High tilt angle flc mixture for tir switching devices

Abstract

The invention provides a series of ferroelectic smectic liquid crystal compounds, FLC, of wide tilt angle and mixtures formulated from them that are useful for high speed modulation or switching of optical radiation. Such FLC mixtures are useful in total internal reflection, TIR switching devices. In such TIR switches, an applied DC voltage rotates the molecules through about a 90.degree. angle which changes the perceived refractive index at the FLC layer and permits rapid optical switching. For an FLC crystal material to be useful in such a device it must possess a value of molecular tilt angle .theta. of approximately 45.degree., since the dipole molecule rotates through an angle of about 2 .theta. upon application of a DC field to the cell. This requirement for a large molecular tilt angle greatly limits the compounds and mixtures thereof which can be employed in such TIR devices. The smectic FLC compounds and mixtures thereof of the present invention provide for TIR switches that exhibit high contrast ratios ( <1,000:1). They can also provide in such switch, 2-position bistable beam deflection. That is, if the electric field of the TIR switches is shut off, the smectic FLC compounds will hold the molecular tilt angle existing at that time without requiring an applied electric field (to hold such pattern) unlike their nematic LC predecessors.