Dynamic information storage or retrieval – Binary pulse train information signal
Reexamination Certificate
2001-09-04
2003-12-02
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Binary pulse train information signal
C369S059120, C369S116000, C369S047510
Reexamination Certificate
active
06657935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of recording information on an optical disc by using a laser beam. This invention also relates to an apparatus for recording information on an optical disc by using a laser beam.
2. Description of the Related Art
It is known to record information on an optical disc in a mark edge recording technique (a mark length recording technique). An example of the recording of information on an optical disc uses a laser beam. Specifically, during the recording of information, a laser beam is intermittently applied to the optical disc while being moved relative thereto. Recording marks are formed in places on the optical disc which are exposed to the laser beam.
In general, the laser beam is generated by a laser diode. To implement the intermittent generation of the laser beam, the laser diode is driven by a pulse signal. In a conventional method, every recording mark on the optical disc corresponds to one drive pulse fed to the laser diode. Furthermore, the length of the recording mark corresponds to the width of the drive pulse. In this case, the heat accumulation effect causes positional and shape errors of the edges of the recording mark.
In a known improved method, every recording mark on an optical disc is caused by a multi-pulse train fed to a laser diode. The multi-pulse train means a sequence of short drive pulses. The duty cycle of the multi-pulse train is chosen to provide a suitable effective recording power of the laser beam at which the heat accumulation effect is sufficiently suppressed. Generally, the width of a first drive pulse in the multi-pulse train is greater than those of other drive pulses therein.
Japanese patent application publication number 11-312311 discloses a method of recording information on an optical disc. In the method of Japanese application 11-312311, a mark data length “nT” is determined on the basis of the period “T” of a recording channel clock signal, where “n” denotes an integer selected from predetermined natural numbers. For the mark data length “nT”, a multi-pulse train is fed to a laser diode to form a recording mark on the optical disc. The multi-pulse train means a sequence of short drive pulses. One of drive pulses in the multi-pulse train is remarkably longer than the other drive pulses. Specifically, the long drive pulse has a width equal to or greater than “1.5T” while the other drive pulses are equal to or shorter than about “T”. In the method of Japanese application 11-312311, a photodiode detects the intensity of a reflected laser beam which results from the reflection of a forward laser beam by the optical disc. During the application of the long drive pulse to the laser diode, the laser beam intensity detected by the photodiode rises and then drops before stabilizing. The detected laser beam is sampled at a moment within the stabilizing stage during the application of the long drive pulse. The sample of the detected laser beam indicates a mark forming condition. Samples of the detected laser beam are generated for multi-pulse trains, respectively. A drive signal to the laser diode which contains multi-pulse trains is controlled in response to samples of the detected laser beam to maintain the mark recording condition in an appropriate range.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide an improved method of recording information on a recording medium such as an optical disc.
It is a second object of this invention to provide an improved apparatus for recording information on a recording medium such as an optical disc.
A first aspect of this invention provides a method of recording information on an optical disc. The method comprises the steps of applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; detecting an intensity of a reflected laser beam which results from reflection of the forward laser beam by the optical disc; dividing the detected intensity by a setting intensity to get a division result; detecting a condition of recording of each of the mark areas in response to the division result; and controlling an amplitude of each of the multi-pulse trains in response to the detected condition.
A second aspect of this invention provides a method of recording information on an optical disc. The method comprises the steps of applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; detecting an intensity of a reflected laser beam which results from reflection of the forward laser beam by the optical disc; detecting a maximal intensity of the reflected laser beam which is caused by first one among pulses in each of the multi-pulse trains; dividing the detected intensity by the detected maximal intensity to get a division result; detecting a condition of recording of each of the mark areas in response to the division result; and controlling an amplitude of each of the multi-pulse trains in response to the detected condition.
A third aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains.
A fourth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a difference between a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains.
A fifth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a ratio between a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains.
A sixth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises one of (1) a difference and (2) a ratio between a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains.
A seventh aspect of this invention is based on the first aspect thereof, and provides a method further comprising the step of controlling a duty cycle of each of the multi-pulse trains in response to the detected condition in cases where the amplitude thereof reaches its upper limit.
An eighth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity consists of a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of selected ones among the multi-pulse trains, and the selected multi-pulse trains correspond to mark data lengths between 7T and 14T, where “T” denotes a channel period.
A ninth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity consists of a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of selected ones among the multi-pulse trains, and the selected multi-pulse trains correspond to a maximum mark data length.
A tenth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity consists of a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of selected ones among the multi-pulse trains, and the select
Eguchi Hideharu
Kamioka Yuuichi
Koishi Kenji
Konno Kohjyu
Osada Yutaka
Edun Muhammad
Victor Company of Japan Ltd.
Woo Louis
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