Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

The design and preparation of azobenzene-containing polymers showing a large photoinduced change in refractive index, and their applications to rewritable Raman-Nath and Bragg holograms are

reviewed. Optically transparent films with a thickness of >200 μm have been prepared with random copolymers, which contain photoresponsive and amplifying components in the side chain.

Various azobenzene chromophores are used as the photoresponsive component. Cyanobiphenyl and tolane moieties are incorporated as the amplifying component, which enhances the change in

refractive index triggered by the azobenzene. When two writing beams are made to overlap in the film, a periodic change in refractive index is induced, and an incident probe beam is

diffracted at ∼100% diffraction efficiency. The recorded holograms can be erased by thermal treatment or by photoirradiation with a single writing beam. Angular multiplicity is discussed

from the viewpoint of high-density information storage.

Holograms, in which we can observe natural three-dimensional (3D) images without eyeglasses, have been of great interest from the viewpoint of 3D television.1, 2, 3 In addition, other

photonic applications such as holographic memory, optical switch and waveguide have been proposed.3, 4, 5, 6, 7, 8, 9 The holograms can be categorized into two types: (1) Raman-Nath type and

(2) Bragg type. The Raman-Nath hologram recorded in a thin film causes multiple diffraction of an incident beam, leading to low diffraction efficiency (