Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-12-07
2004-06-15
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S116000
Reexamination Certificate
active
06751166
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a phase error detection apparatus and method for detecting an error which occurs with a phase difference between a magnetic domain wall displacement which occurs at a leading end of an isothermal region formed on a recording medium and another magnetic domain wall displacement which occurs at a trailing end of the isothermal region, and a laser power control apparatus and method for controlling the laser power using the phase error detection apparatus and method, as well as a magneto-optical recording and/or playback apparatus for playing back an information signal from a magneto-optical recording medium using the laser power control apparatus and method.
Conventionally, various optical disks have been proposed as a recording medium for an information signal, and as an optical disk which allows rewriting of an information signal, a magneto-optical (MO) disk and a phase change (PC) disk have been proposed. Investigations have been and are being performed to allow higher density recording of such magneto-optical disk and phase change disk. However, it is considered to be difficult to read a mark smaller than a reading light spot.
However, for the magneto-optical disk, a super-resolution technique for masking marks which are not an object of playback to eliminate intersymbol interference while playing back only marks of an object of playback has been developed.
Further, a magnetic domain expansion and playback system (MAMMOS: Magnetic AMplifying Magneto-Optical System) and a magnetic domain wall displacement detection system (DWDD) have been proposed recently for playback of a magneto-optical disk recorded in a high density.
Both of the magnetic domain expansion and playback and the magnetic domain wall displacement detection expand the magnetic domain of a mark smaller than a light spot for playback through a distribution of heat generated by the light spot to read the mark. When the magnetic domain expansion and playback and the magnetic domain wall displacement detection are compared with each other, the latter can detect an edge of a mark clearly while the former can detect the position of a mark with certainty. Accordingly, the magnetic domain wall displacement detection is suitable to play back an optical disk which adopts “mark edge recording”.
The principle of playback by the magnetic domain wall displacement detection is described using an isolated mark. In particular, according to the magnetic domain wall displacement detection, presence of a mark is detected making use of the fact that, when a magnetic domain wall of an expansion layer comes to a leading end of an isothermal region in which the temperature generated by a laser beam is higher than the Curie temperature, the magnetic domain wall moves quickly to a maximum temperature portion.
Where such magnetic domain wall displacement detection as described above is used to play back a magneto-optical disk, also when the magnetic domain wall comes to the trailing end of the isothermal region, the magnetic domain wall moves quickly to a maximum temperature portion. Therefore, a read signal (MO signal) by the magnetic domain wall displacement detection includes not only a data signal but also a ghost signal having an equal length to that of the data signal and having a level lower then that of the data signal after a delay of time of “isothermal region length÷linear velocity” from the data signal. If the ghost signal is played back together with the data signal, then it is difficult to play hack an information signal recorded in a high density and also it is difficult to play back a clock signal.
Thus, a technique for canceling a ghost has been proposed in Japanese Patent Laid-open No. Hei 11-296928 by the assignee of the present application. According to the technique, when the magnetic domain wall displacement detection is used to play back a magneto-optical disk, an external clock system is used to play hack a clock signal stably, and the clock signal is used to convert the level of a RF signal read from the magneto-optical disk into a digital signal so that ghost signal processing can be performed by digital signal processing to allow the data signal to be played back correctly.
However, in order to obtain a correct data signal using the technique disclosed in the document specified as above, a process for separating the data signal and the ghost signal from each other is required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a phase error detection apparatus and method which can detect not only an error which occurs with a phase difference of a ghost signal from a data signal in a unit of a clock but also an error of the phase difference which appears in a shorter period than that of the clock.
It is another object of the present invention to provide a laser power control apparatus and method by which the playback laser power can be kept at an optimum level based not only on an error which occurs with a phase difference of a ghost signal from a data signal in a unit of a clock but also an error of the phase difference which appears in a shorter period than that of the clock.
It is a further object of the present invention to provide a magneto-optical recording and/or playback apparatus by which a data signal can be played back in a high S/N ratio from a magneto-optical disk making use of a ghost signal by the magnetic domain wall displacement detection while keeping the playback laser power at an optimum level.
In order to attain the objects described above, according to the present invention, the laser power is first controlled so that the time delay of a ghost may be a fixed multiple of a data detection clock. Then, the laser power is adjusted so that the time delay may be a fixed multiple of the clock nearest to the phase delay amount set in advance of a ghost which appears in the isothermal region with a laser power with which an optimum signal characteristic is obtained. In this instance, the level of the playback signal is detected as a sum of results of displacement of both of a magnetic wall at a leading end of the isothermal region and another magnetic wall at a trailing end of the isothermal region after the fixed multiple at the time.
In particular, according to the present invention, there is provided a phase error detection apparatus, including detection means for detecting, based on a reference pattern including a record mark which appears repetitively at predetermined bit intervals, an error appearing in a phase difference between a magnetic domain wall displacement which occurs with a leading end of an isothermal region formed on a recording medium by irradiation of a laser beam and another magnetic domain wall displacement which occurs with a trailing end of the isothermal region.
The phase error detection apparatus may detect an error of the phase difference which occurs in a unit of the clock signal or an error of the phase difference which appears in a unit of time shorter than a clock signal.
According to another aspect of the present invention, there is provided a phase error detection method for detecting an error appearing in a phase difference between a magnetic domain wall displacement which occurs with a leading end of an isothermal region formed on a recording medium by irradiation of a laser beam and another magnetic domain wall displacement which occurs with a trailing end of the isothermal region, including a step of detecting a reference pattern including a record mark which appears repetitively at predetermined bit intervals, and a step of detecting an error of the phase difference which appears in a unit of time shorter than a clock signal based on the detected reference pattern.
With the phase error detection apparatus and method, not only a phase difference in a unit of a clock of a ghost signal from a data signal but also another phase difference which appears in a time shorter than the clock can be detected.
According to a further aspect of the present invention, there is provided a las
Fujita Goro
Sakamoto Tetsuhiro
Tobita Minoru
Dinh Tan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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