Optoelectronic calculation and calculated holograms

Optoelectronic computing, often referred to as optical information processing (OIP), has been the subject of very active research worldwide, as it is based on the very promising idea of using the speed and parallelism properties of light to process information at very high speed. In the case of optical processing, the information will be optical information in the form of a one-dimensional optical signal or image. Compared with electronic processors, most of which process information in series, optics have the advantage of inherent and natural parallelism, enabling parallel processing of very large quantities of data in real time. What's more, the Fourier transform is performed very simply by a converging lens. All these properties are major advantages of optoelectronic computers for image processing, correlation pattern recognition and free-space optical interconnections. They also explain why, since the 1960s and the advent of the laser, optical processors have been the subject of very active research worldwide, generating a great deal of enthusiasm and promising experimental achievements, particularly between 1980 and 2005. Today, advances in computing power and memory capacity mean that the prospect of an all-optical signal processor is no longer a real possibility, but that the presence of optics in electronic computers is increasingly a necessity. Today, these 50 years of research in a wide variety of fields - processor architecture, signal processing algorithms, optoelectronic components (laser diodes, spatial light modulators, detectors, non-linear components, etc.), diffractive optical elements, imaging techniques, to name but a few - are contributing to the success of photonics and the emergence of new fields such as nanophotonics and biophotonics.

Computed holography originated in the same 1960s as optoelectronic computing, and has long been associated with it as a component of optical processors. Like optically recorded holograms, computer-calculated holograms aim to record and reconstruct a wavefront. However, as the restored wavefront is calculated and encoded on the surface of the calculated hologram, the latter allows much greater flexibility. A wide variety of complex wavefronts can be generated, making the calculated hologram - currently known as a Digital Diffractive Optical Element - the ideal optical component for light manipulation. Calculated holograms have now reached a stage of maturity, both in terms of calculation algorithms and manufacturing methods, which are borrowed from microlithography. Applications are extremely varied, spanning the industrial, scientific and consumer sectors. The production of components with sub-wavelength structures is currently opening up new application prospects.

This article is therefore divided into two...