AJP	ISSN : 0971 – 3093 Vol 10, No 2, April – June, 2001

Asian
Journal of Physics

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Vol 10, No 2, April – June, 2001

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Vol. 10, No 2 (2001) 239-252

Implementation of a hybrid digital/optical correlator system

R Young*, S-P Huang, G Li, T Koukoulas, D Budgett and C Chatwin
Laser and Photonics Systems Research Group
School of Engineering, University of Sussex, Brighton BN1 9QT, United Kingdom

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Coherent optical correlators, exploiting the Fourier transforming properties of 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 of 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. It is now possible to compute a two-dimensional Fourier transform at video-rates with various digital signal processing chip sets. This allows a hybrid correlator to be developed in which the input scene is digitally Fourier transformed at video-rate and multiple templates are searched during the next video frame interval by optical 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 matching with 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. The hybrid correlator configuration is described, including a discussion of the digital implementation the video-rate FFT, the SLM device used as the digital/optical interface and design of the optical sub-system consisting of miniature collimating and Fourier transform lens systems.
Total Refs : 25