Spatial light modulators (SLMs) are key devices for light field modulation, which can modulate the amplitude, phase or polarization of a free-space light beam. Conventional SLMs mainly include two types: liquid crystal SLM based on liquid crystal substrate and digital micromirror device based on micromirror deflection technology. The most obvious shortcoming of the current SLM is the relative low modulation speed, which extremely limits the further applications in high-speed circumstances.

Here, we demonstrate a one-dimension high-speed programmable SLM based on electro-optic effect using LN thin film. In our SLM device, we achieve a low driving voltage of 10 V and high-speed modulation at 5 MHz. The schematic of the SLM device is illustrated in Fig. 1. The electrode-LN crystal consists of the top electrodes layer, the middle crystal layer and the bottom electrode layer. The top layer has 16 parallel electrodes, each of which is about 1.7 cm long, 425 μm wide, and 70 nm thick. The gap between adjacent electrodes is 213 μm. On account of the weak adhesion strength between gold and silicon dioxide, a 10 nm thick chrome adhesive layer between the gold electrodes and the crystal layer is introduced. The middle crystal layer is consisted of a thin cuboid z-cut LN crystal with a dimension of 1 cm×1.7 cm×100 μm and a thin silicon dioxide (SiO2) layer of 2 μm thick on the top and bottom surfaces of LN. The bottom electrode layer connected with grounded electrode of the support device and it is composed of a gold electrode of 70 nm thick and a 10 nm thick chrome adhesive layer. The incident light can be divided into ordinary light (o-light) and extraordinary light (e-light) due to the birefringence of LN. When different voltages are applied to the electrode-LN crystal, the refractive index of o-light and e-light can change differently, which can change the phase or polarization of the output light. On account of high-speed of the electro-optic effect, our SLM can reach 5 MHz modulation speed.

In addition, we also demonstrate an image transmission experiment, as illustrated in Fig. 2. A 256-color bitmap of a parrot with a resolution of 60×112 pixels is chosen in our experiment. Each pixel value of the image is an integer between 0 and 255, which corresponds to an 8-bit sequence. We separately modulate 8 different channels of the SLM to convert the multi-bit sequence into an encoded optical intensity pattern. The bit error ratio is only 0.067%.

Fig1. (a) and (b) show the top and bottom of the LN-SLM structure. (c) The support device, which is used to hold the electrode-LN crystal. The electrodes on the electrode-LN crystal and the support device are connected by metal wires. (d) The view of the LN thin film with electrodes, which consists of three parts: the top electrodes layer; the middle crystal layer and the bottom ground electrode layer. The detailed structures of these three parts are, respectively, shown in (e), (f) and (g).

Fig2. (a) Encode field pattern with 8-bits coding sequences: (a-1) 10010010; (a-2) 00100101; (a-3) 11011010. (b) The process of transmitting a parrot illustration utilizing the LN-SLM to build a parallel data transmission system.

This research was published in “Xuanchao Ye, Fengchao Ni, Honggen Li, Haigang Liu, Yuanlin Zheng, and Xianfeng Chen, High-speed and programmable lithium niobate spatial light modulator, Optics Letters, 46(5), 1037-1040 (2021)”

Link：https://doi.org/10.1364/OL.419623