The diffractive processes within an optical system can be simulated by
computer to compute the diffraction-altered electric-field distributi
on 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 t
he computation such that only a single computational step is required.
We describe two rearrangements of such computations that allow the si
mulation to be expressed in a linear systems formulation, in particula
r using the fast-Fourier-transform algorithm. We investigate the sampl
ing requirements for the kernel-modifying function or chirp that arise
s. We also use the special properties of the chirp to determine the sp
reading imposed by the diffraction. This knowledge can be used to redu
ce the computation if only a limited region of either the input or the
output is of interest. (C) 1998 Optical Society of America.