## Abstract

The diffractive processes within an optical system can be simulated
by computer to compute the diffraction-altered electric-field
distribution at the output of the system from the electric-field
distribution at the input. In the paraxial approximation the system
can be described by an *ABCD* ray matrix whose elements in
turn can be used to simplify the computation such that only a single
computational step is required. We describe two rearrangements of
such computations that allow the simulation to be expressed in a linear
systems formulation, in particular using the fast-Fourier-transform
algorithm. We investigate the sampling requirements for the
kernel-modifying function or chirp that arises. We also use the
special properties of the chirp to determine the spreading imposed by
the diffraction. This knowledge can be used to reduce the
computation if only a limited region of either the input or the output
is of interest.

© 1998 Optical Society of America

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