基于硅基液晶实现激光投影显示系统匀光整形和散斑抑制

Beam Homogenized Shaping and Speckle Suppression in Laser Projection Display System Using Liquid Crystal on Silicon

激光投影显示通常需要解决光束整形匀化和散斑抑制的问题。基于此,提出利用硅基液晶(LCoS)空间光调制器(SLM)同时解决上述问题的方法。利用衍射光学元件(DOE)精细化设计思想设计所需整形DOE的相位分布,可以同时较好地控制采样点与采样点以外的光场强度分布,将圆形高斯分布照明激光束整形成平顶矩形光场;在不同的初始相位条件下,设计得到的多幅DOE生成具有相同强度分布、不同相位分布的衍射图样。当SLM依次调制出这些衍射图样,通过时间积分将这些衍射图样相叠加,不仅可以进一步提高光斑均匀性,同时还可以抑制散斑。仿真结果表明,通过叠加16幅衍射图样,该方法可使照明光斑均匀性从74%提高到92.57%,屏幕上图样散斑对比度由0.991减小为0.2508。该方法稳定性高,能耗低,且所用器件尺寸小,为微投影显示结构设计提供了有益参考。

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.