Write-once type optical recording/reproducing device

When a record mark portion arranged on the upstream side of a data area is reproduced, the peak value of a reproduction signal of the record mark portion is compared with a reference level. An overwrite preventing circuit is arranged so as to output an inhibiting signal for inhibiting data writing when the comparison output exceeds a predetermined level. With this preventing circuit, a data portion need not be checked in a read mode prior to a write mode.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an optical recording/reproducing device 
having a means for preventing overwriting of data in a recording medium. 
2. Description of the Related Art 
Recently, a great deal of attention has been paid to an optical 
recording/reproducing device which can record data in a recording medium 
at high density or can reproduce data, which is recorded in a recording 
medium at high density, at high speed, by radiating a light beam. 
In the above device, since data is recorded at high density, a light beam 
must be focused to be sufficiently small for recording and reproduction. 
For this reason, recording and reproduction are performed by performing 
focusing control of an objective lens for focusing a light beam on a 
recording medium while performing tracking control for causing the light 
beam to follow a current track. 
A recording medium utilizing phase change is available. 
When data is read from an optical disk utilizing phase change by read 
power, since the read power is low-level optical power, the optical disk 
is kept in an amorphous state and has a low reflectivity (or a reflection 
amount is small). However, if a light beam having high-level write power 
is radiated onto the optical disk, the amorphous state is phase-changed 
into crystalline state, and the reflectivity is increased. 
Binary data, therefore, can be recorded in such an optical disk by 
utilizing a difference between these reflection amount levels. 
The optical disk utilizing the above-described phase change is of a 
write-once type in which data can be written in an addition manner. 
Similar to optical disks of other types, in this write-once type optical 
disk, when data is written in a data area allowing data to be written 
therein, overwriting of data in the data area must be prevented. However, 
a means for efficiently preventing overwriting has not been developed. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an optical 
recording/reproducing device which can prevent overwriting, and in which 
checking in a read mode is not necessary prior to data writing. 
In order to achieve the above object, an optical recording/reproducing 
device having a write power mode and a read power mode, according to the 
present invention comprises: 
a circuit for detecting an optical signal in the write power mode from a 
record mark portion arranged on an upstream side of a data area in which 
data is recorded, and generating a reproduction signal corresponding to a 
recording state of the record mark portion; 
a circuit for generating a reference signal; 
a circuit for discriminating whether data is already recorded in the data 
area by comparing the reproduction signal with a reference signal, and 
generating a discriminating signal; 
a circuit for receiving the discriminating signal so as to generate an 
inhibiting signal for inhibiting overwriting of data in the data area 
using the write power mode when the discriminating signal represents that 
data is already recorded in the data area; and 
a circuit for switching the write power mode to the read power mode in 
response to the inhibiting signal. 
With the above-described arrangement, the device can prevent erroneous 
overwriting of data in a data portion in which data has been previously 
recorded. In addition, checking of a data portion in a read mode prior to 
a write mode becomes unnecessary.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in detail below with 
reference to the accompanying drawings. 
FIGS. 1 to 5 show an optical recording/reproducing device according to a 
first embodiment of the present invention. 
As shown in FIG. 1, in optical recording/reproducing device 1 of the first 
embodiment, optical pickup 3 is arranged so as to oppose phase-change 
optical disk 2 rotated by a spindle motor (not shown). Optical pickup 3 is 
can be moved by a driving means such as a VCM (voice coil motor) in the 
radial direction of a phase-change optical disk (to be simply referred to 
as an optical disk hereinafter) 2, i.e., direction R crossing concentrical 
or spiral tracks. 
Optical pickup 3 optically records/reproduces data in/from optical disk 2 
by using a light beam emitted from laser diode 4. Laser diode 4 is 
integrally sealed in housing 6 together with, e.g., monitor pin photodiode 
5. 
Laser diode 4 emits light from its rest surface to monitor photodiode 5. 
Light emitted from the front surface of laser diode 4 is used for 
recording or reproduction. Upon reception of the light from the rear 
surface of laser diode 4 photodiode 5 supplies an optical current 
corresponding to the received light to APC (auto power control) circuit 7. 
The emission output of laser diode 4 is automatically controlled to be a 
proper value by using an output from APC circuit 7. 
Photodetector 8 for receiving a light beam reflected by optical disk 2 is 
constituted by, e.g., four split light-receiving elements. Outputs from 
these light-receiving elements ar supplied to adding/subtracting circuit 
9, and are added to each other so as to be output therefrom as a radio 
frequency signal (RF signal). The RF signal is input to low pass filter 
40, and only a DC component is extracted therefrom, thereby generating a 
DC SUM signal as a reproduction signal. The DC SUM signal is supplied to 
recordingstate discriminating circuit 11, which is a main part of the 
first embodiment, together with a monitor signal from photodiode 5. An 
output signal from recordingstate discriminating circuit 11 is input to 
terminal CK of D-type flip-flop (D-FF) 41. An output from D-FF 41 is 
supplied to controller 12. When this output is set at "L", controller 12 
supplies to, e.g., APC circuit 7, a signal for suppressing a current 
supplied to laser diode 4. As a result, the output from laser diode 4 is 
inhibited from being set to a write emission level. That is, the output is 
kept at a read power. 
Optical pickup 3 is arranged, for example, in the following manner. 
A light beam, e.g., a P-polarized light beam, from laser diode 4 is 
collimated by collimator lens 14 and is supplied to polarization beam 
splitter 15. The light beam which is transmitted through polarization beam 
splitter 15 at substantially 100% transmittance is converted into 
circular-polarized light by 1/4 wave plate 16. Thereafter, the light is 
focused by objective lens 17 and is radiated onto optical disk 2. The 
light beam reflected by optical disk 2 is converted into S-polarized light 
through objective lens 17 and 1/4 wave plate 16, is reflected by beam 
splitter 15 at substantially 100% transmittance, and is incident on 
critical angle prism 18. The light beam reflected by an inclined surface 
of critical angle prism 18 is received by photodetector 8 located at a 
position of a far field. An output signal from photodetector 8 is supplied 
to adding/subtracting circuit 9. As a result, a DC SUM signal as a 
reproduction signal is generated by adders 21, 22, and 23, and LPF 40. In 
addition, tracking error signal TER is generated by adder 21 and 
subtracter 24. Signal TER is supplied to tracking coil 26 constituting a 
lens actuator through tracking servo circuit 25. Adding/subtracting 
circuit 9, tracking servo circuit 25, and tracking coil 26 constitute a 
tracking servo system. By changing a combination of light-receiving 
elements subjected to subtraction, a focus error signal is generated by 
utilizing a critical angle method (not shown). 
Recording-state discriminating circuit 11 for detecting whether data is 
already written in a data area comprises amplifying section 27 for 
amplifying the DC SUM signal, and comparator 28 for comparing the DC SUM 
signal amplified by amplifying section 27 with a monitor signal. 
The input terminal of amplifying section 27 receiving the DC SUM signal is 
connected to the non-inverting input terminal of differential amplifier 29 
through resistor R1. The inverting input terminal of differential 
amplifier 29 is grounded through resistor R2 and is connected to the 
output terminal of differential amplifier 29 through resistor R3. Note 
that resistors R1 and R2 are set to substantially the same value. With 
this arrangement, amplifying section 27 amplifies the DC SUM signal, and 
the amplified signal is compared with the monitor signal by comparator 28, 
thereby outputting a comparison result. 
When a track having a format shown in FIG. 2 is scanned by a light beam, a 
check signal is output upon comparison between the DC SUM signal for 
record mark portion 31 and the monitor signal. Recording-state 
discriminating circuit 11 detects whether data is recorded or not recorded 
in a data portion (data area) located on the downstream side of record 
mark portion 31 by using this check signal. 
According to the format shown in FIG. 2, each track is divided into a 
plurality of sectors. Each sector consists of a sector mark (indicated by 
SM), an ID portion in which an index for identifying a sector is recorded, 
record mark portion 31, a VFO portion, and a data portion. They are formed 
in each sector in the order named. Record mark portion 31 may be located 
on the upstream side of the data portion in the same sector. Note that the 
VFO portion is an area for allowing a data synchronizer (for synchronizing 
data asynchronously transferred from the disk with a clock on the 
controller) to perform a synchronizing operation. Data is written in the 
VFO portion by a 2-7 code using a pattern of 100100 . . . 
The data synchronizer is designed to perform synchronization using a 
pattern written in the VFO portion. 
Since the data portion is formed after the VFO portion, data in the data 
portion is properly synchronized by a sync signal of the VFO portion so as 
to be read. 
When data is to be recorded in non-recorded data portion, record mark 
portion 31 is irradiated with a light beam using the write power. Then, 
the data is written in the data portion. Record mark portion 31 is 
phase-changed from an amorphous state to a crystalline state upon 
radiation of the light beam using the write power so that its reflectivity 
is increased. 
Since the radiation period of the light beam using the write power is 
short, the amorphous state is not completely changed into the crystalline 
state. Therefore, the reflectivity can be further increased by radiating a 
light beam using the write power again. That is, if a light beam is 
radiated using the write power again after radiation of a light beam using 
the write power is performed, a reflection amount, i.e., the peak value of 
the DC SUM signal at this portion can be further increased. 
The first embodiment utilizes this phenomenon. That is, a relationship 
between a monitor signal and the DC SUM signal when record mark portion 31 
is irradiated with a light beam using the write power is established in 
recording-state discriminating circuit 11 as shown in FIG. 3. 
More specifically, if the peak value of the DC SUM signal when record mark 
portion 31 is irradiated with a light beam using the write power once is 
given as DC SUM (1), DC SUM (1) is set to be smaller than signal level MON 
of the monitor signal. That is, DC SUM (1)&lt;MON. If the peak value of the 
DC SUM signal when record mark portion 31 is irradiated with a light beam 
using the write power twice is given as DC SUM (2), signal level MON of 
the monitor is set to be smaller than DC SUM (2). Therefore, a 
relationship of DC SUM (1)&lt;MON&lt;DC SUM (2) can be established. 
Consequently, when a command for writing data in a data portion is output 
after data is written in the data portion once, record mark portion 31 is 
irradiated with a light beam using the write power twice. As a result, a 
check signal from recording-state discriminating circuit 11 is set at "L", 
and circuit 11 outputs a detection signal representing overwriting. In 
response to this signal, controller 12 immediately outputs a command for 
inhibiting data writing using the write power to APC circuit 7, thereby 
preventing overwriting of data in the data portion. 
An operation of the first embodiment will be described below with reference 
to FIGS. 4 and 5. 
When each track of optical disk 2 has the format shown in FIG. 2, the DC 
SUM and monitor signals are changed in a first write mode, as shown in 
FIG. 4. 
Since the output signal from recording-state discriminating circuit 11 is 
set at "H" and is a discriminating signal not representing overwriting, 
data is written in a data portion. 
If a command for recording data in the data portion in which the data is 
written once is erroneously output, record mark 31 is irradiated with a 
light beam using the write power. In this case, the peak value of the DC 
SUM signal exceeds peak value level MON of the monitor signal as shown in 
FIG. 5. Recording-state discriminating circuit 11 detects this, and its 
output level is set at "L". The output from circuit 11 is supplied to 
terminal CK of D-FF 41. 
As shown in FIG. 5, D-FF 41 normally outputs a signal of "H" level to the Q 
terminal. In this case, a laser emission output is switched from a write 
level to a read level in accordance with a normal control operation of 
controller 12, and is switched to the write level at the data portion so 
as to perform data write. Such a control operation is generally performed 
as disclosed in, e.g., U.S. Pat. Nos. 4,426,693 and 4,674,071. 
When the DC SUM signal exceeds peak value MON at record mark portion 31, 
and recording-state discriminating circuit 11 detects the necessity of 
inhibiting data write in the data portion, the output of comparator 28 is 
lowered to "L" level to change the Q terminal of D-FF 41 to "L" level. 
When the signal of "L" level from the Q terminal of D-FF 41 is supplied to 
controller 12, controller 12 performs a control operation for inhibiting 
output of an emission command at the write level to the laser. That is, an 
AND gate for the output from the Q terminal and the emission command is 
arranged in controller 12. An output from the AND gate becomes an 
inhibiting signal for inhibiting overwriting of data in a data area. For 
example, in U.S. Pat. No. 4,674,071, a signal representing a data area and 
an output from the Q terminal may be ANDed. In U.S. Pat. No. 4,426,693, a 
write enable signal and an output from the Q terminal may be ANDed. 
As shown in FIGS. 1 and 5, D-FF 41 is reset by a sector mark (SM signal) 
representing the start of each sector and separated by an RF signal. 
As described above, when signal "L" is supplied to controller 12, 
controller 12 immediately outputs a command for inhibiting data writing in 
a data portion to APC circuit 7. As a result, a current flowing through 
laser diode 4 is held at the read power. This prevents overwriting of data 
in a data portion located on the downstream side of record mark portion 31 
in the same sector. 
According to the first embodiment by simply determining whether an amount 
of light reflected by record mark portion 31 located on the upstream side 
of each data portion exceeds a reference level, it can be discriminated 
whether data is recorded or not in the record portion on the downstream 
side. Therefore, even if a write command is erroneously output, 
overwriting of data in a data portion in which data is previously recorded 
can be prevented. 
According to the first embodiment, since over-writing can be prevented when 
a write command is output, a data portion need not be scanned in a read 
mode prior to a write operation to check whether data is recorded in the 
data portion or not by using a signal level upon scanning. Therefore, the 
write operation can be completed within a short period of time. 
Since the DC SUM signal corresponding to an amount of light reflected by 
record mark portion 31 is compared with the monitor signal in the first 
embodiment, a reference level can be changed in accordance with a change 
in write power. With this operation, if, for example, the write power is 
changed in accordance with a difference in linear velocity between the 
inner and outer peripheral tracks, the reference level can be changed in 
accordance with a change in write power. Therefore, even if a linear 
velocity varies, a decision whether data is recorded or not can be made. 
FIG. 6 shows recording-state discriminating circuit 41 according to a 
second embodiment of the present invention. 
In the second embodiment, a reference level is set to be constant voltage 
VST, and an amplification factor of the DC SUM signal is variably 
controlled by controller 12. That is, a plurality of resistors ri and 
switches Si (i=1, 2, 3) are used in place of resistor R2. Switches Si are 
ON/OFF-controlled by a control signal from controller 12 so that the 
amplification factor (ri+R3)/ri of amplifier 29 is variably controlled. 
For example, controller 12 reads an address from an ID portion of a sector 
of a predetermined track, and recognizes it as a current address. 
Subsequently, controller 12 selects a switch and obtains an optimal 
amplification factor in accordance with the address and on the basis of a 
2-bit conversion table in FIG. 7. 
According to the second embodiment, controller 12 selects/sets an 
amplification factor in accordance with a sector of a track for which a 
write command is performed. In addition, when a track No. is to be 
changed, the influences on laser diode 4 can be taken into consideration. 
Therefore, the same function as in the first embodiment can be obtained. 
Furthermore, the second embodiment can cope with a case wherein optimal 
conditions for determining whether data is recorded or not in the inner 
and outer peripheral tracks are deviated from those in the first 
embodiment. Moreover, even if optical disk 2 varies in quality, this 
variation can be compensated for by changing an amplification factor. 
Note that the reference voltage side may be changed in FIG. 6. In the first 
embodiment, the amplification factor of amplifying section 27 may be 
changed. In addition, in FIG. 6, the amplification factor may be fixed to 
simplify the arrangement. 
A decision whether data is recorded or not can be made in synchronism with 
only the period of the DC SUM signal when it is reflected by record mark 
portion 31. However, when output signal "L" is output in the sector period 
in addition to the above period, recording may be inhibited within the 
corresponding sector. 
When signal "L" is detected, an alarm means may alarm that an overwrite 
command is output. 
The present invention is not limited to optical pickup 3 having the 
arrangement shown in FIG. 1. In addition, the present invention not 
limited to a device utilizing light emitted from the rear surface for the 
monitor signal. A portion of light emitted from the front surface may be 
utilized. 
In the above described embodiments, the reflectivity is increased by phase 
change. However, the present invention can be easily applied to a case 
wherein the reflectivity (or reflection amount) is decreased by phase 
change.