Abstract: The invention relates to an optical drive for reading information from an optical disk (1) with a high birefringence. A radiation beam (5) has a modulated read power level of frequency F1. A polarizing beam splitter (PBS; 6) guides the reflected beam (8) from the disk (1) towards a photo detector (10) that outputs optical response signals (RS). The optical response signals (RS) are converted to optical response parameters (RP) that are compared with a predetermined optical response parameter reference values (RP_ref). If a sufficient deviation (?) is present it is indicative of an optical feedback from the beam splitting means (PBS; 6) towards to the radiation source (4). The processing means (52) can then change the first modulator frequency (F1) of the radiation beam (5) to a second modulator frequency (F2) so as to decrease the optical feedback.

Abstract: A method for recognizing type (CD; DVD) of an optical disc, wherein: a light beam (32) is caused to reflect from the optical disc (2); wherein an optical lens (34) is caused to move axially with respect to said optical disc (2); a detector output signal (SR) is analyzed to detect when (P1; ts) a focus point of said light beam (32) substantially coincides with a disc surface and to detect when (P2; tL) said focus point substantially coincides with an information layer wherein a thickness time At is calculated in accordance with the formula: ?t=tL?ts and wherein the measured thickness time ?t is compared with a reference value (?tREF) which is calculated from an experience-based average value (?tAV(CD)) of the thickness time 66 t of CD discs, or from an experience-based average value (?tAV(DVD)) of the thickness time ?t of DVD discs, or from both.