Polarization domain wall state detection device and method applied to fiber laser

Abstract

The invention discloses a polarization domain wall state detection device and method applied to an optical fiber laser, and the device comprises a sampling module which is connected with a coupling output device of the optical fiber laser, and is used for obtaining the polarization state waveform data of an optical signal outputted by the coupling output device in real time; the control module comprises an electric polarization controller and a detection unit, and the electric polarization controller is used for controlling the polarization state of an optical signal output by the optical fiber laser; and the detection unit is connected with the sampling module and the electric polarization controller, and is used for generating a polarization control signal according to the duty ratio of the polarization state waveform data and the target duty ratio corresponding to the target polarization state based on a direct search algorithm, so that the electric polarization controller adjusts the polarization state of the output optical signal according to the polarization control signal. And searching and detecting the polarization domain wall state corresponding to the target polarization state in the fiber laser until the duty ratio of the polarization state waveform data is close to the target duty ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lasers, and more particularly to a polarization domain wall state detection device and method applied to optical fiber lasers. Background Art

[0002] Fiber lasers, with their compact structure, high efficiency, and excellent beam quality, have become core light sources in industrial processing, optical communications, medical treatment, and scientific research. In recent years, ultrafast fiber lasers (such as mode-locked lasers) have demonstrated unique advantages in precision machining and nonlinear optics research due to their extremely short pulse widths and high peak power.

[0003] Optical polarization domain walls are dynamic boundary structures between different polarization states, phases, or intensity states, and their evolution directly affects the stability and controllability of fiber laser output. Studies have shown that the formation of polarization domain walls is closely related to the coupling of nonlinear effects, dispersion, and birefringence. Their dynamic characteristics (such as polarization domain wall position and switching frequency) can reflect the internal physical state of the laser. For example, by detecting the phase jump or polarization switching of the polarization domain wall, real-time assessment of the laser noise level can be achieved. By regulating the spatiotemporal distribution of the detected polarization domain wall, new approaches can be provided for generating new ultrashort pulses (such as dark solitons and vector solitons). However, existing technologies for detecting polarization domain walls mostly rely on offline spectrometers or high-speed oscilloscopes, which lack real-time feedback capabilities. In addition, traditional control methods (such as mechanical polarization adjustment) during detection are difficult to achieve sub-millisecond dynamic response, which limits the application of polarization domain walls in active frequency stabilization, optical coding, and other fields. Summary of the Invention

[0004] The present invention provides a polarization domain wall state detection device and method for optical fiber lasers, so as to solve the technical problems of the prior art in lacking real-time feedback capability for polarization domain wall detection and difficulty in quickly achieving polarization adjustment response during detection.

[0005] To solve the above technical problems, according to one aspect of the present invention, a polarization domain wall state detection device for an optical fiber laser is provided. The optical fiber laser includes a pump source, a wavelength division multiplexing coupler, a gain fiber, a coupler output, and a unidirectional polarization-dependent isolator connected in sequence. The unidirectional polarization-dependent isolator is connected to the wavelength division multiplexing coupler to form an optical circulation path. The polarization domain wall state detection device for an optical fiber laser includes:

[0006] A sampling module, connected to the output coupler, for acquiring polarization state waveform data of the optical signal output by the output coupler in real time;

[0007] A control module, comprising an electric polarization controller and a detection unit, wherein:

[0008] The electric polarization controller is connected between the unidirectional polarization-dependent isolator and the wavelength division multiplexing coupler, and is used to control the polarization state of the output optical signal;

[0009] The detection unit is connected to the sampling module and the electric polarization controller, and is used to generate a polarization control signal based on a direct search algorithm according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, so that the electric polarization controller adjusts the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, thereby realizing the search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser.

[0010] Its further technical solution is: the detection unit includes:

[0011] A duty cycle calculation unit, configured to calculate the duty cycle of the polarization state waveform data using a mean value method;

[0012] The search and detection unit is configured to, when the calculated duty cycle deviates from the target duty cycle corresponding to the target polarization state or during initialization, search on the Poincare sphere in a direction that reduces the deviation using the Rosenbrock search algorithm, generate a polarization control signal based on the searched fitness value, so that the electric polarization controller adjusts the polarization state of the output optical signal based on the polarization control signal until the duty cycle of the polarization state waveform data approaches the target duty cycle, terminate the search, obtain the polarization domain wall characteristics of the target polarization state, and implement polarization domain wall state detection.

[0013] A further technical solution is: the polarization state waveform data includes the time domain light intensity waveform data corresponding to the vertical polarized light and the parallel polarized light obtained by decomposing the output optical signal; wherein,

[0014] The search detection unit searches on the Poincare sphere using the Rosenbrock search algorithm in a direction that reduces the deviation between the duty cycle of the parallel polarized light and the target duty cycle, and when the sum of the duty cycles of the vertically polarized light and the parallel polarized light is close to 1, according to the formula A fitness value, fitness, is calculated, and a polarization control signal is generated according to a solution corresponding to the fitness value, so that the electric polarization controller adjusts the voltage of its polarizer according to the polarization control signal, thereby adjusting the polarization state of the output light signal. The search is traversed until the fitness value, fitness, is greater than a preset threshold and the duty cycle of the parallel polarized light approaches a target duty cycle, at which point the search is terminated; wherein D1 is the duty cycle of the parallel polarized light, and D0 is the target duty cycle.

[0015] Its further technical solution is: the sampling module includes:

[0016] a polarization beam splitter, connected to the output coupler, and configured to decompose the output optical signal into vertically polarized light and parallel polarized light;

[0017] a photodetector connected to the polarization beam splitter, and configured to convert the vertically polarized light and the parallel polarized light into electrical signals respectively;

[0018] An oscilloscope is connected to the photodetector and is used to obtain polarization state waveform data based on the electrical signals of the vertically polarized light and the parallel polarized light; wherein the polarization state waveform data includes time domain light intensity waveform data corresponding to the vertically polarized light and the parallel polarized light.

[0019] A further technical solution is as follows: the wavelength division multiplexing coupler has a first port, a second port and a third port, wherein:

[0020] The first port is connected to the output end of the pump source, and the first port can transmit a 980nm laser beam;

[0021] The second port is a pump light coupling output port, connected to the gain fiber, and can transmit 980nm and 1550nm laser beams;

[0022] The third port is connected to the electric polarization controller and can transmit the 1550nm laser beam.

[0023] To solve the above technical problems, according to another aspect of the present invention, a method for detecting the polarization domain wall state of a fiber laser is provided, comprising:

[0024] Obtaining polarization waveform data of an optical signal output by a fiber laser;

[0025] Based on a direct search algorithm, a polarization control signal is generated according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, and the polarization state of the output optical signal is adjusted according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, thereby realizing the search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser.

[0026] A further technical solution is that the direct search algorithm is used to generate a polarization control signal according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, specifically including:

[0027] The duty cycle of polarization state waveform data is calculated using the mean method;

[0028] When the calculated duty cycle deviates from the target duty cycle corresponding to the target polarization state or during initialization, the Rosenbrock search algorithm is used to search on the Poincare sphere in a direction that reduces the deviation, and a polarization control signal is generated according to the search fitness value.

[0029] A further technical solution is as follows: the polarization state waveform data includes time-domain light intensity waveform data corresponding to vertically polarized light and parallel polarized light obtained by decomposing the output optical signal; wherein the Rosenbrock search algorithm is used to search on the Poincare sphere in a direction that reduces the deviation, and a polarization control signal is generated according to the fitness value of the search, specifically including:

[0030] When searching on the Poincare sphere using the Rosenbrock search algorithm, the search is performed in the direction of reducing the deviation between the duty cycle of the parallel polarized light and the target duty cycle. When the sum of the duty cycles of the vertically polarized light and the parallel polarized light is close to 1, according to the formula Calculate the fitness value fitness; where D1 is the duty cycle of parallel polarized light and D0 is the target duty cycle;

[0031] A polarization control signal is generated according to the solution corresponding to the adaptation value.

[0032] A further technical solution is: generating a polarization control signal according to a solution corresponding to the adaptation value specifically includes: generating a polarization control signal according to a solution corresponding to the adaptation value, the polarization control signal including a control voltage corresponding to when the polarization degree of the output optical signal reaches a maximum value.

[0033] A further technical solution is: adjusting the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data approaches the target duty cycle, specifically comprising:

[0034] The polarization state of the optical signal output by the fiber laser is adjusted according to the polarization control signal, and the search is terminated when the fitness value fitness is greater than the preset threshold and the duty cycle of the parallel polarized light is close to the target duty cycle.

[0035] Compared with the prior art, the present invention can obtain the polarization state waveform data of the optical signal output by the fiber laser in real time, thereby obtaining the duty cycle of the polarization state domain wall state, and generate a polarization control signal based on the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state based on a direct search algorithm. The electric polarization controller connected between the unidirectional polarization-dependent isolator and the wavelength division multiplexing coupler of the fiber laser adjusts the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, so as to realize the search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser. It can be seen that the present invention can pre-set the target polarization state and obtain the polarization state according to the target duty cycle. The duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state control the polarization state of the output optical signal, so that different polarization states can be generated in the laser cavity of the fiber laser. The search direction of the direct search algorithm is guided by the duty cycle deviation until the duty cycle of the polarization state waveform data of the optical signal output by the fiber laser is close to the target duty cycle, and a stable polarization domain wall state output corresponding to the target polarization state is searched, thereby realizing the detection of the polarization domain wall state. The present invention can quickly control the polarization adjustment response through the method of intelligent control and hardware collaboration, significantly improving the efficiency and stability of domain wall generation, and at the same time can provide real-time feedback detection of the polarization domain wall state, reducing the difficulty of detecting the polarization domain wall state and improving the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a specific embodiment of the polarization domain wall state detection device applied to optical fiber lasers of the present invention.

[0037] Figure 2 It is a flow chart of a specific embodiment of a method for detecting the polarization domain wall state of an optical fiber laser according to the present invention. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to more clearly understand the objectives, technical solutions and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0039] Reference Figure 1 , Figure 1The figure is a schematic structural diagram of a specific embodiment of a polarization domain wall state detection device for a fiber laser according to the present invention. In the embodiment shown in the figure, the fiber laser includes a pump source 1, a wavelength division multiplexing coupler 2, a gain fiber 3, a coupler output 4, and a unidirectional polarization-dependent isolator 5, which are connected in sequence. The unidirectional polarization-dependent isolator 5 is connected to the wavelength division multiplexing coupler 2 to form an optical circulation path. The polarization domain wall state detection device for a fiber laser includes a sampling module 11 and a control module. The control module includes an electric polarization controller 121 and a detection unit 122. The electric polarization controller 121 is connected between the unidirectional polarization-dependent isolator 5 and the wavelength division multiplexing coupler 2 and is controlled by the detection unit 122.

[0040] Wherein, the pump source 1 is used to generate pump light; the wavelength division multiplexing coupler 2 is used to introduce the pump light into the laser cavity of the fiber laser, and can couple multiple optical signals with different wavelengths (for example, pump light with a wavelength of 980nm and signal light with a wavelength of 1550nm) into one optical signal. In this embodiment, the wavelength division multiplexing coupler 2 has a first port, a second port and a third port, wherein the first port is connected to the output end of the pump source 1, and the first port can transmit the 980nm laser beam; the second port is the pump light coupling output port, which is connected to the gain fiber 3 and can transmit the 980nm and 1550nm laser beams; the third port is connected to the electric polarization controller 121 and can transmit the 1550nm laser beam; and the gain fiber 3 is an erbium-doped gain fiber, which is used to amplify the pump light. For example, the 980nm pump light can be absorbed and amplified into a 1550nm signal light; the coupler output 4 is used to output the light amplified by the gain fiber 3 according to the wavelength division multiplexing process. Preset proportional output, the first output end of the coupler 4 is connected to the unidirectional polarization-dependent isolator 5, the unidirectional polarization-dependent isolator 5 is used to ensure unidirectional operation of light, and at the same time can change the correlation between the horizontal component and the vertical component of the light, that is, change the polarization state of the light, and the second output end of the coupler 4 is connected to the sampling module 11, the sampling module 11 is used to obtain the polarization state waveform data of the optical signal output by the coupler 4 in real time, so as to detect the laser changes in the laser cavity of the fiber laser in real time; the detection unit 122 of the control module is connected to the sampling module 11 and the electric polarization controller 121, and is used to generate a polarization control signal based on the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state based on the direct search algorithm, so that the electric polarization controller 121 adjusts the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, thereby realizing the search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser. Based on the above design, the present invention can pre-set the target polarization state, and control the polarization state of the output optical signal according to the duty cycle of the acquired polarization state waveform data and the target duty cycle corresponding to the target polarization state, so that different polarization states can be generated in the laser cavity of the fiber laser. The search direction of the direct search algorithm is guided by the duty cycle deviation until the duty cycle of the polarization state waveform data of the optical signal output by the fiber laser is close to the target duty cycle, and a stable polarization domain wall state output corresponding to the target polarization state is searched, thereby realizing the detection of the polarization domain wall state. It can be seen that the present invention can quickly control the polarization adjustment response through the method of intelligent control and hardware collaboration, significantly improves the efficiency and stability of domain wall generation, and can promote its innovative application in ultrafast laser processing, optical communication coding and topological photonics. At the same time, it can provide real-time feedback detection of the polarization domain wall state, reducing the difficulty of detecting the polarization domain wall state and improving the detection efficiency.

[0041] In some embodiments, the detection unit 122 includes a duty cycle calculation unit 1221 and a search detection unit 1222, wherein the duty cycle calculation unit 1221 is used to calculate the duty cycle of the polarization state waveform data using the mean method; in this embodiment, the duty cycle of the polarization state waveform data is calculated by the mean method, specifically, the mean of the polarization state waveform data is used as a threshold, and the points in the waveform above the threshold are counted to calculate the duty cycle; the search detection unit 1222 is used to search in the direction of reducing the deviation on the Poincare sphere using the Rosenbrock search algorithm when the calculated duty cycle deviates from the target duty cycle corresponding to the target polarization state or during initialization, and generate a polarization control signal according to the search fitness value, so that the electric polarization controller 121 adjusts the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, terminates the search, obtains the polarization domain wall characteristics of the target polarization state (including the polarization domain wall position and type, etc.), and realizes polarization domain wall state detection. In the present invention, the Rosenbrock function used in the Rosenbrock search algorithm is a non-convex function used to test the performance of an optimization algorithm. This direct search algorithm is used to control the voltages of the three polarizers in the motorized polarization controller 121, adjust the polarization state of the optical signal, and generate nearly all polarization states within the laser cavity of the fiber laser. The polarization domain wall state that meets the duty cycle requirements is then searched within the laser cavity. Based on the above design, this embodiment combines the mean value method with the Rosenbrock search algorithm to search for polarization domain wall states of different polarization states within the laser cavity, thereby enabling detection of the polarization domain wall state.

[0042] It can be seen that the control module of the present invention is used to receive and process the output optical signal. It can set the target duty cycle of the target polarization state, combine the mean method and the Rosenbrock search algorithm, calculate the polarization state duty cycle of the polarization state waveform data obtained in real time, and guide the Rosenbrock search algorithm to search in the direction of reducing the deviation according to the deviation between the calculated polarization state duty cycle and the target duty cycle. During the search process, a polarization control signal is provided to control the electric polarization controller 121 to search for the target polarization domain wall state in the laser cavity of the fiber laser.

[0043] Specifically, in this embodiment, the sampling module 11 includes a polarization beam splitter 111, a photodetector 112 and an oscilloscope 113, wherein the polarization beam splitter 111 is connected to the second output end of the coupler output device 4, and is used to decompose the output light signal into vertically polarized light and parallel polarized light; the number of the photodetectors 112 is two, and the two photodetectors 112 are connected to the polarization beam splitter 111, and are used to convert the vertically polarized light and the parallel polarized light into electrical signals respectively; the oscilloscope 113 is connected to the two photodetectors 112 and can be communicatively connected to the control module, and is used to obtain the time domain light intensity waveform data corresponding to the vertical polarized light and the time domain light intensity waveform data corresponding to the parallel polarized light according to the electrical signal of the vertically polarized light and the electrical signal of the parallel polarized light, that is, the polarization state waveform data includes the time domain light intensity waveform data corresponding to the vertically polarized light and the time domain light intensity waveform data corresponding to the parallel polarized light, and send the polarization state waveform data to the detection unit 122 in the control module. In this embodiment, the detection unit 12 in the control module can be implemented by an algorithm program stored in a computer. The oscilloscope 113 has two channels. Channel 1 collects time-domain light intensity waveform data corresponding to parallel polarized light, corresponding to low-amplitude modulation of the orthogonal component. In this embodiment, when its duty cycle is close to 0.2, it can indicate the stable existence of a polarization domain wall; Channel 2 collects time-domain light intensity waveform data corresponding to vertically polarized light, reflecting high-amplitude pulses of the main polarization component, indicating the strong pulse state of laser mode locking or polarization domain wall.

[0044] Furthermore, when the polarization state waveform data includes the time domain light intensity waveform data corresponding to the vertical polarized light and the parallel polarized light obtained by decomposing the output optical signal; the duty cycle calculation unit 1221 is used to calculate the duty cycle of the time domain light intensity waveform data corresponding to the vertical polarized light and the duty cycle of the time domain light intensity waveform data corresponding to the parallel polarized light using the mean method, that is, the duty cycle calculation is performed with the mean of each time domain light intensity waveform data as the threshold; it can be understood that since it is in the polarization domain wall state, a waveform similar to a square wave is displayed on the oscilloscope 113. After noise reduction filtering, the duty cycle of the waveform data corresponding to the waveform transmitted to the detection unit 122 can be calculated by the mean method. The present invention calculates the duty cycle of the detected polarization domain wall state by applying the mean method. When the search detection unit 122 uses the Rosenbrock search algorithm to search on the Poincare sphere, it searches in the direction of reducing the deviation between the duty cycle of the parallel polarized light and the target duty cycle, and when the sum of the duty cycles of the vertical polarized light and the parallel polarized light is close to 1, according to the formula Calculate a fitness value, fitness, and generate a polarization control signal based on the solution corresponding to the fitness value, so that the electric polarization controller 121 adjusts the voltage of its polarizer according to the polarization control signal, thereby adjusting the polarization state of the output optical signal. The search is terminated when the fitness value, fitness, is greater than a preset threshold and the duty cycle of the parallel polarized light approaches a target duty cycle. D1 is the duty cycle of the parallel polarized light, and D0 is the target duty cycle. Preferably, the preset threshold may be 50.

[0045] It can be understood that when the polarization domain wall state detection device of the present invention is applied to a fiber laser, the voltage of the polarizer in the electric polarization controller 121 can be automatically adjusted according to the waveform data initially collected by the oscilloscope 113 and the target duty cycle of the set target polarization state to obtain the corresponding fiber laser output, and then the polarization domain wall state is searched according to the waveform data of different polarization states collected by the adjusted oscilloscope 113. After iteration, a stable polarization domain wall state output is achieved. Specifically, initialization is first performed, the oscilloscope 113 collects polarization state waveform data, performs the first waveform duty cycle calculation, the Rosenbrock search algorithm randomly generates an initial solution, calculates the fitness value of the initial solution, initializes the search direction to the column vector of the unit matrix and the initialization step size can be set to 100; then an iterative search is performed, and the following operations are performed for each direction (a total of 4 directions): a new solution is calculated according to the step size and direction, and the fitness value of the new solution is calculated, a polarization control signal is generated according to the searched new solution, and the electric polarization controller 121 adjusts the light laser according to the polarization control signal. The polarization state of the optical signal output by the optical device, when the new adaptation value is larger than the old adaptation value, the step size in this direction is increased and the direction and step size are recorded, otherwise the step size in this direction is reduced and recorded; then the duty cycle of the polarization state waveform data obtained in real time after adjustment is calculated, the time domain light intensity waveform data corresponding to the vertical polarized light and the time domain light intensity waveform data corresponding to the parallel polarized light obtained in real time can be respectively subjected to median filtering, wavelet denoising, and adaptive IIR filtering denoising, and their mean values ​​are used as thresholds, and the points above the threshold in the waveform are counted and the duty cycles of the waveform data in channel 1 and channel 2 are calculated respectively; then according to Calculate the fitness value fitness, that is, when the sum of the duty cycles of the two channels is close to 1 (for example, when the sum of the duty cycles of the two channels is 0.9), the fitness value Based on the new solution corresponding to the fitness value, a polarization control signal is generated to adjust the polarization state of the output optical signal through the electric polarization controller 121. A traversal search is performed. If the fitness value is less than 50 for multiple consecutive times during the search, or the search step number exceeds 100, the search is reset. If the fitness value is greater than 50 and the duty cycle of channel 1 is close to the target duty cycle, the search is terminated, the polarization control signal corresponding to the final solution is set as the final control state of the electric polarization controller 121, and the search step number is returned. It can be seen that by optimizing the duty cycle of the time domain waveform data of channel 1 (preferably approaching 0.2) while ensuring the stability of the waveform of channel 2, closed-loop control of the polarization state of the optical signal output by the fiber laser and real-time detection of the polarization domain wall state can be achieved.

[0046] From the above, it can be seen that the present invention can quickly control the polarization adjustment response through intelligent control and hardware collaboration methods, significantly improving the efficiency and stability of domain wall generation. At the same time, it can provide real-time feedback detection of the polarization domain wall state, reducing the difficulty of detecting the polarization domain wall state and improving the detection efficiency. It can promote its innovative application in ultrafast laser processing, optical communication coding and topological photonics.

[0047] Reference Figure 2 , Figure 2 The figure is a flow chart of a specific embodiment of the polarization domain wall state detection method for optical fiber lasers according to the present invention. The polarization domain wall state detection method for optical fiber lasers comprises the following steps:

[0048] S201: Obtain polarization waveform data of an optical signal output by a fiber laser.

[0049] In this step, the polarization state waveform data includes time-domain light intensity waveform data corresponding to vertical polarized light and time-domain light intensity waveform data corresponding to parallel polarized light obtained by decomposing the output optical signal.

[0050] In the present invention, the fiber laser includes a pump source, a wavelength division multiplexing coupler, a gain fiber, a coupler output and a unidirectional polarization-dependent isolator connected in sequence. The unidirectional polarization-dependent isolator is connected to the wavelength division multiplexing coupler to form an optical circulation path, and an electric polarization controller for controlling the polarization state of the output optical signal is also connected between the unidirectional polarization-dependent isolator and the wavelength division multiplexing coupler.

[0051] S202. Generate a polarization control signal based on a direct search algorithm according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, and adjust the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, thereby realizing search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser.

[0052] In this step, the direct search algorithm generates a polarization control signal according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, which may specifically include: using the mean method to calculate the duty cycle of the polarization state waveform data; when the calculated duty cycle deviates from the target duty cycle corresponding to the target polarization state or during initialization, using the Rosenbrock search algorithm to search on the Poincare sphere in a direction that reduces the deviation, and generating the polarization control signal according to the search fitness value.

[0053] Furthermore, the method uses the Rosenbrock search algorithm to search on the Poincare sphere in a direction that reduces the deviation, generates a polarization control signal according to the searched fitness value, and adjusts the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data approaches the target duty cycle, specifically including: searching on the Poincare sphere using the Rosenbrock search algorithm in a direction that reduces the deviation between the duty cycle of the parallel polarized light and the target duty cycle, and when the sum of the duty cycles of the perpendicular polarized light and the parallel polarized light is close to 1, according to the formula Calculate the fitness value, fitness, where D1 is the duty cycle of the parallel polarized light and D0 is the target duty cycle. Generate a polarization control signal based on the solution corresponding to the fitness value. Adjust the polarization state of the fiber laser output light signal based on the polarization control signal. Terminate the search until the fitness value, fitness, exceeds the preset threshold and the duty cycle of the parallel polarized light approaches the target duty cycle.

[0054] Preferably, in this embodiment, a polarization control signal is generated according to the solution corresponding to the adaptation value, which includes a control voltage corresponding to when the polarization degree of the output optical signal reaches a maximum value, so as to control the voltage of the three polarizers in the electric polarization controller and adjust the polarization state of the optical signal. That is, the electric polarization controller is controlled by an intelligent algorithm to adjust the polarization state of the output optical signal to realize the detection of the polarization domain wall state.

[0055] It should be noted that, for some specific limitations on the polarization domain wall state detection method applied to a fiber laser, reference can be made to the above limitations on the polarization domain wall state detection device applied to a fiber laser, which will not be repeated here.

[0056] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Those skilled in the art may make various equivalent changes and improvements based on the above embodiment. Any equivalent changes or modifications made within the scope of the claims shall fall within the scope of protection of the present invention.

Claims

1. A polarization domain wall state detection device for a fiber laser, wherein the fiber laser comprises a pump source, a wavelength division multiplexing coupler, a gain fiber, a coupler output, and a unidirectional polarization-dependent isolator connected in sequence, wherein the unidirectional polarization-dependent isolator is connected to the wavelength division multiplexing coupler to form an optical circulation path, characterized in that: The polarization domain wall state detection device applied to the optical fiber laser comprises: A sampling module, connected to the output coupler, for acquiring polarization state waveform data of the optical signal output by the output coupler in real time; A control module, comprising an electric polarization controller and a detection unit, wherein: The electric polarization controller is connected between the unidirectional polarization-dependent isolator and the wavelength division multiplexing coupler, and is used to control the polarization state of the output optical signal; The detection unit is connected to the sampling module and the electric polarization controller, and is used to generate a polarization control signal based on a direct search algorithm according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, so that the electric polarization controller adjusts the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, thereby realizing the search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser.

2. The polarization domain wall state detection device for optical fiber laser according to claim 1, wherein: The detection unit comprises: A duty cycle calculation unit, configured to calculate the duty cycle of the polarization state waveform data using a mean value method; The search and detection unit is configured to, when the calculated duty cycle deviates from the target duty cycle corresponding to the target polarization state or during initialization, search on the Poincare sphere in a direction that reduces the deviation using the Rosenbrock search algorithm, generate a polarization control signal based on the searched fitness value, so that the electric polarization controller adjusts the polarization state of the output optical signal based on the polarization control signal until the duty cycle of the polarization state waveform data approaches the target duty cycle, terminate the search, obtain the polarization domain wall characteristics of the target polarization state, and implement polarization domain wall state detection.

3. The polarization domain wall state detection device for optical fiber laser according to claim 2, characterized in that: The polarization state waveform data includes the time domain light intensity waveform data corresponding to the vertical polarized light and the parallel polarized light obtained by decomposing the output optical signal; wherein, The search detection unit searches on the Poincare sphere using the Rosenbrock search algorithm in a direction that reduces the deviation between the duty cycle of the parallel polarized light and the target duty cycle, and when the sum of the duty cycles of the vertically polarized light and the parallel polarized light is close to 1, according to the formula A fitness value, fitness, is calculated, and a polarization control signal is generated according to a solution corresponding to the fitness value, so that the electric polarization controller adjusts the voltage of its polarizer according to the polarization control signal, thereby adjusting the polarization state of the output light signal. The search is traversed until the fitness value, fitness, is greater than a preset threshold and the duty cycle of the parallel polarized light approaches a target duty cycle, at which point the search is terminated; wherein D1 is the duty cycle of the parallel polarized light, and D0 is the target duty cycle.

4. The polarization domain wall state detection device for optical fiber laser according to claim 1, wherein: The sampling module comprises: a polarization beam splitter, connected to the output coupler, and configured to decompose the output optical signal into vertically polarized light and parallel polarized light; a photodetector connected to the polarization beam splitter, and configured to convert the vertically polarized light and the parallel polarized light into electrical signals respectively; An oscilloscope is connected to the photodetector and is used to obtain polarization state waveform data based on the electrical signals of the vertically polarized light and the parallel polarized light; wherein the polarization state waveform data includes time domain light intensity waveform data corresponding to the vertically polarized light and the parallel polarized light.

5. The polarization domain wall state detection device for optical fiber laser according to claim 1, wherein: The wavelength division multiplexing coupler has a first port, a second port and a third port, wherein: The first port is connected to the output end of the pump source, and the first port can transmit a 980nm laser beam; The second port is a pump light coupling output port, connected to the gain fiber, and can transmit 980nm and 1550nm laser beams; The third port is connected to the electric polarization controller and can transmit the 1550nm laser beam.

6. A method for detecting the polarization domain wall state of a fiber laser, characterized in that: The polarization domain wall state detection method applied to a fiber laser comprises: Obtaining polarization waveform data of an optical signal output by a fiber laser; Based on a direct search algorithm, a polarization control signal is generated according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state, and the polarization state of the output optical signal is adjusted according to the polarization control signal until the duty cycle of the polarization state waveform data is close to the target duty cycle, thereby realizing the search and detection of the polarization domain wall state corresponding to the target polarization state in the fiber laser.

7. The polarization domain wall state detection method for optical fiber laser according to claim 6, characterized in that: Generating a polarization control signal based on the direct search algorithm according to the duty cycle of the polarization state waveform data and the target duty cycle corresponding to the target polarization state specifically includes: The duty cycle of polarization state waveform data is calculated using the mean method; When the calculated duty cycle deviates from the target duty cycle corresponding to the target polarization state or during initialization, the Rosenbrock search algorithm is used to search on the Poincare sphere in a direction that reduces the deviation, and a polarization control signal is generated according to the search fitness value.

8. The polarization domain wall state detection method for optical fiber laser according to claim 7, characterized in that: The polarization state waveform data includes time-domain light intensity waveform data corresponding to vertically polarized light and parallel polarized light obtained by decomposing the output optical signal. The method further includes searching on the Poincare sphere in a direction that reduces deviation using a Rosenbrock search algorithm and generating a polarization control signal based on a fitness value of the search, specifically comprising: When searching on the Poincare sphere using the Rosenbrock search algorithm, the search is performed in the direction of reducing the deviation between the duty cycle of the parallel polarized light and the target duty cycle. When the sum of the duty cycles of the vertically polarized light and the parallel polarized light is close to 1, according to the formula Calculate the fitness value fitness; where D1 is the duty cycle of parallel polarized light and D0 is the target duty cycle; A polarization control signal is generated according to the solution corresponding to the adaptation value.

9. The polarization domain wall state detection method for optical fiber laser according to claim 8, characterized in that: Generating the polarization control signal according to the solution corresponding to the adaptation value specifically includes: generating, according to the solution corresponding to the adaptation value, the polarization control signal including a control voltage corresponding to when the polarization degree of the output optical signal reaches a maximum value.

10. The polarization domain wall state detection method for optical fiber laser according to claim 8, characterized in that: The adjusting the polarization state of the output optical signal according to the polarization control signal until the duty cycle of the polarization state waveform data approaches the target duty cycle specifically includes: The polarization state of the optical signal output by the fiber laser is adjusted according to the polarization control signal, and the search is terminated when the fitness value fitness is greater than the preset threshold and the duty cycle of the parallel polarized light is close to the target duty cycle.

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