CN108646353B - A Fiber-Waveguide Automatic Alignment Coupler Based on Image Processing - Google Patents

Abstract

The invention discloses an image processing-based optical fiber-waveguide automatic alignment coupling instrument, which belongs to the technical field of optical fiber communication and optical fiber sensing, and includes an image acquisition module, an image processing and control module, a motion execution module and a human-computer interaction module. The motion execution module includes fiber-pigtailed pads, Y waveguide components, six-dimensional electric translation stage, motor control board, two sets of manual translation stages, etc.; the image processing and control module includes a processor, a storage module, a communication interface and a display module. The image acquisition module collects the clearly imaged side images and end face images. After being processed by the image processing and control module, the motion execution module extracts edge feature lines from the clearly imaged side images and calculates the relative deviation, eliminates the deviation to realize the initial light pass, and determines the output The point position controls the maximum gray value of the output light point to realize the automatic alignment coupling of the fiber-Y waveguide. The invention has the advantages of small volume, low cost, friendly man-machine interaction and fast operation speed, and avoids long-time operation of manual alignment.

Description

A Fiber-Waveguide Automatic Alignment Coupler Based on Image Processing

technical field

The invention belongs to the technical field of optical fiber communication and optical fiber sensing, and relates to an optical fiber-waveguide automatic alignment coupling instrument based on image processing.

Background technique

In the 21st century, the development and use of optoelectronic devices has become a strategic technology for the development of various countries in the fields of communication and sensing. In terms of optical fiber communication, integrated optoelectronic devices have become the key devices supporting the rapid development of next-generation optical fiber communication due to their stable performance, high degree of integration, fast processing speed and high reliability. Waveguide devices are important basic components of integrated optoelectronic devices, and the low-loss connection and packaging technology of optical fibers and waveguides is the key technology of integrated optoelectronics technology.

In terms of fiber optic sensing, fiber optic gyroscope is an important application. It has become the mainstream gyroscope in the field of inertial technology research and has high application value in military, aviation and many civilian fields. The current high-precision fiber optic gyroscope generally adopts the direct coupling scheme of high birefringence fiber ring and Y waveguide device. The loss and noise caused by the coupling point between the polarization maintaining fiber and the Y waveguide are the main factors restricting the improvement of the measurement accuracy of the fiber optic gyroscope.

The coupling loss between optical fiber and optical waveguide device mainly includes mode field mismatch loss, Fresnel reflection loss, transmission loss and misalignment loss.

Existing alignment coupling technologies for optical fibers and waveguides are mainly divided into active alignment methods and passive alignment methods. Active active alignment method generally adopts the introduction of a light source at the input fiber, and uses an optical power meter to detect the output at the output end of the waveguide or the end of the output fiber. Feedback guides the adjustment of each degree of freedom to optimize the coupling power and achieve high-precision attitude. Adjustment. This method has high precision, but generally manual alignment is used in the initial light-passing stage, and the alignment speed is slow; currently, the algorithms for fine alignment with feedback adjustment include hill-climbing method, polynomial fitting method, simplex method, Hamilton algorithm, and centroid method , genetic method, etc., can effectively search for the maximum coupling position, but they are all limited by the low real-time feedback of the optical power meter and the large data volatility, each has its own advantages and disadvantages.

The passive passive alignment method uses semiconductor processing technology to process U-shaped grooves or V-shaped grooves on the waveguide chip, and directly couples the optical fiber to the waveguide for packaging. This method has a fast alignment speed and does not require sophisticated and expensive instruments and alignment processes. , but the positioning accuracy of the U-shaped groove and the assembly accuracy of the device seriously affect the coupling efficiency of the device. At the same time, the chip manufacturing process is complicated and the coupling loss is high. Therefore, active alignment is generally used in practical applications.

Digital image processing refers to the processing of digital images with the help of digital computers to improve graphical information for human interpretation or machine understanding. A digital image is a discretized image f(x,y) in both spatial coordinates and brightness, which can be represented by a two-dimensional integer array. Digital image processing technology has rich content. It can reduce noise through filtering, extract target objects from the background through threshold segmentation and binarization operations, and identify target features and boundary areas through edge detection and feature extraction. . Digital image processing has the characteristics of high processing precision, good reproducibility, low cost and wide application, and is widely used in various technical fields.

Embedded system is application-centric, based on computer technology, software and hardware can be tailored, and is suitable for special-purpose computer systems with strict requirements on function, reliability, cost, volume and power consumption. Embedded systems mainly include hardware systems and software programs. The core of the hardware system is the microprocessor, as well as memory, various interfaces, measurement and control circuits and other components. ARM microprocessors generally have the characteristics of small size, low power consumption, low cost, high performance, and fast speed. Their internal hardware resources have high performance, can load real-time operating systems, and run interfaces and applications. The processing and computing capabilities are fully capable of general digital image acquisition and processing requirements, and are very suitable for application in image processing systems.

Contents of the invention

In order to realize the pose adjustment of the optical fiber and the waveguide, search for the maximum coupling point, and realize the fast and efficient automatic alignment and coupling of the optical fiber and the waveguide, a fiber-waveguide automatic alignment coupling instrument based on image processing is proposed.

The optical fiber-waveguide automatic alignment coupling instrument includes an image acquisition module, an image processing and control module, a movement execution module and a human-computer interaction module.

The image acquisition module includes a white light source, a laser and an optical fiber adapter, and two sets of microscope-CMOS cameras;

The laser directly couples the red light into the pigtailed liner through the bare fiber adapter; the pigtailed liner is opposite to the Y waveguide element for coupling; the first group of microscope-CMOS cameras are vertically fixed above the fiber-waveguide coupling point, The white light source is supported on the side of the first group of microscopes-CMOS cameras, and coaxially illuminates the coupling point. The second set of microscope-CMOS cameras is fixed horizontally behind the output end of the Y-waveguide element.

The motion execution module includes bushings with pigtails, Y waveguide components, six-dimensional electric translation stage, motor control board, two sets of manual translation stages, etc.;

The liner with pigtail is clamped by the liner fixture and fixed on the six-dimensional electric translation platform; the processor sends instructions to the motor control board, so that the six-dimensional electric translation platform realizes the adjustment of the spatial posture in the six-dimensional direction. The Y waveguide element is used as an alignment material and fixed on the waveguide frame. The first group of microscope-CMOS cameras is fixed on the first manual shift stage, the second group of microscope-CMOS cameras is fixed on the second manual shift stage, and the focus of the cameras is achieved through manual adjustment.

The image processing and control module includes a processor, a storage module, a communication interface and a display module.

The communication interface includes RS232 serial port and USB interface. The RS232 serial port is connected to the motor control board and the six-dimensional electric translation platform, which is used to send commands to control the six-dimensional electric translation platform. The processor is respectively connected to two groups of microscope-CMOS cameras through the USB interface. The processor transmits images; the display module is connected to the touch screen through the LCD interface;

The processor analyzes the position and orientation relationship between the pigtailed liner and the Y waveguide element and the coupled output light intensity in the images transmitted by the two sets of microscope-CMOS cameras, and sends instructions to the motor control board to search for the maximum coupling point;

Human-computer interaction module includes touch screen, mouse and keyboard.

Open the automatic coupling software on the touch screen to realize the automatic alignment coupling of the fiber-Y waveguide.

The automatic alignment coupling process of fiber-Y waveguide, the specific steps are as follows:

Step 1. Fix and clamp the pigtailed liner and the Y waveguide component to be aligned and coupled, and roughly adjust the two to a suitable relative position;

Step 2. Open and run the automatic alignment software, and the two groups of microscope-CMOS cameras collect and present images respectively;

Step 3. Manually adjust the two sets of manual translation stages, so that the side images and end images of the two sets of microscope-CMOS cameras are clearest;

The first group of microscopes - CMOS cameras correspond to side images; the second group of microscopes - CMOS cameras correspond to end face images;

Step 4. For the clearly imaged side image, automatically extract and mark the edge characteristic straight line of the pigtailed liner and the Y waveguide element;

The extracted edge feature straight lines are respectively the horizontal and vertical edges and corner positions of the pigtailed pad, the longitudinal edge of the Y waveguide element and the straight line position of the channel of the Y waveguide element.

The specific extraction process is as follows: the first group of microscope-CMOS cameras collect images and pass them to the processor, the processor converts the color image into a grayscale image, and filters and reduces noise; then uses the Otsu method to find the segmentation threshold of the grayscale image, and converts the image Convert to a binary image, segment the target object and the background; respectively use the vertical and horizontal window shifting methods to search for the area with the most drastic change in gray level, which is the edge position of the Y waveguide element and the pigtailed liner; set the ROI area Extract and fit the straight line segments, and mark them on the image.

The location of the channel of the Y waveguide element is determined by the positions of the two electrode strips. The processing method is similar to the extraction of edge straight lines, the difference is that the grayscale segmentation threshold is calculated according to the grayscale value of the electrode and the nearby small area, and the electrode and the lithium niobate substrate are divided; the straight line equation of the two electrode strips at the fitting place is extracted, and the The straight line at the middle position is used as the straight line at the input end of the Y waveguide, and is marked in the image.

Step 5. Calculate the angle difference between the lateral lower edge of the pigtailed liner and the waveguide channel, the horizontal and vertical distance deviation from the corner position of the liner to the waveguide channel, and move the pigtailed liner to a predetermined position according to the edge feature line;

First, according to the simple point-to-straight line distance formula, or the straight-line distance formula, the angle difference between the lateral lower edge of the pigtailed pad and the waveguide channel, the longitudinal deviation and the lateral deviation from the corner position of the pad to the Y waveguide element channel are obtained respectively. .

The lateral lower edge of the pigtailed pad refers to the position where the fiber core of the optical fiber is located in the pigtailed pad.

Then, according to the size of each pixel, the distance represented by the pixel value on the image is converted into the actual space distance. According to the minimum step distance of the six-dimensional electric translation stage, combined with the deviation distances, the distance corresponding to the elimination of the deviation can be obtained. Motor running steps;

Finally, the processor sends instructions to the motor control board to control the six-dimensional electric translation stage to realize translation and rotation operations, and eliminate the deviation while the pigtailed pad and the Y waveguide element reach the predetermined position.

In the process of eliminating the deviation, it is carried out in the order of eliminating the angular deviation first, then eliminating the longitudinal distance deviation, and finally eliminating the lateral distance deviation; in the process of eliminating the distance, reprocess the side after each axis movement of the six-dimensional electric stage Couple the image, fit the characteristic straight line with the pigtail pad and the Y waveguide element, calculate the relative deviation again, and run the six-dimensional electric translation stage to eliminate the deviation.

Step 6. When the pigtailed liner reaches the predetermined position, the initial light pass is realized, and two output light spots at the tail end of the Y waveguide element appear on the end face image;

Step 7. The system automatically detects and marks the center positions of the two output light spots, and judges whether the label box on the output image completely includes the output light spots. If so, fix the position of the output end; Make fine adjustments until the correct position is reached.

The processor automatically calculates the gray center of gravity of the two output light points;

The formula is:

Where f(i, j) is the gray value of the (i, j) pixel in the image.

The obtained gray center of gravity is the central position of the output light spot, and the predetermined size neighborhood of this central position is fixedly selected and marked out, and used as the position of the output point for statistical processing.

Step 8. After determining the position of the output end, the system automatically adjusts the exposure time of the end face image, controls the maximum value of the image of the output light spot, and calculates the output optical power;

According to the light intensity detection feedback at the output end, the system automatically adjusts the exposure time for the end-face image, and controls the maximum value of the output light spot image between 50-150; at this time, the system automatically detects that there are only two dim small light spots left in the image, Extract the red channel value of each pixel in the neighborhood of the small light spot image and record it as p _ij , and add them up to obtain P=∑ _{i, j} p _ij as the output optical power.

Step 9: The system searches for the maximum coupling point according to the automatic search algorithm of iterative fitting axis by axis, and finds the position of the pigtailed bushing that maximizes the output optical power.

Specific steps are as follows:

Step 901, determine the search axis and activate it, and set the moving distance L and step distance ΔL of the six-dimensional electric translation stage;

Step 902, control the six-dimensional electric translation stage to reversely move the distance L in this axial direction, record the current position x=-L;

Step 903, move the step distance △L in the forward direction, record the current position x=x+△L, the second group of microscope-CMOS cameras collects the output image of the end of the Y waveguide element in real time, and transmits it to the processor, and the system automatically processes the image, The red channel at the output point of statistical extraction is fed back as the output optical power and stored in the sequence Seq(x).

Step 904, verify whether x is greater than L, if yes, enter step 905 for curve fitting; otherwise, return to step 903;

Step 905, after scanning the interval (-L, L), search for the maximum value position in the sequence Seq(x), and extract three groups of data on the left and right sides of the maximum value position and the data at the maximum value as the data group to be processed ( _xi , y _i ), using the least squares method to fit the quadratic function on these 7 sets of data.

Set the fitting function as:

Among them (a ₁ , a ₂ , a ₃ ) are the coefficients of each level of the quadratic function to be fitted. The coefficient group (a ₁ , a ₂ , a ₃ ) of the corresponding quadratic function can be obtained by bringing the data group ( _xi , y _i ) to be processed into the solution formula of the least squares method.

Step 906 , after obtaining the quadratic curve, calculate the position of the extreme point of the curve, replace the position of the maximum value of the actual measured data as the maximum value obtained, and move the pigtailed liner to the maximum value.

Step 907. Verify whether the step distance △L reaches the preset accuracy threshold. If so, scan and traverse the interval (-△L,△L) with the step distance △L/5, search for the position with the maximum output optical power and move the band Pigtail spacer to this maximum position. Go to step 909; otherwise, go to step 908;

Step 908, the step distance △L is greater than the predetermined accuracy threshold, the scanning parameters L and △L are both halved, return to step 902, and the halved interval (-L, L) is scanned again with the halved step distance △L and Select the data set for quadratic curve fitting to find the maximum position.

Step 909, when the ergodic scanning ends, the search for the maximum coupling position of this axis ends; switch and activate the next axis of the six-dimensional electric displacement stage, repeat the above steps until the maximum coupling position of each axis is searched, At this time, the position of the liner with pigtails is the desired maximum coupling position, and the automatic search ends.

The advantages of the present invention are:

(1) An optical fiber-waveguide automatic alignment coupling instrument based on image processing, which uses ARM as the processor and uses a touch screen as the human-computer interaction interface, which has the advantages of small size, low cost, friendly human-computer interaction, and fast computing speed;

(2) A fiber-waveguide automatic alignment coupling instrument based on image processing, which uses digital image processing to realize the initial light passing of fiber-waveguide, which is fast and convenient, achieves sub-pixel alignment accuracy, and avoids manual alignment long time operation;

(3) An optical fiber-waveguide automatic alignment coupling instrument based on image processing, which uses a CMOS camera to image and detect light intensity, instead of an optical power meter, to achieve high real-time output light intensity feedback and closed-loop control, which can realize fiber-waveguide alignment Automatic alignment coupling.

Description of drawings

Fig. 1 is the structural representation of a kind of optical fiber-waveguide automatic alignment coupling instrument based on image processing of the present invention;

Fig. 2 is the alignment coupling point schematic diagram of band pigtail liner block and Y waveguide element in the optical fiber-waveguide automatic alignment coupling instrument of the present invention;

Fig. 3 is the side image of the coupling point collected by the first group of microscope-CMOS camera of the present invention;

Fig. 3 (a) is the image when the present invention manually adjusts the focus of the camera;

Fig. 3 (b) is the image that the present invention carries out automatic extraction edge and label to side image;

Figure 3(c) is the image of the coupling point after the automatic coarse alignment of the present invention eliminates the deviation;

Fig. 4 is the Y-waveguide output terminal image that the second group of microscope-CMOS camera of the present invention gathers;

Fig. 4 (a) is the image when the present invention manually adjusts the focus of the camera;

Fig. 4 (b) is the output light point image when the initial pass light is realized after the rough alignment of the present invention;

Fig. 4 (c) is the image of the output light spot after the automatic dimming of the present invention;

Fig. 5 is the automatic alignment coupling flowchart of the optical fiber-waveguide automatic alignment coupling instrument based on image processing in the present invention;

Fig. 6 is the flow chart of the method for automatically searching for the maximum coupling point according to the automatic search algorithm of axis-by-axis iterative fitting in the present invention;

Fig. 7 is the operation interface of the optical fiber-waveguide automatic alignment coupler software of the present invention;

Fig. 8 is a comparison between the experimental data of the CMOS camera detection output optical power and the theoretical simulation data in the present invention.

In the figure: 1-processor; 2-touch screen; 3-mouse; 4-liner with pigtail; 5-Y waveguide element; Six-dimensional electric translation stage; 10-motor control board; 11-white light source; 12-first group of microscopes-CMOS camera; 13-first manual translation stage; 14-second group of microscope-CMOS camera; 15-second hand moving stage;

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

An optical fiber-waveguide automatic alignment coupling instrument based on image processing of the present invention, as shown in FIG. 1 , includes an image acquisition module, an image processing and control module, a motion execution module and a human-computer interaction module.

The image acquisition unit includes a white light source 11, a laser 8, an optical fiber adapter 7, and two sets of microscope-CMOS cameras.

The laser 8 directly couples the red light into the pigtailed liner 4 through the bare fiber adapter 7; the pigtailed liner 4 is opposite to the Y waveguide element 5 for coupling; two groups of CMOS cameras are connected with the microscope objective lens, the first A group microscope-CMOS camera 12 is vertically fixed above the pad-waveguide coupling point to perform microscopic imaging on the coupling point. The white light source 11 is supported on the side of the first microscope-CMOS camera 12, and coaxially illuminates the coupling point. The second group of microscopes—CMOS cameras 14 are placed horizontally behind the Y waveguide element 5 to perform microscopic imaging on the output end of the Y waveguide element 5 . Both groups of microscopes-CMOS cameras transmit images to the processor 1 through the USB interface for analysis and processing.

The white light source 11 is a point light source, which is inserted into the adapter tube on the side of the microscope objective lens, through which the semi-transparent and semi-reflective mirror surface realizes coaxial lighting, and illuminates the coupling point between the pigtailed liner 4 and the Y waveguide element 5 .

The laser 8 selects 650nm red light with output pigtails. The input end of the polarization-maintaining fiber ring 6 is stripped of the coating layer, and after cleaning, it is inserted into the fiber optic adapter 7, and the ceramic head is exposed for 2-3mm, scratched off with a jewel knife, and then It is directly coupled with the output pigtail of the laser 8 through the flange. The red light passes through the polarization maintaining fiber ring 6 and is coupled into the Y waveguide element 5 at the coupling point, so that the output light spot can be seen at the output end of the Y waveguide element 5 .

The motion execution module includes fiber-tailed pads 4 and pad clamps, Y waveguide components 5, six-dimensional electric translation stages 9, motor control boards 10, two sets of three-dimensional manual translation stages, and waveguide fixing frames.

Because in the fiber optic gyroscope, the alignment accuracy of the direct coupling between the polarization-maintaining fiber and the Y-waveguide is relatively high, so in this embodiment, the alignment coupling between the polarization-maintaining fiber ring and the input end of the Y-waveguide is selected as the operation object. In view of the wide use in optical fiber sensing, the optical fiber selected for alignment in this embodiment is a panda-type polarization-maintaining optical fiber, and the left side of Fig. 2 is a schematic diagram of a pigtailed liner 4. The optical fiber ring is fixed on the lithium niobate liner by the manufacturer through a fixed axis. Using the pigtailed fiber core instead of the polarization-maintaining fiber core as the coupling alignment material, detection alignment can be performed by means of the edge of the fiber pad.

The right side of Figure 2 is the Y waveguide element 5 widely used in optical fiber sensing as an alignment material; the Y waveguide element 5 is an annealed proton exchange waveguide with a lithium niobate substrate, and its channel is obtained by annealing proton exchange. The surface of the substrate infiltrates a small area with a width of about 6 microns and a depth of about 3 microns. The refractive index of the channel region is less than 0.02 different from that of the lithium niobate substrate, so it is difficult to observe using conventional methods. As shown in Figure 3(a), two thin lines can be vaguely seen in the middle area of the Y waveguide surface, which is the Y waveguide channel area, one of which is in the middle of two clear electrode areas, which is the input channel of the Y waveguide, and the other One is the auxiliary observation channel. The Y waveguide element selected by the present invention has been plated with electrode strips indicating the position and auxiliary observation on both sides of the Y waveguide input and output channels during the production stage, so the position of the Y waveguide input channel can be determined by means of the positions of the two electrode strips . During the process of manually placing the fiber pigtailed pad 4 and the Y waveguide element 5 , the pigtailed pad 4 is clamped by the pad clamp and fixed on the six-dimensional electric translation stage 9 .

The fiber-waveguide coupling is essentially a six-degree-of-freedom coupling in three-dimensional space, as shown in Figure 2, which are the transverse dislocation X and Y directions, the longitudinal spacing Z, and the pitch angle α generated by the rotation around the X and Y axes respectively. and the deflection angle β, and the angle θ between the slow axis of the polarization-maintaining fiber and the polarization axis of the optical waveguide. Changes in any of the first five degrees of freedom will affect the insertion loss, while changes in the θ angle mainly affect polarization crosstalk, which is very important in fiber optic sensing. Therefore, it is necessary to carry out process control for each degree of freedom to ensure the lowest insertion loss, polarization crosstalk and good stability.

When the processor 1 sends an instruction to the motor control board 10, the six-dimensional displacement direction of the six-dimensional electric translation stage 9 is set according to the six degrees of freedom of the coupling point, and each direction is orthogonal to each other, and the movement of each other does not interfere with each other under ideal conditions. The six-dimensional electric displacement platform 9 realizes the spatial posture adjustment in the six-dimensional direction. The axes of rotation of the three axes of rotation intersect at one point, which is called the center of rotation. During the fixation phase of the pigtailed spacer 4, the output pigtail end is placed at this center of rotation. The advantage of this is that no additional displacement deviation will be generated due to the existence of the rotating arm during the rotating operation. In the actual assembly of the instrument, the six-dimensional displacement cannot meet the strict orthogonal requirements due to the insufficient assembly accuracy, so there will still be small mutual disturbances in the actual alignment operation.

The first group of microscope-CMOS cameras 12 is fixed on the first manual displacement stage 13, the second group of microscope-CMOS cameras 14 is fixed on the second manual displacement stage 15, and the focus of the cameras is achieved through manual adjustment.

The image processing and control module includes a processor 1, a storage module, a communication interface, a display module and a power supply module.

Processor 1 can choose to use PC or ARM processor, choose PC in the development stage, in actual use, you can choose ARM microprocessor to reduce the size, use Cortex-A9 series ARM processor as the controller, and traditional PC Compared with the control system, the system is small in size, low in cost, and flexible and convenient to use; the embedded environment design of the image acquisition module, motion execution module and human interaction module has been completed, and the system integration degree is high.

The storage module uses DDR3 as RAM memory, and eMMC as FLASH storage; the communication interface includes a RS232 serial port and 3 USB interfaces, the RS232 serial port is connected to the motor control board 10 and the six-dimensional electric translation platform 9, and the RS232 serial port is used to send motion commands and motor control The board 10 converts motion commands into phase currents that drive the stepper motors to rotate. 3 USB ports are respectively connected with the first group of microscope-CMOS camera 12, the second group of microscope-CMOS camera 14 and the mouse 3, and the COMS camera adopts a dedicated driver under Linux to collect images, and transmits them to the ARM processor 1 for image processing; the display module It is connected to the capacitive touch screen 2 through the 45pin LCD interface; the power module adopts a 5V power adapter socket and uses a 5V DC power supply for power supply.

Processor 1 is respectively connected to two groups of microscope-CMOS cameras through the USB interface, and is used to transmit images to processor 1; processor 1 analyzes the images with pigtailed lining block 4 and Y waveguide element 5 in the images transmitted by the two groups of microscope-CMOS cameras. Pose relationship and coupling output light intensity, send instructions to the motor control board 10 to search for the maximum coupling point;

The human-computer interaction module includes a touch screen 2, a mouse and a keyboard 3.

The human-computer interaction interface is developed using Qt, and the automatic alignment coupling software is opened on the touch screen. The operation interface is shown in Figure 7. The first group of microscope-CMOS cameras 12 and the second group of microscope-CMOS cameras 14 start to collect images. displayed on the interface. Observe the coupling point image and the output end image of the Y waveguide element 5, adjust the first manual displacement stage 13 and the second manual displacement stage 15, adjust the two groups of microscope-CMOS cameras to the focus position, so that the image reaches the clearest, and Adjust the orientation to select a suitable field of view.

The automatic alignment and coupling process of the fiber-Y waveguide is mainly divided into two steps, which are the coarse alignment stage for image processing of side coupling points and the fine alignment stage for end face output image processing. As shown in Figure 5, the specific steps are as follows:

Step 1. Fix and clamp the pigtailed liner and the Y waveguide element to be aligned and coupled, and roughly adjust the two to the relative position;

Fix and clamp the pigtailed pad that needs to be aligned and coupled on the pad fixture, and place the pad clamp on the rotation center of the six-dimensional electric translation stage; at the same time, fix the Y waveguide element that needs to be aligned and coupled on the On the waveguide frame; roughly adjust the fiber pigtail liner and the Y waveguide element to a suitable relative position.

Step 2. Open and run the automatic alignment software, and the two groups of microscope-CMOS cameras collect and present images respectively;

Open the automatic alignment software, the operation interface is shown in Figure 7, click to run, and the two groups of microscope-CMOS cameras start to collect images and transmit them to the two image frames in the operation interface.

Step 3. Manually adjust the two sets of manual translation stages, so that the side images and end images of the two sets of microscope-CMOS cameras are clearest;

The first set of microscope-CMOS camera corresponds to the side image, as shown in Figure 3. The second group of microscope-CMOS camera corresponds to the end face image; as shown in Figure 4.

It should be noted that the end-face image needs to correctly find the edge of the output end of the Y waveguide, and adjust the edges on both sides of the image to reach the focus position at the same time.

Step 4. For the clearly imaged side image, automatically extract and mark the edge characteristic straight line of the pigtailed liner and the Y waveguide element;

In the coarse alignment process, the core of the image processing process of the side of the coupling point is the detection and extraction of the characteristic straight line of the pigtailed liner and the Y waveguide element. There are two main types of characteristic lines, the first is the edge line between the pigtailed liner and the Y waveguide component, and the second is the waveguide channel position of the Y waveguide; specifically, the horizontal and vertical edges and corner positions of the pigtailed liner , the longitudinal edge of the Y waveguide element and the linear position of the waveguide channel found by means of two auxiliary electrodes.

After the focus adjustment of the first group of microscopes and CMOS cameras, click the "Extract Edge" button on the operation interface, and the system will automatically perform grayscale processing on the side image on the left side of the interface - threshold segmentation - edge detection - straight line fitting and other digital image processing According to the operation, the edge feature line of the pigtailed liner and the Y waveguide element in the side image is extracted and marked.

As shown in Figure 3(a), the edge points are more obvious and have a large difference in gray level with the background. Therefore, traditional image processing and line extraction methods are used to extract edge lines. The specific process is: the first group of microscopes - CMOS cameras collect After receiving the image, it is passed to the processor. The embedded program embedded in the image processing module first converts the collected color image into a grayscale image, and uses Gaussian filtering to filter and reduce the noise of the image to eliminate the interference of noise abnormal points; then, Use the Otsu method (Otsu method) to find the segmentation threshold of the grayscale image, convert the image into a binary image, and the target object is clearly separated from the background; use the vertical and horizontal window shifting methods respectively to search for grayscale The area with the most drastic change is the edge position of the pigtailed liner and the Y waveguide element. Set the ROI area to extract and fit the straight line segment, and mark it on the image. The result is shown in Figure 3(b) .

For the Y waveguide channel, because it is difficult to observe and the gray level difference with the surrounding area is not large, the location of the Y waveguide input channel is determined by the position of the two electrode strips. The processing method is similar to the extraction of edge straight lines, the difference is that the grayscale segmentation threshold is calculated according to the grayscale value of the electrode and the nearby small area, which can separate the electrode from the lithium niobate substrate. Extract the straight line equations of the two electrode strips at the fitting place, take the straight line at the middle position as the straight line at the input end of the Y waveguide, and mark it in the image, as shown in Figure 3(b). The position of the input end of the Y-waveguide element is placed straight through the image to show its angular deviation from the lower edge of the pigtailed spacer.

Step 5. Calculate the angle difference between the lateral lower edge of the pigtailed liner and the waveguide channel, the horizontal and vertical distance deviation from the corner position of the liner to the waveguide channel, and move the pigtailed liner to a predetermined position according to the edge feature line;

After the processor detects all the characteristic straight lines, it analyzes each straight line segment to obtain the edge distance and angle deviation between the pigtailed liner and the Y waveguide component and the axis of the fiber (generally coincides with the edge of the pigtailed liner) and the Y waveguide The deviation of the component input line. The number of steps required for the motor movement is calculated from the distance or angle deviation, and transmitted to the motor control board through the RS232 interface, and the motor is controlled to align the pigtailed bushing with the Y waveguide element.

Specifically:

First, after obtaining the edge characteristic straight line of the pigtailed spacer and the Y-waveguide element, according to the simple point-to-line distance formula, or the straight-line distance formula, the angle difference between the lateral lower edge of the pigtailed liner and the waveguide channel, Longitudinal deviation and lateral deviation from pad corner position to waveguide channel.

The lateral lower edge of the pigtailed pad refers to the position where the fiber core of the optical fiber is located in the pigtailed pad.

Then, according to the size of each pixel (2.2μm×2.2μm), the distance represented by the pixel value on the image is converted into the actual space distance, and the minimum step distance of the six-dimensional electric translation stage, combined with each deviation distance, is divided The number of motor running steps corresponding to the elimination of the deviation can be obtained;

Finally, click the "Automatic Alignment" button in the operation interface, and the processor sends instructions to the motor control board to control the six-dimensional electric translation stage to achieve translation and rotation operations, and the pigtailed pad reaches the predetermined position while eliminating the deviation.

In the process of eliminating the deviation, choose to eliminate the angular deviation first, then eliminate the vertical distance deviation, and finally eliminate the horizontal distance deviation in order.

In actual operation, because the precision of the six-dimensional electric translation stage is not high enough, there is crosstalk between the axes, so when one axis moves, the other axis will also be displaced, and the deviation will change. Therefore, in the process of eliminating the distance, the side coupling image will be reprocessed after each axis movement, the characteristic straight line with the pigtailed pad and the Y waveguide element will be fitted, the relative deviation will be calculated again, and the electric translation stage will be run to eliminate the deviation. Finally, the pigtailed liner and the Y-waveguide component are placed in the expected position, as shown in Figure 3(c), at which point the initial light-passing step of the fiber-waveguide alignment coupling can generally be completed.

In the process of eliminating the deviation, it is necessary to reserve a certain distance along the longitudinal axis of the Y-waveguide channel, which is conducive to the movement of the pigtailed liner in the next automatic search process, and at the same time provides for automatic alignment after the coupling is completed. Add UV curing glue to leave space.

Step 6. When the pigtailed liner reaches the predetermined position, the initial light pass is realized, and two output light spots at the tail end of the Y waveguide element appear on the end face image;

When the pigtailed bushing reaches the predetermined position, the dimensional deviation between the fiber and the waveguide has been controlled in a small area. When the side coupling image observes that the fiber and the Y waveguide are basically aligned, the Y waveguide collected by the COMS camera Two output light spots can be observed in the image of the output end, that is, the initial light passing through the Y waveguide is realized. After the initial light passing is completed, the image collected by the second group of microscopes-CMOS cameras is shown in Figure 4(b). On the edge of the end face image at the output end of the Y waveguide, two bright light spots appear, that is, the two output endpoints at the end of the Y waveguide, which are transmitted to the processor via RS232 and displayed on the touch screen.

If the output light point is not detected at the output end after the rough alignment is completed, you can select the "motor adjustment" button in the interactive software to open the direct control interface of the six-dimensional motor, and control the motor to make fine adjustments in all directions until the output light point is found. point.

Step 7. The system automatically detects and marks the center positions of the two output light spots, and judges whether the label box on the output image completely includes the output light spots. If so, fix the position of the output end; Make fine adjustments until the correct position is reached.

The processor automatically calculates the gray center of gravity of the two output light points;

The formula is:

Where f(i, j) is the gray value of the (i, j) pixel in the image.

The calculated gray center of gravity is the center position of the output light spot. Click the "Confirm Area" button on the operation interface to fix the predetermined size neighborhood of this center position and mark it out as the position of the output point for statistical processing. .

Step 8. After determining the position of the output end, the system automatically adjusts the exposure time of the end face image, controls the maximum value of the image of the output light spot, and calculates the output optical power;

After confirming the position of the output end, click the "auto light adjustment" button on the operation interface, the system will automatically adjust the exposure time for the end surface image according to the light intensity detection feedback of the output end, and control the maximum value of the output light point image between 50-150 ; At this time, the system automatically detects that there are only two dim small light spots left in the image as shown in Figure 4(c), and extracts the red channel value of each pixel in the neighborhood of the small light spot image as p _ij , and adds And get P=∑ _{i, j} p _ij is the output optical power.

In this embodiment, a CMOS camera is used instead of an optical power meter as a detection device for output optical power, which improves real-time feedback and coupling efficiency. In theory, the CMOS camera and the optical power meter work on the same principle. They are based on the photoelectric effect and count the photocurrent generated by the incident light on the sensor within a certain period of time (that is, the exposure time of the CMOS camera) to characterize the detected optical power. However, compared with the optical power meter, the CMOS camera detects a smaller range of light intensity, and the gray value of the collected image can only be distributed between 0-255. As shown in Figure 4(b), the appearance of white spots at the center of the output light spot indicates that the CMOS camera is overexposed. Therefore, to use a CMOS camera instead of an optical power meter to detect the output light intensity, it is necessary to reduce the detection light intensity and adjust the exposure time of the camera. , so that the maximum value of the output point on the image is within the detectable range, as shown in Figure 4(c), to prevent inaccurate detection caused by overexposure, and the two bright output spots are reduced to two dimmer spots .

After the automatic dimming step, the system automatically detects the output light point, extracts and counts the red channel value of the output light point, and feedbacks it as the output light power. For these two light spots, extract the red channel value, scan the pixel on the one-dimensional axis (such as along the horizontal direction or vertical direction), take the scanning axis as the horizontal axis, and the red channel value as the vertical axis, you can get a good Gaussian-like linetype. It is proved that the two red points are the fundamental mode at the output end, and it is feasible to use the energy change of the statistical fundamental mode to characterize the change of the optical power at the output end.

Extract the red channel values in the smaller neighborhood of the center positions of the two output light spots and statistically sum them as the output light power at this time. Move the bushing with pigtails on a single axis, and record the output light intensity at each point for trend analysis, as shown in Figure 8, which shows the scanning curves on the horizontal and vertical axes on the cross-section of the fiber-waveguide coupling point, the curve The horizontal axis of is the single-axis moving distance, and the vertical axis is the relative coupling efficiency. It can be seen that the experimental data basically agrees with the data obtained from the theoretical simulation of fiber-waveguide coupling in terms of magnitude and trend, and both show good unimodality. Therefore, it is practical and feasible to replace the optical power meter with the CMOS camera adopted in the present invention to detect the output optical power.

Step 9: The system searches for the maximum coupling point according to the automatic search algorithm of iterative fitting axis by axis, and finds the position of the pigtailed bushing that maximizes the output optical power.

Click the "best point search" button in the operation interface, the system will automatically search for the maximum coupling point, and find the position of the pigtailed liner that maximizes the output optical power according to the automatic search algorithm of axis-by-axis iterative fitting. After the maximum coupling point is found, a prompt box of "automatic coupling complete" will appear on the operation interface. At this time, the complete fiber-waveguide automatic alignment and coupling process is over, and further operations such as adding UV-curing glue to the coupling point will be performed.

The maximum coupling point automatic search algorithm of the present invention is based on the unimodality shown by the moving scanning curves of each axis. The place where the coupling loss is the smallest is the position where the output optical power is the largest, and the search for the maximum coupling point is Search for the position where the output optical power is maximum.

Because there is crosstalk between the motors of each axis of the six-dimensional electric translation platform actually used, and there is a certain vibration, resulting in unstable feedback output optical power, so the method of iterative fitting by axis is used to search for the maximum coupling point; And the automatic dimming step is completed, and after the correct optical power feedback can be obtained, the automatic search for the maximum coupling point starts. As shown in Figure 6, the automatic search algorithm flow is as follows:

Step 901, determine the search axis and activate it, and set the moving distance L and step distance ΔL of the six-dimensional electric translation stage;

First determine a search axis, power on the axis motor, and set the search parameters L and △L.

Step 902, control the six-dimensional electric translation stage to reversely move the distance L in this axial direction, record the current position x=-L;

Step 903, move the step distance △L in the forward direction, record the current position x=x+△L, the second group of microscope-CMOS cameras collects the output image of the end of the Y waveguide element in real time, and transmits it to the processor, and the system automatically processes the image, The red channel at the output point of statistical extraction is fed back as the output optical power and stored in the sequence Seq(x).

Step 904, verify whether x is greater than L, if yes, enter step 905 for curve fitting; otherwise, return to step 903;

Step 905, after scanning the interval (-L, L), search for the maximum value position in the sequence Seq(x), and extract three groups of data on the left and right sides of the maximum value position and the data at the maximum value as the data group to be processed ( _xi , y _i ), using the least squares method to fit the quadratic function on these 7 sets of data.

The method of least squares (also known as the method of least squares) is a mathematical optimization technique. It finds the best function fit to the data by minimizing the sum of squared errors.

Set the fitting function as:

Among them (a ₁ , a ₂ , a ₃ ) are the coefficients of each level of the quadratic function to be fitted.

by the principle of least squares Bring the data group to be processed ( _xi , y _i ) into the above formula and calculate the partial derivative of the function S(a, b, c) with respect to a _k (k=1, 2, 3) and make it zero Desired parameters (a ₁ , a ₂ , a ₃ ) can be obtained, then the fitting quadratic function can be obtained.

Step 906 , after obtaining the quadratic curve, calculate the position of the extreme point of the curve, replace the position of the maximum value of the actual measured data as the maximum value obtained, and move the pigtailed liner to the maximum value.

Step 907. Verify whether the step distance △L reaches the preset accuracy threshold. If so, scan and traverse the interval (-△L,△L) with the step distance △L/5, search for the position with the maximum output optical power and move the band Pigtail spacer to this maximum position. Go to step 909; otherwise, go to step 908;

Step 908, the step distance △L is greater than the predetermined accuracy threshold, the scanning parameters L and △L are both halved, return to step 902, and the halved interval (-L, L) is scanned again with the halved step distance △L and Select the data set for quadratic curve fitting to find the maximum position.

Step 909: When the ergodic scanning is completed, the search for the maximum coupling position of this axis is completed; switch the axis, power on and activate the next axis of the six-dimensional electric displacement stage, and repeat the above steps until the maximum coupling position of each axis is After the search is completed, the position of the liner with pigtails is the desired maximum coupling position, and the automatic search ends.

Each axis is automatically searched, and a prompt box of "automatic coupling complete" pops up on the operation interface, indicating that the maximum coupling point has been found. The program can be exited, and the bonding and encapsulation steps such as adding UV-curing glue can be implemented, which will not be described in this article.

Claims (5)

1. An optical fiber-waveguide automatic alignment coupler based on image processing comprises an image acquisition module, an image processing and control module, a motion execution module and a human-computer interaction module;

The image acquisition module comprises a white light source, a laser, an optical fiber converter and two sets of microscope-CMOS cameras;

the laser directly couples red light into the filler block with the tail fiber through the bare fiber adapter; the backing block with the tail fiber is opposite to the Y waveguide element and is coupled; the first group of microscope-CMOS cameras are vertically fixed above the optical fiber-waveguide coupling point, and the white light source is additionally arranged on the side of the first group of microscope-CMOS cameras to coaxially illuminate the coupling point; the second group of microscope-CMOS cameras are horizontally fixed behind the output end of the Y waveguide element;

the motion execution module comprises a filler block with a tail fiber, a Y waveguide element, a six-dimensional electric displacement table, a motor control board and two sets of manual displacement tables;

the filler block with the tail fiber is clamped by a filler block clamp and fixed on a six-dimensional electric displacement table; the processor sends an instruction to the motor control board to enable the six-dimensional electric displacement table to realize the adjustment of the spatial pose in the six-dimensional direction; the Y waveguide component is used as an alignment material and is fixed on the waveguide frame; the first group of microscope-CMOS cameras are fixed on the first manual displacement table, the second group of microscope-CMOS cameras are fixed on the second manual displacement table, and focusing of the cameras is achieved through manual adjustment;

the image processing and controlling module comprises a processor, a storage module, a communication interface and a display module;

the communication interface comprises an RS232 serial port and a USB interface, the RS232 serial port is connected with the motor control board and the six-dimensional electric displacement table and used for sending instructions to control the six-dimensional electric displacement table, and the processor is respectively connected with the two sets of microscope-CMOS cameras through the USB interface and used for transmitting images to the processor; the display module is connected with the touch screen through an LCD interface;

the processor analyzes the pose relation and the coupling output light intensity of the tail fiber filler blocks and the Y waveguide elements in the images transmitted by the two groups of microscope-CMOS cameras, and sends an instruction to the motor control board to search a maximum coupling point;

the human-computer interaction module comprises a touch screen, a mouse and a keyboard;

automatic coupling software is opened on the touch screen to realize automatic alignment coupling of the optical fiber-Y waveguide;

the method is characterized in that the automatic alignment coupling process of the optical fiber-Y waveguide comprises the following specific steps:

Respectively fixedly clamping a backing block with a tail fiber to be aligned and coupled and a Y waveguide element, and roughly adjusting the backing block with the tail fiber and the Y waveguide element to proper relative positions;

step two, opening the automatic alignment software and running, and respectively acquiring and presenting images by two groups of microscope-CMOS cameras;

step three, manually adjusting two sets of manual displacement tables respectively to ensure that side images and end surface images of the two sets of microscope-CMOS cameras are clearest;

a first set of microscope-CMOS camera corresponding side images; a second set of microscope-CMOS camera corresponding end face images;

automatically extracting and marking edge characteristic straight lines of the filler blocks with the tail fibers and the Y waveguide elements aiming at the clearly imaged side images;

the extracted edge characteristic straight lines are respectively the transverse and longitudinal edges and the angular point positions of the filler block with the tail fiber, the longitudinal edge of the Y waveguide element and the straight line position of the channel of the Y waveguide element;

calculating the angle deviation between the transverse lower edge of the filler block with the tail fiber and the waveguide channel and the transverse and longitudinal distance deviation between the angular point position of the filler block and the waveguide channel according to the edge characteristic straight line, and moving the filler block with the tail fiber to a preset position;

Step six, realizing initial light passing after the backing block with the tail fiber reaches a preset position, and enabling two output light spots at the tail end of the Y waveguide element to appear on an end surface image;

step seven, the system automatically detects and marks the central positions of the two output light spots, judges whether a marking frame on the output image completely contains the output light spots, and fixes the positions of the output ends if the marking frame on the output image completely contains the output light spots; otherwise, finely adjusting the pigtail filler block until the pigtail filler block reaches the correct position;

The processor automatically calculates the gray gravity center of the two output light spots;

The formula is as follows:

wherein f (i, j) is the gray value of the (i, j) pixel point in the image;

the obtained gray scale gravity center is the center position of the output light spot, the neighborhood with the preset size of the center position is fixedly selected and marked out to be used as the position of the output point for statistical processing;

Step eight, after the position of the output end is determined, the system automatically adjusts the exposure time of the end face image, controls the image maximum value of the output light spot and calculates the output light power;

the system automatically adjusts the exposure time of the end face image according to the light intensity detection feedback of the output end, and controls the maximum value of the output light spot image to be between 50 and 150; at the moment, the system automatically detects the remaining two dim small light spots in the image, extracts the red channel value of each pixel point in the neighborhood of the small light spot image and records the red channel value as p_ijAdding to obtain P ═ Sigma_i，jp_ijAs the output optical power;

and step nine, searching the maximum coupling point by the system according to an automatic search algorithm of axis-by-axis iterative fitting, and finding out the position of the backing block with the tail fiber, which enables the output optical power to reach the maximum.

2. The fiber-waveguide automatic alignment coupler based on image processing as claimed in claim 1, wherein in the fourth step, the extracted edge feature lines are the positions of the transverse and longitudinal edges and the angular points of the filler block with tail, the longitudinal edge of the Y waveguide element and the line position of the channel of the Y waveguide element, respectively.

3. the fiber-waveguide automatic alignment coupler based on image processing as claimed in claim 1, wherein said step four is specifically extracting as follows:

The first group of microscope-CMOS cameras collects images and transmits the images to the processor, and the processor converts the color images into gray images and carries out filtering and noise reduction; then, solving a segmentation threshold value of the gray-scale image by using the Otsu method, converting the image into a binary image, and segmenting the target object and the background; respectively adopting a longitudinal window moving method and a transverse window moving method to search the areas with the most intense gray scale change, namely the edge positions of the Y waveguide element and the filler block with the tail fiber; setting an ROI (region of interest) area to extract and fit straight line segments in the ROI area, and labeling the straight line segments on an image;

the position of a channel of the Y waveguide element is determined by the positions of the two electrode strips; the processing method is similar to the extraction of edge straight lines, and is different from the method that the gray segmentation threshold is obtained by calculation according to the gray values of the electrode and a small area nearby, and the electrode and the lithium niobate substrate are segmented; and extracting a linear equation of the two electrode strips at the fitting position, taking a straight line at the middle position as a position straight line of the input end of the Y waveguide, and marking the position straight line in the image.

4. The fiber-waveguide automatic alignment coupler based on image processing as claimed in claim 1, wherein said step five is specifically:

Firstly, respectively solving the following according to a simple point-to-straight line distance formula or a straight line distance formula: the angle difference between the transverse lower edge of the filler block with the tail fiber and the waveguide channel, and the longitudinal deviation and the transverse deviation from the angular point position of the filler block to the Y waveguide component channel;

The transverse lower edge of the pigtail filler block refers to the position of an optical fiber core in the pigtail filler block;

then, converting the distance represented by the pixel value on the image into an actual space distance according to the size of each pixel point, and dividing the actual space distance by combining each deviation distance according to the minimum step distance of the six-dimensional electric displacement table to obtain the motor operation step number corresponding to the elimination of the deviation;

finally, the processor sends an instruction to the motor control board to control the six-dimensional electric displacement table to realize translation and rotation operations, and the filler block with the tail fiber and the Y waveguide element reach a preset position while deviation is eliminated;

In the process of eliminating the deviation, the angular deviation is eliminated firstly, then the longitudinal distance deviation is eliminated, and finally the transverse distance deviation is eliminated; in the process of eliminating the distance, after each axis of the six-dimensional electric displacement table moves, the side coupling image is reprocessed, the characteristic straight line of the pigtailed filler block and the Y waveguide element is fitted, the relative deviation is calculated again, and the six-dimensional electric displacement table is operated to eliminate the deviation.

5. The fiber-waveguide automatic alignment coupler based on image processing as claimed in claim 1, wherein said nine specific steps are as follows:

Step 901, determining a search axial direction and activating, and setting a moving distance L and a step distance delta L of the six-dimensional electric displacement table;

Step 902, controlling the six-dimensional electric displacement table to move a distance L in the axial direction in the reverse direction, and recording the position x as-L;

step 903, moving the step distance delta L in the forward direction, recording the position x at the time as x + delta L, acquiring a tail end output image of the Y waveguide element by a second group of microscope-CMOS cameras in real time, transmitting the tail end output image to a processor, automatically processing the image by the system, counting and extracting a red channel at an output point as output light power to feed back, and storing the red channel in a sequence seq (x);

step 904, verifying whether x is larger than L, and if so, entering step 905 for curve fitting; otherwise, returning to step 903;

Step 905, after the scanning of the interval (-L, L) is finished, searching the position of the maximum value in the sequence seq (x), and extracting three groups of data around the position of the maximum value and data at the maximum value as a data group (x) to be processed_i,y_i) Performing quadratic function fitting on the seven groups of data by using a least square method;

set the fitting function to:

wherein (a)₁，a₂，a₃) Coefficients of each level of the quadratic function to be fitted are obtained; to process the data set (x)_i,y_i) Substituting into least square method to solve formula to obtain coefficient group (a) of corresponding quadratic function₁，a₂，a₃)；

step 906, after the secondary curve is obtained, calculating to obtain the extreme point position of the curve, replacing the maximum value position of the actual measurement data as the maximum value position, and moving the filler block with the pigtail to the maximum value position;

Step 907, verifying whether the step distance delta L reaches a preset precision threshold, if so, scanning and traversing the interval (-delta L, delta L) by the step distance delta L/5, searching a position with the maximum output optical power, and moving the pigtail backing block to the maximum position; proceed to step 909; otherwise, go to step 908;

step 908, halving both the scanning parameters L and the scanning parameters Delta L when the step distance Delta L is larger than the preset precision threshold, returning to step 902, scanning the halved interval (-L, L) by the halved step distance Delta L again and selecting a data set for quadratic curve fitting to find the maximum position;

Step 909, when the traversal scanning is finished, the searching of the maximum coupling position in the axial direction is finished; and converting and activating the next axial direction of the six-dimensional electric displacement table, repeating the steps until the maximum coupling position of each axial direction is searched, wherein the position of the filler block with the tail fiber is the required maximum coupling position, and finishing automatic searching.