End face positioning method and system of polarization-maintaining hollow fiber fusion splicer

Abstract

The invention provides an end face positioning method and system of a polarization-maintaining hollow-core fiber fusion splicer, and relates to the technical field of end face positioning of fiber fusion splicers. A fiber is placed at a working position of the fusion splicer, and an image acquisition system is triggered to acquire a fiber end face image; preprocessing the acquired optical fiber end face image; performing edge detection and edge feature extraction on the preprocessed optical fiber end face image; calculating the center position of the optical fiber end face according to the extracted edge features, constructing a feature matrix, and obtaining an angle between a polarization axis and a reference coordinate axis; and feeding the central position and the angle between the polarization axis and the reference coordinate axis back to a control system of the welding machine, so that the end faces of the two optical fibers to be welded are accurately aligned.

Description

Technical Field

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

[0002] Optical fiber connections are usually made using fusion splicing technology, and the positioning accuracy of the fiber end face during fusion splicing directly affects the fusion quality and optical signal transmission performance. If the fiber end face is not positioned accurately, it will lead to increased optical signal loss and changes in polarization state, which will in turn affect the performance of the entire system.

[0003] Traditional fiber end face positioning methods, such as mechanical alignment methods, have limited accuracy and are difficult to meet the high-precision requirements of optical fiber for polarization axis alignment; manual visual alignment methods are not only inefficient, but also easily affected by human factors, and accuracy is difficult to guarantee. As the accuracy requirements for optical fiber application scenarios continue to increase, traditional positioning methods are gradually unable to meet the needs.

[0004] With the continuous advancement of image processing technology, its application in the field of fiber fusion becomes possible. The image acquisition system can quickly and accurately obtain the image information of the fiber end face. Combined with advanced image processing algorithms, it can accurately analyze and extract the features of the fiber end face, 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 of a polarization-maintaining hollow-core optical fiber fusion splicer, comprising the following steps: S1, placing the optical fiber at the working position of the fusion splicer, triggering the image acquisition system to acquire the optical fiber end face image; 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, calculating the center position of the optical fiber end face according to the extracted edge features, constructing a feature matrix, and obtaining 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, so that the end faces of the two optical fibers to be fused are accurately aligned.

[0006] In a preferred embodiment, in step S4, each pixel in the image is traversed, the number of gray level combinations of pixel pairs that satisfy the fixed distance and direction relationship is counted, and a feature matrix is ​​constructed. The size of the matrix is , where A is the number of gray levels after quantization, and the elements in the feature matrix It means that the pixel with gray value I and the pixel with gray value J are at a distance d and in the direction The frequency of co-occurrence of 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 That 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 according to 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.

[0007] In a preferred embodiment, in step S3, the gradient of the optical 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 points of the image pixel point, the gradient strength and direction are calculated based on the gradient 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.

[0008] In a preferred embodiment, a high threshold and a low threshold are set, and pixels with a gradient strength greater than the high threshold are determined as strong edge points; pixels with a gradient strength between the low threshold and the high threshold are determined as weak edge points; pixels with a gradient strength less than the low threshold are directly discarded; strong edge points are directly considered as 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.

[0009] 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).

[0010] In a preferred embodiment, in step S2, the specific steps of enhancing the contrast of the image by the histogram equalization method 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 original histogram to obtain the cumulative distribution value of each gray level, and calculating the cumulative distribution function CDF; S233, according to the cumulative distribution function, the gray level of each pixel in the original image is mapped to a new gray level NP: ; 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 gray level into the new image to obtain the image after histogram equalization.

[0011] The present invention also proposes an end face positioning system of 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; The image acquisition system is used to acquire the optical fiber end face image; The image preprocessing system preprocesses 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 according to 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 enables the end faces of two optical fibers to be fused to be accurately aligned.

[0012] In a preferred embodiment, the image acquisition system includes an illumination light source, which adopts a side-injected coaxial illumination method, and the light propagates along the optical fiber inside the cladding and the core, and finally is emitted from the end face to illuminate the end face.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects: 1. Improve positioning accuracy: The image of the optical fiber end face is collected by the image acquisition system, and technical means such as preprocessing, edge detection and feature extraction are performed to accurately obtain the edge features of the optical fiber end face, 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.

[0014] 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 accuracy of the fusion and ensuring that the polarization characteristics of the optical signal are not destroyed when transmitted in the optical fiber.

[0015] 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.

[0016] The center position and polarization axis angle are fed back to the control system of the fusion splicer, forming 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.

[0017] 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.

[0018] 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.

[0019] 4. Reduce the difficulty of operation: The present invention converts the complex 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 requirements on the operator's technical level and makes the operation easier.

[0020] 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

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0022] Figure 1 The present invention is a flow chart of the end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer.

[0023] Figure 2 The diagram 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.

[0024] Figure 3 It is a schematic structural diagram of the polarization-maintaining hollow-core optical fiber fusion splicer of the present invention.

[0025] Figure 4 This is the end face feature of the hollow core fiber seen on the fiber fusion splicer. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] 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 cannot constitute a limitation on the signal transmission direction, connection sequence and size, dimensions and shape of the components or structures. Example

[0028] like Figure 1 FIG. 1 is a flow chart of an end face positioning method of an optical fiber fusion splicer of the present invention, and the end face positioning method comprises the following steps: S1. Place the optical fiber at the working position of the fusion splicer and trigger the image acquisition system to acquire the optical fiber end face image.

[0029] The image acquisition system uses a high-resolution industrial camera, preferably a 2-megapixel high-resolution dual camera. The dual cameras are installed in an orthogonal manner (mainly for PAS alignment) at the appropriate position of the fusion splicer to collect the fiber end face image. In order to collect the fiber end face image, a 90-degree reflector is used. The reflector end face is designed at a special angle, which can reflect the left and right fiber end faces to one camera at the same time. Using the same camera facilitates calculation and processing, and the imaging quality and magnification can be kept consistent, which improves the accuracy of the calculation.

[0030] Preferably, the focal length, aperture and other parameters of the camera are pre-adjusted according to the size of the optical fiber and the working distance to obtain the best image quality.

[0031] Before end-face imaging, a uniform and appropriate intensity illumination light source needs to be set to illuminate the end face of the optical fiber. Due to the limitation of the optical fiber structure, it is not possible to provide supplementary light from the front. This embodiment adopts the side-injected light 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. The brightness of the illumination can be automatically adjusted by the software to adapt to the configuration parameters of the camera. Appropriate lighting can enhance the contrast of the image, make the details of the optical fiber end face clearer, and avoid the interference of shadows on subsequent image processing.

[0032] Preferably, the divergence angle distribution of the light source conforms to the Gaussian distribution, and the receiving angle of the optical fiber 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, trigger the camera to capture the image of the optical fiber end face, and the acquisition frame rate is not less than 30 frames per second. The acquired image has high enough clarity and resolution to accurately identify the outline and internal structure of the optical fiber.

[0033] S2. Preprocessing the collected optical fiber end face image.

[0034] S21: Grayscale processing.

[0035] The collected color image of the optical fiber end face is converted into a grayscale image by weighted averaging method.

[0036] 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 gray value Gray. Gray=0.299R+0587G+0.144B; where R, G, and B are the red, green, and blue channel values, respectively.

[0037] In the preprocessing of the fiber end face image, the grayscale image can more clearly show the key features such as the fiber outline, the boundary between the core and the cladding. In the subsequent edge detection step, the grayscale image can reduce unnecessary color information interference, making it easier for the edge detection algorithm to focus on the extraction of shape features.

[0038] S22, filtering and denoising.

[0039] The fiber end face image will be affected by factors such as camera sensor noise and ambient light interference, generating salt and pepper noise or Gaussian noise. In the fiber end face image, if there is noise, it may cause inaccurate edge detection or deviation in feature extraction. Filtering denoising is to remove these noises and improve the quality of the image. 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 denoising method combining mean filtering and Gaussian filtering, which can make the image smoother and provide a good foundation for subsequent precise processing.

[0040] S221, mean filtering With each pixel in the image as the center, take a neighborhood window of fixed size k×k (5×5 in this embodiment), calculate the average value of all pixels in the window, and use this average value to replace the value of the central pixel.

[0041] Image I(x,y) is a grayscale image of the fiber end face, where x and y represent the coordinates of the pixels. To perform mean filtering on the image, use a mean filter template of size k×k. 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 by the following formula:

[0042] (2) 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 filtering 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, and the closer the pixel is to the center pixel, the greater the weight. This filtering method is effective in removing Gaussian noise (a type of noise that conforms to the normal distribution), while also preserving the details and edges of the image to a certain extent.

[0043] 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 on the image. For each window position, the image pixel value in 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 of the corresponding position in the output image.

[0044] Then the Gaussian filtered image H(x,y) is calculated by 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, where the weights of the two filtering results are both set to 0.5. Then the filtered image f(x,y) can be calculated by the following formula: ; S23, Enhance contrast The contrast of the image is enhanced by the histogram equalization method. Since the contrast between the fiber end face and the surrounding environment is low, it will affect the subsequent edge detection and feature recognition. Histogram equalization can stretch the grayscale histogram of the image to make the grayscale distribution of the image more uniform, thereby improving the contrast.

[0045] S231, calculating the original histogram: counting the frequency of occurrence of each gray level in the image to obtain the histogram of the original image.

[0046] 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 cumulative distribution function represents the proportion of pixels less than or equal to a certain gray level in the image.

[0047] S233, gray level mapping: according to the cumulative distribution function, the gray level of each pixel in the original image is mapped to a new gray level NP. The mapping formula is: ; 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 gray level into the new image to obtain an image after histogram equalization.

[0048] S3. Perform edge detection and edge feature extraction on the preprocessed optical fiber end face image.

[0049] This step uses edge detection algorithm to extract the edge of the fiber end face. The edge position is determined by calculating the gradient of the pixel points in the image. First, the gradient amplitude and direction are calculated, and finally the accurate edge is extracted through non-maximum suppression and double threshold detection.

[0050] 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 points of the image pixel.

[0051] 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 yRepresents the gradient in the x direction and y direction respectively, and calculates the gradient strength M(x,y) and direction of the pixel point They are: S32, non-maximum suppression 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.

[0052] S33, dual threshold detection sets two thresholds, the high threshold T max and low threshold T min , the pixels with gradient strength greater than the high threshold are determined as strong edge points; the pixels with gradient strength between the low threshold and the high threshold are determined as weak edge points; the pixels with gradient strength less than the low threshold are directly discarded and considered not to be edge points. This paper will use an adaptive threshold based on statistical methods 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 in the x direction is e 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 the pixel grayscale value in the x direction.

[0053] Grayscale change value e in y direction y It 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 the pixel grayscale value in the y direction.

[0054] The maximum grayscale change value e(x,y) is and 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. S34, edge connection The strong edge points and weak edge points are processed and connected. The strong edge points are directly considered as part of the edge. For the weak edge points, if they are connected to the strong edge points, they are retained as part of the edge; if the weak edge points are not connected to the strong edge points, they are discarded. In this way, the isolated weak edge points are removed and the coherent edges are obtained.

[0055] In a preferred embodiment, the shape features of the fiber end face can be further extracted based on the edge information: circularity, aspect ratio, etc. Multiple templates of commercially available optical fibers are stored in the system. These templates can be typical shape features in the fiber end face, such as the shape template of the fiber core, the shape template of the stress area, etc. The template is then slid in the image, and the area matching the template is found by calculating the similarity between the template and the image sub-area (such as using the normalized correlation coefficient method).

[0056] 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.

[0057] S41. Calculate the center position of the optical fiber end face according to the extracted edge features.

[0058] 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.

[0059] S42, extracting texture features of the optical fiber end face image, and determining the angle between the polarization axis and the reference coordinate axis.

[0060] 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.

[0061] The optical fiber has a specific polarization direction, and the angle between the polarization axis and the reference coordinate axis is calculated by analyzing the distribution of the end face texture in different directions. Preferably, the direction with the largest feature value in the texture statistical information is used as the polarization axis direction, and then the angle with the reference coordinate axis is calculated.

[0062] The feature matrix algorithm is used to extract the texture features of the optical fiber end face image.

[0063] 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.

[0064] The feature matrix algorithm is used to extract the texture features of the 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.

[0065] A variety of texture feature parameters, such as contrast, correlation, energy and entropy, can be extracted from the feature matrix. 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.

[0066] 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.

[0067] Traverse each pixel in the image, count the number of gray level combinations of pixel pairs that meet the fixed distance and direction relationship, and construct the feature matrix. The size of the matrix is , where A is the number of quantized features, which is 16 in this embodiment. The elements in the feature matrix Indicates that the pixel with feature I and the pixel with feature J are at a distance d and in a direction Finally, the feature matrix is ​​normalized so that the sum of the matrix elements is 1. The matrix energy, that is, the sum of the squares of the elements in the feature matrix, reflects 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° to 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. Sent to the control system of the fusion splicer. The control system receives the angle information between the center position of the fiber end face and the polarization axis and the reference coordinate axis as feedback, and compares the angle information between the center position of the fiber end face and the polarization axis and the reference coordinate axis with the preset ideal alignment position and angle to obtain 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. Repeat the above comparison and adjustment process 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 according to the instructions of the decision-making layer, such as the motor speed, direction and number of movement steps; the execution layer is the motor that actually moves according to the parameters of the control layer to drive the optical fiber to adjust the position and angle.

[0068] In a preferred embodiment, during the fusion process, images are continuously collected and processed to monitor the position change of the fiber end face in real time. If the position of the fiber end face is offset due to mechanical vibration, fiber movement, etc., the control system is adjusted in time to realign the fiber end face to ensure the fusion quality. Example

[0069] The present invention also proposes an end face positioning system for an optical fiber fusion splicer, such as Figure 2 As shown in FIG. 1 , it is a schematic diagram of the structure module of the end face positioning system of the optical fiber fusion splicer. Figure 3 As shown, it is a structural schematic diagram of a fiber fusion splicer. The end face positioning system includes: an image acquisition system, an image preprocessing system, a data processing system, a communication system and a control system.

[0070] The image acquisition system is mainly used to collect optical fiber end face images, including high-resolution industrial cameras, lighting sources and other accessories.

[0071] High-resolution industrial camera: used to capture the end face image of the optical fiber. This embodiment uses a 2-megapixel high-resolution dual camera, which is installed in an orthogonal manner (mainly for PAS alignment) at the appropriate position of the fusion splicer to capture the side image of the optical fiber.

[0072] Light source: End-face imaging requires illuminating the end face of the optical fiber. Due to structural limitations, it is not possible to provide supplementary light from the front. Provide a uniform and appropriately intense light source to illuminate the end face of the optical fiber from the side or front. This embodiment uses side-injected light coaxial illumination. The 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 adapt to the configuration parameters of the camera. Appropriate lighting can enhance the contrast of the image, make the details of the optical fiber end face clearer, and avoid interference of shadows on subsequent image processing.

[0073] In a preferred embodiment, injection-type fill-in lights are provided at the front and rear. Preferably, two groups of injection-type fill-in lights are provided. In the end-face imaging mode, the corresponding fill-in lights can be turned on according to different fiber types and fusion procedures. By adopting the side injection-type fill-in light, the fiber end face can be illuminated, and the software calculates the end face brightness and automatically adjusts the fill-in light power to achieve the best effect. The purpose of using two groups at the front and rear is to adapt to a wider range of various optical fibers. The brightness accuracy can be as high as 0.4%.

[0074] Other accessories: used to assist image acquisition, such as reflectors, elevators, etc. Add a high-precision reflector. In order to simultaneously detect the end faces of the left and right optical fibers, the reflector needs to be designed at a special angle to simultaneously image and ensure the consistency of the end face image. The position of the reflector coincides with the discharge center. In order not to affect the discharge welding, a lifting mechanism is required to achieve precise positioning of the reflector to meet the imaging requirements in different modes.

[0075] 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 fiber, photonic fiber, and hollow core fiber is complex. The traditional side imaging alignment method cannot guarantee accurate core alignment. The end face positioning method has high feature extraction accuracy, good consistency, and accurate calculation results.

[0076] In a preferred embodiment, a dual-end reflector lifting control is provided. End face imaging needs to be achieved by a high-precision reflector. In order to simultaneously detect the end faces of the left and right optical fibers, the reflector needs to be designed at a special angle to simultaneously image and ensure the consistency of the end face images. The position of the reflector coincides with the discharge center. In order not to affect the discharge welding, a lifting mechanism is required to achieve precise positioning of the reflector to meet the imaging requirements in different modes.

[0077] The image preprocessing system is used to preprocess the collected optical fiber end face images.

[0078] 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 according to the extracted edge features, construct a feature matrix, and obtain the angle between the polarization axis and the reference coordinate axis.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] In a preferred embodiment, the end face positioning system has a built-in Bluetooth module that can communicate with a mobile phone. The device is connected to smart devices such as mobile phones and tablets via Bluetooth, and the mobile phone can control the device through an APP, read recorded data, images and other information, and upgrade the device firmware.

[0083] 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 images. 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

[0084] 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.

[0085] There are fast axis and slow axis inside the polarization-maintaining optical fiber. During fusion alignment, the fast axis and slow axis must be precisely aligned to ensure the maximum extinction ratio.

[0086] When optical fibers are 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.

[0087] If the fast axis and slow axis alignment angle are 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 polarized light power is , then the extinction ratio formula is 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 The end face positioning system of the present invention can be used to weld hollow core optical fibers. Hollow core optical fibers have 5 or 6 sub-cores and transmit by anti-resonance. Such optical fibers cannot be aligned by PAS and can only be aligned and welded by calculating the angle by end face method. Figure 4 The figure shows the end face features of the hollow core optical fiber seen on the optical fiber fusion splicer.

[0088] The side imaging rotates 360 degrees to find the center positions of the five capillaries; the features of the five capillaries are identified through end face imaging, 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 rotates left and right until the features of the five capillaries are completely aligned. Example

[0089] 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 light transmission services.

[0090] It should be noted that the evaluation of the fusion splicing results of the hollow-core optical fiber in Example 4 and the multi-core optical fiber in Example 5 is based on the loss evaluation, not the extinction ratio evaluation. In actual projects, there is a specified control value range for the optical fiber fusion splicing loss. 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 exceeds the range, the cause needs to be analyzed and re-fusion spliced.

[0091] In one embodiment, a computer device is further provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above method embodiments when executing the computer program.

[0092] In one embodiment, a computer-readable storage medium is provided, storing a computer program, which implements the steps in the above method embodiments when executed by a processor.

[0093] In one embodiment, a computer program product or computer program is provided, the computer program product or computer program includes computer instructions, the computer instructions are stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device performs the steps in the above-mentioned method embodiments.

[0094] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and 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 the memory, database or other medium 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. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited thereto. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processors, digital signal processors, programmable logic devices, data processing logic devices based on quantum computing, etc., but are not limited thereto.

[0095] The technical features of the above embodiments may 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.

[0096] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached 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, placing the optical fiber at the working position of the fusion splicer, triggering the image acquisition system to acquire the optical fiber end face image; 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, calculating the center position of the optical fiber end face according to the extracted edge features, constructing a feature matrix, and obtaining 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 to control 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, each pixel in the optical fiber end face image is traversed, and the number of gray level combinations of pixel pairs that satisfy the fixed distance and direction relationship is counted to 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 It means that the pixel with gray value I and the pixel with gray value J are at a distance d and in the direction The frequency of co-occurrence of 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 It is the angle between the polarization axis and the reference coordinate axis.

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 S4, the center position of the optical fiber end face is determined by calculating the geometric center according to 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 the minimum circumscribed rectangle is used to estimate the center position.

4. 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 gradient of the optical 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 points of the image pixel point, the gradient strength and direction are calculated based on the gradient in the horizontal and vertical directions, and 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.

5. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 4, 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 the weak edge point is not connected to the strong edge point, the weak edge point is discarded.

6. The end face positioning method of the polarization-maintaining hollow-core optical fiber fusion splicer according to claim 5, 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).

7. 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 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, according to the cumulative distribution function, the gray level of each pixel in the original image is mapped to a new gray level NP: ; 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 gray level into the new image to obtain an image after histogram equalization.

8. 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 7, 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 the optical fiber end face image; 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 according to 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 end faces of two optical fibers to be fused to be accurately aligned.

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

Images