Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1997-12-19
2001-03-20
Tran, Thang V. (Department: 2753)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S053130
Reexamination Certificate
active
06205108
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk drive for driving a compact disk or similar optical disk and, more particularly, to an optical head capable of recording and reproducing data out of optical disks each having a substrate of particular thickness.
It is a common practice with an optical disk to form a transparent substrate having a preselected thickness in order to protect the recording surface of the disk of the order of microns. Rays issuing from an optical head form a fine spot on the recording surface of the disk by being transmitted through the transparent substrate. Because the resulting converged beam propagates through the transparent substrate which is parallel and flat, wavefront aberration occurs in the beam in accordance with the substrate thickness. The wavefront aberration refers to the deviation of the equiphase wave surface of the converged beam from a spherical surface. Should the wavefront aberration increase, the diameter of the converged spot would exceed a diffraction limit and would thereby degrade the recording and reproducing characteristic. In light of this, a lens included in the optics of an optical head is so designed as to correct the wavefront aberration, so that a fine spot close to the diffraction limit can be formed on the recording surface.
Generally, the substrate of an optical disk has a particular thickness matching with a desired application. Because the wavefront aberration stated above depends on the thickness of the substrate, the conventional optical head cannot record or reproduced data in or out of optical disks other than one having a particular substrate thickness. That is, the conventional optical head cannot meet the demand for the recording and reproduction with two or more different optical disks having different substrate thicknesses.
To solve the above problem, a mask area may be formed on an objective lens, as proposed in the past. This, however, brings about a problem that the mask area existing on the lens at all times reduces the optical efficiency. In addition, the mask area reduces the numerical aperture applicable to the head.
Technologies relating to the present invention are disclosed in, e.g., “A Compact-Disk-Compatible Digital Versatile Disk Pickup Using Annular Mask” by Chul Woo Lee et al, Jpn. J. Appl. Phys., Vol. 36 (1997), pp. 486-490 and Japanese Patent Application Laid-Open Nos. 3-52132, 5-6569, 5-73945, 6-203405, 7-57271, 7-65409, 7-98431, 7-302437, and 8-77594.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical head for an optical disk drive and capable of reproducing data out of optical disks having different substrate thicknesses, and insuring a high optical efficiency and a large numerical aperture.
In accordance with the present invention, an optical head includes a laser having a wavelength &lgr;, an objective lens for causing a beam issuing from the laser to be transmitted through the substrate of an optical disk having a preselected thickness and to form a fine spot on the recording surface of the optical disk, and optics for sensing the resulting reflection from the recording surface of the optical disk. A light-transmitting phase shifting device extends along an annular zone symmetrical with respect to the optical axis of the beam incident to the objective lens, and shifts the phase of the beam by 0.3&lgr; or less.
Also, in accordance with the present invention, an optical head includes a laser having a wavelength &lgr;, an objective lens for causing a beam issuing from the laser to be transmitted through the substrate of an optical disk having a preselected thickness and to form a fine spot on the recording surface of the optical disk, and optics for sensing the resulting reflection from the recording surface of the optical disk. A light-transmitting phase shifting device extends along an annular zone symmetrical with respect to the optical axis of the beam incident to the objective lens, and effects a phase shift selectively variable to zero or to a preselected value other than zero in response to a signal input from the outside of the head.
Further, in accordance with the present invention, an optical head includes a laser having a first wavelength for reproducing data out of an optical disk whose substrate has a first thickness, a laser having a second wavelength for reproducing data out of an optical disk whose substrate has a second thickness, a wavelength combiner for causing each of beams issuing from the lasers to propagate in the same direction, an objective lens for causing each of the beams issuing from the lasers to be transmitted through the substrate of the optical disk having a particular thickness and to form a fine spot on the recording surface of the optical disk, and optics for sensing the resulting reflection from the recording surface of the optical disk. A light-transmitting phase shifting device extends along an annular zone symmetrical with respect to the optical axis of the beam incident to the objective lens, and effects a substantially zero phase shift with the beam having the first wavelength, but shifts the phase of the beam having the second wavelength by a value other than zero.
Moreover, in accordance with the present invention, an optical head includes a laser, an objective lens for causing a beam issuing from the laser to be transmitted through the substrate of an optical disk having a preselected thickness and to form a fine spot on the recording surface of the optical disk, and optics for sensing the resulting reflection from the recording surface of the optical disk. A plurality of phase shifting devuces extend along an annular zone symmetrical with respect to the optical axis of the beam incident to the objective lens, and shifts the phase of each incident beam by a particular amount.
REFERENCES:
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patent: 0803867A2 (1997-10-01), None
patent: 058009 (1911-03-01), None
patent: 3-52132 (1991-03-01), None
patent: 5-6569 (1993-01-01), None
patent: 5-73945 (1993-03-01), None
patent: 5-144073 (1993-06-01), None
patent: 6-203405 (1994-07-01), None
patent: 7-57271 (1995-03-01), None
patent: 7-98431 (1995-04-01), None
patent: 7-302437 (1995-11-01), None
patent: 7-65409 (1995-11-01), None
patent: 8-17068 (1996-01-01), None
patent: 8-55363 (1996-02-01), None
patent: 8-77594 (1996-03-01), None
patent: 8-153336 (1996-06-01), None
Document No: 5-234122; Date: Sep. 10, 1993; Country: Japan.
A Compact-Disc-Compatible Digital Versatile Disc Pickup Using Annular Mask, Jpn. J. Appl. Phys. vol. 36 (1997) pp. 486-400, Part 1. No. 1B, Jan. 1997.
Laff, Whitesel & Saret, Ldt.
NEC Corporation
Tran Thang V.
Whitesel J. Warren
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