Research On Light Field Focusing And Inversion Algorithm Based On Random Scattering Medium

The Orbital Angular Momentum(OAM)beam has an infinite number of mutually orthogonal eigenstates.The transmission capacity of the communication system can be improved by OAM multiplexing technology to meet the demand of high speed and large capacity of current communication.Focusing and imaging OAM beams through scattering medium is of great significance for space optical communication,underwater object detection and lesions observation in biomedicine.However,in the field of light focusing,it is difficult to focus the target point by scattering the OAM beam through the scattering medium such as ground glass,fog,and biological tissue.In the field of light field imaging,the received light field is difficult to discern the transmission of original information.Although the scattered light carries information about the object,how to extract the information from the scattered light and reconstruct the original object,or"decode" the original object,is a difficult problem in the field of optics.Scattering focusing and imaging in computational optics.Therefore,this study aims to explore the focusing and imaging of light through scattering media.The specific work is as follows:1.By analyzing the characteristics of scattering media,a simulation system model of random scattering focusing based on OAM light field is established,and the process of single point focusing scattering by Wave Front Shaping(WFS)technology is analyzed.Aiming at the defect that the iterative algorithm used in WFS focusing is susceptible to noise interference,a combination of harmony search and simulated annealing algorithm based on superpixel Digital Micromirror Device(DMD)array was proposed to compensate the optical wavefront.Simulation results show that when the number of iterations is 500,the number of populations is 100,and the number of modulation units is 1024,the peak-to-background ratio of 500 can be achieved,which is 200%higher than that of the existing genetic algorithm.When the signal-to-noise ratio of the system is as low as 15dB,the peak-to-background ratio of the proposed algorithm reaches more than 300,which is 200%higher than that of the existing genetic algorithm.The proposed algorithm can improve the focused peak-to-background ratio and resist noise effectively.2.A multi-point focusing scheme of OAM light field based on superpixel DMD is proposed.The optical wavefront is compensated by archive-Nondominated Sorting Genetic Algorithm Ⅱ(archive-NSGA-Ⅱ).The simulation results show that the proposed scheme effectively improves the total peak-tobackground ratio while maintaining the uniformity:the total peak-to-background ratio is 800.2 with a relative standard deviation less than 0.2%at 2 points of focus,the total peak-to-background ratio is 670 with a relative error of 0.6%at 5 points of focus,and the total peak-to-background ratio is 530 with a relative standard deviation of 10%at 52 points of focus.Based on this scheme,a combined multipoint focusing scheme is studied,which achieves 5-point focusing on the target surface by stacking five masks corresponding to single point focusing.The total peak-to-background ratio is 600,and the relative error is 6%.3.This paper studies the inversion technology of the OAM scattered light field through the strong scattering medium,establishes the simulation system of the OAM light field inversion of the strong scattering medium,and proposes an optimal spectrum initialization method based on the scaling idea to invert the scattered light field.Broyden-Fletcher-Goldfarb-Shanno(BFGS)algorithm is used to iteratively optimize the retrieved light field.The simulation results show that when the sampling rate is small,that is,the ratio of the number of sampling modes to the number of preset input modes is y=4,the correlation of light field retrieval can be increased to more than 0.99,and the inversion error can be reduced to less than 10-15,which achieves high fidelity recovery.