Beam homogenized shaping and speckle suppression in laser projection display system using liquid crystal on silicon

Laser projection display usually need to solve the issues of beam shaping homogenization and speckle suppression. This paper proposes a method that liquid crystal on silicon (LCoS) spatial light modulator (SLM) is used to solve the problems simultaneously. The idea of fine design for diffractive optical element (DOE) is used to design phase distribution of DOE that needs to be shaped, which can control the intensity distribution of sampling points and other points. The circular Gaussian laser illumination beam is shaped into a flat-top rectangular profile. Under different initial phase conditions, the designed DOEs generate diffraction patterns with the same intensity distributions and different phase distributions. When diffraction patterns are modulated by SLM and they are overlapped by time integral, the uniformity of illumination spot can be improved, and image speckles can be suppressed. The simulation results show that by overlapping 16 diffraction patterns, the proposed method can improve the uniformity from 74% to 92.57%, and reduce the speckle contrast of the screen from 0.991 to 0.2508. The proposed method has high stability, low power consumption and small size, which provide good reference for display structure of pico-projector. © 2016, Chinese Lasers Press. All right reserved.