Optical correlator for industrial applications, quality control and target tracking (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

Real-time optical scanning correlator

Applied Optics, 1984

A real-time large-capacity rapid-scanning optical correlator utilizing a rotating grating concept is described. We have shown that the proposed optical scanning correlator (OSC) is capable of processing large-capacity optical memories with rapid spectrum scanning. With the implementation of a closed-circuit TV system, the OSC system can be applied in real-world situations. We have also experimentally tested the overall correlation sensitivity of the OSC system due to spectrum scanning, object orientation, scale changes, and tilting of the rotating grating. Several experimental results obtained with this proposed OSC system are included.

Optical and electronic design of a hybrid digital-optical correlator system

Optical Engineering, 2002

The design of a digital-optical hybrid correlator is detailed. The optical Fourier transform lens design and mechanical lens housing are detailed as well as the video rate fast Fourier transform digital signal processing (DSP) hardware and overall electronic control. Example results using several different filters and modulation techniques are described.

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.

Engineering implementation of a hybrid optical correlator using SLMs

Optics and Lasers in Engineering, 2004

Optical correlators have been widely used for such applications as automatic target identification, invariant pattern recognition and machine vision. In hybrid optical correlators, Spatial light modulators (SLMs) are used to dynamically update the input and the filter. However, implementation is difficult because of the interference of ''ghost'' images; rigorous requirements for filter registration, accurate and effective filter sizing and complex valued filtering functions. This paper proposes some practical approaches to handle these issues and provides engineering details of how to build a hybrid optical correlator, where a SLM serves as an updateable intensity filter for real-time pattern recognition.

Real-time digital–optical correlator-systems design

Microprocessors and Microsystems, 1999

The systems design of a real-time hybrid digital–optical correlator is detailed. Emphasis is on: partitioning of the digital and optical systems such that the efficiency of the optical image train is maximised; and the parallelisation of tasks within the digital sub-system to maximise throughput. The significance of communication bottlenecks are emphasised in the digital system and the constraints this enforces on the initial selection of DSP devices.

Optical correlator as a tool for physicists and engineers training in signal processing

Sixth International Conference on Education and Training in Optics and Photonics, 2000

In many fields of Physics and Engineering the linear systems are studied. The Fourier Transform is a powerftu[ tool for analyzing their behaviour in terms of the frequency contents, both for the input signal and the output signal. The concept of Fourier Transform is generally intrOdUced by mathematical tools. An optical correlator is a set-up that allows to display the decomposition of a signal (1D or 2D) and the processing of this signal. In this communication we use an optical correlator with two arms that gives the display of the Fourier plane and the final plane simultaneously. In the first arm, we can visualize the decomposition ofthe signal in the Fourier space with the application of a given filter. The effect of the filter on the signal is observed in the second arm. The detection is performed by means of CCD cameras and displayed on the computer monitor. Binary filters help to understand the frequency contents of a signal by substraction of frequencies. Gray level ifiters and complex valued filters allow the synthesis of any transfer function. In particular we show the application to pattern recognition.

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.