A ferroelectric liquid crystal spatial light modulator encoded with orthogonal arrays and its optimized design for laser speckle reduction

- Speckle is the bottleneck problem in laser displays. Speckle reduction can be achieved by fast vibrating random phase diffusers (RPDs) during the detector integration time. Binary phase diffusers (BPDs) generated from two-level orthogonal arrays were firstly proposed by our group (App. Optics 49(33), 6425-6429 (2010)). BPDs are the optimization over RPDs, where the number of phase patterns realization step can be greatly reduced.
- In this paper, we demonstrate the feasibility of using the ferroelectric liquid crystal spatial light modulator (FLC-SLM) programmed by orthogonal arrays to reduce laser speckle. The FLC-SLM works under “0” and “255” grayscales to generate the “0” and “π” radian phase modulation depths, respectively. The speckle contrast ratio is reduced from Cb = 0.71 before to Ca = 0.1 after driving the FLC-SLM.
- We suggest a transparent FLC-SLM with a passive matrix addressing scheme. The proposed FLC-SLM can be driven electronically with reduced number of controlling electrodes, and only two grayscales are needed. Therefore, it is a great optimization over our currently used FLC-SLM. The proposed FLC-SLM has a higher fill factor compared to our previously reported binary micromirror array (Sensor. Actuat. A-Phys. 210, 209-216 (2014).

In laser projectors, speckle reduction can be achieved by projecting a changing binary phase diffuser onto the screen. Here, we sequentially encoded a commercialized ferroelectric liquid crystal spatial light modulator (FLC-SLM) with the rows of a two-level orthogonal array of order sixty-four, thus obtaining a changing binary phase diffuser. With the help of this binary phase diffuser, the subjective speckle contrast ratio on the screen is reduced from Cb=0.71 to Ca=0.1. Based on the experimental results, a simplified transparent FLC-SLM design is first proposed. This newly designed FLC-SLM has two phase modulation depths and can be driven with the passive matrix addressing scheme. Therefore, the control electronics of the proposed FLC-SLM can be significantly simplified compared to the currently used one.