Improved correlation discrimination is achieved by using a fringe-adjusted joint transform correlator (JTC). This technique is found to yield significantly better correlation output than the classical and binary JTC's for input scenes involving single as well as multiple objects. It also avoids the computation-intensive Fourier-plane joint power spectrum binarization processing of a binary JTC. Two optical implementations for the proposed technique are also suggested.

Fringe-adjusted joint transform correlation.

We report on complete wave-front control with amplitude- and phase-modulation liquid-crystal devices (LCD’s) A twisted nematic device is used for amplitude modulation, and an electrically controlled birefringent device is used for phase modulation Because the LCD’s are optically coupled with afocal optics and are driven by individual LCD driver circuits, the amplitude and the phase can be controlled two dimensionally and independently Complex amplitude data are calculated, and on-axis computer-generated holograms are directly recorded Furthermore, we discuss LCD performance requirements for high-quality reconstruction

Wave-front control using liquid-crystal devices.

Optimization of twisted nematic liquid crystal panels for spatial light phase modulation

A modified fringe-adjusted joint transform correlator is proposed that is able to accommodate noise in the input scene. The effect of noise in the input scene on the performance of the joint transform correlator is analyzed and quantified. When the target is embedded in a severely noise-corrupted input scene, it is shown that the proposed modified fringe-adjusted filter joint transform correlator delivers a better correlation performance and the capacity to accommodate this noise than does the fringe-adjusted filter-based correlator. When the power spectra of the input image and the reference image are subtracted from the power spectrum of the joint-input image, it is found that the noise effect on the output plane is independent of the objects in the input scene and originates from the convolution of the reference image and noise in the input scene.

Modified fringe-adjusted joint transform correlation to accommodate noise in the input scene

A range of space-invariant and space-variant holographic optical interconnections are demonstrated with the aid of a nematic liquid-crystal panel that is capable of nearly continuous phase modulation. Results on fan-out, nearest-neighbor/next-nearest-neighbor interconnects, and 8-bit perfect shuffle are presented. The diffraction efficiencies are close to 15% of incident light in all cases.

Reconfigurable free-space optical interconnections with a phase-only liquid-crystal spatial light modulator

A theoretical analysis of a joint transform correlator that uses a 
phase-only spatial light modulator to input joint transform plane intensity data into the second Fourier transform system is presented. It is shown that this correlator produces signals that differ from, but are related to, the mathematical correlation between the test and reference input images. An undesirable characteristic of the correlator is that the form of the output signals depends on both the intensity-to-phase transfer characteristic of the phase modulator and the intensities of the input images. However, apodization of the joint transform intensity distribution by the reciprocal of the intensity distribution of the reference image Fourier transform can overcome this problem, and results in a correlator with narrow matching output peaks and high discrimination, in which the autocorrelation peak can be eliminated. Theoretical results are demonstrated by computer simulation.

Analysis of a joint transform correlator using a phase-only spatial light modulator

A Joint Transform Optical Correlator is described which uses a phase only spatial light modulator for input of the Joint Transform plane information into the second stage of the correlator. This, combined with suitable apodizing of the Joint Transform plane intensity distribution, brings several advantages including high optical efficiency, good signal-to-noise ratio, and the ability to correct system aberrations.

Joint Transform Correlator Using a Phase Only Spatial Light Modulator

Joint Transform Correlator Using a Phase Only Spatial Light Modulator ( OPTICAL COMPUTING 1)

A simple optoelectronic system for high-speed determination of binary phase-only filters for use in an optical correlator is described. Filters determined using the system were implemented using a liquid crystal spatial light modulator in the Fourier plane of an optical correlator. Results demonstrating the operation of the system are presented.

Francis T.J. Johnson

Papers

Analysis of a joint transform correlator using a phase-only spatial light modulator

Joint Transform Correlator Using a Phase Only Spatial Light Modulator

Joint Transform Correlator Using a Phase Only Spatial Light Modulator ( OPTICAL COMPUTING 1)

Opto-electronic determination of binary phase-only filters for optical correlation