Aberration detection device and optical information recording and reproducing apparatus

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 beam splitter for separating a returning light beam that has been reflected by the information carrier and passed through said object lens from an incoming light beam;
• a hologram for partitioning and diffracting the returning light beam, that has been separated by said light beam splitter, into a light beam passing a first region and light beam passing a second region;
• and
• a plurality of light detectors for receiving a diffracted light beam passing through the first region;
• wherein said plurality of light detectors receive both a +1-order diffractive light beam and a −1-order diffractive light beam that have passed through the first region and been diffracted,
• said plurality of light detectors comprises a photo-detector partitioned into at least two portions,
• the photodetector is arranged such that both the +1-order diffractive light beam and the −1-order diffractive light beam are irradiated onto a partition line of the at least two portions, and
• spherical aberration, coma aberration, and astigmatism are detectable from an output signal from the photodetector.