Preparation method for accurately controlling core diameter of optical fiber

Abstract

The invention relates to the technical field of optical fiber manufacturing, in particular to an optical fiber core diameter accurate control preparation method which comprises the following steps: step 1, providing an optical fiber preform; 2, heating the optical fiber preform to a softening temperature; step 3, carrying out wire drawing on the heated optical fiber preform through a wire drawing device; 4, in the wire drawing process, measuring the core diameter of the optical fiber in real time by using an optical measurement system; 5, comparing the core diameter measurement value with a preset target core diameter value, and calculating a core diameter deviation value; 6, dynamically adjusting wire drawing parameters through a control algorithm; and 7, repeating the step 4 to the step 6, and continuously performing real-time measurement, comparison and adjustment in the whole wire drawing process until the wire drawing process is finished. Manual intervention is replaced by an automatic control system, introduction of personal errors is reduced, and the stability and consistency of the optical fiber preparation process are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber manufacturing, and particularly relates to a method for precisely controlling the core diameter of an optical fiber. BACKGROUND

[0002] As an important optical transmission medium, optical fibers are widely used in communication, sensing, medical and industrial fields. The performance of optical fibers depends largely on the precise control of their core diameter, and the uniformity and consistency of the core diameter directly affect the transmission loss, bandwidth and mode characteristics of the optical fiber. In the prior art, the preparation of optical fibers is usually realized by a preform rod drawing method, which includes heating the optical fiber preform rod to a softening temperature and then forming an optical fiber through a drawing process. However, the existing method has significant problems in core diameter control.

[0003] The existing method often relies on open-loop control, that is, the drawing parameters (such as drawing speed, heating temperature) are preset empirically, but in the actual drawing process, due to environmental fluctuations, material non-uniformity and equipment aging, etc., the core diameter is prone to deviation. For example, during the drawing process, unstable heating temperature will cause the softening degree of the preform rod to change, thereby causing core diameter fluctuations; slight changes in drawing speed will also directly affect the diameter of the optical fiber. In the prior art, some methods attempt to adjust the parameters by periodically sampling measurements, but this method cannot achieve real-time control, resulting in poor core diameter uniformity, especially in long-distance optical fiber preparation, the cumulative error will seriously affect the quality of the optical fiber.

[0004] The measurement of the core diameter in the existing method is usually carried out offline, for example, after the drawing is completed, it is detected by a microscope or an optical measurement device. This offline measurement has a delay and cannot be fed back to the control system in time, so it cannot correct the core diameter deviation in real time during the drawing process. Some advanced methods attempt to introduce online measurement, such as laser scattering or optical imaging, but these methods are often limited by measurement accuracy and environmental interference, such as dust, vibration or temperature changes that can affect the measurement results, resulting in inaccurate control. In addition, the existing online measurement method is usually based on a single sensor and lacks multi-data fusion, making it difficult to compensate for system errors.

[0005] The existing method lacks adaptive capability in parameter adjustment. The drawing process is a multivariate coupled system, and parameters such as drawing speed, heating temperature and cooling rate affect each other, but the existing control strategy often uses simple proportional-integral-derivative (PID) control, which cannot handle nonlinear dynamic changes. For example, when the composition of the preform rod material changes, the existing method needs manual intervention to adjust the parameters again, which is not only inefficient but also prone to human error. In some high-precision applications, such as photonic crystal fibers or multi-mode fibers, the core diameter control requires sub-micron level, and the existing method is difficult to meet such precision requirements.

[0006] In summary, the existing optical fiber core diameter control preparation method has the problems of poor real-time performance, insufficient measurement accuracy, simple control strategy, etc., resulting in low core diameter uniformity, low production efficiency and poor product consistency. Therefore, there is an urgent need for a preparation method that can accurately control the core diameter of the optical fiber, which can improve the core diameter control accuracy and preparation efficiency through real-time monitoring and dynamic adjustment. SUMMARY

[0007] Based on the above purpose, the present application provides a method for accurately controlling the core diameter of an optical fiber, which comprises the following steps:

[0008] Step 1: providing an optical fiber preform, the optical fiber preform comprising a core layer and a cladding layer, the core layer material being doped silica, and the cladding layer material being pure silica;

[0009] Step 2: heating the optical fiber preform to a softening temperature, the softening temperature being determined by a preheating experiment, the preheating experiment comprising heating optical fiber preform samples at different temperatures and observing the deformation temperature point, and the temperature being monitored in real time by a temperature sensor and feedback controlled during the heating process;

[0010] Step 3: drawing the heated optical fiber preform through a drawing device to form an optical fiber, the drawing device comprising a traction wheel and a take-up wheel, the traction wheel rotating at a preset initial speed, and the drawing device controlling the drawing speed through a servo motor;

[0011] Step 4: during the drawing process, using an optical measurement system to measure the core diameter of the optical fiber in real time, the optical measurement system comprising a light source, an optical lens and an image sensor, the light source emitting a light beam to irradiate the optical fiber, the light beam being focused by the optical lens and then the image sensor collecting the cross-sectional image of the optical fiber, and the image sensor transmitting the image data to an image processing unit;

[0012] Step 5: the image processing unit processes the image data through an edge detection algorithm, extracts the core layer boundary of the optical fiber and calculates the core diameter measurement value, compares the core diameter measurement value with a preset target core diameter value, and calculates the core diameter deviation value;

[0013] Step 6: based on the core diameter deviation value, dynamically adjusting the drawing parameters through a control algorithm, the drawing parameters including the drawing speed and the heating temperature, the control algorithm adopting an adaptive proportional-integral-derivative control strategy, calculating the drawing speed adjustment amount and the heating temperature adjustment amount according to the size and change trend of the core diameter deviation value, and executing the adjustment through the servo motor and the heating furnace power controller;

[0014] Step 7: repeating steps 4 to 6, continuously measuring, comparing and adjusting in real time throughout the drawing process until the drawing process is completed.

[0015] Preferably, in step 4, the light source of the optical measurement system is an LED light source, the wavelength of which is determined by spectral analysis, which includes testing the transmission characteristics of light beams of different wavelengths in the optical fiber, and selecting the wavelength with the highest transmittance as the working wavelength;

[0016] The image sensor is a CCD camera, and the acquisition frequency of the CCD camera is set through experiments, which include testing the clarity and delay of image acquisition at different drawing speeds, and selecting an acquisition frequency that meets the real-time requirements;

[0017] The focal length of the optical lens is determined by a calibration procedure, which includes imaging tests using standard-sized optical fiber samples, and adjusting the focal length until the image boundary clarity reaches a preset threshold.

[0018] Preferably, in step 5, the edge detection algorithm is implemented based on gray level gradient changes, specifically including the following sub-steps: first, perform gray scale processing on the image to convert the color image to a gray scale image;

[0019] Then use the Sobel operator to calculate the gradient of the gray scale image and detect the boundary points through convolution operation; then apply a threshold segmentation method to identify the interface between the core layer and the cladding layer according to the gradient amplitude;

[0020] Finally, smooth the boundary points through a curve fitting algorithm, calculate the core diameter measurement value, and the curve fitting algorithm uses the least squares method with a fitting error controlled within an allowable range.

[0021] Preferably, in step 6, the parameter setting process of the adaptive proportional-integral-derivative control strategy includes introducing a test disturbance in the initial drawing stage, the test disturbance being a human change in drawing speed or heating temperature, observing the system response curve, and recording the overshoot and settling time;

[0022] Adjust the proportional coefficient, integral coefficient, and derivative coefficient according to the system response curve to make the overshoot lower than the preset upper limit and the settling time shortest;

[0023] The proportional coefficient is used to quickly respond to core diameter deviation, the integral coefficient is used to eliminate steady-state error, and the derivative coefficient is used to predict the trend of core diameter change;

[0024] The control algorithm also includes a nonlinear compensation module for processing the coupling effect between the drawing speed and the heating temperature, the nonlinear compensation module establishes a mapping relationship based on historical data and corrects the adjustment amount in real time through a lookup table method.

[0025] Preferably, in step 6, the calculation process of the drawing speed adjustment amount includes:

[0026] First, determine the adjustment direction according to the positive and negative signs of the core diameter deviation value, increase the drawing speed when the deviation is positive, and decrease the drawing speed when the deviation is negative;

[0027] Then, based on the absolute value of the deviation value and the change rate, the preliminary adjustment amount is calculated through the proportional-integral-derivative operation formula;

[0028] Finally, in combination with the mechanical inertia constraint of the drawing device, the preliminary adjustment amount is limited in amplitude to ensure that the adjustment amount does not exceed the maximum acceleration capability of the servo motor;

[0029] The calculation process of the heating temperature adjustment amount includes: determining the urgency of temperature adjustment according to the size of the core diameter deviation change rate, and preferentially adjusting the heating temperature when the change rate exceeds a preset threshold;

[0030] The temperature adjustment amount is obtained by querying a pre-stored temperature-core diameter relationship table, and the relationship table is established through preheating experiments to record the change law of the core diameter at different temperatures.

[0031] Preferably, before step 4, the calibration step of the optical measurement system is also included, and the calibration step includes:

[0032] A plurality of standard size optical fiber samples are used, and the core diameter of the standard size optical fiber samples is certified by a national standard measurement institution;

[0033] The standard size optical fiber samples are sequentially placed in the optical measurement system, images are collected, and the core diameter measurement value is calculated;

[0034] The measurement value is compared with the standard value, and the system error is calculated;

[0035] An error compensation model is established by a linear regression method, the error compensation model represents the system error as a function of the ambient temperature and humidity, and the measurement value is automatically corrected according to the real-time environmental parameters in actual measurement.

[0036] Preferably, in step 2, the heating process uses a resistance heating furnace, and the power control of the resistance heating furnace is realized through a closed loop, specifically including:

[0037] The temperature sensor collects the temperature in the heating furnace in real time, and transmits the temperature data to the temperature controller;

[0038] The temperature controller uses a fuzzy logic control algorithm to adjust the heating power according to the temperature deviation and the deviation change rate;

[0039] The rule base of the fuzzy logic control algorithm is constructed through experiments, including control strategies in different temperature intervals;

[0040] The surface state of the preform rod is monitored during heating, a hot spot is detected by an infrared thermal imager, and the heating power distribution is automatically adjusted when the hot spot is detected to ensure temperature uniformity.

[0041] Preferably, in step 3, the control process of the drawing speed includes:

[0042] The servo motor receives a control signal generated by a control algorithm;

[0043] The rotation speed of the servo motor is fed back by an encoder, which collects the actual rotation speed and compares it with the target rotation speed to generate a rotation speed deviation;

[0044] The rotation speed deviation is adjusted by a proportional-integral controller to ensure stable drawing speed;

[0045] The fiber tension is also monitored during the drawing process, and the tension data is collected in real time by a tension sensor, and when the tension exceeds the preset range, the take-up speed of the take-up wheel is automatically adjusted to prevent the optical fiber from breaking or relaxing.

[0046] Preferably, in step 1, the preparation process of the optical fiber preform rod includes:

[0047] The core layer and the cladding layer are formed by chemical vapor deposition, and the deposition parameters are controlled to make the initial value of the core diameter close to the target value;

[0048] The deposition parameters include gas flow, deposition temperature and deposition time, the gas flow is accurately controlled by a mass flow controller, the deposition temperature is monitored by a thermocouple, and the deposition time is calculated according to the size of the preform rod;

[0049] After the preform rod is formed, the end face is processed by grinding and polishing to ensure that the flatness of the end face meets the drawing requirements.

[0050] Preferably, in step 7, the continuous monitoring process includes data recording and abnormality handling:

[0051] The data recording unit stores the core diameter measurement value, the drawing speed, the heating temperature and the environmental parameters in real time, the environmental parameters include the environmental temperature and humidity, which are collected by a temperature and humidity sensor;

[0052] The abnormality handling module calculates the mean and standard deviation of the core diameter data based on the statistical process control principle, and when a plurality of consecutive measurement values exceed the control limit, an alarm is triggered and the drawing process is suspended;

[0053] After the alarm, the system automatically executes a diagnostic program to check the working state of the optical measurement system, the drawing device and the heating furnace, and prompts maintenance measures according to the diagnostic results.

[0054] The beneficial effects of the present application are:

[0055] 1. By measuring the fiber core diameter in real time and dynamically adjusting the drawing parameters, precise control of the fiber core diameter is achieved, the core diameter deviation is significantly reduced, and the uniformity and consistency of the fiber are improved.

[0056] 2. The use of optical measurement systems and image processing ensures high precision and real-time of core diameter measurement, overcoming the delay problem of existing offline measurement.

[0057] 3. Through the adaptive control algorithm, it can handle the nonlinear changes in the drawing process, enhance the robustness and adaptability of the system, and reduce the need for human intervention.

[0058] 4. The whole method is simple and feasible, suitable for industrial production, improving production efficiency and product yield. BRIEF DESCRIPTION OF DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0060] Fig. 1 The step flow chart of the method of the present application;

[0061] Fig. 2 The step flow chart of the gray scale gradient change in the method of the present application;

[0062] Fig. 3 The step flow chart of the calculation process of the drawing speed adjustment amount in the method of the present application. DETAILED DESCRIPTION

[0063] The present application will be described in detail below in combination with the drawings and specific embodiments. It should be noted here that in order to make the embodiments more detailed, the following embodiments are the best, preferred embodiments, and other alternative ways can also be used by those skilled in the art to implement them; and the drawings are only used to describe the embodiments more specifically, and are not intended to limit the present application specifically.

[0064] Please refer to Figs. 1-3 The present application provides a kind of optical fiber core diameter precision control preparation method, in step 1, the core layer of optical fiber preform adopts doped silica material, cladding uses pure silica.This selection helps to ensure the optical performance and transmission efficiency of optical fiber.The core layer of doped silica can provide the required refractive index, ensure the effective transmission of optical signal;And the cladding of pure silica plays a protective and reflective role for optical signal, improves the overall performance of optical fiber.

[0065] In step 2, the optical fiber preform needs to be heated to a softening temperature before fiber drawing. This temperature is determined through a preheating experiment. The preheating experiment involves heating the preform sample at different temperatures and observing its deformation temperature points. Temperature changes during the heating process are monitored in real time using a temperature sensor, and a feedback control mechanism ensures precise temperature regulation. This precise control avoids changes in the fiber core diameter caused by temperature fluctuations, ensuring uniformity and stability in the subsequent fiber drawing process.

[0066] In step 3, the heated optical fiber preform is drawn into optical fibers using a drawing device. The drawing device includes a traction wheel and a take-up wheel. The traction wheel rotates at a preset initial speed, and a servo motor controls the drawing speed as needed. This configuration allows for flexible adjustment of the drawing speed, thus affecting the final core diameter of the optical fiber. In actual operation, precise speed adjustment controlled by the servo motor enables real-time response during the optical fiber production process, ensuring the fiber core diameter remains within a predetermined range.

[0067] In step 4, during the fiber drawing process, the core diameter of the optical fiber is measured in real time using an optical measurement system. This system includes a light source, an optical lens, and an image sensor. The light beam emitted by the light source illuminates the optical fiber and is focused onto the fiber by the optical lens. The image sensor captures a cross-sectional image of the fiber and transmits the image data to the image processing unit. The accuracy of the image sensor enables the measurement of the fiber core diameter quickly and efficiently, providing reliable data support for subsequent data processing and control.

[0068] In step 5, the image processing unit uses an edge detection algorithm to process the acquired optical fiber cross-sectional image, accurately extracting the boundaries of the fiber core and calculating the fiber core diameter. The core diameter deviation is calculated by comparing it with a preset target core diameter value. This process provides real-time fiber dimensional information, facilitating the determination of whether the fiber meets quality requirements and providing feedback data to the control system.

[0069] In step 6, based on the core diameter deviation, the control system employs an adaptive proportional-integral-derivative (PID) control strategy to dynamically adjust parameters such as drawing speed and heating temperature. According to the magnitude and trend of the core diameter deviation, the control algorithm calculates the adjustment amounts for the drawing speed and heating temperature, and makes real-time adjustments via the servo motor and the heating furnace power controller. The adaptive PID control strategy can automatically adjust parameters according to real-time changes during the fiber drawing process, ensuring that the fiber core diameter remains within the ideal range and avoiding errors caused by manual adjustments.

[0070] In step 7, steps 4 through 6 are repeated until the fiber drawing process is complete. The entire process is a continuous, real-time measurement, comparison, and adjustment process to ensure precise control of the fiber core diameter. This closed-loop control system effectively avoids core diameter deviations caused by environmental fluctuations, equipment aging, and other factors, thereby maintaining the consistency of fiber quality.

[0071] By combining real-time measurement with adaptive control, the technical solution effectively solves the problems of core diameter fluctuation and precision control in traditional optical fiber manufacturing methods, improves production efficiency and product quality, and has significant technical significance and application value.

[0072] In one possible implementation, an LED light source is used as the light source in the optical measurement system. This choice is primarily based on the high stability and adaptability of LEDs. The wavelength of the LED light source is determined through spectral analysis. Specifically, spectral analysis tests the transmission characteristics of light beams of different wavelengths in the optical fiber. During the test, the transmittance of light beams of different wavelengths is observed, and the wavelength with the highest transmittance is ultimately selected as the working wavelength. The core objective of this process is to select the wavelength with the least transmission loss in the optical fiber, thereby obtaining the clearest image and ensuring the accuracy and reliability of the fiber core diameter measurement. By optimizing the wavelength of the light source, the efficiency of the optical fiber measurement process can be maximized, and measurement errors caused by beam attenuation or reflection can be reduced.

[0073] In the optical measurement system, a CCD camera was selected as the image sensor. This type of camera boasts high image resolution and sensitivity, enabling it to accurately capture details of the fiber cross-section. In practical applications, the CCD camera's acquisition frequency was experimentally determined. The specific experimental steps included testing the image acquisition sharpness and latency at different fiber drawing speeds to ensure the selected acquisition frequency met real-time requirements. This means that during fiber drawing, the image acquisition frequency needs to be matched with the fiber drawing speed to guarantee real-time feedback of core diameter data and dynamic adjustments to the drawing process. The implementation of this experimental procedure ensured the accuracy and timeliness of image acquisition, avoiding core diameter measurement errors caused by acquisition delays or insufficient resolution.

[0074] The focal length of the optical lens in the optical measurement system is determined through a calibration procedure. Specifically, imaging tests are performed using a standard-sized fiber sample, and the lens focal length is adjusted until the image boundary sharpness reaches a preset threshold. This calibration process ensures that the optical system maintains a clear image throughout the fiber drawing process, regardless of changes in the actual core diameter, guaranteeing the accuracy and consistency of core diameter measurements. By applying this calibration procedure, the image blurring problem that may be caused by changes in fiber size can be effectively resolved, thereby improving the measurement accuracy of fiber core diameter.

[0075] The optical measurement system of this invention significantly improves the accuracy and reliability of fiber core diameter control through precise light source selection, image acquisition frequency setting, and lens focal length calibration, thereby enhancing the overall quality management level in the fiber fabrication process and possessing significant application value.

[0076] In one possible implementation, the acquired color fiber optic image is first converted into a grayscale image. Color images contain a large amount of color information, while in fiber optic measurements, the boundaries of the fiber are mainly reflected in grayscale variations. Therefore, converting to a grayscale image allows for a more concise highlighting of the image's structural information. Grayscale conversion eliminates color interference, making subsequent edge detection more efficient and accurate.

[0077] Next, the Sobel operator is used to process the grayscale image and calculate the gradient values ​​in the image. The Sobel operator is a commonly used edge detection operator. It calculates the gradient value of each pixel in the image through convolution operations, thereby finding the region with the largest grayscale change in the image, which usually corresponds to the boundary of an object. In fiber optic images, the interface between the core and cladding usually appears as a place with a large grayscale change, so the Sobel operator can effectively detect the edge location of the fiber.

[0078] After calculating the gradient of the image, a thresholding method is applied to set a threshold based on the gradient magnitude, thereby distinguishing the boundary between the fiber core and cladding. Thresholding is a common method in image processing. It divides pixels in an image into two categories by setting a predetermined threshold: one category consists of pixels that meet certain characteristics (such as high gradient values), which are boundary points; the other category consists of pixels from other regions. This step effectively identifies the boundary between the fiber core and cladding, thus providing an accurate reference for subsequent core diameter measurements.

[0079] Finally, the identified boundary points are smoothed using a curve fitting algorithm, and the core diameter of the optical fiber is calculated. To ensure the accuracy of the fitting results, the least squares method is used for curve fitting. The least squares method is a commonly used mathematical optimization method that finds the optimal fitting curve by minimizing the sum of squared errors between the fitted curve and the actual data points. In this invention, this method is used to smooth the boundaries of the optical fiber, eliminating noise interference and measurement errors, ensuring the accuracy of the core diameter measurement, and controlling the fitting error within an allowable range to improve the reliability of the measurement.

[0080] By combining grayscale processing, Sobel operator, threshold segmentation and least squares curve fitting, the measurement of fiber core diameter becomes more accurate and is suitable for real-time detection in industrial production, which has significant application value.

[0081] In one possible implementation, during the parameter tuning of the adaptive PID control strategy, a test disturbance is first introduced in the early stages of the wire drawing process. This test disturbance typically involves artificially changing the wire drawing speed or heating temperature. This disturbance is used to disrupt the system's equilibrium state, thereby stimulating the system's response. This artificial disturbance helps to observe the system's response under different conditions, particularly the system's overshoot and settling time. Overshoot refers to the maximum deviation of the system from the target value during the response process, while settling time is the time required for the system to return to a steady state after the disturbance.

[0082] Based on the observed system response curve, the control system adjusts the proportional, integral, and derivative coefficients of the PID controller. The purpose of adjusting these parameters is to optimize the system's dynamic performance.

[0083] Proportional coefficient: Used for rapid response to deviations in fiber core diameter. When a deviation occurs in the fiber core diameter, the proportional controller immediately generates a corrective action to reduce the deviation.

[0084] Integral coefficient: Used to eliminate steady-state error of the system. Even if the system deviation is very small, integral control can gradually accumulate the error and eventually eliminate any persistent deviation in the steady state.

[0085] Differential coefficients: used to predict the trend of core diameter changes, especially in the early stages of system changes. Differential control can react in advance to avoid over-adjustment or lag.

[0086] By adjusting these parameters, it can be ensured that the system's overshoot is always kept within the preset upper limit and the settling time is minimized, thereby improving the efficiency and quality of the optical fiber production process.

[0087] To further improve the system's control accuracy, the control algorithm of this invention also includes a nonlinear compensation module. There is a certain coupling effect between the drawing speed and the heating temperature, which may cause the fiber core diameter to vary unexpectedly under different production conditions. The nonlinear compensation module establishes a mapping relationship between the drawing speed and the heating temperature by analyzing historical data. This mapping relationship can correct the control input in real time and adjust the PID control parameters using a lookup table method, thereby effectively compensating for errors caused by the coupling effect.

[0088] In one possible implementation, the drawing speed is a crucial parameter for controlling the fiber core diameter. During the drawing process, when a core diameter deviation occurs, measures must be taken quickly to correct it. The specific calculation steps are as follows:

[0089] First, the direction of adjusting the fiber drawing speed is determined by the sign of the core diameter deviation. When the core diameter deviation is positive, it indicates that the core diameter is too large, and the fiber drawing speed needs to be increased to make the fiber thinner; when the core diameter deviation is negative, it indicates that the core diameter is too small, and the fiber drawing speed should be decreased to make the fiber thicker.

[0090] Then, based on the absolute value and rate of change of the core diameter deviation, the initial drawing speed adjustment is calculated using a proportional-integral-derivative (PID) formula. The proportional part responds to the magnitude of the core diameter deviation, the integral part eliminates the steady-state error of the system, and the derivative part considers the trend of core diameter change and reacts in advance, thereby ensuring the timeliness and accuracy of the speed adjustment.

[0091] Because the wire drawing device has mechanical inertia, it cannot immediately respond to excessive speed changes. Therefore, the initial adjustment amount needs to be limited. This means that the adjustment amount must be limited to the maximum acceleration capability of the servo motor to prevent excessive adjustment from causing equipment overload or instability.

[0092] Heating temperature is also crucial for controlling the fiber core diameter. Temperature changes directly affect the physical properties of the fiber and the stress distribution during stretching, thus influencing the core diameter. The calculation steps for the temperature adjustment process are as follows:

[0093] First, the rate of change of the core diameter deviation is used to determine whether the heating temperature needs to be adjusted. If the core diameter changes too quickly, i.e., the rate of change exceeds the preset threshold, it means that the change in the core diameter deviation is relatively drastic, and measures need to be taken immediately to adjust the heating temperature to prevent the core diameter from deviating further from the target value.

[0094] The temperature adjustment amount is determined by consulting a pre-stored temperature-core diameter relationship table. This table, established during preheating experiments, records the variation of fiber core diameter under different heating temperatures. By consulting the table, the corresponding temperature adjustment amount can be obtained in real time and adjusted according to the needs of the actual production process.

[0095] By precisely calculating and adjusting the drawing speed and heating temperature, accurate control of the fiber core diameter is achieved. This method not only improves production efficiency but also ensures the quality stability of optical fiber products, possessing high industrial application value.

[0096] In one possible implementation, firstly, multiple standard-sized optical fiber samples are prepared. The core diameters of these samples are all certified by national metrology institutions, ensuring high accuracy and authority. The standard samples should cover the range of core diameters that may occur during optical fiber production to guarantee comprehensive calibration. By using these samples, a reliable benchmark can be established for the optical measurement system, ensuring that the system operates accurately at different core diameters.

[0097] Each standard-sized fiber optic sample is sequentially placed in the measurement area of ​​the optical measurement system, and images of the fiber are acquired using the system's imaging device. Then, image processing algorithms are used to calculate the fiber core diameter, yielding a preliminary measurement value. This step can be achieved using a high-resolution camera and a precision optical lens, ensuring that each acquired image is clear and distortion-free, thus obtaining accurate measurement results.

[0098] The core diameter value measured by the optical measurement system is compared with the known core diameter value of the standard sample to calculate the error of the measurement system. Error can manifest as system bias, linear drift, or fluctuations caused by environmental influences. By analyzing the measurement errors of samples with different core diameters, the overall error distribution of the system can be obtained, providing a basis for subsequent error compensation.

[0099] Using the aforementioned measurement error data, an error compensation model was established through linear regression. This model correlates measurement errors with environmental parameters such as temperature and humidity, reflecting the deviation patterns of the measurement system under different environmental conditions. In actual production, the system collects ambient temperature and humidity data in real time and automatically corrects the measured values ​​according to the compensation model, thereby eliminating the influence of environmental factors on core diameter measurement.

[0100] Through standard sample measurement, error analysis, and environmental compensation, high precision, high reliability, and environmental adaptability of optical fiber core diameter measurement have been achieved, providing solid technical support for precise control of optical fiber production.

[0101] In one possible implementation, the heating furnace is equipped with temperature sensors to collect temperature information inside the furnace in real time. This temperature data is transmitted to a temperature controller, which continuously monitors the temperature changes in the heating furnace based on the received real-time data to ensure that the temperature during the heating process meets predetermined requirements.

[0102] The temperature controller incorporates a fuzzy logic control algorithm, enabling it to adjust heating power based on temperature deviation (the difference between the current and target temperatures) and the rate of change of this deviation (the speed of temperature change). In this way, the temperature controller can adjust power output in real time according to the dynamic changes in temperature within the furnace, responding quickly to temperature fluctuations.

[0103] Fuzzy logic control algorithms do not rely on precise numerical calculations. Instead, they use a rule base built from experience and experimental data to judge temperature deviations and rates of change, and determine how to adjust power accordingly. For example, when the temperature deviation is large, the system increases power output, while when the temperature approaches the target value, it reduces power output to ensure that the temperature remains stable within the set range.

[0104] The rule base for fuzzy logic control was constructed experimentally, covering control strategies across different temperature ranges. During the experiments, appropriate power adjustment strategies were determined based on the actual heating requirements of different temperature ranges. These strategies were applied within different temperature deviation ranges to ensure that the temperature change of the heating furnace remained stable throughout the heating process, avoiding excessive fluctuations.

[0105] In addition to temperature sensors, an infrared thermal imager is used to monitor the surface temperature of the preform in real time during the heating process. The infrared thermal imager can accurately detect hot spots on the preform surface, indicating areas where the temperature is too high, which could lead to uneven temperature distribution or quality issues in the finished fiber optic cable. Once a hot spot is detected, the system automatically adjusts the distribution of heating power to reduce the heating intensity in the hot spot area, ensuring temperature uniformity throughout the entire heating process.

[0106] By using closed-loop control, fuzzy logic adjustment, and infrared thermal imaging monitoring of the resistance heating furnace, precise control and temperature uniformity of the heating process in optical fiber production have been successfully achieved, ensuring accurate control of the optical fiber core diameter and improving production efficiency and product quality.

[0107] In one possible implementation, the servo motor's rotational speed is adjusted via a control signal during the wire drawing process. This control signal is generated by a control algorithm that calculates the required servo motor speed based on real-time feedback data and the set wire drawing speed target. The control signal precisely indicates the target speed the servo motor needs to achieve, ensuring speed consistency throughout the wire drawing process.

[0108] The actual speed of the servo motor is fed back in real time via an encoder. The encoder continuously monitors the motor's speed and returns the actual speed data to the control system. The control system compares this actual speed with the target speed and calculates the speed deviation. The speed deviation represents the difference between the actual speed and the target speed, reflecting whether the servo motor is operating as expected. By monitoring the speed deviation, the control system can adjust the motor's operating state in a timely manner to ensure that the wire drawing speed does not deviate from the predetermined target.

[0109] Speed ​​deviation is adjusted via a proportional-integral (PI) controller. The PI controller adjusts the servo motor control signal based on the speed deviation and the cumulative amount of speed changes, thereby achieving precise speed control. The proportional control section adjusts the speed according to the current speed deviation, while the integral control section focuses on the cumulative deviation, effectively eliminating long-term deviations and ensuring the stability and accuracy of the wire drawing speed.

[0110] During the fiber drawing process, the fiber tension is crucial. To ensure fiber quality and prevent breakage or loosening during drawing, the system is equipped with a tension sensor. The tension sensor monitors the fiber tension in real time and transmits the tension data to the control system. When the sensor detects that the fiber tension exceeds a preset safe range, the system automatically adjusts the take-up speed of the take-up reel. By adjusting the take-up speed, the system ensures that the fiber tension remains within a safe range, preventing excessive tension from causing fiber breakage or insufficient tension from causing fiber loosening, thus ensuring the continuity and stability of the fiber during drawing.

[0111] By employing technologies such as servo motor control, proportional-integral regulation, and tension monitoring, precise control of the optical fiber drawing process has been achieved, which not only improves the production efficiency of optical fibers but also ensures the consistency and stability of optical fiber quality.

[0112] In one possible implementation, the optical fiber preform is fabricated using chemical vapor deposition (CVD). This method involves introducing a gaseous feedstock into a reaction chamber and depositing the gas onto a predetermined substrate under specific conditions, forming the core and cladding of the optical fiber layer by layer. By controlling the gas flow rate, deposition temperature, and deposition time during the deposition process, the structure and dimensions of the optical fiber preform can be precisely adjusted.

[0113] To ensure that the initial core diameter is close to the target value, key parameters during the deposition process need to be precisely controlled:

[0114] Gas flow rate: Gas flow rate directly affects the concentration of reactive gases, thus influencing the deposition rate and fiber quality. A mass flow controller (MFC) is used to precisely regulate the gas flow rate, ensuring a stable and uniform gas supply during the deposition process.

[0115] Deposition temperature: Deposition temperature is a crucial factor affecting the reaction rate and deposition quality. Temperatures that are too high or too low can lead to inhomogeneities in the core and cladding layers, thus impacting the optical performance of the fiber. The deposition temperature is monitored in real-time using thermocouples, and its stability within a set range is ensured to prevent adverse effects of temperature fluctuations on deposition quality.

[0116] Deposition time: The deposition time determines the thickness of the optical fiber preform. Based on the preform size and target core diameter, the required deposition time is calculated and precisely controlled to ensure that the thickness of the deposited layer meets the design requirements.

[0117] After the optical fiber preform is formed, the flatness of its end face is crucial for the subsequent fiber drawing process. To ensure that the preform end face meets the drawing requirements, grinding and polishing are necessary. Using precision grinding equipment, the end face of the preform is uniformly treated to remove irregularities, and polishing further improves its smoothness. This step ensures a flat end face, providing stable stretching conditions during fiber drawing and preventing fiber quality problems caused by uneven end faces.

[0118] By precisely controlling the deposition parameters of chemical vapor deposition and subsequent grinding and polishing processes, the quality of optical fiber preforms is effectively controlled, providing an important guarantee for achieving precise control of optical fiber core diameter.

[0119] In one possible implementation, during the wire drawing process, the data recording unit monitors and stores several key parameters in real time, including:

[0120] Core diameter measurement: The core diameter of the optical fiber is continuously measured using an optical measurement system, and the data is recorded and transmitted in real time. This is the core of ensuring precise control of the core diameter.

[0121] Fiber drawing speed: The fiber drawing speed directly affects the fiber elongation and final core diameter, so it needs to be accurately recorded and controlled.

[0122] Heating temperature: The heating temperature during the fiber drawing process has a significant impact on the physical properties and stretching quality of the optical fiber, so it needs to be monitored and recorded in real time.

[0123] Environmental parameters: Temperature and humidity also have a certain impact on the quality of optical fibers. Temperature and humidity sensors are used to collect ambient temperature and humidity data in real time, allowing for appropriate adjustments when environmental conditions change significantly.

[0124] By collecting and storing this data in real time, the system can comprehensively monitor key parameters throughout the entire wire drawing process, ensuring that each step is within the preset control range.

[0125] The anomaly handling module, based on the principles of Statistical Process Control (SPC), monitors the optical fiber production process in real time by calculating the mean and standard deviation of core diameter data. This module can automatically determine fluctuations in core diameter data.

[0126] Mean and Standard Deviation: By statistically analyzing the core diameter data, the mean and standard deviation of the core diameter during the current production process are calculated. If the fluctuation range of the data exceeds the predetermined control limits, it means that an anomaly may have occurred in the production process.

[0127] Alarm Trigger: When multiple consecutive core diameter measurements exceed the control limit, the system will immediately trigger an alarm, notifying the operator of the deviation and automatically pausing the fiber drawing process. This prevents the production of defective optical fibers and ensures that no more substandard products are produced.

[0128] After an alarm is triggered, the system will automatically execute a diagnostic procedure to check for potentially problematic equipment.

[0129] Optical Measurement System: Check whether the optical measurement equipment is working properly and whether there are problems such as lens contamination or sensor failure, to ensure the accuracy of core diameter measurement data.

[0130] Fiber drawing device: Check whether there are any faults in the motor, transmission system and tension control system of the fiber drawing machine, and check for problems such as mechanical jamming or friction that may affect the drawing speed and fiber quality.

[0131] Operating status of the heating furnace: Check whether the temperature control of the heating furnace is normal, whether there is uneven temperature or heating system malfunction, and ensure the stability of the heating temperature.

[0132] Based on the diagnostic results, the system will automatically provide maintenance suggestions, such as cleaning the equipment, replacing parts, or adjusting parameters, to help operators quickly locate and resolve problems.

[0133] By using real-time data recording, statistical process control, and automatic fault diagnosis functions, the accuracy of fiber core diameter control has been greatly improved, the production process has been optimized, the generation of defective products has been reduced, and the consistency and quality stability of fiber optic products have been ensured.

[0134] Example:

[0135] This embodiment takes the fabrication of single-mode optical fiber as an example. The application scenario is the manufacturing of communication optical fibers. The target core diameter is 9 micrometers, and the core diameter control accuracy is required to be within ±0.05 micrometers.

[0136] Step 1: Provide optical fiber preforms;

[0137] The optical fiber preform consists of a core layer and a cladding layer. The core layer is made of germanium-doped silicon dioxide, and the cladding layer is made of pure silicon dioxide. The preform is fabricated using chemical vapor deposition, and the specific process is as follows:

[0138] Deposition parameter control: Gas flow rate is precisely controlled via a mass flow controller; for example, the flow rate of the mixed gas of silicon tetrachloride and germanium tetrachloride is set to 100 standard milliliters per minute. The deposition temperature is monitored by a thermocouple and maintained at 1600 degrees Celsius. The deposition time is calculated based on the preform size; for example, for a preform with a diameter of 50 mm, the deposition time is 10 hours. These parameters ensure that the initial core diameter is close to the target value of 9 micrometers.

[0139] Preform post-processing: After deposition, the preform's end face is ground and polished to ensure a flatness of less than 0.1 micrometers to meet wire drawing requirements. Diamond grinding wheels are used for grinding, and chemical mechanical polishing is employed for polishing.

[0140] Step 2: Heat the preform to the softening temperature;

[0141] The optical fiber preform is fed into a resistance heating furnace and heated to its softening temperature. The softening temperature is determined through a preheating experiment.

[0142] Preheating experiment: Multiple optical fiber preform samples were taken and heated at different temperatures (e.g., 1950°C, 2000°C, 2050°C), and the temperature at which the samples began to deform was observed. The sample surface was monitored using an optical microscope, and the temperature was recorded when slight flow appeared on the surface. The softening temperature was finally determined to be 2000°C.

[0143] Heating Control: During the heating process, temperature sensors (such as K-type thermocouples) collect the temperature inside the furnace in real time, and the data is transmitted to the temperature controller. The temperature controller uses a fuzzy logic control algorithm.

[0144] The fuzzy logic control algorithm uses a rule base built through experiments. It includes temperature deviation (the difference between the set temperature and the actual temperature) and the rate of change of deviation as input variables, and heating power adjustment as the output variable. The input variables are divided into five fuzzy sets: "negative large," "negative small," "zero," "positive small," and "positive large." The output variables are categorized as "decrease power," "fine-tuning," and "increase power," etc. For example, when the temperature deviation is negative large and the rate of change of deviation is positive small, the output is to increase power. The rule base contains 25 rules, optimized through experimental testing of responses in different temperature ranges.

[0145] Temperature uniformity control: Infrared thermal imagers are used to monitor the temperature distribution on the surface of the preform. When hot spots (local temperatures exceeding the average temperature by 10 degrees Celsius) are detected, the power distribution of the heating furnace is automatically adjusted, for example, by independently controlling the power of different areas through multi-zone heaters.

[0146] Step 3: Drawing the fibers to form optical fibers;

[0147] The heated preform is drawn into wires by a wire-drawing device, which includes a traction wheel and a take-up wheel. The traction wheel rotates at a preset initial speed of 10 meters per minute. The wire-drawing speed is controlled by a servo motor.

[0148] Servo motor control: The servo motor receives control signals generated by the control algorithm, and the encoder provides real-time feedback on the actual rotational speed. The speed deviation (the difference between the target speed and the actual speed) is adjusted by a proportional-integral controller, with the proportional coefficient set to 0.5 and the integral coefficient set to 0.1. These coefficients are calibrated experimentally to ensure that the rotational speed is stable within ±0.1 m / min.

[0149] Tension monitoring: Fiber optic tension data is collected in real time using a tension sensor (such as a strain gauge sensor). The preset tension range is 5-15 Newtons. When the tension exceeds this range, the take-up speed of the take-up reel is automatically adjusted; for example, the take-up speed is reduced when the tension is too high to prevent fiber breakage.

[0150] Step 4: Measure the fiber core diameter in real time;

[0151] During the fiber drawing process, an optical measurement system is used to measure the fiber core diameter in real time. The optical measurement system includes an LED light source, optical lenses, and a CCD camera.

[0152] Light source selection: The wavelength of the LED light source is determined through spectral analysis. Spectral analysis process: The transmission characteristics of beams of different wavelengths (e.g., 600 nm, 650 nm, 700 nm) in the optical fiber are tested. The transmittance is measured using a spectrometer, and the 650 nm wavelength, which has the highest transmittance, is selected as the working wavelength.

[0153] Image sensor: The acquisition frequency of the CCD camera was set experimentally. Experimental procedure: The image acquisition clarity and latency were tested at different drawing speeds (5 m / min, 10 m / min, 15 m / min). By analyzing the degree of image blur and data processing time, an acquisition frequency of 100 times per second was selected to ensure real-time performance.

[0154] Optical Lens: The lens focal length is determined through a calibration procedure. Calibration Procedure: Using a standard-sized fiber optic sample (9 micrometers core diameter, certified by a national standards metrology institution), imaging tests are performed, and the focal length is adjusted until the image boundary sharpness reaches a preset threshold (e.g., the image grayscale gradient amplitude is greater than 50).

[0155] System Calibration: A calibration procedure is performed before fiber drawing. Multiple standard-sized fiber samples (core diameters of 8.5 μm, 9 μm, and 9.5 μm) are sequentially placed in the optical measurement system, images are acquired, and core diameter measurements are calculated. The measured values ​​are compared with standard values ​​to calculate the systematic error (e.g., an average error of 0.02 μm). An error compensation model is established using a linear regression method: the error compensation model expresses the systematic error as a function of ambient temperature (in degrees Celsius) and humidity (in percentage), with the model form: Error = a × Temperature + b × Humidity + c, where the coefficients a, b, and c are obtained through regression analysis, for example, a = 0.001, b = 0.005, c = -0.1. In actual measurements, the measured values ​​are automatically corrected based on real-time environmental parameters (collected by temperature and humidity sensors).

[0156] Step 5: Compare the measured value with the target value;

[0157] The image processing unit processes image data using an edge detection algorithm, extracts the fiber core boundary, calculates the core diameter measurement, and then compares it with a preset target core diameter value of 9 micrometers to calculate the core diameter deviation. The edge detection algorithm is based on grayscale gradient changes and includes the following sub-steps:

[0158] Grayscale conversion: Convert the color image to a grayscale image by using a weighted average method (e.g., red component weight 0.299, green component weight 0.587, blue component weight 0.114) to calculate the grayscale value of each pixel.

[0159] Sobel operator gradient calculation: The Sobel operator (two 3x3 convolution kernels, one for the horizontal direction and one for the vertical direction) is used to perform convolution operations on the grayscale image to calculate the gradient magnitude of each pixel. The gradient magnitude formula is: magnitude = √(G_x² + G_y²), where G_x and G_y are the gradients in the horizontal and vertical directions, respectively.

[0160] Threshold segmentation: A threshold is set based on the gradient magnitude. The threshold is determined experimentally: In multiple test images, the gradient magnitude distribution at the core boundary is statistically analyzed, and pixels with a magnitude greater than 100 are selected as boundary points.

[0161] Curve fitting: The least squares method is used to fit the curve to the boundary points, with the fitting error controlled within 0.01 micrometers. The least squares method fits a circular curve, and the objective function is to minimize the sum of squared distances from the boundary points to the fitted circle.

[0162] After calculating the core diameter measurement, compare it with the target value of 9 micrometers. The deviation value is calculated as: measured value - target value.

[0163] Step 6: Adjust the wire drawing parameters to reduce deviation;

[0164] Based on the core diameter deviation, the drawing parameters (drawing speed and heating temperature) are dynamically adjusted through a control algorithm. The control algorithm employs an adaptive proportional-integral-derivative control strategy.

[0165] Parameter Tuning: Introduce a test disturbance during the initial wire drawing stage, such as artificially increasing the wire drawing speed by 1 m / min or decreasing the heating temperature by 10 degrees Celsius, and observe the system response curve (core diameter changes over time). Record the overshoot (the ratio of maximum deviation to steady-state deviation) and the settling time (the time from the start of the disturbance to when the deviation recovers to within 5%). Adjust the proportional, integral, and derivative coefficients based on the response curve: for example, with an overshoot target of less than 10% and a settling time target of less than 5 seconds, adjust the coefficients through trial and error, ultimately setting the proportional coefficient to 0.8, the integral coefficient to 0.2, and the derivative coefficient to 0.1.

[0166] Nonlinear compensation module: Handles the coupling effect between drawing speed and heating temperature. It establishes a mapping relationship based on historical data, such as recording core diameter changes under different combinations of drawing speed and heating temperature, forming a two-dimensional lookup table. The adjustment amount is corrected in real time using the lookup table method; for example, when the drawing speed increases, the corresponding heating temperature is reduced by consulting the lookup table.

[0167] Calculation of wire drawing speed adjustment: First, determine the adjustment direction based on the sign of the core diameter deviation value. Increase the wire drawing speed for a positive deviation and decrease it for a negative deviation. Then, based on the absolute value and rate of change of the deviation, calculate the initial adjustment amount using the proportional-integral-differential formula: Adjustment amount = proportional coefficient × deviation + integral coefficient × deviation integral + differential coefficient × deviation rate of change. Finally, considering mechanical inertia constraints, limit the initial adjustment amount to ensure it does not exceed the maximum acceleration capability of the servo motor (e.g., acceleration limit of ±2 m / min²).

[0168] Heating temperature adjustment calculation: The urgency of temperature adjustment is determined based on the rate of change of core diameter deviation. When the rate of change exceeds a preset threshold (e.g., 0.1 μm / s), the heating temperature is adjusted first. The temperature adjustment amount is obtained by querying a pre-stored temperature-core diameter relationship table, which was established through preheating experiments: recording the core diameter changes at different temperatures (1980°C, 2000°C, 2020°C), for example, for every 10°C increase in temperature, the core diameter increases by 0.05 μm.

[0169] Step 7: Continuous monitoring and adjustment;

[0170] Repeat steps 4 through 6, continuously measuring, comparing, and adjusting in real time throughout the entire fiber drawing process. The data recording unit stores the core diameter measurement, fiber drawing speed, heating temperature, and environmental parameters (ambient temperature and humidity) in real time. The anomaly handling module is based on statistical process control principles.

[0171] Statistical process control: Calculate the mean and standard deviation of the core diameter data, and set the control limit to the mean ± 3 times the standard deviation. When five consecutive measurements exceed the control limit, an alarm is triggered and the wire drawing process is paused.

[0172] Diagnostic Procedure: Upon alarm activation, the system automatically executes a diagnostic procedure to check the operational status of the optical measurement system (e.g., light source brightness, lens cleanliness), the wire drawing device (e.g., servo motor status), and the heating furnace (e.g., heating element resistance). Based on the diagnostic results, maintenance measures are suggested, such as cleaning the lens or replacing the heating element.

[0173] The fiber core diameter is controlled within the range of 9 ± 0.05 micrometers, meeting the high precision requirements of single-mode communication optical fibers. This method achieves closed-loop control, improving production efficiency and product consistency.

[0174] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0175] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for precisely controlling the core diameter of optical fibers, characterized in that, The method includes the following steps: Step 1: Provide an optical fiber preform, the optical fiber preform comprising a core layer and a cladding layer, the core layer material being doped silicon dioxide and the cladding layer material being pure silicon dioxide; Step 2: Heat the optical fiber preform to the softening temperature, which is determined by a preheating experiment. The preheating experiment includes heating the optical fiber preform sample at different temperatures and observing the deformation temperature point. During the heating process, the temperature is monitored in real time by a temperature sensor and feedback control is provided. Step 3: The heated optical fiber preform is drawn into an optical fiber using a drawing device. The drawing device includes a traction wheel and a take-up wheel. The traction wheel rotates at a preset initial speed, and the drawing speed is controlled by a servo motor. Step 4: During the fiber drawing process, the fiber core diameter is measured in real time using an optical measurement system. The optical measurement system includes a light source, an optical lens, and an image sensor. The light source emits a light beam to illuminate the fiber. After the light beam is focused by the optical lens, the image sensor acquires an image of the fiber cross-section. The image sensor transmits the image data to the image processing unit. Step 5: The image processing unit processes the image data using an edge detection algorithm, extracts the fiber core boundary and calculates the core diameter measurement value, compares the core diameter measurement value with the preset target core diameter value, and calculates the core diameter deviation value; Step 6: Based on the core diameter deviation value, dynamically adjust the drawing parameters through a control algorithm. The drawing parameters include drawing speed and heating temperature. The control algorithm adopts an adaptive proportional-integral-derivative control strategy, calculates the adjustment amount of drawing speed and heating temperature according to the magnitude and trend of the core diameter deviation value, and executes the adjustment through the servo motor and the heating furnace power controller. Step 7: Repeat steps 4 to 6, continuously measuring, comparing and adjusting in real time throughout the entire wire drawing process until the wire drawing process is completed.

2. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 4, the light source of the optical measurement system is an LED light source, and the wavelength of the LED light source is determined by spectral analysis. The spectral analysis includes testing the transmission characteristics of light beams of different wavelengths in the optical fiber and selecting the wavelength with the highest transmittance as the working wavelength. The image sensor is a CCD camera, and the acquisition frequency of the CCD camera is set through experiments. The experiments include testing the clarity and delay of image acquisition at different drawing speeds, and selecting an acquisition frequency that meets the real-time requirements. The focal length of the optical lens is determined through a calibration procedure, which includes performing imaging tests using standard-sized fiber optic samples and adjusting the focal length until the image boundary sharpness reaches a preset threshold.

3. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 5, the edge detection algorithm is based on grayscale gradient changes and specifically includes the following sub-steps: First, the image is converted to grayscale, transforming the color image into a grayscale image; Then, the Sobel operator is used to calculate the gradient of the grayscale image, and boundary points are detected through convolution operations; next, a threshold segmentation method is applied, and a threshold is set according to the gradient magnitude to identify the interface between the core layer and the cladding layer. Finally, the boundary points are smoothed using a curve fitting algorithm, and the core diameter is calculated. The curve fitting algorithm uses the least squares method, and the fitting error is controlled within the allowable range.

4. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 6, the parameter tuning process of the adaptive proportional-integral-derivative control strategy includes: introducing a test disturbance in the initial wire drawing stage, wherein the test disturbance is to artificially change the wire drawing speed or heating temperature, observing the system response curve, and recording the overshoot and settling time; Adjust the proportional coefficient, integral coefficient, and derivative coefficient according to the system response curve to make the overshoot lower than the preset upper limit and the settling time the shortest possible. The proportional coefficient is used to quickly respond to core diameter deviation, the integral coefficient is used to eliminate steady-state error, and the differential coefficient is used to predict the core diameter change trend. The control algorithm also includes a nonlinear compensation module to handle the coupling effect between drawing speed and heating temperature. The nonlinear compensation module establishes a mapping relationship based on historical data and corrects the adjustment amount in real time by looking up a table.

5. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 6, the calculation process for the wire drawing speed adjustment includes: First, determine the adjustment direction based on the sign of the core diameter deviation value: increase the drawing speed for a positive deviation and decrease the drawing speed for a negative deviation. Then, based on the absolute value and rate of change of the deviation, the initial adjustment is calculated using the proportional-integral-differential formula. Finally, taking into account the mechanical inertia constraint of the wire drawing device, the initial adjustment amount is limited to ensure that the adjustment amount does not exceed the maximum acceleration capability of the servo motor. The calculation process for the heating temperature adjustment includes: determining the urgency of temperature adjustment based on the magnitude of the core diameter deviation change rate; and prioritizing the adjustment of the heating temperature when the change rate exceeds a preset threshold. The temperature adjustment amount is obtained by querying a pre-stored temperature-core diameter relationship table, which is established through preheating experiments to record the variation of core diameter at different temperatures.

6. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, Prior to step 4, a calibration step for the optical measurement system is included, which includes: Multiple standard-sized optical fiber samples were used, and the core diameter of the standard-sized optical fiber samples was certified by the national standard metrology agency. The standard-sized optical fiber samples are placed sequentially in the optical measurement system, images are acquired, and the core diameter measurement value is calculated. Compare the measured values ​​with the standard values ​​and calculate the systematic error; An error compensation model is established using linear regression, which represents the systematic error as a function of ambient temperature and humidity. In actual measurements, the measured values ​​are automatically corrected based on real-time environmental parameters.

7. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 2, the heating process employs a resistance heating furnace, and the power control of the resistance heating furnace is achieved through a closed loop, specifically including: The temperature sensor collects the temperature inside the heating furnace in real time and transmits the temperature data to the temperature controller. The temperature controller uses a fuzzy logic control algorithm to adjust the heating power based on the temperature deviation and the rate of change of the deviation. The rule base of the fuzzy logic control algorithm was constructed through experiments, including control strategies for different temperature ranges; During the heating process, the surface condition of the preform is also monitored, and hot spots are detected by infrared thermal imager. When a hot spot is detected, the heating power distribution is automatically adjusted to ensure temperature uniformity.

8. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 3, the process of controlling the wire drawing speed includes: The servo motor receives control signals, which are generated by a control algorithm. The servo motor's speed is fed back through an encoder. The encoder collects the actual speed and compares it with the target speed to generate a speed deviation. The rotational speed deviation is adjusted by a proportional-integral controller to ensure stable wire drawing speed; During the fiber drawing process, the fiber tension is also monitored. Tension data is collected in real time through a tension sensor. When the tension exceeds the preset range, the take-up speed of the take-up reel is automatically adjusted to prevent the fiber from breaking or loosening.

9. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 1, the fabrication process of the optical fiber preform includes: The core and cladding layers are formed by chemical vapor deposition, and the deposition parameters are controlled to make the initial core diameter close to the target value. The deposition parameters include gas flow rate, deposition temperature, and deposition time. The gas flow rate is precisely controlled by a mass flow controller, the deposition temperature is monitored by a thermocouple, and the deposition time is calculated based on the preform size. After the preform is formed, the end face is ground and polished to ensure that the flatness of the end face meets the requirements for wire drawing.

10. The method for precisely controlling the core diameter of an optical fiber according to claim 1, characterized in that, In step 7, the continuous monitoring process includes data logging and anomaly handling: The data recording unit stores core diameter measurements, drawing speed, heating temperature, and environmental parameters in real time. The environmental parameters include ambient temperature and humidity, which are collected by temperature and humidity sensors. The anomaly handling module is based on the statistical process control principle. It calculates the mean and standard deviation of the core diameter data. When multiple consecutive measurements exceed the control limits, an alarm is triggered and the wire drawing process is paused. After an alarm is triggered, the system automatically executes a diagnostic procedure to check the working status of the optical measurement system, wire drawing device, and heating furnace, and provides maintenance suggestions based on the diagnostic results.

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