Pulstec Industrial Co., Ltd.

Ricardo Musashi Okamoto

Kenji Fukui

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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Yokohama, Japan

Ricardo Musashi Okamoto