Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-11-06
2001-08-21
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044140, C369S044180
Reexamination Certificate
active
06278682
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical system to be employed in an optical disc drive to read/write data from/to an optical disc.
Recently, technology in the field of magneto-optical disc drives has been greatly improved such that a data recording density on a magneto-optical disc has reached in excess of 10 Gbits/inch
2.
In an example of such an optical disc drive, an objective optical system is mounted on an arm which is movable in a transverse direction of tracks formed on an optical disc for rough tracking. Firstly, the rough tracking is performed to locate the optical head in the vicinity of the track.
Then, an incident angle of a beam incident on the objective optical system is controlled to locate a beam spot formed by the objective optical system for fine tracking, with use of a galvano mirror or the like. During the fine tracking operation, the beam spot is accurately located on one of the tracks whose pitch is, for example, 0.34 &mgr;m.
In the optical disc drive as described above, however, if a rotation amount of the galvano mirror exceeds a predetermined range, optical performance thereof is remarkably lowered. Thus, it is necessary to detect the rotation amount of the galvano mirror, and the rotation amount should be controlled to be maintained within the predetermined range.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved optical disc drive capable of detecting a rotation angle of a galvano mirror so that the galvano mirror is prevented from being rotated to a position out of a predetermined range.
For the above object, according to the invention, there is provided an optical disc drive for reading/writing data from/on an optical disc, which is provided with: a laser source that emits a parallel laser beam; an objective lens system that receives the laser beam emitted by the laser source and converges the laser beam on the optical disc; a deflection mirror provided between the laser source and the objective lens system, an incident angle of the laser beam incident on the objective lens system being changed as the deflection mirror is rotated, a position, on the optical disc, at which the laser beam is converged varying in accordance with the incident angle; a relay lens system including at least first and second relay lens groups, the relay lens system being provided between the deflection mirror and the objective lens system, the relay lens system makes the vicinity of the deflection mirror and a principal plane of the objective lens conjugate; a diffraction grating provided between the laser source and the deflection mirror, the diffraction grating dividing an incident beam into at least 0th order beam and ±1st order diffraction beams having predetermined diffraction angles, the at least 0th order beam and ±1st order diffraction beams being incident on and deflected by the deflection mirror; and a detecting system that receives the ±1st order diffraction beams deflected by the deflection mirror and determines a rotational position of the deflection mirror in accordance with the received ±1st order diffraction beams.
Since the incident beam is divided into diffraction beams, and with the diffraction beams, the rotational position of the deflection mirror is detected, an extra light source for detecting the rotational position of the deflection mirror is not necessary. Further, since the rotational position of the deflection mirror can always be monitored, the deflection mirror is prevented from being rotated exceeding a predetermined range, and accordingly, the tracking operation can be performed accurately without lowering the optical performance.
The optical disc drive may be provided with a light shielding system that prevents the ±1st order diffraction beams from being incident on the objective lens system and allows only the 0th order beam to be incident on the objective lens system. Thus, unnecessary light, which may cause noises or the like, will not be incident on the objective lens system.
In a particular case, the detecting system may detect the rotational position of the deflection mirror in accordance with amounts of light of the ±1st order diffraction beams deflected by the deflection mirror.
Specifically, the detecting system may have at least two light receiving areas arranged in a direction perpendicular to an axis of rotation of the deflection mirror for receiving at least a part of the ±1st order diffraction beams, respectively. With this structure, the detecting system may detect the rotational position of the deflection mirror in accordance with a difference between amounts of light respectively received by the two light receiving areas.
Alternatively, the detecting system may detect the rotational position of the deflection mirror in accordance with beam incident positions of the detecting system on which the ±1st order diffraction beams are incident.
In a specific example, the diffraction grating may be formed with a plurality of linearly extending grooves extending in a direction parallel to a rotation axis of the deflection mirror. The detecting system may have first and second light receiving areas arranged in a direction perpendicular to the rotation axis of the deflection mirror for receiving at least a part of the ±1st order diffraction beams, respectively. In such a configuration, the detecting system may detect the rotational position of the deflection mirror in accordance with a difference between amounts of light received by the first and second light receiving areas.
In one case, the detecting system may be provided between the deflection mirror and the relay lens groups.
Optionally, the detecting system may be provided with a plate member on which the first and second light receiving areas are provided, and an opening is formed between the first and second light receiving areas. A part of the ±1st order diffraction beams is received by the first and second light receiving areas, and a remaining part of the ±1st order diffraction beams and the 0th order beam may pass through the opening.
Optionally, the detecting system may be provided with a plate member on which the first and second light receiving areas are provided, and an opening is formed between the first and second light receiving areas. A part of the ±1st order diffraction beams is received by the first and second light receiving areas, and a remaining part of the ±1st order diffraction beams and the 0th order beam may pass through the opening.
Further optionally, a light shielding member may be provided between the first and second relay lens groups. The light shielding member may prevent the remaining part of the ±1st order diffraction beams passed through the opening from being incident on the objective lens system and allow only the 0th order beam to be incident on the objective lens system.
Alternatively, the detecting system may be provided between the first and second the relay lens groups.
In this case, the detecting system may have a plate member on which the first and second light receiving areas are provided, and an opening may be formed between the first and second light receiving areas. At least a part of the ±1st order diffraction beams may be received by the first and second light receiving areas, and the opening may allow only the 0th order beam to pass through.
Still alternatively, the diffraction grating is formed with a plurality of linearly extending grooves, the plurality of grooves extending in a direction perpendicular to a rotation axis of the deflection mirror. Further, the detecting system may have a plate member provided with first through fourth light receiving areas. The first and second light receiving areas are arranged in a direction perpendicular to the rotation axis of the deflection mirror, and the third and fourth light receiving areas are arranged in a direction perpendicular to the rotation axis of the deflection mirror. The first and second light receiv
Nishikawa Hiroshi
Takishima Suguru
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Hindi Nabil
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