Abstract: An optical head has a semiconductor laser for emitting light, a collimator lens for converting the light from the laser into a parallel light beam, a semiconductor substrate for reflecting the light beam, and an objective lens for focussing the light beam reflected from the substrate on the optical disk. A 1/4 wavelength plate is situated between the substrate and the objective lens. A beam splitter which transmits the light from the laser and reflects the light returning from the disk is provided between the collimator lens and the substrate. Following the beam splitter, a collective lens, a cylindrical lens and an optical detector are arranged in this order on an optical path for the returning light. A light receiving element for outputting a signal corresponding to the intensity of the light received is formed on the semiconductor substrate, and a polarizing film is formed on the surface thereof.

Abstract: An opto-magnetic pick-up device for use in an information recording and reproducing device is disclosed. The device comprises a phase difference correcting device capable of correcting the phase difference between the linearly polarized component of the reflected light from the recording medium and a polarized component vertical to the linearly polarized component.

Abstract: An apparatus for detecting unused sectors in an optical disk or opto-magnetic disk including an envelope detection circuit for detecting an envelope of a read signal to derive an envelope detection signal when data is recorded in a data area of sector. Sector mark and address marks recorded in an identification area are detected to derive sector mark detection signal is generated and address mark detection signals, and an interpolated mark signal corresponding to a synchronizing signal recorded in the data area in accordance with the sector mark detection signal and address mark detection signals. When the envelope detection signal is not produced, the generation of the interpolated mark signal is inhibited. Thus when the synchronizing signal is not detected in the data area and the generation of the interpolated signal is inhibited, the relevant sector is detected as the unused sector.

Abstract: A photo-magnetic (magneto-optic) recording device having recording medium in the form of a rotating magnetic disc having magnetic characteristics in a direction perpendicular to its surface has a pickup head (7) disposed on one side of the disc and movable radially of the disc to scan selected areas of the disc. On the side of the disc opposite to that on which the pickup head is located, there are provided a plurality of coils (8) generating a bias-magnetic field applied to the disc. The coils are disposed in overlapping arrangement with their centers disposed on a line extending radially of the disc. The coils are energized by electric circuitry which comprises means for sensing the position of the pickup head and energizing a respective coil located in position to apply a bias-magnetic to the area of the disc scanned by the pickup head.

Abstract: Based on an output signal of a sector mark reading circuit reading a sector mark signal representing a sector mark area, the interval in which the next sector mark signal is to be detected is anticipated, and a quasi-sector mark is generated at a time when the next sector mark is to be detected in each sector. Even if the sector mark reading fails, the sector mark will be able to be output at an accurate timing. Also, if the read sector mark signal, which is mis-detected or not, is determined, a highly reliable sector mark signal may be produced.

Abstract: In the present invention, a discriminating means of recording media is formed in a cartridge containing a magneto-optical type recording media and in a cartridge containing other recording media, a sheltering height of a field applying means is changed according to the loading of each cartridge so that said field applying means is held close to the recording media in the case of the magneto-optical type cartridge while said means is sheltered high in the case of other type cartridge, and at the same time a discriminating means for recording media is provided to perform the signal processing corresponding to the recording media loaded.

Abstract: In a method of detecting track crossings on an optical disc, a light source irradiates a light beam onto an optical disc having guide tracks in the form of a recess and the light beam is reflected and diffracted into a zero order light beam and positive and negative primary light beams. The light beams are defocused so as to produce interference patterns between the zero light beam and the positive and negative primary light beams. The interference patterns are detected by a four split light detector disposed between two parts of a two split detector. The outputs of the detectors are fed to an adder and to a subtractor for producing a sum signal and a difference signal respectively. The sum signal and difference signal are fed to a phase detector. Defocusing of the light beams is effected by a focusing coil to which is fed the amplified output of an adder of a reference signal controlled by a control circuit.

Abstract: In a method of recording an information signal in an opto-magnetic record disc which has an easily magnetizable axis perpendicular to its surface, a constant erasing light beam and a modulated recording light beam are focussed by a single objective lens on adjacent tracks and an external magnetic field is applied to the record medium. The erasing and recording operations can be carried out at the same time by inverting the polarity of the external magnetic field track by track.