  Astigmatic Defocus Sensor is a very simple and easy technique for measuring
the amount of defocus (deviation from the focal plane) present in an optical
beam. The approach uses a cylindrical lens to focus the beam and the measure of
the intensity at the focal plane is used to find out the amount of defocus
present in the beam. In this paper, we provide a theoretical discussion, on the
Astigmatic Defocus Sensor, based on Fourier optics. The theoretical discussion
is validated through simulation results. Two ways to optimize the performance
of the astigmatic defocus sensor were also established. Further, the process of
implementing the Astigmatic Defocus Sensor using computer-generated hologram is
presented.
