Two-way holographic image storage in photosensitive polymers

We report two-way holographic image storage in azo polymers. Urethane-urea copolymers involve two photochemical reactions, photoanisotropic modificati on and surface modification. We can realize the recording of two holograms: (polarization volume hologram due to the anisotropy of azo side chain and surface relief hologram) that have different types of information. This is possible because the polarization volume hologram is rewritable while the s urface relief hologram is thermally stable. Using the fact that the polariz ation volume hologram acts like a half wave plate, we can separately readou t the different types of information.