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Claims  |
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What is claimed is:
1. A phase-change optical recording medium comprising:
a data recordable area containing land tracks and groove tracks on both of
which user information is recorded, said land tracks and said groove
tracks being alternately disposed on said data recordable area; and
a header area on which header information is recorded in rows of prepits,
said rows of prepits being arranged in every other track with respect to
said tracks included in said data recordable area.
2. A phase-change optical recording medium according to claim 1, wherein
said rows of prepits are disposed in said header area in correspondence
with said land tracks.
3. A phase-change optical recording medium according to claim 1, wherein
said groove tracks have a groove depth of approximately .lambda./6, where
.lambda. is a wavelength of an optical beam landing on said recording
medium.
4. A phase-change optical recording medium according to claim 1, wherein
when an optical beam landing on said recording medium has a diameter of an
optical beam whose intensity is 1/e.sup.2 of a maximum intensity, where e
is an natural logarithm, a track pitch between adjacent tracks is set at
one-third said diameter of said optical beam.
5. A phase-change optical recording medium according to claim 1, wherein
said header information is further recorded in rows of prepits
corresponding to each track in said data recordable area, said prepits in
adjacent rows being placed in a staggered fashion so that a binary
information signal corresponding to said header information has a sign
which is inverted at each of said tracks.
6. A phase-change optical recording medium according to claim 1, wherein
said header information includes track numbers set so as to increase in
every other track from an inner to an outer circumference of said
recording medium or from said outer to said inner circumference, and to
again increase in every other track of said remaining tracks from said
inner to said outer circumference or from said outer to said inner
circumference.
7. A phase-change optical recording medium according to claim 1, wherein
said header information includes track numbers set so as to increase
sequentially from an innermost or an outermost circumference of said
recording medium.
8. A phase-change optical recording medium comprising:
a data recordable area containing land tracks and groove tracks on both of
which user information is recorded, said land tracks and said groove
tracks being alternately disposed in said data recordable area, and
a header area in which header information is recorded in a plurality of
rows of prepits, each row of prepits in said plurality of rows of prepits
being arranged so as to correspond to one of said land and said groove
tracks.
9. A phase-change optical recording medium according to claim 8, wherein
said groove tracks have a groove depth of approximately .lambda./6, where
.lambda. is a wavelength of an optical beam landing on said recording
medium.
10. A phase-change optical recording medium according to claim 8, wherein
when an optical beam landing on said recording medium has a diameter of an
optical beam whose intensity is 1/e.sup.2 of a maximum intensity, where e
is an natural logarithm, a track pitch between adjacent tracks is set at
one-third said diameter of said optical beam.
11. A phase-change optical recording medium according to claim 8, wherein
said prepits in each row of prepits are placed in a staggered fashion
between adjacent prepit rows so that a binary information signal
corresponding to said header information has a sign that is inverted at
each of said tracks.
12. A phase-change optical recording medium according to claim 8, wherein
said header information includes track numbers set so as to increase in
every other track from an inner to an outer circumference of said
recording medium or from said outer to said inner circumference, and to
again increase in every other track of said remaining tracks from said
inner to said outer circumference or from said outer to said inner
circumference.
13. A phase-change optical recording medium according to claim 8, wherein
said header information includes track numbers set so as to increase
sequentially from an innermost or an outermost circumference of said
recording medium.
14. An optical recording and readout system for recording and reading out
information onto and from a phase-change optical recording medium,
comprising:
first optical means for projecting a plurality of optical beams onto said
phase-change optical recording medium;
second optical means for picking out reflected light from said optical
recording medium;
optical sensor means for sensing said reflected light picked out by said
second optical means to output a light sense signal; and
signal generating means for producing an information signal from said light
sense signal from said optical sensor means, wherein said phase-change
optical recording medium contains a data recordable area containing land
tracks and groove tracks on both of which main information is recorded,
said land tracks and said groove tracks being alternately disposed on said
data recordable area, and a header area in which header information is
recorded in rows of prepits, said rows of prepits being arranged in every
other track with respect to said tracks included in said data recordable
area.
15. A phase-change optical recording and readout system according to claim
14, wherein said optical sensor means produces three light sense signals
corresponding to three optical beams, said three optical beams including a
central optical beam and two side optical beams on both sides of said
central optical beam, and wherein said signal generating means includes
readout means for processing said light sense signals and generating three
readout signals, and recording control means for sensing a data recording
address from at least one of said three readout signals and generating a
data recording start signal.
16. A phase-change optical recording and readout system according to claim
15, wherein said recording control means includes three address sensing
circuits for receiving said three readout signals to detect an address
therefrom, and outputting address coincidence signals, two delay circuits
for delaying said address coincidence signals from said readout signals
corresponding to said side optical beams for a specified period of time,
and means for selecting one of said output signals, which are output from
said address sensing circuit receiving said readout signal corresponding
to said central optical beam and said delay circuits, as a data recording
start signal.
17. A phase-change optical recording and readout system according to claim
15, wherein said recording control means includes switching circuit means
for switching between said three readout signals according to header
information, an address sensing circuit for sensing an address from said
readout signal selected by said switching circuit means and outputting an
address coincidence signal, two delay circuits for delaying said address
coincidence signals sensed from said readout signals corresponding to said
side optical beams for specified periods of time, and means for selecting
signals from one of said delay circuits and said address coincidence
signal sensed from said readout signal corresponding to said central
optical beam as a data recording start signal.
18. A phase-change recording and readout system according to claim 14,
wherein said optical sensor means includes a light-receiving surface
having a nonphotosensitive area and at least two photosensitive areas
divided by said nonphotosensitive area, wherein when an image
corresponding to said reflected light is projected onto said
photosensitive areas of said light-receiving surface as at least two
divided images, and when said output signals corresponding to said
photosensitive areas of said optical sensor means are determined to be A
and B, said signal generating means produces said information signal using
an expression (A-B) or (A-B)/(A+B).
19. An optical recording and readout system according to claim 14, wherein
when each of said optical beams has a diameter of an optical beam whose
intensity is 1/e.sup.2 of a maximum intensity, where e is an natural
logarithm, a track pitch between adjacent tracks is set at one-third said
diameter of said optical beam.
20. An optical recording and readout system for recording and reading out
information onto and from a phase-change optical recording medium,
comprising:
first optical means for projecting at least one optical beam onto said
phase-change optical recording medium;
second optical means for picking out reflected light from said optical
recording medium;
optical sensor means for sensing said reflected light picked out by said
second optical means; and
signal generating means for producing an information signal from an output
signal from said optical sensor means, wherein said phase-change optical
recording medium contains a data recordable area containing land tracks
and groove tracks on both of which main information is recorded, said land
tracks and said groove tracks being alternately disposed on said data
recordable area, and a header area in which header information is recorded
in rows of prepits, wherein each row of prepits is arranged in
correspondence with one of said land and said groove tracks.
21. A phase-change optical recording and readout system according to claim
20, wherein said optical sensor means produces a light sense signal
corresponding to a single optical beam, and wherein said signal generating
mean contains readout means for processing said light sense signal and
generating a single readout signal, and recording control means for
sensing a data recording address from said readout signal and generating a
data recording start signal.
22. A phase-change optical recording and readout system according to claim
21, wherein said recording control means comprises means which delays an
address coincidence signal for a specified period of time to produce a
data recording start signal when a recording position of header
information is on a track in the front in an optical beam scanning
direction, and which outputs an address coincidence signal as a data
recording gate signal when the recording position of header information is
on a track in the rear in the optical beam scanning direction.
23. A phase-change optical recording and readout system according to claim
20, wherein said optical sensor means produces light sense signals
corresponding to two optical beams, and said signal generating mean
contains readout means for processing said light sense signals and
generating two readout signals, and recording control means for sensing a
data recording address from said readout signals and generating a data
recording start signal.
24. A phase-change optical recording and readout system according to claim
23, wherein said recording control means comprises two address sensing
circuit means for receiving said two readout signals to detect an address,
and outputting address coincidence signals, and means for selecting one of
said address coincidence signals from said two address sensing circuits as
a data recording start signal.
25. A phase-change optical recording and readout system according to claim
20, wherein said optical sensor means contains a light-receiving surface
having a nonphotosensitive area and at least two photosensitive areas
divided by the nonphotosensitive area, wherein when an image corresponding
to said reflected light is projected onto said photosensitive areas of
said light-receiving surface as two divided images, and when said output
signals corresponding to said photosensitive areas of said optical sensor
means are determined to be A and B, said signal generating mean produces
said information signal using an expression (A-B) or (A-B)/(A+B).
26. An optical recording and readout system according to claim 20, wherein
when said optical beam has a diameter of an optical beam whose intensity
is 1/e.sup.2 of a maximum intensity, where e is an natural logarithm, a
track pitch between adjacent tracks is set at one-third said diameter of
said optical beam.
27. A method of recording or reading out information on or from a
phase-change optical recording medium, comprising:
a step of preparing a phase-charge optical recording medium comprising a
data recordable area containing land tracks and groove tracks on both of
which user information is recorded, said land tracks and said groove
tracks being alternately disposed on said data recordable area, and a
header area on which header information is recorded in rows of prepits,
said rows of prepits being arranged in every other track with respect to
said tracks included in said data recordable area; and
a step of scanning said land tracks, said groove tracks and said rows of
prepits using three optical beams to record information thereon or read
out information therefrom.
28. A method of recording or reading out information on or from a
phase-change optical recording medium, comprising:
a step of preparing a phase-change optical recording medium comprising a
data recordable area containing land tracks and groove tracks on both of
which user information is recorded, said land tracks and said groove
tracks being alternately disposed in said data recordable area, and a
header area in which header information is recorded in rows of prepits,
wherein each row of prepits is arranged in correspondence with one of said
land and said groove tracks; and
a step of scanning said land tracks, said groove tracks and said rows of
prepits using an optical beam to record information thereon or read out
information therefrom.
29. A phase-change optical recording and reproducing system comprising:
a recording medium comprising:
a data recordable area containing land tracks and groove tracks on both of
which user information is recorded, said land tracks and said groove
tracks being alternately disposed on said data recordable area; and
a header area on which header information is recorded in rows of prepits,
wherein said rows of prepits are arranged in every other track with
respect to said tracks included in said data recordable area;
wherein at least two optical beams are impinged on said recording medium
for recording or reproducing information so that said header information
is reproduced by one of said two optical beams.
30. A phase-change optical recording and reproducing system according to
claim 29, wherein said two optical beams are used for recording
information on said data recordable area and for reproducing recorded
information therefrom.
31. A phase-change optical recording and reproducing system according to
claim 30, wherein one of said two optical beams is used for recording
information on said data recordable area and reproducing recorded
information therefrom. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an information recording medium such as an
optical disk and an optical recording and readout system which optically
records information onto such an information recording medium and
optically reads out the recorded information.
2. Description of the Related Art
Recently, tremendous research and development efforts have been directed
toward high density recording and readout techniques in the field of
information recording and readout equipment using optical information
recording mediums. For signal recording techniques, the mark position
recording method that causes a signal to correspond to the center of a
recording mark has been largely replaced with the mark edge recording
method that causes a signal to correspond to a recording mark edge to
achieve much higher recording density. Also, efforts are now being put
into the development of much larger capacity optical disks by recording
signals between tracks.
As a first conventional example, a method of achieving high track density
using the sample servo system has been described in Moore, G. S., "High
Density Format for Sperry Information Storage Inc. Second Generation
Optical Drives," SPIE Vol. 695, pp230-238, 1986. With this method,
recording marks are formed on a recording medium so as to be 180 degrees
out-of-phase track by track. When the readout optical beam is positioned
at the center of a recording mark significant for an information readout
signal, the readout optical beam does not overlap with the recording marks
located in adjacent tracks, thereby in reducing crosstalk. In this way,
crosstalk from both adjacent tracks is decreased by changing the recording
clock timing between even-numbered tracks and odd-numbered tracks, thereby
achieving a large capacity as compared with a conventional equivalent.
A second conventional example has been described in K. Kayanuma et al.,
"High Track Density Magneto-Optical Recording using a Crosstalk Canceler,"
SPIE Vol. 1316, pp35-29, 1990. According to this example, three optical
beams are caused to follow an inner-circumference land track, a central
groove track, and an outer-circumference land track respectively, these
tracks adjoin each other. The readout signals obtained by the three
optical beams are adjusted in phase. Then, the two phase-adjusted readout
signals obtained by the optical beams on both sides are adjusted in gain.
The gain-adjusted signals are added to each other. The added signal is
subtracted from the readout signal obtained by the central optical beam,
thereby producing a readout signal by means of the central optical beam
with reduced crosstalk.
In the case of applying the first conventional example to the mark edge
recording method, when the readout optical beam is located at the edge
portion of a prepit significant for an information readout signal, simply
shifting the phase of the prepit 180 degrees permits the readout optical
beam to illuminate two prepits in adjacent tracks, causing noticeable
crosstalk. This not only reduces the reliability of the information
readout signal, but also makes it difficult to apply this example to the
mark edge recording method capable of realizing high density.
For the land & groove recording method explained in the second conventional
example, it is necessary to eliminate crosstalk from adjacent tracks on
both sides in the complicated three-beam optical head and the signal
processing circuit. When the second conventional example is applied to an
optical disk where the presence/absence of prepits or recording marks is
sensed by the change of reflectivity, such as a readonly optical disk, a
write once optical disk, or a phase-change optical disk, crosstalk caused
by prepits or recording marks located on the adjacent tracks on both sides
reduces the amplitude of the focus and track error signals seriously,
which makes the focus and track servos unstable, thus reducing the
reliability of the information readout signal.
SUMMARY OF THE INVENTION
The object of the present invention is to realize an optical recording
medium from which a stable servo signal can be obtained, to provide a
simple optical head capable of reducing crosstalk from adjacent tracks on
both sides, and to provide an optical recording and readout system which
assures high data reliability and enables high-density recording.
According to the present invention, it is possible to provide a
phase-change optical recording medium comprising a data area containing
land tracks and groove tracks on both of which user information is
recorded, the land and groove tracks being formed alternately, and a
header area in which header information is recorded in the form of prepit
rows arranged in every other track with respect to the tracks including
the land and groove tracks arranged alternately.
According to the invention, it is possible to provide a phase-change
optical recording medium comprising a data area containing land tracks and
groove tracks on both of which user information is recorded, the land and
groove tracks being formed alternately, and a header area in which header
information is recorded in the form of prepit rows each arranged in
correspondence with one of the land and groove tracks.
The track numbers in the header information recorded only in either the
groove tracks or the land tracks in the optical recording medium are set
so as to increase consecutively or increment every other track
successively from the inner to the outer circumference of the disk or the
outer to the inner circumference.
According to the invention, it is possible to provide an optical recording
and readout system comprising a first optical system for projecting a
plurality of optical beams onto a phase-change optical recording medium, a
second optical system for picking out the reflected light from the optical
recording medium, a photodiode for sensing the reflected light picked out
by the second optical system, and a signal generator circuit for producing
an information signal from the photoelectric sense signal from the
photodiode, wherein the phase-change optical recording medium contains a
data area containing land tracks and groove tracks on both of which main
information is recorded, the land and groove tracks being formed
alternately, and a header area in which header information is recorded in
the form of prepit rows arranged every other track with respect to the
tracks including the land and the groove tracks alternately.
According to the invention, it is possible to provide an optical recording
and readout system comprising a first optical system for projecting at
least a single optical beam onto a phase-change optical recording medium,
a second optical system for picking out the reflected light from the
optical recording medium, a photodiode for sensing the reflected light
picked out by the second optical system, and a signal generator for
producing an information signal from the output signal from the
photodiode, wherein the phase-change optical recording medium contains a
data area containing land tracks and groove tracks on both of which main
information is recorded, the land and groove tracks being formed
alternately, and a header area in which header information is recorded in
the form of prepit rows each arranged in correspondence with one of the
land and groove tracks.
According to the invention, it is possible to provide an optical recording
and readout system which records and reads out data onto or from each of
groove and land tracks by projecting at least two optical beams onto
adjacent tracks on an optical disk 2 to 20 times the converged beam
diameter apart, and sensing coincidence with the target address number and
sector number on the basis of the readout signal from the optical beam
positioned on a track in which header information is recorded,
By recording header information in every other track or by shifting the
recording position of the header section alternately among the tracks
including the land and groove tracks, it is possible not only to reduce
crosstalk caused by prepits in the adjacent tracks on both sides, but also
to suppress a decrease in the amplitude of the focus and track error
signals as compared with a conventional device. Accordingly, a stable
focus servo and track servo can be realized.
Furthermore, inverting the sign of the binary information signal track by
track as described above makes it possible to reduce crosstalk caused by
prepits or recording marks on the adjacent tracks on both sides. This
makes less a decrease in the amplitude of the focus and track error
signals than a conventional device. As a result, a stable focus and track
servos can be realized.
Additionally, by designing and arranging photodiodes as described in the
invention, and using only the output from the light-receiving surface
located in the direction of the track projected image as an information
readout signal, crosstalk due to the adjacent tracks on both sides can be
reduced further, thereby improving the data reliability.
Additional objects and advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate presently preferred embodiments of the
invention, and together with the general description given above and the
detailed description of the preferred embodiments given below, serve to
explain the principles of the invention.
FIG. 1 is a view of a portion of an optical recording medium according to
an embodiment of the present invention;
FIG. 2 is a block diagram of a data recording gate signal generating
circuit for producing a signal determining the recording start and end
positions of the optical recording medium of FIG. 1;
FIG. 3 is a block diagram of another data recording gate signal generating
circuit;
FIG. 4 is a view of a portion of an optical recording medium according to
another embodiment of the present invention;
FIG. 5 is a block diagram of a data recording gate signal generating
circuit for producing a signal determining the recording start and end
positions of the optical recording medium of FIG. 4;
FIG. 6 is a block diagram of another data recording gate signal generating
circuit used for recording onto the optical recording medium of FIG. 4;
FIG. 7 is a drawing to help explain a method of recording information onto
adjacent tracks;
FIG. 8 is a drawing to help explain a method of recording information onto
adjacent tracks by a land & groove recording technique;
FIG. 9 is a drawing to help explain another method of recording information
onto adjacent tracks by another land & groove recording technique;
FIG. 10 is a drawing to help explain another method of recording
information onto adjacent tracks by still another land & groove recording
technique;
FIG. 11 is a view for explaining a method of numbering tracks by a land &
groove recording technique;
FIG. 12 is a view for explaining another method of numbering tracks by a
land & groove recording technique;
FIG. 13 shows a configuration of a portion of an optical recording and
readout system according to an embodiment of the present invention;
FIG. 14 is a block diagram of a data binarization signal generating circuit
for mark position recording by the difference signal of the optical sensor
output;
FIGS. 15A-15F are timing charts explaining the operation of the data
binarization signal generating circuit of FIG. 14;
FIG. 16 is a block diagram of a data binarization signal generating circuit
for mark edge recording by the difference signal of the optical sensor
output;
FIGS. 17A-17I are timing charts explaining the operation of the data
binarization signal generating circuit of FIG. 16;
FIG. 18 is a block diagram of a data binarization signal generating circuit
for mark position recording by the sum signal of optical sensor outputs;
FIG. 19A-19F timing charts explaining the operation of the data
binarization signal generating circuit of FIG. 18;
FIG. 20 is a block diagram of a data binarization signal generating circuit
for mark position recording by the sum signal of optical sensor outputs;
FIGS. 21F-21J are timing charts explaining the operation of the data
binarization signal generating circuit of FIG. 20;
FIG. 22 shows the structure and layout of an optical sensor used in the
optical recording and readout system; and
FIG. 23 shows the structure and layout of another optical sensor used in
the optical recording and readout system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a portion of an optical recording medium, or a phase-change
optical disk, according to an embodiment of the present invention. The
phase-change optical disk is an optical disk on or from which data is
recoded or erased by using a reversible phase change between two states,
one being an amorphous state (recording state) and the other a crystal
state (erasing state), and from which data is read out by detecting a
difference between the reflection factors of the two states. The
phase-change optical disk is suitable for land & groove recording, where
header information items including track numbers and sector numbers are
recorded in a header area 101, and the user can record data in a data area
102. Continuous track guide grooves are formed only in the data area 102.
The information tracks include projected tracks, i.e., land tracks 104 and
recessed tracks, i.e., groove tracks 105.
In this embodiment, the header information is recorded in every other
track, or only on the land track 104 in the form of intermittent bumpy
prepits 103 on the header area 101. The user information is recorded on
the disk in the form of phase-change recording marks 106 represented by
hatched circles. At this time, the depth of the groove 110 is set at
nearly .lambda./6 (where .lambda. is the wavelength of a light source), so
that crosstalk between the land track 104 and the groove track 105 may be
small in the data area 102. When the optical beam diameter is defined as a
diameter of the beam where the intensity is 1/e.sup.2 of the maximum
intensity (where e is an natural logarithm), the track pitch is set at
one-third the diameter of the optical beam.
The embodiment is based on what is called a three beam method, where three
optical beams 107, 108, and 109 represented by broken lines are projected
2 to 20 times the converged beam diameter apart onto the center of each of
three adjacent tracks. Like an ordinary three beam method, the central
optical beam 108 is used as a recording beam. The intensity of optical
beams 107 and 109 on both sides serving as tracking beams is set at 1/5 to
1/10 the intensity of the central optical beam 108. When the land track
104 on which the header information is recorded is recorded onto or
readout from, the header information is readout by projecting the central
optical beam 108 onto the land track 104. On the basis of the header
information, coincidence with the target track number and sector number is
sensed, followed by a record/readout operation as in the prior art.
On the other hand, when the groove track 105 on which no header information
is recorded is recorded onto or readout from, because the central optical
beam 108 is positioned on the groove track 105, the optical beams 107 and
109 on both sides are positioned on the land tracks 104. Thus, by sensing
coincidence with the target track number and sector number using one or
both of the optical beams on both sides, the groove track 105 can be
recorded onto or read out from.
In this way, forming headers every other track prevents not only the focus
servo and the track servo from becoming unstable in the header area 101,
but also the header information from being unable to be read out due to an
increase in crosstalk, thereby assuring as high reliability as compared to
that of a conventional optical disk apparatus. While in the illustrated
embodiment, three optical beams are positioned on three adjacent tracks,
it is apparent that a similar effect can be obtained by positioning two
optical beams of the same density on two adjacent tracks. In this case, by
reading out the header information by either optical beam, data can be
simultaneously recorded on or read out from the land track and the groove
track, thus doubling the recording/readout speed.
Referring to FIG. 2, a signal generating circuit will be described which
produces a data recording gate signal (a signal indicating the data
recording start and end positions) required to record data on a
phase-change recording medium of the above-mentioned structure by a three
beam method.
The readout signals from the side optical beam 107, the central optical
beam 108, and the side optical beam 109 are supplied to address sensing
circuits 1111, 1112, and 1113, respectively. A case will be considered
where the central optical beam 108 is tracking on the land track 104 on
which the header information is recorded, and the side optical beams 107
and 109 are tracking on the groove tracks 105 on which no header
information is recorded. In this case, when data is recorded on the land
track 104, address coincidence is sensed at the address sensing circuit
1112 on the basis of the readout signal obtained by the central optical
beam 108, followed by the generation of a data recording gate start signal
1132, as with a conventional optical disk apparatus. On the basis of the
data recording start signal 1132, a data recording gate signal is produced
at the data recording gate generating circuit 1130. In response to the
data recording gate signal, a data recording operation is carried out.
Next, a case will be considered where data is recorded on the groove track
105 on which no header information is recorded. In this case, the central
optical beam 108 scans the groove track 105 without header information,
and the side optical beams 107 and 109 scan the land tracks 104 with
header information. Consequently, the address sensing circuits 1111 and
1113 to which the readout signals obtained by the side optical beams 107
and 109 sense address coincidence and output address coincidence signals
1131 and 1133. Because the side optical beam 107, the central optical beam
108, and the side optical beam 109 are spaced at specific intervals in the
direction of the track, the address coincidence signal 1131 has an earlier
address coincidence sense timing than the address confidence signal 1133.
Thus, delay circuits 1121 and 1123 generate data recording start signals
1134 and 1135 delayed for time .tau..sub.1 and .tau..sub.3 (where
.tau..sub.1 >.tau..sub.3) corresponding to the time from the address sense
timing of the address coincidence signals 1131 and 1133 to when the
central optical beam 108 reaches the data recording start position on the
groove track 105. The generated signals are supplied to the data recording
gate generating circuit 1130. In response to both or one of the data
recording start signals 1134 and 1135, the data recording gate generating
circuit 1130 operates to produce a data recording gate signal. According
to the data recording gate signal, the central optical beam 108 records
data on the groove track 105.
While in the CAV (Constant Angular velocity) recording system, the delay
times .tau..sub.1 and .tau..sub.3 of the delay circuits 1121 and 1123 are
fixed, in the ZCAV (Zone CAV) recording system, the delay times
.tau..sub.1 and .tau..sub.3 must be changed depending on the disk radius
position. To realize this, programmable delay lines can be used.
FIG. 3 shows a modification of the data recording gate signal generating
circuit. With this modification, when track numbers are given previously
to land tracks and groove tracks as explained later, it is possible to
distinguish the land tracks from the groove tracks on the basis of track
numbers or whether the track number is even or odd. Thus, the readout
signals obtained by the optical beams 107 and 108 are switched depending
on the number of the target track to be recorded onto at a readout-signal
switching circuit 1240 in response to a switching signal. Then, the
switched signal is supplied to an address sensing circuit 1210. On the
basis of the input readout signal, the address sensing circuit 1210 senses
address coincidence. When address coincidence is sensed using the readout
signal from the central optical beam 108, the address coincidence signal
1232 will be directly supplied to a data recording gate generating circuit
1230.
On the other hand, when address coincidence is sensed using the readout
signal obtained by the side optical beam 107, the address coincidence
signal 1231 is delayed for .tau..sub.1 by the delay circuit 1221 as with
the circuit of FIG. 2, and a data recording start signal 1234 is produced.
When address coincidence is sensed using the readout signal obtained by
the side optical beam 108, the address coincidence signal 1233 is delayed
for .tau..sub.3 by the delay circuit 1223, and a data recording start
signal 1235 is produced. These start signals are supplied to the data
recording gate generating circuit 1230. In this case, the switching of the
address coincidence signal is done by an address coincidence signal
switching circuit 1250, which may be operated by the above-mentioned
switching signal with the modification, use of only one address sensing
circuit makes the circuit configuration simpler than that of FIG. 2.
FIG. 4 shows a portion of an optical disk serving as an optical recording
medium according to another embodiment of the present invention. As with
the embodiment of FIG. 1, grooves are formed only in a data area 202. The
land tracks 204, groove tracks 205, and recording marks 206 function as do
those in FIG. 1. In this embodiment, in a header area 201, the header
recording positions are staggered alternately between the land tracks 204
and the groove tracks 205. Specifically, rows of prepits forming header
information are arranged in a staggered fashion so as to correspond to the
land tracks 204 and the groove tracks 205. Because the prepit rows are
spaced at one-track intervals, crosstalk will never develop in a readout
by a single optical beam 207.
Accordingly, in the header area 201, neither the servo characteristic nor
the crosstalk characteristic deteriorates. In this case, because the
header area 201 needs twice the length required in a conventional
equivalent, this may lead to a decrease in the disk recording capacity.
However, since the length of the header area 201 is generally nearly 5% to
7% of the sector length, a decrease in the recording capacity is only 5%
to 7% at most. On the contrary, because the header information is recorded
on all the tracks, it is possible to achieve as highly reliable a
recording/readout operation using a single optical beam 207 as a
conventional optical disk apparatus.
In the above embodiment, the portion having no prepit between the prepit
rows in the header area 201 has a mirror surface as shown in FIG. 4, but a
groove may be formed on that portion.
FIG. 5 shows a data recording gate signal generating circuit for producing
a data recording gate signal needed when data is recorded on the
phase-change optical recording medium of FIG. 4. In the phase-change
optical recording medium of FIG. 4, the header information recording
positions are staggered alternately track by track. Thus, by knowing the
track number or whether the track number is even or odd, it can be known
whether the header information recording position of the target track is
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