U.S. patent application number 12/133651 was filed with the patent office on 2008-10-09 for method and apparatus for writing data on a storage medium.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Shigeru FURUMIYA, Atsushi NAKAMURA.
Application Number | 20080247292 12/133651 |
Document ID | / |
Family ID | 33161505 |
Filed Date | 2008-10-09 |
United States Patent
Application |
20080247292 |
Kind Code |
A1 |
NAKAMURA; Atsushi ; et
al. |
October 9, 2008 |
METHOD AND APPARATUS FOR WRITING DATA ON A STORAGE MEDIUM
Abstract
A data recording method according to the present invention is a
method for recording data as edge position information, including
marks and spaces of multiple different lengths, on a storage medium
by irradiating the storage medium with a pulsed energy beam. The
method includes the steps of: (A) generating a write code sequence
based on the data to be recorded; (B) determining a write pulse
waveform, defining the power modulation of the energy beam,
according to the code lengths of respective codes included in the
write code sequence; and (C) modulating the power of the energy
beam based on the write pulse waveform. If the shortest code length
of the write code sequence is n (which is an integer equal to or
greater than one), a write pulse waveform that has only one write
pulse is assigned to recording mark making periods corresponding to
codes with code lengths x of n, n+1 and n+2, and a write pulse
waveform that has multiple write pulses Pw is assigned to recording
mark making periods corresponding to codes with code lengths x of
n+3 or more.
Inventors: |
NAKAMURA; Atsushi;
(Moriguchi-shi, JP) ; FURUMIYA; Shigeru;
(Himeki-shi, JP) |
Correspondence
Address: |
MARK D. SARALINO (MEI);RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, 19TH FLOOR
CLEVELAND
OH
44115
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
|
Family ID: |
33161505 |
Appl. No.: |
12/133651 |
Filed: |
June 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10551573 |
Oct 3, 2005 |
|
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PCT/JP04/04224 |
Mar 25, 2004 |
|
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12133651 |
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Current U.S.
Class: |
369/59.12 ;
G9B/7.028 |
Current CPC
Class: |
G11B 7/0062
20130101 |
Class at
Publication: |
369/59.12 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2003 |
JP |
2003-101248 |
Jul 24, 2003 |
JP |
2003-279108 |
Claims
1. (canceled)
2. A data recording method for recording data as edge position
information, including marks and spaces of multiple different
lengths, on a storage medium by irradiating the storage medium with
a pulsed energy beam, the method comprising: (A) generating an NRZI
data based on the data to be recorded; (B) determining a write
pulse waveform, defining the power modulation of the energy beam,
according to the code lengths x of respective codes included in the
NRZI data, the code lengths x (where x is an integer equal to or
greater than one) corresponding to mark lengths of xTw (where Tw is
a detection window width); and (C) modulating the power of the
energy beam based on the write pulse waveform, wherein if the
shortest code length of the NRZI data is n (where n is an integer
equal to or greater than one), the step (B) includes assigning a
write pulse waveform that has only one write pulse Pw to recording
mark making periods corresponding to codes with code lengths x of
n, and n+1, and a write pulse waveform that has multiple write
pulses Pw to recording mark making periods corresponding to codes
with code lengths x of n+2 or more, respectively, wherein the write
pulse waveform in the recording mark making period corresponding to
codes with code lengths x of n+2 or more includes write pulses, of
which the number is equal to the quotient obtained by dividing x by
two, and wherein the shortest code length of the NRZI data is
2.
3. A storage medium comprising a recording region for recording
data as edge position information, including marks and spaces of
multiple different lengths, on a storage medium by being irradiated
with a pulsed energy beam, wherein a power modulation of the energy
beam is defined by a write pulse waveform, according to the code
lengths of respective codes included in an NRZI data that is
generated based on data to be recorded, the code lengths x (where x
is an integer equal to or greater than one) corresponding to a mark
length xTw (where Tw is a detection window width); and wherein if
the shortest code length of the NRZI data is n (where n is an
integer equal to or greater than one), each write pulse waveform
for code lengths x of n and n+1 has only one write pulse, and each
write pulse waveform for code lengths x of n+2 or more has multiple
write pulses, wherein the write pulse waveform in the recording
mark making period corresponding to codes with code lengths x of
n+2 or more includes write pulses, of which the number is equal to
the quotient obtained by dividing x by two, and wherein the
shortest code length of the NRZI data is 2.
4. A data reproduction method for reproducing data recorded on the
storage medium according to claim 3, the method comprising:
reproducing the data recorded on the recording region of the
storage medium by irradiating the storage medium with a light beam.
Description
[0001] This application is a continuation application of U.S.
patent application Ser. No. 10/551,573 filed on Oct. 3, 2005, which
is a .sctn.371 of International Application No. PCT/JP2004/004224
filed Mar. 25, 2004, the entire disclosures of which are
incorporated herein by reference, and is related to co-pending
sibling Attorney Docket Nos. OKUDP0135USA (U.S. application Ser.
No. ______), and OKUDP0135USC (U.S. application Ser. No. ______),
both filed on Jun. 5, 2008.
TECHNICAL FIELD
[0002] The present invention relates to a method and apparatus for
recording data (or information) on a storage medium such as an
optical disk by irradiating the storage medium with a laser beam or
any other energy beam so as to make a mark having a different
physical property from a non-recorded portion thereof.
BACKGROUND ART
[0003] A rewritable optical disk such as a DVD-RAM has a phase
change recording layer on its substrate. When this phase change
recording layer is irradiated with a laser beam having a high
energy density, the irradiated portion is locally heated to a
temperature exceeding the melting point and melted. Since the
optical disk being irradiated with the laser beam is spinning at a
high velocity, the beam spot of the laser beam will be moving along
the track on the phase change recording layer at a high velocity,
too. That is why that portion of the phase change recording layer
that has been melted by the passage of the beam spot is quickly
cooled and solidified naturally. If the power of the laser beam is
adjusted in such a situation, then the melted portion of the phase
change recording layer is rapidly cooled and amorphized. The
amorphized portion of the phase change recording layer has a
different refractive index and a different optical reflectance from
those of the other crystalline portions. The amorphized portion
formed in this manner is called a "mark". On the other hand, an
intervening portion between those "marks" on the track is called a
"space".
[0004] By arranging those marks and spaces on the track, data can
be recorded on the optical disk. If a laser beam with a low power
for reading is radiated toward the optical disk and if the
intensity of its reflected light is measured, then the mark/space
boundary (which is often called a "mark edge") can be sensed and
data can be read. The power of the read laser beam is kept low
enough to avoid melting the phase change recording layer.
[0005] To increase the information transfer rate while data is
being read from, or written on, any of those optical disks, either
the recording linear density or the scanning rate of the beam spot
on the optical disk may be increased.
[0006] In order to increase the recording linear density, it is
effective to reduce the mark length and space length or to narrow
the mark edge position detecting interval by reducing the steps of
variations in mark and space lengths.
[0007] However, if the recording linear density were increased,
then the SNR of the read signal would decrease. For that reason, a
significant increase in recording linear density should not be
expected.
[0008] To make very small marks on an optical disk with high
precision, a write strategy, in which each of those marks is left
on the recording layer by continuously irradiating that layer with
either a single laser pulse or multiple laser pulses, is
adopted.
[0009] According to a conventional technique as disclosed in
Japanese Patent Application Laid-Open Publication No. 5-298737
(which will be referred to herein as a "first conventional
technique"), a train of laser pulses is assigned to each of
multiple marks with different lengths. In other words, a train of
laser pulses to be radiated to make each mark, i.e., a waveform
showing the intensity variation of the laser beam (which will be
referred to herein as a "write pulse waveform"), is determined by
the length of that mark to leave. The number and amplitude of
pulses to be radiated during the period of making each mark are
controlled according to the length of a write code sequence.
[0010] The write pulse waveform during the mark making period can
be divided into a top portion and a succeeding portion. The
respective pulses generally have different pulse heights. Also, in
the periods other than the mark making period, a write auxiliary
pulse is generated to follow the space.
[0011] According to the technique disclosed in Japanese Patent
Application Laid-Open Publication No. 5-298737, the diffusion of
heat from a preceding mark toward the front edge of the very next
mark can be compensated for, and the mark width and mark edge
position can be controlled with high precision, irrespective of the
space length.
[0012] According to another conventional technique as disclosed in
Japanese Patent Application Laid-Open Publication No. 8-7277 (which
will be referred to herein as a "second conventional technique"),
each write code is broken down into a plurality of primitive
elements with multiple different lengths such that a single write
pulse is associated with each of those elements. And each write
code is formed by a series of recording marks associated with
respectively independent write pulses.
[0013] Still another conventional technique as disclosed in
Japanese Patent Application Laid-Open Publication No. 9-134525
(which will be referred to herein as a "third conventional
technique") adopts a multi-pulse writing method that uses the first
heating pulse, a number of succeeding heating and cooling pulses
that follow the first pulse, and the last cooling pulse. According
to the third conventional technique, in recording a mark, of which
the length is either an odd number of times or an even number of
times as long as one period of a write channel clock, the pulse
width of the succeeding heating and cooling pulses is made nearly
equal to the length of one period of the write channel clock.
[0014] According to yet another conventional technique as disclosed
in Japanese Patent Application Laid-Open Publication No. 11-175976
(which will be referred to herein as a "fourth conventional
technique"), the energy and the number of pulses that are applied
while a mark of an arbitrary length is being made are changed
according to the length of the mark in a write code sequence such
that the gap between two arbitrary variation points of the energy
applied per unit time during the mark making period becomes longer
than a half of the detection window width.
[0015] According to the first conventional technique, the length of
a mark, corresponding with the detection window width, is
associated with one shot of write pulse. Thus, if the detection
window width is shortened, then the semiconductor laser diode,
functioning as a source of generating write energy, needs to be
driven faster than usual. For example, if one tries to realize a
burst transfer rate of 10 megabytes per second, which is almost as
high as that of a magnetic disk drive, by a normal (1, 7)
modulation technique, then the detection window width of the read
signal will be about 8.3 ns (nanoseconds) and therefore the
shortest write current pulse width will be about 4.2 ns, which is
approximately a half as long as the detection window width.
However, it usually takes several nanoseconds to activate a
semiconductor laser, and it is difficult to generate a write beam
pulse accurately. Also, even if a write beam pulse could be
generated accurately, normal marks could not be made in a situation
where multi-pulse writing is carried out on a medium such as a
phase change disk in which the mark making is controlled by the
cooling rate of its heated portion. This is because the next beam
pulse is radiated before the heated portion is cooled sufficiently.
Also, if one tries to realize a burst transfer rate of 10 megabytes
per second by the (1, 7) modulation technique, for example, then
the amount of time it takes to cool the storage medium will also be
about 4.2 ns, which is equal to the shortest write current pulse
width. Consequently, marks could not be made properly depending on
the property of the storage medium.
[0016] According to the second conventional technique mentioned
above, each write code is broken down into a plurality of primitive
elements with multiple different lengths such that a single write
pulse is associated with each of those elements and that each write
code is formed by a series of recording marks associated with
respectively independent write pulses. However, this conventional
technique does not consider thermal balance between write pulses
for respective elements at all. That is why as the recording linear
density is increased, it becomes more and more difficult to control
the mark edge position. That is to say, in making marks that will
form a single write code, the recording marks will have variable
widths from one position to another because the quantity of heat
accumulated in the recording layer for the top portion of the write
code is different from that of heat accumulated there for the
terminal portion of the write code. As a result, the edge recording
cannot be carried out as intended.
[0017] In the third conventional technique, a pulse, which is much
shorter than the detection window width, may be inserted into the
write pulse waveform in the vicinity of the center of the mark
making period, and the mark width changes significantly around
there compared to the other portions. According to the document
disclosing this conventional technique, when a mark edge recording
operation is carried out, the variation in signal amplitude around
the center portion of a mark should cause no serious problem as
long as the mark edge position is accurate. In a read/write drive
that determines read/write conditions by detecting the average
level of a read signal, however, such distortion of the read signal
should affect the operation of the drive. As to a phase change
storage medium, for example, a signal can be detected as a
variation in reflectance just like a phase pit type storage medium.
That is why the phase change storage medium and phase pit type
storage medium can easily share the same read drive in common.
However, since the read signal of the phase pit type storage medium
has no such distortion, it is actually difficult to read the phase
change storage medium and phase pit type storage medium using the
same drive.
[0018] Also, according to the fourth conventional technique, the
write power level of the write pulse train changes stepwise, thus
requiring complicated power control. Also, in writing a signal with
a code length of 4 Tw, the laser beam needs to be emitted so as to
achieve a higher power level than the average power level at least
for a period of time corresponding to 3 Tw. When a very small mark
needs to be made on a high-density storage medium in the near
future, such an emission time will be too long to make desired
recording marks.
[0019] As can be seen, none of the conventional techniques
mentioned above can contribute to making marks sufficiently
accurately when the transfer rate is high or achieving sufficiently
high storage plane density and reliability.
[0020] In order to overcome the problems described above, an object
of the present invention is to provide a method and apparatus for
recording data that can make marks with high accuracy even when the
transfer rate is high.
DISCLOSURE OF INVENTION
[0021] A data recording method according to the present invention
is a method for recording data as edge position information,
including marks and spaces of multiple different lengths, on a
storage medium by irradiating the storage medium with a pulsed
energy beam. The method includes the steps of: (A) generating a
write code sequence based on the data to be recorded; (B)
determining a write pulse waveform, defining the power modulation
of the energy beam, according to the code lengths of respective
codes included in the write code sequence; and (C) modulating the
power of the energy beam based on the write pulse waveform. If the
shortest code length of the write code sequence is n (which is an
integer equal to or greater than one), the step (B) includes
assigning a write pulse waveform that has only one write pulse to
recording mark making periods corresponding to codes with code
lengths x of n, n+1 and n+2, and a write pulse waveform that has
multiple write pulses Pw to recording mark making periods
corresponding to codes with code lengths x of n+3 or more,
respectively.
[0022] In one preferred embodiment, if the shortest code length of
the write code sequence is n (which is an integer equal to or
greater than one), the step (B) includes classifying the code
lengths x into at least four lengths including n, n+1, n+2 and n+3
or more. As to two codes, which have code lengths m and m+1,
respectively, and which have the same number of write pulses Pw in
the recording mark making period of their write pulse waveforms,
the step (B) includes determining the write pulse waveforms so as
to satisfy the inequality: (write pulse width of code length
m).ltoreq.(write pulse width of code length m+1), where the "write
pulse width of code length m" is the width of an arbitrary Kth
write pulse period included in the recording mark making period
corresponding to the code length m and the "write pulse width of
code length m+1" is the width of the Kth write pulse period
included in the recording mark making period corresponding to the
code length m+1.
[0023] In another preferred embodiment, as to two codes, which have
code lengths m and m+1, respectively, and which have the same
number of write pulses Pw and the same number of periods with a
bottom power level Pb between two write pulses Pw in the recording
mark making period of their write pulse waveforms, the step (B)
includes determining the write pulse waveforms so as to satisfy the
inequality: (pulse width of code length m).ltoreq.(pulse width of
code length m+1), where the "pulse width of code length m" is the
width of an arbitrary Kth period with the bottom power level Pb
included in the recording mark making period corresponding to the
code length m and the "pulse width of code length m+1" is the width
of the Kth period with the bottom power level Pb included in the
recording mark making period corresponding to the code length
m+1.
[0024] In another preferred embodiment, the write pulse waveform in
the recording mark making period corresponding to codes with code
lengths x of n+3 or more includes write pulses, of which the number
is equal to the quotient obtained by dividing (x-1) by two.
[0025] In another preferred embodiment, in the recording mark
making period corresponding to codes with code lengths x of n+3 or
more, the length of a period in which the write pulse waveform has
an erasure power level Pe is set to be at least equal to 1 Tw.
[0026] In another preferred embodiment, in each said recording mark
making period, the length of a period in which the write pulse
waveform has the bottom power level Pb is set to be at least equal
to 1 Tw.
[0027] In another preferred embodiment, in each said recording mark
making period, the length of a period in which the write pulse
waveform has a cooling power level Pc is set to be at least equal
to 1 Tw.
[0028] In another preferred embodiment, the start position of the
first pulse, included in a recording mark making period of the
write pulse waveform, and the end position of a cooling pulse, also
included in the recording mark making period, are shifted according
to the length x of a code associated with the recording mark making
period.
[0029] In another preferred embodiment, the positions are shifted
to at least four different degrees corresponding to the code
lengths x of n, n+1, n+2 and n+3 or more.
[0030] An apparatus according to the present invention is an
apparatus for recording data as edge position information,
including marks and spaces of multiple different lengths, on a
storage medium by irradiating the storage medium with a pulsed
energy beam. The apparatus includes: laser driving means for
modulating the power of the energy beam; coding means for
converting the data to be recorded on the storage medium into a
write code sequence; and mark length classifying means for
determining a write pulse waveform, defining the power modulation
of the energy beam, according to the code lengths x of respective
codes included in the write code sequence. If the shortest code
length of the write code sequence is n (which is an integer equal
to or greater than one), the mark length classifying means assigns
a write pulse waveform that has only one write pulse Pw to
recording mark making periods corresponding to codes with code
lengths x of n, n+1 and n+2, and a write pulse waveform that has
multiple write pulses Pw to recording mark making periods
corresponding to codes with code lengths x of n+3 or more,
respectively.
[0031] In one preferred embodiment, as to two codes, which have
code lengths m and m+1, respectively, and which have the same
number of write pulses Pw and the same number of periods with a
bottom power level Pb between two write pulses Pw in the recording
mark making period of their write pulse waveforms, the write pulse
waveforms are determined so as to satisfy the inequality: (pulse
width of code length m).ltoreq.(pulse width of code length m+1),
where the "pulse width of code length m" is an arbitrary Kth period
with the bottom power level included in the recording mark making
period corresponding to the code length m and the "pulse width of
code length m+1" is the Kth period with the bottom power level
included in the recording mark making period corresponding to the
code length m+1.
[0032] In another preferred embodiment, if the shortest code length
of the write code sequence is n (which is an integer equal to or
greater than one), the code lengths x are classified into at least
four lengths including n, n+1, n+2 and n+3 or more. As to two
codes, which have code lengths m and m+1, respectively, and which
have the same number of write pulses Pw in the recording mark
making period of their write pulse waveforms, the write pulse
waveforms are determined so as to satisfy the inequality: (write
pulse width of code length m).ltoreq.(write pulse width of code
length m+1), where the "write pulse width of code length m" is the
width of an arbitrary Kth write pulse period included in the
recording mark making period corresponding to the code length m and
the "write pulse width of code length m+1" is the width of the Kth
write pulse period included in the recording mark making period
corresponding to the code length m+1.
[0033] In another preferred embodiment, as to two codes, which have
code lengths m and m+1, respectively, and which have the same
number of write pulses Pw and the same number of periods with a
bottom power level Pb between two write pulses Pw in the recording
mark making period of their write pulse waveforms, the write pulse
waveforms are determined so as to satisfy the inequality: (pulse
width of code length m).ltoreq.(pulse width of code length m+1),
where the "pulse width of code length m" is the width of an
arbitrary Kth period with the bottom power level Pb included in the
recording mark making period corresponding to the code length m and
the "pulse width of code length m+1" is the width of the Kth period
with the bottom power level Pb included in the recording mark
making period corresponding to the code length m+1.
[0034] In another preferred embodiment, the write pulse waveform in
the recording mark making periods corresponding to codes with code
lengths x of n+3 or more is determined so as to include a number of
write pulses that is equal to the quotient obtained by dividing
(x-1) by two.
[0035] In another preferred embodiment, the write pulse waveforms
are determined such that every interval between trailing and
leading edges of a fundamental waveform of a laser pulse in the
mark making periods becomes at least equal to a detection window
width Tw.
[0036] In another preferred embodiment, the apparatus includes
pulse shifting means for shifting the start position of the first
pulse, included in a recording mark making period of the write
pulse waveform, and the end position of a cooling pulse, also
included in the write pulse waveform, according to the length x of
a code associated with the recording mark making period.
[0037] In another preferred embodiment, the apparatus includes
write compensating means for shifting the positions to at least
four different degrees corresponding to the code lengths x of n,
n+1, n+2 and n+3 or more.
[0038] Another data recording method according to the present
invention is a method for recording data as edge position
information, including marks and spaces of multiple different
lengths, on a storage medium by irradiating the storage medium with
a pulsed energy beam. The method includes the steps of: (A)
generating a write code sequence based on the data to be recorded;
(B) determining a write pulse waveform, defining the power
modulation of the energy beam, according to the code lengths of
respective codes included in the write code sequence; and (C)
modulating the power of the energy beam based on the write pulse
waveform. The step (B) includes setting the number of write pulses
Pw, included in respective recording mark making periods of the
write pulse waveforms corresponding to code lengths n and n+1, to
be equal to one, and making the width of the write pulse Pw,
included in the recording mark making period of the write pulse
waveform corresponding to the code length n, equal to or smaller
than that of the write pulse Pw included in the recording mark
making period of the write pulse waveform corresponding to the code
length n+1. The step (B) also includes setting the number of write
pulses Pw, included in respective recording mark making periods of
the write pulse waveforms corresponding to code lengths n+2 and
n+3, to be equal to two, and making the width of a first write
pulse Pw, included in the recording mark making period of the write
pulse waveform corresponding to the code length n+2, equal to or
smaller than that of a first write pulse Pw included in the
recording mark making period of the write pulse waveform
corresponding to the code length n+3. And the step (B) further
includes making the width of a second write pulse Pw, included in
the recording mark making period of the write pulse waveform
corresponding to a code length n+2, equal to or smaller than that
of a second write pulse Pw included in the recording mark making
period of the write pulse waveform corresponding to a code length
n+3.
[0039] Still another data recording method according to the present
invention is a method for recording data as edge position
information, including marks and spaces of multiple different
lengths, on a storage medium by irradiating the storage medium with
a pulsed energy beam. The method includes the steps of: (A)
generating a write code sequence based on the data to be recorded;
(B) determining a write pulse waveform, defining the power
modulation of the energy beam, according to the code lengths of
respective codes included in the write code sequence; and (C)
modulating the power of the energy beam based on the write pulse
waveform. If the shortest code length of the write code sequence is
n (which is an integer equal to or greater than one), the step (B)
includes classifying the code lengths x into at least four lengths
including n, n+1, n+2 and n+3 or more. As to two codes, which have
code lengths m and m+1, respectively, and which have the same
number of write pulses Pw in the recording mark making period of
their write pulse waveforms, the step (B) includes determining the
write pulse waveforms so as to satisfy the inequality: (write pulse
width of code length m).ltoreq.(write pulse width of code length
m+1), where the "write pulse width of code length m" is the width
of an arbitrary Kth write pulse period included in the recording
mark making period corresponding to the code length m and the
"write pulse width of code length m+1" is the width of the Kth
write pulse period included in the recording mark making period
corresponding to the code length m+1.
[0040] Yet another data recording method according to the present
invention is a method for recording data as edge position
information, including marks and spaces of multiple different
lengths, on a storage medium by irradiating the storage medium with
a pulsed energy beam. The method includes the steps of: (A)
generating a write code sequence based on the data to be recorded;
(B) determining a write pulse waveform, defining the power
modulation of the energy beam, according to the code lengths of
respective codes included in the write code sequence; and (C)
modulating the power of the energy beam based on the write pulse
waveform. As to two codes, which have code lengths m and m+1,
respectively, and which have the same number of write pulses Pw and
the same number of periods with a bottom power level Pb between two
write pulses Pw in the recording mark making period of their write
pulse waveforms, the step (B) includes determining the write pulse
waveforms so as to satisfy the inequality: (pulse width of code
length m).ltoreq.(pulse width of code length m+1), where the "pulse
width of code length m" is the width of an arbitrary Kth period
with the bottom power level Pb included in the recording mark
making period corresponding to the code length m and the "pulse
width of code length m+1" is the width of the Kth period with the
bottom power level Pb included in the recording mark making period
corresponding to the code length m+1.
[0041] Another apparatus according to the present invention is an
apparatus for recording data as edge position information,
including marks and spaces of multiple different lengths, on a
storage medium by irradiating the storage medium with a pulsed
energy beam. The apparatus includes: laser driving means for
modulating the power of the energy beam; coding means for
converting the data to be recorded on the storage medium into a
write code sequence; and mark length classifying means for
determining a write pulse waveform, defining the power modulation
of the energy beam, according to the code lengths x of respective
codes included in the write code sequence.
[0042] The mark length classifying means sets the number of write
pulses Pw, included in respective recording mark making periods of
the write pulse waveforms corresponding to code lengths n and n+1,
to be equal to one, and makes the width of the write pulse Pw,
included in the recording mark making period of the write pulse
waveform corresponding to the code length n, equal to or smaller
than that of the write pulse Pw included in the recording mark
making period of the write pulse waveform corresponding to the code
length n+1. The mark length classifying means also sets the number
of write pulses Pw, included in respective recording mark making
periods of the write pulse waveforms corresponding to code lengths
n+2 and n+3, to be equal to two, and makes the width of a first
write pulse Pw, included in the recording mark making period of the
write pulse waveform corresponding to the code length n+2, equal to
or smaller than that of a first write pulse Pw included in the
recording mark making period of the write pulse waveform
corresponding to the code length n+3. And the mark length
classifying means further makes the width of a second write pulse
Pw, included in the recording mark making period of the write pulse
waveform corresponding to a code length n+2, equal to or smaller
than that of a second write pulse Pw included in the recording mark
making period of the write pulse waveform corresponding to a code
length n+3.
[0043] Still another apparatus according to the present invention
is an apparatus for recording data as edge position information,
including marks and spaces of multiple different lengths, on a
storage medium by irradiating the storage medium with a pulsed
energy beam. The apparatus includes: laser driving means for
modulating the power of the energy beam; coding means for
converting the data to be recorded on the storage medium into a
write code sequence; and mark length classifying means for
determining a write pulse waveform, defining the power modulation
of the energy beam, according to the code lengths x of respective
codes included in the write code sequence. If the shortest code
length of the write code sequence is n (which is an integer equal
to or greater than one), the mark length classifying means
classifies the code lengths x into at least four lengths including
n, n+1, n+2 and n+3 or more. As to two codes, which have code
lengths m and m+1, respectively, and which have the same number of
write pulses Pw in the recording mark making period of their write
pulse waveforms, the mark length classifying means determines the
write pulse waveforms so as to satisfy the inequality: (write pulse
width of code length m).ltoreq.(write pulse width of code length
m+1), where the "write pulse width of code length m" is the width
of an arbitrary Kth write pulse period included in the recording
mark making period corresponding to the code length m and the
"write pulse width of code length m+1" is the width of the Kth
write pulse period included in the recording mark making period
corresponding to the code length m+1.
[0044] Yet another apparatus according to the present invention is
an apparatus for recording data as edge position information,
including marks and spaces of multiple different lengths, on a
storage medium by irradiating the storage medium with a pulsed
energy beam. The apparatus includes: laser driving means for
modulating the power of the energy beam; coding means for
converting the data to be recorded on the storage medium into a
write code sequence; and mark length classifying means for
determining a write pulse waveform, defining the power modulation
of the energy beam, according to the code lengths x of respective
codes included in the write code sequence. As to two codes, which
have code lengths m and m+1, respectively, and which have the same
number of write pulses Pw and the same number of periods with a
bottom power level Pb between two write pulses Pw in the recording
mark making period of their write pulse waveforms, the mark length
classifying means determines the write pulse waveforms so as to
satisfy the inequality: (pulse width of code length
m).ltoreq.(pulse width of code length m+1), where the "pulse width
of code length m" is the width of an arbitrary Kth period with the
bottom power level Pb included in the recording mark making period
corresponding to the code length m and the "pulse width of code
length m+1" is the width of the Kth period with the bottom power
level Pb included in the recording mark making period corresponding
to the code length m+1.
[0045] Yet another data recording method according to the present
invention is a method for recording data as edge position
information, including marks and spaces of multiple different
lengths, on a storage medium by irradiating the storage medium with
a pulsed energy beam. The method includes the steps of: (A)
generating a write code sequence based on the data to be recorded;
(B) determining a write pulse waveform, defining the power
modulation of the energy beam, according to the code lengths of
respective codes included in the write code sequence; and (C)
modulating the power of the energy beam based on the write pulse
waveform. As to two codes, which have code lengths m and m+1,
respectively, and which have the same number of write pulses Pw in
the recording mark making period of their write pulse waveforms,
the write pulse waveforms are determined so as to satisfy the
inequality: (write pulse width of code length m).ltoreq.(write
pulse width of code length m+1), where the "write pulse width of
code length m" is the width of an arbitrary Kth write pulse period
included in the recording mark making period corresponding to the
code length m and the "write pulse width of code length m+1" is the
width of the Kth write pulse period included in the recording mark
making period corresponding to the code length m+1.
[0046] Yet another data recording method according to the present
invention is a method for recording data as edge position
information, including marks and spaces of multiple different
lengths, on a storage medium by irradiating the storage medium with
a pulsed energy beam. The method includes the steps of: (A)
generating a write code sequence based on the data to be recorded;
(B) determining a write pulse waveform, defining the power
modulation of the energy beam, according to the code lengths of
respective codes included in the write code sequence; and (C)
modulating the power of the energy beam based on the write pulse
waveform. As to two codes, which have code lengths m and m+1,
respectively, and which have the same number of write pulses Pw and
the same number of periods with a bottom power level Pb between two
write pulses Pw in the recording mark making period of their write
pulse waveforms, the write pulse waveforms are determined so as to
satisfy the inequality: (pulse width of code length
m).ltoreq.(pulse width of code length m+1), where the "pulse width
of code length m" is the width of an arbitrary Kth period with the
bottom power level Pb included in the recording mark making period
corresponding to the code length m and the "pulse width of code
length m+1" is the width of the Kth period with the bottom power
level Pb included in the recording mark making period corresponding
to the code length m+1.
BRIEF DESCRIPTION OF DRAWINGS
[0047] FIG. 1 shows an overall configuration for an apparatus
according to the present invention.
[0048] FIG. 2 shows a configuration for the recording processing
system shown in FIG. 1.
[0049] Portions (a) through (h) of FIG. 3 show how the recording
processing system works in the present invention and in the prior
art.
[0050] Portions (a) through (j) of FIG. 4 show write pulse
waveforms adopted in a first preferred embodiment of an apparatus
according to the present invention.
[0051] Portions (a) through (i) of FIG. 5 show write pulse
waveforms for the recording processing system of a conventional
data recorder (as a comparative example).
[0052] Portions (a) through (j) of FIG. 6 show write pulse
waveforms adopted in a second preferred embodiment of an apparatus
according to the present invention.
[0053] Portions (a) through (j) of FIG. 7 show write pulse
waveforms adopted in a third preferred embodiment of an apparatus
according to the present invention.
[0054] FIG. 8 shows how adaptive mark compensation can be done
according to the present invention.
[0055] FIG. 9 shows how adaptive mark compensation can be done
according to the present invention.
[0056] FIG. 10 shows a configuration for the recording processing
system of a conventional data recorder.
[0057] Portions (a) through (j) of FIG. 11 show write pulse
waveforms adopted in a fourth preferred embodiment of an apparatus
according to the present invention.
[0058] Portions (a) through (j) of FIG. 12 show write pulse
waveforms adopted in a fifth preferred embodiment of an apparatus
according to the present invention.
[0059] FIGS. 13(a) and 13(b) show two types of write pulse
waveforms for making a 4Tw mark, and FIGS. 13(c) and 13(d)
schematically illustrate the shapes of marks left.
BEST MODE FOR CARRYING OUT THE INVENTION
[0060] In a conventional write strategy for optical disk drives,
the number of pulses for multi-pulse writing is increased such that
the resultant mark will not have an expanded end portion.
[0061] The present inventors discovered that when data needed to be
recorded at a high rate, the mark shape could be kept appropriate
by increasing the pulse width, not the number of pulses for
multi-pulse writing, thus acquiring the basic idea of the present
invention. Suppose the data transfer rate will go beyond 72 Mbps in
the near future. In that case, according to the conventional write
strategy that uses a lot of pulses for multi-pulse writing, a
semiconductor laser, functioning as a light source in a drive for
recording data, will need to have a further increased operating
frequency. Actually, however, it is difficult to further increase
the operating frequency of semiconductor lasers.
[0062] In contrast, in a preferred embodiment of the present
invention, data is recorded with just one pulse applied in making
relatively short marks with code lengths of 2 Tw to 4 Tw as will be
described later, and there is no need to further improve the
performance of semiconductor lasers. In addition, since resultant
marks have appropriate shapes, read errors never increase,
either.
[0063] Hereinafter, preferred embodiments of the present invention
will be described with reference to the accompanying drawings.
EMBODIMENT 1
[0064] A first preferred embodiment of a data recorder according to
the present invention will be described.
[0065] In this preferred embodiment, a phase change optical disk is
used as a storage medium. However, the storage media that may be
used in the present invention are not limited to optical disks of
that type. Any other type of storage medium can also be used
effectively in the present invention as long as the storage medium
can locally make a "mark" with a different physical property from
the other portions by applying some non-optical energy such as
magnetic energy or electron beam to the storage medium.
[0066] The present invention is characterized by its write strategy
of controlling the level of energy applied to a storage medium in
recording data on the storage medium (i.e., write energy) highly
precisely. As used herein, the "write energy level" means the
average energy level of a laser beam in a period of time that is
approximately a half as long as the detection window width (which
is a unit of variation in the edge position of marks and spaces).
If a frequency component that is much higher than the frequency of
a period corresponding to the detection window width is superposed
on a write pulse waveform for some reason (e.g., to minimize laser
noise), then the "write energy level" means an average energy level
of a period of time that is long enough to neglect the influence of
that frequency component.
[0067] First, referring to FIG. 1, illustrated is an overall
configuration for a data recorder according to a preferred
embodiment of the present invention. As shown in FIG. 1, the
apparatus of this preferred embodiment includes an optical pickup,
a write processing system and a read processing system.
[0068] The optical pickup includes a laser 110 for radiating a
laser beam 123, a collimator lens 109 for transforming the laser
beam 123 into parallel light, a half mirror 108, an objective lens
116 for condensing the laser beam 123 onto an optical disk 117, a
detector lens 106 for condensing the light that has been reflected
from the optical disk 117, a photodetector 100 for detecting the
reflected light, and a pre-amplifier 101 for amplifying the output
of the photodetector 100.
[0069] In this preferred embodiment, the laser 110 may be a
semiconductor laser that oscillates at a wavelength of 405 nm and
the objective lens 116 may have an NA of 0.85, for example. Only
one laser 110 and its accompanying optical system are shown in FIG.
1. However, the single optical pickup may include a light source
module for emitting laser beams with multiple different wavelengths
and their associated optical systems.
[0070] The write processing system shown in FIG. 1 includes a data
modulator 113 for converting write data 127 into a write code
sequence (NRZI) 126, a write pulse waveform generator 112 for
generating a level producing signal 125 based on the write code
sequence (NRZI) 126, a pulse shifter 115 for generating a pulse
generation signal 130 based on the level producing signal 125, and
a laser driver 111 for outputting laser drive current 124
responsive to the pulse generation signal 130. A reference clock
signal 128 is supplied from a reference clock generator 119 to the
data modulator 113 and write pulse waveform generator 112. In this
preferred embodiment, the reference clock signal 128 has a
frequency of 72 MHz and a detection window width Tw of 7.58 ns. The
write processing system further includes a power setter 114 and a
write compensator 118.
[0071] The read processing system shown in FIG. 1 includes a
equalizer 103 that receives the read signal 120 as the output
signal of the pre-amplifier 101 of the optical pickup and subjects
the signal to waveform equalizing process, a digitizer 104 for
converting the read signal into a digital read signal 121, and a
decoder 105 for generating read data 122 by decoding the digital
read signal 121.
[0072] Next, it will be described how the data recorder shown in
FIG. 1 operates.
[0073] The data modulator 113 of the write processing system
receives the write data 127 to be written on the optical disk 117
and converts this write data 127 into the write code sequence
(NRZI) 126 representing the marks and spaces to be made on the
optical disk 117. The write wave generator 112 receives the write
code sequence 126 and converts it into the level producing signal
125 corresponding to the write pulse waveform. The data modulator
113 and write pulse waveform generator 112 operate in response to
the reference clock signal 128 generated by the reference clock
generator 119.
[0074] The pulse shifter 115 receives the level producing signal
125 and forwards it as the pulse generation signal 130 to the laser
driver 111. In this case, the pulse shifter 115 compensates for the
pulsed waveform of the level generating signal 125 on the time axis
in accordance with a write compensation table value of the write
compensator 118, thereby making the pulse generation signal
130.
[0075] The laser driver 111 generates the laser drive current 124
responsive to the pulse generation signal 130. This laser drive
current 124 is injected to the laser 110, thereby driving the laser
110. In accordance with a predetermined write pulse waveform, the
laser 110 radiates the laser beam 123. In this manner, the power
level of the laser beam 123 changes in accordance with the "write
pulse waveform".
[0076] The laser beam 123 emitted from the laser 110 passes the
collimator lens 109, half mirror 108 and objective lens 116 and is
condensed onto the optical disk 117. The condensed pulsed laser
beam 123 locally heats a portion of the phase change recording
layer of the optical disk 117 that is spinning at a high velocity,
thereby making marks and spaces along the track on the optical disk
117. In this case, if the phase change recording layer is
irradiated with the pulsed laser beam 123 at short intervals, then
the melted portions of the phase change recording layer will
combine together to form a single long mark. The power level of the
laser beam 123 depends on the write pulse waveform as described
above. For that reason, if the write pulse waveform is controlled
appropriately, a single long mark can be made by applying a
plurality of pulses.
[0077] In reading data from the optical disk 117, the rows of marks
on the optical disk 117 are scanned with the laser beam 123 with a
power level that is low enough to avoid destroying (i.e., melting)
the marks on the phase change recording layer. The light that has
been reflected from the optical disk 117 passes the objective lens
116 and half mirror 108 and then enters the detector lens 106.
[0078] The laser beam that has been reflected from the optical disk
117 passes the detector lens 106 and then is condensed on the
photodetector 100. According to the light intensity distribution of
the laser beam on the photosensitive plane, the photodetector 100
converts the incoming light into an electrical signal. This
electrical signal is amplified by the pre-amplifier 101 provided
for the photodetector 100, thereby generating the read signal 120
that indicates whether or not there is a mark at the scan point on
the optical disk 117.
[0079] The read signal 120 is subjected by the equalizer 103 to a
waveform equalization process and then converted by the digitizer
104 into the digital read signal 121. The decoder 105 converts this
digital read signal 121 in the opposite way to the data modulator
113, thereby generating the read data 122.
[0080] The optical disk 117 may be either a single-layer disk that
has only one information storage layer or a double-layer disk that
has two information storage layers. Also, the optical disk 117 may
be either a rewritable optical disk that uses a phase change
recording material or a write-once optical disk that allows the
user to write data there only once.
[0081] The coding method does not have to be the (1, 7) modulation
but may also be a 17 PP modulation or an 8-16 modulation. The 8-16
modulation has the shortest code length of 3 T. In that case, an
extra code length of one may be added to this preferred embodiment
that uses the (1, 7) modulation.
[0082] Next, an exemplary configuration for the write processing
system shown in FIG. 1 will be described in further detail with
reference to FIG. 2.
[0083] The write data 127 is converted by the data modulator 113
into the write code sequence 126 representing mark lengths, space
lengths, and information about their top positions. The write code
sequence 126 is transmitted to a mark length classifier 201 and a
write pulse waveform table 202. The mark length classifier 201
classifies the mark lengths of the write code sequence 126
following a predetermined rule and inputs the results as a mark
length classification signal 204 to the write pulse waveform table
202.
[0084] The counter 200 refers to the write code sequence 126 and
measures the length of time from a mark top position responsive to
the reference clock signal 128, thereby generating a count signal
205. In accordance with the write code sequence 126, mark length
classification signal 204 and count signal 205, the write pulse
waveform table 202 outputs the level producing signal 125,
reflecting a predetermined write pulse waveform, to the pulse
shifter 115.
[0085] The pulsed waveform of the level producing signal 125 is
compensated for on the time axis according to the write
compensation table value of the write compensator 118 and then sent
out as the pulse generation signal 130 to the laser driver 111. The
pulse generation signal 130 includes a Pc generation signal 206, a
Pb generation signal 207, a Pe generation signal 208 and a Pw
generation signal 209 that represents a power level defining the
write pulse waveform. Responsive to the pulse generation signal
130, the laser driver 111 drives the laser 110.
[0086] Next, the write code sequence of this preferred embodiment
will be described with reference to portions (a) through (h) of
FIG. 3. In some cases, the length or level of a portion of the
write pulse waveform needs to be finely adjusted (i.e., write
compensation needs to be carried out) in a certain period for some
reason by reference to the preceding and succeeding write patterns
and code lengths. In the following description of the write pulse
waveform, when such write compensation is carried out, the write
pulse waveform is supposed to be compared to the original write
pulse waveform yet to be finely adjusted. For that reason, the
write pulse waveform will be described on the supposition that the
write pattern remains the same over a rather long distance before
and after the mark to be made. As used herein, the "rather long
distance" means a distance that is much longer than the distance on
a medium to be affected by the application of the write energy for
a period of time approximately corresponding to the detection
window width.
[0087] Portion (a) of FIG. 3 shows the reference clock signal 128
that is used as a time reference for a write operation. Tw denotes
one clock period.
[0088] Portion (b) of FIG. 3 shows the write code sequence 126
obtained by getting the write data subjected to the NRZI conversion
by the data modulator 113. The signal waveform representing the
write code sequence 126 changes between level "1" and level "0".
The detection window width is equal to Tw, which is the minimum
unit of variation in the mark or space length in the write code
sequence 126.
[0089] Portion (c) of FIG. 3 schematically illustrates the planar
shapes of marks and spaces to be actually recorded on the optical
disk. The beam spot of the laser beam, which is incident on the
optical disk to write data thereon, shifts from the left to the
right in portion (c) of FIG. 3 while varying its power level,
thereby leaving a series of marks shown in portion (c) of FIG. 3.
The mark 301 shown in portion (c) of FIG. 3 is made so as to
represent level "1" in the write code sequence 126. The length of
the mark 301 is proportional to that of the period that has level
"1" in the write code sequence 126.
[0090] Portion (d) of FIG. 3 shows the count signal 205, in which
the amount of time that has passed since the top of the mark 301 or
space 302 is measured on a Tw basis.
[0091] Portion (e) of FIG. 3 shows a mark length classification
signal 307 in a conventional apparatus for the purpose of
comparison. In this conventional apparatus, the mark lengths are
classified into odd-number-of-times longer ones and
even-number-of-times longer ones.
[0092] Portion (f) of FIG. 3 shows a write pulse waveform 303 in
the conventional apparatus, which is the counterpart of the write
code sequence 126 shown in portion (b) of FIG. 3. The write pulse
waveform 303 is generated by reference to the count signal 205,
write code sequence 126 and mark length classification signal
307.
[0093] Portion (g) of FIG. 3 shows the mark length classification
signal 204 of this preferred embodiment. In this preferred
embodiment, the mark lengths are classified into the shortest code
length of 2T, the second shortest code length of 3T, the third
shortest code length of 4T, and the fourth shortest or less short
code lengths, which are further classified into odd-number-of-times
longer code lengths and even-number-of-times longer code
lengths.
[0094] Portion (h) of FIG. 3 shows the write pulse waveform 304 of
this preferred embodiment corresponding to the write code sequence
126 shown in portion (b) of FIG. 3. This write pulse waveform 304
is generated by reference to the count signal 205, write code
sequence 126 and mark length classification signal 204. The
shortest cooling time of this write pulse waveform 304 is about 1
Tw.
[0095] Hereinafter, signal waveforms for making marks according to
the present invention will be described in detail with reference to
FIG. 2 and portions (a) through (j) of FIG. 4. Portions (a) through
(j) of FIG. 4 show write pulse waveforms 400 through 407,
respectively.
[0096] In this preferred embodiment, the data modulator 113 (see
FIG. 2) adopts a coding method in which the (1, 7) code modulation
is followed by the NRZI modulation, each and every mark or space
length falls within the range of 2 Tw to 8 Tw. This coding method
is also applicable to even a situation where a signal of 9 Tw, for
example, is intentionally inserted as a sync signal. However, this
does not amend the coding rule of the data modulator 113. Rather,
the present invention is applicable for use in the data modulator
113 that complies with any arbitrary coding rule (e.g., 8-16
modulation).
[0097] First, the mark length classifier 201 of this preferred
embodiment classifies the code lengths n of the marks to be made
into the four groups of 2T, 3T, 4T and 5T or more. If the code
length n is 5T or more, the mark length classifier 201 divides
(n-1) by the divisor of two (i.e., performs a remainder
calculation), thereby obtaining a quotient. Then, the mark length
classifier 201 outputs this quotient as a mark length
classification signal. For example, if the code length n is five,
then (5-1)=4 and four divided by the divisor of two is two, which
is the quotient obtained. Meanwhile, if the code length n is six,
then (6-1)=5 and five divided by the divisor of two is also two,
which means the same quotient is obtained. That is why the same
mark length classification signal is output for a mark with 5 Tw
length and a mark with a 6 Tw length.
[0098] By using such a mark length classification signal, the marks
and spaces of the write code sequence can be classified into ones
that are even-number-of-times as long as the detection window width
Tw and ones that are odd-number-of-times as long as the detection
window width Tw. In this preferred embodiment, the divisor is
supposed to be two for the sake of simplicity. However, three or
any other greater divisor may be used instead. Also, the mark
length classifier 201 of this preferred embodiment operates so as
to perform a remainder calculation. However, the present invention
is in no way limited to this specific preferred embodiment.
[0099] Portions (a) through (j) of FIG. 4 will be referred to
next.
[0100] Portion (a) of FIG. 4 shows the waveform of the reference
clock signal 128, while portion (b) of FIG. 4 shows the count
signal 205 generated by the counter 200. The amount of time that
has passed since the top of a mark is counted on a detection window
width (Tw) basis. The time at which the count signal goes zero
corresponds to the top of a mark or space. Portions (c) through (j)
of FIG. 4 show signal waveforms for making marks with 2 Tw to 9 Tw
lengths, respectively.
[0101] As used herein, the "mark making period" is defined as a
period of time between the leading edge of the first pulse and the
trailing edge of the last pulse as shown in portion (j) of FIG.
4.
[0102] In making a mark with the 2 Tw length, the write pulse
waveform during the mark making period consists of a single pulse
with a length of 0.5 Tw to 1 Tw and a level Pw as shown in portion
(c) of FIG. 4.
[0103] In making a mark with the 3 Tw length, the write pulse
waveform during the mark making period consists of a single pulse
with a length of 1 Tw or more but less than 2 Tw and with a level
Pw as shown in portion (d) of FIG. 4. It should be noted that in
this case, the mark making period is supposed to be longer than
that of the 2 Tw long one by at least 0.5 Tw.
[0104] In making a mark with the 4 Tw length, the write pulse
waveform during the mark making period consists of a single pulse
with a length of 1.5 Tw or more but less than 2.5 Tw and with a
level Pw as shown in portion (e) of FIG. 4. It should be noted that
in this case, the mark making period is supposed to be longer than
that of the 3 Tw long one by at least 0.5 Tw.
[0105] In a conventional data recorder such as a DVD
player/recorder, a mark with the 4 Tw length is made by using a
write pulse waveform that has two write pulses Pw during a single
mark making period as shown in FIG. 13(a). As for DVDs, the write
pulses have a wavelength of about 650 nm. In such an apparatus, if
one tries to make a 4 Tw long mark using a single write pulse Pw
such as that shown in FIG. 13(b), then the mark width broadens at
the end portion as shown in FIG. 13(c). In contrast, according to
this preferred embodiment, even by using a single write pulse such
as that shown in FIG. 13(b), a mark of an appropriate shape can be
made with good reproducibility as shown in FIG. 13(d).
[0106] A Blu-ray Disc (BD) is now being developed as a
next-generation optical disk. In a BD, the laser beam for reading
and writing has a wavelength of about 400 nm. Also, the material
and composition of the storage layer of a BD are different from
those of the storage layer of a DVD. Besides, BD and DVD have a lot
of other differences in their physical structures. In a BD, the
width and interval of the write pulses need to be narrower than
those of a DVD. For that reason, if the data transfer rate
increases, a 4 Tw long mark may have a deformed shape even when
write pulses having the waveform shown in FIG. 13(a) are used. On
the other hand, if a 4 Tw long mark is made by using a single write
pulse such as that shown in FIG. 13(b), a mark of a preferred shape
can also be obtained even in a BD.
[0107] In making a mark with the 5 Tw length, the write pulse
waveform during the mark making period includes a pulse with a
length of 1 TTw and a level Pw, which is followed by a period with
a length of 1 Tw and a level Pe and then a period with a length of
1 Tw and a level Pw as shown in portion (f) of FIG. 4.
[0108] In making a mark with the 6 Tw length, the write pulse
waveform during the mark making period includes a pulse with a
length of 1 TTw and a level Pw, which is followed by a period with
a length of 2 Tw and a level Pe and then a period with a length of
1 Tw and a level Pw as shown in portion (g) of FIG. 4.
[0109] In making a mark with the 7 Tw length and a mark with the 9
Tw length (i.e., odd-number-of-times longer marks with code lengths
over 5 Tw and a detection window width Tw), the write pulse
waveform during the mark making period includes an additional
period with a length of 1 Tw and a level Pe and another additional
period with a length of 1 Tw and a level Pw per mark length of 2 Tw
at the center of the mark making period as shown in portions (h)
and (j) of FIG. 4.
[0110] In making a mark with the 8 Tw length (i.e., an
even-number-of-times longer mark with a code length more than 5 Tw
and a detection window width Tw), the write pulse waveform during
the mark making period includes an additional period with a length
of 1 Tw and a level Pe and another additional period with a length
of 1 Tw and a level Pw per mark length of 2 Tw at the center of the
mark making period as shown in portion (i) of FIG. 4. Thus, in a
situation where In a non-mark-making period, the level of the
signal waveform is maintained at Pe until the next mark making
period irrespective of the space length. In this preferred
embodiment, the shortest Pe level period (i.e., the shortest
cooling period) during the mark making period 305 has a length of 1
Tw.
[0111] According to this preferred embodiment that adopts such a
write strategy, a mark of an appropriate shape can be made with
good reproducibility without being affected by the rising or
falling rate of the optical output of a semiconductor laser diode.
For example, if the data transfer rate is 72 Mbps, then Tw becomes
7.6 ns. In this case, 0.5 Tw=3.8 ns. Accordingly, if the rising and
falling rates of the optical output of the semiconductor laser
diode are about 2 ns, neither the peak power level nor the bottom
power level can be reached and no mark of a desired shape can be
obtained. Meanwhile, by adopting the write strategy of this
preferred embodiment, the laser power can be modulated just as
represented by the write pulse waveform even without increasing the
current rising and falling rates of the optical output of the
semiconductor laser diode.
[0112] Also, in this preferred embodiment, as to two codes, which
have code lengths m and m+1, respectively, and to which a write
pulse waveform with the same number of write pulses Pw is assigned
in the recording mark making period, the write pulse waveforms are
determined so as to satisfy the inequality: (write pulse width of
code length m).ltoreq.(write pulse width of code length m+1), where
the "write pulse width of code length m" is the width of an
arbitrary Kth write pulse period included in the period in which a
recording mark with the code length m is made and the "write pulse
width of code length m+1" is the width of an arbitrary Kth write
pulse period included in the period in which a recording mark with
the code length m+1 is made.
[0113] As a result, the marks can be made in even more appropriate
shapes.
[0114] Furthermore, in this preferred embodiment, in a period in
which a recording mark corresponding to a code with a code length x
of (n+3) or more is made, a portion of the write pulse waveform
with the erasure power level Pe has a length of at least 1 Tw. In
that case, even if the optical output of the semiconductor laser
diode has a rising or falling rate of about 2 ns, the laser power
can be modulated with a desired write power. As a result, marks can
be made with good reproducibility.
EMBODIMENT 2
[0115] Hereinafter, a data recording method according to a second
preferred embodiment of the present invention will be described
with reference to FIG. 6.
[0116] The data recording method of this preferred embodiment can
be carried out just by modifying the operation program for the data
recorder of the first preferred embodiment described above. That is
why the data recorder for use in this preferred embodiment has
substantially the same configuration as the counterpart shown in
FIGS. 1 and 2, and detailed description thereof will be omitted
herein.
[0117] The write pulse waveforms 600 through 607 of this preferred
embodiment will be described with reference to portions (a) through
(j) of FIG. 6.
[0118] As can be seen easily by comparing portions (a) through (j)
of FIG. 6 to the counterparts of FIG. 4, the signal waveforms 600
through 607 adopted in this preferred embodiment are similar to the
signal waveforms 400 through 407 shown in FIG. 4. Among other
things, the signal waveforms 600 through 602 are identical with the
signal waveforms 400 through 402, respectively, as shown in
portions (c) through (e) of FIG. 6. The difference between the
first and second preferred embodiments lies in the shapes of signal
waveforms with code lengths n exceeding 5 Tw.
[0119] Referring to portion (f) of FIG. 6, in making a mark with
the 5 Tw length, the write pulse waveform includes a pulse with a
length of 1 TTw and a level Pw, which is followed by a period with
a length of 1 Tw and a level Pb and then a period with a length of
1 Tw and a level Pw. In this case, it should be noted that the
level Pb in the period interposed between the two pulses is lower
than the level Pe.
[0120] In making a mark with the 6 Tw length, the write pulse
waveform includes a pulse with a length of 1 Tw and a level Pw,
which is followed by a period with a length of 2 Tw and a level Pb
and then a period with a length of 1 Tw and a level Pw as shown in
portion (g) of FIG. 6.
[0121] In making odd-number-of-times longer marks with code lengths
over 5 Tw and a detection window width Tw, the write pulse waveform
includes an additional period with a length of 1 Tw and a level Pb
and another additional period with a length of 1 Tw and a level Pw
per mark length of 2 Tw at the center of the mark making period as
shown in portions (h) and (j) of FIG. 6.
[0122] In making an even-number-of-times longer mark with a code
length over 5 Tw and a detection window width Tw, the write pulse
waveform includes an additional period with a length of 1 Tw and a
level Pb and another additional period with a length of 1 Tw and a
level Pw per mark length of 2 Tw at the center of the mark making
period as shown in portion (i) of FIG. 6.
[0123] According to this preferred embodiment, as to two codes,
which have code lengths m and m+1 (where m is an integer equal to
or greater than one), respectively, and to which a write pulse
waveform with the same number of write pulses Pw and the same
number of periods with a bottom power level Pb between two write
pulses Pw is assigned in a recording mark making period, the write
pulse waveforms are determined so as to satisfy the inequality:
(pulse width of code length m).ltoreq.(pulse width of code length
m+1), where the "pulse width of code length m" is the width of an
arbitrary Kth period with the bottom power level Pb included in the
period in which a recording mark with the code length m is made and
the "pulse width of code length m+1" is the width of an arbitrary
Kth period with the bottom power level Pb included in the period in
which a recording mark with the code length m+1 is made. The
shorter the code length, the more easily the heat is accumulated in
the end portion of a mark. However, by satisfying the inequality
(pulse width of code length m).ltoreq.(pulse width of code length
m+1), the accumulation of heat can be reduced and the mark shapes
can be adjusted.
[0124] Furthermore, in this preferred embodiment, in each recording
mark making period, a portion of the write pulse waveform with the
bottom power level Pb has a length of at least 1 Tw. In that case,
even if the optical output of the semiconductor laser diode has a
rising or falling rate of about 2 ns, the laser power can be
modulated with a desired write power. As a result, marks can be
made with good reproducibility.
EMBODIMENT 3
[0125] Hereinafter, a data recording method according to a third
preferred embodiment of the present invention will be described
with reference to FIG. 7.
[0126] The data recording method of this preferred embodiment can
be carried out just by modifying the operation program for the data
recorder of the first preferred embodiment described above. That is
why the data recorder for use in this preferred embodiment has
substantially the same configuration as the counterpart shown in
FIGS. 1 and 2, and detailed description thereof will be omitted
herein.
[0127] The write pulse waveforms 700 through 707 of this preferred
embodiment will be described with reference to portions (a) through
(j) of FIG. 7.
[0128] As can be seen easily by comparing portions (a) through (j)
of FIG. 7 to the counterparts of FIG. 6, the signal waveforms 700
through 707 adopted in this preferred embodiment are similar to the
signal waveforms 600 through 607 shown in FIG. 6. The difference
between the second and third preferred embodiments is that a
non-mark-making period begins with a period with a length of 1 Tw
to 1.5 Tw and a level Pc and then the Pe level is maintained until
the next mark making period. In this preferred embodiment, these
levels Pc and Pb are supposed to be two different power levels.
Alternatively, the levels Pc and Pb may be set equal to each
other.
EMBODIMENT 4
[0129] Hereinafter, a data recording method according to a fourth
preferred embodiment of the present invention will be described
with reference to FIG. 11.
[0130] The data recording method of this preferred embodiment can
be carried out just by modifying the operation program for the data
recorder of the first preferred embodiment described above. That is
why the data recorder for use in this preferred embodiment has
substantially the same configuration as the counterpart shown in
FIGS. 1 and 2, and detailed description thereof will be omitted
herein.
[0131] The write pulse waveforms 1100 through 1107 of this
preferred embodiment will be described with reference to portions
(a) through (j) of FIG. 11.
[0132] As can be seen easily by comparing portions (c) through (j)
of FIG. 11 to the counterparts of FIG. 4, the signal waveforms
1100, 1101 and 1103 through 1107 adopted in this preferred
embodiment are identical with the signal waveforms 400, 401 and 403
through 407 shown in FIG. 4. This preferred embodiment is
characterized in that in making a mark with the 4 Tw length, the
write pulse waveform includes a pulse with a length of 0.5 Tw and a
level Pw, which is followed by a period with a length of 1 Tw and a
level Pe and then a period with a length of 0.5 Tw and a level Pw
as shown in portion (e) of FIG. 11. After that, the level Pe is
maintained until the next mark making period.
[0133] Portion (b1) of FIG. 11 shows a count signal 205 generated
by the counter 200 to measure the amount of time that has passed
since the top of a mark on a detection window width (Tw) basis. The
time at which the count signal goes zero corresponds to the top of
a mark or a space.
[0134] Portion (b2) of FIG. 11 shows a sub-count signal 210
generated by the counter 200 and having a phase difference of 180
degrees with respect to the reference signal. The time at which
this count signal goes zero has a phase lag of 180 degrees with
respect to the top of a mark or a space.
[0135] As shown in portion (e) of FIG. 11, Pw has a pulse width of
0.5 Tw. However, this width may be any value that is equal to or
greater than 0.5 Tw. In this case, either or both of the leading
and trailing edges of each pulse are synchronous with the sub-count
signal.
[0136] In this preferred embodiment, the trailing edge of the first
pulse and the leading edge of the second pulse in the signal
waveform 1102 with the 4 Tw length are synchronous with the
sub-count signal 210.
EMBODIMENT 5
[0137] Hereinafter, a data recording method according to a fifth
preferred embodiment of the present invention will be described
with reference to FIG. 12.
[0138] The data recording method of this preferred embodiment can
be carried out just by modifying the operation program for the data
recorder of the first preferred embodiment described above. That is
why the data recorder for use in this preferred embodiment has
substantially the same configuration as the counterpart shown in
FIGS. 1 and 2, and detailed description thereof will be omitted
herein.
[0139] The write pulse waveforms 1200 through 1207 of this
preferred embodiment will be described with reference to portions
(a) through (j) of FIG. 12.
[0140] Portion (a) of FIG. 12 shows the waveform of the reference
clock signal 128. Portion (b1) of FIG. 12 shows a count signal 205
generated by the counter 200 to measure the amount of time that has
passed since the top of a mark on a detection window width (Tw)
basis. The time at which the count signal goes zero corresponds to
the top of a mark or a space. Portion (b2) of FIG. 12 shows a
sub-count signal 210 generated by the counter 200 and having a
phase difference of 180 degrees with respect to the reference
signal. The time at which this count signal goes zero has a phase
lag of 180 degrees with respect to the top of a mark or a
space.
[0141] In making a mark with the 2 Tw length, the write pulse
waveform consists of a pulse with a length of 1 Tw and a level Pw
as shown in portion (c) of FIG. 12. The non-mark-making period
begins with a period with a length of 1 Tw and a level Pc and then
maintains a level Pe until the next mark making period.
[0142] In making a mark with the 3 Tw length, the write pulse
waveform consists of a pulse with a length of 2 Tw and a level Pw
as shown in portion (d) of FIG. 12. The non-mark-making period
begins with a period with a length of 1 Tw and a level Pc and then
maintains a level Pe until the next mark making period. However,
the mark making period is supposed to be longer than that of the 2
Tw long one by at least 0.5 Tw.
[0143] In making a mark with the 4 Tw length, the write pulse
waveform includes a pulse with a length of 1 Tw and a level Pw,
which is followed by a period with a length of 1 Tw and a level Pb
and then a period with a length of 1 Tw and a level Pw as shown in
portion (e) of FIG. 12. The non-mark-making period begins with a
period with a length of 1 Tw and a level Pc and then maintains a
level Pe until the next mark making period.
[0144] In making even-number-of-times longer marks with a detection
window width Tw, the write pulse waveform includes an additional
period with a length of 1 Tw and a level Pb and another additional
period with a length of 1 Tw and a level Pw per mark length of 2 Tw
at the center of the mark making period as shown in portions (g)
and (i) of FIG. 12. The non-mark-making period begins with a period
with a length of 1 Tw and a level Pc and then maintains a level Pe
until the next mark making period.
[0145] In making a mark with the 5 Tw length, the write pulse
waveform includes a pulse with a length of 1 Tw and a level Pw,
which is followed by a period with a length of 2 Tw and a level Pb
and then a period with a length of 1 Tw and a level Pw as shown in
portion (f) of FIG. 12. The non-mark-making period begins with a
period with a length of 1 Tw and a level Pc and then maintains a
level Pe until the next mark making period.
[0146] In making a mark with the 7 Tw length, the write pulse
waveform includes a pulse with a length of 1 Tw and a level Pw,
which is followed by a period with a length of 1.5 Tw and a level
Pb, a period with a length of 1 Tw and a level Pw, and then a
period with a length of 1.5 Tw and a level Pb as shown in portion
(h) of FIG. 12. The non-mark-making period begins with a period
with a length of 1 Tw and a level Pc and then maintains a level Pe
until the next mark making period.
[0147] In this case, either or both of the leading and trailing
edges of the intermediate pulse is/are synchronous with the
sub-count signal. In FIG. 12, the leading and trailing edges of the
second pulse are synchronous with the sub-count signal.
[0148] After that, in making odd-number-of-times longer marks with
a detection window width Tw, a period with a length of 1 Tw and a
level Pb and another period with a length of 1 Tw and a level Pw
are added per mark length of 2 Tw to the center of the mark making
period as shown in portion (j) of FIG. 12. The non-mark-making
period begins with a period with a length of 1 Tw and a level Pc
and then maintains a level Pe until the next mark making
period.
[0149] In some waveforms of this preferred embodiment, the level Pe
is supposed to be the same as the level Pb or Pc. However, the
level Pe may be different from the level Pb or Pc.
[0150] Next, an example of adaptive mark compensation will be
described with reference to the accompanying drawings. A
high-density optical write operation sometimes causes write
interference in which mark edges shift depending on the writing
conditions. To prevent the write signal from being deteriorated by
such interference, adaptive mark compensation may be carried
out.
[0151] The adaptive mark compensation means a compensation
operation of changing the top incidence points or pulse widths of
the laser beam according to the length of the given mark, i.e.,
whether the length of the mark is 2T (2Tm), 3T (3Tm), 4T (4Tm) or
5T or more (.gtoreq.5Tm), as shown in FIG. 8.
[0152] FIG. 8 shows exemplary adaptive mark compensation in a
situation where the write power is represented by binary values. By
shifting dTtop and Ttop with respect to the beginning of the mark
and also shifting Tlp or dTlp with respect to the end of the
recording mark according to the code length of the recording mark
among other parameters described above, the edge shifting at the
beginning and end of the mark can be minimized and good signal
quality is realized.
[0153] FIG. 9 shows exemplary adaptive mark compensation in a
situation where the write power is represented by four values. By
shifting dTtop and Ttop with respect to the beginning of the mark
and also shifting dTe with respect to the end of the recording mark
according to the code length of the recording mark among other
parameters described above, the edge shifting at the beginning and
end of the mark can be minimized and good signal quality is
realized. Although the write power is supposed to be represented by
four values in this example, the same mark compensation is equally
applicable to even a situation where three values are used by
setting Pb=Pc.
[0154] The magnitude of shift that can be caused by the write
compensation may be defined by a very small step (of Tw/16, for
example) with respect to the reference clock signal using a delay
line, for instance.
[0155] Also, the write compensation may be started either from a
point in time on the fundamental waveform responsive to the count
signal or another point in time responsive to the sub-count
signal.
[0156] In the fundamental waveform of this preferred embodiment,
each pulse width and the widths of a period with the bottom power
level and a period with the cooling power level in each mark making
period are supposed to be at least equal to 1 T. However, after the
write compensation has been done, each pulse for a mark of any of
various lengths preferably has a width of at least 0.5 Tw. In that
case, the writing conditions can be relaxed without being affected
by the laser response speed so much.
COMPARATIVE EXAMPLE
[0157] Hereinafter, the patterns of write pulse waveforms 500
through 506 for an apparatus of a comparative example will be
described with reference to portions (a) through (j) of FIG. 5 and
FIG. 10.
[0158] First, referring to FIG. 10, illustrated is a configuration
for the write processing system of this apparatus.
[0159] The data modulator 1013 shown in FIG. 10 receives write data
1027 and converts it into a write code sequence 1026. The mark
length classifier 1001 divides the code length n by the divisor of
two (i.e., performs a remainder calculation) on the write code
sequence 1025. This mark length classifier 1001 classifies the
marks and spaces of the write code sequence into ones of which the
lengths are even numbers of times as long as the detection window
width Tw and ones of which the lengths are odd numbers of times as
long as the detection window width Tw.
[0160] The counter 1000 measures the length of time from a mark top
position on a detection window width Tw basis, thereby generating a
count signal 1005. Portion (b) of FIG. 5 shows the count signal
1005. The time at which the count signal 1005 goes zero corresponds
to the top of a mark or space.
[0161] A reference clock signal 1028 is input to the counter 1000
and the data modulator 1013. The count signal 1005 is input to the
write pulse waveform table 1002, which outputs a level producing
signal 1025 to the laser driver 1011. In response, the laser driver
1011 outputs laser drive current 1024.
[0162] Portion (c) of FIG. 5 shows a write pulse waveform while a
mark with the 2 Tw length is being made. The mark making period 305
includes a pulse with a length of 1 Tw and a level Pw1. The
non-mark-making period begins with a period with a length of 1 Tw
and a level Pb and then maintains a level Pa until the next mark
making period.
[0163] Portion (d) of FIG. 5 shows a write pulse waveform while a
mark with the 3 Tw length is being made. The mark making period 305
includes a pulse with the same length of 1 Tw and the same level
Pw1 as the counterpart shown in portion (c) of FIG. 5, which is
followed by a period with a length of 1 Tw and a level Pw2. The
non-mark-making period begins with a period with a length of 1 Tw
and a level Pb and then maintains the level Pa until the next mark
making period just like the write pulse waveform shown in portion
(c) of FIG. 5. The non-mark-making period has the same waveform in
any of portions (e) and (f) of FIG. 5. That is to say, irrespective
of the length of the space, every non-mark-making period begins
with a period with a length of 1 Tw and a level Pb and then
maintains the level Pa until the next mark making period. Thus, the
shortest cooling period in the mark making period 305 has a length
of 1 Tw.
[0164] Portion (e) of FIG. 5 shows a write pulse waveform while a
mark with the 4 Tw length is being made. The mark making period 305
includes a pulse with the same length of 1 Tw and the same level
Pw1 as the counterpart shown in portion (c) of FIG. 5, which is
followed by a period with a length of 1 Tw and a level Pa and then
a period with a length of 1 Tw and a level Pw3.
[0165] Portions (f) and (h) of FIG. 5 show write pulse waveforms in
making marks with 5 Tw and 7 Tw lengths, respectively. Thus, in
making a mark of which the length is an odd number of times as long
as the detection window width Tw, a period with a length of 1 Tw
and a level Pa and another period with a length of 1 Tw and a level
Pw3 are added per mark length of 2 Tw to the end of the mark making
period. The non-mark-making period always begins with a period with
a length of 1 Tw and a level Pb irrespective of the space length
and then maintains the level Pa until the next mark making
period.
[0166] Portions (g) and (i) of FIG. 5 show write pulse waveforms in
making marks with 6 Tw and 8 Tw lengths, respectively. Thus, in
making a mark of which the length is an even number of times as
long as the detection window width Tw, a period with a length of 1
Tw and a level Pa and another period with a length of 1 Tw and a
level Pw3 are added per mark length of 2 Tw to the end of the mark
making period.
[0167] In this comparative example, the write power of the write
pulse train changes stepwise, thus requiring a more complicated
power control than any preferred embodiment of the present
invention. Also, in recording a mark with a code length of 4 Tw,
the semiconductor laser diode needs to emit radiation at a higher
power level than the average power level at least during a period
with the 3 Tw length. When the storage density of optical disks
rises in the near future to the point that very small marks need to
be made, the radiation will have to be emitted for too long a time
in the comparative example. As a result, marks of a desired shape
will not be obtained.
INDUSTRIAL APPLICABILITY
[0168] According to the present invention, an apparatus for
recording data on a storage medium by applying energy to the
storage medium and making marks that have a different physical
property from the non-recorded portion can make those marks quickly
and accurately. As a result, the mark edge recording technique,
which will effectively contribute to increasing the recording
linear density, can be adopted as the method of recording.
[0169] Consequently, the read/write operations can be done more
quickly and with more reliability, and yet the sizes of the
apparatus for recording information and the storage medium can be
reduced as well. That is why the present invention is very
cost-effective.
* * * * *