Image processing and coherent feedback with a modified confocal resonator

Confocal resonators used for image processing with coherent optical feedback techniques are limited in space bandwidth product. Positive (negative resp.) feedback in these resonators can only be achieved over an image field of ∼√λƒ around the optical axis. We propose two techniques to overcome this limit. One consists in inserting a phase shifting element into the resonator. An increase in space bandwidth product by a factor of 16 is demonstrated experimentally. The second consists in scanning the resonator length during the recording of the output image.