Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-04-10
2001-04-10
Psitos, Aristotelis M. (Department: 2752)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053130, C369S116000
Reexamination Certificate
active
06215741
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an optical recording device having a defect detection system and, more particularly, to a technique for detecting a defect generated in a groove pattern or in a recorded/reproduced data and the cause of the defect during the operation of the optical recording device.
(b) Description of the Related Art
Exposure of an optical disk to form a groove pattern on an optical disk or recording/reproducing operation of an optical disk is generally performed by an optical recording device having a laser source. In the exposure or recording/reproducing operation by using a laser beam, the focal position of the beam spot and a laser power from a laser source should be fixed without fluctuation in order to form a stable pattern in the exposure, to record an accurate data in the recording operation or reproduce an accurate data in the reproduction.
However, a fluctuation of the focal position or laser power is sometimes observed in the optical recording device after a continuous long time operation because of the change of the characteristics in the constituent elements or unstable factors of the optical recording device, and causes a defect in the exposure or recording/reproducing operation. If a defect is found in the resultant groove pattern or in the recorded data, the cause of the defect is generally examined in the optical recording device after the exposure or recording/reproducing operation is finished, because the examination and the operation cannot be performed concurrently.
The fluctuation of the focal position enlarges the diameter of the beam spot on the optical disk, which reduces the effective laser energy per unit area for the resultant groove pattern or in the recorded mark. As a result, an effective exposure or recording/reproducing operation can be achieved only in the central part of the beam spot which has a higher power density compared to the peripheral area of the beam spot. Accordingly, the size of a resultant groove pattern or recorded mark becomes smaller in the case of fluctuation of the focal position compared to the case of a normal focal position, and degrades the quality of the groove pattern, recorded data or reproduced data.
The defects caused by the fluctuation of the focal point and by the fluctuation of the laser power are similar so that it is generally difficult to determine the cause of the defect by examining the recorded mark or reproduced data during the exposure or recording operation, i.e., whether the defect is due to the fluctuation of the focal position or laser power from the laser source. The determination of the cause takes a long time examination, which reduces the throughput of the exposure or recording/reproducing.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical recording device for use in an exposure of an optical disk to form a groove pattern or for use in a recording/reproducing operation, which is capable of detecting a defect in a resultant groove pattern or recorded/reproduced data and determining the cause of the defect during the exposure or recording/reproducing operation of the optical-recording device.
In accordance with the present invention, there is provided an optical recording device comprising a laser source for emitting a laser beam, an optical system for focusing the laser beam to irradiate the focused laser beam onto an optical disk and for passing the laser beam reflected by the optical disk, a first photodetector for receiving the laser beam before reflection by the optical disk to generate a first electric signal, a second photodetector for receiving the laser beam after reflection by the optical disk to generate a second electric signal, and a signal processor for calculating a laser power of the laser beam based on the first electric signal and a peak value of an energy distribution profile of the laser beam on the optical disk based on the second electric signal, the signal processor generating a defect signal representing an occurrence of a defect based on the laser power and the peak value.
The optical recording device according to the present invention can detect a defect caused by a laser power fluctuation and/or a peak value fluctuation of the energy profile of the laser beam on the optical disk, as well as the cause of the defect, during exposure or recording/reproducing operation of the optical recording device, thereby raising the throughput of the operation.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.
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McGuireWoods LLP
NEC Corporation
Psitos Aristotelis M.
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