Azobenzene-containing polymers: Digital and holographic storage

Films of amorphous high-Tg ate-containing polymers can be used as reversible optical storage materials. Information can be ''written'' by inducing orientation with a linearly polarized laser beam and ''erased'' by restoring disorder with a circularly polarized laser beam. The higher the Tg of the polymer, the higher the stability of the ''written'' information. One important factor affecting the rate of writing and the level of induced birefringence is cooperative motion of neighboring azo groups, due to dipolar coupling taking place between these groups. Volume holograms can be inscribed by this orientation process, but the efficiency is below 1%. Long exposure times to circularly polarized light produce surface gratings of high efficiency (30% is typical), by a mechanism which involves photoisomerization. Such gratings can be used as coupling elements into a film waveguide. These two phenomena are reported on a carbazole-containing polymer of high Tg (160 degrees C). Asymmetrical two-beam gain coupling in the presence and absence of an electric field is demonstrated, allowing for design of optical switches. In principle, a whole photonic device can be designed on a simple polymer film.