An Optically Addressable Transmissive Liquid Crystal Metasurface Spatial Light Modulator

Abstract: Active wavefront control in high-power laser illumination systems is important for technologies such as additive manufacturing, free-space laser communication, and power transmission. Conventional spatial light modulators (SLMs) and mechanical beam-steering devices are unsuitable for such applications as they rely on metal mirrors and electrical contacts which are damaged under high laser irradiances. Here, we report on the design and realization of an optically addressable metasurface liquid crystal (LC)-based SLM for the modulation of high-power transmitted light. Our device uses a photoactive top contact which is optically addressed with a patterned 435 nm laser, creating a transient electrical contact that selectively switches the underlying LC medium. A TiO$_2$ metasurface, resonant in the 915-985 nm wavelength range, is embedded within a thin (~2 $μ$m) LC layer and enables large optical tunability. We demonstrate 90$^\circ$ linear polarization rotation in reconfigurable patterns across a 5x5 mm$^2$ active area with an overall transmittance of >60%. Additionally, we develop a multiphysics approach to simulate transmittance modulation in our device by modeling the LC interactions with TiO$_2$ nanopillars under an applied electrostatic field. This model exhibits good agreement with measurements and provides improved understanding of how LCs interact with both transmitted light and nanoscale metastructures in active devices. We show that our design and fabrication approach can yield high-efficiency transmissive metasurface SLM devices and lay the groundwork for the design of future LC-based active nanophotonics.