Optimization of the contrast ratio of a ferroelectric liquid crystal optical modulator

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 orientations of the principal axes rotate under the action of a bipolar applied voltage. It is designed to produce a binary intensity modulation when the phase shift introduced between the principal axes is equal to pi radians. 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 uses elliptically polarized light and requires the use of an additional quarter-wave-plate. This situation is experimentally demonstrated using a commercially available ferroelectric liquid crystal cell and two He-Ne lasers with wavelengths of 543 and 633 nm, respectively.