Hitachi, Ltd.

Yasumitsu Mizoguchi

Takeshi Maeda

Masahiro Takasago

Yoshito Tsunoda

Motoo Uno

Kazuo Shigematsu

Tokuya Kaneda

Takakazu Huno

Zenji Tsutsumi

Tokuya Kaneko

Kouji Muraoka

In an optical memory apparatus wherein predetermined information is optically recorded on a recording medium along guide grooves previously formed and then played back; an optical memory apparatus wherein, using a tracking signal and a signal indicating the quantity of reflected light at the time at which a projected light beam passes through the guide grooves, the directions in which the light beam passes through the grooves and the number of the guide grooves to be passed are detected, a seek control is performed by adding and subtracting the numbers of the guide grooves to be passed, depending upon the directions of passage, and fine positioning is thereafter performed by the use of the tracking signal.

Optical memory apparatus

A method of detecting a light spot control signal is disclosed in which, when information is reproduced from an optical disk for optically recording information, a signal level obtained at a high-reflectivity portion of the optical disk is taken out of a signal reproduced from the optical disk, and is used as a control signal, which controls a light spot so that it tracks information stored in the optical disk.

Method of detecting light spot control signal

An optical information processor records predetermined information along a track on a recording medium through the irradiation of a light beam intensity-modulated in accordance with the predetermined information. A tracking signal obtained when the light beam traces the track, is compared with first and second preset values which define a predetermined range. When the tracking signal departs from the predetermined range, the intensity modulation of the light beam or the recording operation is stopped, thereby preventing data destruction which otherwise occurs due to the digression of the light beam from the track.

Optical information processor

An optical information disc apparatus includes a laser source, a recording medium with an information track, an optical system for emitting a laser beam from the laser source onto the information track, a photodetector detecting the focus error of the optical system using the light reflected from the information track, and an auto-focusing servo system operating the optical system to make the focus of the system follow the upward and downward movement of the recording medium, the optical information disc apparatus being further provided with a control circuit to make the auto-focusing servo system effective only when the optical system is in a position equivalent to the linear region of a defocusing signal having an S-curve characteristic.

Optical information disc apparatus with autofocusing servo system

A driving circuit for driving a semiconductor laser by a driving signal containing a pulse signal representing given information and superposed on a DC bias signal includes means for monitoring intensity of laser light emitted when the DC bias is applied, and means for monitoring the intensity of laser light emitted when the pulse signal is applied. The DC bias signal and the pulse signal are varied in dependence on the result of comparisons between the outputs of the monitoring means and respective predetermined reference values.

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Odawara, Japan

Yasumitsu Mizoguchi