Infrared optical modulators for missile testing

The continued proliferation of imaging infrared ((IR)-R-2) missile systems has created the need for fully representative infrared scene generators. In order to test these (IR)-R-2 systems correctly a very large dynamic range is required of the scene generator. This cannot easily be produced by the standard approach of an array of suspended resistor heater elements. This paper therefore describes the fabrication of infrared optical modulators for use in high dynamic range and high frame rate scene generation. Modulation is produced by the heating of a variable reflectivity coating. This is achieved by coating a suitable substrate with a thin film of vanadium dioxide (VO2) via a reactive sputtering process. VO2 undergoes a semiconductor to metal phase transition at approximately 68 degrees C and the associated change in reflectivity is exploited to create the modulator. The correct stoichiometry of the thin film of VO2 is critical in producing high frame rate devices. Both transmissive and reflective modulators are described. (C) 1998 Elsevier Science Ltd. All rights reserved.