Threshold light modulator for analog-to-digital image conversion

A threshold light modulator with an internal singular optical feedback is proposed. It consists of a photoconductor and an electrooptic medium between which are located a semitransparent mirror, a biaxial crystal film, and a Polaroid sheet. The proposed modulator is an optical analog of a Schmitt trigger and it can be used to quantize images setting an arbitrarily selected threshold level. In addition, it can function as a parallel digital optical adder. A theoretical analysis is made of the dynamic properties of the threshold modulator, taking into account the real characteristics of its component layers such as the dark current of the photoconductor, the residual transmission of the Polaroid sheet, etc.