Reconfigurable multi-beam steering using segmented spatial light modulator for indoor optical wireless communication

Abstract

Spatial light modulators (SLM) are experimentally characterized to be used as reconfigurable-intelligent surfaces (RIS) for smart beam steering of multiple beams for indoor optical wireless communication application. The SLM surface is segmented into two separate regions to perform multibeam steering of two separate incident laser beams to two user devices. Beam steering is achieved here by applying blazed-grating and de-centered lens profile using liquid-crystal-onsilicon (LCoS) phase-only SLM. Experimental measurements of beam steering using blazed grating profiles results in ±3.6 ° steering. The first-order diffraction efficiency decreases from 54.5% to 21.8% for right half and 39.8% to 14.5% for the left half SLM with increase in steering angle as a function of decreasing in blazed grating pitch. The blaze grating-based beam steering is however prone to blind zones in which steering is not possible and the non-linear dependence of the steering angle on grating pitch. To overcome these limitations, we investigate de-centered lens profile as a mechanism to steer the beam. This results in a linear relationship between lens decentring of the lens profile and steering at high resolution. The measured resolution with this technique is ~0. 0018 °/pixel with angular span of ±4.26 °. The first-order diffraction efficiency is found to be varied from 40.1% to 8.5%. We have also designed additional magnification optics to further increase the above steering angle by a factor of 10-times using Zemax-based ray-tracing.