Stimulated backscattering and nonlinear propagation of optical waves in liquid crystal fibers

his work has been focused on the study of stimulated backward scattering and nonlinear propagation of optical waves in isotropic liquid crystal-cored fibers (ILC-fibers). The nonlinear properties of isotropic phase liquid crystals induced by nanosecond laser pulses are analyzed in the context of nonlinear mode-coupling and propagation in ILC-fibers. The basic principles of nonlinear optics are presented with emphasis on the theories of stimulated light scattering processes using the classical wave equation approach. Among different light scattering processes covered throughout the chapters, stimulated Brillouin scattering (SBS) has been reviewed in a relatively detailed manner. Optical phase conjugation is also included with a brief but complete review of the theory of phase conjugation by degenerate four wave mixing, because a stimulated backward scattering signal is actually a phase conjugation of the input laser field and it is essentially a wave mixing process.;Background knowledge on the principle optical and electro-optical properties of thermotropic liquid crystals, as well as a brief review of principle nonlinear optical properties of isotropic and nematic liquid crystals are also given. The negative thermal-density nonlinearity of isotropic liquid crystals is revisited in detail because it is believed to be the origin of nonlinear wave propagation and self-limiting effect in an ILC-fiber. Theory of optical limiting effect in liquid crystal thin films is briefly given as a comparison to the self-limiting effect in fiber structures.;A systematic study of nonlinear mode-coupling and self-limiting in such guided wave structures is presented. This study includes a preliminary theory, detailed experimental results and discussions. The theory is developed based on the lead that the negative thermal-density nonlinearity of the isotropic liquid crystal core gives rise to basic parameter changes in optical fibers, which in turn effect the mode coupling, power distribution in the core and cladding, and hence the transmission of laser energy. Analytical result of transmitted power versus the input laser power is obtained using a numerical method following the approximations for weakly guiding fibers. A series of experiments have been conducted on stimulated backward scattering and self-limiting in ILC-fibers. Experimental results have shown that the optical limiting threshold for nanosecond laser pulses can be as low as 0.9...