Study On The Diffractive Optical Element To Generate Structured Light For 3D Measurement

Structured light 3D measurement technology,as a new type of 3D measurement technology,plays a very important role in the field of 3D measurement due to its simple structure,high precision,large range and good real-time performance,and widely used in industrial design and production.This paper is based on Fraunhofer far-field diffraction theory,combined with the working principle and design method of Dammann grating,laser beam shaping principle and related algorithms.The phase-type gratings that can generate 3×3,5×5,7×7 and 9×9 dots arrayss are designed respectively,and the experimental verification is carried out by using a liquid crystal spatial light modulator(LCSLM).The numerical simulation and optical experimental results prove that when the diffractive structure is loaded on the liquid crystal spatial light modulator,the laser can clearly reproduce the dots arrays in the diffractive field through the diffractive structure.And the distance between the points in the structured light remains unchanged within a certain range.Compared with the traditional implementation of structured light,this paper optimizes the phase structure of the diffraction grating to achieve higher light energy utilization.The system structure is simple and the adjustment is convenient and flexible.The main work of this paper is as follows:1.In view of the application requirements of the three-dimensional measurement that the structured light spacing is unchanged within a certain range,a series of phase beam splitting gratings are designed using Fraunhofer far-field diffraction theory.Taking the Dammann grating structure as the initial structure,the simulated annealing algorithm(SA algorithm)was used to optimize the structure parameters.The phase distribution value within one period of the grating is optimized according to the expected light energy utilization,spot light intensity inhomogeneity and root mean square error.Phase structures that can form four types of dots arrays of 3×3,5×5,7×7 and 9×9 are designed.2.According to the working principle of the beam shaping diffractive element,the Adaptive-Additive algorithm(AA algorithm)is used to design the diffractive microstructure to generate two-dimensional dots arrays.Perform forward and inverse diffraction transformation on the light field distribution between the output surface and the input surface to inversely solve the phase structure,and continue to optimize and iterate until the expected light energy utilization,point light intensity inhomogeneity and root mean square error are achieved.Phase structures that can form four types of dots arrays of 3×3,5×5,7×7 and 9×9 are designed.Compare the results of the two design approaches and analyze the pros and cons of each.The four-step quantization calculation is carried out on the grating phase structure obtained after the optimization calculation.3.A structured light reproduction experimental system is built,and the structured light reproduction experiment is carried out on the previously optimally designed grating diffraction structure using a liquid crystal spatial light modulator.The light emitted from the laser with the wavelength of 650 nm passes through the phase structure,dots arrays of 3×3,5×5,7×7 and9×9 are respectively generated in the diffraction field.The optical experimental results show that the period of the dots arrays remains unchanged in the diffraction distance from 30 cm to50cm,which achieves the expected result.