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Optical Computing: A 60-Year Adventure Pierre Ambs To cite this version: Pierre Ambs. Optical Computing: A 60-Year Adventure. Advances in Optical Technologies, 2010, 2010, pp.1-15. 10.1155/2010/372652. hal-00828108 HAL Id: hal-00828108 https://hal.archives-ouvertes.fr/hal-00828108 Submitted on 30 May 2013 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Hindawi Publishing Corporation Advances in Optical Technologies Volume 2010, Article ID 372652, 15 pages doi:10.1155/2010/372652 Research Article Optical Computing: A 60-Year Adventure Pierre Ambs Laboratoire Mod´elisation Intelligence Processus Syst`emes, Ecole Nationale Sup´erieure d’Ing´enieurs Sud Alsace, Universit´e de Haute Alsace, 12 rue des Fr`eres Lumi`ere, 68093 Mulhouse Cedex, France Correspondence should be addressed to Pierre Ambs, [email protected] Received 15 December 2009; Accepted 19 February 2010 Academic Editor: Peter V. Polyanskii Copyright © 2010 Pierre Ambs. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Optical computing is a very interesting 60-year old field of research. This paper gives a brief historical review of the life of optical computing from the early days until today. Optical computing generated a lot of enthusiasm in the sixties with major breakthroughs opening a large number of perspectives. The period between 1980 and 2000 could be called the golden age with numerous new technologies and innovating optical processors designed and constructed for real applications. Today the field of optical computing is not ready to die, it has evolved and its results benefit to new research topics such as nanooptics, biophotonics, or communication systems. 1. Introduction and the future of electronics. Caulfield wrote in 1998 an interesting and enlightening paper on the perspectives in The knowledge of some history of sciences is useful for optical computing [7] where he discusses this competi- understanding the evolution of a research domain, its tion between optics and electronics and shows that there successes and failures. Optical computing is an interesting were three phases, first “ignorance and underestimation”of candidate for a historical review. This research field is electronics then “awakening and fear inferiority” and now also named optical information processing, and now the “realistic acceptance that optical computing and electronics are terms of information optics or information photonics are eternal partners”. frequently used, reflecting the evolution of the domain. The purpose of this paper is to show a short history of Optical computing is approximately 60 years old and it is optical computing from the origin until today. This historical a well-defined domain with its own specialized conferences, overview will show that the first years generated a lot of sections in the scientific journals and its own research enthusiasm regarding the potential of optics for information programs and funding. It was also very active worldwide and processing, this period was followed by a small slowdown therefore it is impossible in the frame of a paper to describe before the golden age that started around 1980 until the all the research results. Numerous books were written on the beginning of the new century. subject, for example, the following books describe the state of Section 2 presents the basic principles of optical infor- the art of optical computing at the time of their publication mation processing, Section 3 gives a historical review of in 1972 [1], in 1981-82 [2, 3], in 1989 [4], and in 1998-99 the research from the first years until 1980 and Section 4 [5, 6]. describes the research activity from 1980 to 2004. Section 5 Since optical computing is such a well defined field over shows the evolution of the domain until today. such a long period of time, it is interesting to study its evolution and this study can be helpful to understand why some research domains were very successful during only a 2. Fundamentals of Optical Information limited period of time while other have generated numerous Processing applications that are still in use. From the beginning there was a lot of questioning about the potential of optics for Optical information processing is based on the idea of using computing whereas there was no doubt about the potential all the properties of speed and parallelism of the light in 2 Advances in Optical Technologies order to process the information at high-data rate. The most promising application of optical processors and there- information is in the form of an optical signal or image. fore the following two architectures of optical correlators The inherent parallel processing was often highlighted as were proposed. one of the key advantage of optical processing compared to Figure 2(a) shows the basic correlator called 4-f since the electronic processing using computers that are mostly serial. distance between the input plane and the output plane is Therefore, optics has an important potential for processing four times the focal length of the lenses. This very simple largeamountofdatainrealtime. architecture is based on the work of Marechal´ and Croce [9] The Fourier transform property of a lens is the basis in 1953 on spatial filtering and was developed during the of optical computing. When using coherent light, a lens following years by several authors [10, 11]. performs in its back focal plane the Fourier transform The input scene is displayed in the input plane which of a 2D transparency located in its front focal plane. Fourier transform is performed by Lens 1. The complex The exact Fourier transform with the amplitude and the conjugated of the Fourier transform of the reference is phase is computed in an analog way by the lens. All the placed in the Fourier plane and therefore multiplied by the demonstrations can be found in a book published in 1968 by Fourier transform of the input scene. Lens 2 performs a Goodman [8] and this book is still a reference in the field. second Fourier transform that gives in the output plane The well-known generic architecture of optical processors the correlation between the input scene and the reference. and the architectures of the optical correlators will be Implementing a complex filter with the Fourier transform presented successively. of the reference was the main challenge of this set-up, and Vander Lugt proposed in 1964 to use a Fourier hologram of the reference as a filter [12]. Figures 2(b) and 2(c) show 2.1. Optical Processor Architecture. Thearchitectureofa respectively, the output correlation peak for an autocorrela- generic optical processor for information processing is given tion when the correlation filter is a matched filter and when in Figure 1. it is a phase only filter [13]. The processor is composed by three planes: the input In 1966, Weaver and Goodman [14] presented another plane, the processing plane, and the output plane. optical correlator architecture, the joint transform correlator The data to be processed are displayed in the input (JTC) that is represented by Figure 3(a). The two images, plane, most of the time this plane will implement an the reference r(x, y) and the scene s(x, y)areplacedside electrical to optical conversion. A Spatial Light Modulator by side in the input plane that is Fourier transformed by (SLM) performs this conversion. The input signal can be the first lens. The intensity of the joint spectrum is detected 1D or 2D. An acousto-optic cell is often used in the case and then its Fourier transform is performed. This second of a 1D input signal and 2D SLMs for 2D signals. The Fourier transform is composed by several terms including different types of 2D SLMs will be described later. In the the crosscorrelations between the scene and the reference. early years, due to the absence of SLMs, the input plane Using a SLM this Fourier transform can be implemented consisted of a fixed slide. Therefore the principles and optically as shown on Figure 3(a). Figure 3(b) shows the the potential of optical processors could be demonstrated output plane of the JTC when the reference and the scene but no real-time applications were possible, making the are identical [13]. Only the two crosscorrelation peaks are processor most of the time useless for real life applica- of interest. To have a purely optical processor, the CCD tions. camera can be replaced by an optical component such as an The processing plane can be composed of lenses, optically addressed SLM or a photorefractive crystal. One of holograms (optically recorded or computer generated) or the advantages of the JTC is that no correlation filter has to be nonlinear components. This is the heart of the processing, computed, therefore the JTC is the ideal architecture for real- and in most optical processors, this part can be performed at time applications such as target tracking where the reference the speed of the light. has to be updated at a high-data rate. A photodetector, a photodetector array or a camera com- Figures 2 and 3 represent coherent optical processors. poses the output plane where the results of the processing are Incoherent optical processors were also proposed: the infor- detected.

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