Beam steering limitation of a Risley prism system due to total internal reflection.

Limitations of beam steering in Risley prisms, induced by total internal reflection, are investigated for the four typical configurations. The incident angles at the exit surfaces of double prisms are calculated by nonparaxial ray tracing and compared with the critical angle. On this basis, the limitations of the opening angle, relative orientation of the prisms, and ray deviation power of the system are derived. It is shown that the ray deviation power reaches its extreme value when the opening angles increase to a certain limit value for a given prism material. As the opening angles exceed the limit value, the prisms' relative orientation is limited. With the increase in refractive index, the limit value of opening angles decreases, while the extreme value of deviation power increases. In comparison to a 21-12, 12-12 configuration, a 21-21, 12-21 configuration has a larger limit value of opening angles and also a larger extreme value (90°) of deviation power, so that it leaves a wider margin for the design of wide-angle beam steering system. The research can afford guidance for prism material and geometry choices in the design of a wide-angle Risley-prism-based beam steering system.