We describe work over recent years, in particular with the group of Professor Bertero at the University of Genoa and the optical storage group at Philips Laboratories Eindhoven, to increase the resolution of optical imaging systems. In particular, we are interested in scanning systems, such as the confocal microscope, using both coherent and incoherent fluorescent light, and the optical disc. The basic optical imaging principles of both CDs and current DVDs and those of a confocal scanning microscope using coherent illumination are very similar and thus some of our considerations can be applied to both.
We will show how the application of inverse-problem theory allows us to obtain improvements beyond the classical Rayleigh resolution limit for so-called type I systems and also beyond the performance of ideal so-called type II or confocal systems, both with coherent and incoherent light. We have applied these results to achieve robust increases in resolution in high-aperture confocal fluorescence microscopy, using specially calculated image-plane masks, which can reach nearly twice the conventional Rayleigh limit. By the use of such masks in optical disc systems in either the image- or the pupil-plane we find point spread functions, measured in the square-law detector electrical outputs, to be up to twice as sharp as in the present CD/DVD systems. We will discuss present theoretical and experimental work and the potential storage capacity gains.
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