Optical head device including diffraction grating

Details Optical head device including diffraction grating Optical head device including diffraction grating

1991-05-28

1993-04-13

Young, Wayne R.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4441, 369112, G11B 709

Patent

active

052028690

ABSTRACT:
An optical head device having an optical system provided with at least a light source, a shaping prism, a diffracting element and a photodetector. The light source emits light whose cross-sectional intensity distribution has an elliptic shape. The shaping prism directs the light to a recording medium after shaping the intensity distribution thereof into a circular shape. The diffracting element has diffracting regions formed by at least one division line parallel to a reference direction. The light reflected from the recording medium forms an elliptic bright portion on the diffracting element. The photodetector is divided by a plurality of division lines, at least one of which is parallel to the reference direction. When there is no focus error, the diffracting element diffracts the reflected light so as to converge it on the division line substantially parallel to the reference direction in the photodetector. For example, when the shaping prism is adapted to shape the elliptic intensity distribution with respect to its major axis direction, the optical system is arranged so that the major axis of the bright portion coincides with the division line of the diffracting element. Thus, it is possible to obtain preferable focusing control.

REFERENCES:
patent: 4333173 (1982-06-01), Yonezawa et al.
patent: 4983017 (1991-01-01), Tsuji et al.
patent: 5066138 (1991-11-01), Toide et al.
patent: 5111448 (1992-05-01), Komma et al.
patent: 5111449 (1992-05-01), Kurata et al.
Patent Abstracts of Japan, vol. 14, No. 50 (P-0998) Jan. 30, 1990, & JP 01-279433.
Yoshida et al., "CD Optical Head Using Holographic Optical Element", Jul. 1989, pp. 102-107.
Japan Society of Precision Engineering, "CD Pickup Using a Holographic Optical Element", date unknown, (56-10-90-10-1775) and an English Abstract thereof.

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