基于像素结构空间光调制器的全息再现像问题研究

基于纯相位空间光调制器的全息显示系统在重构显示时,再现像的视觉效果受到空间光调制器像素结构引起的多级衍射光和多级再现像的干扰。在分析具有有限填充因子空间光调制器的像素结构对再现像影响的基础上,提出了一种提高全息再现像的视觉效果并且再现像成像位置和大小可调节的方法。先加载闪耀光栅到纯相位全息图,其次通过叠加会聚球面波相位,分离再现像与空间光调制器像素结构引起的多级衍射光的聚焦平面的位置,再利用光阑和高通滤波器的共同作用,消除高级衍射光、多级再现像以及零级光干扰对重构视觉效果的影响,最后引入成像透镜,调节再现像的成像位置与大小。建立了一套基于硅基液晶的全息显示系统用于实验验证。实验结果表明,最终的单一再现像清晰且可以方便地调节成像位置和大小。该方法同样适用于各种基于像素结构空间光调制器的全息光学系统。

Research on Issues about Reconstructed Holographic Image Based on a Pixelated Spatial Light Modulator

When utilizing the phase-only spatial light modulator (SLM) for holographic display, the visual impression of reconstructed image is disturbed by multi-order diffraction beams and multi-order reconstructed images because of the pixelated structure of the SLM. After the effects of a pixelated SLM with a limited fill factor on the reconstructed image are analyzed, the method that improves the visual impression of reconstructed image and adjusts the position and size of the image is investigated. Firstly, synthesizing phase-only hologram and digital blazed grating, subsequently adding the phase of the convergent spherical wave, the two focus planes of reconstructed image and the multi-order beams caused by the pixelated structure of the SLM can be separated. Then both the aperture and the high pass filter are used to eliminate the influences of higher diffraction orders, multi-order images and zero order light on the visual impression of reconstructed image simultaneously. Eventually an imaging lens is used to adjust position and size of the reconstructed image. A holographic display system based on liquid crystal on silicon (LCOS) is set up to demonstrate this method. The experimental results show that the final reconstructed image not only has good quality but also has the conveniently adjustable position and size. This method can also be applied to various optical systems based on pixelated SLMs.