Mu Cheng-Ta, Chen Cheng-Huan
Appl Opt. 2020 Aug 20;59(24):7153-7159. doi: 10.1364/AO.394650.
Computer-generated holograms (CGHs) have their phase and/or amplitude modulation pattern calculated rather than recorded as for traditional holograms. In practice, the CGH devices are normally pixelated, no matter if they are passive or active ones. In many cases, the reconstruction light illuminates on the CGH devices obliquely, and the pattern generated on the target plane will be distorted from the originally desired one, even if the modulation on the CGH devices has been calibrated for the corresponding illumination angle in CGH calculation and optimization. The distortion is purely related to the diffraction behavior resulting from the geometry of the pixel on the CGH, and therefore diffractive distortion has been coined for this specific phenomenon. In this paper, quantitative analysis of diffractive distortion and a corresponding scheme for correction have been given based on scalar diffraction theory. The proposed concept is that the distortion of the reconstructed image is proportional to the distortion of the signal window. An experiment has been conducted with a phase-type liquid crystal on silicon spatial light modulator (SLM). Both the distortion analysis and the correction scheme have been verified quantitatively for various illumination angles and the direction of the reconstruction light.
计算机生成全息图（CGH）的相位和/或幅度调制图案是通过计算得出的，而不是像传统全息图那样记录下来。实际上，CGH器件通常是像素化的，无论它们是无源还是有源器件。在许多情况下，重建光以倾斜角度照射在CGH器件上，即使在CGH计算和优化过程中已针对相应的照明角度对CGH器件上的调制进行了校准，目标平面上生成的图案仍会与最初期望的图案产生偏差。这种偏差纯粹与CGH上像素的几何形状所导致的衍射行为有关，因此这种特定现象被称为衍射畸变。本文基于标量衍射理论对衍射畸变进行了定量分析，并给出了相应的校正方案。所提出的概念是，重建图像的畸变与信号窗口的畸变成正比。利用硅基液晶空间光调制器（SLM）进行了实验。针对各种照明角度和重建光方向，对畸变分析和校正方案都进行了定量验证。
