Design And Application Research Of The Equal-intensity Beam Splitter Based On Wire Grid Polarizer Array

Laser display has the advantages of high brightness,wide color gamut and long lifetime.The strong coherence of the laser source will lead to laser speckle and reduce the quality of the display image,so laser speckle is the key problem in laser display.There are two main methods to achieve speckle suppression: static speckle suppression and dynamic speckle suppression.The working principle of the dynamic speckle suppression method is to generate different speckle images within the response time of the human eye-brain to achieve speckle suppression.For example,using MEMS galvanometer and rotating scattering plate.Compared with dynamic speckle suppression method,static speckle suppression has no dynamic elements in the optical path.The purpose of speckle suppression is achieved by using diffractive optical elements and Hadamard matrix scattering plates to destroy the coherence of the laser.The existence of external drives will lead to problems such as large volume,high power consumption and noise,so we should vigorously develop static speckle suppression methods and avoid using external drives.According to the static speckle suppression method based on destroying the temporal and spatial coherence of the laser,we designed an equal-intensity beam splitter(EIBS)based on wire grid polarizer(WGP)array,which is composed of two parts: WGPs with different orientations and mirrors.By controlling the distance between the WGPs and the mirrors and introducing sufficient optical path difference,it is concluded that the sub-laser beams are incoherent.By specially designing the orientation of each WGP,the light intensities of the sub-laser beams are equal.After a laser beam passes through EIBS,multiple incoherent sub-laser beams with equal intensity are obtained.Applying EIBS to a laser projection display can achieve speckle suppression and improve the quality of the projected image.The specific research content mainly includes the following two aspects:1.Design of EIBS based on WGP.First,the distance between WGPs and mirrors is designed to ensure that the optical path difference between the outgoing sub-lasers is greater than or equal to the coherent length of the incident laser,so that the emitted sublasers are incoherent.Then the wire grid direction of each WGP is calculated by the transmittance and reflectance formula of WGP obtained through simulation and experiment.After polarization modulation,the light intensity of the sub-laser beams is equal.Finally,a beam of laser passes through EIBS to obtain multiple incoherent lasers with equal light intensity.2.Speckle suppression and laser projection experiment based on EIBS.We built a speckle test system and used EIBS to obtain three incoherent sub-laser beams with equal intensity,and the speckle contrast was reduced from 0.82 to 0.5.Then EIBS is applied to a simple laser projection system.The experimental results show that the quality of the projection image is improved.