Page 667 - Introduction to Information Optics

11.4. Information Display Using Electro-Optic Spatial Light Modulators 65.1

Fig. 11.27. Real-time optical reconstruction of hologram shown in Fig. 11.26 through three depths:
(a) shows that "V" is in focus, while (c) shows that "T" is in focus; (b) reconstructs the hologram
at a depth between "V" and "T."

as ellipsoids or have rodlike shapes and have a length-to-breadth ratio of
approximately 10 with a length of several nanometers. Liquid crystals are
classified in terms of their phases. In the so-called nematic phase of the crystals,
the molecules tend to align themselves with their long axes parallel, but their
molecular centers of gravities are random. The situation is shown in Fig. 11.28.
Note that the vector h denotes the macroscopic direction of the aligned
nematic liquid crystal molecules and is called a director. The director can be
reoriented by an external electric field. Because of the elongated shape of the
molecules, individual molecules have an anisotropic index of refraction, and the
materials in bulk form, therefore, are birefringent. Denoting n L and m, as the
respective refractive indices of the liquid crystal when an electric field is applied
perpendicularly or parallelly to its director, the amount of birefringence is
«,, — n ±. Birefringence in the range of 0.2 or more is often found, which makes
LCs highly useful.