Title:
OUT-OF-FOCUS DETECTION DEVICE AND OPTICAL HEAD USING IT
Document Type and Number:
Japanese Patent JP3348873
Kind Code:
B2
Abstract:
PURPOSE: To achieve a focusing operation stably by a method wherein a means which makes the diameter of a subbeam passed through a convergence means smaller than the diameter of a main beam and the linear region of an out-of- focus detection signal, is made wide.
CONSTITUTION: A beam from an optical-body laser 11 is set as a main beam via a lens 12. It is separated into a beam of + primary diffraction light 15b and a beam of - primary diffraction light 15c by means of a diffraction grating 14. The astigmatism of a 1/2 wavelength and that of a -1/2 wavelength are given, respectively. The individual beams are transmitted through a beam splitter 16; they are converged by means of a lens 17 (a pupil 18), and a focus 19a is formed. The beams 15b, 15c are focused respectively at points 19b, 19c. The beams are reflected by a pit on an optical disk 20 and condensed by means of a convex lens 22. The individual beams are photodetected by means of photodetectors 23a to 23c; a light-quantity signal 24 is generated. Modulation- factor signals 26b, 26c are output via an envelope detection circuit 25; they are subtracted by means of a differential operation circuit 27; an out-of-focus detection signal 28 is output.
Inventors:
Shigeru Nakamura
Mariko Umeda
Mariko Umeda
Application Number:
JP13221192A
Publication Date:
November 20, 2002
Filing Date:
May 25, 1992
Export Citation:
Assignee:
株式会社日立製作所
International Classes:
G11B7/085; G11B7/09; (IPC1-7): G11B7/09
Domestic Patent References:
| JP5242497A | ||||
| JP6173246A | ||||
| JP59223944A | ||||
| JP4159618A |
Attorney, Agent or Firm:
Masayuki Watanabe (1 person outside)