Optical disc recording or playback device with corrected focus o

Details Optical disc recording or playback device with corrected focus o Optical disc recording or playback device with corrected focus o

1997-08-28

1999-09-14

Hindi, Nabil

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

369103, G11B 700

Patent

active

059533048

ABSTRACT:
A device for corrected-focus scanning of information while recording on and/or replaying information from a recording medium is based on a radiation source which provides a scanning beam, a focusing objective lens and a radiation-sensitive detector system. A diffraction element for deriving a focus error signal is arranged in the space between the focusing objective lens and the detector system, at a predetermined, fixed distance, the diffraction element being designed such that two focus planes result which are physically separated from one another. The detector system is located between the separate focus planes such that the size ratios, which change in the event of defocusing, of the symmetrically imaged focus spot can be used to derive the focus error signal.

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