2-D wavelength multiplex correlator (original) (raw)

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.

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.

Wavelength-compensated time-sequential multiplexed color joint transform correlator

Applied Optics, 2010

We report a wavelength-compensated three-channel (RGB) joint transform correlator (JTC) for color pattern recognition using a ferroelectric liquid-crystal spatial light modulator (SLM) operating in binary pure phase modulation. We apply a previously reported time-multiplexing technique useful in creating wavelength-compensated diffraction patterns, based on the synchronization of properly scaled diffraction masks with the input wavelength selection obtained by applying a rotating RGB color-filter wheel to an Ar-Kr laser. The application of this technique to a JTC architecture permits real-time color object detection. In order to achieve a high light efficiency for the correlation process, we combine the design of zeroorder joint power spectra in all color channels with the selection of a certain polarization configuration of the SLM, producing a broadband phase-only modulation. Excellent experimental results demonstrating color-object detection are provided.

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.

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.

Coherent optical correlator based on combined halftone and position modulation of light phase

Applied Optics, 2013

Usually only a halftone (grayscale) modulation of light is used to present the processed and reference signals in the input plane of analog coherent optical (ACO) correlators, based on spatially integrating the product of two (processed and reference) signals. The halftone modulation requires two transparencies to record two signals separately, as the desired product of two spatial signals is obtained by sequential location of two spatial halftone records along the light path. Such an optical layout leads to the need for precision mutual alignment of two separate signal recordings. This paper presents a one-stage ACO correlation method based on combined halftone and position modulation of the light phase, which is produced by joint phase recording two signals on a single transparency. The joint phase recording provides the high optical efficiency of informational light modulation, automatically supports the spatial coincidence of corresponding elements of both recorded signals, and provides the same spatial scale for both recordings. The suggested method can also be used for introducing phase weight functions in the schemes of space-time ACO processing of wave signals. Advantages of ACO signal processing methods in comparison with corresponding electronic approaches are briefly noted.

Tunable optical correlator using an optical frequency comb and a nonlinear multiplexer

Optics Express, 2014

We experimentally demonstrate a tunable optical correlator to search for multiple patterns among QPSK symbols in 20 Gbuad stream. We use an optical frequency comb to generate coherent signals and add them coherently using a single PPLN waveguide. Multiple patterns with different lengths are successfully searched on QPSK signals.

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

Multichannel single-output color pattern recognition by use of a joint-transform correlator

Applied Optics, 1996

A novel method for performing color image recognition by the use of the coherent joint-transform correlator is introduced. The input plane of the proposed method is a spatial rearrangement of the separation into color channels of both the color input scene and the color target. This input plane is gray scaled and monochromatic, thus it can be displayed by the use of amplitude spatial light modulators to achieve real-time operation. The system provides a single output-plane result of the optical coherent addition of the separate channels' correlation outputs. At the output plane no electronic postprocessing is needed, and the detection decision is achieved simply by the application of threshold detection. Experimental results and computer simulations are presented to demonstrate the abilities of this system.