The optical properties of grating coupled waveguides are theoretically
modeled and practically demonstrated using nematic and smectic liquid
crystals as thin (0.7 mum) waveguide layers. Voltage induced reorient
ation of the liquid crystal is shown to lead to large changes in refle
ctivity and transmissivity when the angle of incidence initially corre
sponds to a guided mode resonance. Time resolved measurements using th
ese thin cells show that the switching time for the nematic phase can
be faster than the smectic phase.