Patent ID: 7269113
Filing Date: 2007-09-11
Classification: G11B

Abstract:
1. A device for scanning a record carrier having a track for recording information represented by marks, the device comprising: a scanning unit comprising a radiation source and optical elements for generating a beam of radiation from the radiation source via a scanning spot on the track to a detector for detecting at least one read signal, the scanning unit further comprising means for generating an asymmetry signal β based on a read signal from the detector when scanning a part of the track comprising marks, the asymmetry signal β being a measure of correspondence of the marks to desired lengths thereof, a sensor for detecting a sense signal from the beam, a control unit for controlling radiation source power of the radiation source to a desired value in dependence on the sense signal, and correction means for generating a correction signal indicative of local optical properties of the record carrier in dependence on at least one sense signal measured on at least one part of the track near the scanning spot, and for correcting at least one of said detected signals in dependence on the correction signal, wherein the correction means are coupled to the control unit for correcting the desired value of the radiation source power, and wherein the asymmetry signal β is generated by: