Laser Spot Analysis And Research Of Focal Length Testing Algorithm

The focal length parameter is an important index of the laser diode.The purpose of the laser focal length test is to provide a distance reference for the coupling package,thereby reducing the coupling time,increasing the coupling efficiency,and reducing the coupling cost.At present,in the field of focal length testing,the power feedback method is mainly used to perform repetitive search in the three-dimensional plane,the search time is long,and it is easy to fall into local extremes.The thesis aims to improve the accuracy of measurement and reduce the measurement time.Based on the CCD direct method,by analyzing the difference between the laser spot type and the spot image of the adjacent frame,the algorithm of CCD measurement laser focal length based on the gray-scale variance is proposed from the perspective of image gray information.The research work of this thesis is as follows:(1)Research on laser focal length test: The thesis analyzes the existing laser focal length testing algorithm based on power feedback.The problem of focal length testing is that the accuracy is not high and the test time is long.Due to the differences in laser manufacturing processes,the laser beam is not an ideal Gaussian beam.Due to diffraction and different packaging processes,different types of light spots are formed on the CCD photoreceptor surface,resulting in a large error in the CCD beam waist method with the spot radius as the evaluation value.(2)Different types of spot analysis: This thesis analyzes and experimentally tests the laser spot energy distribution.When the laser beam is incident perpendicularly,the distribution of the laser spot energy density is analyzed theoretically,and the CCD is used to sample and measure the spot.Experimental verification.(3)The analysis of focal length test algorithm in this thesis: In order to improve the accuracy and efficiency of the test,this thesis studies the different spot types received on the CCD photo-sensing surface,analyzes the principle of the spot formation and the change law,and proposes the determination algorithm of the focal plane for different spot types.The large and small light spots were analyzed.According to the change of the image spot of their adjacent frames,a focus-following algorithm that uses the second-order derivative of the gray variance as the evaluation function of the large spot and the gray variance function as the evaluation function of the small spot was proposed.Measurements of microscopic spot,non-ideal Gaussian beam spot.Secondly,the repetitive search in the process of focal plane search results in a long time.This paper proposes to use a large-area coarse-collection and small-cell acquisition motion search to collect laser spot images.(4)Experimental results and analysis: This article tests and analyzes the laser to verify the feasibility and stability of the algorithm,and provides a theoretical and practical reference for the testing of laser performance parameters.