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Coherent Optical Computing Disclosure Number: IPCOM000131366D
Original Publication Date: 1979-Jan-01
Included in the Prior Art Database: 2005-Nov-10
Document File: 17 page(s) / 58K

Publishing Venue

Software Patent Institute

Related People

David Casasent: AUTHOR [+3]


Optical computing has a great many applications in data processing, owing in part to the high speed and parallelism inherent in optical devices.

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Coherent Optical Computing

David Casasent

Camegie-Mellon University

Optical computing has a great many applications in data processing, owing in part to the high speed and parallelism inherent in optical devices.

Optical computing in the broadest sense is the acquisition and (or) manipulation of information by electromagnetic or acoustic waves or rays. It has been the subject of six conferences! since 1972 and has spawned numerous special issues,2~3 survey papers,7~l2 and books.~3~~6 The more important applications of optical computing are those in which information is manipulated or processed (rather than simply acquired) by an optical wavefront in which the input source is coherent laser light. We can achieve several basic operations in such an optical processor, and they have a number of applications in image and signal processing. Hybrid opticaVdigital processors are also of interest, since they are used in the final embodiment of any optical processor.

Basic operations of a coherent optical data processor

The classic operations possible in optical computing systems are the Fourier transform and the linear space-invariant convolution. But a good many additional operations are possible, including spatial filtering, matched spatial filtering, 3D imaging (holography), multichannel ID processing, movingwindow correlation, nonlinear filtering, and linear space-variant processing.

Optical Fourier transform.

Figure 1 is a schematic representation of an optical computer -- that is, a processor operating on coherent (laser) light. The basic operation of a coherent optical processor is the Fourier transform, which is described mathematically as follows. If the transmittance of the input plane Pi in Figure 1 is g(x1,yl), the light distribution incident on P2 in Figure 1 is the exact complex twodimensional Fourier transform G of the input function g i the capital letter denoting the transform). This operation is described for an optical processor by:

?|g 1 Ye | ) (Afar 1fL1 ) ( ) +m = ~j g(XI,yl) exp ~ -- j2~(xlx2 + Y1Y2) | dx1 dy1 -- oo 1fLl

In Equation 1, the transmittance of the input plane Pi is described in terms of spatial (x1,yl) rather than temporal coordinates. The coordinates (u,v) of the FT -- Fourier transform -- plane P2 thus have units of cycles/mm rather than hertz and are related to the distance coordinates (x2, Y2) Of P2 by

u = x211f~,~, u -- Y2/Af~1, (2)

where A is the wavelength of the input laser light used and fL1 is the focal length of the lens L1. If the input data in plane Pi is placed a distance...