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The spatial light modulator (SLM) based on liquid crystal on silicon (LCoS) technology has been widely used in applications such as holography and wavelength selective switches (WSS). Although there is some progress in terms of larger filling factor, improved surface process engineering, the concern lies in the light efficiency of SLM. For the reflectivity, various dielectric layer design have been proposed. This paper presents experimental results on the reflectivity of different filling factors and surface treatments. On the diffraction efficiency, factors such as liquid crystal material, voltage control and fringe field effect are also discussed. Previous research has focus on the phase depth and phase linearity of the SLM, but this paper emphasizes the importance of cell design and voltage control in achieving higher efficiency. The efficiency of blazed gratings with different numbers of steps are compared and intentionally increasing the driving voltage for gratings with a small pitch to compensate for the decrease in sharpness in the fly-back zone are suggested. Then, to estimate the influence of the fringe field effect, four simplified model are analyzed and the calculation result with two panels applied in optical communication in different grating cases, including small pitch grating and larger pitch grating are compared with real test results. The conclusion is valuable for guiding cell design and providing insight into the small pitch large angle blazed grating. Additionally, the diffraction efficiency of a two pi blazed grating is compared for different voltage ranges, starting from the lowest to the highest, with four types of liquid crystal materials filled into identical LCoS cells. Although the changing slope and efficiency values differ, the overall trend remains similar. In conclusion, both material selection and driving voltage control are crucial. A 1550nm LCoS based SLM is designed with more than 80% reflectivity, and the diffraction efficiency is higher than 50% with 4 step single pixel grating and 83% with 16 step single pixel grating.
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