Patent ID: 6856584

Claim:
An aberration detection device comprising: a radiation source for emitting a light beam; an object lens for focusing the light beam on an information carrier; a light deflector for partitioning a returning light beam that has been reflected by the information carrier and passed through said object lens into a first light beam passing a first region and a second light beam passing a second region, and diffracting the first light beam that has passed the first region away from said radiation source; and a first light detector for receiving the first light beam and a second light detector fro receiving the second light beam; wherein said first light detector and said second light detector each comprise a photo-detector partitioned into at least two portions, said first light detector and said second light detector are arranged such that the first light beam and the second light beam are each irradiated onto a corresponding partition line of said first light detector and said second light detector, the object lens has a numerical aperture of at least 0.6, and a spherical aberration, a coma aberration or an astigmatism is detected and identified individually from an output signal from said first light detector and said second light detector.