Abstract

It has been speculated that homeotropically aligned smectic-A liquid crystals in a cylindrical configuration would prefer the Frank solution with an isotropic core, instead of the non-singular transition found in nematics. However, homeotropic alignment of the smectic-A in a cylindrical structure has never been reported. We have made liquid crystal cylindrical waveguides with low optical loss, which allows us to systematically study the physical, electro-optical and opto-optical properties in these structures. In our study of the smectic-A 8 CB (4 cyano-4′-octylbiphenyl) cylindrical waveguide, we have shown that the homeotropic alignment of the 8 CB molecular director is confined in the radial plane. The free energy diverges at the center of the waveguide to form an isotropic core satisfying the Franksolution. This result is surprising considering the large radius (75 m) of the waveguide. The alignment of the liquid crystals in the waveguide is critical in determining the index profile of the guide since the liquid crystals are highly biréfringent. Modulation of the liquid crystal alignment through electrical or optical fields would result in the modulation of the index profiles and hence the light propagation properties in the waveguides. Unique behaviors under heat treatment and interesting light propagation characteristics in the smectic and nematic liquid crystal cylindrical waveguides have been observed for the first time.

© 1990 Optical Society of America