Study on Improving Quality of Liquid Crystal Spatial Light Modulator Holographic Reproduction Images by Phase Compensation Method of Reproduction Domain Model

Objective With the continuous development of spatial light modulators, it has been widely applied in many fields, such as light field control, beam shaping, beam deflection, and holographic reproduction, with unparalleled advantages. However, due to limitations of process conditions, it also has many defects. The existence of zero-order spots and multi-order diffraction images caused by its own "black-matrix effect" will exert certain effects on the quality of the output light field, which leads to a low utilization rate of light energy and poor uniformity of reproduced images. However, most studies nowadays are conducted from the perspective of algorithm design to improve the reproduced image quality of holographic display. But when the liquid crystal spatial light modulator (LC-SLM) is employed for holographic display, due to the influence of the "black-matrix effect", the light energy distribution of the reproduced results follows the sinc function distribution, so that the energy distribution of the reproduced images is not uniform. We propose a method to improve the uniformity of the reproduced images through digital blazed grating to deviate the reproduced images and combine with the phase compensation method of the holographic reproduction domain model. This method provides theoretical assistance to improve the quality of reproduction results when LC-SLMs are leveraged for holographic reproduction. Methods Based on the principle of Fresnel hologram calculation, our main design principle is analyzing the influence of zero-order spots and multi-order diffraction images produced by the "black-matrix effect" of the LC-SLM adopted for holographic reproduction on the results. Then with an aim at avoiding the offset of the zero-order spots on the reproduced images by digital blazed grating superimposed on the hologram, and finally to compensate for the uneven distribution of light energy, the phase is compensated according to the proposed reproduction domain model. The steps are as follows. First, the reproduction domain is determined according to the size of the reproduction image, and after loading a certain period of digital blazed grating based on the original design hologram, the compensation amount is inverted according to the light intensity distribution of the reproduction domain reproduction results and then synthesized with the original light wave. Recalculating the hologram can achieve the adjustment of the reproduction results. The quality of the holographic reproduction results is improved by avoiding the influence of zero-order spots on the reproduction results. Results and Discussions Due to the influence of the grid structure when LC-SLM performs holographic reproduction (Fig. 2), when the hologram is loaded, the reproduction results shown in Fig. 4 will have multi-order diffraction images and zero-order spots, which seriously affects the quality of the reproduction results. We propose the phase compensation method of the reproduction domain model (Fig. 6) according to the digital blazed grating deviation from the reproduction image and then compensate the phase according to the light energy of the reproduction domain, which can improve the uniformity of reproduction results. the calculation flow chart is shown in Fig. 8(b). Through the optimization calculation and simulation verification of the phase compensation amount and the construction of the holographic reproduction optical path (Fig. 14), the phase after compensation calculation is loaded onto the SLM for reproduction experimental verification and tests. The experimental results show that the uniformity of the reproduced image after compensation is twice as much as that of the original one, and the utilization rate of light energy is also improved to a certain extent, as shown in Figs. 16 and 17. Conclusions We analyze the light energy distribution of the reproduced image when the LC-SLM performs holographic reproduction, and propose a phase compensation method through the reproduction domain model to compensate for its phase. The results show that after adding a certain period of digital blazed grating to the design hologram, the compensation amount is inverted according to the distribution of light energy in the reproduction domain, and then synthesized with the original light wave and redesigned to calculate the hologram. The uniformity of the reproduced results is twice as much as that of the unimproved one, and the utilization rate of light energy is also improved. The experimental results prove that the method can effectively improve the uniformity and light energy utilization of holographic reproduction results while avoiding the effect of zero-order spots when LC-SLMs are employed for holographic reproduction. The results of this study are useful for improving the quality of output results when spatial light modulators are adopted for light field modulation and holographic reproduction.