Tdk Corporation

Giichi Shibuya

Hideki Hirata

Yasufumi Takasugi

Kazuki Suzawa

Takashi Namioka

Toshikazu Hosobuchi

Kazuo Fukunaga

Takashi Onodera

Suguru Takayama

Masanori Shibahara

Teiichiro Oka

Hideo Kobayashi

Yoshinori Sato

Koji Mishima

Hajime Utsunomiya

Kenji Yamaga

Daisuke Yoshitoku

Tsutomu Kotani

Osamu Murakami

The invention relates to a diffraction grating, a light-receiving element, and an optical head and an optical recording/reproducing apparatus utilizing them and provides a diffraction grating and a light-receiving element capable of detecting a signal of high quality and an optical head and an optical recording/reproducing apparatus utilizing them. A diffraction grating includes a diffracting region which is formed only on a light exit surface and which diffracts and separates first laser light or second laser light emitted by a two-wavelength semiconductor laser to generate a main beam and positive and negative first order sub beams. The depth of concavity formed on the diffracting region is 220 nm. The irregularities are formed such that the pitch length thereof is 22 &#x3bc;m and such that a convexity thereof has a width of 17.6 &#x3bc;m. The ratio of the width of the convexity to the pitch length of the irregularities is 0.8.

Diffraction grating, light-receiving element, and optical head and optical recording/reproducing apparatus utilizing them

The invention relates to a light-receiving element for receiving a reflection of laser light irradiated to a rotating multi-layer recording medium having a plurality of information recording layers stacked one over another and for converting the light into an electrical signal, an optical head having the element for recording information in the multi-layer recording medium or reproducing information recorded therein, and an optical recording/reproducing apparatus and a method of optical recording and reproduction. The invention provides a light-receiving element, an optical head, an optical recording/reproducing apparatus, and a method of optical recording and reproduction which make it possible to eliminate a noise component superimposed on reflected light from a multi-layer recording medium to reproduce an RF signal of high quality. The light receiving element receives a reflection of laser light irradiated through an objective lens to a rotating multi-layer recording medium having a plurality of information recording layers stacked one over another through a return path optical system and converts the reflected light into an electrical signal. The element has a first light-receiving section having a circular light-receiving region and a second light-receiving section disposed adjacent to the outer circumference of the first light-receiving section in the form of a circle concentric therewith.

Light-receiving element, optical head, optical recording/reproducing apparatus, and method of optical recording and reproduction

It is an object of the present invention is to provide an apparatus for discriminating an optical recording medium and a method for discriminating an optical recording medium which can reliably discriminate the kind of an optical recording medium even in the case where the optical recording medium to be discriminated is formed with periodical undulation in the circumferential direction thereof. The apparatus for discriminating an optical recording medium according to the present invention includes a first electrode, a second electrode, an alternate current signal generation circuitfor applying an alternate current A to the first electrode, a detection circuitfor detecting a level of an alternate current B appearing at the second electrode, and a control circuitfor controlling the operations of the alternate current signal generation circuitand the detection circuit

Apparatus for discriminating optical recording medium and method for discriminating optical recording medium

The present invention provides a method and an apparatus for discriminating the type of an optical recording medium and the number of recording layers in the medium. The apparatus includes a first electrode and a second electrode placed in the vicinity of a light transmission layer of the recording medium, an alternating current signal generation circuit for applying an alternating current A to the first electrode, a detection circuit for detecting the level of an alternating current B appearing at the second electrode, and a control circuit for controlling the operations of the alternating current signal generation circuit and the detection circuit, and a table provided in the control circuit.

To provide a light receiving device, a light detecting device, and an optical signal reproducing device each of which allows one to perform many different computations in detecting aberration amounts and focus error quantities without requiring exact position relations between laser light to be received and light receiving elements, and between the light receiving elements. First and second light receiving elementsandare used which receive condensed light at positions equidistantly spaced from an focal point X before and after the light images, respectively.

Condenser with first and second photodetectors with three sections each and having focal points before and after the surface of detectors

It is an object of the present invention to provide an apparatus for discriminating an optical recording medium which can reliably discriminate the kind of an optical recording medium even in the case where the optical recording medium to be discriminated is warped and formed with periodical undulation in the circumferential direction thereof. The apparatusfor discriminating an optical recording medium according to the present invention includes a first electrodea second electrodea third electrodea fourth electrodean alternating current signal generation circuitfor applying an alternating current signal A to the first electrodeand the third electrodea detection circuitfor detecting the level of an alternating current signal Bappearing at the second electrodeand the level of an alternating current signal Bappearing at the fourth electrodea supporting mechanismfor supporting the first electrodeand the second electrodea supporting mechanismfor supporting the third electrodeand the fourth electrodea driving mechanismfor vertically moving the supporting mechanisma driving mechanismfor vertically moving the supporting mechanismand a control circuitfor controlling the operations of the alternating current signal generation circuitthe detection circuitthe driving mechanismand the driving mechanismand a tableis provided in the control circuit

A laser diode driving circuit includes two chip capacitors disposed in the vicinity of one side portion of an IC along which a high voltage power supply terminal, a low voltage power supply terminal and a driving signal output terminal are disposed. One end portion of each of the chip capacitors is connected to the high voltage power supply terminal and the other end portion of each of the chip capacitors is connected to the low voltage power supply terminal. The chip capacitors are adapted for serving to reduce a ripple component superposed on a power supply voltage when a switching element is operated. The chip capacitors are disposed so that the distance between itself and the high voltage power supply terminal, the low voltage power supply terminal and the driving signal output terminal is equal to or shorter than 10 mm. According to the thus constituted laser diode driving circuit, it is possible to generate a good driving signal even when the pulse width of pulsed light emitted from a laser diode is narrow.

Laser diode driving circuit and an optical head

It is an object of the present invention to provide an apparatus for discriminating an optical recording medium and a method for discriminating an optical recording medium which can reliably discriminate the kind of an optical recording medium even in the case where the optical recording medium to be discriminated is warped. The apparatus for discriminating an optical recording medium according to the present invention includes a first electrode, a second electrode, an alternating current signal generation circuitfor applying an alternating current signal A to the first electrode, a detection circuitfor detecting the level of an alternating current signal B appearing at the second electrode, a supporting mechanismfor supporting the first electrodeand the second electrode, a driving mechanismfor vertically moving the supporting mechanism, and a control circuitfor controlling the operations of the alternating current signal generation circuitand the detection circuitand the driving mechanism

A semiconductor laser driving circuit comprises a driving IC and a substrate on which the IC is mounted. The IC incorporates: a switching element for generating a driving signal; a high-potential power terminal and a low-potential power terminal for feeding supply voltage to the switching element; and a driving signal output terminal for outputting the driving signal generated at the switching element to an external device. These three terminals are disposed side by side at one of sides of a main body of the IC. The substrate incorporates three conductors to be connected to the three terminals. Two chip capacitors are disposed beside the one of the sides of the IC at which the three terminals are disposed. An end of each of the capacitors is connected to the high-potential power terminal while the other end is connected to the low-potential power terminal.

Semiconductor laser driving circuit and optical head

Two light sources radiating two light beams having different wavelengths are simultaneously operated. Reflected beams of these two types of laser beams from an optical recording medium are simultaneously detected by two detectors. When one of the two types of light beams having different wavelengths is used while being focused on an optical recording medium, the spot diameter of the other non-focused metering beam on the optical recording medium is set larger than that of the one of the two light beams. A reflected light having a larger spot diameter is used to reduce DC offset in a tracking error signal.

Optical head, optical recording/reproducing apparatus and laser module

The spot diameter D of a side beam imaged on a disc is set to at least 2.5 times as large as that of a main beam. Via this configuration, an output signal from a detector detecting a reflected light via a side beam, that is, a signal representing a different in the output from photo-detection devices split by split lines in the radial contains a negligible track cross component caused by a beam spot crossing a track. The signal substantially contains a DC offset component alone caused by the shift of an objective lens in the radial direction under tracking control. Thus, by subtracting the output signal of the detector from the push-pull signal of the main beam, a tracking signal substantially containing no DC offset.

Optical head, lazer diode module and optical recording-reproducing apparatus

In a magneto-optical recording disc of the magnetic field modulation recording mode, recording of information for the first time is carried out in an optical modulation mode at a linear velocity which is higher than a reading linear velocity. The time required for recording is reduced while the recorded disc produces satisfactory outputs on playback.

Magneto-optical recording method and method for making

An apparatus for generating a modulated magnetic field includes a magnetic head coil and a pair of additional inductive coils. The ratio of the average inductance of the additional inductive coils to the inductance of the head coil is from 2 to 8. The apparatus ensures a magneto-optical recording system of the magnetic field modulation mode having an increased switching speed and a minimized overshoot of recording current.

Magneto-optical head circuit for minimizing the overshoot reversing

An improved information-modulate magnetic field generating circuit for magneto-optical recording which uses a step-down transformer whose secondary winding has less turns than the primary winding, thus permitting substantial reduction of electric power for driving the magnetic head coil.

Magneto-optical recording head comprising a step-down transformer

Magneto-optical recording method for a magneto-optical recording disk using a non-flying magnetic head. The magnetic head produces a magnetic field extending from a primary magnetic pole and returning to an auxiliary magnetic pole while the disk is rotated. The magnetic head is spaced apart from one major surface of the disk such that the primary magnetic pole applies a magnetic field across the disk. Magneto-optical recording is effected in a magnetic field-modulation mode while properly controlling the projected area of the primary magnetic pole and the distance between the magnetic head and the disk surface. A satisfactory C/N is obtained in a consistent manner while jitter is reduced.

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Tokyo, Japan

Giichi Shibuya