Incoherent-only joint-transform correlator

Optical image encryption with Hartley transforms

We propose a new method for image encryption based on Hartley transforms that is a real transform and can be realized by spatially incoherent or coherent illumination. The proposed optical implementation is based on a Michelson-type interferometer in which the pure random intensity is distributed at the Hartley plane in encryption. Computer simulations prove it is possible. A Hartley hologram method is also given and described to resolve the sign ambiguity problem that would be encountered in image reconstruction.

Novel real-time joint-transform correlation by use of acousto-optic heterodyning

To replace the film recording aspect of performing optical correlation, conventional real-time joint-transform correlation (JTC) optical systems make use of a spatial light modulator (SLM) located in the Fourier plane to record the joint-transform power spectrum (JPS) to achieve real-time processing. The use of an SLM in the Fourier plane, however, is a major drawback in these systems because SLMs are limited in resolution, phase uniformity, and contrast ratio, which are, therefore, not desirable for robust applications. We propose a hybrid (optical/electronic) processing technique to achieve real-time joint-transform correlation. The technique employs acousto-optic heterodyning scanning. The proposed real-time JTC system does not require an SLM at the Fourier plane as in other real-time JTC systems. This departure from the conventional scheme is extremely important as the proposed approach does not depend on SLM issues. We develop the theory of the technique and substantiate it with experimental results.

Phase-encoded joint transform correlator to reduce the influence of extraneous signals

A technique to reduce the influence of the dc and the complex-conjugate correlation signals that are inherent in a joint transform correlator is proposed. The key part of this technique is the use of a phase mask. The mask contributes only extraneous signals, so the influence of the signals is reduced. The desirable correlation signal is not affected, and its shape is retained. Computer simulations confirm the performance of the proposed phase-encoded joint transform correlator.

Incoherent fractional Fourier transform and its optical implementation

The fractional Fourier transform is redefined for working with incoherent light. As a real transformation, the incoherent fractional Fourier transform overcomes coherent system disadvantages such as the speckle effect and the need for incoherent-coherent conversion. It also might have some applications for digital image and signal processing owing to its decreased computing complexity. An incoherent optical implementation of the new transform based on the shearing interferometer is suggested. Laboratory experimental results are given.