Optical information reproducing device forming light spot on photo-detector with major axis along push-pull signal detection

An optical information reproducing device comprising:

• a semiconductor laser for generating incident light having a first linear polarization direction,
• an opto-magnetic recording medium for recording information thereon,
• an optical system provided between the semiconductor laser and the opto-magnetic recording medium and including a first beam splitter for separating a path of the incident light from a path of return light reflected by the medium and having about 100% transmittivity or reflectance for a polarization component of the return light which has a second linear polarization direction perpendicular to said first linear polarization direction, and
• an optical detecting means comprising a photodetector and a second beam splitter of about plane-parallel plate shape disposed to incline to an optical axis of the return light as the return light is incident on the second beam splitter and for receiving the return light to separate the return light into two light fluxes including a first light flux with astigmatism and a second light flux with no astigmatism, said optical detecting means being arranged in such a manner that a major axis of an ellipsoidal spot formed on the photodetector due to the astigmatism lies along a push-pull signal direction, thereby detecting a push-pull signal based on an output of the photodetector.