Optical information storage device having phase compensating mechanism and polarization plane rotating mechanism

• US 6,472,651 B1
• Filed: 01/07/2000
• Issued: 10/29/2002
• Est. Priority Date: 06/18/1999
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Ukai, Hirataka
• Primary Examiner(s): Pyo, Kevin
• Assistant Examiner(s): Sohn, Seung C
• Application Number:
  US09/478,910
• Time in Patent Office: 1,026 Days
• Field of Search: 369/13.01, 369/13.32, 369/244, 369/13-9-, 250/201.5, 250/201.2, 250/201.3, 250/201.4, 250/225
• US Class Current: 250/201.5
• CPC Class Codes: G02B 27/28 for polarising used in stereoscopes G02B30/25
• CPC Class Codes: G11B 11/10545 interacting directly with the magnetisation on the record carrier
• CPC Class Codes: G11B 7/1381 Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops G11B7/1353 - G11B7/1369 take precedence

Abstract

An optical information storage device including a first photodetector for detecting a regenerative signal from reflected light from an optical recording medium, a second photodetector for detecting a tracking error signal and a focusing error signal from the reflected light, and a beam splitter for separating the reflected light into a first beam directed toward the first photodetector and a second beam directed toward the second photodetector. The optical information storage device further includes a phase compensating mechanism provided between the beam splitter and the first photodetector for compensating for a phase difference of the first beam, a Wollaston prism provided between the phase compensating mechanism and the first photodetector for separating the first beam into two beams having orthogonal polarization planes, and a polarization plane rotating mechanism for rotating the polarization plane of the first beam incident on the Wollaston prism.

Claims

1. An optical information storage device comprising:

an optical source;

an optical head having an objective lens for focusing light from said optical source onto a recording surface of an optical recording medium;

a first photodetector for detecting a reproducing signal from reflected light from said optical recording medium;

a second photodetector for detecting a tracking error signal and a focusing error signal from said reflected light;

a beam splitter for separating said reflected light into a first beam directed toward said first photodetector and a second beam directed toward said second photodetector;

a phase compensating mechanism provided between said beam splitter and said first photodetector for compensating for a phase difference of said first beam, said phase compensating mechanism including a phase plate and a support member for supporting said phase plate so that said phase plate is rotationally adjustable about an axis perpendicular to an optical path of said first beam, said phase plate having a thickness such that a phase difference larger than the sum of the maximum values of variations in phase difference in all optical components constituting an optical system through which said reflected light passes is given to said first beam when the angle of incidence of said first beam on said phase plate is 0°

;

beam separating means provided between said phase compensating mechanism and said first photodetector for separating said first beam into two beams having different polarization planes; and

polarization plane rotating means for rotating a polarization plane of said first beam incident on said beam separating means.

2. An optical information storage device according to claim 1, further comprising:

a condenser lens for focusing said first beam on said first photodetector;

said beam separating means comprising a Wollaston prism.

3. An optical information storage device according to claim 2, wherein an effective diameter of said condenser lens and an effective region of said Wollaston prism are set so as to make allowance for a shift amount of said first beam generated in rotationally adjusting said phase plate so as to compensate for the phase difference of said first beam.

4. An optical information storage device according to claim 2, wherein said Wollaston prism, said condenser lens, and said first photodetector have a common optical axis shifted from a center of an optical path of said first beam incident on said phase plate by a distance equal to a shift amount of said first beam generated in rotationally adjusting said phase plate so as to compensate for the phase difference of said first beam.

5. An optical information storage device according to claim 2, wherein said polarization plane rotating means comprises:

a rotatable lens holder for commonly accommodating said condenser lens and said Wollaston prism; and

an optical base for mounting said lens holder so that said lens holder is rotationally adjustable about the optical axis thereof.

6. An optical information storage device according to claim 2, wherein said polarization plane rotating means comprises means for rotating said Wollaston prism about the optical axis thereof.

7. An optical information storage device according to claim 5, wherein:

said optical base has a V groove for receiving said lens holder; and

said polarization plane rotating means further comprises means for fixing said lens holder to said optical base so that said lens holder received in said v groove is rotationally adjustable about the optical axis thereof.

8. An optical information storage device according to claim 1, wherein said polarization plane rotating means comprises:

a half-wave plate;

a cylindrical support for accommodating said half-wave plate; and

means for holding said cylindrical support so that said cylindrical support is rotationally adjustable about the optical axis thereof.

9. An optical information storage device according to claim 1, wherein said phase compensating mechanism is adjusted so as to compensate for the phase difference of said first beam so that an undulation amount of a DC component of said regenerative signal is minimized.

10. An optical information storage device according to claim 9, wherein said polarization plane rotating means is adjusted so as to rotate the polarization plane of said first beam so that an offset amount of the DC component of said regenerative signal is minimized.

11. An optical system for an optical information storage device, comprising:

an optical source;

an optical head having an objective lens for focusing light from said optical source onto a recording surface of an optical recording medium;

a first photodetector for detecting a reproducing signal from reflected light from said optical recording medium;

a second photodetector for detecting a tracking error signal and a focusing error signal from said reflected light;

a beam splitter for separating said reflected light into a first beam directed toward said first photodetector and a second beam directed toward said second photodetector;

a phase compensating mechanism provided between said beam splitter and said first photodetector for compensating for a phase difference of said first beam, said phase compensating mechanism including a phase plate and a support member for supporting said phase plate so that said phase plate is rotationally adjustable about an axis perpendicular to an optical path of said first beam, said phase plate having a thickness such that a phase difference larger than the sum of the maximum values of variations in phase difference in all optical components constituting an optical system through which said reflected light passes is given to said first beam when the angle of incidence of said first beam on said phase plate is 0°

;

beam separating means provided between said phase compensating mechanism and said first photodetector for separating said first beam into two beams having different polarization planes; and

polarization plane rotating means for rotating a polarization plane of said first beam incident on said beam separating means.

12. An optical information storage device comprising:

an optical source;

an optical head having an objective lens for focusing light from said optical source onto a recording surface of an optical recording medium;

a first photodetector for detecting a reproducing signal from reflected light from said optical recording medium;

a second photodetector for detecting a tracking error signal and a focusing error signal from said reflected light;

a beam splitter for separating said reflected light into a first beam directed toward said first photodetector and a second beam directed toward said second photodetector;

a phase compensating mechanism provided between said beam splitter and said first photodetector for compensating for a phase difference of said first beam;

a Wollaston prism provided between said phase compensating mechanism and said first photodetector for separating said first beam into two beams having different polarization planes;

polarization plane rotating means for rotating a polarization plane of said first beam incident on said beam separating means; and

a condenser lens for focusing said first beam on said first photodetector;

wherein said phase compensating mechanism includes a phase plate and a support member for supporting said phase plate so that said phase plate is rotationally adjustable about an axis perpendicular to an optical path of said first beam, and

wherein said Wollaston prism, said condenser lens, and said first photodetector have a common optical axis shifted from a center of an optical path of said first beam incident on said phase plate by a distance equal to a shift amount of said first beam generated in rotationally adjusting said phase plate so as to compensate for the phase difference of said first beam.