A High-Capacity Digital Light Deflector Using Wollaston Prisms

A digital light deflector ( D L D ) is a device t h a t can switch a light beam to a number of distinguishable positions and has been previously described by a number of authors. 1 - 4 Such a device can be made from a number of modulators and passive deflectors. T h e modulator, for this application, is one t h a t is capable of switching the sense of polarization, and the deflector unit is a passive element which has different optical p a t h s corresponding to the two senses of polarization. A basic unit of a D L D is shown in Fig. 1. It has been previously 1-1 · t PASSIVE DEFLECTOR Fig. 1--Basic unit in a digital light deflector. 057 958 T H E BELL SYSTEM TECHNICAL J O U R N A L , M A Y - J U N E 19(i7 shown 1 - 3 t h a t n such units in series can generate 2" distinguishable positions. A modulator can be made from any material which can become birefringent with the application of an external signal. A minimum of 7T retardation is needed in order to switch t h e sense of polarization. Examples of modulators t h a t have been considered for this application are Kerr cells, 5 stressed plate shutters, 8 and crystals such as K D P 3 and KTN 7 - 8 which exhibit an electro-optic effect. T h e Kerr cells, although very fast, cannot be used at high repetition rates because of heating difficulties. Stressed plate shutters, since they depend on mechanical strain, are limited to lower frequencies. T h e most attractive modulator materials are the electro-optic crystals and are t h e ones t h a t are being seriously considered for the D L D .