Command surface controlled liquid crystalline waveguide structures as optical information storage

We report on optical waveguide structures in which light propagates within a liquid crystal (LC) thin film. In this configuration, the orientation, and therefore the optical properties of the LC waveguide structure are controlled by two photochromic command surfaces, consisting of an ultra thin film of a polymer with azobenzene side chains [K. Ichimura, Y. Suzuki, T. Seki, A. Hosoki, and K. Aoki, Langmuir 4, 1214 (1988)]. When exposed to light of appropriate wavelength, the azobenzene side chains undergo a trans↔cis photoisomerization process inducing a commensurate change in the LC alignment and therefore, in the set of refractive indices of the LC film. Using this effect we could reversibly write information into the LC cell. The size of our test structure was in the range of 50 μm. The stored information was read out by optical waveguide microscopy [W. Hickel and W. Knoll, Appl. Phys. Lett. 57, 1286 (1990)]; the storing times were in the range of several hours.