Diffractive and Refractive Liquid Crystal Devices Based on Multilayer Matrices

Abstract

Tunable photonic devices based on self-organized materials like liquid crystals are opening new alternatives for photonic applications, especially when several optical functions can be implemented into one device. Beam steering devices based on liquid crystals usually work either as digital beam steerers (phase gratings), or as analog steerers (prisms). Digital steerers move laser beams to fixed positions; they cannot be tuned continuously. Analog beam steerers produce a continuous angular deviation of laser beams but with very limited deviation angles. In this paper, we developed a tunable grating prism, that can work as a prism and as a phase grating at the same time. This combination of refractive and diffractive effects is achieved with multilayer indium tin oxide (ITO) electrode matrices in a liquid crystal device. This solution is completely different from previous approaches, like blaze gratings or Fresnel configurations - the tunability range here is completely continuous, or completely stepped, or a combination of both at the same time - as there are no interpixels or dead areas in the multilayer configuration. The proposed grating prism is able to deviate a light beam to a large fixed angle by diffraction, and then fine tune the beam over small angle ranges by refraction. Additionally, the light losses produced by ITO diffraction in conventional liquid crystal gratings are significantly reduced using the layered configuration.