Real-time incoherent-to-coherent optical converter

This paper describes the fabrication and demonstration of a real-time incoherent-to-coherent optical converter having applications in image processing systems. Briefly, it utilizes the photoconductivity effect in the single-crystalline electrooptic material, Bi12SiO20to spatially modulate its electrical polarization. An optically absorbed write-in image is stored as an image wise polarization pattern in the device. Readout is accomplished electrooptically by means of the subsequent phase retardation that a polarized beam of coherent light undergoes in passing through the Bi12SiO20. An operating mode for achieving continuous image conversion with high-speed recyclability is described. The following performance characteristics have been demonstrated : write-in intensity of 300 µW/cm²at 400 nm yielded a contrast ratio of 50:1 after 40-ms exposure. When the converter was operated at a frame rate of 10/s, a sampled read-out contrast ratio of greater than 1000:1 was achieved. Resolution in excess of 80 1p/mm has been recorded and read out. The crystal growing and device fabrication methods by which 1-square-in converters have been built and operated are described. Results achieved in using this device to Fourier transform images are also presented.