Widely tunable chiral nematic liquid crystal optical filter with microsecond switching time.

A wavelength shift of the photonic band gap of 141 nm is obtained by electric switching of a partly polymerized chiral liquid crystal. The devices feature high reflectivity in the photonic band gap without any noticeable degradation or disruption and have response times of 50 µs and 20 µs for switching on and off. The device consists of a mixture of photo-polymerizable liquid crystal, non-reactive nematic liquid crystal and a chiral dopant that has been polymerized with UV light. We investigate the influence of the amplitude of the applied voltage on the width and the depth of the reflection band.