Erasable optical disk and optical information recording/reproduction apparatus

This invention provides an erasable optical disk, on which information is recorded and reproduced repeatedly through the irradiation of laser beams, and an optical information recording/reproduction apparatus which records and reproduces information on the erasable optical disk. In erasing and then recording information on the erasable optical disk by using an erasing laser beam and a recording/reproduction laser beam, respectively, the tracking of both laser beams on the same track is detected so as to prevent erroneous erasing. The apparatus uses the optical disk having a mark signal disposed between a sector identifier and a data field, which mark signal is capable of determining the presence of the erasing laser beam on an adjacent track on the erasable optical disk, and the apparatus reproduces and detects the mark signal by using the erasing laser beam. The apparatus discriminates the position of the erasing laser beam depending on whether the mark signal has been detected or not, thereby preventing erroneous erasing of data on the adjacent track and simultaneously assuring the presence of the erasing laser beam on the same track along with the recording/reproduction laser beam.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an optical disk and optical information 
recording/reproduction apparatus, and particularly to an erasable optical 
disk on which information is recorded, reproduced and erased repeatedly 
through irradiation of a laser beam, and to an optical information 
recording/reproduction apparatus which records and reproduces information 
on the erasable optical disk. 
2. Description of the Related Art 
FIG. 8 shows, as an example, the phase transition between the 
noncrystalline state (A) and the crystalline state (C) of a phase varying 
recording medium on a conventional optical disk. The recording medium 
records a signal by a variation between the noncrystalline state (A) of a 
small reflectivity and the crystalline state (C) of a large reflectivity. 
A signal is recorded in such a way that a portion of the recording medium 
in the crystalline state (C) having a large reflectivity is heated locally 
to a temperature near the fusing point and then cooled quickly to bring it 
into the noncrystalline state (A) having a small reflectivity. The 
recorded signal is erased by heating the recording medium to a temperature 
near the fusing point and then cooling it slowly so that the portion 
irradiated by the laser beam is brought into the crystalline state (C) 
having a large reflectivity. 
FIGS. 9A and 9B are diagrams illustrating the principle of signal recording 
and erasing by using a recording/reproduction laser beam and an erasing 
laser beam. FIG. 9A shows the spot shape of laser beams for realizing the 
heating and rapid cooling condition and the heating and slow cooling 
condition for the recording medium. FIG. 9B shows the respective laser 
intensity distributions. In these figures, indicated by 23 is a spot of a 
recording/reproduction laser beam of a short longitudinal length of the 
order of 1 .mu.m, 23a is its laser intensity distribution, 24 is a spot of 
an erasing laser beam of a long longitudinal length in the range from 
several .mu.m to ten-odd .mu.m, and 24a is its laser intensity 
distribution. Indicated by 25 is a guide track on which the recording 
medium is deposited by evaporation. Depending on the differences in the 
laser spot longitudinal length and intensity distribution, the two 
distinct heating and cooling conditions are determined, i.e., the short 
longitudinal length beam spot determines the heating and rapid cooling 
condition, and the long longitudinal length beam spot determines the 
heating and slow cooling condition. 
In operation, the erasing laser beam 24, which precedes the 
recording/reproduction laser beam 23 irradiates the information section on 
the guide track 25 with a constant intensity so that an old signal 
recorded in the information section is erased and then the following 
recording/reproduction laser beam 23 records a new signal in the 
information section. 
With the above-mentioned structure, however, it is necessary that the 
recording/reproduction laser beam 23 and the erasing laser beam 24 are 
positioned on the same guide track 25. In a two-beam optical information 
recording/reproducing apparatus generally in use, two separate 
semiconductor laser sources are used to produce two respective laser beams 
23 and 24 which are arranged as shown in FIG. 9A. Hence, it is difficult 
to maintain both laser beam spots 23 and 24 positioned on the same guide 
track only by the precision of mechanical structure. Accordingly, it 
becomes necessary to apply tracking servo control to the erasing laser 
beam 24 in the same way as the recording/reproduction laser beam 23. 
However, even when the tracking servo control is applied to the erasing 
laser beam 24, the tracking actuator provides a movable range of 2-3 .mu.m 
in the disk radial direction. Therefore, even when the tracking servo 
system is in operation, it is not guaranteed that the erasing laser beam 
24 tracks the same guide track 25 in the same way as the 
recording/reproduction laser beam 23. On this account, there has been a 
problem that the erasing laser beam erroneously erases the record on an 
adjacent track. Besides, the same problem has been the case where the 
laser beam brings about track jump due to the vibration or shock. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an optical disk 
and optical information recording/reproduction apparatus capable of 
detecting and assuring that the recording/reproduction light beam and the 
erasing light beam are positioned on the same guide track and causing the 
erasing and recording operation to be stopped immediately when it is 
determined that both beams are not on the same track. 
This invention relates to an optical disk having a sector identifier which 
records sector address information, a data field in which information is 
recorded and a mark signal disposed between the sector identifier and the 
data field for identifying that the erasing light beam is positioned on an 
adjacent track, and also relates to an optical information 
recording/reproduction apparatus comprising means for sequentially 
projecting an erasing light beam and a recording/reproduction light beam, 
recording and reproducing means for recording and reproducing information 
by using the recording/reproduction light beam, erasing means for erasing 
recorded information by using the erasing light beam, and mark signal 
detecting means for reproducing and detecting a mark signal by using the 
erasing beam. 
With the optical disk of this invention, it is possible to detect the mark 
signal by using the erasing light beam and to determine that the erasing 
light beam is positioned on the same track along with the 
recording/reproduction light beam, and with the optical information 
recording/reproduction apparatus of this invention, it is possible to 
determine the position of the erasing light beam according to the 
detection or nondetection of the mark signal by the mark signal detecting 
means, whereby it is made possible to prevent erroneous erasure of data on 
an adjacent track and to guarantee that the erasing light beam and the 
recording/reproduction light beam are positioned on the same track.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1A shows the sector format for odd-numbered track addresses, and FIG. 
1B shows the sector format for even-numbered track addresses. In the 
figures, indicated by ID is a sector identifier which is a record of 
sector address information, DF denotes a data field in which data is 
recorded, M1 and M2 are mark signals indicative of an even or odd track 
address as detected by an erasing beam, G11 and G12 are gaps having 
respective different lengths T1 and T2 for identifying the mark signals M1 
and M2, and G21, G22 and G3 are gaps for absorbing a transient response 
time of the laser beam output and a variation of the disk rotational 
speed. 
FIGS. 2A, 2B and 2C show the concrete structure of the mark signals M1 and 
M2 shown in FIG. 1. FIG. 2A is a diagram showing the intensity of the 
laser beam reflected from the track, FIG. 2B is a plan view of pits and 
grooves which give rise to changes in the reflected laser intensity as 
shown in FIG. 2A, and FIG. 2C is a perspective view of the track. The 
sector identifier ID is formed in the shape of pits having a constant 
depth, whereby address information is modulated and recorded. The mark 
signals M1 and M2 are flat land portoins intervening between the grooves 
as shown in FIG. 2C, each having a length in the range from several .mu.m 
to ten-odd .mu.m detectable by the erasing beam. The mark signals are 
detected through a phase variation of the laser beam caused by the groove 
depth. The mark signals M1 and M2 have their land portions arranged in 
accordance with the track number, even or odd, as shown in FIG. 2C, and 
they are discriminated and detected by a difference in the amount of the 
laser beam reflected from the groove and flat portions. The data signal is 
recorded in the data field DF by the variable density type recording in 
which a laser beam is controlled to irradiate grooves, where a recording 
film is deposited by evaporation, so that a crystalline state thereof is 
changed to an amorphous state thereby to cause the reflectivity to be 
changed. 
In order to effect the optical recording using the above-mentioned sector 
format, the optical head is designed to have mechanical precision so that 
the erasing light beam does not cause a track offset in excess of .+-.1 
track. This allowance of .+-.1 track offset is considered to be a 
reasonable condition from a practical point of view. 
In the case where the recording/reproduction light beam 23 is tracking an 
odd-numbered track shown in FIG. 1A, if the erasing light beam 24 is 
positioned on an even-numbered track shown in FIG. 1B, a reproduction 
signal produced by the erasing light beam 24 causes the mark signal M2 to 
be detected, while, if the erasing light beam 24 is positioned on an 
odd-numbered track, the mark signal M1 is detected. On the other hand, in 
the case where the recording/reproduction light beam 23 is tracking an 
even-numbered track, if the erasing light beam 24 is tracking the same 
even-numbered track, the erasing light beam 24 causes the mark signal M2 
to be detected, while, if the erasing light beam 24 is positioned on an 
odd-numbered track, it causes the mark signal M1 to be detected. 
Accordingly, by detecting the mark signal M1 or M2 with the erasing light 
beam 24, on-tracking or off-tracking of the erasing light beam 24 can be 
determined. 
In the example of FIGS. 2A, 2B and 2C, the data field is recorded in a 
groove. Alternatively, if the data field is recorded on a land, the mark 
signals M1 and M2 are formed as grooves. 
FIG. 3 is a block diagram showing a first embodiment of the optical 
information recording/reproduction apparatus using the optical disk of 
this invention. In the figure, indicated by 1 is an address reproduction 
circuit which reads out a track address and a sector address from the ID, 
2 is an M1 gate signal generation circuit for producing a gate signal 104 
for gating the mark signal M1, 3 is an M2 gate generation circuit for 
producing a gate signal 105 for gating the mark signal M2, 4 is an 
inverter, 5 and 6 are 3-input AND gates, 7 is a 2-input OR gate, 8 is a 
sector control circuit which generates a gate signal for erasing or 
recording data in an addressed sector, 9 is a comparator for converting an 
analog signal into a binary signal, 10 is a differentiation circuit for 
detecting a rising edge of a signal, 11 is a set-reset flip-flop, 12 is a 
2-input AND gate, 13 is an erasing laser drive circuit, 14 is a data 
modulation circuit which produces write data 114 obtained by adding a 
clock resynchronizing pattern, a data section start mark, etc. to a 
digitally modulated signal obtained by digitally modulating data to which 
an error correction code has been added, 15 is a recording/reproduction 
laser drive circuit, 16 is an erasing laser source, 17 is a 
recording/reproduction laser source, 100 is a signal reproduced from the 
optical disk by a recording/reproduction light beam 23 emitted from the 
recording/reproduction laser source 17, 101 is a signal reproduced from 
the optical disk by an erasing light beam 24 emitted from the erasing 
laser source 16, 102 is a binary representation of a signal reproduced by 
the erasing light beam 24, 103 is an address detection signal indicating 
that an address has been read out, 104 is an M1 gate signal for gating the 
mark signal M1, 105 is an M2 gate signal for gating the mark signal M2, 
106 is an address odd/even signal indicating whether an associated track 
address is even or odd, 107 is a tracking deviation detection signal 
indicating the tracking deviation or aberrance of an erasing beam, 108 is 
an address data signal, 109 are command signals for erasing recording, 
reading and the like, 110 is an erasing gate signal for activating the 
erasing laser source 16, 111 is a modulation start signal, 112 is an 
enabling signal for activating the erasing laser drive circuit 13, 113 is 
a write gate signal indicating the validity of the write data 114 recorded 
in the data field, and 114 is the write data. 
FIG. 4 shows signal waveforms appearing at various portions of the optical 
information recording/reproduction apparatus shown in FIG. 3. Shown in 
FIG. 4(a) is the positional relationship between the respective light 
spots of the recording/reproduction light beam 23 and the erasing light 
beam 24. In FIG. 4, waveforms shown by solid lines denote a case where the 
recording/reproduction light beam 23 is positioned on a track of an 
odd-numbered address as shown in FIG. 4(b) and the erasing light beam 24 
is positioned on a track of an even-numbered address as shown in FIG. 
4(c). While, waveforms shown by broken lines denote a case where the 
recording/reproduction light beam 23 is positioned on a track of an 
even-numbered address as shown in FIG. 4(c) and the erasing light beam 24 
is positioned on a track of an odd-numbered address as shown in FIG. 4(b). 
The recording/reproduction light beam 23 and the erasing light beam 24 are 
apart from each other by time t as shown in FIG. 4(a). Therefore, the 
reproduced signal 101 by the erasing light beam 24 shown in FIG. 4(e) 
precedes the reproduced signal 100 by the recording/reproduction light 
beam 23 shown in FIG. 4(d) by time t. 
The following describes the operation of the optical information 
recording/reproduction apparatus according to the first embodiment of this 
invention having the construction as described above. The operation is 
based on the assumption that the recording/reproduction light beam 23 is 
positioned on a track of an odd-numbered address as shown in FIG. 4(b) and 
the erasing light beam 24 now under tracking deviation or aberrance is 
positioned on a track of an even-numbered address. 
The address reproduction circuit 1 reads an address in the ID in the 
reproduced signal 100 by the recording/reproduction light beam 23 and 
produces the address detection signal 103, address data 108 and address 
odd/even signal 106. The address data 108 and address detection signal 103 
are applied to the sector control circuit 8. The sector control circuit 8 
supplies the erasing gate signal 110 to the erasing laser drive circuit 13 
and the modulation start signal 111 to the data modulation circuit 14 in 
accordance with the erasing/recording command indicated by the command 
signals 109. 
The data modulation circuit 14 supplies the write data 114 and the write 
gate signal 113 to the recording/reproduction laser drive circuit 15 and 
the AND gate 12, respectively. 
The differentiation circuit 10 detects a rising edge of the erasing gate 
signal 110 to set the flip-flop 11, which validates the erasing laser 
drive circuit enabling signal 112. Consequently, the erasing laser drive 
circuit 13 operates to turn on the erasing laser source 16 and causes it 
to start an erasing operation as shown in FIG. 4(m). As a result, the 
signal 101 shown in FIG. 4(e) is produced by an erasing light beam emitted 
from the erasing laser source 16. 
The address detection signal 103 is supplied to the M1 gate signal 
generation circuit 2 and M2 gate signal generation circuit 3, which 
circuits 2 and 3 produce an M1 gate signal 104 and an M2 gate signal 105 
shown in FIG. 4(h) and FIG. 4(i), respectively. The M1 gate signal 104 and 
the M2 gate signal 105 operate to detect that the erasing light beam 24 is 
positioned on an even-numbered track or an odd-numbered track by 
separating in time the mark signals M1 and M2 in the reproduced signal 101 
by the erasing light beam 24. 
The signal 101 shown in FIG. 4(e) reproduced from the optical disk by the 
erasing light beam 24 having a beam spot in the shape of an elongated 
ellipse has an inferior resolution as compared with that of the signal 
shown in FIG. 4(d) reproduced by the recording/reproduction light beam 23, 
so that it cannot reproduce the ID. However, it can satisfactorily 
reproduce the mark signals M1 and M2 formed as a land or a groove of 
several .mu.m such as shown in FIGS. 2A to 2C. The reproduced signal 101 
by the erasing light beam 24 is converted through the comparator 9 into a 
binary signal 102 at a predetermined threshold value, and the resulting 
binary reproduced signal 102 is supplied to the AND gates 5 and 6. 
The address odd/even signal 106 is applied straightly to the AND gate 6, 
while, it is inverted through the inverter 4 and applied to the AND gate 
5. The AND gates 5 and 6 and a NOR gate 7 in combination operate to select 
the mark signal M1 or M2 in the binary reproduced signal 102. The address 
odd/even signal 106 presently indicates an odd track, and therefore the 
AND gate 6 is selected, and the tracking deviation detection signal 107 
corresponding to the mark signal M2 is produced as shown in FIG. 4(j). The 
tracking deviation detection signal 107 resets the flip-flop 11 thereby to 
invalidate the erasing laser drive circuit enabling signal 112. 
Consequently, the erasing laser source 16 is turned off as shown in FIG. 
4(m). The data recording operation is also interrupted by blocking a write 
gate signal 113 through the AND gate 12. 
The signal waveforms appearing when the recording/reproduction light beam 
23 is positioned on an even-numbered track is shown by the broken lines in 
FIG. 4, and they are identical with those in the above-mentioned case 
except that the AND gate 5 is selected by the address odd/even signal 106 
thereby to detect the mark signal M1. 
According to this embodiment, as described above, the mark signal M1 or M2 
immediately behind the ID is identified depending on the odd or even 
number of the address of the track at the timing of generation of the M1 
or M2 gate signal caused by the address detection signal 103, which is 
outputted from the address reproduction circuit 1, whereby erroneous 
erasing and recording can be prevented even when .+-.1 track deviation of 
the erasing light beam from the recording/reproduction light beam occurs. 
FIG. 5 is a block diagram showing a second embodiment of the optical 
information recording/reproduction apparatus using the optical disk of the 
present invention. In the figure, circuit blocks and signals identical 
with those shown in FIG. 3 are denoted by the same reference numerals and 
symbols. In FIG. 5, indicated by 18 is an inverter, 19 is an OR gate, and 
115 is an erasing light beam in-track detection signal indicating that the 
erasing light beam 24 is positioned on the same track with the 
recording/reproduction light beam 23. 
The following describes the operation of the optical information 
recording/reproduction apparatus according to the second embodiment of 
this invention having the construction as described above. The explanation 
is based on the assumption that the erasing light beam 24 is positioned on 
the same odd address track with the recording/reproduction light beam 23. 
The address reproduction circuit 1 reads an address in the ID in the 
reproduced signal 100 by the recording/reproduction light beam 23 and 
produces an address detection signal 103 and an address odd/even signal 
106. The address detection signal 103 is applied to the M1 gate generation 
circuit 2 and the M2 gate generation circuit 3, which circuits 2 and 3 
produce an M1 gate signal 104 and an M2 gate signal 105, respectively. 
The reproduced signal 101 by the erasing light beam 24 reproduces a mark 
signal M1. The reproduced signal 101 is converted through the comparator 9 
into a binary signal 102 at a predetermined threshold value, and it is 
supplied to the AND gates 5 and 6 as a binary reproduced signal 102 by the 
erasing light beam 24. The address odd/even signal 106 becomes a high 
level, which causes the AND gate 5 and the OR gate 19 to produce the mark 
signal M1 of the binary reproduced signal 102 by the erasing light beam 24 
as an erasing light beam in-track detection signal 115. On the other hand, 
when the erasing light beam 24 is positioned on the same even address 
track with the recording/reproduction light beam 23, the address odd/even 
signal 106 is a low level, and then it is inverted through the inverter 
18, which inverted signal causes the AND gate 6 and the OR gate 19 to 
produce the mark signal M2 of the binary reproduced signal 102 by the 
erasing light beam 24 as an erasing light beam in-track detection signal 
115. 
Next, an explanation will be given of the operation of the apparatus of the 
present invention in which the erasing light beam 24 is positioned on a 
track deviated by .+-.1 track from a track on which the 
recording/reproduction light beam 23 is positioned. The reproduced signal 
101 by the light erasing beam 24 produces a mark signal M2 when the 
recording/reproduction light beam 23 is positioned on an odd address 
track, while, it produces a mark signal M1 when the recording/reproduction 
light beam 23 is positioned on an even address track. Therefore, the AND 
gates 5 and 6 operate to block the binary reproduced signal 102 by the 
erasing light beam 24 in any case, and, as a result, an erasing light beam 
intrack detection signal 115 is not detected. Thus, by monitoring the 
erasing light beam in-track detection signal 115 with a CPU or the like, 
it is possible to detect the coexistence of the erasing light beam 24 and 
the recording/reproduction light beam 23 on the same track. 
As described above, according to this embodiment, it is possible to confirm 
that the erasing light beam 24 and the recording/reproduction light beam 
23 are positioned on the same track, by identifying the mark signal M1 or 
M2 immediately behind the ID depending on the odd or even number of the 
address of the track at the timing of generation of the M1 or M2 gate 
signal caused by the address detection signal 103, which is outputted from 
the address reproduction circuit 1. 
FIG. 6 is a block diagram showing a third embodiment of the optical 
information recording/reproduction apparatus of the present invention. In 
the figure, reference numerals 1, 16, 100, 101, 103, 106 and 110 denote 
the same constitutional elements and signals shown in FIG. 3. Indicated by 
20 is a mark signal detection circuit, 21 is a D-input type flip-flop, 22 
is an erasing laser drive circuit, 16 is an erasing laser source, 116 is a 
mark signal detection signal, and 117 is an output signal from the D-FF 
21. 
FIG. 7 shows signal waveforms appearing at various portions of the optical 
information recording/reproduction apparatus shown in FIG. 6 for 
explaining the operation thereof. FIGS. 7(a) and FIG. 7(b) show reproduced 
signals 100 reproduced from an odd address track and an even address track 
by the recording/reproduction light beam 23, respectively. FIG. 7(c) shows 
a reproduced signal 101 reproduced by the erasing light beam 24. FIG. 7(d) 
shows an erasing gate signal 110, FIG. 7(e) a mark signal detection signal 
116, FIG. 7(f) an output signal 117 from the D-FF 21, and FIG. 7(g) an 
erasing light beam output signal 24 from the erasing laser source 16. 
The following explains the operation of the optical information 
recording/reproduction apparatus of the third embodiment of the present 
invention having the construction as described above. 
As an example, the following explanation assumes a case where the 
recording/reproduction light beam 23 is positioned on an odd address track 
as shown in FIG. 7(a). 
The erasing laser source 16 is operating continuously at a reproduction 
power level. When the erasing light beam 24 is positioned on an odd 
address track on the optical disk, the reproduced signal 101 reproduced 
from the odd address track by the erasing light beam 24 is applied to the 
mark signal detection circuit 20, which then outputs a mark signal M1 as 
the mark signal detection signal 116. 
The mark signal detection signal 116 operates to latch the erasing gate 
signal 110 in the D-FF 21 to actuate the erasing laser drive circuit 22, 
which then supplies an erasing power output current to the erasing laser 
source 16 to cause it to produce a laser beam of the erasing power level 
so that the data field DF is erased over the period shown in FIG. 7(g). 
If the erasing light beam 24 is positioned on an even address track as 
shown by the broken line waveform in FIG. 7(c), the reproduced signal 101 
reproduced by the erasing light beam 24 reproduces the mark signal M2, and 
therefore the mark signal detection circuit 20 does not produce the mark 
signal detection signal 116. Accordingly, the erasing laser drive circuit 
22 is not actuated to produce an erasing power level output signal, even 
if the erasing gate signal 110 is applied to the D-FF 21. Thus, erroneous 
erasing of the even address track can be prevented. 
According to this third embodiment, the mark signal M1 or M2 immediately 
behind the ID is respectively identified depending on an odd or even 
address of the track, at the timing of generation of the M1 or M2 gate 
signal caused by the address detection signal 103 which is outputted from 
the address reproduction circuit 1, whereby it becomes possible to prevent 
erroneous erasing or recording which occurs when the tracking of the 
erasing light beam 24 deviates by .+-.1 track from that of the 
recording/reproduction light beam 23. It is of course possible to use the 
mark signals M1 and M2 of this embodiment as a mirror section so that it 
is used commonly with the TOF (tracking offset detection flag) for 
correcting an inclination of the optical disk. 
As described above, the present invention has a great practical advantage 
of being capable of detecting the tracking deviation of the erasing light 
beam and preventing erroneous erasing caused by the tracking deviation.