Photo-detection device used in an optical pickup head for detect

Details Photo-detection device used in an optical pickup head for detect Photo-detection device used in an optical pickup head for detect

1995-05-16

1999-06-01

Hindi, Nabil

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

369110, 369 4423, 369 4424, 369112, G11B 700

Patent

active

059094230

ABSTRACT:
There is provided an optical pickup head which can accurately detect a focusing error even when the wavelength of light emitted from a light source varies. A holographic element diffracts a light beam reflected by an optical disk to obtain .+-.1st-order diffracted light beams, and has a diffracting area formed using a Fresnel zone plate, and a light-shading area for shading the reflected light beam. A photo-detector has four-elements light-receiving areas. The photo-detector detects the .+-.1st-order diffracted light beams diffracted by the diffracting area and focused by a convex lens, and converts these light beams into electrical signals. The photo-detector is disposed at substantially the middle point between the focal points of the -1st-order diffracted light beams formed by the convex lens. Since the middle point does not move even when the lasing wavelength of a semiconductor laser diode varies, the photo-detector can obtain stable signals.

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