Abstract: An optical recording medium in which a medium identification code is recorded by using a nonvolatile mark which is formed through irreversible change of a recording film, such as magnetization characteristic change, deformation and formation of a hole, so as to prevent illegal copy of the optical recording medium, and a recording/reproducing method for the same.

Abstract: An optical head includes a lens system forming light reflected from an optical disk into parallel rays, a focal error and tracking error detection system detecting focal error and tracking error based on the parallel rays, an optical reproduced signal detection system detecting a reproduced signal reproduced from the optical disk based on the parallel rays, and a light blocking part for blocking, out of the parallel rays, at least a central portion in a light amplitude distribution of parallel rays supplied to the optical reproduced signal detection system.

Abstract: A data reproducing system obtains a reproduction signal via a head from an optical disk recording medium in which signals obtained by modulation of recording data in accordance with a rule corresponding to a partial response characteristic have been recorded and generates a data signal corresponding to the recording data based on the reproduction signal. The data reproducing system includes a clock generator for generating a synchronizing clock based on the reproduction signal, and a signal generating unit, operating in synchronism with the synchronizing clock generated by the clock generator, for sampling levels of the reproduction signal and for generating the data signal from the sampled levels in accordance with a maximum likelihood sequence estimation method.

Abstract: A magneto-optic recording method and a magneto-optic recording apparatus in which a magneto-optic overwritable medium having two layers, which layers have different coercive force--temperature characteristics and are coupled by exchange interaction, is heated by applying a light beam while an external magnetic field is being applied to the medium and in which data coded to invariably have FALSE states between two TRUE states is turned into a light beam having dual power levels and recorded on the medium, the magneto-optic recording method including the steps of: forming record marks by heating the magneto-optic overwritable medium to a high temperature by means of a high light beam power associated with a FALSE state in the write data; and of heating the magneto-optic overwritable medium to a low temperature by means of a low light beam power associated with a TRUE state in the write data.

Abstract: A magneto-optic overwrite disk recording system capable of canceling shifts of the front edge and the rear edge of the record mark due to accumulation of heat. The recording system includes a magneto-optic overwrite disk having a memory magnetic film and a record magnetic film, a first magnet for applying an initialization magnetic field with a first strength vertically to the disk, and a second magnet for applying a bias magnetic field with a second strength smaller than the first magnetic field to the disk in the direction opposite to the initialization magnetic field. The recording system further includes a laser diode for generating laser beams, an optical head for focusing the laser beam on the disk, a pulse generator for generating square wave pulses with a predetermined period, and a duty ratio controller for alternately increasing and decreasing the duty ratio of the square wave pulses every time data "1" of binary record data is generated.

Abstract: An apparatus for reading out data recorded on a magneto-optic disk by detecting edges of magnetic domains formed such that the direction of magnetization thereof is opposite to the direction of the magnetization initially formed on the magneto-optic disk, the edges of the magnetic domains corresponding to "1"s of the recorded data. The data read out apparatus includes a read out signal generation portion for generating a read out signal by scanning the magnetic domains on the magneto-optic disk, a binarization portion for converting the read out signal into a binarized signal, and an edge detection portion for detecting from the binarized signal a front edge signal and a rear edge signal corresponding to the front edge and the rear edge of the magnetic domains, respectively. A front edge signal from a fixed delay device and a rear edge signal from a variable delay device are input to an OR circuit and an edge signal is output therefrom.

Abstract: A method and apparatus for optical recording addresses a problem of edge shift which occurs during the recording. The apparatus includes a rotating mechanism for rotating an optical medium, and an optical head having a light source for recording information on the optical medium. A moving mechanism moves the optical head to a predetermined position on the optical medium, and a recording controlling device controls light source of the optical head in accordance with a recording pulse. The recording controlling device includes a pulse width measuring device for measuring the pulse width of a recording pulse, and fall controlling device effects a recording compensation by advancing a fall of the recording pulse with a lead, such that the lead increases with the measured pulse width.

Abstract: A read out apparatus reads out prerecorded information from a magneto-optic disk by detecting intervals of edges of magnetic domains formed on the magneto-optic disk with different directions of magnetization, where the intervals of the edges of the magnetic domains correspond to data "1"s or "0""1"s of the prerecorded information.