Aberration detection device and optical information recording and reproducing apparatus

Claim 1

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.