基于位相分布限制衍射光学元件的散斑抑制方法

Speckle Reduction Method with Phase Range Limited Diffractive Optical Element

根据散斑产生的机理,利用像素点之间干涉的概念,提出了通过限制光场的位相分布范围来抑制投影图像中散斑对比度的方法.在部分发展散斑的条件下,推导了位相均匀分布情况下的散斑对比度公式,揭示了当相位分布范围在0.6π~2π之间时,散斑对比度随相位分布范围的变化而震荡变化,当把相位分布范围限制在0.6π以下时,散斑对比度会随相位分布范围的减小而迅速下降.建立了理想仿真模型和实际仿真模型来验证该方法的正确性和可行性.在理想仿真模型中,当位相分布范围从2π变到0,所得散斑图样对比度从66.44%降到0;在实际仿真模型中,模拟了实际激光投影系统的光路结构,并运用了两片衍射光学元件,一片用于激光整形匀化,一片用于光场的位相分布范围限制,散斑图样对比度从92.78%降低到2.09%.该方法稳定性高、耗能低、使用元件尺寸小,为全息投影显示的散斑抑制提供了参考.

According to the generation mechanism of speckle, utilizing the concept of interference on a pixel point, a speckle suppression method was proposed which can reduce the Speckle Contrast （SC） of the projection image by limiting the phase distribution range in the optical field.The SC formula is derived in the uniform interval phase range for partially developed speckle conditions, showing that when phase distribution rang is limited between 0.6π and 2π, a quasi-oscillatory behavior of SC appears with the change of phase distribution rang;and SC will be falling rapidly with the lessening of phase distribution rang when phase distribution rang is smaller than 0.6π.An ideal simulation model and a real simulation model were established to verify the correctness and feasibility of this method.In the ideal simulation model, the SC can be reduced from 66.44% to 0% as the phase range limitation varying from 2π to 0.In the real simulation model, the actual structure of the optical path was simulated in the laser projection system, there are two diffractive optical elements in the real simulation model, one is for laser shaping, and the other one is for limiting the phase range of optical field, the SC is reduced from 92.78% down to 2.09% in the real simulation model.The proposed approach presents a significant reference with a low power consumption and a stable display architecture for speckle suppression application in holographic display.