Optical disk readout analysis using an extended point-spread function

Abstract

troduction The scalar diffraction theory represented by the Hopkins’ method has been widely used for simulating the readout signals from optical pickups. This method is based on the partially coherence theory, and was well improved by previous works, for example the classification into the two types of scanning microscopes,2< extension for MO pickups, and so on. Furthermore, various super-resolution techniques and the crosstalk reduction technique were analyzed theoretically by using this scalar diffraction theory. On the use of this theory, the light amplitude distribution on the exit pupil of the objective lens or the modulation transfer function (MTF) is usually employed for the explanation of the functions of optics. Meanwhile, the method we present here is based on the work by Velzel. His method is basically an approximation of the scalar theory and concentrates on the point spread function (PSF) of the illumination optics in the pickup. And it provides a simple and practical way for computations and understanding of the readout process. For example, Kubota presented in his study the influences of wave front aberrations on the readout characteristics by using jitter calculations, in which the readout signal was calculated as a convolution of the pits on the disk and the PSF. In this paper, we present a method using an extended point spread function (EPSF) that can be applied for the case when the detector has an arbitrary shape and information pits are recorded on a groove. After that, two examples, differential phase detection (DPD) method and jitter analysis of the readout signal from pits on a groove, will be shown. Although our method is also an approximation, physical and intuitive considerations will be acquired even under such complex cases.