Optical recording and reproducing methods for optical disk

Details Optical recording and reproducing methods for optical disk Optical recording and reproducing methods for optical disk

1999-10-07

2002-11-26

Huber, Paul W. (Department: 2653)

Dynamic information storage or retrieval

Control of storage or retrieval operation by a control...

Control of information signal processing channel

C369S047510, C369S053310

Reexamination Certificate

active

06487149

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to optical recording and reproducing methods for an optical disk having a disk surface portion in which prepits, indicative of preformat information, are formed.
(2) Description of the Related Art
Recordable optical storage media are known. Generally, in a recordable optical disk, preformat information, including address information, rotation control sync marks and record position control sync marks, is recorded. For example, a CD-R (compact disk recordable) or a MD (mini-disk) includes a disk surface portion in which wobble grooves are formed in order to derive a wobble signal, indicative of the rotation control sync information, from the wobble grooves.
As disclosed in Japanese Laid-Open Patent Application No. 9-326138, there is known an optical disk having a disk surface portion in which prepits, indicative of the preformat information (for example, the address information), are formed. In the optical disk disclosed in the above publication, the wobble grooves are formed as the tracks, and the lands between neighboring grooves are used to form the prepits at given distances along the track. These prepits are called the land prepits (LPP). Even when the track pitch is small, the prepits can be continuously formed on the lands of the disk without interruption, and the preformat information derived from such prepits of the optical disk is useful for obtaining accurate address information and accurate rotation control sync information.
FIG. 10
shows a track structure of an optical disk as disclosed in the above publication.
As shown in
FIG. 10
, in the disk surface portion of the optical disk, wobble grooves G are formed to extend in a tangential track direction TT of the disk, and land prepits LPP are formed on the lands L between neighboring grooves. In the optical disk in the above preformat structure, data is written in the grooves and the lands acting as a guard band. It is intended to prevent the influence of the prepits (on the lands) to the data recorded in the grooves. The lowering of recording density of the optical disk due to the preformat information can be avoided, and the compatibility with read-only optical storage media, such as CD (compact disk) and DVD (digital video disk), can be maintained.
As disclosed in the above publication or Japanese Laid-Open Patent Application No. 9-17029, a method of detecting the preformat information from the optical disk of the above type is known.
In the preformat information detection method of the above publications, a push-pull signal is derived from a reflected laser beam from the optical disk by using a 4-segment photodetector. The push-pull signal is supplied to a high-pass filter, and the direct-current component of the push-pull signal is eliminated by the high-pass filter. The resulting signal is converted into a digital signal by using a slicer (comparator). The digital signal is subjected to demodulation so that a prepit signal indicative of the preformat information, such as the address information, is produced.
In a conventional optical recording method, an optimal recording power is predetermined which is the most suitable laser power of a laser light source for minimizing the amount of jitter in data recording. In the conventional optical recording method, this optimal recording power is used to record data to the optical disk, with respect to the entire track of the optical disk, even when the optical disk of the type shown in
FIG. 10
is accessed.
FIG.
12
A through
FIG. 12E
are diagrams for explaining a conventional optical recording method.
FIG. 12A
shows a waveform of a push-pull signal produced at an output of a high-pass filter.
FIG. 12B
shows a waveform of a prepit signal derived from the push-pull signal.
FIG. 12C
shows a waveform of a data signal produced by an EFM (eight-to-fourteen modulation) decoder.
FIG. 12D
shows a waveform of an LD (laser diode) emission power signal.
FIG. 12E
shows a pattern of write marks recorded along a track of the optical disk in accordance with the LD emission power signal.
When recording write marks along a track (groove) of the optical disk at the optimal recording power, the LD emission power waveform of
FIG. 12D
is used. As shown in
FIG. 12E
, the groove “G” is interposed between the neighboring lands “L”, and this prevents the write marks from radially extending beyond the boundaries between the groove G and the lands L. Hence, the write marks “M” have a radial width which is substantially equal to a radial width of the groove “G”.
However, in the optical disk of the type of
FIG. 10
, the prepits “LPP” are formed on the lands L before data is recorded to the optical disk. As shown in
FIG. 12E
, the center write mark “M” which is located radially adjacent to the prepit “LPP” may extend beyond the boundary between the groove G and the land L (with the prepit LPP). This causes the reflected laser beam from the prepit LPP of the optical disk to be lowered due to the presence of the write mark M adjacent to the prepit LPP. Also, the amplitude of the push-pull signal corresponding to this position of the optical disk will be lowered. The amplitude of a prepit signal in the conventional optical recording method may be significantly degraded due to the presence of the write mark radially adjacent to the corresponding prepit in the optical disk.
FIG. 11A
shows a prepit signal before recording, and
FIG. 11B
shows a prepit signal after recording which may be produced in the conventional optical recording method.
When recording the write marks along the track (groove) of the optical disk in accordance with the data signal as shown in
FIG. 12C
, the write marks and the spaces between write marks on the groove are likely to confront the positions of the prepits on the neighboring lands with equal probability. The amplitude of the prepit signal always varies in accordance with the prepit pattern.
As shown in
FIG. 11A
, the amplitude of the prepit signal before the write marks are recorded to the optical disk is highly stable without significant degradation. By comparing the prepit signal with a slice level of the slicer, it is possible to accurately detect the preformat information from the optical disk.
However, if the write marks are already recorded along the entire track of the optical disk at the optimal recording power, the amplitude of the prepit signal becomes significantly unstable as shown in FIG.
11
B. For example, when the prepit on the land aligns with the write mark on the neighboring groove, the peak amplitude of the prepit signal is reduced to below ½ of the peak amplitude of FIG.
11
A. In such a case, the prepit signal cannot be properly detected by using the slice level of the slicer. When the prepit on the land aligns with the space between write marks on the neighboring groove, the peak amplitude of the prepit signal is substantially the same as the peak amplitude of FIG.
11
A. For this reason, it is difficult for the conventional optical recording method to provide accurate detection of the preformat information from the optical disk.
Further, as disclosed in Japanese Laid-Open Patent Application No. 5-128564, a method of detecting the wobble signal from the optical disk of the above type is known. The conventional optical reproducing method of the above publication is aimed at obtaining accurate detection of the wobble signal even when a tilt of the optical axis of the objective lens with respect to the optical disk surface arises. In the method of the above publication, the gains of outputs from two photodiodes of a 2-segment photodetector are adjusted to be equal to each other. A difference signal indicative of a difference between the reproducing signals output from the photodiodes is produced by subtraction, and the difference signal is passed through a wobble decoder so that the rotation control sync information is produced the wobble signal. However, when the write mark is radially adjacent to the prepit in the optical disk, it is diffi

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