| Liquid crystals (LCs) possess effective electro-optic coefficients orders of magnitude larger than other materials used in integrated optics such as lithium niobate or poled polymers. In addition, the relatively simple fabrication of huge arrays of LC-based devices has made them the technology of choice in the flat panel display market. When nematic LC displays were introduced in the 1970's, researchers investigated waveguiding in these material, but found they scattered light too strongly to be of practical use. In 1980, the surface stabilized ferroelectric liquid crystal (FLC) display element was introduced, which used the smectic C liquid crystalline state. The smectic state has a higher degree of ordering than the nematic state, and therefore exhibits far less scattering loss. However, in stark contrast to the large volume of nematic waveguiding research performed following the introduction of the nematic based displays, there have been relatively few studies of FLC waveguides.; This research described an FLC cladded waveguide as well as an FLC film waveguide. The performance of these two structures was calculated, and it was shown that the switching effect of the FLC film waveguide is greater but more sensitive to FLC defects. Several different modulator configurations are described and their performance is modeled theoretically. These configurations include Mach-Zehnder and directional couplers, a cut-off modulator, a deflection modulator, and a prism/total internal reflection modulator. Coupling light into a liquid crystal waveguide is complicated by the thick substrates and covers required to mechanically support the liquid film. Techniques for coupling light into the waveguide are described including techniques that directly excite the mode in the waveguide, and indirect techniques that first excite a mode in an intermediary waveguide (such as a polymer waveguide or an optical fiber), then transfer power to the FLC film. An experimental FLC waveguide modulator was designed and built. It was found that these devices require virtually defect-free uniform alignments because defects in the FLC cause significant scattering. Finally, the surface mode which propagates at the interface including an anisotropic material (like FLCs) was investigated and possible implications to FLC waveguides was discussed. |
