Binary Light Beam Deflection in Single Crystal Barium Titanate

Abstract

This paper describes a new type of binary electro-optic light beam deflector capable of wide angle deflection. A linearly polarized light beam is deflected by total internal reflection at the boundary of a 90° domain wall wedge in single-crystal barium titanate. The wedge is moved through the crystal by an applied electric field. The crystal is held at a temperature where it is ferroelectric, birefringent, and has tetragonal 4-mm symmetry. The angle of deflection can be set at any angle from 0° to greater than 45°, limited only by the exit aperture of the temperature bath. The electric field required to operate the deflector varies from approximately 200 V/mm at 80°C to less than 50 V/mm at 130°C. It is shown theoretically and experimentally that a threshold field exists for the operation of the beam deflector, and that this threshold field is a function of temperature. The operating frequency of the deflector is limited by heating effects, and the switching risetime is limited by the presence of 180° domain walls. Two possible modes of operation are suggested: (1) continuously operating binary switch, and (2) gated switch.