Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-03-15
2002-06-18
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S199000
Reexamination Certificate
active
06407975
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical disk drive.
An optical disk drive is so constituted as to write data on and/or read data from an optical disk by means of laser beam or the like. In the optical disk drive, an object optical system is carried on a linearly movable carriage that is movable along a surface of the optical disk.
Recently, an optical disk drive for double-sided optical disk has been developed. Such an optical disk drive has two movable carriages carrying objective lenses, which are linearly movable along the surfaces of the optical disk. Further, two separate optical units (such as laser source modules) are provided to stationary parts of the optical disk drive, each of which emits a beam to the respective carriage. However, because of the provision of two separate optical units, the structure of the optical disk drive may be complicated.
Thus, it is desired to provide a simple-structured optical device for a double-sided optical disk.
Further, a general optical disk drive (for a single-sided optical disk or a double-sided optical disk) is arranged to perform a ‘fine tracking’ using a so-called galvano mirror. The galvano mirror is rotated, thereby to change the incident angle of the beam on an objective lens, so that the beam spot minutely moves on the record surface of the optical disk.
FIGS. 1A and 1B
schematically show the beam converged on a record surface
2
a
of an optical disk
2
. When the incident angle of the beam on an objective lens
500
varies, the incident position of the beam on the objective lens
500
may also vary as shown in
FIGS. 1A and 1B
. In such a case, the incident beam is partially interfered with a surrounding member A (such as an aperture or the like) which surrounds the objective lens
500
. This phenomena is called ‘wane’. When such wane occurs, the intensity of the beam on the record surface is lowered as shown in FIG.
2
B. It may cause incorrect tracking operation.
Thus, it is desired to provide an optical disk drive capable of fine tracking without changing the incident position of the beam on the objective lens.
In order to increase the data storage capacity of the
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a simple-structured optical device for a double-sided optical disk.
For the above object, according to one aspect of the present invention, there is provided an optical disk drive including two object optical systems, two carriage which carry the object optical systems and is movable along the surfaces of the optical disk, a separate optical unit (includes a laser source module) separated from the carriage, and a beam path selection system which selectively introduces the beam from the laser source to one of the object optical systems.
As constructed above, it is possible to selectively introduce the beam from the laser source module to one of the first and second carriages. Thus, one laser source module is commonly used for emitting beam to the first and second object optical systems. Accordingly, it is not necessary to provided two laser source modules, so that the structure of the optical disk drive is simplified.
In a particular arrangement, the beam path selecting system includes a movable mirror movable between first and second positions. Since the selecting of the beam path-selecting operation is performed by vertically moving the optical disk, it is necessary to increase NA (numerical aperture) of the objective lens, without increasing the size of the objective lens. For this purpose, a so-called near-field recording (NFR) technology is proposed. As shown in
FIG. 3
, the NFR technology has a hemisphere lens
510
provided between the objective lens
500
and the optical disk
2
. The flat surface
511
of the hemisphere lens
510
is faced with the record surface
2
a
of the optical disk
2
. A gap between the hemisphere lens
510
and the record surface
2
a
is less than 1 &mgr;m. The beam that has passed through the objective lens
500
is converged on the flat surface
511
of the hemisphere lens
510
. The converged beam is converted to a so-called ‘evanescent beam’ which propagates across the minute gap. Since the diameter of the evanescent beam is smaller than the converged beam, NA is remarkably increased. However, such NFR technology has a disadvantage that dust may easily be caught in the gap between the hemisphere lens
510
and the record surface
2
a
. Additionally, due to the use of the evanescent beam, the energy efficiency is relatively low, i.e., the intensity of the beam incident on the optical disk is relatively low.
Thus, it is desired to increase NA of an object optical system, without increasing the size of lenses and without using evanescent beam. movable mirror between two positions, the structure of the disk drive device is further simplified.
It is a second object of the present invention to enable a fine tracking operation without changing the incident of a beam on an object optical system.
For the above object, according to one aspect of the present invention, there is provided an optical disk drive including an object optical system which converges a beam on an optical disk, a movable carriage which carries the object optical system and is movable along the optical disk, a separate optical unit separated from the carriage. The separate optical unit includes a laser source module which emits a beam and a galvano mirror which is rotated thereby to change the incident direction of the beam on the object optical system. The optical disk drive device further includes a compensation system having a movable mirror provided in a beam path between the laser source module and the object optical system. The compensation system moves the movable mirror so that the beam from the laser source module is reflected by the galvano mirror and is incident on the object optical system substantially at the same position regardless of rotation amount of the galvano mirror.
As constructed above, the beam is incident on the object optical system substantially at the same position regardless of rotation amount of the galvano mirror. Thus, even when the galvano mirror rotates, the beam directing toward the object lens is not interfered with a surrounding member around the object optical system. That is, a ‘wane’ (as in
FIG. 1B
) does not occur. Therefore, the intensity of the beam on the optical disk is not lowered during the fine tracking operation. Accordingly, incorrect tracking operation is prevented.
Advantageously, the compensation system includes a distance detector which detects a distance between the galvano mirror and the object optical system. The amount (H) of movement of the movable mirror is determined based on a equation: H=L tan (2&thgr;). L represents a distance between the galvano mirror and the object optical system. &thgr; represents a rotation angle of the galvano mirror.
It is a third object of the present invention to increase NA of an object optical system without increasing the size thereof and without using so-called evanescent beam.
For the above object, according to one aspect of the present invention, there is provided an optical disk drive including a laser source module which emits a beam, and an object optical system which converges the beam onto a optical disk. The optical disk includes a first lens, and a second lens that is substantially hemisphere-shaped (with a flat surface and a sphere surface). The second lens is located between the first lens and the optical disk so that a flat surface of the second lens is faced with the optical disk. A center of curvature of the sphere surface of the second lens is positioned between the first lens and a focal point of the first lens.
As constructed above, when the converging beam (directing toward the focal point) passes the sphere surface of the second lens, the beam refracts in a direction in which the beam further converges. Thus, NA is remarkably increased. Further, since evanescent beam (as in the NFR technology) is not used, the energy effici
Asahi Kogaku Kogyo Kabushiki Kaisha of Tokyo
Greenblum & Bernstein P.L.C.
Tran Thang V.
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