Research On Computer-generated Holographic Display Based On Phase Optimization

Holographic display is known as the most promising three-dimensional display technology in the future because it can truly reproduce the actual three-dimensional scene without wearing any auxiliary device,has a wide range of viewing angles and can provide people with all the psychological and physiological hints needed for three-dimensional perception.The earliest optical holographic display technology uses coherent fringes to record and reproduce three-dimensional scenes.With the rapid development of computer science and technology,computational holographic display technology came into being.Computational holography can produce holograms of any scene or object by means of calculation,which overcomes the disadvantages of the complexity,unstable performance and difficult storage of holograms prepared by optical methods.As the core device of computational holography,spatial light modulator is used to carry and modulate the wavefront information of incident light.At present,it is difficult to achieve simultaneous modulation of amplitude and phase due to the modulation characteristics of spatial light modulator.Therefore,when using a spatial light modulator for holographic display,it is necessary to encode the complex amplitude of the object wave into an amplitude-only or phase-only computational hologram.Pure phase holographic display has attracted much attention from researchers due to its high diffraction efficiency and no twin image.The problem of solving the phase-only hologram can be approximated as an optimization problem that is finding a hologram function that meets the corresponding constraints.However,the loss of amplitude information caused by the traditional phase-only hologram reduces the quality of holographic three-dimensional display to a certain extent,and the phase-only hologram optimization algorithm is used for further optimization.Over the past few decades,phase-only hologram optimization algorithms have emerged.However,some of the current phase-only CGH optimization algorithms have the problems of high computational cost,iterative divergence,slow convergence speed and limited reconstruction quality,which cannot meet the requirements of high-quality holographic display.In view of the above problems,this paper has carried out related research work based on the optimization algorithm of phase-only spatial light modulator and phase-only holographic display:(1)Aiming at the problems of slow convergence speed and limited reconstruction quality of iterative phase retrieval algorithm,an adaptive mixed constraint iterative algorithm is proposed.According to the spatial distribution of the target image in the image plane,the signal region and the noise region are defined,and different adaptive feedback mechanisms are set for different regions according to the iterative process,which constrains the amplitude of the reconstructed image and accelerates the convergence speed of the iterative optimization.A frequency band constraint strategy is introduced on the holographic plane to optimize the edge pixels of the phase-only CGH and compensate for the loss of frequency information.After 100 iterations,the average correlation coefficient of the holographic reconstructed image of the adaptive hybrid constraint iterative algorithm is about 0.9857,and the average peak signal-to-noise ratio is about 31 d B.Numerical simulation and optical experimental results show that the adaptive hybrid constraint iterative algorithm can obtain a pure phase computer generated hologram with higher reconstruction quality in a shorter calculation time,which has important application value for high quality holographic display.(2)Aiming at the problem that the traditional phase mask optimization algorithm is not accurate enough and the reconstruction quality is not high,a feedback phase mask optimization algorithm is proposed.The forward and backward wavefront transmission of the wave field is simulated by the angular spectrum propagation model without paraxial approximation to ensure the accuracy of the calculation.The adaptive feedback mechanism is set up to improve the degree of freedom of iterative optimization,enhance the convergence of iteration and the image quality of holographic reconstruction.Secondly,the layered angular spectrum algorithm is introduced to obtain high-quality holographic reconstructed images while quickly generating holograms,which can be applied to three-dimensional holographic display scenes with high timeliness requirements.