Photonics Operating Principles

The Photonics product line is based on the electro-optic principle of switchable halfwave plates. The FLC cell contains a thin layer of FLC material sandwiched between two glass plates. The plates carry transparent electrodes on their inner surfaces that allow an electric field to be impressed on the FLC layer.

The liquid crystal is optically anisotropic and behaves as a uniaxial medium with its optic axis in the plane of the layer. When an electric field is applied, the optic axis assumes a uniform direction throughout the layer. When the polarity of the electric field is reversed, the optic axis rotates 45. This gives the cell exactly two stable states that are determined by the polarity of the applied electric field. By selecting the appropriate thickness of the FLC layer (i.e., where retardance is one-half of the operating wavelength), it functions as an electrically switchable halfwave plate.

The thickness of Displaytech's standard cells is manufactured to give a retardance of 255 nm. Thus, the device is a halfwave retarder at 510 nm. This standard is adequate for most shutter applications in the visible spectrum and for many applications utilizing polarization rotators. The birefringence of the FLC material decreases significantly through the visible spectrum then stabilizes at longer wavelengths. As a consequence, the retardance of a FLC cell of fixed thickness will also decrease with wavelength. Custom cells can be made for precision polarization rotators at wavelengths ranging from 400-1550 nm.