Visible-to-infrared image converter for dynamic infrared target simulation applications

A visible-to-infrared image converter based on the Hughes 2-in. liquid-crystal light valve¹ is under development at Hughes Research Laboratories. The system is designed to operate in the 2- to 5-μm and 8- to 12-μm spectral ranges. The device consists of an IR-visible transparent input substrate electrode; an IR-transparent, visible-sensitive photoconductor (CdS); and a thin layer of liquid crystal acting as the light modulator medium. The readout window is transparent in the IR range used. The required IR dynamic scenery, generated for convenience in a visible form (e.g., on a CRT), is projected onto the input window, thus activating the photoconductor. This spatial voltage pattern of the required image is transferred to the liquid crystal, thus converting the image to a birefringent spatial modulation. The polarized infrared readout beam projected through the light valve is modulated as it passes through the liquid crystal. The latter operates in the 90° twisted nematic mode. The required IR scenery is then formed as the polarization-modulated IR beam passes a 90° cross-polarizer. The device offers the advantages of (1) maximum flexibility in presenting versatile dynamic IR sceneries and (2) high resolution and contrast. Good performance was demonstrated by a device operating in the 2- to 5-μm range. The proposed approach strongly benefits from the technology that has been developed for the visible-to-visible liquid-crystal light valve over the last few years.