Abstract

Chiral smectic liquid crystal devices are currently used for modulation of complex amplitude, intensity, polarization, and wavelength. For phase-only modulation, both surface stabilized smectic A* and smectic C* devices are characterized by two-level absolute phase, with no intrinsic analog phase capability. Therefore, multiplelevel phase must be achieved by using cascaded single-pass phase shifters.¹ It is most attractive, however, to achieve adequate phase modulation by using a single active layer. A method analogous to the Fox² rotating phase shifter can be implemented by using surface stabilized devices, with the potential for analog phase by using smectic A* materials. This technique was also described by Pancharatnam³ for producing a variable retardation at optical frequencies. We describe a novel reflection-mode phase modulator that utilizes rapid switching smectic A* material to achieve analog phaseonly switching. As the induced phase is twice the reorientation angle of the molecular director, a 2π analog phase requires an unrealistic tilt angle. This problem is overcome by using a resonator structure⁴ to enhance the phase modulation depth.

© 1992 Optical Society of America