Beam steering by combing two binary-phase-modulated FLC SLMs

Abstract

Ferroelectric Liquid Crystal (FLC) Spatial Light Modulators (SLMs) are attractive because of their high switching speed. However, conventional FLC SLMs are only capable of binary phase modulation. This is inconvenient for beam steering since as much as 60% of the incident power is lost to unwanted diffraction orders. To overcome this problem two cascaded FLC SLMs were used in this work. By coherently imaging a 180° binary-phase FLC SLM onto a 90° FLC SLM, with high precision, an effective four-level phase modulator was realized experimentally. Beam steering was demonstrated in the angular range ±10.9 mrad. The angular inaccuracy of the steered beam was found to be about 0.1 mrad, which equals about 25% of the beam diameter. The beam steering device has also been used for tracking experiments.