An optical CCD convolver

Some experimental and practical considerations of performing convolution or transversal filtering with charge-coupled devices (CCD's) using optical inputs are described. The basic principle involves shining light from a signal-modulated light-emitting diode (LED) onto an optical mask which controls the amount of light reaching the various CCD electrodes. The experimental results for a 91-tap Hamming window are presented. The relative advantages of using this approach as a means of obtaining fixed tap-weight transversal filters are discussed in comparison with the split electrode CCD filter. It is shown that a compact lens free optical signal processor is possible, using standard imaging structures. Although there is a disadvantage in terms of the need for an LED and current driver, this may be outweighed in certain contexts by improvements in linearity, intermodulation, dynamic range, and the scale of processing which is possible.