Research And Implementation Of Lithium Niobate Crystal Automatic Alignment System Based On Machine Vision

Optical communication has become an important pillar of information transmission in today's society because of its large capacity,high rate,low loss,good confidentiality and other advantages.With the wide application of optical communication,the demand for optical communication devices is increasing,and the volume and power consumption of optical communication devices are becoming increasingly demanding.The electro-optic modulator made of lithium niobate?LiNbO₃?crystal has been widely used in high-speed optical fiber communication system because of its low power consumption,small volume and high modulation bandwidth.In the process of processing lithium niobate into an electro-optic modulator,the traditional assembly method using artificial six-dimensional alignment coupling has the disadvantages of low efficiency and poor device consistency,and it is difficult to meet the growing demand for optical communication.Therefore,the automatic assembly technology of light modulators made of lithium niobate crystals has become an urgent problem to be solved.Through reading the literature,it is found that the automatic alignment of electro-optical elements based on machine vision at home and abroad are mostly waveguide devices.In this paper,the studies based on the alignment of lithium niobate crystal.By designing the alignment model and using image processing technology reasonably to obtain the edge location of transparent lithium niobate crystal,the efficient alignment of lithium niobate crystal is realized,which has high innovation values and application value.The specific research results and contents are summarized as follows:1.In response to the needs of lithium niobate automatic alignment,the basic principle of coupling alignment is brief introduced.According to the theoretical analysis of coupling loss,a six-dimensional automatic alignment model basing on three-dimensional space position and angle is established,and carried out simulation according to the model.The influence of alignment error on coupling efficiency and coupling loss is analyzed in detail.Through simulation comparison,The results show that the radial deviation of the alignment system is higher than the axial deviation,and the angle deviation is very sensitive to the rotation angle error.2.After the transparent optical communication device is imaged,the edge characteristics are relatively blurry,and it is difficult to accurately obtain the edge characteristics of the device,which reduces the precision of alignment coupling.To solve the problem that the median filter cannot accurately restore the edge characteristics of the image of the transparent optical device in the case of medium and high density noise This paper proposes a kind of median filter based on mutual information.which has better performance than the median filter good,even in the case of high-density noise.Even in the case of high-density noise,it can filter out the noise and accurately restore the transparent light.Device image edge features;the performance of traditional edge detection operators is affected by threshold selection.In this paper,the optimal threshold selection problem of the operator is studied,and the double edge threshold connection is used to improve the traditional edge detection operator,simplify the threshold selection,and obtain the optimal effect.;Because the detection results of traditional edge operators are pixel level,this paper studies the sub-pixel edge detection technology,improves the sub-pixel edge detection algorithm of local area effect,improves the detection accuracy,and makes it more suitable for transparent optical device image edge feature extraction and Precise positioning.3.In view of the problems of long time-consuming manual alignment of lithium niobate crystals,low yield,and poor consistency between the various bodies,an automatic alignment system for lithium niobate crystals is designed in this paper,and introduced the system composition and implementation methods in detail.Firstly,Zhang's calibration method is used to calibrate the camera for the distortion of the optical imaging system;secondly,because the lighting mode is the key to the success of the whole system,this paper tests whether the light source is even in the experiments;finally,the side view and top view of lithium niobate crystal are collected,and sub-pixel edge detection and edge straight line fitting are carried out respectively according to the simulation The whole alignment process is completed by calculating the steps of the moving structure with the combined data.The experimental results show that the total insertion loss of the system less than 3.5dB,which meets the requirements of LiNbO₃ crystal alignment.