A mode coupling control method and device based on long period fiber grating

Abstract

The application discloses a mode coupling control method and device based on a long-period fiber grating, relates to the field of lasers, and provides the method, which comprises the following steps: preparing a long-period fiber grating, wherein the long-period fiber grating comprises at least one grating area, a preset offset exists between the resonant peak central wavelength of any grating area and the central wavelength of incident laser, and the preset offset makes the initial working transmittance of the grating area be in the maximum slope region of the transmittance spectrum of the grating area; for any grating area, a deformation control device is driven to adjust the curvature radius of the grating area multiple times, the coupling efficiency corresponding to each curvature radius is recorded, and a record data point set is constructed; an actual coupling model is constructed by using the record data point set; and the deformation control device is controlled to adjust the curvature radius of the grating area by using the actual coupling model, so that the actual coupling efficiency of the grating area is consistent with a target coupling efficiency. The application can realize high-precision and continuously adjustable grating mode control, and significantly improves the laser processing quality.

Description

Technical Field

[0001] This application relates to the field of lasers, and in particular to a mode coupling control method and apparatus based on a long-period fiber grating. Background Technology

[0002] As fiber laser power increases from kilowatts to tens of kilowatts, welding capabilities improve, but the welding process becomes more difficult to control. Traditional single-mode / quasi-single-mode lasers output Gaussian beams with highly concentrated energy at the center. During welding, this creates a highly unstable "keyhole" (vapor channel) in the laser irradiation area. The metal on the keyhole's front wall vaporizes violently, generating high-pressure steam and plasma. Due to the temperature gradient on the molten pool surface, a surface tension gradient exists, driving the molten metal to flow from the keyhole towards the edges. This intense convection can push liquid metal from the edges of the molten pool, creating "spatter." Spatter introduces serious quality defects. Spatter adheres to the workpiece surface, requiring expensive subsequent cleaning (such as sandblasting and pickling). Spatter also means material and energy loss, leading to an unstable molten pool, unsightly weld formation, and potential internal porosity that reduces the workpiece's structural strength. This limits welding speed and poses a significant challenge to the stable operation of automated production lines.

[0003] Composite spot technology is an important means to solve the "splatter" problem. A spot with a more uniform and wider energy distribution is used to preheat the material outside the high-energy-density central spot action area, which expands the molten pool area, reduces the temperature gradient, and suppresses molten pool fluctuations. This can significantly reduce the vapor pressure of the material, making the subsequent keyhole formation smoother and more stable, and can greatly reduce spatter.

[0004] There are various approaches to achieving composite beam technology. The core idea is to generate two or more independent and controllable beams and precisely combine them in time and / or space to act on the same processing point. The mainstream implementation schemes include: The beam is split and axially superimposed with the ring beam. Using diffractive optical elements (such as axial cones) or special refractive / reflective mirror sets, the single Gaussian beam is converted into a ring beam. Then, the original central portion (or another independent laser) is coaxially combined with the ring beam. This is typical of some early ring beam welding joints. This scheme has a fixed power ratio between the center and the ring beam, resulting in low flexibility.

[0005] A special fiber optic design uses a specially made multi-core fiber. Two independent lasers are coupled into this fiber via a combiner. This custom-designed fiber can emit a central beam and a ring beam, both independently. The main challenges of this approach lie in the high difficulty and cost of fiber design and manufacturing. As a result, this type of fiber often costs hundreds of times more than conventional fiber, making it unsuitable for large-scale use in the industrial market.

[0006] In view of the problems of the prior art, those skilled in the art urgently need a dynamic energy conversion control method and coupler for all-fiber optic cables. Summary of the Invention

[0007] The purpose of this application is to provide a mode coupling control method and device for long-period fiber gratings, which can control the energy distribution of core light and cladding light in fiber in real time and continuously, and output a composite light spot.

[0008] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a mode coupling control method for long-period fiber Bragg gratings, the control method comprising: A long-period fiber grating is fabricated, wherein the long-period fiber grating includes at least one grating region, and there is a preset offset between the center wavelength of the resonance peak of any grating region and the center wavelength of the incident laser, and the preset offset makes the transmittance of the grating region initially operate in the region with the largest slope in the transmission spectrum of the grating region. For any raster region: The deformation control device is driven to adjust the radius of curvature of the grating region multiple times and the coupling efficiency corresponding to each radius of curvature is recorded to construct a set of recorded data points; the set of recorded data points includes multiple recorded data points, and each recorded data point includes a radius of curvature and a corresponding coupling efficiency; The actual coupling model of the grating region is constructed using the set of recorded data points; the actual coupling model characterizes the relationship between the radius of curvature and the coupling efficiency. Using the actual coupling model, the deformation control device is used to adjust the radius of curvature of the grating region so that the actual coupling efficiency of the grating region is consistent with the target coupling efficiency.

[0009] The actual coupling model is as follows: ; in, For actual coupling efficiency, k For cross-coupling coefficients, L The length of the grating region. F The constant is determined by the waveguide dispersion in the grating region. k c The bending sensitivity coefficient of the grating region. R denoted as the radius of curvature of the grating region.

[0010] Using an actual coupling model, the deformation control device is adjusted to change the radius of curvature of the grating region, so that the actual coupling efficiency of the grating region matches the target coupling efficiency. Specifically, this includes: Calculate the difference between the current coupling efficiency of the grating region and the target coupling efficiency; Based on the difference, the curvature radius adjustment is calculated using the actual coupling model; The deformation control device is controlled according to the curvature radius adjustment amount.

[0011] Based on the difference, the curvature radius adjustment is calculated using the actual coupling model, specifically including: The curvature radius adjustment amount is linearized and deformed to obtain the deformed coupled model; The curvature radius adjustment corresponding to the difference is calculated using the deformed coupling model.

[0012] The deformed coupling model is as follows: in, For coupling efficiency, or op This represents the coupling efficiency corresponding to the initial operating point of the grating region. β The linear sensitivity coefficient is... R denoted as the radius of curvature of the grating region.

[0013] The formula for calculating the curvature radius adjustment corresponding to the difference using the deformed coupling model is as follows: ; in, This is the adjustment amount for the radius of curvature. This represents the difference between the current coupling efficiency and the target coupling efficiency.

[0014] In one embodiment of this application, the long-period fiber grating element includes a first grating region and a second grating region distributed along the length of the fiber; the first grating region and the second grating region have different grating periods or different structural types, both used to couple the fiber core fundamental mode to cladding modes of different orders.

[0015] In one embodiment of this application, the grating period of the first grating region is 440μm to 470μm, which is used to couple the core fundamental mode to the LP15 and LP06 cladding modes; the second grating region is a misaligned structure, and the period of the second grating region has a lateral misalignment of 2.5μm to 3.5μm with the grating period of the first grating region, which is used to couple the core fundamental mode to the LP14 cladding mode.

[0016] Secondly, this application provides a coupling mode control device for a long-period fiber Bragg grating, characterized in that it comprises: A long-period fiber grating, wherein the long-period fiber grating includes at least one grating region, and there is a preset offset between the center wavelength of the resonant peak of any grating region and the center wavelength of the incident laser, and the preset offset makes the transmittance of the grating region initially operate in the region with the largest slope in the transmission spectrum of the grating region. The optical detection device is optically connected to the output end of the grating region of the long-period fiber grating to obtain the actual coupling efficiency of the grating region in real time. A deformation control device is connected to the grating region of a long-period fiber grating and is used to change the radius of curvature of the grating region of the long-period fiber grating. A controller, connected to the deformation control device and the optical detection device, is used to record the coupling efficiency corresponding to each radius of curvature, constructing a set of recorded data points; using the set of recorded data points to construct an actual coupling model, and using the actual coupling model to control the deformation control device to adjust the radius of curvature of the grating region of the long-period fiber grating element, so that the actual coupling efficiency of the grating region of the long-period fiber grating is consistent with the target coupling efficiency; the set of recorded data points includes multiple recorded data points, and each recorded data point includes a radius of curvature and a corresponding coupling efficiency.

[0017] In one embodiment of this application, the coupling mode control device based on a long-period fiber Bragg grating further includes: A laser source is connected to the input end of the grating region of the long-period fiber grating and is used to input laser light into the grating region. A laser processing head is connected to the output end of the grating region of the long-period fiber grating and is used to form a laser spot on the workpiece.

[0018] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application provides a mode coupling control method and apparatus based on a long-period fiber grating. The control method includes: fabricating a long-period fiber grating, the long-period fiber grating including at least one grating region, wherein there is a preset offset between the center wavelength of the resonant peak of any grating region and the center wavelength of the incident laser, and the preset offset makes the transmittance of the grating region initially operate in the region with the largest slope in the transmission spectrum of the grating region; for any grating region: driving a deformation control device to adjust the radius of curvature of the grating region multiple times, and recording the coupling efficiency corresponding to each radius of curvature to construct a set of recorded data points; using the set of recorded data points to construct an actual coupling model of the grating region; using the actual coupling model, controlling the deformation control device to adjust the radius of curvature of the grating region so that the actual coupling efficiency of the grating region is consistent with the target coupling efficiency. This application achieves maximum differential sensitivity by setting the initial operating point at the maximum slope of the transmission spectrum, enabling rapid linear control of the grating. Through coupling model calibration and closed-loop feedback of the process, it can achieve high-precision, continuously adjustable mode coupling efficiency control, and can control the energy distribution of core light and cladding light in the fiber in real time and continuously. It can output Gaussian-ring composite light spots of arbitrary proportions, significantly improving the quality of laser processing. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the steps of a mode coupling control method for a long-period fiber grating according to the present invention.

[0021] Figure 2 This is a schematic diagram of the core transmission spectrum of a long-period fiber grating according to the present invention.

[0022] Figure 3 This is a schematic diagram of the mode coupling device of a long-period fiber grating in one embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the mode coupling device of a long-period fiber grating in another embodiment of the present invention.

[0024] Figure 5 This is a schematic diagram of the controller structure in one embodiment of the present invention.

[0025] Figure 6 This is a schematic diagram of the structure of a computer device provided in an embodiment of this application.

[0026] Reference numerals: laser source 10, few-mode fiber waveguide 20, long-period fiber grating region 21, first grating region 211 (grating A), second grating region 212 (grating B), deformation control device 30, first drive mechanism 301, second drive mechanism 302, photoelectric detection unit 40, controller 50, memory 501, processor 502, calibration module 503, real-time control module 504, adaptive optimization module 505, and laser output head 60. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, this embodiment provides a mode coupling control method for long-period fiber Bragg gratings, including the following steps: S1: Fabricate long-period fiber grating elements to achieve a resonant peak center wavelength of... l lpfg There is a preset offset between the incident laser center wavelength λ0 and the incident laser center wavelength. Dl ,like Figure 2 The diagram shows the transmission spectrum of a long-period fiber grating core, with the horizontal axis representing wavelength. l The vertical axis represents the fiber core transmittance. In the transmission spectrum, the transmittance is lowest (coupling efficiency is highest) at the grating resonant wavelength corresponding to the center of the resonance peak. The two sides of the transmission spectrum are transition regions. In this embodiment, the center wavelength of the incident laser is set in the transition region of the transmission spectrum, rather than at the center of the resonance peak, so that the center wavelength of the resonance peak is... l lpfg There is a preset offset between the incident laser center wavelength λ0 and the incident laser center wavelength. D l This setting ensures that the long-period fiber grating initially operates in the region of maximum slope in its transmission spectrum, and the preset offset... Dl The phase mismatch condition that enables the long-period fiber grating element to initially operate in the region of maximum slope in its transmission spectrum is satisfied. ,in k For the cross-coupling coefficient, from Figure 2It can be seen that at the point of maximum slope, even a small change in bending can cause a significant change in the resonance peak drift, thereby achieving the maximum coupling tuning sensitivity.

[0030] For any raster region: S2: Before closed-loop control, the drive deformation control device causes the long-period fiber grating element to traverse a preset curvature range [R]. min R max Record each radius of curvature. R i Corresponding actual coupling efficiency or i A set of recorded data points is constructed; the set of recorded data points includes multiple recorded data points, and each recorded data point includes a radius of curvature and a corresponding coupling efficiency. S3: Construct an actual coupling model of the grating region using the set of recorded data points; the actual coupling model characterizes the relationship between the radius of curvature and the coupling efficiency.

[0031] S4: Using the actual coupling model, control the deformation control device to adjust the radius of curvature of the grating region so that the actual coupling efficiency of the grating region is consistent with the target coupling efficiency.

[0032] Specifically, step S4 includes: acquiring the current actual coupling efficiency of the long-period fiber Bragg grating element in real time through the optical detection unit. or actual Calculate the actual coupling efficiency or actual Coupling efficiency with target or target The difference See you later. Determine the difference. See you later. The corresponding required radius of curvature adjustment ΔR The drive deformation control device applies bending deformation to the long-period fiber Bragg grating element, changing its radius of curvature. R This makes the actual coupling efficiency or actual Approaching the target coupling efficiency or target ( or actual and or target The absolute value of the deviation is less than or equal to 0.01.

[0033] In one specific embodiment, the coupling model the(R) for: ; in, For actual coupling efficiency, kFor cross-coupling coefficients, L The length of the grating region. F The constant is determined by the waveguide dispersion in the grating region. k c The bending sensitivity coefficient of the grating region. R denoted as the radius of curvature of the grating region.

[0034] In one specific embodiment, based on the preset offset Dl And the initial operating point setting, the coupling efficiency or With radius of curvature R reciprocal 1 / R The coupling model exhibits a linear relationship within a predetermined working range, and can be simplified to a linearized calculation formula: .

[0035] in, For coupling efficiency, or op This represents the coupling efficiency corresponding to the initial operating point of the grating region. β The linear sensitivity coefficient is... R The radius of curvature of the grating region. In step S6, the required radius of curvature adjustment is directly calculated based on the difference Δη. ;in, This is the adjustment amount for the radius of curvature. This represents the difference between the current coupling efficiency and the target coupling efficiency. Fast linear control is achieved.

[0036] In one embodiment of this application, the coupling efficiency can also be established using historical datasets before fabricating long-period fiber Bragg grating elements. or With the radius of curvature of the bend R A coupling model is established between the parameters to maximize the tuning sensitivity of the long-period fiber grating (FBG) and optimize its initial operating state. The coupling model is then corrected using the recorded data point set to obtain a calibrated actual coupling model or update the lookup table. Parameter correction of the coupling model includes fitting the recorded data points using the least squares method, optimizing at least one parameter in the coupling model, and generating a calibrated coupling model. In one specific embodiment, during closed-loop control, control data from the most recent N cycles, including the radius of curvature R and the corresponding actual coupling efficiency η, is continuously cached. Every preset number of times or time interval, based on the cached control data, the calibrated actual coupling model is re-identified, and the parameters of the coupling model are updated. The updated coupling model parameters replace the original model for subsequent control quantity determination steps.

[0037] In one specific embodiment of this application, the linear working interval is the coupling efficiency. or The linear sensitivity coefficient β is within the range of [0.25, 0.80], and its absolute value is greater than 10m. It should be noted that the linear operating range of 0.25-0.80 is the preferred range determined experimentally under specific fiber parameters in this embodiment. The linear operating range may vary slightly for different fiber types, grating designs, or target cladding modes. Those skilled in the art can determine the corresponding linear range through conventional experiments. However, the core of this invention lies in obtaining high-sensitivity linear control by setting the initial operating point at the point of maximum transmission spectrum slope, rather than being limited to a specific numerical range.

[0038] The linear operating range may vary slightly. In one specific embodiment, those skilled in the art set the center wavelength to 1080nm, the maximum output power to 3kW, the few-mode transmission fiber to be a 20 / 400um double-clad fiber, and a long-period grating written in the fiber core with a grating period of 420um and a grating length of 50mm, and a cross-coupling coefficient of... k =0.47mm -1 The deformation control device includes a piezoelectric ceramic actuator with a response frequency >10kHz, bidirectional bending capability, and a curvature control range of -2m. -1 ~2m -1 In this embodiment, the calculation is as follows: After calibration, when the grating is pre-bent to the radius of curvature... R op When the initial coupling efficiency is 2.8m, =0.52, the operating point is exactly located at the point of maximum slope. Near the operating point, the coupling efficiency is... or With curvature 1 / R A linear relationship exists: .

[0039] Where 12.8 is the linear sensitivity coefficient (unit: m), and the linear operating range is... or ∈[0.25,0.80]. When the target coupling efficiency is required. or target At that time, the bending curvature of the grating is derived using the formula above, and the long-period fiber grating is driven to bend.

[0040] In one specific embodiment, the long-period fiber grating element includes a first grating region and a second grating region distributed along the fiber length direction. The first grating region and the second grating region are respectively used to couple the fiber core fundamental mode to cladding modes of different orders. The control method independently controls the deformation state of each grating region to form a composite optical field distribution of multiple modes superimposed at the output end.

[0041] In one specific embodiment, the first grating region and the second grating region have different grating periods or different structural types, respectively used to couple the core mode to cladding modes of different orders, so as to form a composite light field distribution of multiple modes superimposed at the output end. For example, the grating period of the first grating region is 440μm to 470μm, used to couple the core mode to LP15 and LP06 order cladding modes; the second grating region is a misaligned structure, and the period of the second grating region has a lateral misalignment of 2.5μm to 3.5μm with the period of the first grating region, used to couple the core mode to LP14 order cladding mode. This embodiment can generate a composite light field of multiple modes superimposed by independently controlling the coupling efficiency of the two grating regions. By adjusting the power ratio of each mode, a continuous gradient from center enhancement to edge enhancement can be achieved, meeting the process requirements of new energy vehicle battery welding, aerospace precision machining, etc., which are highly sensitive to the light spot morphology.

[0042] In another specific embodiment, the system includes a laser source 10, a few-mode fiber waveguide 20, a first grating region 211 (grating A), a second grating region 212 (grating B), a deformation control device 30, a first driving mechanism 301 and a second driving mechanism 302, a photoelectric detection unit 40, a controller 50, and a laser output head 60; wherein the center wavelength is 1080nm, the output is fixed, and the maximum power is 3kW; the first grating region 211 is written into a 20 / 400μm double-clad fiber, the grating period is 650μm, the length is 40mm, and the cross-coupling coefficient is... k A =0.25mm -1 It is used for LP01 to LP11 mode conversion.

[0043] Second grating region (grating B): written into a 20 / 400μm double-clad fiber, with a grating period of 420μm and a length of 45mm, and a cross-coupling coefficient of... k B =0.19mm -1 It is used for LP01 to LP02 mode conversion; the first drive mechanism 301 and the second drive mechanism 302 are piezoelectric ceramic actuators, which respectively control the first grating region 211 (grating A) and the second grating region 212 (grating B), with a response frequency >10kHz and independent bidirectional bending; the first grating region 211 is set as or A ≈0 (uncoupled), the second grating region 212 is continuously adjusted in the linear region: when or B =0.25, the output is mainly based on the core energy, with a Gaussian distribution and a small amount of toroidal distribution; when or B =0.50, the output includes core output and cladding light output, and the energy of the Gaussian spot and the ring spot are proportional; when or B =0.75, the output is mainly cladding light output, mainly ring spot energy, with a small amount of Gaussian; in some embodiments, the first grating region 211 is set to or A =0.6, the second grating region 212 is or B =0.4, the output is a composite light spot of three modes: LP01, LP11 and LP02, which can realize more complex light field distribution.

[0044] In one specific embodiment, before the step of traversing the preset curvature range, the deformation control device is zero-point calibrated to determine the initial curvature radius of the long-period fiber grating element when it is in a flat state.

[0045] like Figure 3-Figure 5 As shown, in one specific embodiment, the present invention also provides a mode coupling device for a long-period fiber grating, employing the aforementioned mode coupling control method based on a long-period fiber grating, which includes: few-mode fiber waveguide 20, such as Figure 3 As shown, in one specific embodiment, at least one long-period fiber grating region 21 is formed in the fiber core, the long-period fiber grating region 21 being used to couple at least a portion of the energy of the fiber core fundamental mode input therein to the cladding mode.

[0046] The deformation control device 30 clamps a segment on the few-mode fiber waveguide 20 corresponding to the long-period fiber grating region 21 and is configured to apply controllable bending deformation to the segment to change the radius of curvature R of the long-period fiber grating region 21.

[0047] The optical detection unit 40 is optically connected to the output end of the few-mode fiber waveguide 20, and is used to monitor the output optical signal in real time and obtain the actual coupling efficiency. or actual .

[0048] The controller 50 is connected to the photoelectric detection unit 40 and the deformation control device 30, respectively. The controller 50 includes a memory 501 and a processor 502. The memory 501 stores a coupling model to describe the coupling efficiency. or With radius of curvature R The correspondence between them; the initial operating point parameters, corresponding to the initial radius of curvature of the long-period fiber grating region in a flat state, wherein the initial radius of curvature is related to the incident laser center wavelength. l 0 Together, the center wavelength of the resonance peak of the long-period fiber grating region was determined. l 0 Preset offset between Dl This ensures that the long-period fiber grating region 21 initially operates in the region with the maximum slope in its transmission spectrum; the real-time control module 504 is configured to, during the closed-loop control process, adjust the actual coupling efficiency obtained in real time by the photoelectric detection unit 40. or actual Coupling efficiency with the preset target or target The difference See you later. The required radius of curvature adjustment is determined by querying the calibrated actual coupling model or a lookup table. ΔR And drive the deformation control device to perform corresponding bending adjustments, repeating the process until... or actual Approaching or target .

[0049] In one embodiment of this application, corresponding to the above-described step of correcting the coupling model, the controller 50 further includes: a calibration module 503, configured to drive the deformation control device 30 to traverse a preset curvature range before closed-loop control, receive the actual coupling efficiency measured by the photoelectric detection unit 40 at each curvature radius, and correct the parameters of the coupling model according to the recorded data points to generate a calibrated actual coupling model or update the lookup table. In one specific embodiment, the coupling model η(R) is: .

[0050] in, For actual coupling efficiency, k For cross-coupling coefficients, L The length of the grating region. F The constant is determined by the waveguide dispersion in the grating region. k c The bending sensitivity coefficient of the grating region. R denoted as the radius of curvature of the grating region.

[0051] In one specific embodiment, the preset offset Dl Satisfying the initial phase mismatch condition , among which, among which d op This is the initial phase mismatch. k The cross-coupling coefficient is used to initially operate the long-period fiber grating region at the point of maximum slope in its transmission spectrum; the calibrated actual coupling model is in a linearized form: ; in, For coupling efficiency, or opThis represents the coupling efficiency corresponding to the initial operating point of the grating region. β The linear sensitivity coefficient is... R The radius of curvature of the grating region. In step S6, the required radius of curvature adjustment is directly calculated based on the difference Δη. ;in, This is the adjustment amount for the radius of curvature. This represents the difference between the current coupling efficiency and the target coupling efficiency. Fast linear control is achieved. The linear operating range is the coupling efficiency η ∈ [0.25, 0.80], and the absolute value of the linear sensitivity coefficient β is greater than 10m.

[0052] like Figure 4 As shown, in one specific embodiment, the long-period fiber grating region 21 includes a first grating region 211 and a second grating region 212 distributed along the length direction of the few-mode fiber waveguide 20. The first grating region 211 and the second grating region 212 are respectively used to couple the fiber core fundamental mode to cladding modes of different orders. The deformation control device 30 includes a first driving mechanism 301 and a second driving mechanism 302 corresponding to the first grating region 211 and the second grating region 212, respectively, for independently controlling the curvature radius of each grating region. The calibration module 503 is configured to perform independent calibration procedures on the first grating region 211 and the second grating region 212 respectively, generating their respective calibrated actual coupling models. The real-time control module 504 is configured to independently control the first grating region 211 and the second grating region 212 according to their respective target coupling efficiencies, so as to form a composite optical field distribution of multiple modes superimposed at the output end.

[0053] In one specific embodiment, the deformation control device 30 includes: a clamp for fixing both ends of the long-period fiber grating region; and a precision drive mechanism connected to at least one of the clamps for changing the relative angle or position between the clamps.

[0054] like Figure 5 As shown, in one specific embodiment, the controller 50 is further configured with an adaptive optimization module 505, which is used to periodically trigger the calibration module 503 to execute a calibration procedure during the closed-loop control process, so as to update the calibrated actual coupling model and compensate for parameter drift caused by environmental changes or device aging.

[0055] In one specific embodiment, the optical detection unit 40 includes: a photodetector for converting the output optical signal into an electrical signal; and a signal processing circuit connected to the photodetector for calculating the actual coupling efficiency based on the electrical signal. or actual .

[0056] In one specific embodiment, the coupling mode control device based on a long-period fiber Bragg grating of this application, such as... Figure 3 and 4 As shown, it also includes: a laser source 10 for outputting laser light, wherein the center wavelength of the laser light is... l 0 It also includes the aforementioned mode coupling device based on a long-period fiber grating, whose input end is connected to the laser source 10, and the center wavelength of the resonant peak in the medium-long period fiber grating region of the mode coupling device is... l lpfg With the l 0 There is a preset offset Dl ; and a laser processing head connected to the output of the adjustable mode coupler; wherein the mode coupling device responds to an external control signal or according to a preset program to dynamically adjust the ratio of the core guiding light component and the cladding guiding light component in the beam output to the laser processing head, thereby forming a variable composite light spot on the workpiece.

[0057] In one exemplary embodiment, a computer device is provided, which may be a server or a terminal, and its internal structure diagram may be as follows. Figure 6 As shown, this computer device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and databases. The internal memory provides the environment for the operating system and computer programs stored in the non-volatile storage media to run. The I / O interfaces are used for exchanging information between the processor and external devices. The communication interface is used for communicating with external terminals via a network connection.

[0058] Those skilled in the art will understand that Figure 6 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0059] In one exemplary embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0060] In one exemplary embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0061] In one exemplary embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0062] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0063] Those skilled in the art will understand that all or part of the processes in 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. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0064] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0065] 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.

[0066] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A mode coupling control method based on a long-period fiber grating, characterized in that, The control method includes: A long-period fiber grating is fabricated, wherein the long-period fiber grating includes at least one grating region, and there is a preset offset between the center wavelength of the resonance peak of any grating region and the center wavelength of the incident laser. The preset offset makes the transmittance of the grating region initially operate in the region with the largest slope in the transmission spectrum of the grating region. For any raster region: The deformation control device is driven to adjust the radius of curvature of the grating region multiple times and the coupling efficiency corresponding to each radius of curvature is recorded to construct a set of recorded data points; the set of recorded data points includes multiple recorded data points, and each recorded data point includes a radius of curvature and a corresponding coupling efficiency; The actual coupling model of the grating region is constructed using the set of recorded data points; the actual coupling model characterizes the relationship between the radius of curvature and the coupling efficiency. Using the actual coupling model, the deformation control device is used to adjust the radius of curvature of the grating region so that the actual coupling efficiency of the grating region is consistent with the target coupling efficiency.

2. The mode coupling control method based on a long-period fiber grating according to claim 1, characterized in that, The actual coupling model is as follows: ； in, For actual coupling efficiency, κ For cross-coupling coefficients, L The length of the grating region. F The constant is determined by the waveguide dispersion in the grating region. k c The bending sensitivity coefficient of the grating region. R denoted as the radius of curvature of the grating region.

3. The mode coupling control method based on a long-period fiber grating according to claim 1, characterized in that, Using an actual coupling model, the deformation control device is adjusted to change the radius of curvature of the grating region, so that the actual coupling efficiency of the grating region matches the target coupling efficiency. Specifically, this includes: Calculate the difference between the current coupling efficiency of the grating region and the target coupling efficiency; Based on the difference, the curvature radius adjustment is calculated using the actual coupling model; The deformation control device is controlled according to the curvature radius adjustment amount.

4. The mode coupling control method based on a long-period fiber grating according to claim 3, characterized in that, Based on the difference, the curvature radius adjustment is calculated using the actual coupling model, specifically including: The curvature radius adjustment amount is linearized and deformed to obtain the deformed coupled model; The curvature radius adjustment corresponding to the difference is calculated using the deformed coupling model.

5. The mode coupling control method based on a long-period fiber grating according to claim 4, characterized in that, The deformed coupling model is as follows: ； in, For coupling efficiency, η op This represents the coupling efficiency corresponding to the initial operating point of the grating region. β The linear sensitivity coefficient is... R denoted as the radius of curvature of the grating region.

6. The mode coupling control method based on a long-period fiber grating according to claim 5, characterized in that, The formula for calculating the curvature radius adjustment corresponding to the difference using the deformed coupling model is as follows: ； in, This is the adjustment amount for the radius of curvature. This represents the difference between the current coupling efficiency and the target coupling efficiency.

7. The mode coupling control method based on a long-period fiber grating according to claim 1, characterized in that, The long-period fiber grating element includes a first grating region and a second grating region distributed along the fiber length direction; the first grating region and the second grating region have different grating periods or different structural types, both used to couple the fiber core fundamental mode to cladding modes of different orders.

8. The mode coupling control method based on a long-period fiber grating according to claim 7, characterized in that, The first grating region has a grating period of 440μm to 470μm, which is used to couple the core mode to the LP15 and LP06 cladding modes. The second grating region is a misaligned structure, and the period of the second grating region is laterally misaligned with the period of the first grating region by 2.5μm to 3.5μm, which is used to couple the core mode to the LP14 cladding mode.

9. A mode coupling control device based on a long-period fiber grating, characterized in that, include: A long-period fiber grating, wherein the long-period fiber grating includes at least one grating region, and there is a preset offset between the center wavelength of the resonance peak of any grating region and the center wavelength of the incident laser. The preset offset makes the transmittance of the grating region initially operate in the region with the largest slope in the transmission spectrum of the grating region. The optical detection device is optically connected to the output end of the grating region of the long-period fiber grating to obtain the actual coupling efficiency of the grating region in real time. A deformation control device is connected to the grating region of a long-period fiber grating and is used to change the radius of curvature of the grating region of the long-period fiber grating. The controller, connected to the deformation control device and the optical detection device, is used to record the coupling efficiency corresponding to each radius of curvature and construct a set of recorded data points. An actual coupling model is constructed using the set of recorded data points, and the deformation control device is used to adjust the radius of curvature of the grating region of the long-period fiber grating element so that the actual coupling efficiency of the grating region of the long-period fiber grating is consistent with the target coupling efficiency. The set of recorded data points includes multiple recorded data points, and each recorded data point includes a radius of curvature and a corresponding coupling efficiency.

10. The mode coupling control device based on a long-period fiber grating according to claim 9, characterized in that, The control device further includes: A laser source is connected to the input end of the grating region of the long-period fiber grating and is used to input laser light into the grating region. A laser processing head is connected to the output end of the grating region of the long-period fiber grating and is used to form a laser spot on the workpiece.

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