Optical system for optical disc drive

Details Optical system for optical disc drive Optical system for optical disc drive

2001-02-20

2001-11-27

Huber, Paul W. (Department: 2651)

Dynamic information storage or retrieval

Condition indicating, monitoring, or testing

Including radiation storage or retrieval

C369S112240, C369S112290, C369S119000

Reexamination Certificate

active

06324141

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 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, the incident angle of a beam which is incident on the objective optical system is changed (i.e., a fine tracking is performed), with use of a deflector such as 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 order to control the tracking operation, it is necessary to detect the amount of rotation of the galvano mirror. Specifically, in the optical disc drive described above, if the galvano mirror is rotated to a position out of a certain rotational range to adjust the position of the beam spot, optical performance of the disc drive may be significantly lowered. Thus, the rotation angle of the deflection mirror should be monitored and controlled so as not to exceed a predetermined rotational range.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved optical system, which is applicable to an optical disc drive having a rotatable deflection system, and enables to perform the tracking operation accurately.
For the above object, according to the present invention, there is provided a head of an optical data recording/reproducing device, which is provided with: a laser source that emits a laser beam; a deflector on which the laser beam emitted by the laser source is incident; a relay optical system including a first relay lens and a second relay lens; an objective lens system, the laser beam emitted by the laser source being incident on the objective lens system through the deflector and the relay optical system; a beam splitter provided between the first relay lens and the second relay lens, the beam splitter dividing a beam passed through the first relay lens into a first beam directed to the second relay lens and a second beam directed away from the optical axis of the relay lens system; a detector having a light receiving surface on which the second beam is incident; and a controller which determines a direction and amount of rotation of the deflector based in accordance with the position of the light receiving surface on which a beam is incident.
Optionally, the relay lens system may be configured such that a position in the vicinity of a rotation axis of the deflector and a front principal plane of the objective optical system have a conjugate relationship. Further, it is preferable that the laser source emits a parallel beam.
Further optionally, it is preferable that the first relay lens and the second relay lens area arranged such that focal points thereof substantially coincide with each other.
In one case, the beam splitter may be located between the first relay lens and a focal point of the second relay lens.
Specifically, the light receiving surface of the detector may have two light receiving areas arranged in a direction where a beam spot moves when the deflector rotates, and the controller may determine the direction and amount of rotation of the deflector by comparing the amounts of light received by the two light receiving areas.
Alternatively, the beam splitter may be located between the focal point of the first relay lens and the second relay lens.
Specifically, the light receiving surface may have two light receiving areas arranged in a direction where a beam spot moves when the deflector rotates, and the controller may determine the direction and amount of rotation of the deflector by comparing the amounts of light received by the two light receiving areas.
Optionally, the beam splitter and the second relay lens may be formed integrally.
Further alternatively, the beam splitter may be located substantially at the focal point of the first relay lens.
Specifically, the detector may include a PSD (Position Sensitive Device) for detecting a position of the light receiving surface on which the beam spot is formed, the light receiving surface extending in a direction where a beam spot moves when the deflector rotates, and wherein the controller determines the direction and amount of rotation of the deflector based on the position of the beam spot on the light receiving surface.


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