Influence of the spatial frequency on the diffractive optical elements fabrication in PDLCs

Abstract

Photopolymers are classical holographic recording materials. Recently their chemical composition and the fabrication techniques have been optimized for many new applications such as interconnectors, solar concentrations, 2-D photonic structures, or wave-guides. Their potential usefulness has been drastically increased by the introduction of dispersed liquid crystal molecules; these components can be concentrated in the non-exposed zones of the material by a photopolymerization induced phase separation process (PIPS). Therefore, by combining polymer and dispersed liquid crystal (PDLC) has emerged as a new composite material for switchable diffractive optical elements (DOEs). Parallel to the material advances some techniques have been proposed to record very low spatial frequencies DOE’s. Different researchers have reported proposes to record DOE like fork gratings, photonics structures, lenses, sinusoidal, blazed or fork gratings. In this work we have studied the behavior of a PDLC material to record DOE’s with different spatial periods: from 1 μm, using holographic technique, to more than 200 μm, Liquid Cristal on Silicon (LCoS) display working in mostly amplitude mode as a master. Due to the improvement in the spatial light modulation technology and the pixel miniaturization, this technique permits us store gratings with spatial frequencies until few microns. Additionally, this technology permits us an accurate and dynamic control of the phase and the amplitude of the recording beam. In particular, for our case, to generate the blazed gratings, we use an LCoS-Pluto provided by Holoeye with a resolution of 1920x1080 (HDTV) pixels and a pixel size of 7.7x7.7 m2.