Large capacity optical correlator by wavelength-angle multiplexing

Abstract

A novel approach of building a large capacity optical correlator using VanderLugt’s matched spatial filter is introduced in which a tunable dye laser is used as the coherent light source and a rotatable diffraction grating is placed at the input object plane. While sequentially rotating the grating about the optical axis and tuning the wavelength of the dye laser, the input signal spectrum is scanned along trajectories of concentric circles at the Fourier plane. With this 2-D scanning approach, the number of matched filters that can be built at the Fourier plane is greatly increased due to the more effective use of the system space-bandwidth product. In synthesizing the spatially multiplexed matched filters, a monochromatic laser is used instead of a dye laser since the latter generally does not provide adequate coherence length. To accommodate the wavelength shift between the filters recording and signal correlation detection, a compensation technique which includes the scaling of the signal spectrum and the reference beam angle according to the wavelength ratio is utilized during filter fabrication. This large capacity of the optical correlator can be effectively used with high speed and accuracy for multisignal detections with scale and orientation variations. Several illustrating experimental demonstrations of this correlation system using wavelength-angle multiplexing are presented.