Magneto-optic readout apparatus using polarization switching of readout beam

A magneto-optic playback apparatus for playing back information recorded in a magnetic recording layer of a magneto-optic recording element, such information being recorded in the form of vertically magnetized magnetic domains of opposite orientation, such recording layer being of the type which exhibits a differential absorption of left- and right-hand circularly polarized radiation, depending upon the orientation of the magnetic domains irradiated by such incident radiation, said apparatus including a laser adapted to operate in two different modes to produce two different linearly-polarized beams of radiation, the plane of polarization of one beam mode being perpendicular to the plane of polarization of the other beam mode, said laser being arranged to direct both of said beam modes along an optical path toward the magnetic recording layer, such recording layer serving to reflect a portion of a beam of radiation travelling along said path back toward the laser;

• means for scanning the recording layer with both of said beam modes of radiation to irradiate the prerecorded information thereon according to a predetermined procedure;
• optical means for coupling said laser with the recording layer so that, as said beam scans the recording layer and the recording element reflects such beam back to the laser, said optical means selects in which beam mode the laser operates by the orientation of the magnetic domains irradiated by the beam;
• and photodetector means for continuously detecting in which of the two modes the laser is operating, wherein said optical means comprises:
• a) an optical loss control element for controlling losses for said beam modes whereby a probability of operation in either beam mode by the laser is substantially equal for either of said two modes in the absence of any coupling of radiation between the laser and recording layer, and b) a polarization converter arranged in the optical path between the laser and recording layer, said polarization converter functioning to (i) convert an incident beam of linearly polarized radiation to a beam of either left-hand or right-hand circularly polarized radiation depending upon the operating mode of the laser, such beam of circularly polarized radiation striking the recording element and being reflected therefrom, and (ii) reconvert the beam of circularly polarized radiation reflected from the recording element to a beam of linearly polarized radiation having a plane of polarization substantially the same as that of said incident beam.