Patent ID: 7843774

Claim:
An optical information recording and reproducing apparatus for performing, using a light beam, at least one of recording information on and reproducing recorded information from a plurality of recording layers on an information recording medium, said apparatus comprising: an objective lens for receiving a light beam and for condensing the light beam onto the plurality of recording layers of the information recording medium, to perform the at least one of recording and reproducing of the information; a light beam expander for correcting spherical aberration caused by a difference in substrate thickness between the plurality of recording layers of the information recording medium by changing one of a divergent angle and a convergent angle of the light beam entering the objective lens; coma aberration correcting means for correcting coma aberration caused by tilt of the recording medium; and a drive circuit for driving the coma aberration correcting means with a drive signal having a value that varies for each of the plurality recording layers, depending on (i) an amount of coma aberration caused by correcting spherical aberration by changing one of the divergent angle and the convergent angle by the light beam expander, and (ii) an amount of coma aberration caused in each recording layer due to a transmission thickness from a light incidence surface of the recording medium to each of the plurality of the recording layers.