Disc drive for an optical scanning device

Abstract

The invention relates to an optical disc drive that comprises rotating means, defining a rotating axis for an optical disc, and an optical scanning device, for scanning said optical disc with a light beam. These optical scanning means themselves comprise a first light source, for producing said first light beam, focusing means, provided between the first light source and a focusing point on an information layer on the disc, an optical detector, for receiving a first backward beam reflected from said information layer, and a second light source, for producing a second light beam also transmitted to said focusing means and for measuring tilt from the position, on said optical detector, of a second spot corresponding to a second backward beam obtained after reflection of the second light beam on the information layer. According to the invention, a diffractive structure, provided with diffracting elements for substantially refocusing the returning second beam onto the detector, is provided between said focusing point and said optical detector. This diffractive structure, consisting of a series of ring-shaped prisms, is attached either to one surface of a servo-lens positioned just before said optical detector, or to one surface of an objective lens used as focusing means, or to a separate plate. The diffractive structure may also be approximated by a step-wise structure.

Description

field of invention [0001] The present invention relates generally to an optical scanning device for storing information on or reading information from a disc-shaped storage medium, wherein the disc is rotated and a write / read optical head is rotated relative to the disc-shaped storage medium. The disc moves radially. More particularly, the present invention relates to an optical disc drive comprising rotation means for determining the axis of rotation of the optical disc and optical scanning means for scanning said optical disc with a light beam. [0002] The present invention can be applied in the case of an optical disk system or a magneto-optical disk system. In the following, the term "optical disc system" will be used, but it should be understood that this term is meant to also cover magneto-optical disc systems. Background of the invention [0003] As is known, optical storage discs comprise at least one track of storage space in which information (eg images, data, m...

AI Technical Summary

Problems solved by technology

However, when using this method, the spot size on the optical detector has proven to be too large compared to the size of standard four-quadrant detectors commonly used in optical disc drives: no quadrant from the detector can be measured. Significant difference in the signals of quadrants, so no tilt error signal can be obtained

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