Method for determining working distance of slow axis collimating lens in optical fiber coupling module

Abstract

The invention relates to the field of optical fiber coupling modules, in particular to a method for determining the working distance of a slow-axis collimating lens in an optical fiber coupling module, and the method comprises the steps: obtaining the temperature distribution range of a pumping chip and the slow-axis collimating lens in an actual working state through thermal simulation or actual measurement; testing the performance parameters of the pumping chip along with the temperature change in the temperature range; constructing a thermal-optical coupling simulation model, configuring the temperature distribution and performance parameters in the model, setting a gradient temperature field and a change relation of system simulation coupling efficiency along with a working distance between a lens and a chip, and obtaining multiple groups of simulation data; and determining a globally optimal fixed working distance through optimization calculation by taking the efficiency stability of the whole temperature zone as a constraint and taking the maximization of the average efficiency as a target. According to the invention, the problems of safety risk and efficiency of traditional power-up adjustment are avoided, and optical performance drift caused by working temperature change is compensated, so that the improvement of coupling efficiency, precision and stability in a full-temperature region is realized, and the yield of mass production is improved.

Description

Technical Field

[0001] This invention relates to the field of fiber optic coupling modules, and more specifically to a method for determining the working distance of a slow-axis collimating lens in a fiber optic coupling module. Background Technology

[0002] In the manufacturing process of fiber optic coupling modules, the coupling of optical components is a critical step, directly affecting the optical transmission efficiency, output power stability, and lifespan of the pump source module. Among these, the precise coupling of components such as slow-axis collimating lenses, coupling lenses, FAC (FastAxis Collimator) lenses, and VBG (Volume Bragg Grating) with the pump chip and passive optical fiber is the core of improving coupling efficiency.

[0003] Traditional fiber optic coupling module coupling processes often employ a power-on adjustment method. This involves energizing the pump chip to emit light and then manually or semi-automatically adjusting the positions of optical components such as the slow-axis collimating lens to optimize coupling efficiency. However, this method has several drawbacks: First, the high-power laser emitted by the pump chip during the power-on process poses serious safety risks, threatening the personal safety of operators and the safety of the equipment. Second, the operating environment (such as temperature and humidity) during power-on adjustment often differs from the actual operating environment of the pump source module, leading to deviations between the adjusted coupling state and the actual application, thus affecting the performance of the pump source. Furthermore, the power-on adjustment process is cumbersome, requiring repeated start-ups and shutdowns for debugging, resulting in low operating and adjustment efficiency, severely restricting the mass production efficiency of fiber optic coupling modules, and the repeated start-ups and shutdowns also increase the risk of laser chip failure.

[0004] Furthermore, experiments have verified that the traditional power-adjusted process, under operating conditions, suffers from thermally induced wavelength drift (0.03 nm / ℃) and lens refractive index change (Δn = 1.2 × 10⁻⁶). -5 / ℃). However, the impact of temperature changes on the performance of optical components is generally overlooked in related technologies. Fiber optic coupling modules generate a large amount of heat during operation, causing significant changes in the operating temperature of the pump chip and optical components. These temperature changes can lead to a series of third-order coupling failures: 1) Pump chip wavelength drift (typically 0.03 nm / ℃), resulting in VBG wavelength mismatch; 2) Lens refractive index change (Δn = 1.2 × 10⁻⁶). -5 These problems cause a working distance offset of ±3μm / 10℃; 3) changes in the slow axis divergence angle of the chip (0.02° / ℃), leading to beam distortion. These issues result in decreased coupling efficiency and unstable output power in fiber optic coupling modules during actual operation due to temperature fluctuations, and the yield rate of traditional mass production is low, only around 80%. Therefore, a method is urgently needed that can avoid the defects of traditional power-on adjustment, consider the effects of temperature, and improve coupling efficiency. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for determining the working distance of a slow-axis collimating lens in an optical fiber coupling module to improve coupling efficiency. By employing thermal-optical parameter coupling simulation, it avoids the safety risks and efficiency problems associated with traditional power-on adjustment and compensates for optical performance drift caused by changes in operating temperature. This results in improved coupling efficiency, accuracy, and stability across the entire temperature range, and also increases the mass production yield.

[0006] The technical solution of the present invention provides a method for determining the working distance of a slow-axis collimating lens in an optical fiber coupling module, comprising the following steps: S1. Through thermal simulation or actual testing, obtain the first operating temperature range of the pump chip position and the second operating temperature range of the slow-axis collimating lens position of the fiber laser pump source module under actual working conditions. S2, select multiple temperature points within the first operating temperature range, control the operating temperature of the pump chip to each set temperature point through the temperature control platform, and measure the operating performance parameters of the pump chip at each temperature point. S3. Construct an optical coupling simulation model including a slow-axis collimating lens and a pump chip. In the simulation model, configure temperature parameters and working performance parameters corresponding to the first working temperature range for the pump chip, and configure lens material temperature properties corresponding to the first working temperature range for the slow-axis collimating lens. Set a non-uniform gradient temperature field to simulate the relationship between the coupling efficiency of the fiber coupling module and the working distance between the slow-axis collimating lens and the pump chip in the first and second working temperature ranges, and obtain multiple sets of simulation data. S4, based on multiple sets of simulation data, with the constraint of meeting preset stability requirements and the goal of maximizing the average coupling efficiency across the entire temperature range, determines the optimal fixed working distance between the slow-axis collimating lens and the pump chip through optimization calculation.

[0007] As can be seen from the above technical solutions, this application has the following advantages: (1) By replacing the traditional power-on adjustment method with thermal-optical parameter coupling simulation and micron-level composite positioning, the safety risks of high-power lasers during the power-on process are fundamentally eliminated, and the coupling deviation caused by the incompatibility between the adjustment environment and the actual working environment is avoided. At the same time, the mass production efficiency is greatly improved, the necessary working time of a single SAC lens is reduced from 2 minutes to 5 seconds, and there is no need to repeatedly start and stop the pump chip, which reduces the risk of laser chip failure. (2) The operating temperature range was obtained through thermal simulation (including heat flux density distribution) or actual testing, and non-sequential simulation of the optical design software was performed in combination with the pump chip performance parameters at this temperature (using the temperature-dependent refractive index model). The problem of third-order coupling failure caused by temperature fluctuation was considered, ensuring that the optimal operating distance of the simulation could adapt to the temperature changes in the actual operation of the fiber coupling module, effectively solving the problems of decreased coupling efficiency and unstable output power caused by temperature fluctuation. In the range of 40-70℃, the coefficient of variation (CV) of coupling efficiency was ≤2.2%, while the coefficient of variation of coupling efficiency of traditional process reached 8.5%, which was 74% lower than that of traditional process, thus improving the stability of module operation; (3) Accurate simulation is performed using non-sequential ray tracing in optical design software. Key parameters such as the thermal expansion coefficient and temperature derivative of the refractive index of the lens are input, and a gradient temperature field is set to match the glass refractive index with the ambient temperature. The calculated optimal working distance is closer to the actual working state, achieving micron-level assembly accuracy and significantly improving the coupling accuracy between components such as the slow-axis collimating lens and the pump chip. The wavelength matching accuracy of VBG at the 976nm center wavelength is improved to ±0.1nm, while the original traditional process is only ±2nm, which is an 80% improvement over the traditional process, thereby improving the coupling efficiency and output power of the fiber coupling module. Attached Figure Description

[0008] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying 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.

[0009] Figure 1 This is a schematic flowchart illustrating a method for determining the working distance of a slow-axis collimating lens in an optical fiber coupling module, as provided in an embodiment of the present invention.

[0010] Figure 2 This is a graph showing the changes in the thermal parameters of the pump chip.

[0011] Figure 3 The graph shows the comparison of coupling efficiency as a function of temperature. Detailed Implementation

[0012] To make the purpose, features, and advantages of this application more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solution protected by this application. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this application and in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0014] Figure 1 This is a schematic flowchart illustrating a method for determining the working distance of a slow-axis collimating lens in an optical fiber coupling module, as provided in an embodiment of the present invention. Figure 1 As shown, the method includes the following steps.

[0015] S1. Through thermal simulation or actual testing, obtain the first operating temperature range of the pump chip position and the second operating temperature range of the slow-axis collimating lens position of the fiber laser pump source module under actual working conditions.

[0016] S2, select multiple temperature points within the first operating temperature range, control the operating temperature of the pump chip to each set temperature point through the temperature control platform, and measure the operating performance parameters of the pump chip at each temperature point.

[0017] Among them, the operating performance parameters include at least the wavelength and the slow axis divergence angle.

[0018] S3. Construct an optical coupling simulation model including a slow-axis collimating lens and a pump chip. In the simulation model, configure temperature parameters and operating performance parameters corresponding to the first operating temperature range for the pump chip, and configure lens material temperature properties corresponding to the first operating temperature range for the slow-axis collimating lens. Set a non-uniform gradient temperature field to simulate the relationship between the coupling efficiency of the fiber coupling module and the working distance between the slow-axis collimating lens and the pump chip in the first and second operating temperature ranges, and obtain multiple sets of simulation data.

[0019] Among them, the material temperature properties of the slow-axis collimating lens include at least the coefficient of thermal expansion and the temperature coefficient of refractive index.

[0020] S4, based on multiple sets of simulation data, with the constraint of meeting preset stability requirements and the goal of maximizing the average coupling efficiency across the entire temperature range, determines the optimal fixed working distance between the slow-axis collimating lens and the pump chip through optimization calculation.

[0021] This embodiment: 1) Improves coupling efficiency by determining the optimal fixed working distance, and the entire process is cold simulation and design. Low-power parameter testing of a single chip in step S2 transforms the potentially dangerous online manual adjustment into safe offline software simulation and pre-positioning, eliminating personal and equipment safety hazards; 2) By acquiring the temperature distribution in step S1 and performing thermal-optical coupling simulation in step S3, the actual working temperature field can be actively and accurately acquired and simulated, rather than being adjusted at room temperature. This ensures the simulation environment matches the actual thermal state of the module during operation, determining the optimal working distance based on the thermal state, thereby eliminating coupling deviations caused by environmental mismatch; 3) Temperature is used as a core design variable, and three failures are modeled one-to-one: a) Wavelength drift: a) Measure the chip wavelength at different temperatures in S2, and assign this variation parameter to the light source in S3; b) Lens refractive index change: Configure the lens with a refractive index temperature coefficient that matches the second temperature range in S3; c) Working distance offset: Configure the thermal expansion coefficient (CTE) of the lens in S3, and finally optimize an optimal fixed working distance that remains stable when the temperature changes in S4; thereby realizing the proactive prediction and supplementation of optical efficiency in the design stage, and the determined optimal fixed working distance already includes temperature compensation; 4) Steps S3 and S4 output the determined and optimal values, and subsequent assembly can be performed based on this distance value without repeated trial and error, eliminating the inefficient links of repeated start-stop, observation, and fine-tuning, making mass production faster, more consistent, and improving the pass rate.

[0022] As a refinement and extension of the specific implementation of the above embodiments, in order to fully explain the specific implementation process of this embodiment, the following will provide possible embodiments to describe the specific implementation of the above steps in a non-limiting manner.

[0023] In some optional implementations, step S1, which involves obtaining the temperature range through thermal simulation, specifically includes: constructing a three-dimensional thermal simulation model of the fiber laser pump source module, which at least includes a pump chip as a heat source, a slow-axis collimating lens, a thermal interface material, and a heat sink; in the three-dimensional thermal simulation model, setting the heating power of the pump chip corresponding to its rated operating state, and setting the ambient temperature and surface convection heat transfer boundary conditions; meshing the three-dimensional thermal simulation model, and refining the mesh in the areas where the pump chip and the slow-axis collimating lens are located; performing transient thermal simulation analysis, with the simulation duration covering the entire process of the fiber laser pump source module from startup to reaching thermal equilibrium, and obtaining the first operating temperature range at the pump chip location and the second operating temperature range at the slow-axis collimating lens location under steady-state or quasi-steady-state conditions.

[0024] Specifically, using professional thermal simulation software such as ANSYS Icepak and FloTHERM, a three-dimensional geometric model containing all key thermally related components is established based on the physical design drawings of the pump source module. These components include at least: the pump chip (as the core heat source), the slow-axis collimating lens, the thermal pad / thermal grease, the heat sink / heat radiator, and the module housing.

[0025] The model is defined with material properties and boundary conditions, including: assigning accurate material properties to each component in the model, such as the chip's heat generation power density, the thermal conductivity, specific heat capacity, and density of each component; defining the pump chip as a volumetric heat source or a surface heat source, and setting its heat generation power consumption according to its rated operating current, voltage, and electro-optical conversion efficiency; defining the heat transfer coefficients for natural convection or forced convection on the outer surface of the heat sink and the surface of the module shell to simulate actual heat dissipation conditions; and setting an initial ambient temperature as the starting and reference boundary for the simulation.

[0026] The model is meshed using an unstructured grid. To ensure computational accuracy in critical areas such as the vicinity of the chip and lens, the grid needs to be refined in these areas, ensuring that the grid size is ≤0.01mm. The solver is set to transient analysis, and the total simulation time covers the entire process from module startup to reaching thermal equilibrium, for example, 0 to 120 minutes.

[0027] Running the solver performs calculations, and the simulation outputs temperature field contour maps and heat flux density vector maps showing the time-varying characteristics of the module's internal environment. In the results, locate the temperature monitoring point of the pump chip (usually its active region or upper surface) and record its temperature data from heating to steady state or quasi-steady state to obtain its temperature fluctuation range, i.e., the "first operating temperature range," for example, 45-70℃. Similarly, locate the temperature monitoring point of the slow-axis collimating lens (usually its lens body or mounting base) and record its temperature data to obtain the "second operating temperature range," for example, 30-45℃.

[0028] In some optional implementations, the process of obtaining the temperature range through actual testing in step S1 specifically includes: placing temperature sensors on the surface of the pump chip and at the mounting base of the slow-axis collimating lens; placing the fiber laser pump source module in a temperature-controlled environment chamber and powering it on under rated operating conditions; continuously recording temperature data for at least three complete operating cycles, and extracting and determining the first operating temperature range and the second operating temperature range from the recorded data.

[0029] Specifically, a sample of the fiber-coupled module to be tested is selected, ensuring that its mechanical structure and heat dissipation design are consistent with the mass-produced model. The first sensor A is attached and fixed to the surface of the pump chip (usually the non-light-emitting surface or the upper surface of the heat sink adjacent to the light-emitting area) using high-temperature thermally conductive adhesive to directly sense the junction temperature or near-junction temperature of the chip during operation. A second sensor B is attached and fixed to the mounting base or outer surface of the slow-axis collimating lens (as close as possible to the optical center of the lens) to sense the actual ambient temperature of the lens during module operation.

[0030] The module sample with the sensors installed was placed in a high and low temperature controlled test chamber, and the initial temperature of the chamber was set to the module's expected minimum operating ambient temperature. The data acquisition instrument was started, continuously and synchronously recording the temperature data of sensor A and sensor B at a frequency of no less than 1Hz. The laser driver was activated to start the module operating at its rated current, while maintaining a constant ambient temperature in the controlled chamber. The internal temperature of the module will continuously rise due to its own heat generation. When the temperature readings of both sensors change by less than ±0.2℃ within 10 consecutive minutes, the system is considered to have reached thermal steady state.

[0031] To simulate intermittent operation or load variations that may occur in real-world applications, periodic operation tests are conducted. For example, the module's operating cycle is set as follows: 30 minutes of full-power operation, followed by a 15-minute rest period with the drive current turned off (lighting stops, but the cooling system remains operational), constituting one complete cycle. Temperature data is continuously recorded for at least three such complete operating cycles. Data acquisition should cover the entire process from startup, heating up, steady state, to shutdown and cooling down.

[0032] After the test, export the temperature-time data curve. For each working cycle, extract a data segment of at least 10 minutes after reaching thermal steady state. Statistically analyze the temperature values ​​at all sampling points of sensor A (chip) and sensor B (lens) within this data segment, identifying the minimum value T_min and the maximum value T_max. Combine the data analysis results from at least three working cycles. The first working temperature range (at the chip) is defined as the range from the minimum chip temperature T_min across all cycles to the maximum chip temperature T_max across all cycles. The second working temperature range (at the lens) is determined in the same manner.

[0033] In some optional implementations, the operating performance parameters of the pump chip measured in step S2 include at least the wavelength and the slow-axis divergence angle. Step S2 selects multiple temperature points within the first operating temperature range, controls the operating temperature of the pump chip to each set temperature point through a temperature control platform, and measures the operating performance parameters of the pump chip at each temperature point. Specifically, this includes: installing the pump chip on a high-precision temperature control platform; sequentially setting a spectrometer and a beam analyzer in the optical path output direction of the pump chip; sequentially setting at least three discrete target temperature points within the first operating temperature range; sequentially controlling the operating temperature of the pump chip to each target temperature point through the temperature control platform; driving the pump chip to emit light under a constant current when the operating temperature of the pump chip is at each target temperature point; simultaneously using a spectrometer to measure the center wavelength of its output laser and using a beam analyzer to measure its divergence angle in the slow-axis direction; and recording each target temperature point and its corresponding measured values ​​of center wavelength and slow-axis divergence angle to form a dataset of the operating performance parameters of the pump chip.

[0034] Specifically, the first step is to set up a platform by mounting the pump chip under test on the thermally conductive surface of a high-precision temperature control platform, such as the Thorlads TED4015. Thermal grease is applied between the chip and the platform to ensure good thermal contact. The temperature sensor of the temperature control platform is then placed close to or embedded near the chip's heat sink to accurately sense and report the chip's operating temperature. The temperature sensor can be a thermistor or an RTD. Finally, a spectrometer for measuring wavelength and a beam quality analyzer or beam profiler for measuring divergence angle are placed and calibrated sequentially in front of the chip's light output.

[0035] Within the first operating temperature range obtained in step S1, at least three, typically five or more, discrete temperature points are selected at equal intervals or based on the characteristics of the temperature rise curve. For example, within the 45-70℃ range, 45℃, 50℃, 55℃, 60℃, and 65℃ are selected. The target temperature point is set through the controller of the temperature control platform. The TEC (thermoelectric cooler) inside the platform will automatically operate to actively heat or cool the chip, ensuring its temperature is precisely stabilized at the set point. Temperature control accuracy is required to be better than ±0.1℃, and after reaching thermal equilibrium at each temperature point (temperature fluctuation < ±0.05℃), the temperature must remain stable for at least 30 seconds to ensure uniform heat distribution within the chip.

[0036] Wavelength Measurement: After the chip temperature stabilizes, a constant, low operating current is applied to the chip to ensure stable light output. A spectrometer is used to collect the laser spectrum at a sampling frequency of at least 10 Hz, and the center wavelength is recorded. Multiple measurements can be taken consecutively at the same temperature point, and the average value is calculated to eliminate noise.

[0037] Slow-axis divergence angle measurement: Keeping the chip in operation, switch the optical path to a beam analyzer. At a fixed distance behind the chip, collect the intensity distribution of the laser spot along the slow axis. Calculate the slow-axis divergence angle using software analysis. Similarly, perform multiple measurements and take the average value.

[0038] The measured wavelength and slow-axis divergence angle values ​​are correlated with their corresponding chip set temperature points to form multiple sets of discrete data pairs (temperature T, wavelength λ(T), divergence angle θ(T)). This data is the chip performance parameter required for subsequent simulations. Figure 2 The graph shows the thermal parameters of the pump chip, with temperature (°C) on the horizontal axis and wavelength (nm) and slow-axis divergence angle (°) on the vertical axis. The graph clearly shows that within the temperature range of 45-60°C, the wavelength and slow-axis divergence angle of the pump chip increase linearly with increasing temperature.

[0039] In some alternative implementations, the optical coupling simulation model in step S3 is constructed in optical design software in a non-sequential ray tracing mode.

[0040] Specifically, the process of building an optical coupling simulation model includes: opening the optical design software, creating a new optical system project, and enabling the "non-sequential ray tracing" mode due to the potential for multiple reflections and scattering in the optical path. In the system settings, enable the "thermal analysis" and "temperature-dependent materials" functions. Then, perform geometric modeling and positioning of the components, configure key physical properties, and finally set the simulation parameters and execute the simulation.

[0041] The geometric modeling and positioning of components include: Pump chip model: Create a rectangular light source or a surface light source that conforms to the geometric dimensions of the chip's light-emitting surface, and place it at a predetermined position in the three-dimensional coordinate system; Lens Model: Based on the design drawings of the slow-axis collimating lens, model it using the "Lens" or "Standard Surface" component library in the software; place it along the optical axis at an initial distance from the chip light source; Aperture and detector: A rectangular or circular detector representing the fiber end face or ideal focal point is placed at an appropriate position behind the lens to receive light and calculate the coupling efficiency.

[0042] Configuring key physical properties includes configuring the light source properties and lens material properties. Light source property configuration: Set the light source type to laser, and input the chip center wavelength λ(T_i) obtained in step S2 at a specific temperature T_i; set the slow-axis divergence angle property of the light source to the corresponding value θ_slow(T_i) obtained in step S2. The fast-axis divergence angle is set to the design value or another set of measured values.

[0043] It should be noted that the temperature properties of the lens material configured for the slow-axis collimating lens include at least its coefficient of thermal expansion and temperature coefficient of refractive index. Lens material property configuration: Select the actual glass model of the slow-axis collimating lens from the software material library. In the material property settings, manually input or import the temperature coefficient of refractive index and the coefficient of thermal expansion of the glass. Specify a specific temperature value for the lens element itself. This value is taken from the second operating temperature range obtained in step S1 and matches the current light source temperature T_i. For example, when the chip is at 55℃, the lens may be at 40℃, achieving a discretized setting of the gradient temperature field.

[0044] The simulation parameters set include: setting a sufficiently large number of tracing rays, for example, ≥10. 6 To ensure statistical accuracy and reduce noise, the working distance is set as a variable, usually based on the initial position of the lens, to define a scanning range and set the scanning step size.

[0045] For each set working distance D_j, the software traces a large amount of light emitted from the chip, passing through a lens at a specific temperature, and finally reaching the detector. The software calculates and outputs the coupling efficiency, which is the ratio of the luminous flux reaching the target area of ​​the detector to the total luminous flux of the light source. Finally, a set of coupling efficiency data η(T_i,D_j) corresponding to temperature T_i and working distance D_j is obtained.

[0046] In some optional implementations, the pump chip is configured with temperature parameters and operating performance parameters corresponding to the first operating temperature range in the simulation model. Specifically, this includes: establishing a mapping table or fitting function for the correspondence between the operating temperature of the pump chip and its input wavelength and slow-axis divergence angle based on the operating performance parameters obtained in step S2; setting a specific temperature value selected from the first operating temperature range for the pump chip element in the light source properties of the simulation model to define its thermal state; and configuring the wavelength measurement value corresponding to the temperature value as the emission wavelength of the light source, and configuring the slow-axis divergence angle measurement value corresponding to the temperature value as the slow-axis divergence angle of the light source.

[0047] Specifically, the dataset obtained in step S2 is organized into mapping relationships, such as: T1: 45℃ -> λ1: 974.57nm, θ1: 8.4°; T2: 50℃ -> λ2: 974.91nm, θ2: 8.5°, etc. In the optical simulation software, the attribute setting panel representing the light source element of the "pump chip" is located.

[0048] For configuring temperature parameters, directly enter a specific temperature value in the "Temperature" or "Ambient Temperature" property field of the light source element. This value is a discrete simulation point selected from the first operating temperature range (such as 45-70℃), for example, T=55℃, informing the software that the light source is in this specific thermal environment.

[0049] For configuring the operating performance parameters, in the "Spectrum" or "Wavelength" settings of the light source, select the "Monochromatic Light" mode and set the wavelength value to the measured value λ(T) corresponding to the currently configured temperature point T. Here, instead of entering a fixed value, enter a value bound to temperature; for example, you can enter a wavelength-temperature lookup table or fitting formula. In the "Spatial Distribution" or "Diffusion Angle" settings of the light source, there are component settings for both the "Fast Axis" and "Slow Axis." Set the value of the slow axis divergence angle to the measured value corresponding to the current temperature point T, and similarly establish a fitting formula between temperature and the slow axis divergence angle. The fast axis divergence angle usually changes little and can be set to a fixed value or another set of measured values.

[0050] In some optional implementations, a non-uniform gradient temperature field is set, specifically including: defining a first temperature point and a second temperature point in the space of the simulation model, and assigning a value within a first operating temperature range as the temperature of the first temperature point, and assigning a value within a second operating temperature range as the temperature of the second temperature point; setting the temperature change from the first temperature point to the second temperature point as a continuous change, and constraining its spatial temperature gradient to not exceed a preset threshold; applying the temperature field that satisfies the gradient rule to the simulation space region containing the pump chip and the slow-axis collimating lens.

[0051] Specifically, in the thermal analysis module of the simulation software, a physical field with continuously varying temperature along the optical axis (from the chip to the lens) is defined, and the following parameters are configured: Temperature boundary: The two temperature ranges obtained in step S1 are converted into specific boundary conditions. For example, the temperature of the chip position (coordinate point A) is set as T_chip, such as 65℃, taken from the first range, and the temperature of the lens center position (coordinate point B) is set as T_lens, such as 45℃, taken from the second range. Gradient constraint: Defines the spatial temperature variation pattern between point A and point B. This can be a linear gradient or calculated by software using the material's thermal conductivity. To ensure the engineering feasibility and simplification of the simulation, the magnitude of this gradient can be limited, for example, "temperature gradient ≤ 2°C / mm," meaning the temperature change over each millimeter of spatial distance does not exceed 2°C.

[0052] The predefined non-uniform temperature field is applied to the corresponding spatial region of the entire simulation model, covering the chip, lens, and the air gap between them. Based on this field, the software will assign a specific temperature value to each point in the space, including the light source and the lens glass.

[0053] In some optional implementations, the coupling efficiency of the fiber optic coupling module is simulated as a function of the working distance between the slow-axis collimating lens and the pump chip within the first and second operating temperature ranges, obtaining multiple sets of simulation data, specifically including: a) Set the position of the slow-axis collimating lens in the optical axis direction as a variable, and define a scanning range and scanning step size for it; b) For each position value within the scanning range, perform ray tracing under the gradient temperature field and calculate the coupling efficiency of the light emitted from the pump chip after passing through the slow-axis collimating lens and coupling to the target fiber. c) Record each position value and its corresponding coupling efficiency value to form a set of simulation data characterizing the change of coupling efficiency with working distance under a specific temperature field; d) By changing the values ​​of the first and second temperature points, iteratively execute steps a) to c) to obtain multiple sets of simulation data corresponding to different operating temperature states.

[0054] Specifically, in the software, the position coordinates of the slow-axis collimating lens element along the optical axis are set as optimization or analysis variables. Changes in this variable directly correspond to changes in the working distance d. Based on the feasible range of the mechanical design and the initial optical prediction, a scanning range and a scanning step size are set for the working distance d to ensure data continuity.

[0055] Establish an evaluation function or optimization objective in the software, which is defined as the ratio of the light flux (or power) reaching the detector at the target fiber end face to the total light flux (or power) emitted by the pump chip light source, i.e., the coupling efficiency η.

[0056] The software automatically executes a loop, that is, for each working distance value d_i within the scanning range, the system will: update the temperature of each point in the model according to the defined gradient temperature field; dynamically adjust the wavelength / divergence angle of the light source and the refractive index / size of the lens according to the updated temperature; trace a large number of light rays from the light source to the detector; and calculate and record the coupling efficiency value η_i at the distance d_i.

[0057] After the loop ends, the software outputs a data list or curve representing the correspondence between (working distance d_i) and coupling efficiency η_i. Since the simulation is performed under a specific, fixed gradient temperature field, this set of data represents the efficiency-distance relationship under that specific thermal environment.

[0058] Different combinations of (T_chip, T_lens) are selected to cover extreme and typical cases in the first and second temperature ranges. For each temperature combination, a full-range scan is run to obtain multiple sets of (d, η) relationship data. Ultimately, a three-dimensional dataset η=f(d,T_chip,T_lens) or simplified to η=f(d,T) is obtained, where T represents a specific thermal state.

[0059] In some optional implementations, step S4, based on multiple sets of simulation data, with the constraint of satisfying a preset stability requirement and the objective of maximizing the average coupling efficiency across the entire temperature range, determines the optimal fixed working distance between the slow-axis collimating lens and the pump chip through optimization calculation. Specifically, this includes: constructing an objective function and a constraint function with the working distance as the variable based on multiple sets of simulation data; wherein the objective function represents the average coupling efficiency of the fiber coupling model within the first and second operating temperature ranges; the constraint function characterizes the fluctuation range of the average coupling efficiency across the entire temperature range; and the preset stability requirement characterizes the numerical constraint on the constraint function; within the mechanically feasible range of the working distance, executing a numerical optimization algorithm to find the solution that maximizes the objective function while satisfying the preset stability requirement of the constraint function; and determining the solution as the optimal fixed working distance between the slow-axis collimating lens and the pump chip.

[0060] Specifically, the multiple sets of simulation data obtained in step S3 are integrated. Each set of data corresponds to a specific temperature field state, denoted as state k, with a total of K states, containing a series of (working distance d_i, coupling efficiency η_{ik}) data pairs. To improve accuracy, curve fitting is performed on the discrete (d_i, η_{ik}) data under each temperature state k to obtain the continuous function η_k(d) of the coupling efficiency with respect to the working distance under that state.

[0061] For any working distance d to be evaluated, calculate the average of its coupling efficiency under all K temperature conditions, and use it as the comprehensive performance index for that distance:

[0062] The F_avg(d) function is the objective function that needs to be maximized.

[0063] Define efficiency fluctuation: For any working distance d to be evaluated, assess its stability over the entire temperature range, specifically by calculating the standard deviation σ(d) of its coupling efficiency under all temperature conditions.

[0064] Preset stability requirements: Based on the product performance specifications, set a stability threshold. For example, the requirement is that "the fluctuation range of coupling efficiency does not exceed ±1.5% across the entire temperature range," which is equivalent to requiring Δη(d) ≤ 3.0%. This threshold is the constraint condition.

[0065] The physically feasible range [d_min, d_max] of the working distance d is determined, which is the feasible region. Within the feasible region [d_min, d_max], an optimization algorithm is executed to find the optimal solution d_opt. The search process of this algorithm satisfies the following conditions: the objective is to maximize F_avg(d), and the constraint Δη(d) ≤ 3.0%.

[0066] The optimization algorithm can be a grid search method: within the feasible region, enumerate all possible d values ​​with fine step sizes (e.g., 0.001 mm), calculate their F_avg(d) and Δη(d) respectively, filter out all d values ​​that satisfy the constraints, and then select the one with the largest F_avg(d) as d_opt.

[0067] After the optimization algorithm converges, the output solution d_opt is the optimal fixed working distance. That is, when the slow axis collimating lens is fixed at a position d_opt away from the chip, the assembled fiber optic coupling module can achieve the theoretically highest average coupling efficiency within the preset full temperature range, while ensuring that its efficiency fluctuation is strictly controlled within the allowable threshold.

[0068] Actual testing has verified that the fiber optic coupling module determined and assembled using the method of this invention exhibits significantly improved performance. Within the operating temperature range (e.g., 40-70℃), the module's coupling efficiency demonstrates excellent stability. Figure 3 This is a graph comparing the coupling efficiency as a function of temperature. The horizontal axis represents temperature (°C), and the vertical axis represents coupling efficiency (%). The graph contains two curves: one for the traditional power-adjusted process and the other for the method of this invention. Figure 3 As shown, the traditional process curve (dashed line) fluctuates drastically in the range of 40-65℃, with a coupling efficiency coefficient of variation (CV) as high as 8.5%; while the module optimized by the method of this invention (solid line) has a smooth coupling efficiency curve with a coefficient of variation ≤2.2% in the entire temperature range, and its stability is improved by more than 74% compared with the traditional process.

[0069] Then, based on the optimal working distance determined in step S4, a high-precision bonding process is used to fix the slow-axis collimating lens to the preset position on the fiber optic coupling module; the high-precision bonding process employs a ceramic-based mechanical limiting structure (CTE=8×10). -6 / ℃, accuracy ±1μm) and visual positioning system (dual telecentric lens + sub-pixel algorithm, positioning error ±0.5μm) are used for composite positioning; when pasting, UV curing adhesive is used (cured by irradiation with 365nm UV lamp at 800mW / cm² intensity for 10±0.5 seconds; after curing, temperature cycling (-40-85℃) is performed to verify that the position offset is ≤0.5μm.

[0070] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the working distance of a slow-axis collimating lens in an optical fiber coupling module, characterized in that, Includes the following steps: S1. Through thermal simulation or actual testing, obtain the first operating temperature range of the pump chip position and the second operating temperature range of the slow-axis collimating lens position of the fiber laser pump source module under actual working conditions. S2, select multiple temperature points within the first operating temperature range, control the operating temperature of the pump chip to each set temperature point through the temperature control platform, and measure the operating performance parameters of the pump chip at each temperature point. S3. Construct an optical coupling simulation model including a slow-axis collimating lens and a pump chip. In the simulation model, configure temperature parameters and working performance parameters corresponding to the first working temperature range for the pump chip, and configure lens material temperature properties corresponding to the first working temperature range for the slow-axis collimating lens. Set a non-uniform gradient temperature field to simulate the relationship between the coupling efficiency of the fiber coupling module and the working distance between the slow-axis collimating lens and the pump chip in the first and second working temperature ranges, and obtain multiple sets of simulation data. S4, based on multiple sets of simulation data, with the constraint of meeting preset stability requirements and the goal of maximizing the average coupling efficiency across the entire temperature range, determines the optimal fixed working distance between the slow-axis collimating lens and the pump chip through optimization calculation.

2. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 1, characterized in that, The process of obtaining the temperature range through thermal simulation in step S1 specifically includes: A three-dimensional thermal simulation model of the pump source module of a fiber laser is constructed. The model includes at least the pump chip as a heat source, the slow-axis collimating lens, the thermal interface material, and the heat sink. In the three-dimensional thermal simulation model, the heating power of the pump chip corresponding to its rated operating state is set, and the ambient temperature and surface convection heat transfer boundary conditions are set. The three-dimensional thermal simulation model was meshed, and the mesh was refined in the areas where the pump chip and slow-axis collimating lens were located. Transient thermal simulation analysis was performed, covering the entire process of the fiber laser pump source module from startup to reaching thermal equilibrium. The first operating temperature range of the pump chip position and the second operating temperature range of the slow-axis collimating lens position were obtained under steady-state or quasi-steady-state conditions.

3. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 1, characterized in that, Step S1, which involves obtaining the temperature range through actual testing, specifically includes: Temperature sensors are installed on the surface of the pump chip and at the mounting base of the slow-axis collimating lens, respectively. Place the fiber laser pump source module in a temperature-controlled environment chamber and power it on under rated operating conditions; Temperature data is continuously recorded for at least three complete operating cycles. The first operating temperature range and the second operating temperature range are extracted and determined from the recorded data.

4. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 1, characterized in that, The operating performance parameters of the pump chip measured in step S2 include at least the wavelength and the slow axis divergence angle.

5. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 4, characterized in that, Step S2 specifically includes: The pump chip is installed on a high-precision temperature control platform, and a spectrometer and a beam analyzer are set in sequence in the optical output direction of the pump chip. Within the first operating temperature range, at least three discrete target temperature points are sequentially set; the operating temperature of the pump chip is then controlled sequentially at each target temperature point by the temperature control platform. When the pump chip operates at each target temperature point, drive the pump chip to emit light under constant current; simultaneously use a spectrometer to measure the center wavelength of its output laser and use a beam analyzer to measure its divergence angle in the slow axis direction; Record the measured values ​​of each target temperature point and its corresponding center wavelength and slow axis divergence angle to form a dataset of the pump chip's operating performance parameters.

6. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 1, characterized in that, In step S3, the optical coupling simulation model is constructed in the optical design software in a non-sequential ray tracing mode.

7. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 6, characterized in that, Configuring the pump chip with temperature parameters and operating performance parameters corresponding to the first operating temperature range specifically includes: Based on the working performance parameters obtained in step S2, establish a mapping table or fitting function for the correspondence between the working temperature of the pump chip and its input wavelength and slow axis divergence angle. In the light source properties of the simulation model, a specific temperature value selected from the first operating temperature range is set for the pump chip element to define its thermal state. Based on the established mapping relationship, the wavelength measurement value corresponding to the temperature value is configured as the emission wavelength of the light source, and the slow axis divergence angle measurement value corresponding to the temperature value is configured as the slow axis divergence angle of the light source.

8. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 6, characterized in that, The temperature properties of the lens material configured for a slow-axis collimating lens include at least its coefficient of thermal expansion and temperature coefficient of refractive index.

9. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 6, characterized in that, The simulation examined the relationship between the coupling efficiency of the fiber optic coupling module and the working distance between the slow-axis collimating lens and the pump chip within the first and second operating temperature ranges, obtaining multiple sets of simulation data, specifically including: a) Set the position of the slow-axis collimating lens in the optical axis direction as a variable, and define a scanning range and scanning step size for it; b) For each position value within the scanning range, perform ray tracing under the gradient temperature field and calculate the coupling efficiency of the light emitted from the pump chip after passing through the slow-axis collimating lens and coupling to the target fiber. c) Record each position value and its corresponding coupling efficiency value to form a set of simulation data characterizing the change of coupling efficiency with working distance under a specific temperature field; d) By changing the values ​​of the first and second temperature points, iteratively execute steps a) to c) to obtain multiple sets of simulation data corresponding to different operating temperature states.

10. The method for determining the working distance of the slow-axis collimating lens in the fiber optic coupling module according to claim 1, characterized in that, Step S4 specifically includes: Based on multiple sets of simulation data, an objective function and a constraint function with working distance as the variable are constructed. The objective function represents the average coupling efficiency of the fiber coupling model within the first and second working temperature ranges. The constraint function characterizes the fluctuation range of the average coupling efficiency across the entire temperature range, and the preset stability requirement is represented as a numerical constraint on the constraint function. Within the mechanically feasible range of the working distance, a numerical optimization algorithm is executed to find the solution that maximizes the objective function, provided that the constraint function meets the preset stability requirements. The solution is determined to be the optimal fixed working distance between the slow-axis collimating lens and the pump chip.

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