Organic Thin-Films For Spatial Light Modulation

Abstract

In the field of image and beam processing, there is great need for devices in which a spatial light-intensity profile such as an image can be recorded and transformed into a transmission or a phase retardation profile. A solution in order to process a still increasing volume of information issued from sensors and data banks is indeed to treat it in parallel. And as information is often available as optical images, a simple idea is to pre-process or to compress it prior to acquisition. This is performed using correlation or novelty filtering techniques [1]. A key device in this respect is the optically addressed spatial light modulator (SLM) [2]. It permits the achievement of input functions in optical image processors based on holographic and Fourier optics. The principle of the SLM process is the same as with the more classical silver-halide photography, except that SLM must perform real-time operations. The drawback of silver-halide photography is indeed the delay, larger than a minute, between exposure and processing. Different techniques, with commercially available devices, already permit the achievement of real-time spatial light modulation. They use a juxtaposition of photoconductor and liquid-crystal films in an artificial photorefractive-like sandwich [3]. However, operation with typical pixel densities of 1µm2, beam surfaces of 1cm2 and processing speeds larger than 100MHz is far from being realised with commercial SLMs. It is the reason for considering the performances offered by organic thin films in this respect [4].