Optical recording method and optical recorder

Details Optical recording method and optical recorder Optical recording method and optical recorder

1998-10-01

2002-02-05

Edun, Muhammad (Department: 2651)

Dynamic information storage or retrieval

Binary pulse train information signal

Binary signal processing for controlling recording light...

C369S116000

Reexamination Certificate

active

06345026

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an optical recording method and an optical recording device in which information is recorded as lengths of marks and spaces at high density by irradiating optical beams onto a recording thin film formed on a substrate.
BACKGROUND OF THE INVENTION
Recently, optical recording media capable of recording, reading and erasing information have been commercialized. Furthermore, high-density rewritable optical recording media capable of recording qualified animation have been actively researched and developed.
Well-known rewritable optical recording media include phase-change optical recording media with recording layers either of chalcogenide thin films or semimetal thin films on a disc-shape substrate. The chalcogenide thin films comprise Te or Se, for example, Ge—Sb—Te, In—Se, or the like, as a base. The semimetal thin films comprise In—Sb or the like. Magneto-optical recording media having metal thin films such as Fe—Tb—Co as their recording layers also are well known. Further, there are also write-once-type optical recording media using pigment materials.
In phase-change optical recording media, recording thin films comprising the above-mentioned phase-change materials are instantly irradiated with laser beams focused on submicron-order size optical spots to heat the irradiated parts partially. When the temperature of the irradiated portion becomes equal to or higher than the crystalline temperature, the irradiated portion is changed to the crystalline state. When the irradiated portion is melted at a temperature higher than its melting point and is quenched, its state is changed to the amorphous state. Once either the crystalline state or the amorphous state is determined so as to correspond to the recording state, and the other to the erasing state (unrecorded state), information can be recorded reversibly by forming a pattern changing between the amorphous state and the crystalline state corresponding to information signals. Since the crystalline state and the amorphous state are different from each other in their optical characteristics, recorded signals can be read by optically detecting such different characteristics as a reflectivity change or a transmittance change.
In a magneto-optical recording medium, focused laser beams are irradiated on a magneto-optical recording thin film, so that the irradiated portions are partially heated. A magnetic field is applied to the heated portion in order to reverse the magnetizing direction of the magneto-optical recording thin film at the irradiated portions corresponding to the information to be recorded, thus recording information.
Methods of recording data on optical recording media at a high density include a mark-length recording. In the mark-length recording, marks with various lengths are recorded at various intervals (spaces), and the recording information is allocated to both the mark lengths and the space lengths. For example, in a phase-change recording medium, information can be recorded by setting amorphous regions as marks and crystalline regions as spaces.
In order to record information at higher density, it is necessary to shorten the mark lengths and the space lengths to be recorded. However, when the space lengths become shorter, the heat of a recorded mark-end affects the temperature increase at the starting-end of a mark to be recorded next. The position shift of a recorded-mark front-edge from the proper position caused by such thermal interference contributes to the aggravation of BER (bit error rate) when reading the information.
Examples of the method for improving the problem mentioned above are described, for example, in Unexamined Japanese Patent Application Tokkai Hei 5-234079 and Tokkai Hei 7-129959. In the applications mentioned above, a method of recording information by delaying the starting-end position of a recording pulse beforehand so as to compensate for the shift quantity of a mark-front-end position due to thermal interference is proposed. This recording method will be explained with reference to FIGS.
9
(
a
)-(
e
).
FIG.
9
(
a
) shows a pulse shape of data to be recorded. Levels of logic 1 and logic 0 correspond to marks and spaces, respectively. In accordance with the data shown in FIG.
9
(
a
), the recording pulse shown in FIG.
9
(
b
) is generated, thus forming the recording marks shown in FIG.
9
(
c
) on an optical recording medium.
As shown in FIG.
9
(
c
), when the recording density increases and therefore a space length between marks becomes shorter, the heat of a recorded mark
90
affects the front-edge of a mark
91
to be recorded. Consequently, the front-edge temperature becomes higher than that when the space length is sufficiently long. As a result, the front-edge of the mark
91
expands greatly as shown with a reference number
92
, and therefore the front-edge is formed ahead of the proper position.
When a space (a period at level 0) in the data to be recorded is short, the correction for delaying the front-edge of the recording pulse so as to compensate for the delay quantity
93
is made as shown in FIG.
9
(
d
). By this correction, the front-edge of the mark
91
is formed at the proper position corresponding to the front-edge of the recording data.
At a further higher density, not only a space length directly in front of a mark to be recorded but also a mark length in front of the space and a space length and a mark length further ahead, cause the temperature increase at the front-edge of the mark to be recorded, thus further affecting the front-edge shift quantity. Especially, the mark length in front of the space directly in front of the mark to be recorded affects greatly. This is because a long mark length requires a correspondingly long heating time by laser beams, and therefore the larger amount of heat is conducted to the front-edge of a mark to be recorded next. Thus, it is preferable that the delay quantity of the front-edge of a recording pulse is determined based on the lengths of a space directly in front of the mark to be recorded and of a mark in front of the space. When determining the delay quantity considering the lengths of a mark and a space further ahead, the front-edge shift can be corrected more precisely. Considering recording density, allowable error rate, processor capacity used in a device, cost, and the like, it will be decided how many spaces and marks before the mark to be recorded should be taken into account.
As described above, conventionally, a recording method in which front-edge shift is corrected considering the relation between a space length and a mark length directly in front of a recording mark and the front-edge shift of the recording mark is suggested. However, the position-shifts of not only the front-edge but also the end-edge of the mark cause the deterioration in the error rate when reading signals. It was found that the end-edge position of the recording mark was affected not only by space and mark lengths in front of the recording mark but also by space and mark lengths behind the recording mark. It can be conceived that this is because a cooling process of the recording mark is affected by the heat of the mark to be recorded next.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical recording-reading method and an optical recording-reading device in which the deterioration in the error rate when reading signals is restrained by correcting the front- and end-edge shifts of recording marks caused by heat interference, thus obtaining high-quality reading signals.
In an optical recording-reading method of the present invention, when recording information on a recording thin film as lengths of marks and spaces, the position of a mark-end at the end of recording is changed according to the lengths of a mark to be recorded, of a space directly behind the recording mark and of a mark behind the space. According to this recording method, the edge shift of the mark-end caused by heat interference is corrected, thus preventing the error rate when rea

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