Abstract: A modulation and demodulation system for an optical data recording and reproducing apparatus is disclosed in which, in an optical disc having an optical guide track and capable of recording and reproducing optically, the guide track is divided into a plurality of data sectors and the recording or reproduction or reading is effected by data sector. The modulation system for the data field for recording the data is different from that for the identification field containing identification data such as a track address and a sector address in such a way that the identification field is reproduced at high reliability and high demodulation speed while at the same time recording data at high density in the data field.

Abstract: A track searching system for an optical information recording and reproducing apparatus in which a disc-like information carrier provided with concentric or spiral guide tracks of a channel-like configuration is used as an information recording and storing means and adapted to be scanned by a light beam for recording or retrieval of information. Light flux reflected by the information carrier and presenting variable distribution of light intensity is received by paired photoelectric elements. A difference signal and a sum signal derived from the output signals from the photoelectric elements or a reproduced RF signal representative of reproduced information undergo phase comparison processing, the result of which is utilized for determining the direction and number of guide tracks traversed by the scanning light beam.

Abstract: An optical information recording and reproducing apparatus for optically recording and reproducing information on and from a disk-shaped information carrier having a guide track is disclosed. A digital track address prerecorded on the guide track is reproduced and the intensity of a recording laser beam is controlled by the reproduced digital track address so that the exposures of the recording laser beam at an inner periphery and an outer periphery of the disk-shaped information carrier rotated at a constant rotation speed are corrected to enable an optimum recording over an entire surface of the disk-shaped information carrier.

Abstract: An optical reproducing device for reproducing still image signals recorded on circular tracks and moving image or audio signals recorded on spiral tracks on a disk. Concentric and spiral tracks may be intermingled on the same disk. The address signals for each concentric track or each coil of a spiral track are previously recorded. When the address signals are reproduced, they are processed so as to detect whether the readout address signals changes with time, thereby detecting whether the accessed track is concentric or spiral. An optical head drive system is controlled in a manner depending on whether the track is circular or spiral, so that an optical head can scan the desired concentric or spiral track.

Abstract: An optical recording and reproducing disc for recording and/or reproducing information by the application of laser beams having a wavelength .lambda. in the range of 0.7 to 1.0 .mu.m, the disc being constituted by a disc-shaped base having at least one spiral guide track thereon with top surfaces parallel to the surface of the base at a height above the base different from the top surfaces of the portions of the base between the spires of the track, which height is in the range of .lambda./12 to .lambda./6, the guide track having a width approximately equal to the effective diameter of the laser beams; and a uniform thickness coating of a light recording material on the top surface of the guide track and the portions of the base between the spires of the guide track, the light recording material being a material the transmittance and/or the reflectance of which is varied by irradiation by the laser beams.

Abstract: A servo control system includes an error amplifier for deriving an error signal representing the displacement of a focus point of laser beam from different planes of an optical record disc, a differentiator for differentiating the error signal to detect its rate of variation, and a comparator for detecting the maximum peak of the differentiated signal which corresponds to reflections from the plane on which information is recorded. The focus point is moved in a direction toward the disc in an open loop mode until the maximum peak of the differentiated signal is detected, whereupon the focus point is controlled in response to the error signal in a closed loop mode to keep track of the recording plane.

Abstract: In an optical recording device in which the writing laser light beam is focused to a small spot on a disk which is coated with a photosensitive medium and spins at a predetermined velocity so that the data are recorded in terms of variable density or surface irregularities, the forward DC current applied to a semiconductor laser is varied depending upon the radius position of the writing laser beam spot on the disk but the AC current which is superposed on the DC current and rises or drops above or below the DC current level by a predetermined amplitude depending upon the data to be recorded is maintained constant regardless of the radius position of the writing laser beam spot, whereby the duty ratio can be maintained constant regardless of the distance from the center of the disk of a selected recording track.

Abstract: An optical system for an optical data recording and reproducing apparatus such as an optical video disc apparatus comprising a diode laser light source, a condenser lens disposed adjacent to the diode laser, a cylindrical lens assembly arranged to exhibit different magnifications to light beams emitted by the diode laser in the direction perpendicular to a junction plane thereof and in the direction parallel to the junction plane, and a concentrating lens for constricting the resulting light beam into a light spot of a small size for projection on a recording medium. Recording of information is attained by the constricted light beam of a substantially circular cross-section with a high recording density at a low energy consumption. When reproducing the recorded information, the constricted beam is laterally enlarged in the transverse direction of the information recording track thereby to assure generation of a signal utilized for tracking control.