Coherent synthesis fiber laser tilt noise acquisition and tilt control method and system

Abstract

In order to improve the precision of coherent synthesis fiber laser tilt control, the present application provides a kind of coherent synthesis fiber laser tilt noise acquisition and tilt control method and system, utilize the data processing method of Fourier transform and numerical fitting combination, obtain more accurate x and y two directions of stripe number, respectively in x and y two dimensions on tilt correction, can realize smaller tilt residual, realize the fine control of high-precision tilt in large element coherent synthesis system.The present application can be applied to the control of high-precision tilt in sub-aperture coherent synthesis, improve the synthesis efficiency of coherent synthesis system.

Description

Technical Field

[0001] This invention mainly relates to the field of coherent fiber laser technology, and in particular to a method and system for acquiring and controlling tilt noise in coherent fiber lasers. Background Technology

[0002] Coherent combining of fiber lasers can overcome the power limitations of a single fiber and is an effective way to obtain high average power and high quality lasers. In practical applications, coherent combining of fiber laser arrays is not simply a matter of superimposing multiple fiber laser beams; rather, it requires real-time phase control of each fiber laser beam to coherently superimpose them, thereby obtaining high-brightness lasers.

[0003] To obtain a high-brightness synthesized laser, it is necessary to compensate for various noises in each fiber laser involved in the synthesis in real time to ensure that the synthesized laser maintains the energy concentration of the central main lobe at all times. Since mechanical vibrations in the environment are unavoidable, each fiber laser will introduce tilt errors due to jitter, causing a shift in the beam direction of each fiber laser and thus degrading the beam quality of the synthesized spot. Therefore, to maintain beam quality, it is essential to perform high-precision compensation for the tilt errors of each fiber laser.

[0004] Current methods for tilt control systems include using a single photodetector to achieve simultaneous control of the piston and tilt, typically employing time-division multiplexing in the algorithm, which reduces the bandwidth of tilt control; using multiple photodetectors can also achieve tilt control, but this complicates the system; using a high-speed camera to capture interference fringes can enable synchronous high-speed calculation of piston phase and tilt error based on the fringe data. According to existing theoretical models, the accuracy of tilt control affects the accuracy of piston phase calculation, therefore improving the accuracy of tilt control is a core problem that urgently needs to be solved for this system. Summary of the Invention

[0005] In order to improve the accuracy of tilt control of coherently synthesized fiber lasers and address the technical problems existing in the prior art, this invention proposes a method and system for acquiring tilt noise and controlling tilt in coherently synthesized fiber lasers.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] Methods for obtaining tilt noise in coherently synthesized fiber lasers include:

[0008] Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays;

[0009] The interference fringe image is cropped into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser, where M≥4, and M is the number of horizontal and vertical pixels in the image selected according to the number of pixels covered by each laser on the target surface of the high-speed camera. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser.

[0010] One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0011] The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on an M*1 array of center coordinates in the x and y directions of each interference fringe sub-image.

[0012] The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image.

[0013] Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis is calculated.

[0014] Furthermore, the precise number of interference fringes in the x and y directions in each interference fringe sub-image is calculated, including:

[0015] Construct a trigonometric function to be fitted based on the light intensity data of the M*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions;

[0016] Based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image, the initial values ​​of the undetermined coefficients of the corresponding trigonometric functions to be fitted are assigned.

[0017] The sum of squares of the differences between the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the x-direction and the trigonometric functions to be fitted in the M*1 array in the x-direction, and the sum of squares of the differences between the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the y-direction and the trigonometric functions to be fitted in the M*1 array in the y-direction, are used as the target functions in the x-direction and y-direction, respectively. Based on the initial values ​​of the undetermined coefficients of the corresponding trigonometric functions to be fitted, the least squares method is used to fit the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the x-direction and y-direction, respectively. The trigonometric function frequency parameters and phase parameters that minimize the target functions in the x-direction and y-direction are taken respectively.

[0018] Based on the calculated trigonometric function frequency parameters, the exact number of interference fringes in the x and y directions in the i-th interference fringe sub-image is calculated.

[0019] Specifically, for the light intensity data of the M*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions, the following trigonometric function to be fitted is constructed:

[0020]

[0021] in, Let k be the trigonometric function to be fitted for the light intensity data of the M*1 array of the center coordinates of the i-th interference fringe image in the x and y directions. x k y The unknown frequencies of the trigonometric function to be fitted. Let K be the undetermined phase of the trigonometric function to be fitted, and K be a constant chosen based on the size of the original interference fringe image data. Generally, let a be the maximum value of the fringe light intensity in the original interference fringe image data, then the range of K can be [0.8a / 2, 1.2a / 2].

[0022] Based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image, initial values ​​are assigned to the undetermined coefficients of the corresponding trigonometric functions to be fitted. Specifically, the initial values ​​of the undetermined coefficients of the trigonometric functions to be fitted are assigned as follows:

[0023]

[0024] In the formula, (δ fft,x ,δ fft,y ) represents the approximate integer number of interference fringes in the x and y directions obtained from the Fourier transform calculation of the M*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions.

[0025] Specifically, the objective functions in the x and y directions for:

[0026]

[0027] In the formula, I i (x), I i (y) represents the light intensity data of an M*1 array of coordinates of the center of the i-th interference fringe sub-image in the x and y directions. This is the sum of the squares of the differences between the two functions.

[0028] Based on the calculated trigonometric function frequency parameter k x k yThe exact number of interference fringes in the x and y directions in the i-th interference fringe sub-image is calculated. Specifically, it is calculated using the following formula:

[0029]

[0030] In the formula, k x k y In order to make The parameter that takes the minimum value, (δ) cal,x ,δ cal,y ) represents the precise number of interference fringes in the x and y directions in the i-th interference fringe sub-image obtained after calculation.

[0031] Furthermore, the tilt noise of each sub-laser beam in the laser array relative to the x-axis and y-axis is calculated, including:

[0032] Based on the fringe spacing introduced by the unified reference light, the tilt angles of the reference light in the x and y directions are TILT respectively. ref,x and TILT ref,y ;

[0033] Based on the tilt angles of the reference light in the x and y directions and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise TILT of each sub-laser beam relative to the x and y axes in the array laser is obtained. x and TILT y :

[0034]

[0035] In the formula, δ CCD This refers to the single pixel size of a high-speed camera.

[0036] On the other hand, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, performs the following steps:

[0037] Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays;

[0038] The interference fringe image is cropped into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each sub-laser in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each sub-laser in the array laser.

[0039] One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0040] The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on an M*1 array of center coordinates in the x and y directions of each interference fringe sub-image.

[0041] The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image.

[0042] Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis is calculated.

[0043] On the other hand, the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the following steps:

[0044] Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays;

[0045] The interference fringe image is cropped into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each sub-laser in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each sub-laser in the array laser.

[0046] One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0047] The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on an M*1 array of center coordinates in the x and y directions of each interference fringe sub-image.

[0048] The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image.

[0049] Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis is calculated.

[0050] The technical effects that this invention can produce through the above technical solution are:

[0051] This invention utilizes a high-speed camera to acquire more images per unit time, and with the help of computer processing, it can obtain more accurate tilt information for each laser beam, thereby enabling compensation.

[0052] This invention utilizes a data processing method that combines Fourier transform and numerical fitting to obtain a more accurate number of fringes for tilt correction, thereby achieving a smaller tilt residual.

[0053] This invention utilizes the number of fringes in the x and y directions to perform correction in two dimensions. This method can not only be applied to high-precision tilt control in aperture-separated coherent synthesis, but also has the potential to be extended to high-precision tilt control in coherent synthesis with a common aperture. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0055] Figure 1 This is a schematic diagram of the coherent combining fiber laser tilt control system provided in one embodiment of the present invention;

[0056] Figure 2 The diagram shows the arrangement of the laser array in the detection surface before and after beam shrinking in one embodiment of the present invention, wherein (a) is the arrangement of the laser array in the detection surface before beam shrinking, and (b) is the arrangement of the laser array in the detection surface after beam shrinking.

[0057] Figure 3 The images show the interference fringe pattern of the fiber laser unit beams involved in the synthesis without tilt noise in one embodiment of the present invention, and an enlarged view of the interference fringe pattern of one of the fiber laser beams. (a) is the interference fringe pattern of the fiber laser unit beams involved in the synthesis, and (b) is an enlarged view of the interference fringe pattern of one of the fiber laser beams.

[0058] Figure 4 for Figure 3 (b) contains the high-speed camera sampling data enclosed by the white dashed line, where (a) is... Figure 3 (b) contains the high-speed camera sampling data enclosed by the dashed line in the x-direction. (b) is... Figure 3 (b) High-speed camera sampling data contained in the dashed line in the y-direction;

[0059] Figure 5The images show the interference fringe pattern of the fiber laser unit beams involved in the synthesis and an enlarged view of the interference fringe pattern of one of the fiber laser beams in one embodiment of the present invention with added tilt noise, wherein (a) is the interference fringe pattern of the fiber laser unit beams involved in the synthesis and (b) is an enlarged view of the interference fringe pattern of one of the fiber laser beams.

[0060] Figure 6 for Figure 5 (b) contains the high-speed camera sampling data enclosed by the white dashed line, where (a) is... Figure 5 (b) contains the high-speed camera sampling data enclosed by the dashed line in the x-direction. (b) is... Figure 5 (b) High-speed camera sampling data contained in the dashed line in the y-direction;

[0061] Figure 7 The number of interference fringes in the x and y directions is obtained after Fourier transform calculation in one embodiment of the present invention, where (a) is the number of interference fringes in the x direction after Fourier transform calculation, and (b) is the number of interference fringes in the y direction after Fourier transform calculation.

[0062] Figure 8 In one embodiment of the present invention Figure 7 The exact number of fringes in the x and y directions is obtained by fitting method based on the above, where (a) is the exact number of fringes in the x direction and (b) is the exact number of fringes in the y direction.

[0063] Figure 9 In one embodiment of the present invention, 100 sets of tilt noise are applied in the x and y directions, wherein (a) is 100 sets of tilt noise applied in the x direction and (b) is 100 sets of tilt noise applied in the y direction.

[0064] Figure 10 In one embodiment of the present invention, there are 100 sets of tilt residuals in the x and y directions, where (a) is 100 sets of tilt residuals in the x direction and (b) is 100 sets of tilt residuals in the y direction. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the disclosed content will be clearly explained below with reference to the accompanying drawings and detailed description. Any person skilled in the art, after understanding the embodiments of the present invention, can make changes and modifications based on the techniques taught in the present invention without departing from the spirit and scope of the present invention. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0066] In one embodiment of the present invention, a method for obtaining tilt noise in coherently synthesized fiber lasers is provided, comprising the following steps:

[0067] Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays;

[0068] The interference fringe image is cropped into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser. Here, M ≥ 4, and M is the number of horizontal and vertical pixels in the image selected based on the number of pixels covered by each laser beam on the high-speed camera target surface. In this embodiment, M is set to 128, resulting in 128*128 interference fringe sub-images. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser.

[0069] One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N 128*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0070] The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on the 128*1 array of the center coordinates of each interference fringe sub-image in the x and y directions.

[0071] The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image.

[0072] Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis is calculated.

[0073] In the above embodiment, the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image is calculated. Specifically, for the i-th interference fringe sub-image, Fourier transform calculations are performed on the 128*1 arrays in the x and y directions, as follows:

[0074]

[0075] In the formula, (x,y) are the position coordinates of a pixel in the i-th interference fringe sub-image, (u,v) are the spectral coordinates of a pixel in the image obtained after the Fourier transform of the i-th interference fringe sub-image, || is the modulo operation in complex number operations, I i (x), I i (y) represents the light intensity data of a one-dimensional array of the center coordinates of the i-th interference fringe sub-image in the x and y directions. M is the Fourier transform of the light intensity data of a one-dimensional array of the center coordinates of the i-th interference fringe sub-image in the x and y directions. i (u), M i (v) represents the amplitude of the Fourier transform of the one-dimensional array of the center coordinates of the i-th interference fringe sub-image in the x and y directions. In studying interference fringes, the physical meaning of the spectral coordinates (u,v) is the number of interference fringes contained in the 128*1 array. Due to the limitations of discretization sampling, the number of fringes can only be calculated to the integer level; therefore, (u,v) is an integer. However, the exact number of fringes is not strictly equal to an integer, which introduces a significant error when calculating tilt error. Here, (u,v) is defined as (δ... fft,x ,δ fft,y ), where is the approximate integer number of interference fringes in the x and y directions obtained by Fourier transform calculation of the 128*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions.

[0076] Furthermore, in another specific embodiment, the precise number of interference fringes in the x and y directions in each interference fringe sub-image is calculated, including:

[0077] Construct a trigonometric function to be fitted based on the light intensity data of a 128*1 array with the center coordinates of the i-th interference fringe image in the x and y directions;

[0078] Based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image, the initial values ​​of the undetermined coefficients of the corresponding trigonometric functions to be fitted are assigned.

[0079] The sum of squares of the differences between the light intensity data of the 128*1 array of the center coordinates of each interference fringe sub-image in the x-direction and the trigonometric functions to be fitted in the 128*1 array of the x-direction, and the sum of squares of the differences between the light intensity data of the 128*1 array of the center coordinates of each interference fringe sub-image in the y-direction and the trigonometric functions to be fitted in the 128*1 array of the y-direction, are used as the target functions in the x-direction and y-direction, respectively. Based on the initial values ​​of the undetermined coefficients of the corresponding trigonometric functions to be fitted, the least squares method is used to fit the light intensity data of the 128*1 array of the center coordinates of each interference fringe sub-image in the x-direction and y-direction, respectively. The trigonometric function frequency parameters and phase parameters that minimize the target functions in the x-direction and y-direction are selected respectively.

[0080] Based on the calculated trigonometric function frequency parameters, the exact number of interference fringes in the x and y directions in the i-th interference fringe sub-image is calculated.

[0081] Specifically, for the light intensity data of the 128*1 array in the x and y directions of the center coordinates of the i-th interference fringe sub-image, a trigonometric function to be fitted is constructed as follows:

[0082]

[0083] in, Let k be the trigonometric function to be fitted for the 128*1 array of light intensity data of the center coordinates of the i-th interference fringe image in the x and y directions. x k y The unknown frequencies of the trigonometric function to be fitted. Let K be the undetermined phase of the trigonometric function to be fitted, and K be a constant selected based on the size of the original interference fringe image data. Let the maximum value of the fringe light intensity in the original interference fringe image data be a, then the range of K is [0.8a / 2, 1.2a / 2].

[0084] Based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image, initial values ​​are assigned to the undetermined coefficients of the corresponding trigonometric functions to be fitted. Specifically, the initial values ​​of the undetermined coefficients of the trigonometric functions to be fitted are assigned as follows:

[0085]

[0086] In the formula, (δ fft,x ,δ fft,y ) represents the approximate integer number of interference fringes in the x and y directions obtained from the Fourier transform calculation of the 128*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions.

[0087] Specifically, the objective functions in the x and y directions for:

[0088]

[0089] In the formula, I i (x), I i (y) represents the light intensity data of a 128*1 array in the x and y directions, representing the center coordinates of the i-th interference fringe sub-image. This is the sum of the squares of the differences between the two functions.

[0090] Based on the calculated trigonometric function frequency parameter k x k y The exact number of interference fringes in the x and y directions in the i-th interference fringe sub-image is calculated. Specifically, it is calculated using the following formula:

[0091]

[0092] In the formula, k x k y In order to make The parameter that takes the minimum value, (δ) cal,x ,δcal,y ) represents the precise number of interference fringes in the x and y directions in the i-th interference fringe sub-image obtained after calculation.

[0093] Furthermore, the tilt noise of each sub-laser beam in the laser array relative to the x-axis and y-axis is calculated, including:

[0094] Based on the fringe spacing introduced by the unified reference light, the tilt angles of the reference light in the x and y directions are TILT respectively. ref,x and TILT ref,y ;

[0095] Based on the tilt angles of the reference light in the x and y directions and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise TILT of each sub-laser beam relative to the x and y axes in the array laser is obtained. x and TILT y :

[0096]

[0097] In the formula, δ CCD This refers to the single pixel size of a high-speed camera.

[0098] On the other hand, based on the above-described method for obtaining tilt noise in coherently synthesized fiber lasers, this invention also provides, in one embodiment, a device for obtaining tilt noise in coherently synthesized fiber lasers, comprising:

[0099] The acquisition module is used to acquire the interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays;

[0100] The first image processing module is used to crop the interference fringe image into N interference fringe sub-images with a resolution of 128*128 according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser.

[0101] The second image processing module is used to extract one-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located, and obtain 2N 128*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0102] The first calculation module calculates the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image by performing a Fourier transform on a 128*1 array of the center coordinates of each interference fringe sub-image in the x and y directions.

[0103] The second calculation module calculates the precise number of interference fringes in the x and y directions of each interference fringe sub-image based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image.

[0104] The third calculation module calculates the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x-direction and y-direction of each interference fringe sub-image.

[0105] On the other hand, based on the above-mentioned method for obtaining tilt noise in coherently synthesized fiber lasers, this invention also provides a method for controlling the tilt of coherently synthesized fiber lasers in one embodiment, comprising the following steps:

[0106] Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays;

[0107] The interference fringe image is cropped into N interference fringe sub-images with a resolution of 128*128 according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser.

[0108] One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N 128*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0109] The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on the 128*1 array of the center coordinates of each interference fringe sub-image in the x and y directions.

[0110] The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image.

[0111] Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser in the array laser relative to the x-axis and y-axis is calculated.

[0112] Real-time tilt compensation is performed on each sub-laser beam in the array laser based on the tilt noise of each sub-laser beam relative to the x-axis and y-axis, thereby achieving high-precision tilt control.

[0113] On the other hand, based on the above-mentioned method for obtaining tilt noise of coherently synthesized fiber laser, the present invention also provides a coherently synthesized fiber laser tilt control system in one embodiment, including a laser array coherent synthesis subsystem, an image preprocessing module, a high-precision tilt calculation module, and a tilt device control module. In the laser array coherent synthesis subsystem, the seed laser is divided into two parts, one part is used to generate the array laser, and the other part is used as a reference light. The array laser is beam-constricted after passing through a double lens and interferes with the reference light emitted through a mirror. The interference fringe image of the array laser and the reference light is acquired using a high-speed camera. The array laser is composed of N sub-laser arrays.

[0114] The image preprocessing module includes a first image processing module and a second image processing module;

[0115] The first image processing module is used to crop the interference fringe image into N interference fringe sub-images with a resolution of 128*128 according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser.

[0116] The second image processing module is used to extract one-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located, and obtain 2N 128*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis.

[0117] The high-precision tilt calculation module includes a first calculation module, a second calculation module, and a third calculation module;

[0118] The first calculation module calculates the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image by performing a Fourier transform on a 128*1 array of the center coordinates of each interference fringe sub-image in the x and y directions.

[0119] The second calculation module calculates the precise number of interference fringes in the x and y directions of each interference fringe sub-image based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image.

[0120] The third calculation module calculates the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x-direction and y-direction of each interference fringe sub-image.

[0121] The tilting device control module performs real-time tilt compensation for each sub-laser in the array laser based on the tilt noise of each sub-laser relative to the x-axis and y-axis, thereby achieving high-precision tilt control.

[0122] like Figure 1 As shown, in one embodiment of the present invention, a high-precision tilt control method and system based on interference fringe calculation is provided. The laser wavelength used in this system is 1064nm. It includes an optical fiber seed laser 101, a preamplifier 102, a 1×N optical fiber beam splitter 103, a phase modulator 104, a cascaded optical fiber amplifier 105, an adaptive optical fiber collimator array 106, an adjustable amplifier 107, a reference light collimator 108, a mirror 109, a semi-transparent mirror 110, a first lens 111 and a second lens 112, a high-speed camera 201, an image preprocessing module 202, a high-precision tilt calculation module 203, and a tilt device control module 204.

[0123] In this example, taking a 7-channel laser unit (N=8) as an example, the laser output from the fiber seed laser 101 is first amplified by the preamplifier 102, and then split into 8 beams by the 1×8 fiber beam splitter 103. One beam is used as a reference beam, and the other 7 beams are used as unit beams for coherent combining.

[0124] Each beam of the unit beam undergoes phase modulation by phase modulator 104 and further power amplification by cascaded fiber amplifier 105. It is then input to adaptive fiber collimator array 106 for tilt control before being output. The output light spot shape is as follows: Figure 2 As shown in (a), the beam waist size is 20 mm. Because... Figure 2 The size of the left image is much larger than the target surface size of a high-speed camera. A beam-shrinking system is formed by a first lens 111 and a second lens 112 with a focal length ratio of 20 / 1. The shape of the array laser spot after beam shrinking is as follows: Figure 2 As shown in (b).

[0125] In one embodiment, the reference beam, after being collimated by the adjustable amplifier 107 and the reference beam collimator 108, is reflected at the reflector 109 and then transmitted to the semi-transparent mirror 110. It is then superimposed on the beam spot of the seven-channel unit beam, which has been compressed by the second lens 112 and the first lens 111 after being transmitted to the semi-transparent mirror. An image of the beam spot is obtained using the high-speed camera 201, such as... Figure 3 and Figure 5 As shown, where, Figure 3 (a) shows the interference pattern of the array laser without tilt noise, and (b) shows a magnified view of the interference fringes of one of the laser beams. Figure 5 (a) shows the interference pattern of the array laser carrying tilt noise, and (b) is a magnified view of the interference fringes of one of the laser beams.

[0126] The interference fringe pattern captured by the high-speed camera is calculated and controlled by a high-precision tilt control system, and high-precision compensation for tilt noise is achieved by adjusting AFOC.

[0127] The high-precision tilt control system includes an image preprocessing module 202, a high-precision tilt calculation module 203, and a tilt device control module 204.

[0128] The image preprocessing module 202 first crops the complete interference fringe image into seven sub-images with a resolution of 128*128 according to the center position of each laser beam in the array, such as... Figure 5 As shown in the left figure, the center point of each sub-image is then extended along the x and y axes, resulting in 14 128*1 arrays. Each array carries information about the tilt noise of the sub-beam along the x / y axes. Figure 5 Taking the laser in the upper left corner of the left image as an example, the cropped 128*128 sub-image is as follows: Figure 5 As shown in the right figure, the two white dashed lines represent the two selected 128*1 arrays. Detailed data is as follows... Figure 6 As shown, the data carries information on the tilt noise along the x and y axes of the upper left corner beam, respectively. This is compared with the detailed data when the fiber laser array does not carry tilt noise. Figure 4 The spacing of the stripes was significantly altered by the tilt noise.

[0129] The high-precision tilt calculation module 203 first calculates the Fourier transform of 14 128*1 arrays:

[0130]

[0131] In the formula, (x,y) are the position coordinates of a pixel in the interference fringe sub-image, (u,v) are the spectral coordinates of a pixel in the image obtained after the Fourier transform of the interference fringe sub-image, || is the modulo operation in complex number operations, I i (x), I i (y) represents the light intensity data of a one-dimensional array of the center coordinates of the i-th interference fringe sub-image in the x and y directions. M is the Fourier transform of the light intensity data of a one-dimensional array of the center coordinates of the i-th interference fringe sub-image in the x and y directions. i (u), M i (v) represents the amplitude of the Fourier transform of the one-dimensional array of the center coordinates of the i-th interference fringe sub-image in the x and y directions. In the study of interference fringes, the physical meaning of the spectral coordinates (u,v) is the number of fringes contained in the 128*1 array.

[0132] Due to the limitations of discretization sampling, the number of stripes can only be calculated to the integer level. Figure 6 Taking the data as an example, the result after Fourier transform is as follows: Figure 7As shown, the calculation results for the x-axis and y-axis indicate 24 and 9 fringes respectively. However, the exact number of fringes is not strictly an integer, which introduces significant errors when calculating the tilt error. Therefore, after the Fourier transform calculation, a high-precision tilt calculation module performs even more precise data processing to obtain a more accurate fringe count.

[0133] For the light intensity data of the 128*1 array with the center coordinates of the i-th interference fringe sub-image in the x and y directions, according to the general formula of the trigonometric function for undetermined frequency and phase, and considering that the high-speed camera in this embodiment outputs 8-bit data with an output value of 0-255, the maximum fringe light intensity is adjusted to 200 to avoid intensity saturation. K is a constant selected based on the size of the original interference fringe image data. In this embodiment, the maximum fringe light intensity in the original interference fringe image data is 200, so the range of K can be [80, 120]. Since the output light intensity of the fiber laser is Gaussian-like, in Figure 6 The data in the dataset exhibits a Gaussian-like envelope; therefore, in this embodiment, K is chosen to be 80, and the trigonometric function to be fitted is constructed as follows:

[0134]

[0135] in, Let k be the trigonometric function to be fitted for the 128*1 array of light intensity data of the center coordinates of the i-th interference fringe image in the x and y directions. x k y The unknown frequencies of the trigonometric function to be fitted. The phase to be determined is the trigonometric function to be fitted.

[0136] Based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image, initial values ​​are assigned to the undetermined coefficients of the corresponding trigonometric functions to be fitted. Specifically, the initial values ​​of the undetermined coefficients of the trigonometric functions to be fitted are assigned as follows:

[0137]

[0138] In the formula, (δ fft,x ,δ fft,y ) represents the approximate integer number of interference fringes in the x and y directions obtained from the Fourier transform calculation of the 128*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions.

[0139] Specifically, the objective functions in the x and y directions for:

[0140]

[0141] In the formula, Ii (x), I i (y) represents the light intensity data of a 128*1 array in the x and y directions, representing the center coordinates of the i-th interference fringe sub-image. This is the sum of the squares of the differences between the two functions.

[0142] The original 128*1 array data is fitted using the least squares method, and the result is found to be... The trigonometric function frequency parameter k that takes the minimum value x k y and trigonometric function phase parameters The results are as follows Figure 8 As shown.

[0143] Based on the calculated trigonometric function frequency parameter k x k y Further calculations are performed using the following formula to obtain the precise number of interference fringes in the x and y directions of the i-th interference fringe sub-image.

[0144]

[0145] In the formula, k x k y In order to make The parameter that takes the minimum value, (δ) cal,x ,δ cal,y The number of interference fringes in the x and y directions in the i-th interference fringe sub-image obtained after calculation is denoted as . By calculating the number of fringes to a decimal point, a more accurate result is obtained.

[0146] Based on the fringe spacing introduced by the unified reference beam, the tilt angle of the reference beam can be determined to be TILT. ref,x and TILT ref,y The tilt noise of the sub-beam can be obtained using the following formula:

[0147]

[0148] In the formula, δ CCD This refers to the single pixel size of a high-speed camera.

[0149] The tilt device control module 204 performs reverse compensation based on the tilt noise data in the two directions calculated in the above formula, thereby achieving high-precision tilt control.

[0150] To further demonstrate the superiority of this method, a Monte Carlo simulation was performed in this embodiment. First, 100 sets of tilt errors in the x and y directions were initialized, with an error amplitude of 400 μrad (e.g., ...). Figure 9(As shown), then, the tilt error is calculated using this method to obtain the calculated value for each Monte Carlo simulation. By comparing the initial tilt error with its corresponding calculated value, the residuals of 100 sets of data can be obtained (e.g., Figure 10 (As shown). Through Figure 10 It is evident that the residual amplitude is within 1 μrad. The relative tilt error can be obtained using the following formula:

[0151]

[0152] Where η is the combining efficiency, δp is the obtained residual, θ0 is the beam divergence angle, ω0 is the beam waist of a single laser beam, and λ is the laser wavelength. In this embodiment, the laser wavelength is 1064 nm, the beam waist size is 20 mm, and δp is 1 μrad. The calculated relative tilt error is less than 5.91%, and the combining efficiency is higher than 99.65% under this tilt error.

[0153] Matters not covered in this invention are common knowledge.

[0154] In one embodiment, a computer device is provided, which may be a server. The computer device includes a processor, memory, a network interface, and a database connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database stores sample data. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements the steps of the coherently synthesized fiber laser tilt noise acquisition method described in the above embodiment.

[0155] In one embodiment, a computer device is provided, including a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the method for obtaining tilt noise of coherently synthesized fiber lasers in any of the above embodiments.

[0156] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for obtaining tilt noise of coherently synthesized fiber lasers in any of the above embodiments.

[0157] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0158] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0160] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for obtaining tilt noise in coherently synthesized fiber lasers, characterized in that, include: Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays; The interference fringe image is cropped into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser, where M≥4, each interference fringe sub-image corresponds one-to-one with each sub-laser in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each sub-laser in the array laser. One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis. The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on an M*1 array of center coordinates in the x and y directions of each interference fringe sub-image. The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image. Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis is calculated.

2. The method for obtaining tilt noise in coherently synthesized fiber lasers according to claim 1, characterized in that, Calculate the exact number of interference fringes in the x and y directions in each interference fringe sub-image, including: Construct a trigonometric function to be fitted based on the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the x and y directions; Based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image, the initial values ​​of the undetermined coefficients of the corresponding trigonometric functions to be fitted are assigned. The sum of squares of the differences between the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the x-direction and the trigonometric functions to be fitted in the M*1 array in the x-direction, and the sum of squares of the differences between the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the y-direction and the trigonometric functions to be fitted in the M*1 array in the y-direction, are used as the target functions in the x-direction and y-direction, respectively. Based on the initial values ​​of the undetermined coefficients of the corresponding trigonometric functions to be fitted, the least squares method is used to fit the light intensity data of the M*1 array of the center coordinates of each interference fringe sub-image in the x-direction and y-direction, respectively. The trigonometric function frequency parameters and phase parameters that minimize the target functions in the x-direction and y-direction are taken respectively. Based on the calculated trigonometric function frequency parameters, the exact number of interference fringes in the x and y directions in the i-th interference fringe sub-image is calculated.

3. The method for obtaining tilt noise in coherently synthesized fiber lasers according to claim 2, characterized in that, The trigonometric function to be fitted is as follows: in, Let k be the trigonometric function to be fitted for the light intensity data of the M*1 array of the center coordinates of the i-th interference fringe image in the x and y directions. x k y The unknown frequencies of the trigonometric function to be fitted. Let K be the undetermined phase of the trigonometric function to be fitted, and K be a constant selected based on the size of the original interference fringe image data. Let the maximum value of the fringe light intensity in the original interference fringe image data be a, then the range of K is [0.8a / 2, 1.2a / 2].

4. The method for obtaining tilt noise in coherently synthesized fiber lasers according to claim 3, characterized in that, The initial values ​​of the undetermined coefficients of the trigonometric function to be fitted are: In the formula, (δ fft,x ,δ fft,y ) represents the approximate integer number of interference fringes in the x and y directions obtained from the Fourier transform calculation of the M*1 array of the center coordinates of the i-th interference fringe sub-image in the x and y directions.

5. The method for obtaining tilt noise in coherently synthesized fiber lasers according to claim 3 or 4, characterized in that, Based on the calculated trigonometric function frequency parameter k that minimizes the target functions in the x and y directions. x k y The exact number of interference fringes in the x and y directions in the i-th interference fringe sub-image can be calculated using the following formula:

6. The method for obtaining tilt noise in coherently synthesized fiber lasers according to claim 5, characterized in that, TILT based on the tilt angle of the reference light in the x and y directions ref,x and TILT ref,y And by obtaining the precise number of interference fringes in the x and y directions of each interference fringe sub-image, the tilt noise TILT of each sub-laser beam relative to the x and y axes in the array laser is obtained. x and TILT y : In the formula, δ CCD This refers to the single pixel size of a high-speed camera.

7. The method for obtaining tilt noise in coherently synthesized fiber lasers according to claim 6, characterized in that, Based on the fringe spacing introduced by the unified reference light, the tilt angles of the reference light in the x and y directions are TILT respectively. ref,x and TILT ref,y .

8. A device for acquiring tilt noise in a coherently synthesized fiber laser, characterized in that, include: The acquisition module is used to acquire the interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays; The first image processing module is used to cut the interference fringe image into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser. The second image processing module is used to extract one-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located, and obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis. The first calculation module calculates the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image by performing Fourier transform on the M*1 array of the center coordinates of each interference fringe sub-image in the x and y directions. The second calculation module calculates the precise number of interference fringes in the x and y directions of each interference fringe sub-image based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image. The third calculation module calculates the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x-direction and y-direction of each interference fringe sub-image.

9. A method for controlling the tilt of a coherently synthesized fiber laser, characterized in that, Includes the following steps: Obtain an interference fringe image between the array laser and the reference light, wherein the array laser is composed of N sub-laser arrays; The interference fringe image is cropped into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each sub-laser in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each sub-laser in the array laser. One-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located are obtained to obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis. The approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image is obtained by performing a Fourier transform on an M*1 array of center coordinates in the x and y directions of each interference fringe sub-image. The exact number of interference fringes in the x and y directions in each interference fringe sub-image is calculated based on the approximate integer number of interference fringes in the x and y directions in each interference fringe sub-image. Based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x and y directions in each interference fringe sub-image, the tilt noise of each sub-laser in the array laser relative to the x-axis and y-axis is calculated. Real-time tilt compensation is performed on each sub-laser beam in the array laser based on the tilt noise of each sub-laser beam relative to the x-axis and y-axis, thereby achieving high-precision tilt control.

10. A coherent combining fiber laser tilt control system, characterized in that, The system includes a laser array coherent combining subsystem, an image preprocessing module, a high-precision tilt calculation module, and a tilt device control module. In the laser array coherent combining subsystem, the seed laser is divided into two parts: one part is used to generate the array laser, and the other part is used as a reference light. The array laser is beam-contracted after passing through a double lens and interferes with the reference light emitted through a reflector. The interference fringe image of the array laser and the reference light is acquired using a high-speed camera. The array laser is composed of N sub-laser arrays. The image preprocessing module includes a first image processing module and a second image processing module; The first image processing module is used to cut the interference fringe image into N interference fringe sub-images with a resolution of M*M according to the corresponding position of each sub-laser in the array laser. Each interference fringe sub-image corresponds one-to-one with each laser beam in the array laser, and the center position of each interference fringe sub-image corresponds to the center position of each laser beam in the array laser. The second image processing module is used to extract one-dimensional data of the x-axis and y-axis where the center coordinates of each interference fringe sub-image are located, and obtain 2N M*1 arrays. Each array carries information about the tilt noise of the corresponding sub-laser x-axis or y-axis. The high-precision tilt calculation module includes a first calculation module, a second calculation module, and a third calculation module; The first calculation module calculates the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image by performing Fourier transform on the M*1 array of the center coordinates of each interference fringe sub-image in the x and y directions. The second calculation module calculates the precise number of interference fringes in the x and y directions of each interference fringe sub-image based on the approximate integer number of interference fringes in the x and y directions of each interference fringe sub-image. The third calculation module calculates the tilt noise of each sub-laser beam in the array laser relative to the x-axis and y-axis based on the tilt angle of the reference light relative to the x-axis and y-axis and the precise number of interference fringes in the x-direction and y-direction of each interference fringe sub-image. The tilting device control module performs real-time tilt compensation for each sub-laser in the array laser based on the tilt noise of each sub-laser relative to the x-axis and y-axis, thereby achieving high-precision tilt control.

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