Page 376 - Introduction to Information Optics

7.1. Basic Architectures 36i

Driving
Mechanism

Input
Direct

Fig. 7.8. An optical-disk based JTC OD.

transforms the JTPS, the resulting correlation is recorded by a CCD camera,
The operation can be seen as the OD advances to the next reference pattern,
and so on, until a match is found.
If binary patterns of 200 x 200 pixels are to be recorded, each pattern will
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occupy an 0.2 x 0.2mm on the OD. If a 0.01 mm spacing is assumed between
adjacent blocks, then more than 27,000 reference patterns can be recorded on
a single 120mm diameter OD. To estimate the sequential access time for a
2
block of 0.2 x 0.2 mm on a standard OD, assume that the average revolution
speed is 1122 r/min and the average radius is 40mm, and that all the images
are scanned sequentially on each consecutive band of the OD. The minimum
access time is approximately 40 ^s. To further estimate the operating speed of
this system, assume that the write side of an optically addressed ferroelectric
liquid SLM is used as the square-law detector, the response time of which is
between 10/is and 155/is. Thus, we see that to complete one correlation
process should take 40-155/ts. This is equivalent to performing more than
6400 correlations per second, a number that can hardly be matched using
current electronic counterparts.
Advances in photorefractive (PR) materials have stimulated interest in
phase-conjugate correlators for pattern recognition. Although SLMs can be
used to display complex spatial filters, current state-of-the-art SLMs are
low-resolution and low-capacity devices. On the other hand, PR materials offer
real-time recording, high resolution, and massive storage capacity; all desirable
traits for multiplexed matched filter synthesis. Thick PR material has high