Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2000-12-18
2004-03-30
Hindi, Nabil (Department: 2655)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S112010, C369S112160
Reexamination Certificate
active
06714495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a pickup device for writing information to an information recording medium or reading information from the information recording medium and an information recording/reproducing apparatus having the pickup device.
2. Description of Related Art
In recent years, phase change type information recording media have been developed as information recording media of a large capacity which allows the recording of information at high density. The known kinds of the phase change type recording media are: a read only optical disc; a WORM-type optical disc in which information can be recorded once; and a rewritable type optical disc in which erasure and rerecording of information can be performed.
Those phase change type information recording media have a structure that information is recorded by causing a phase change of a crystal or amorphous recording layer or the like by means of light energy. The read only optical disc and WORM-type optical disc have such a characteristic that information is recorded only once by using its recording layer which is irreversibly changed by a light energy. The rewritable type optical disc has such a characteristic that information can be rewritten by using its recording layer which is reversibly changed by light energy. According to those phase change information recording media, the high density recording of information can be performed by narrowing the so called track pitch.
To realize an information recording/reproducing apparatus adapted to the information recording media that can perform the high density recording, there considered is a method for increasing a numerical aperture (NA) of an objective lens provided in the so-called pickup device, thereby a laser beam of a small irradiation diameter is irradiated to the recording layer. Thus, high density recording of information or reproduction of the information recorded at high density is performed.
It is also considered to apply a crosstalk cancelling technique in order to perform a precise reproduction of information in a limited range of the numerical aperture NA of the objective lens.
In the case of the reproduction of information from the phase change type information recording medium by using the conventional crosstalk cancelling technique, however, there are the following problems.
First, according to the conventional crosstalk cancelling technique, different laser beams are simultaneously irradiated to both of a track on which information to be reproduced has been recorded (hereinafter, referred to as a main track) and tracks adjacent to the main track (hereinafter, referred to as adjacent tracks), the reflection light by the laser beam irradiated to the main track (hereinafter, referred to as a main beam) and the reflection light by the laser beams irradiated to the adjacent tracks (hereinafter, referred to as sub beams) are optically detected, and a predetermined arithmetic operating process is performed based on each of detection signals detected, thereby removing a crosstalk component included in the detection signal reproduced from the main track.
In the conventional pickup device, an optical system having such a structure that an objective lens is used commonly for the recording of information and the reproduction of information in order to realize miniaturization, reduction of the weight, or the like. More specifically, there used is a construction such that a light emitted from a laser light source provided for the optical system is divided into a 0th order light beam and ±1 primary light beams by means of a grating (diffraction grating), the 0th order light beam is irradiated as a main beam to the main track through the objective lens, and the ±1 primary light beams are irradiated as sub beams to the adjacent tracks through the objective lens. That is, according to the conventional pickup device, the main beam and the sub beams are irradiated in each of the recording of information and the reproduction of information.
Therefore, if the power of a laser light source is raised in order to raise the power of the main beam (0th order light) to record information to the WORM-type optical disc or rewritable type optical disc, the powers of the sub beams (±1 primary light) are also raised accordingly. A problem is that, upon recording of information, the information already recorded on the adjacent tracks is erased or destroyed by the sub beams of the high powers, consequently.
To avoid the problem associated with the recording of information mentioned above, a method of reducing the powers of the sub beams (±1 primary light) by using a grating of a low diffraction efficiency has been considered. In this case, however, the power of the main beam (0th order light) rises by an amount corresponding to the reduced amount of the powers of the sub beams (±1 primary light) due to the use of the grating. Therefore, if the main beam and the sub beams are irradiated in order to effect the crosstalk cancellation when the information is reproduced from the read only optical disc, WORM-type optical disc, or rewritable type optical disc, a problem arises that the information on the main track is erased or destroyed by the high power main beam although the erasure or breakage of the information on the adjacent tracks by the sub beams is avoided.
OBJECTS AND SUMMARY OF THE INVENTION
The invention has been made to solve the problems of the conventional arrangement mentioned above, and it is an object of the invention to provide a pickup device and an information recording/reproducing apparatus, which allows execution of a precise recording of information to an information recording medium to which high density recording can be performed and a precise reproduction of information from the information recording medium to which the information has been recorded at high density.
Another object of the invention is to provide a pickup device which enables the recording of information and the reproduction of information to be performed by a same objective lens even when the crosstalk cancelling technique is applied.
According to a first aspect of the invention, there is provided a pickup device for recording information to an information recording medium and/or reproducing information from the information recording medium, comprising: a light source for emitting first light for irradiating a first laser beam for recording information or reproducing information onto the information recording medium at the time of the recording of information or the reproduction of information and second light for irradiating a second laser beam onto a track adjacent to a track on which the first laser beam is irradiated at least at the time of the reproduction of information; and control means for independently controlling powers of the first light and the second light.
According to the pickup device with this construction, by properly controlling the powers of the first light and the second light, the powers of the first light and the second light which are irradiated to the track of the information recording medium at the time of the recording of information or reproduction of information are adjusted, so that erasure or the like of the information which has already been recorded on the track can be prevented. At the time of the reproduction of information, each reflection light which is caused when the first and second laser beams are reflected by the track is detected and information in which crosstalk components have been suppressed can be reproduced on the basis of detection results.
According to the second aspect of the invention, the pickup device further has a grating arranged between the light source and the information recording medium, the light source has a structure such that the first and second lights whose polarizing directions cross perpendicularly are emitted, and the grating has a structure such that the first light is transmitted without being diffracted and the second light is diffracted and transm
Hindi Nabil
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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