Page 419 - Introduction to Information Optics

7. Pattern Recognition with Optics

Fig. 7.41. (a) Input objects, (b) With phase compensation, (c) Obtained from CJTC

output correlation spots as obtained with the preceding phase-conjugation
detection. For comparison, the result obtained without using phase compensa-
tion is shown in Fig. 7.4 Ic; it fails to detect the target object.

7.7.2. WAVELENGTH-MULTIPLEXED MATCHED FILTERING

We discussed Bragg diffraction-limited correlators in Chapter 2, in which we
showed that a reflection-type thick-crystal filter performs better. Added to high
wavelength selectivity, a wavelength-multiplexed matched filter can be realized.
For convenience, we recall this reflection-type correlator (RC) as depicted
in Fig. 7.42, in which q t and q 2 represent the input scene and reference target,
respectively. Besides the Bragg limitation, the PR crystal also imposes a
focal-depth limitation, as given by

f\2
2/(f (7.52)
b
where b is the width of the reference target, / is the focal length, and 1 is the
illuminating wavelength. It is apparent that focal depth within the crystal
should be limited by

(7.53)