search space, and the process of simulating light path propagation and evaluating light path performance is repeated until the preset number of iterations is reached, and the final light path parameters are determined as the light path design scheme; The final optical path parameters are used as an optical path design scheme to adjust the physical structure of the fiber laser, including the position and angle of the reflector, to form a semi-open cavity structure.

[0009] Furthermore, the calculation formula of the comprehensive evaluation function is: ; in, Represents the comprehensive evaluation function value; Represents the weight coefficient of reflection efficiency; represents the effective reflection efficiency; The weight coefficient representing the stability of the optical path; Indicates the effective diameter of the light beam; The scale coefficient indicating the degree of fluctuation; Indicates the total length of the optical path; The weight coefficient representing the uniformity of multi-band output; Represents the average output power of all bands; Indicates the band index; Indicates the number of bands; Indicates The output power of each band.

[0010] Furthermore, a plurality of pump light beams are coupled to generate a pump light beam, including: Analyze the number, wavelength range, power level, and output mode parameters of the pump light sources, and determine the fiber coupler based on the number and wavelength range of the pump light sources; Determine the power capacity of the fiber coupler based on the power level of the pump light source; Multiple pump light beams are coupled through a fiber coupler, and during the coupling process, the power and phase of each pump light beam are adjusted to obtain a coupled pump light beam.

[0011] Furthermore, under the action of pump light, stimulated Raman scattering occurs to generate multi-order Stokes light, and the multi-order Stokes light is spectrally analyzed by Fourier transform method to obtain the frequency components and power distribution of each order of Stokes light, and finally a multi-band random Raman fiber laser signal is formed, including: When the pump light interacts with the phonons in the optical fiber, part of the energy of the pump light is transferred to the phonons and generates photons with a frequency lower than that of the pump light, namely, first-order Stokes light; The first-order Stokes light acts as a new pump light, interacting with the phonons in the optical fiber to generate the second-order Stokes light. The process of each order of Stokes light acting as the pump light for the next order of Stokes light is repeated, and finally multiple orders of Stokes light are generated. A spectrometer is used to collect multi-order Stokes optical signals, and the collected time domain signals are converted into frequency domain signals through Fourier transform; Analyze the frequency domain signal to determine the frequency components and power distribution of each order of Stokes light, and integrate the various order Stokes light signals after spectrum analysis to form a random Raman fiber laser signal containing multiple bands; Further, the laser mode in the laser is regulated to output single-mode or multi-mode laser, including: Set the initial operating conditions of the laser, including pump power, resonant cavity structure, and determine the target mode and target mode shape of the laser output; Using a mode matching algorithm, according to the spatial distribution of the target mode, the structure and parameters of the resonant cavity are designed to match the spatial distribution of the target mode, including selecting lenses and concave lens optical elements to obtain the relative position and focal length parameters of the optical elements; Physically adjust the laser or replace and position the optical elements according to the position and focal length parameters of the optical elements; Start the laser and monitor the pattern of the output beam in real time.

[0012] Furthermore, the pattern matching algorithm is used to design the structure and parameters of the resonant cavity according to the spatial distribution of the target mode to match the spatial distribution of the target mode, including selecting lenses and concave lens optical elements to obtain the relative positions and focal length parameters of the optical elements, including: Inputting the spatial distribution information of the target pattern into the pattern matching algorithm, including the shape, size, and spot radius parameters of the target pattern, and setting the initial parameters of the pattern matching algorithm, including the search range, genetic algorithm, and convergence condition; Create an optical component library, which contains models and data of various lenses and concave lenses, and start the pattern matching algorithm to try different optical component combinations and relative positions and focal length parameters according to the spatial distribution of the target pattern; According to the principle of genetic algorithm, a population is initialized, and each individual represents a combination of the structure and parameters of a resonant cavity; For each individual in the population, i.e., each combination of resonant cavity structure and parameters, the overlap integral and mode purity index between the output beam and the target mode are calculated using a mode matching algorithm; According to the overlap integral and mode purity index between the beam and the target mode, the fitness of each individual is evaluated, that is, the degree of matching between the current resonant cavity structure and the target mode; Select parent individuals for reproduction according to fitness, and perform crossover operations on the selected parent individuals to generate new offspring individuals; Perform mutation operation on offspring individuals and add the mutated offspring individuals to the population; The process of selection, crossover and mutation is repeated until the preset number of iterations is reached, the resonant cavity structure matching the target mode is determined as the final matching solution, and the optical element parameters in the final matching solution are output, including element type, relative position, and focal length.

[0013] Furthermore, the calculation formula for each individual's fitness is: ; in, represents the fitness function; , represents the weight coefficient; represents the amplitude of the beam intensity distribution; represents the total amplitude of the target pattern; Represents the mathematical constant pi; Indicates the outer radius of the circle where the target pattern is located; Indicates the inner radius of the circle; represents the number of mode coefficients; The mode coefficient representing the target mode; represents radial coordinates; Coefficients representing design parameters; represents a constant term; Express Perform integration; represents the sum index; represents the coefficients of the linear function; represents the design parameters; Represents the constant term of a linear function.

[0014] Furthermore, the reflectivity of the high-reflectivity fiber Bragg grating is greater than 0.9.

[0015] In a second aspect, a computing device includes: one or more processors; A storage device is used to store one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement the semi-open cavity multi-band random Raman fiber laser.

[0016] The above solution of the present invention includes at least the following beneficial effects: The pump module matches the wavelength emitted by the laser diode with the absorption wavelength of the pump ytterbium-doped fiber, providing an efficient and stable pump light source. This matching ensures the effective absorption and conversion of pump energy and improves the overall efficiency of the laser.

[0017] The total reflection module is composed of a high-reflection fiber Bragg grating and a fiber reflector. It combines a grid search algorithm to intelligently control the total reflection path of the pump light, the emission light, and the multi-order Stokes light generated by the stimulated Raman scattering effect. This intelligent control not only forms a stable semi-open cavity structure, but also optimizes the propagation path of light in the cavity, thereby improving the stability and performance of the laser.

[0018] The pump beam combining module couples multiple pump beams to generate a high-intensity pump beam. This coupling effect increases the energy density of the pump light, making the stimulated Raman scattering effect more significant, which is conducive to the generation of multi-order Stokes light.

[0019] Under the action of pump light, the Raman gain module generates multi-order Stokes light by stimulated Raman scattering. The frequency components and power distribution of each order of Stokes light can be obtained by spectrum analysis using the Fourier transform method. This spectrum analysis capability enables the laser to output multi-band, randomly distributed Raman fiber laser signals, meeting a variety of application requirements.

[0020] The mode control module can adjust the laser mode in the laser to achieve single-mode or multi-mode laser output. This flexibility allows the laser to adapt to different application scenarios, such as single-mode lasers that require high coherence or multi-mode lasers that require high power.

[0021] The polarization control module is used to adjust the polarization state in the laser and optimize the polarization characteristics of the laser output. By optimizing the polarization state, the output efficiency and stability of the laser can be improved, while meeting the requirements of certain specific applications for polarized light. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a semi-open cavity multi-band random Raman fiber laser provided by an embodiment of the present invention.

[0023] Figure 2 It is a flow chart of forming a semi-open cavity structure by intelligently controlling the total reflection path of the pump light, the emission light generated by the pump ytterbium-doped fiber and the multi-order Stokes light generated by the stimulated Raman scattering effect of the semi-open cavity multi-band random Raman fiber laser provided by an embodiment of the present invention through a grid search algorithm. DETAILED DESCRIPTION

[0024] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0025] like Figure 1 As shown, an embodiment of the present invention proposes a semi-open cavity multi-band random Raman fiber laser, comprising: A pump module 11 is used to match the wavelength emitted by the laser diode with the absorption wavelength of the pump ytterbium-doped optical fiber to provide a pump light source; The total reflection module 12 is composed of a high-reflection fiber Bragg grating and a fiber reflector, and is used to intelligently control the total reflection path of the pump light, the emission light generated by the pump ytterbium-doped fiber, and the multi-order Stokes light generated by the stimulated Raman scattering effect through a grid search algorithm to form a semi-open cavity structure; A pump beam combining module 13, used for coupling multiple pump light beams to generate a pump light beam; The Raman gain module 14 is used to generate multi-order Stokes light by stimulated Raman scattering under the action of pump light, and the multi-order Stokes light is subjected to spectrum analysis by Fourier transform method to obtain the frequency components and power distribution of each order of Stokes light, and finally form a multi-band random Raman fiber laser signal; A mode control module 15 is used to adjust the laser mode in the laser to perform single-mode or multi-mode laser output; The polarization control module 16 is used to adjust the polarization state in the laser and optimize the polarization characteristics of the laser output.

[0026] In the embodiment of the present invention, the pump module 11 ensures efficient absorption of pump energy by matching the wavelength emitted by the laser diode with the absorption wavelength of the pump ytterbium-doped fiber. This matching reduces energy loss, improves the stability and efficiency of the pump light source, and provides reliable and continuous pump energy for the laser.

[0027] The total reflection module 12 is composed of a highly reflective fiber Bragg grating and a fiber reflector, and intelligently controls the total reflection path of light through a grid search algorithm. This intelligent control mechanism not only forms a stable semi-open cavity structure, but also optimizes the propagation of light in the cavity, reduces light loss, and improves the output power and stability of the laser. At the same time, it can also flexibly adjust the path of light to meet different laser output requirements.

[0028] The pump beam combining module 13 couples multiple pump beams to generate a high-intensity pump beam. This coupling effect improves the energy density and uniformity of the pump light, making the stimulated Raman scattering effect more significant and stable. This helps to generate higher power and more stable laser output.

[0029] Under the action of pump light, the Raman gain module 14 generates multi-order Stokes light by stimulated Raman scattering. The frequency components and power distribution of each order of Stokes light can be accurately obtained by spectrum analysis using the Fourier transform method. This spectrum analysis capability enables the laser to output multi-band, randomly distributed Raman fiber laser signals, meeting the needs of scientific research, industry and other fields for multi-wavelength lasers.

[0030] The mode control module 15 can adjust the laser mode in the laser to achieve single-mode or multi-mode laser output. This flexibility allows the laser to adapt to different application scenarios and requirements. For example, in applications requiring high coherence and low noise, single-mode laser output can be selected; in applications requiring high power and a wide spectrum, multi-mode laser output can be selected.

[0031] The polarization control module 16 is used to adjust the polarization state in the laser and optimize the polarization characteristics of the laser output. By optimizing the polarization state, the output efficiency and stability of the laser can be improved, and the polarization-related loss and noise can be reduced. At the same time, it can also meet the needs of certain specific applications for polarized light, such as optical communications, optical storage and other fields.

[0032] In a preferred embodiment of the present invention, the pump module 11 is used to match the wavelength emitted by the laser diode with the absorption wavelength of the pump ytterbium-doped optical fiber and provide a pump light source, which may include: In the embodiment of the present invention, the absorption wavelength of the pumped ytterbium-doped fiber is clearly defined. The ytterbium-doped fiber is a gain medium used in fiber lasers, and its absorption wavelength range generally includes 915nm and 976nm. Next, a laser diode is selected as a pump source to ensure that its emitted wavelength matches the absorption wavelength of the ytterbium-doped fiber. For example, for an ytterbium-doped fiber with an absorption wavelength of 976nm, a laser diode with an emission wavelength of 976nm should be selected as a pump source. The laser diode is mounted on a suitable radiator to ensure its stability and life during operation. The design of the radiator needs to take into account factors such as the power of the laser diode and the operating environment temperature.

[0033] Design a suitable drive circuit to control the current and temperature of the laser diode to stabilize its output power and wavelength. This usually includes a constant current source, a temperature sensor, and a feedback control circuit. Combine the laser diode with an optical system (such as a lens, a fiber coupler, etc.) to efficiently couple the laser beam into the ytterbium-doped fiber. This requires the use of specific coupling techniques such as direct coupling, lens coupling, or fiber coupler.

[0034] The pump light source (including laser diode, driving circuit and optical system) is integrated with the ytterbium-doped fiber into a compact module. This requires the use of specific packaging technologies, such as metal housing, sealing technology, etc., to protect the internal components from the external environment. During the system integration process, special attention should be paid to the adjustment and calibration of the optical path to ensure that the pump light can be efficiently coupled into the ytterbium-doped fiber. This requires the use of specific optical instruments, such as spectrometers, power meters, etc.

[0035] In a preferred embodiment of the present invention, a grid search algorithm is used to intelligently control the total reflection paths of the pump light, the emission light generated by the pump ytterbium-doped fiber, and the multi-order Stokes light generated by the stimulated Raman scattering effect to form a semi-open cavity structure, which may include: Determine the value range of the total reflection path parameters of the pump light, the emission light and each order of Stokes light, including the reflection angle and the position of the reflection surface, and combine the total reflection path parameters into a multi-dimensional grid search space; According to the multi-dimensional grid search space, an initial grid point set is generated, each grid point represents a set of optical path parameters; Set the step size and iteration number parameters of the grid search, and for each grid point, simulate the propagation process of the pump light, emission light and each order of Stokes light in the fiber laser, calculate the reflection, refraction and scattering effects of each light in the optical path, and obtain the output characteristics of the optical path; According to the preset performance indicators, including reflection efficiency, optical path stability, and multi-band output uniformity, the optical path performance corresponding to each grid point is evaluated through a comprehensive evaluation function to obtain the final grid point and the corresponding optical path parameters; According to the step size and iteration number of the grid search, the grid point set is adjusted to generate a new search space, and the process of simulating light path propagation and evaluating light path performance is repeated until the preset number of iterations is reached, and the final light path parameters are determined as the light path design scheme; The final optical path parameters are used as an optical path design scheme to adjust the physical structure of the fiber laser, including the position and angle of the reflector, to form a semi-open cavity structure.

[0036] In an embodiment of the present invention, relevant data about the propagation of pump light, emission light and each order of Stokes light in the fiber laser are collected, including the refractive index of the optical fiber, the reflectivity of the reflector, the parameters of the scattering effect, etc. Based on the collected data and the design requirements of the fiber laser, the value range of the total reflection path parameters such as the reflection angle and the position of the reflection surface is determined. The determined parameter range is divided according to a certain step size, and all parameters are combined into a multidimensional grid search space. According to the multidimensional grid search space, an initial set of grid points is generated. Each grid point represents a set of optical path parameters, including the reflection angle, the position of the reflection surface, etc., and the generated grid points are stored in a data structure.

[0037] Set the step size and iteration number parameters of the grid search to control the accuracy and efficiency of the search. For each grid point, use optical simulation software or algorithms to simulate the propagation process of pump light, emission light and each order of Stokes light in the fiber laser. Considering the reflection, refraction and scattering effects, calculate the propagation path and output characteristics of each light in the optical path. According to the design requirements of the fiber laser, define performance indicators such as reflection efficiency, optical path stability, and multi-band output uniformity. Write a comprehensive evaluation function to evaluate the optical path performance corresponding to each grid point according to the performance indicators. For each grid point, call the comprehensive evaluation function to calculate the corresponding optical path performance evaluation result.

[0038] According to the step size and number of iterations of the grid search, the grid point set is adjusted to generate a new search space. In the new search space, the process of simulating optical path propagation and evaluating optical path performance is repeated to check whether the preset number of iterations has been reached or whether optical path parameters that meet the design requirements have been found. If so, the search is stopped; otherwise, the grid point set is adjusted and the search is repeated. Among all the evaluated grid points, the grid point with the best performance is selected as the final optical path parameter. The final optical path parameters are recorded for subsequent physical structure adjustments of the fiber laser.

[0039] Assume that there is a fiber laser model, which contains pump light, emission light and first-order Stokes light. It is hoped that the optimal total reflection path parameters will be found through a grid search algorithm to form a semi-open cavity structure.

[0040] Initialize the range of the reflection angle to [0°, 90°], and the range of the reflection surface position to [0mm, 100mm]. Combine these two parameters into a two-dimensional grid search space with a step size of 1° and 1mm. Generate an initial grid point set containing 101×101 grid points based on the defined range and step size. Set the step size of the grid search to 1° and 1mm, and the number of iterations to 100. For each grid point, use optical simulation software to simulate the propagation process of pump light, emission light, and first-order Stokes light in the fiber laser.

[0041] Reflection efficiency, optical path stability, and multi-band output uniformity were defined as performance indicators, and a comprehensive evaluation function was written to evaluate the optical path performance corresponding to each grid point. The grid point set was adjusted according to the evaluation results, a new search space was generated, and the process of simulating propagation and evaluating performance was repeated. After 100 iterations, the grid point with the best performance was found, and the optical path parameters corresponding to the grid point with the best performance were recorded as the final optical path design solution.

[0042] By intelligently controlling the total reflection path parameters through the grid search algorithm, the optical path design of the fiber laser can be optimized, and performance indicators such as reflection efficiency, optical path stability, and multi-band output uniformity can be improved. Traditional optical path design methods may require a lot of experimentation and debugging time, while the grid search algorithm can quickly simulate and evaluate multiple optical path schemes on the computer, thereby shortening the design cycle. By simulating and evaluating the optical path scheme by computer, the cost of materials and equipment required for the experiment can be reduced, and the overall design cost can be reduced. The grid search algorithm can process multi-dimensional parameter space, allowing designers to explore optical path design schemes in a wider range and enhance design flexibility. By applying advanced grid search algorithms and optical simulation techniques, the innovation and development of fiber laser technology can be promoted.

[0043] In a preferred embodiment of the present invention, the calculation formula of the comprehensive evaluation function is: ; in, Represents the comprehensive evaluation function value; Represents the weight coefficient of reflection efficiency; represents the effective reflection efficiency; The weight coefficient representing the stability of the optical path; Indicates the effective diameter of the light beam; The scale coefficient indicating the degree of fluctuation; Indicates the total length of the optical path; The weight coefficient representing the uniformity of multi-band output; Represents the average output power of all bands; Indicates the band index; Indicates the number of bands; Indicates The output power of each band.

[0044] In the embodiment of the present invention, the reflection efficiency is determined according to the design objectives and importance of the fiber laser. , Optical path stability and multi-band output uniformity Specifically, set , indicating that reflection efficiency accounts for half of the importance in the comprehensive evaluation; , indicating that optical path stability accounts for 30% of the importance; , indicating that multi-band output uniformity accounts for 20% of the importance.

[0045] Through simulation, the effective reflection efficiency of pump light, emission light and each order of Stokes light in the fiber laser is measured. Assuming that after accurate measurement, the effective reflection efficiency is , which means a reflection efficiency of 90%.

[0046] The optical path stability indicator is the effective diameter of the beam , the total length of the optical path and the complexity scale coefficient of the volatility Jointly decided, the calculation formula is .

[0047] The multi-band output uniformity index takes into account the average value of the output power in all bands. , output power in each band And the number of bands , the calculation formula is .

[0048] Substitute the calculated reflection efficiency (0.9), optical path stability index and multi-band output uniformity index into the comprehensive evaluation function formula, and calculate the comprehensive evaluation function value according to the determined weight coefficient .

[0049] The comprehensive evaluation function quantifies performance indicators such as reflection efficiency, optical path stability, and multi-band output uniformity, and can more intuitively compare the advantages and disadvantages of different optical path design schemes. Through the comprehensive evaluation function, the optical path design scheme with better performance can be quickly screened out, reducing the time cost of experiments and debugging, and improving design efficiency. The comprehensive evaluation function takes into account multiple performance indicators and assigns different weight coefficients. It can find a balance between multiple performance indicators and optimize the optical path design. The application of the comprehensive evaluation function has promoted the innovation and development of fiber laser technology. The performance and application scope of fiber lasers can be improved by continuously improving the optical path design scheme. Fiber laser products with high performance and stability will be more competitive. By optimizing the optical path design scheme through the comprehensive evaluation function, fiber laser products with better performance and more stability can be produced to meet market demand.

[0050] In a preferred embodiment of the present invention, coupling multiple pump light beams to generate a pump light beam may include: Analyze the number, wavelength range, power level, and output mode parameters of the pump light sources, and determine the fiber coupler based on the number and wavelength range of the pump light sources; Determine the power capacity of the fiber coupler based on the power level of the pump light source; Multiple pump light beams are coupled through a fiber coupler, and during the coupling process, the power and phase of each pump light beam are adjusted to obtain a coupled pump light beam.

[0051] In an embodiment of the present invention, relevant information of the pump light source is obtained through a sensor or input interface, the obtained data is processed, the number of pump light sources is analyzed, and it is determined how many light sources need to be coupled. The wavelength range of each pump light source is analyzed to ensure that they are within the wavelength range that can be coupled, and the power level of each pump light source is measured or queried, and the specific value is recorded. The output mode parameters (such as single mode, multimode, etc.) of the pump light source are analyzed. According to the number and wavelength range of the pump light sources obtained by the analysis, the database or preset rules are queried to select a suitable fiber coupler type (such as 1x2, 1xN, etc.), and the wavelength range is considered to select a coupler that can cover all pump light source wavelengths, and the insertion loss, return loss and other performance indicators of the coupler are determined to ensure that the system requirements are met.

[0052] Calculate the total power of all pump light sources, and consider a certain power margin, check the power capacity specifications of the fiber coupler, and select a coupler that can withstand the total power. Introduce multiple pump lights into the fiber coupler through optical fibers. During the coupling process, use a variable optical attenuator or phase modulator to adjust the power and phase of each pump light, monitor the output light after coupling, and adjust the power and phase through the feedback mechanism until the coupling light that meets the requirements is obtained.

[0053] Assume that there are three pump light sources with wavelengths of 1060nm, 1064nm and 1065nm, powers of 10W, 15W and 12W, all of which are single-mode outputs.

[0054] After obtaining this information, it was analyzed that there were three pump light sources with a wavelength range of 1060-1065nm and a total power of 37W. Based on this information, a 1x3 fiber coupler was selected, which can cover the wavelength range of 1060-1065nm and has a power capacity greater than 37W. The three pump lights were introduced into the coupler through optical fibers, and the power and phase of each beam were adjusted using a variable optical attenuator and a phase modulator. After adjustment, a coupled pump light with a total power of 37W and a wavelength range of 1060-1065nm was obtained.

[0055] By coupling multiple pump beams, the power of the pump light source can be used more effectively and the pumping efficiency can be improved. Coupling multiple pump beams into one beam can simplify the system structure of the fiber laser and reduce the complexity and cost of the system. By accurately adjusting the power and phase of each pump beam, stable coupled light can be obtained to enhance the stability of the system. The coupling of multiple pump beams can broaden the wavelength range of the pump light and meet the needs of more types of fiber lasers.

[0056] In a preferred embodiment of the present invention, under the action of pump light, stimulated Raman scattering occurs to generate multi-order Stokes light, and the multi-order Stokes light is subjected to spectrum analysis by Fourier transform method to obtain the frequency components and power distribution of each order of Stokes light, and finally a multi-band random Raman fiber laser signal is formed, which may include: When the pump light interacts with the phonons in the optical fiber, part of the energy of the pump light is transferred to the phonons and generates photons with a frequency lower than that of the pump light, namely, first-order Stokes light; The first-order Stokes light acts as a new pump light, interacting with the phonons in the optical fiber to generate the second-order Stokes light. The process of each order of Stokes light acting as the pump light for the next order of Stokes light is repeated, and finally multiple orders of Stokes light are generated. A spectrometer is used to collect multi-order Stokes optical signals, and the collected time domain signals are converted into frequency domain signals through Fourier transform; The frequency domain signal is analyzed to determine the frequency components and power distribution of each order of Stokes light, and the various order Stokes light signals after spectrum analysis are integrated to form a random Raman fiber laser signal containing multiple bands.

[0057] In the embodiment of the present invention, the pump light is emitted by the laser, and the pump light enters the optical fiber. In the optical fiber, the pump light interacts with the phonon, and part of the energy of the pump light is transferred to the phonon through the stimulated Raman scattering effect. After the phonon gains energy, it re-radiates photons, and the frequency of these photons is lower than the frequency of the pump light, forming first-order Stokes light.

[0058] The first-order Stokes light is guided back into the optical fiber as a new pump light. The first-order Stokes light interacts with the phonons in the optical fiber again to generate the second-order Stokes light. This process is repeated, and each order of Stokes light serves as the pump light for the next order of Stokes light, continuously generating higher-order Stokes light. By continuously monitoring and recording the generation of each order of Stokes light, multiple orders of Stokes light are eventually generated.

[0059] A spectrometer is used to collect multi-order Stokes optical signals, which are time domain signals. The collected time domain signals are input into the Fourier transform module. The Fourier transform module transforms the time domain signals, converts them into frequency domain signals, and outputs frequency domain signals.

[0060] The frequency domain signal is analyzed, and the frequency components of each order of Stokes light are determined by identifying the peaks in the spectrum. At the same time, the power corresponding to each frequency component is measured to obtain the power distribution of each order of Stokes light. The Stokes light signals of each order after spectrum analysis are integrated to form a random Raman fiber laser signal containing multiple bands, and the final random Raman fiber laser signal is output.

[0061] Assume that a pump light with a wavelength of 1064nm is launched into the optical fiber.

[0062] The pump light interacts with the phonons in the optical fiber to generate first-order Stokes light with a wavelength of 1070nm. The first-order Stokes light acts as a new pump light and interacts with the phonons again to generate second-order Stokes light with a wavelength of 1076nm. This process is repeated to generate third-order, fourth-order and other multi-order Stokes light. These multi-order Stokes light signals are collected using a spectrometer and converted into frequency domain signals. The frequency domain signals are analyzed to determine the frequency components (such as 1070nm, 1076nm, etc.) and power distribution of each order of Stokes light. These various order Stokes light signals after spectral analysis are integrated to form a random Raman fiber laser signal containing multiple bands (such as 1064nm pump light band, 1070nm first-order Stokes light band, 1076nm second-order Stokes light band, etc.).

[0063] By generating multi-order Stokes light, the energy of the pump light can be fully utilized and the spectrum utilization rate can be improved. The generation of multi-order Stokes light broadens the wavelength range of the laser and provides more options for the application of fiber lasers. Random Raman fiber laser signals are random and diverse and can be used in fiber optic communications, fiber optic sensing and other fields to improve the safety and reliability of the system.

[0064] In a preferred embodiment of the present invention, regulating the laser mode in the laser to output single-mode or multi-mode laser may include: Set the initial operating conditions of the laser, including pump power, resonant cavity structure, and determine the target mode and target mode shape of the laser output; Using a mode matching algorithm, according to the spatial distribution of the target mode, the structure and parameters of the resonant cavity are designed to match the spatial distribution of the target mode, including selecting lenses and concave lens optical elements to obtain the relative position and focal length parameters of the optical elements; Physically adjust the laser or replace and position the optical elements according to the position and focal length parameters of the optical elements; Start the laser and monitor the pattern of the output beam in real time.

[0065] In an embodiment of the present invention, the initial pump power of the laser is set through the control interface to ensure that it is within a safe and effective range. According to the preset or experimental requirements, the structure of the resonant cavity is selected and configured, such as selecting a combination of a plane mirror, a concave mirror, or a convex mirror. The target mode (such as single mode or multimode) output by the laser and the shape of the target mode (such as Gaussian type, flat top type, etc.) are determined. These initial working conditions and target mode information are stored in the control system.

[0066] The pattern matching algorithm is called, and the algorithm performs calculations based on the spatial distribution characteristics of the target pattern (such as beam radius, curvature, etc.). Based on the calculation results, the algorithm designs the structure and parameters of the resonant cavity, such as the curvature radius of the mirror, the focal length of the lens, etc. According to the algorithm's suggestions, suitable optical elements such as lenses and concave lenses are selected, and their relative positions and focal length parameters are determined. These design results are output to the control system for the next step of physical adjustment or replacement and positioning of optical elements.

[0067] According to the design results, make physical adjustments to the laser, such as adjusting the position and angle of the mirror. If the optical component needs to be replaced, remove the old component manually and install the new one. Precisely position the newly installed optical components to ensure that their position and focal length parameters are consistent with the design results. After the adjustment is completed, perform a preliminary test on the laser to ensure that the adjusted laser can work properly. Start the laser through the control interface to start working, and use a beam quality analyzer or similar equipment to monitor the pattern of the output beam in real time. If the pattern of the output beam does not match the target pattern, adjust the parameters of the laser or the position of the optical component until a satisfactory result is achieved.

[0068] Suppose a solid-state laser needs to be regulated to output Gaussian single-mode laser.

[0069] The initial pump power of the laser was set to 10W, and a plane mirror and a concave mirror were selected as the mirrors of the resonant cavity. The target mode was determined to be a Gaussian single-mode laser, and the mode matching algorithm was called for calculation. The algorithm recommended adding a lens with a focal length of 100mm to the resonant cavity, and gave the relative position and focal length parameters of the lens. According to the algorithm's recommendations, the laser was physically adjusted, the lens was installed, and the position of the mirror was adjusted. The laser was started, and the mode of the output beam was monitored in real time using a beam quality analyzer. After adjustment, the output of a Gaussian single-mode laser was successfully achieved.

[0070] By adjusting the laser mode, it is possible to ensure that the laser outputs high-quality laser beams to meet various application requirements. The laser output mode can be flexibly adjusted according to different application requirements to achieve single-mode or multi-mode laser output. High-quality laser output helps promote scientific research and technological development in fields such as material processing, optical communications, and biomedicine. In industrial production, high-quality laser output can improve production efficiency and product quality and reduce production costs.

[0071] In another preferred embodiment of the present invention, the structure and parameters of the resonant cavity are designed according to the spatial distribution of the target mode using a pattern matching algorithm to match the spatial distribution of the target mode, including selecting a lens or a concave lens optical element to obtain the relative position and focal length parameters of the optical element, which may include: Inputting the spatial distribution information of the target pattern into the pattern matching algorithm, including the shape, size, and spot radius parameters of the target pattern, and setting the initial parameters of the pattern matching algorithm, including the search range, genetic algorithm, and convergence condition; Create an optical component library, which contains models and data of various lenses and concave lenses, and start the pattern matching algorithm to try different optical component combinations and relative positions and focal length parameters according to the spatial distribution of the target pattern; According to the principle of genetic algorithm, a population is initialized, and each individual represents a combination of the structure and parameters of a resonant cavity; For each individual in the population, i.e., each combination of resonant cavity structure and parameters, the overlap integral and mode purity index between the output beam and the target mode are calculated using a mode matching algorithm; According to the overlap integral and mode purity index between the beam and the target mode, the fitness of each individual is evaluated, that is, the degree of matching between the current resonant cavity structure and the target mode; Select parent individuals for reproduction according to fitness, and perform crossover operations on the selected parent individuals to generate new offspring individuals; Perform mutation operation on offspring individuals and add the mutated offspring individuals to the population; The process of selection, crossover and mutation is repeated until the preset number of iterations is reached, the resonant cavity structure matching the target mode is determined as the final matching solution, and the optical element parameters in the final matching solution are output, including element type, relative position, and focal length.

[0072] In an embodiment of the present invention, spatial distribution information of the target pattern is received through a user interface or a program interface, including parameters such as shape (such as Gaussian type, flat top type, etc.), size (such as beam diameter), and spot radius. This information is input into the pattern matching algorithm as input data of the algorithm. The initial parameters of the pattern matching algorithm are set, including the search range (such as the search range of the lens focal length), the parameters of the genetic algorithm (such as population size, crossover probability, mutation probability, etc.), and the convergence conditions (such as fitness threshold, number of iterations, etc.).

[0073] Create an optical component library, which contains models and data of various optical components such as lenses and concave lenses, such as focal length, radius of curvature, refractive index, etc. Start the pattern matching algorithm, which tries different combinations of optical components and relative positions and focal length parameters in the optical component library according to the spatial distribution of the target pattern.

[0074] The algorithm evaluates the matching degree of each combination and parameter to the target mode through simulation or calculation. According to the principle of genetic algorithm, a population is initialized, and each individual in the population represents a combination of the structure and parameters of a resonant cavity. The genetic code of the individual can include parameters such as the type, relative position, and focal length of the optical element.

[0075] For each individual in the population, that is, each combination of resonant cavity structure and parameters, the overlap integral between the output beam and the target mode is calculated using a mode matching algorithm. The overlap integral is an important indicator to measure the similarity between the output beam and the target mode. At the same time, the mode purity index is calculated to evaluate the single-mode nature or mode quality of the output beam.

[0076] According to the overlap integral and mode purity indicators, the fitness of each individual is evaluated. Individuals with high fitness indicate that their corresponding resonant cavity structure matches the target mode more closely, and the fitness is used as the basis for selecting parent individuals for reproduction. Parent individuals are selected for reproduction based on fitness, and the roulette wheel selection method is used to perform crossover operations on the selected parent individuals, generating new offspring individuals by exchanging gene fragments.

[0077] The crossover operation helps introduce new solutions during the search process and increase the diversity of the population. Perform mutation operations on the offspring individuals to introduce new mutations by randomly changing the values ​​of certain parameters in the gene encoding. The mutation operation helps to jump out of the local optimal solution and increase the possibility of searching for the global optimal solution. Add the mutated offspring individuals to the population and prepare for the next round of selection, crossover and mutation operations. Repeat the selection, crossover and mutation process until the preset number of iterations is reached. During the iteration process, the fitness of individuals in the population is continuously evaluated and the final solution is updated. When the iteration ends, the resonant cavity structure that matches the target mode is determined as the final matching solution. Output the optical element parameters in the final matching solution, including element type, relative position, focal length, etc.

[0078] Suppose you need to design a resonant cavity for a solid-state laser to output Gaussian single-mode laser.

[0079] Receive the spatial distribution information of the target mode, including Gaussian shape, beam diameter and spot radius, and create an optical component library containing models and data of various lenses and concave lenses. Start the pattern matching algorithm and initialize a population, each individual represents a combination of the structure and parameters of a resonant cavity. For each individual in the population, the pattern matching algorithm is used to calculate the overlap integral and pattern purity index between the output beam and the target mode. Select the parent individual for reproduction according to the fitness, and perform crossover and mutation operations on the offspring individuals. Repeat the above process until the preset number of iterations is reached. Finally, a resonant cavity structure that matches the target mode is determined, and the optical component parameters in the final matching scheme are output, including the type, relative position and focal length of the lens.

[0080] Through the automated design process, multiple optical component combinations and parameters can be quickly tried to improve design efficiency. The matching degree between each resonant cavity structure and the target mode can be accurately evaluated, so as to optimize the resonant cavity structure and improve the quality of the output beam. According to different target mode requirements, the design parameters and optical component combinations can be flexibly adjusted to meet diverse application requirements. High-quality laser output helps promote scientific research and technological development in fields such as material processing, optical communications, and biomedicine. By optimizing the resonant cavity structure, more advanced laser light sources can be provided for these fields.

[0081] In another preferred embodiment of the present invention, the calculation formula of the fitness of each individual is: ; in, represents the fitness function; , represents the weight coefficient; represents the amplitude of the beam intensity distribution; represents the total amplitude of the target pattern; Represents the mathematical constant pi; Indicates the outer radius of the circle where the target pattern is located; Indicates the inner radius of the circle; represents the number of mode coefficients; The mode coefficient representing the target mode; represents radial coordinates; Coefficients representing design parameters; represents a constant term; Express Perform integration; represents the sum index; represents the coefficients of the linear function; represents the design parameters; Represents the constant term of a linear function.

[0082] In the embodiment of the present invention, the weight coefficient is set and , these coefficients determine the relative importance of overlap integral and mode purity in the fitness function. The total amplitude of the input target mode , the amplitude of the amplitude distribution , the inner radius of the ring and outer radius. Calculate the mode coefficient of the target mode (Assumption ) and the number of mode coefficients . Initialize design parameters , and coefficients related to the design parameters and constant term .

[0083] Compute radial coordinates using numerical integration methods such as Simpson's rule from arrive Points , multiply the integral result by , to get the contribution to the overlap integral.

[0084] For each mode coefficient (from 1 to 5), calculate the design parameters The corresponding linear function value (Assumption and There are specific values, such as ) and the target mode coefficient The square of the difference between , divide the sum by the sum of the squares of the target mode coefficients , we get a measure of mode impurity. We subtract the measure of mode impurity from 1 to get the contribution to mode purity.

[0085] Multiply the contribution of the overlap integral by the weight coefficient 0.6, multiply the contribution of the mode purity by the weight coefficient 0.4, and add the two parts to get the fitness function The value of .

[0086] By comprehensively considering the overlap integral and pattern purity, the fitness function can more accurately evaluate the matching degree between the design parameters and the target pattern, thereby improving the matching accuracy. , The relative importance of overlap integral and mode purity in the fitness function can be adjusted according to specific needs, thereby enhancing the flexibility of the design. The explicit expression of the fitness function enables the genetic algorithm to automatically search for the optimal design parameters without human intervention, thereby promoting the development of automated design. Through numerical integration and efficient genetic algorithms, the fitness function can quickly calculate and optimize the design parameters, thereby accelerating the design process. High-quality matching schemes can improve the performance of optical systems, such as improving the output efficiency of lasers and reducing mode impurity, thereby meeting more diverse application requirements.

[0087] In a preferred embodiment of the present invention, the polarization control module 16 is used to adjust the polarization state in the laser and optimize the polarization characteristics of the laser output, which may include: Clarify the functional requirements of the polarization control module, that is, adjust the polarization state within the laser to optimize the polarization characteristics of the laser output, which includes determining the required polarization state type (such as linear polarization, circular polarization, elliptical polarization, etc.) and polarization characteristic indicators (such as polarization degree, polarization direction, etc.). Select appropriate polarization control components according to requirements, such as polarizers, wave plates (such as λ / 2 wave plates, λ / 4 wave plates), Faraday rotators, liquid crystal polarization modulators, etc., which can change the polarization state of light. Integrate the selected polarization control components into the laser system to ensure that they can work accurately and stably.

[0088] After the integration is complete, a polarimeter is used to measure the initial polarization state of the laser output. Based on the measurement results, the position or parameters of the polarization control element are adjusted to make the polarization state of the laser output as close to the target polarization state as possible, which requires multiple iterations and adjustments. Suitable sensors, such as photodetectors or polarization sensors, are installed in the laser system to monitor the polarization characteristics of the laser output in real time. Through a real-time control algorithm, the parameters of the polarization control element are adjusted according to the feedback signal from the sensor to maintain or optimize the polarization characteristics of the laser output. The sensor, control algorithm, and polarization control element are integrated into a closed-loop control system to achieve automatic adjustment and optimization of the laser polarization characteristics.

[0089] In another preferred embodiment of the present invention, the reflectivity of the high-reflectivity fiber Bragg grating is greater than 0.9, which may include: In the embodiment of the present invention, an optical fiber is selected as the substrate of the grating, and the characteristics of the optical fiber such as the refractive index, core diameter, and cladding diameter are considered to ensure the performance of the grating. The period of the grating is calculated according to the Bragg condition. The Bragg condition is: λB=2HΛ, where λB is the center wavelength, H is the refractive index of the optical fiber, and Λ is the grating period. According to the type of optical fiber and the required grating characteristics, a suitable writing method is selected, such as ultraviolet light writing.

[0090] Using ultraviolet light source and phase mask, write grating in optical fiber, and adjust the reflectivity of grating by controlling the intensity and exposure time of ultraviolet light. Use femtosecond laser pulse to write grating directly in optical fiber. By controlling the pulse energy, repetition frequency and scanning speed of laser, the period and reflectivity of grating can be precisely controlled.

[0091] During the writing process, the reflectance spectrum of the grating is monitored in real time, and the writing parameters are adjusted according to the change in reflectivity to ensure that the reflectivity reaches 0.9.

[0092] An embodiment of the present invention further provides a computing device, comprising: a processor, and a memory storing a computer program, wherein when the computer program is executed by the processor, the semi-open cavity multi-band random Raman fiber laser as described above is executed. All implementation methods in the above-mentioned semi-open cavity multi-band random Raman fiber laser embodiment are applicable to this embodiment, and can also achieve the same technical effect.

[0093] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. Semi-open cavity multi-band random Raman fiber laser, characterized in that: include: A pump module is used to match the wavelength emitted by the laser diode with the absorption wavelength of the pump ytterbium-doped optical fiber to provide a pump light source; The total reflection module, which is composed of a high-reflection fiber Bragg grating and a fiber reflector, is used to intelligently control the total reflection path of the pump light, the emission light generated by the pump ytterbium-doped fiber, and the multi-order Stokes light generated by the stimulated Raman scattering effect through a grid search algorithm to form a semi-open cavity structure; A pump beam combining module is used to couple multiple pump beams to generate one pump beam; The Raman gain module is used to generate multi-order Stokes light by stimulated Raman scattering under the action of pump light, and the multi-order Stokes light is subjected to spectrum analysis by Fourier transform method to obtain the frequency components and power distribution of each order of Stokes light, and finally form a multi-band random Raman fiber laser signal; A mode control module, used to adjust the laser mode in the laser to perform single-mode or multi-mode laser output; The polarization control module is used to adjust the polarization state within the laser and optimize the polarization characteristics of the laser output.

2. The semi-open cavity multi-band random Raman fiber laser according to claim 1, characterized in that: The grid search algorithm is used to intelligently control the total reflection paths of the pump light, the emission light generated by the pump Yb-doped fiber, and the multi-order Stokes light generated by the stimulated Raman scattering effect to form a semi-open cavity structure, including: Determine the value range of the total reflection path parameters of the pump light, the emission light and each order of Stokes light, including the reflection angle and the position of the reflection surface, and combine the total reflection path parameters into a multi-dimensional grid search space; According to the multi-dimensional grid search space, an initial grid point set is generated, each grid point represents a set of optical path parameters; Set the step size and iteration number parameters of the grid search, and for each grid point, simulate the propagation process of the pump light, emission light and each order of Stokes light in the fiber laser, calculate the reflection, refraction and scattering effects of each light in the optical path, and obtain the output characteristics of the optical path; According to the preset performance indicators, including reflection efficiency, optical path stability, and multi-band output uniformity, the optical path performance corresponding to each grid point is evaluated through a comprehensive evaluation function to obtain the final grid point and the corresponding optical path parameters; According to the step size and iteration number of the grid search, the grid point set is adjusted to generate a new search space, and the process of simulating light path propagation and evaluating light path performance is repeated until the preset number of iterations is reached, and the final light path parameters are determined as the light path design scheme; The final optical path parameters are used as an optical path design scheme to adjust the physical structure of the fiber laser, including the position and angle of the reflector, to form a semi-open cavity structure.

3. The semi-open cavity multi-band random Raman fiber laser according to claim 2, characterized in that: The calculation formula of the comprehensive evaluation function is: ; in, Represents the comprehensive evaluation function value; Represents the weight coefficient of reflection efficiency; represents the effective reflection efficiency; The weight coefficient representing the stability of the optical path; Indicates the effective diameter of the light beam; The scale coefficient indicating the degree of fluctuation; Indicates the total length of the optical path; The weight coefficient representing the uniformity of multi-band output; Represents the average value of output power in all bands; Indicates the band index; Indicates the number of bands; Indicates The output power of each band.

4. The semi-open cavity multi-band random Raman fiber laser according to claim 3, characterized in that: Multiple pump beams are coupled to generate a pump beam, including: Analyze the number, wavelength range, power level, and output mode parameters of the pump light sources, and determine the fiber coupler based on the number and wavelength range of the pump light sources; Determine the power capacity of the fiber coupler based on the power level of the pump light source; Multiple pump light beams are coupled through a fiber coupler, and during the coupling process, the power and phase of each pump light beam are adjusted to obtain a coupled pump light beam.

5. The semi-open cavity multi-band random Raman fiber laser according to claim 4, characterized in that: Under the action of pump light, stimulated Raman scattering occurs to generate multi-order Stokes light, and the multi-order Stokes light is spectrally analyzed by Fourier transform method to obtain the frequency components and power distribution of each order of Stokes light, and finally a multi-band random Raman fiber laser signal is formed, including: When the pump light interacts with the phonons in the optical fiber, part of the energy of the pump light is transferred to the phonons and generates photons with a frequency lower than that of the pump light, namely, first-order Stokes light; The first-order Stokes light acts as a new pump light, interacting with the phonons in the optical fiber to generate the second-order Stokes light. The process of each order of Stokes light acting as the pump light for the next order of Stokes light is repeated, and finally multiple orders of Stokes light are generated. A spectrometer is used to collect multi-order Stokes optical signals, and the collected time domain signals are converted into frequency domain signals through Fourier transform; The frequency domain signal is analyzed to determine the frequency components and power distribution of each order of Stokes light, and the various order Stokes light signals after spectrum analysis are integrated to form a random Raman fiber laser signal containing multiple bands.

6. The semi-open cavity multi-band random Raman fiber laser according to claim 5, characterized in that: Control the laser mode in the laser to produce single-mode or multi-mode laser output, including: Set the initial operating conditions of the laser, including pump power, resonant cavity structure, and determine the target mode and target mode shape of the laser output; Using a mode matching algorithm, according to the spatial distribution of the target mode, the structure and parameters of the resonant cavity are designed to match the spatial distribution of the target mode, including selecting lenses and concave lens optical elements to obtain the relative position and focal length parameters of the optical elements; Physically adjust the laser or replace and position the optical elements according to the position and focal length parameters of the optical elements; Start the laser and monitor the pattern of the output beam in real time.

7. The semi-open cavity multi-band random Raman fiber laser according to claim 6, characterized in that: Using the mode matching algorithm, according to the spatial distribution of the target mode, the structure and parameters of the resonant cavity are designed to match the spatial distribution of the target mode, including selecting the lens and concave lens optical elements, and obtaining the relative position and focal length parameters of the optical elements, including: Inputting the spatial distribution information of the target pattern into the pattern matching algorithm, including the shape, size, and spot radius parameters of the target pattern, and setting the initial parameters of the pattern matching algorithm, including the search range, genetic algorithm, and convergence condition; Create an optical component library, which contains models and data of various lenses and concave lenses, and start the pattern matching algorithm to try different optical component combinations and relative positions and focal length parameters according to the spatial distribution of the target pattern; According to the principle of genetic algorithm, a population is initialized, and each individual represents a combination of the structure and parameters of a resonant cavity; For each individual in the population, i.e., each combination of resonant cavity structure and parameters, the overlap integral and mode purity index between the output beam and the target mode are calculated using a mode matching algorithm; According to the overlap integral and mode purity index between the beam and the target mode, the fitness of each individual is evaluated, that is, the degree of matching between the current resonant cavity structure and the target mode; Select parent individuals for reproduction according to fitness, and perform crossover operations on the selected parent individuals to generate new offspring individuals; Perform mutation operation on offspring individuals and add the mutated offspring individuals to the population; The process of selection, crossover and mutation is repeated until the preset number of iterations is reached, the resonant cavity structure matching the target mode is determined as the final matching solution, and the optical element parameters in the final matching solution are output, including element type, relative position, and focal length.

8. The semi-open cavity multi-band random Raman fiber laser according to claim 7, characterized in that: The calculation formula for each individual's fitness is: ； in, represents the fitness function; , represents the weight coefficient; represents the amplitude of the beam intensity distribution; represents the total amplitude of the target pattern; Represents the mathematical constant pi; Indicates the outer radius of the circle where the target pattern is located; Indicates the inner radius of the circle; represents the number of mode coefficients; The mode coefficient representing the target mode; represents radial coordinates; Coefficients representing design parameters; represents a constant term; Express Perform integration; represents the sum index; represents the coefficients of the linear function; represents the design parameters; Represents the constant term of a linear function.

9. The semi-open cavity multi-band random Raman fiber laser according to claim 8, characterized in that: The reflectivity of the high-reflectivity fiber Bragg grating is greater than 0.

9.

10. A computing device, characterized in that: include: one or more processors; A storage device for storing one or more programs, when the one or more programs are executed by the one or more processors, the one or more processors implement the semi-open cavity multi-band random Raman fiber laser as described in any one of claims 1 to 9.

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