Generalized joint fractional fourier transform correlators: a compact approach

Optimization of orders in multichannel fractional Fourier-domain filtering circuits and its application to the synthesis of mutual-intensity distributions

Owing to the nonlinear nature of the problem, the transform orders in fractional Fourier-domain filtering configurations have usually not been optimized but chosen uniformly. We discuss the optimization of these orders for multi-channel-filtering configurations by first finding the optimal filter coefficients for a larger number of uniformly chosen orders, and then maintaining the most important ones. The method is illustrated with the problem of synthesizing desired mutual-intensity distributions. The method we propose allows those fractional Fourier domains, which add little benefit to the filtering process but increase the overall cost, to be pruned, so that comparable performance can be attained with less cost, or higher performance can be obtained with the same cost. The method we propose is more likely to be useful when confronted with low-cost rather than high-performance applications, because larger improvements are obtained when the use of a smaller number of filters is desired.

Nonlinear processing and fractional-order filtering in a joint fractional fourier-transform correlator: performance evaluation in multiobject recognition

We investigated the correlation performance of a joint fractional Fourier-transform correlator (JFRTC) using computer simulation results. We present a mathematical analysis suggesting use of processing techniques based on a nonlinear transformation and fractional-order fractional-power fringe-adjusted filter to attain improved performance in terms of discrimination sensitivity and input space-bandwidth utilization. Optimal noise performance for the JFRTC is predicted in the presence of additive white Gaussian noise. An all-optical implementation scheme based on incoherent erasure in a photorefractive crystal is proposed.

Nonlinear joint fractional transform correlator

An important tool in optical pattern recognition, the joint fractional transform correlator (JFTC), was introduced recently. We analyze the peak properties of fractional correlation (FC) by symbolic derivation and computer simulation. We show that the FC has a maximum correlation peak when the second fractional Fourier transform is reduced to the conventional Fourier transform. We introduce nonlinear operations in a joint fractional transform power spectrum and propose a differential JFTC and a binary differential JFTC. Numerical simulations show that such nonlinear JFTCs exhibit remarkable improvement in correlation peak intensity, discrimination capability, and signal-to-noise ratio. An optoelectronic setup that can implement such nonlinear JFTCs is also proposed.

Perspective projections in the space-frequency plane and fractional Fourier transforms

Perspective projections in the space-frequency plane are analyzed, and it is shown that under certain conditions they can be approximately modeled in terms of the fractional Fourier transform. The region of validity of the approximation is examined. Numerical examples are presented.