Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2002-04-26
2002-12-17
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S053100, C369S275300
Reexamination Certificate
active
06496459
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for recording and reproducing information on and from an optical disc. In addition, this invention relates to a method of recording and reproducing information on and from an optical disc. Furthermore, this invention relates to an optical disc.
2. Description of the Related Art
Optical discs contain an MD (Mini Disc). MD players include shock-proof memories having a capacity of 4 MB which corresponds to a playback time of about 10 seconds. During the playback mode of operation of the MD player, a pickup sequentially accesses sectors on an MD and reproduces data therefrom. In the MD player, the reproduced data are temporarily stored in the shock-proof memory and are read out therefrom so that the contents of the data are played back. When the pickup jumps from a sector to a next sector, the pickup does not reproduce any data from the MD. Thus, during the playback mode of operation of the MD player, the reproduction of data from the MD by the pickup is sometimes interrupted for a short time. The shock-proof memory absorbs such an interruption of the reproduction of data from the MD, thereby providing continuous playback of the contents of the data. Specifically, data remain read out from the shock-proof memory and playback of the contents of the data continues even for a time during which the pickup jumps from a sector to a next sector while kicking across recording tracks on the MD and waiting for disc rotation to meet the next sector.
During the recording mode of operation of the MD player, a pickup sequentially accesses sectors on the MD and records data thereon. In the MD player, compressed data to be recorded are temporarily stored in the shock-proof memory. The compressed data are intermittently read out from the memory before being fed to the pickup and being recorded on the MD thereby. Thus, during the recording mode of operation of the MD player, the feed of data to the pickup is intermittently executed. The absence of data feed to the pickup is synchronized with jump of the pickup from a sector to a next sector. Accordingly, during the absence of data feed, the pickup jumps from a sector to a next sector while kicking across recording tracks on the MD and waiting for disc rotation to meet the next sector.
Optical discs contain a DVD (Digital Video Disc or Digital Versatile Disc). DVD players include shock-proof memories similar in function to those in the MD players. Typical shock-proof memories in the DVD players have a capacity of 16 MB which corresponds to a playback time of about 2 seconds. Advanced shock-proof memories in the DVD players have a capacity of more than 16 MB which corresponds to a playback time of longer than 2 seconds. Optical discs are of a read only type (a playback only type), a recordable type (a write once type), and a rewritable type. A CD (Compact Disc), a VCD (Video CD), and a DVD are optical discs of the read only type. A CD-R and a DVD-R are optical discs of the recordable type. A CD-RW, a DVD-RAM, and a DVD-RW are optical discs of the rewritable type.
Optical discs of the rewritable type have thin recording films which are reversibly changed between two or more different states in accordance with conditions of laser beams applied thereto. Rewritable optical discs include magneto-optical discs and phase change discs.
In the case of a phase change optical disc, while a recording film is scanned by a laser beam, the recording film is reversibly changed between an amorphous state and a crystalline state by changing conditions of the laser beam in response to a signal to be recorded. Thus, the signal is recorded on the recording film as a pattern of amorphous portions and crystalline portions of the recording film. The signal is reproduced from the phase change optical disc as follows. The surface of an amorphous portion of the disc and the surface of a crystalline portion thereof are different in reflectivity with respect to a laser beam. While the phase change optical disc is scanned by a laser beam, a change in reflectivity of the disc surface with respect to the laser beam is optically detected so that the signal is reproduced from the disc.
The phase change optical disc is similar to a read only optical disc and a recordable optical disc in the point that signal reproduction is implemented by detecting a change in the disc surface reflectivity with respect to a laser beam. Signal overwriting on the phase change optical disc can be performed by use of only one laser beam when the laser power is modulated between an erasing level Pe and a recording level Pw. Therefore, the structure of a drive device for the phase change optical disc can be simple.
It is conceivable to use a PWM (pulse width modulation) system to record a signal on a rewritable optical disc at a high density. According to the PWM system, the positions of the front and rear edges of every recording mark on the disc correspond to “1” in a digital signal.
In the PWM system, the width of every recording mark represents information. Thus, a desirable shape of the recording mark is free from distortion. Specifically, it is desirable that the shapes of the front and rear halves of the recording mark are symmetrical with each other. During the PWM-based recording of a signal on the disc, the disc is exposed to a laser beam while being rotated and moved relative thereto. In addition, the intensity of the laser beam is changed between strong and weak levels in response to the signal to be recorded. Recording marks are formed on portions of the disc which are exposed to the stronger laser beam. Regarding every recording mark, the heat accumulation effect causes the stronger-beam-application ending point on the disc to be higher in temperature than the stronger-beam-application starting point on the disc. As a result, the rear end of the recording mark is wider than the front end thereof. Thus, the shape of the recording mark is distorted.
Japanese published unexamined patent application 3-185628 discloses a method of reducing distortion in the shape of a recording mark. The method in Japanese application 3-185628 is an overwriting method in which one recording mark is formed by the application of a train of short pulses (narrow pulses) of a laser beam to a disc.
Japanese published unexamined patent application 6-12674 discloses a method of correcting the waveform of a train of electric pulses fed to a laser source. According to the method in Japanese application 6-12674, an input signal repetitively changes between a high level state and a low level state. The input signal being continuously in the high level state corresponds to one recording mark. The input signal being continuously in the high level state is converted into a train of electric short pulses (electric narrow pulses). The first pulse in the train is wider than the second and later pulses therein. The number of the pulses in the train is determined by a desired length of the recording mark. The electric pulse train is fed to the laser source. The electric pulse train is converted by the laser source into a corresponding train of short pulses (narrow pulses) of a laser beam. The laser beam pulse train is applied to a disc. One recording mark is formed on the disc in response to the laser beam pulse train. Since the first pulse in the train is relatively wide, the temperature of the beam-train-application starting point on the disc quickly rises. On the other hand, since the second and later pulses in the train are relatively narrow, the temperature of the beam-train-application ending point on the disc is prevented from excessively rising. Therefore, it is possible to compensate for the heat accumulation effect which would cause distortion of the recording mark.
The shape-distortion reducing technique in Japanese application 6-12674 is less effective as the linear velocity related to the scanning of a disc increases. In the method of Japanese application 6-12674, a train of short pulses (narrow pulses) of a laser beam is applied
Edun Muhammad
Victor Company of Japan Ltd.
Woo Louis
LandOfFree
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