Optical correlator as a tool for physicists and engineers training in signal processing (original) (raw)

Current Summary of the Practical Using of Optical Correlators

Acta Electrotechnica et Informatica, 2012

Optical Computing has long been a reportable as the solution of real-time high resolution data processing. Optical processing uses the fastest medium (light) to same calculations as serial electronic systems so process time of these calculations is shorter. The best results in data processing can be obtained by using hybrid, digital-optical, processors as a Optical Correlators which use speed of light (optical part) in cooperation with the electronic components, (digital part). Optical Correlator is optical device to compare two images or two-dimensional data in real time. There are two main types of Optical Correlators, Match Filter and Joint Transform Correlator. In this paper are described both types of correlators and there are shown examples of realized Optical Correlators. Optical Correlators use Optical Fourier Transform to produce transformed image from input image and then second Fourier Transform to obtained correlations in correlation plane. Optical Fourier Transform vs. Fast Fourier Transform process time comparison will be discussed. Main components of Optical Correlators will be presented. Optical Correlators thanks its fast process time and recent advances in liquid crystal technology become more commercially available. Potential applications of these optical processors will be also presented and discussed.

Experimental Systems Implementation of a Hybrid Optical–Digital Correlator

Applied Optics, 1999

A high-speed hybrid optical-digital correlator system was designed, constructed, modeled, and demonstrated experimentally. This correlator is capable of operation at approximately 3000 correlations͞s. The input scene is digitized at a resolution of 512 ϫ 512 pixels and the phase information of the two-dimensional fast Fourier transform calculated and displayed in the correlator filter plane at normal video frame rates. High-fidelity reference template images are stored in a phase-conjugating optical memory placed at the nominal input plane of the correlator and reconstructed with a high-speed acousto-optic scanner; this allows for cross correlation of the entire reference data set with the input scene within one frame period. A high-speed CCD camera is used to capture the correlation-plane image, and rapid correlation-plane processing is achieved with a parallel processing architecture. A.-R. Pourzand, and M. Duelli were with the Institute of Microtechnology, University of Neuchâtel, Rue A-L Breguet 2, CH-2000, Neuchâtel, Switzerland. A. Grattarola and C. Braccini were with the

A multichannel optical correlator

Optics Communications, 1987

A multichannel parallel optical pattern recognition system is proposed. The synthesis of a large capacity matched filter is discussed. The technique uses a phase mask and telescopic arrangement for the mass filter construction. The processing capacity of the proposed optical correlator, which is over 400 times of a single channel system, is evaluated.

Implementation and performance considerations of hybrid digital/optical correlator configurations

Optical Pattern Recognition X, 1999

Two-dimensional correlation between a reference template and an input scene is a powerful pattern recognition technique but is demanding of computational power. Coherent optical correlators, exploiting the Fourier transforming properties of a lens and the capability to impart a phase modulation on a wavefront with an appropriate spatial light modulator (SLM), hold the promise of real-time implementation of two-dimensional correlation for realistic pattern recognition problems. However, their practical use has been delayed in many applications by the lack of availability of suitable SLM devices with the required speed and dynamic range, with different needs for input and frequency plane modulators. It is now possible to compute a two-dimensional Fourier transform at video-rates with various digital signal processing chip sets. Thus a hybrid correlator is proposed in which the input scene is digitally Fourier transformed at video-rate, and multiple templates searched during the next video frame interval by optical mixing and Fourier transformation at a speed at least two orders of magnitude faster than possible with digital methods. In this way, the input SLM is avoided and a precise spectrum is available for subsequent digital or optical mixing with the stored templates. The speed advantage over all-digital processing allows unconstrained pattern recognition problems to be tackled that require many template searches to match the input with a reference function. Different hybrid correlator configurations are considered, together with discussion of the various digital chip sets available to perform the videorate FFT, as well as the SLM devices currently available that are suitable as frequency domain phase modulators.

Fresnel transform-based correlator

Applied Optics, 1997

We present a new technique for information processing using Fresnel transform-based correlation. The main emphasis is on the design of a correlator involving the reference object and its near-field diffraction pattern at an optimized distance. The input-scene image and its diffraction pattern constitute the input pattern of the new correlator. The new technique shows a significant increase in discrimination ability and optical efficiency. Moreover, different encoding methods, such as the phase-only filter or the matched filter, can be used in conjunction with this method. A theoretical analysis as well as examples are given.

Experimental implementation of a Wiener filter in a hybrid digital--optical correlator

Optics Letters, 2001

We present the implementation of a clutter-tolerant filter in a hybrid correlator system. Wiener filters were mapped with a complex encoding technique onto a smectic A ‫ء‬ liquid-crystal spatial light modulator (SLM). The technique overcomes the problem of representing high-dynamic-range data on SLM's that have limited modulation capabilities. It also provides a compact image recognition system that is robust enough for many real-world applications. Experimental results are presented.