GRATING COUPLING TO MIXED-MODES IN A VOLTAGE-CONTROLLED LIQUID-CRYSTAL CELL

The novel geometry of grating coupling to optical modes in a thin, voltage-controllable liquid crystal layer is examined. For a grating, aligned with its grooves twisted out of the radiation plane of incidence, strong transverse electric (s) to transverse magnetic (p) polarization conversion occurs. This leads to peaks in the p to s reflectivity for a fixed wavelength as a function of angle of incidence, or for a fixed angle as a function of wavelength. The application of small voltages to a hybrid aligned liquid crystal layer (which has planar alignment on one surface and homeotropic alignment on the other) then leads to substantial movement of the peaks. This behaviour is quantified and the potential for the use of such a structure in device technology is briefly considered.