Patent ID: 7911890

Claim:
An optical disc drive comprising: a light source; an optical branching element for splitting light emitted from the light source into a main beam and at least one sub-beam; a condenser element for condensing the main beam and the sub-beam; a photodetector section including a main photodetector and a sub-photodetector to receive the main beam and the sub-beam, respectively, that have been reflected from a storage layer of an optical disc, each said photodetector having a number of photosensitive areas, each of which outputs a signal representing the intensity of light received there; and a computing section for generating a first focus signal, representing where the focal point of the main beam is located with respect to the storage layer, based on the signals of the respective photosensitive areas of the main photodetector, and also generating a second focus signal based on the signals of the respective photosensitive areas c of the main photodetector and the sub-photodetector, wherein the optical disc drive performs a first type of control in order to shift the focal point to a vicinity of the storage layer based on the first focus signal, and determines whether the focal point has reached the vicinity of the storage layer by comparing a level of the first focus signal to at least one reference value, and after determining that the focal point has reached the vicinity, then starts a second type of control in order to make the focal point moved from the vicinity to the storage layer.