Optimization of optical switching with a ferroelectric liquid crystal modulator

Abstract

In this work we present a simple method for the characterization of a ferroelectric liquid crystal (FLC) optical modulator and the optimization of its contrast ratio. This device acts as switchable wave-plate, where the orientation of the principal axes rotates under the action of an applied bipolar voltage. It is designed to produce a binary intensity modulation when the phase shift introduced between the principal axes is equal to 180 degrees (half wave-plate). We present a simple technique to optimize its response when the phase shift differs from this ideal value, in order to produce a highly contrasted intensity modulation. The technique involves using elliptically polarized light and requires the use of an additional quarter wave-plate in front of the FLC modulator. We represent the polarization transformations on the Poincaré sphere to provide a physical explanation of the FLC optical performance, both in the standard operational mode as well as in the optimized configuration for non-ideal phase shifts. These situations are experimentally demonstrated using a commercially available ferroelectric liquid crystal cell and two He-Ne lasers with wavelengths of 543 nm and 633 nm respectively.