Optical data storage tracking system

DETAILED DESCRIPTION An optical data storage system comprises an optical data storage medium, an optical head and a fixed optical system.
The optical head contains a first lens located along an optical axis for focussing light to the medium.
The fixed optical system comprises a laser for generating a beam of light, a fine tracking system and a second lens.
The second lens is located along the optical axis and images light from a first point to a second point proximate the aperture of the first lens.
The fine tracking system includes a means for converging light from the laser to a focal point and means for displacing the focal point a distance from the optical axis such that from the perspective of the second lens, the central axis of the beam of light always passes through the first point.
The result is that the location of the focused spot on the optical medium may be controlled by the fine tracking actuator located in the fixed optical optical system without significant light loss.
The central axis of the light beam will pass through the aperture of the objective lens even though the spot on the optical medium is displaced.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.