Method and arrangement for regulating the light power of a scanning beam in an apparatus for reading from or for writing to optical recording media
View Patent ↗In order to compensate for so-called clipping effects, it is proposed, in an apparatus for reading from and/or writing to an optical recording medium in which the light power of a laser diode ( 1 ) is to be set to a plurality of light power levels,to perform a calibration to a specific light power level (LP 2 ) before the actual regulation of the light power. On account of the calibration, the instantaneous gradient of the characteristic curve which describes the dependence of the laser light power on the laser diode current can be inferred in order, on the basis of this information, to take account f a change—caused, for example, by ageing r clipping effects—in the characteristic curve gradient in the course of the subsequent regulation of the light power of the scanning beam generated by the laser diode ( 1 ).
1. Apparatus for regulating the light power of a scanning beam to one of a plurality of desired light power levels in an apparatus for reading from and/or writing to an optical recording medium,
and said apparatus comprises a driving apparatus for sequentially supplying a plurality of driving currents to a light source for providing the desired light power level of the scanning beam, monitoring means for detecting a predetermined light power level of the light source and setting means as well as regulating means for setting plural desired light power levels,
wherein provision is made of calibration means for carrying out a calibration of a driving current to a light power level of the light source, and the regulating means are configured in such a way that they carry out the regulation of the driving current for the light power of the scanning beam by a comparison between a driving current supplying the light source for regulating the light source with a calibration factor to a predetermined light power level and a present driving current to provide said predetermined light power level with said driving apparatus for setting the driving current of said driving apparatus for one of said plurality of desired light power levels of the scanning beam.
2. Apparatus according to claim 1 , wherein the calibration means comprise at least a first regulating circuit and a second regulating circuit,
the first regulating circuit, by the setting of a calibration factor, being provided for the regulation of the light power of the scanning beam of the light source to a first light power level and the second regulating circuit being provided for the regulation of the light power of the scanning beam of the light source to a second light power level using the same calibration factor, and
in that the calibration means have measurement means for measuring the current fed to the light source in the course of the regulation to the first light power level and the current fed to the light source in the course of the regulation to the second light power level, the measurement means being connected to the regulating means, and
in that the regulating means are configured in such a way that, as a function of the measurement signals supplied by the measurement means, they determine a characteristic curve which describes the relationship between the current fed to the light source and the light power generated by the light source and subsequently take it into account in the course of the regulation of the light power of the scanning beam of the light source.
3. Apparatus according to claim 2 , wherein the first and second regulating circuits are coupled to a means for detecting the light power instantaneously generated by the light source.
4. Apparatus according to claim 2 , wherein the first and second regulating circuits in each case have a sample/hold element for storing a value which describes the current which is fed to the light source and corresponds to the first and second light power level, respectively.
5. Apparatus according to claim 1 , wherein the light source is a laser diode, and the calibration means and also the regulating means are configured for calibrating and also for regulating the light intensity of the laser diode.
6. Apparatus according to claim 1 , wherein the desired light power level corresponds to a light power level prescribed by the manufacturer of the optical recording medium.