Prewritten data storage medium and optical scanning device therefor

Abstract From the Canadian patent

Data is stored on a prewritten optical data storage medium along a track made up of adjacent elements. A scanning light spot focussed on the medium has to be able to access any element to write read or, modify data there. Prewritten patterns on the medium define a radial graduation scale that is analysed by an optical scanning device using a sampling technique to determine the absolute position of the scanning light spot relative to the track elements, the only material representation of which may be discrete prewritten elements. The technology is particularly applicable to very high density optical memories using a prewritten disk written by thermo-optical interaction with an intensity …