LENSLESS JOINT TRANSFORM CORRELATOR

The lensless joint transform correlator optically determines the relat ive x-y position of two pinholes. The pinholes are placed in parallel arms of a Mach-Zehnder interferometer. The Fraunhaufer diffraction pat terns combine to form a joint transform plane. Because of the interfer ence of the two signals, a Fresnel zone is formed in the joint Fraunha ufer diffraction pattern. This is captured and used in a second stage, just as the joint power spectrum is in a joint transform correlator. The joint transform is illuminated with a plane wave, and the output t aken in the focal plane of the Fresnel zone. As with the single-lens j oint transform correlator, the lensless joint transform correlator exh ibits magnification between the input displacement and the output peak displacement. By using the third or fifth order focus of the Fresnel zone, the output resolution can be improved by a factor of three or fi ve in both the x and y dimensions, The output has very good peak-to-no ise ratio and position resolution. A peak-to-noise ratio of 106 dB wit h a resolution of 1.4 mu m are observed when using the fifth order foc us of the Fresnel zone. (C) 1997 Society of Photo-Optical Instrumentat ion Engineers.