Optically addressed modulator for tunable spatial polarization control

Abstract

We present an optically addressed non-pixelated spatial light modulator. The system is based on reversible photoalignment of a LC cell using a red light sensitive novel azobenzene photoalignment layer. It is an electrode-free device that manipulates the liquid crystal orientation and consequently the polarization via light without artifacts caused by electrodes. The capability to miniaturize the spatial light modulator allows the integration into a microscope objective. This includes a miniaturized 200 channel optical addressing system based on a VCSEL array and hybrid refractive-diffractive beam shapers. As an application example, the utilization as a microscope objective integrated analog phase contrast modulator is shown.

Liquid Crystal Devices for Beam Steering Applications

“…Here, the electrodes are designed to change their resistivity when exposed to the writing beam, allowing a spatially dependent voltage (shown in Figure 5e) to be achieved [110,111]. Alternatively, the writing beam can directly reorient specially designed alignment layers [112] or NLC materials [113][114][115] to create the same effect. The drawbacks of such devices usually lie in the relatively bulky and complicated setups required for the writing beam to reorient the NLC.…”

Recent Progress in Active Optical Metasurfaces

“…The phase of an LC depends on several factors, including the chemical composition of its constituent molecules, its temperature, and critically, the local electrical/magnetic conditions. While some designs explicitly rely on changes in the temperature of the unit cell for tuning, most induce changes on the liquid crystal electrically by applying voltage or by irradiation, often UV . LC molecules will in general align with an impressed electric field, which allows for the material phase to be modified using an appropriately oriented external voltage or by illumination at a specific frequency and polarization.…”

“…Modification of an incident wave's phase is an immediate application of adjustable anisotropy that can allow applications like electrically controlled zoom using an LC layer or temperature tuned laser steering when the LC on dielectric metasurface transitions from nematic to isotropic . Transmissive phase delay has been observed in an LC tuned metasurface which modifies the Tamm‐plasmon resonance between a photonic crystal and metallic film, an optically addressed nonpixelated spatial light modulator that used a reversible photoalignment of LC with a light sensitive azobenzene layer for potential use in phase‐contrast microscopy, and an LC enhanced voltage tunable dielectric metasurface lattice structure, which exhibits polarization dependent electromagnetically induced transparency (EIT) among others. Reflective phase delay has similarly been identified in a temperature or voltage controlled metasurface‐like self‐organizing chiral LC in the visible spectrum .…”