End face positioning method and system for polarization-maintaining hollow-core optical fiber fusion splicer

Abstract

The present invention proposes a method and system for end face positioning of a polarization-maintaining hollow-core optical fiber fusion splicer, which relates to the technical field of end face positioning of optical fiber fusion splicers. The method comprises the following steps: placing an optical fiber at a working position of the fusion splicer, triggering an image acquisition system to acquire an image of the optical fiber end face; preprocessing the acquired image of the optical fiber end face; performing edge detection and edge feature extraction on the preprocessed image of the optical fiber end face; calculating the center position of the optical fiber end face based on the extracted edge features, constructing a feature matrix, and obtaining the angle between the polarization axis and the reference coordinate axis; and feeding back the center position and the angle between the polarization axis and the reference coordinate axis to a control system of the fusion splicer, so that the end faces of two optical fibers to be fused are accurately aligned.

Description

Technical Field

[0001] The invention provides an end face positioning method and system for a polarization-maintaining hollow-core optical fiber fusion splicer, and relates to the technical field of optical fiber positioning. Background Art

[0002] Fiber optic connections are typically made using fusion splicing. The positioning accuracy of the fiber endface during fusion splicing directly impacts the splice quality and optical signal transmission performance. Inaccurate fiber endface positioning can lead to increased optical signal loss and changes in polarization, impacting overall system performance.

[0003] Traditional methods for locating fiber end faces, such as mechanical alignment, have limited accuracy and are unable to meet the high-precision requirements for polarization axis alignment. Manual visual alignment methods are not only inefficient but also susceptible to human factors, making accuracy difficult to guarantee. As the precision requirements for fiber optic applications continue to increase, traditional positioning methods are becoming increasingly difficult to adapt.

[0004] With the continuous advancement of image processing technology, its application in the field of fiber fusion splicing has become possible. Image acquisition systems can quickly and accurately obtain image information of fiber end faces. Combined with advanced image processing algorithms, they can accurately analyze and extract the characteristics of fiber end faces, providing technical support for achieving high-precision fiber end face positioning. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes an end face positioning method for a polarization-maintaining hollow-core optical fiber fusion splicer, comprising the following steps:

[0006] S1. Place the optical fiber in the working position of the fusion splicer and trigger the image acquisition system to capture the image of the optical fiber end face;

[0007] S2. preprocessing the collected optical fiber end face image;

[0008] S3, performing edge detection and edge feature extraction on the preprocessed optical fiber end face image;

[0009] S4. Calculate the center position of the optical fiber end face based on the extracted edge features, construct a feature matrix, and obtain the angle between the polarization axis and the reference coordinate axis;

[0010] S5. Feedback the center position and the angle between the polarization axis and the reference coordinate axis to the control system of the fusion splicer, so that the end faces of the two optical fibers to be fused are accurately aligned.

[0011] In a preferred embodiment, in step S4, each pixel in the image is traversed, and the number of occurrences of grayscale combinations of pixel pairs that meet a fixed distance and direction relationship is counted to construct a feature matrix. The size of the matrix is , where A is the number of gray levels after quantization, and the elements in the feature matrix Indicates that the pixel with gray value I and the pixel with gray value J are at a distance d and in a direction The frequency of simultaneous occurrence of

[0012] Calculate the matrix energy E: ;Fix the distance d between pixel pairs and traverse different directions , calculate the matrix energy E, and find the direction corresponding to the maximum matrix energy E This is the angle between the polarization axis and the reference coordinate axis. In a preferred embodiment, in step S4, the center position of the optical fiber end face is determined by calculating the geometric center based on the extracted edge features. For circular edges, the center position is determined by calculating the coordinate mean of the edge pixel points; for other shapes, the minimum circumscribed circle or minimum circumscribed rectangle method is used to estimate the center position.

[0013] In a preferred embodiment, in step S3, the gradients of the optical fiber end face image in the horizontal and vertical directions are calculated based on the grayscale differences of the upper and lower and left and right adjacent points of the image pixel point, the gradient strength and direction are calculated based on the gradients in the horizontal and vertical directions, and the gradient strength of the current pixel is compared with the gradient strength of the adjacent pixels along the gradient direction. If the gradient strength of the current point is the largest, the gradient value is retained; otherwise, the gradient value of the point is set to 0.

[0014] In a preferred embodiment, a high threshold and a low threshold are set. Pixels with gradient strengths greater than the high threshold are identified as strong edge points; pixels with gradient strengths between the low and high thresholds are identified as weak edge points; pixels with gradient strengths less than the low threshold are directly discarded; strong edge points are directly considered part of the edge. For weak edge points, if they are connected to strong edge points, they are retained as part of the edge; if they are not connected to strong edge points, they are discarded.

[0015] In a preferred embodiment, the high threshold T max and low threshold T min The calculation formula is: ;in, ; Among them, h(x,y) is the grayscale value of the pixel (x,y), h(x-1,y) is the grayscale value of the pixel (x-1,y), h(x+1,y) is the grayscale value of the pixel (x+1,y), h(x,y-1) is the grayscale value of the pixel (x,y-1), h(x,y+1) is the grayscale value of the pixel (x,y+1), and the grayscale change value in the x direction is e x , the grayscale change value in the y direction is e y , the maximum grayscale change value is e(x,y).

[0016] In a preferred embodiment, in step S2, the specific steps of enhancing the contrast of the image by using the histogram equalization method are as follows:

[0017] S231, counting the frequency of occurrence of each gray level in the image to obtain a histogram of the original image;

[0018] S232, performing cumulative summation on the original histogram to obtain the cumulative distribution value of each gray level, and calculating the cumulative distribution function CDF;

[0019] S233. Map the grayscale of each pixel in the original image to a new grayscale NP according to the cumulative distribution function: ; Where L is the total number of gray levels of the image, D is the gray level of the original pixel, and CDF is the cumulative distribution function of the gray level. Indicates rounding down; S233, filling the pixels mapped to the new grayscale into the new image to obtain an image after histogram equalization.

[0020] The present invention also proposes an end face positioning system for a polarization-maintaining hollow-core optical fiber fusion splicer, which is used to implement the end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer, including: an image acquisition system, an image preprocessing system, a data processing system, a communication system, and a control system;

[0021] The image acquisition system is used to acquire optical fiber end face images;

[0022] The image preprocessing system preprocesses the collected optical fiber end face image;

[0023] The data processing system is used to perform edge detection and edge feature extraction on the preprocessed optical fiber end face image; calculate the center position of the optical fiber end face based on the extracted edge features, construct a feature matrix, and obtain the angle between the polarization axis and the reference coordinate axis;

[0024] The image storage system is used to store the collected optical fiber end face images and the pre-processed optical fiber end face images;

[0025] The communication system feeds back the center position and the angle between the polarization axis and the reference coordinate axis to the control system of the welding machine;

[0026] The control system enables the end faces of two optical fibers to be fused to be accurately aligned.

[0027] In a preferred embodiment, the image acquisition system includes an illumination light source, which adopts a side-injected coaxial illumination method. The light propagates along the optical fiber inside the cladding and core, and finally emerges from the end face to illuminate the end face.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] 1. Improve positioning accuracy: By collecting the image of the optical fiber end face through the image acquisition system and performing preprocessing, edge detection and feature extraction and other technical means, the edge features of the optical fiber end face can be accurately obtained, thereby accurately calculating the center position of the optical fiber end face. Compared with traditional positioning methods, the positioning accuracy is greatly improved, laying the foundation for subsequent high-precision optical fiber welding.

[0030] By constructing a characteristic matrix to obtain the angle between the polarization axis and the reference coordinate axis, the direction of the polarization axis can be accurately determined, so that the two optical fibers to be fused can also be accurately aligned in the direction of the polarization axis, further improving the precision of the fusion splicing and ensuring that the polarization characteristics of the optical signal are not destroyed when transmitted in the optical fiber.

[0031] 2. Enhanced stability: Based on image analysis technology, the present invention can accurately judge and process various conditions of the optical fiber end face. It is not affected by external environmental factors (such as vibration, light, etc.) and has strong anti-interference ability, thereby improving the stability of end face positioning and ensuring that the optical fiber end face positioning task can be reliably completed in different working environments.

[0032] Feedback of the center position and polarization axis angle to the control system of the fusion splicer forms a closed-loop control system that can adjust the position of the optical fiber in real time, making the positioning process more stable and effectively avoiding positioning deviations caused by external factors.

[0033] 3. Improve fusion efficiency: Accurate end face positioning can reduce the number and time of adjustments during the fusion process, improve the success rate of optical fiber fusion, thereby saving fusion time and improving work efficiency.

[0034] Since the optical fiber end face can be positioned quickly and accurately, the fusion splicer can enter the fusion splicing state more quickly, reducing the idle time of the equipment and improving the utilization rate of the equipment.

[0035] 4. Reduce operational difficulty: The present invention transforms the complex optical fiber end face positioning process into a simple image analysis and data processing process through automated image acquisition and analysis processing. The operator only needs to place the optical fiber in the working position of the fusion splicer and trigger the system to complete the positioning. There is no need for complex manual adjustment and measurement, which reduces the technical requirements for the operator and makes the operation easier.

[0036] 5. Wide scope of application: The present invention performs processing based on the image features of the optical fiber end face. For optical fibers of different types and specifications, as long as their end face images can be clearly acquired by the acquisition system, this method can be used for end face positioning. It has strong versatility and adaptability, and can meet the needs of optical fiber fusion splicing in different application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 The figure is a flow chart of the end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer of the present invention.

[0039] Figure 2 This is a schematic structural diagram of the end face positioning system module of the polarization-maintaining hollow-core optical fiber fusion splicer of the present invention.

[0040] Figure 3 It is a structural schematic diagram of the polarization-maintaining hollow-core optical fiber fusion splicer of the present invention.

[0041] Figure 4 This is the end face feature of the hollow-core fiber seen on the fiber fusion splicer. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0043] In the drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the various components in the system, the connection relationship of the various parts in the device is shown, which only clearly distinguishes the relative position relationship between the various components, and does not constitute a limitation on the signal transmission direction, connection sequence and size, dimension and shape of the components or structures. Example

[0044] like Figure 1 FIG. 1 is a flow chart of an end face positioning method of an optical fiber fusion splicer according to the present invention, wherein the end face positioning method comprises the following steps:

[0045] S1. Place the optical fiber in the working position of the fusion splicer and trigger the image acquisition system to capture the image of the optical fiber end face.

[0046] The image acquisition system uses high-resolution industrial cameras, preferably dual 2-megapixel high-resolution cameras. These cameras are mounted orthogonally (primarily for PAS alignment) at appropriate locations within the fusion splicer to capture images of the fiber end faces. To capture these images, a 90-degree reflector is used. The reflector's end face is designed at a special angle to simultaneously reflect the left and right fiber end faces onto a single camera. Using the same camera facilitates computational processing, maintains consistent image quality and magnification, and improves computational accuracy.

[0047] Preferably, the camera's parameters such as focal length and aperture are pre-adjusted according to the size of the optical fiber and the working distance to obtain the best image quality.

[0048] Before imaging the end face, a uniform, appropriately intense illumination source needs to be set up to illuminate the end face of the optical fiber. Due to limitations in the optical fiber structure, supplemental lighting cannot be applied from the front. This embodiment uses side-injected coaxial illumination, where light propagates along the optical fiber inside the cladding and core, and finally exits from the end face to illuminate the end face. The brightness of the illumination can be automatically adjusted by the software to suit the camera's configuration parameters. Appropriate lighting can enhance the contrast of the image, making the details of the optical fiber end face clearer and preventing shadows from interfering with subsequent image processing.

[0049] Preferably, the divergence angle distribution of the light source conforms to the Gaussian distribution, and the receiving angle of the optical fiber is Determined by the numerical aperture NA, n0 is the refractive index of the medium surrounding the optical fiber Assume that the light intensity coupling efficiency is , combined with the required light intensity I in the optical fiber f , calculate the required light source output intensity I through the following relationship S : After placing the optical fiber in the working position of the fusion splicer, the camera is triggered to capture the image of the optical fiber end face, with a frame rate of no less than 30 frames per second. The captured image has sufficient clarity and resolution to accurately identify the outline and internal structure of the optical fiber.

[0050] S2. Preprocess the collected optical fiber end face image.

[0051] S21, grayscale processing.

[0052] The collected color image of the optical fiber end face is converted into a grayscale image by the weighted averaging method.

[0053] Multiply the RGB channel values ​​of each pixel in the color image of the fiber end face by a weight coefficient and add them together to obtain the grayscale value Gray = 0.299R + 0.587G + 0.144B; where R, G, and B are the red, green, and blue channel values, respectively.

[0054] In fiber end-face image preprocessing, grayscale images can more clearly display key features such as the fiber's outline and the boundaries between the core and cladding. In the subsequent edge detection step, grayscale images can reduce unnecessary color information interference, making it easier for edge detection algorithms to focus on extracting shape features.

[0055] S22, filtering and denoising.

[0056] The fiber end face image can be affected by factors such as camera sensor noise and ambient light interference, resulting in salt and pepper noise or Gaussian noise. If there is noise in the fiber end face image, it may lead to inaccurate edge detection or deviation in feature extraction. Filtering and denoising is to remove this noise and improve image quality. Mean filtering can effectively remove salt and pepper noise, while Gaussian filtering has a good inhibitory effect on Gaussian noise. The present invention adopts a filtering and denoising method that combines mean filtering and Gaussian filtering to make the image smoother, providing a good foundation for subsequent precise processing.

[0057] S221, mean filtering

[0058] With each pixel in the image as the center, a fixed k×k neighborhood window (5×5 is used in this example) is taken, the average value of all pixels in the window is calculated, and the value of the center pixel is replaced by this average value.

[0059] Image I(x,y) is a grayscale image of the fiber end face, where x and y represent the pixel coordinates. To perform mean filtering on the image, a mean filter template of size k×k is used. i and j are variables used to traverse the pixel positions in the mean filter template. The filtered image J(x,y) can be calculated using the following formula: (2)

[0060] When k is an odd number, the center of the template is located at (0,0); when k is an even number, the center of the template is located at Position (in this embodiment, k=5). S222, Gaussian filter

[0061] Gaussian filtering is a weighted average filtering method based on the Gaussian function. The Gaussian function determines the weight of each pixel in the filtering calculation, with pixels closer to the center pixel receiving a greater weight. This filtering method is effective in removing Gaussian noise (a type of noise that follows a normal distribution) while also preserving image details and edges to a certain extent.

[0062] Image I(x,y) is a grayscale image of the fiber end face, where x and y represent the coordinates of the pixel points. The two-dimensional Gaussian function G(x,y) is used as a filter: (3) Among them, is the standard deviation of the Gaussian distribution, and the filter is convolved with the filtered image. The convolution process can be understood as sliding a Gaussian kernel window over the image. For each window position, the image pixel value within the window is multiplied by the corresponding Gaussian kernel weight value, and then these products are added together to obtain the result as the pixel value at the corresponding position in the output image.

[0063] The Gaussian filtered image H(x,y) is calculated using the following formula: ; When k is an odd number, the center of the template is located at (0,0); when k is an even number, the center of the template is located at Position (in this embodiment, k=5). S223. Linearly combine the results of mean filtering and Gaussian filtering. Here, the weights of both filtering results are set to 0.5. The filtered image f(x, y) can be calculated using the following formula: ; S23, Enhance contrast

[0064] Histogram equalization is used to enhance image contrast. The low contrast between the fiber endface and its surroundings can affect subsequent edge detection and feature recognition. Histogram equalization stretches the image's grayscale histogram, making the grayscale distribution more uniform and improving contrast.

[0065] S231. Calculate the original histogram: Count the frequency of each gray level in the image to obtain the histogram of the original image.

[0066] S232. Calculate the cumulative distribution function (CDF): Perform cumulative summation on the original histogram to obtain the cumulative distribution value of each gray level. The CDF represents the proportion of pixels less than or equal to a certain gray level in the image.

[0067] S233, perform grayscale mapping: Map the grayscale of each pixel in the original image to a new grayscale NP according to the cumulative distribution function. The mapping formula is:

[0068] ; Where L is the total number of gray levels of the image, D is the gray level of the original pixel, and CDF is the cumulative distribution function of the gray level. Indicates rounding down; for an 8-bit image, L = 256. S233, generating an equalized image: filling the pixels mapped to the new grayscale into the new image to obtain an image after histogram equalization.

[0069] S3. Perform edge detection and edge feature extraction on the preprocessed optical fiber end face image.

[0070] This step uses an edge detection algorithm to extract the edge of the fiber end face. The edge location is determined by calculating the gradient of the pixels in the image. The gradient magnitude and direction are first calculated, and then non-maximum suppression and dual threshold detection are used to accurately extract the edge.

[0071] The gradient of the fiber end face image in the horizontal and vertical directions is calculated based on the grayscale difference between the upper and lower and left and right adjacent pixels of the image pixel.

[0072] The gradient of the fiber end face image f(x,y) at point (x,y) is a vector with magnitude and direction. Let S x and S y Represents the gradient in the x direction and y direction respectively, and calculates the gradient intensity M(x,y) and direction of the pixel point They are: S32, non-maximum suppression

[0073] After obtaining the gradient strength and direction, a non-maximum suppression operation is performed on each pixel in the image. The gradient strength of the current pixel is compared with the gradient strength of the adjacent pixels along the gradient direction. If the gradient strength of the current point is the largest, the gradient value is retained; otherwise, the gradient value of the point is set to 0.

[0074] S33, dual threshold detection sets two thresholds, the high threshold T max and low threshold T min , the pixels whose gradient intensity is greater than the high threshold are determined as strong edge points; the pixels whose gradient intensity is between the low threshold and the high threshold are determined as weak edge points; the pixels whose gradient intensity is less than the low threshold are directly discarded and considered not to be edge points. This paper will use the adaptive threshold based on the statistical method to perform image segmentation. This method will determine the appropriate threshold based on the pixel grayscale characteristics of the image itself. The high threshold T max and low threshold T min The calculation formula is: in, ; h(x,y) is the grayscale value of the pixel (x,y). The grayscale change value e in the x direction x It is obtained by calculating the difference between the grayscale values ​​of two adjacent pixels with coordinates (x-1, y) and (x+1, y), and is used to measure the change in pixel grayscale value in the x direction.

[0075] Grayscale change value e in y direction yIt is obtained by calculating the difference between the grayscale values ​​of two adjacent pixels with coordinates (x, y-1) and (x, y+1), and is used to measure the change in pixel grayscale value in the y direction.

[0076] The maximum grayscale change value e(x,y) is taken

[0077] and

[0078] The maximum value in comprehensively reflects the intensity of grayscale changes of the pixel at the coordinate (x, y) in the horizontal and vertical directions.

[0079] Strong and weak edge points are processed and connected. Strong edge points are directly considered part of the edge. Weak edge points are retained as part of the edge if they are connected to a strong edge point; if they are not connected to a strong edge point, they are discarded. In this way, isolated weak edge points are removed and a coherent edge is obtained.

[0080] In a preferred embodiment, the shape features of the fiber end face, such as circularity and aspect ratio, can be further extracted based on edge information. The system stores multiple templates of commercially available optical fibers. These templates can represent typical shape features of fiber end faces, such as core shape templates and stress zone shape templates. The templates are then slid across the image, and regions matching the templates are found by calculating the similarity between the templates and image subregions (e.g., using methods such as normalized cross-correlation coefficients).

[0081] S4. Calculate the center position of the optical fiber end face and the angle between the polarization axis and the reference coordinate axis based on the extracted edge features.

[0082] S41. Calculate the center position of the optical fiber end face according to the extracted edge features.

[0083] Based on the extracted edge features, the center position of the fiber end face is determined by calculating the geometric center. For circular edges, the center position is determined by calculating the coordinate mean of the edge pixel points; for other shapes, the minimum circumscribed circle or minimum circumscribed rectangle method is used to estimate the center position.

[0084] S42. Extract texture features of the optical fiber end face image and determine the angle between the polarization axis and the reference coordinate axis.

[0085] After completing the center positioning, preparations are made to determine the direction of the polarization axis based on the characteristic that the optical fiber has a specific polarization direction.

[0086] Optical fibers have a specific polarization direction. By analyzing the distribution of the endface texture in different directions, the angle between the polarization axis and the reference coordinate axis is calculated. Preferably, the direction with the largest characteristic value in the texture statistics is used as the polarization axis direction, and the angle between the polarization axis and the reference coordinate axis is then calculated.

[0087] The texture features of optical fiber end face image are extracted using the feature matrix algorithm.

[0088] There are certain texture differences between different structures inside the optical fiber end face. Therefore, in the optical fiber end face image, different areas (such as the core, cladding, stress area, etc.) have different texture characteristics.

[0089] The feature matrix algorithm is used to extract the texture features of the optical fiber end face image. It constructs a matrix by calculating the frequency of pixel pairs with different features in the image at specific directions and distances.

[0090] A variety of texture feature parameters can be extracted from the feature matrix, such as contrast, correlation, energy, and entropy. By analyzing the feature matrix feature parameters, the microscopic structural uniformity of the fiber end face can be determined, which is very important for evaluating the quality and performance of the fiber.

[0091] First determine the parameters required to calculate the feature matrix, including the distance d and direction of the pixel pair . To fully capture texture information in different directions.

[0092] Traverse each pixel in the image, count the number of grayscale combinations of pixel pairs that meet the fixed distance and direction relationship, and construct the feature matrix. The size of the matrix is

[0093] , where A is the number of quantized features, which is 16 in this embodiment. The elements in the feature matrix

[0094] Indicates that the pixel point with feature I and the pixel point with feature J are at a distance d and in a direction

[0095] Finally, the feature matrix is ​​normalized so that the sum of the matrix elements is 1. The matrix energy is calculated, which is the sum of the squares of the elements in the feature matrix, reflecting the uniformity of the image feature distribution. The calculation formula of the matrix energy E is: ;Fix the distance d between pixel pairs and traverse different directions , calculate the matrix energy E, the distance d of the pixel pair in this embodiment is 1, the direction Select 0°, 45°, 90° and 135° and find the direction where the matrix energy E is maximum. , which is the direction of the polarization axis. Assume that the reference coordinate axis is the positive direction of the x-axis. Based on the polarization axis direction , the angle between the polarization axis and the reference coordinate axis is S5. Feedback the center position and the angle between the polarization axis and the reference coordinate axis to the control system of the fusion splicer so that the end faces of the two optical fibers to be fused are accurately aligned. The data is sent to the control system of the fusion splicer. The control system receives the angular position of the optical fiber end face and the angle between the polarization axis and the reference coordinate axis as feedback, and compares the angular position of the optical fiber end face and the polarization axis with the reference coordinate axis with the preset ideal alignment position and angle to obtain an error signal. Based on the error signal, the control system sends a control instruction to the motor to drive the motor to adjust the position and angle of the optical fiber. The above comparison and adjustment process is repeated until the error signal approaches zero, that is, the optical fiber reaches an accurate alignment state. The control tasks are divided into different levels: decision-making layer, control layer and execution layer. The decision-making layer formulates adjustment strategies and goals based on the received optical fiber position and angle information; the control layer calculates the specific control parameters of the motor, such as the motor speed, direction and number of movement steps, according to the instructions of the decision-making layer; the execution layer is the actual movement of the motor according to the parameters of the control layer, driving the optical fiber to adjust the position and angle.

[0096] In a preferred embodiment, images are continuously captured and processed during the splicing process, monitoring the position of the fiber end face in real time. If the fiber end face shifts due to mechanical vibration, fiber movement, or other factors, the control system is promptly adjusted to realign the fiber end face, ensuring splice quality. Example

[0097] The present invention also proposes an end face positioning system for an optical fiber fusion splicer, such as Figure 2 As shown in the figure, it is a schematic diagram of the module structure of the end face positioning system of the optical fiber fusion splicer. Figure 3 The figure shows the structure of the optical fiber fusion splicer. The end face positioning system includes: image acquisition system, image preprocessing system, data processing system, communication system and control system.

[0098] The image acquisition system is mainly used to capture images of the optical fiber end face, including high-resolution industrial cameras, lighting sources and other accessories.

[0099] High-resolution industrial camera: used to capture images of the fiber end face. This embodiment uses a 2-megapixel high-resolution dual camera. The dual cameras are installed in an orthogonal manner (mainly for PAS alignment) at appropriate positions on the fusion splicer to capture images of the fiber side.

[0100] Illumination source: End-face imaging requires illuminating the end face of the optical fiber. Due to structural limitations, supplemental lighting cannot be provided from the front. A uniform, appropriately intense illumination source is provided to illuminate the optical fiber end face from the side or front. This embodiment uses side-injected coaxial illumination. The light propagates along the optical fiber through the cladding and core, and finally exits from the end face, illuminating the end face. The brightness of the illumination can be automatically adjusted by the software to suit the camera configuration parameters. Appropriate lighting can enhance the contrast of the image, making the details of the optical fiber end face clearer and preventing shadows from interfering with subsequent image processing.

[0101] In a preferred embodiment, injection-type fill lights are installed at the front and rear. Preferably, two sets of injection-type fill lights are provided. In end-face imaging mode, the corresponding fill light can be activated according to the fiber type and fusion procedure. Using side-injection fill lights, the fiber end face can be illuminated. The software calculates the end face brightness and automatically adjusts the fill light power to achieve the optimal effect. The purpose of using two sets of front and rear lights is to accommodate a wider range of fiber types. The brightness accuracy can reach 0.4%.

[0102] Other accessories: Assist with image acquisition, such as reflectors and elevators. High-precision reflectors are designed for simultaneous imaging of both left and right fiber end faces, ensuring consistent end-face images. The reflectors' position coincides with the discharge center. To avoid affecting discharge splicing, an elevator mechanism is required to precisely position the reflectors and adapt to the imaging requirements of different modes.

[0103] With the help of a reflector, the camera of the fusion splicer can view the features of the optical fiber end face. The internal structure of special optical fibers such as optical fibers, photonic fibers, and hollow-core fibers is complex, and the traditional side imaging alignment method cannot guarantee accurate core alignment. The end face positioning method, however, can extract features with high accuracy, good consistency, and accurate calculation results.

[0104] In a preferred embodiment, dual end-face reflectors are equipped with lift control. End-face imaging requires high-precision reflectors. To simultaneously inspect the end faces of the left and right optical fibers, the reflectors must be designed at specific angles to achieve simultaneous imaging and ensure consistent end-face images. The reflectors' positions coincide with the discharge center. To avoid affecting discharge welding, a lift mechanism is required to precisely position the reflectors and adapt to the imaging requirements of different modes.

[0105] The image preprocessing system is used to preprocess the collected optical fiber end face images.

[0106] The data processing system is used to perform edge detection and edge feature extraction on the preprocessed optical fiber end face image; calculate the center position of the optical fiber end face based on the extracted edge features, construct a feature matrix, and obtain the angle between the polarization axis and the reference coordinate axis.

[0107] The data processing system includes an image feature extraction module and an end face positioning module; the image feature extraction module is responsible for edge detection and edge feature extraction of the preprocessed optical fiber end face image; the end face positioning module is responsible for calculating the center position of the optical fiber end face based on the extracted edge features, constructing a feature matrix, and obtaining the angle between the polarization axis and the reference coordinate axis.

[0108] The communication system feeds back the center position and the angle between the polarization axis and the reference coordinate axis to the control system of the fusion splicer; the control system accurately aligns the end faces of the two optical fibers to be fused through the left and right propulsion systems.

[0109] The image storage system stores the optical fiber end face image information collected during use, and can also store typical optical fiber end face image templates.

[0110] In a preferred embodiment, the end face positioning system has a built-in Bluetooth module that allows communication with a mobile phone. The device connects to smart devices such as mobile phones and tablets via Bluetooth. The mobile phone can control the device through an app, access recorded data, images, and other information, and upgrade the device firmware.

[0111] In a preferred embodiment, the end face positioning system has an AI adaptive welding function. As the number of welding times increases, the discharge capacity of the electrode rod will gradually deteriorate. The software system will automatically correct the discharge intensity according to the changes in the collected image. The end face positioning system has built-in temperature, humidity, and atmospheric pressure sensors, which can automatically correct the discharge parameters according to different conditions, such as current intensity, welding time, etc., to adapt to changes in external environmental conditions, achieve consistent and stable welding results, and ensure the stability of the discharge power. Example

[0112] The end face positioning system of the present invention can be used to fuse polarization-maintaining optical fibers of various types, such as panda optical fibers, bow tie optical fibers, and elliptical optical fibers.

[0113] Polarization-maintaining optical fiber has a fast axis and a slow axis. During fusion splicing and alignment, the fast axis and the slow axis must be precisely aligned to ensure the maximum extinction ratio.

[0114] When optical fiber is fused, the extinction ratio is related to the alignment angle between the fast axis and the slow axis. The calculation formula is as follows: ; Where ER is the extinction ratio, P max is the polarization component power along the original axial direction (aligned with the fast axis or slow axis), P min is the power of the polarization component in the vertical direction.

[0115] If the alignment angle between the fast axis and the slow axis is considered The impact on the extinction ratio, under ideal conditions and ignoring other factors such as loss, assuming that the incident light intensity is I0, the polarized light power along the fast axis or slow axis is: , the vertical polarization power is

[0116] , then the extinction ratio formula is

[0117] ER=log20(cot The rotating mechanism aligns the fast and slow axis ends with an accuracy of 0.1 degrees. After the welding is completed, the maximum extinction ratio can reach 36.8dB. Example 4

[0118] The end face positioning system of the present invention can be used to splice hollow core optical fibers. Hollow core optical fibers have 5 or 6 sub-cores and transmit through anti-resonance. Such optical fibers cannot be aligned through PAS and can only be aligned and spliced ​​after calculating the angle through the end face method. Figure 4 The figure shows the end face features of the hollow-core fiber seen on the fiber fusion splicer.

[0119] The side imaging rotates 360 degrees to find the center positions of the five capillaries; the end-face imaging identifies the characteristics of the five capillaries, including: the diameter and deformation of the capillaries; the alignment angle is found through positioning calculation, and the control system gives instructions to rotate the mechanism and the optical fiber left and right until the characteristics of the five capillaries are completely aligned. Example

[0120] The end face positioning system of the present invention can fuse multi-core optical fibers. The multi-core optical fibers can be accurately aligned through end face imaging alignment. At the same time, the reference points of the multi-core optical fibers are found according to the end face images, so that the optical fiber sub-cores are aligned in sequence without affecting the existing optical services.

[0121] It should be noted that the evaluation of the hollow-core fiber fusion splicing results in Example 4 and the multi-core fiber fusion splicing results in Example 5 is based on loss, not extinction ratio. In actual projects, fiber fusion splicing loss has a specified control value range. During the evaluation, the estimated loss value is compared with the value specified in the standard. If it is within the specified range, the fusion splicing result is qualified. If it is outside the range, the cause must be analyzed and the fusion splicing must be re-spliced.

[0122] In one embodiment, a computer device is further provided, including a memory and a processor. The memory stores a computer program, and the processor implements the steps in the above method embodiments when executing the computer program.

[0123] In one embodiment, a computer-readable storage medium is provided, storing a computer program, which implements the steps in the above-mentioned method embodiments when executed by a processor.

[0124] In one embodiment, a computer program product or computer program is provided, the computer program product or computer program including computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the computer device to perform the steps of each of the above-described method embodiments.

[0125] Those skilled in the art will understand that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, database or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. The database involved in the embodiments provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited to this. The processor involved in the embodiments provided in this application may be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, etc., but is not limited to this.

[0126] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for end face positioning of a polarization-maintaining hollow-core optical fiber fusion splicer, characterized in that: The steps include: S1. Place the optical fiber in the working position of the fusion splicer and trigger the image acquisition system to capture the image of the optical fiber end face; S2. preprocessing the collected optical fiber end face image; S3, performing edge detection and edge feature extraction on the preprocessed optical fiber end face image; S4. Calculate the center position of the fiber end face based on the extracted edge features, construct a feature matrix, and obtain the angle between the polarization axis and the reference coordinate axis; traverse each pixel in the fiber end face image, count the number of grayscale combinations of pixel pairs that meet the fixed distance and direction relationship, and construct a feature matrix. The size of the feature matrix is , where A is the number of gray levels after quantization, and the elements in the feature matrix Indicates that the pixel with gray value I and the pixel with gray value J are at a distance d and in a direction The frequency of simultaneous occurrence of Calculate the matrix energy E: ； Fixed distance d between pixel pairs, traversing different directions , calculate the matrix energy E, and find the direction corresponding to the maximum matrix energy E That is, the angle between the polarization axis and the reference coordinate axis; S5. Feedback the center position and the angle between the polarization axis and the reference coordinate axis to the control system of the fusion splicer. The control system receives the angle information between the center position of the optical fiber end face and the polarization axis and the reference coordinate axis as feedback, compares the angle information between the center position of the optical fiber end face and the polarization axis and the reference coordinate axis with the preset ideal alignment position and angle, and obtains an error signal. According to the error signal, the control system sends a control instruction to the motor to drive the motor to adjust the position and angle of the optical fiber until the error signal approaches zero, thereby controlling the end faces of the two optical fibers to be fused to be accurately aligned.

2. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 1, characterized in that: In step S4, the center position of the optical fiber end face is determined by calculating the geometric center based on the extracted edge features. For circular edges, the center position is determined by calculating the coordinate mean of the edge pixel points; for other shapes, the minimum circumscribed circle or minimum circumscribed rectangle is used to estimate the center position.

3. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 1, characterized in that: In step S3, the gradients of the optical fiber end face image in the horizontal and vertical directions are calculated based on the grayscale differences of the upper and lower and left and right adjacent pixels of the image pixel point. The gradient strength and direction are calculated based on the gradients in the horizontal and vertical directions. The gradient strength of the current pixel point is compared with the gradient strength of the adjacent pixel points along the gradient direction. If the gradient strength of the current pixel point is the largest, the gradient value is retained; otherwise, the gradient value of the pixel point is set to 0.

4. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 3, characterized in that: Set a high threshold and a low threshold, and determine the pixel points with gradient strength greater than the high threshold as strong edge points; determine the pixel points with gradient strength between the low threshold and the high threshold as weak edge points; directly discard the pixel points with gradient strength less than the low threshold; strong edge points are part of the edge, for weak edge points, if they are connected to strong edge points, they are retained as part of the edge; if weak edge points are not connected to strong edge points, they are discarded.

5. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 4, characterized in that: High threshold T max and low threshold T min The calculation formula is: ； in, ； Among them, h(x,y) is the grayscale value of the pixel (x,y), h(x-1,y) is the grayscale value of the pixel (x-1,y), h(x+1,y) is the grayscale value of the pixel (x+1,y), h(x,y-1) is the grayscale value of the pixel (x,y-1), h(x,y+1) is the grayscale value of the pixel (x,y+1), and the grayscale change value in the x direction is e x , the grayscale change value in the y direction is e y , the maximum grayscale change value is e(x,y).

6. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 1, characterized in that: In step S2, the contrast of the image is enhanced by using a histogram equalization method, and the specific steps are as follows: S231, counting the frequency of occurrence of each gray level in the image to obtain a histogram of the original image; S232, performing cumulative summation on the histogram of the original image to obtain the cumulative distribution value of each gray level, and calculating the cumulative distribution function CDF; S233. Map the grayscale of each pixel in the original image to a new grayscale NP according to the cumulative distribution function: ； Where L is the total number of gray levels of the image, D is the gray level of the original pixel, and CDF is the cumulative distribution function of the gray level. Indicates rounding down; S233: Fill the pixels mapped to the new grayscale into the new image to obtain a histogram-equalized image.

7. An end face positioning system for a polarization-maintaining hollow-core optical fiber fusion splicer, used to implement the end face positioning method for a polarization-maintaining hollow-core optical fiber fusion splicer according to any one of claims 1 to 6, characterized in that: include: Image acquisition system, image preprocessing system, image storage system, data processing system, communication system and control system; The image acquisition system is used to acquire optical fiber end face images; The image preprocessing system is used to preprocess the collected optical fiber end face image; The data processing system is used to perform edge detection and edge feature extraction on the preprocessed optical fiber end face image; calculate the center position of the optical fiber end face based on the extracted edge features, construct a feature matrix, and obtain the angle between the polarization axis and the reference coordinate axis; The image storage system is used to store the collected optical fiber end face images and the pre-processed optical fiber end face images; The communication system feeds back the center position and the angle between the polarization axis and the reference coordinate axis to the control system of the welding machine; The control system controls the accurate alignment of the end faces of two optical fibers to be spliced.

8. The end face positioning system of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 7, characterized in that: The image acquisition system includes an illumination light source, which adopts a side-injected coaxial illumination method. The light propagates along the optical fiber in the cladding and the core, and finally emerges from the end face to illuminate the end face.

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