Page 82 - Introduction to Information Optics

Chapter 2 Signal Processing with Optics

Francis T. S. Yu
PENNSYLVANIA STATE UNIVERSITY

Optical processing can perform a myriad of processing operations. This is
primarily due to its complex amplitude processing capability. Optical signal
processors can perform one- or two-dimensional spatial functions using single
linear operators, such as conventional linear systems. However, all those
inherent processing merits of optical processing cannot happen without the
support of good coherence property of light. For this reason, we shall begin
our discussion with the fundamental coherence theory of light.

2.1. COHERENCE THEORY OF LIGHT

When radiation from two sources maintains a fixed-phase relation between
them, they are said to be mutually coherent. Therefore, an extended source is
coherent if all points of the source have fixed-phase differences among them.
We first must understand the basic theory of coherent light.
In the classic theory of electromagnetic radiation, it is usually assumed that
the electric and magnetic fields are always measurable quantities at any
position. In this situation there is no need for the coherence theory to interpret
the property of light. There are scenarios, however, in which this assumption
cannot be made; for these it is essential to apply coherence theory. For
example, if we want to determine the diffraction pattern caused by radiation
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