A Microwave Analog of Optical Rotation in Cholesteric Liquid Crystals

A microwave structure was built that is, essentially a scaled up model of a cholesteric liquid crystal. The model consists of a series of thin plastic sheets to which copper wires are attached of dimensions small compared to the microwave length. The direction of the wires on successive sheets varies in a screw-type fashion while the distance between successive sheets and thus the pitch of the screw can be varied. This model shows optical rotation and also, when the period of the screw structure is approximately equal to the wavelength of the microwaves used, the behavior typical of cholesteric crystals, that is, one sense of circular polarization is reflected, the opposite sense is transmitted. Qualitative agreement with experiments in light reflection and transmission using a cholesteric liquid crystal was obtained.