OPTICAL AXIS GRATINGS IN LIQUID CRYSTALS AND THEIR USE FOR POLARIZATION INSENSITIVE OPTICAL SWITCHING

Abstract

The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ±1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission. Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation. Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm2 power density level, while the diffractive state is restored within ~ 1 s in the absence of radiation. High contrast optical switching is demonstrated with violet as well as green laser beams. A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state. The thinness of OAGs required for high contrast switching ensures high overall transmission of the system. Given also the spectrally and angularly broadband nature of OAG diffraction and the capability of azo LC material systems to respond both to cw as well as short laser pulses makes the optical system under discussion very promising for optical switching applications. Presentation of these results is preceded by an "opinionated" review of prior developments and demystifying of the fabrication technique of high efficiency large area OAGs.