Sony Corporation

Masamichi Utsumi

Akio Yamakawa

Kiyoshi Ohsato

Kamon Uemura

Tetsuo Usui

An optical pickup including a light source for radiating a light beam, a diffraction element for separating a light beam radiated from the light source into at least three beams, namely a main beam and two side beams, an objective lens for converging the light beams separated by the diffraction element on a signal recording surface of the optical recording medium, a light receiving unit having a four-segment first light receiving portion for receiving the main beam reflected by the recording surface of the optical recording medium and second and third light receiving portions arranged on both sides of the first light receiving portion for receiving the side beams reflected by the recording surface of the optical recording medium, and a calculation unit for generating a first tracking signal based on respective outputs of the first light receiving portion and for generating a second tracking signal based on outputs of the second and third light receiving portions.

Optical pickup for discriminating between and reading different types of optical discs

An optical pickup and a reproducing apparatus includes an objective lens having a hologram lens formed over the entire area of one surface thereof. A central portion of the hologram lens and peripheral portions of the hologram lens are formed differently, so that a laser beam diffracted by the central portion of the hologram lens is focused at plane A, and a laser beam diffracted by the peripheral portion is directed outward. As a result of this, the light intensity distribution after light has passed through the objective lens becomes substantially uniform, so that almost no primary ring is produced, thus preventing cross talk caused by reflected light from an adjacent track.

Hologram formed on an objective lens for one defracting light beams

The type of optical disc having different track pitch is identified simply. A light emitted from the LED 21 is irradiated through a condenser lens 22 onto an optical disc 1. The incident light is diffracted and reflected by the pit 3. When, if the optical disc 1 is a CD, the first order diffracted light is received by the first light receiver 10, on the other hand, if the optical disc 1 is a DVD having a smaller track pitch Pt, the first order diffracted light is received by the second light receiver 11. Therefore, the type of the optical disc 1 is identified based on a light receiving signal of the first light receiver 10 and the second light receiver 11.

Method and device for identifying disc

There is disclosed a method of playing back information from an optical multilayer disk having a plurality of recording disks stacked on top of each other, by the use of an optical pickup device. In order to switch the focused recording layer from a first one to a second one so that data is read from the second recording layer, the focus balanced condition of the pickup device is switched from a setting providing a focus error characteristic adapted for the first recording layer to a reference setting providing a neutral focus error characteristic. Then, the focal point of the pickup device is moved from the first recording layer. Subsequently, the pickup device is focused onto the second recording layer, and data is read from the second recording layer. Thereafter, the focus balanced condition of the pickup device is switched to a setting adapted to the second recording layer.

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Chiba, Japan

Masamichi Utsumi