Abstract

We present a light modulator fabricated with a diffraction grating. Liquid crystal is filled in the grooves of the fine grating base, and it works as a phase tunable material. In the turn-off state, liquid crystal is forced to orient parallel to the grooves due to the geometry and shows an extraordinary refractive index which is different from that of the groove–grating base. In this state, we can minimize the zeroth-order diffracted light using an optimally designed groove–grating shape. When a voltage is applied to the liquid crystal in the turn-on state, the liquid crystal turns itself perpendicular to the base and shows the ordinary refractive index, which almost matches that of the groove–grating base. The incident light is fully transmitted as zeroth-order diffracted light. Forced orientation causes a fast turn-off transition. As the groove pitch is decreased, turning-on becomes slow and turning-off becomes fast. We have obtained more than 90% transmittance including surface reflection loss of the device. The extinction ratio is as muchas 100. When the switching voltage is 15 V, turn-on time is <100 μs, and turn-off time is several milliseconds.

© 1987 Optical Society of America