Patent ID: 8144560

Claim:
A method for preventing interchange of a first optical information carrier ( 1 ) with a second optical information carrier in an optical apparatus, the optical apparatus being capable of reproducing information from an optical information carrier, the method comprising the steps of: detecting that the first information carrier ( 1 ) is present in the optical apparatus by focusing the light ( 5 ) at the first optical information carrier ( 1 ) in the optical apparatus, detecting reflected light ( 8 ) from the first optical information carrier ( 1 ), and generating a plurality of signals comprising a central aperture (CA) signal, RF signal, and a focus error (FE) signal from the detected light ( 8 ); upon obtaining an indication of unexpected behavior in at least one of the plurality of signals, after detection of the presence of the first information carrier: assessing if the first optical information carrier ( 1 ) has been removed from the optical apparatus, and rendering any further reproduction of information by the optical apparatus impossible until some pre-determined measures have been taken when said assessing indicates the first optical information carrier has been removed, wherein the assessing of the removal of the first optical carrier comprises: initiating a ramping process of the focused light; and determining an absence of peaks in at least one of the central aperture (CA) signal and the focus error (FE) signal.