Optical information recording method

A recording apparatus overwrites an input signal having pulse duration periods and pulse spacing periods to an optical disk by irradiation of a laser beam to form recording marks corresponding to the pulse duration periods. The apparatus includes a detector for detecting a leading edge of the pulse duration period and for producing a start signal thereupon, another detector for detecting a trailing edge of the pulse duration period and for producing a stop signal thereupon, a pattern setting circuit for setting a predetermined basic pattern, and a pattern generator for generating the basic pattern from its beginning in response to the start signal and for terminating the generation of the basic pattern in response to the stop signal. The apparatus further includes a circuit for forming a modulated signal using a full or portion of the basic pattern produced from the pattern generator. The laser output is produced in according with the modulated signals.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a recording method for recording a signal 
on an optical information recording medium, primarily an optical disk to 
and from which optical information can be recorded and read at high speed 
and high density using a leaser beam or other optical source. 
2. Description of the Prior Art 
Technologies which apply laser beams to read and/or write high density 
information are commonly known, and are primarily used with optical disks. 
Optical disks can be classified into three broad categories: read-only, 
write-once read-many, and rewritable. Read-only disks include compact 
disks (CD), mainly used for recording musical information, and video disks 
(LVD), mainly used for recording image information. With these media, the 
signal is pre-recorded to the optical disk, and the user can playback the 
music or video information but is unable to record any additional signals. 
Recent research has therefore concentrated on the development of a 
rewritable type of media and drive which enables free and repeated writing 
and erasure of the signal. 
Rewritable types use a recording thin film in which a reversible change 
between two states is induced by changing the emission conditions of the 
laser beam or other light source; the principal types of thin films used 
are magneto-optical and phase change media. Magneto-optical types use a 
ferromagnetic thin film as the recording thin film, and a signal is 
recorded by changing the orientation of the magnetic domain. Phase change 
types principally use a tellurium or selenium alloy as the recording thin 
film, and record a signal by changing the state of the thin film between 
amorphous and crystalline or between two types of crystal structures. 
One of the merits of magneto-optical phase change media is that so-called 
single beam overwriting, wherein a single laser spot erases the old signal 
as it records the new signal, can be achieved with relative ease 
(Proceedings of SPIE Vol. 695, pp. 105-109). As shown in FIG. 22 and FIG. 
23(a), a new signal can be recorded while erasing the old signal by 
changing the laser power between two power levels, a recording level and 
an erase level. 
However, according to the prior art recording system, the distortion of the 
recording mark into a teardrop-shaped mark which results in increased 
jitter and error rate also occurs, as explained below. When a signal as 
shown in FIG. 23(a) is used for recording, the achieved temperature of the 
recording film is relatively low at the front and gradually increases 
toward the back as shown in FIG. 23(b) due to the effects of preheating. 
This results in a teardrop-shaped recording mark as shown in FIG. 23(c). 
The distortion of the recording mark leads to distortion of the playback 
signal waveform, and is a cause of increased jitter. A number of improved 
recording systems are proposed for resolving this problem, and are 
described, for example, in Japanese patent publication (unexamined) Nos. 
S63-266632 and S63-279431, and in also in U.S. patent application Ser. No. 
07/311,362 (corresponding to EP application 89301389.6) which is assigned 
to the same assignee as the present application. 
The proposed systems for reducing recording mark shape distortion, such as 
disclosed in Japanese patent publication (unexamined) Nos. S63-266632 and 
S63-279431 are accomplished by composing the recording waveform used to 
form one recording mark from a pulse string comprising a short pulse of 
the same shape. In U.S. patent application Ser. No. 07/311,362 
(corresponding to EP application 89301389.6), a recording waveform forming 
a recording mark is converted to a pulse string comprising multiple pulses 
wherein the interval between pulses is gradually decreased (or the pulse 
width is gradually increased), or both the recording waveform and the 
erase beam are modulated by a pulse string, to control the achieved 
temperature of the recording film and thus reduce the distortion of the 
recording mark. 
Each of the above systems for reducing the distortion of the recording mark 
in a single beam overwrite system presents specific problems. Those 
described in Japanese Patent publication (unexamined) Nos. S63-266632 and 
S63-279431 are achieved with a simple construction, but are nominally 
effective in improving the recording mark shape. 
The invention described in U.S. patent application Ser. No. 07/311,362 
(corresponding to EP application 89301389.6) can achieve a large 
distortion reduction effect, but because it requires pulse strings 
optimized for pulses of all possible pulse widths in the input signal to 
be preset, the result is a device of extremely complex construction. In 
other words, a recording method and recording apparatus using single beam 
overwriting to form a recording mark with low shape distortion by means of 
a device of extremely simple construction has not heretofore existed. 
SUMMARY OF THE INVENTION 
The object of the present invention is therefore to provide a recording 
method which is able to significantly reduce recording mark distortion and 
thereby reduce jitter in the playback signal to a low level by recording a 
new signal while erasing an old signal in a data overwrite operation by 
means of a device of extremely simple construction. 
In order to achieve the aforementioned objective, according to the present 
invention, a recording method which overwrites an input signal having 
pulse duration periods and pulse spacing periods to a recording medium by 
irradiation of an optical beam by a beam emitter to form recording marks 
corresponding to said pulse duration periods, comprises the steps of: 
converting said pulse duration period of said input signal to a modulation 
pattern of pulse string such that: 
(I) the pulse width of at least one of the first and second pulses of said 
pulse string is made greater than the pulse width of each in successive 
pulses succeeding thereto and made constant irrespective of the length of 
the recording mark, 
(II) the pulse width and pulse cycle period of each pulse in said 
successive pulses is equal to each other, and 
(III) when forming a recording mark of Mth shortest entry, the number of 
narrow pulses in the modulation pattern is 
EQU {Ma+b} 
pulses, wherein a and b are constants, a being a positive integer and b 
being an integer; 
applying a first predetermined power level during the presence of pulse in 
said modulation pattern and applying a second predetermined power level 
during the absence of pulse in said modulation pattern to form a modulated 
signal; and driving said beam emitter by said modulated signal. 
According to one preferred embodiment of the present invention, the above 
item (III) can be rewritten as follow: 
(III) when forming a recording mark of length nT with n being an integer 
between 3 and 11 and T being one cycle period of successive pulses, the 
number of successive pulses in the modulation pattern is 
EQU {(n-2)a+b} 
pulses, wherein a and b are constants, a being a positive integer and b 
being an integer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is described hereinbelow with reference to the 
accompanying figures. 
The general feature of the optical information recording system is that 
when a recording mark is formed according to an input signal while erasing 
the old signal during signal recording, a pulse width of the input digital 
signal is either 3T, 4T, 5T, 6T, 7T, 8T, 9T, 10T or 11T, as shown FIG. 
2(a) in which T is a unit time. According to the present invention, the 
input pulse signal as shown in FIG. 2(a) is converted to a modulated 
signal as shown in FIG. 2(b) and the modulated signal is used for driving 
the laser beam for forming the recording mark on a recording medium, such 
as an optical disk. According to the present invention, a modulation 
pattern as shown in FIG. 7(b) is used for making the modulated signal as 
shown in FIG. 2(b) and such a modulated signal is previously stored in a 
pattern setting circuit. According to the present invention, there are 
fundamentally four different modulated signals (FIG. 1(b) and FIG. 2(b); 
FIG. 3(b) and FIG. 3(c); FIG. 4(b); and FIG. 4(c). 
Referring to FIG. 1(a)-1(c), the first modulated signal is described. It is 
assumed that a waveform as shown in FIG. 1(a) is produced for the digital 
recording signal. In this case, the input signal would be as shown in FIG. 
1(a), having a pulse duration of 11T, pulse spacing of 6T and another 
pulse duration of 4T. Based on input signal of FIG. 1(a), a modulated 
signal as shown in FIG. 1(b) is formed which is used to modulate the laser 
beam to record the corresponding signal onto an optical disk. The reasons 
for modulating the laser beam as shown in FIG. 1(b) are described 
hereinbelow. 
In FIG. 1(b), Pb is the erase power level. Thus, by holding the laser power 
constant at this level, the amorphous area on the optical disk is 
crystallized, and, accordingly, the old signal is erased. 
Furthermore, when recording a new signal, i.e., when forming a new 
recording mark, the laser power is further increased to a recording power 
level Pp. 
According to the first modulated signal, the pulse duration period is 
modulated to form a pulse string comprising narrow pulses which vary 
between the recording power level Pp and erase power level Pb. 
Furthermore, during the first two unit times (2T), the recording power 
level Pp is maintained, and thereafter, the power is alternately changed 
between the erase power level Pb and recording power level Pp at the rate 
of unit time T. 
In other words, according to the present invention, in order to reduce the 
distortion of the recording mark to become a teardrop shape while also not 
making the construction of the recording apparatus complex, such a method 
is employed that (1) modulating the input signal pulse which forms a 
single recording mark to form a modulated signal comprising multiple 
narrow pulses, and (2) optimizing the pulse width of the first or second 
pulse in said modulated signal so that it is wider than the pulse width of 
any pulses succeeding thereto. Furthermore, a device of simple 
construction can be achieved by (3) holding the recording power constant 
and controlling the achieved temperature by varying the pulse width of the 
pulses in the modulated signal, and (4) maintaining a constant 
relationship between the pulse width of the input signal and the number of 
pulses contained in the modulated signal when creating a modulated signal 
from said input signal. For example, if the pulse width of the input 
signal becomes greater by a unit of one, the number of narrow pulses in 
the modulated signal is increased by one. Moreover, according to the 
present invention, (5) it is necessary to keep the pulse width of the 
added narrow pulses always constant. 
The modulated signals shown in FIG. 2(b) are formed according to the first 
modulated signal which fulfills the above given criteria (1) to (5). 
Specifically, according to the first modulated signal, the bias power Pb 
for erasing is continuously emitted to the recording track during the 
signal recording period. When a leading edge of the input pulse signal is 
detected, the modulation pattern is produced. The modulation pattern has 
such features that (i) the pulse width of only the first pulse in the 
modulation pattern is greater than the pulse widths of all pulses 
succeeding thereto, (ii) the pulse widths of all successive pulses are 
equal, (iii) one pulse is added for each increase of unit time T in the 
pulse width of the input signal, and (iv) the laser is modulated and 
emitted at a power between a bias power Pb and peak power Pp by a 
modulated signal formed by the modulation pattern wherein the repeat cycle 
of the successive pulses is T. The first pulse has a pulse width of 2T so 
as to provide sufficient laser power to the optical disk to defuse and to 
present an amorphous state. 
A recording apparatus employing the modulation method of this type can be 
simply achieved as will be described in detail later ,in connection with 
FIG. 6. 
Referring to FIGS. 3(b) and 3(c) the second modulated signal which fulfills 
the above given criteria (1) to (5) is shown. 
According to the second modulated signal, the modulated signal has narrow 
pulses which vary between peak power level Pp and playback power level Pr 
or between peak power level Pp and power off level (0 level). In this 
case, the recording film will cool rapidly after irradiation with a narrow 
pulse, and formation of an amorphous recording mark is made easier. 
In addition, as shown in FIG. 3(c) the playback power level Pr (or power 
off level) is passed immediately after the detection of the leading edge 
of the input pulse signal or immediately before the detection of the 
trailing edge of the input pulse signal, i.e., in the transition from the 
erase power level Pb and the record power level Pp, and conversely in the 
transition from the record power level Pp to the erase power level Pb. 
Thus, the temperature change at the beginning and end of the input pulse 
signal is made rapid, and the boundary between crystalline and amorphous 
structures, i.e., the edge position of the recording mark, becomes clearly 
defined. 
Referring to FIG. 4(b) the third modulated signal which fulfills the above 
given criteria (1) to (5) is shown. 
According to the third modulated signal, during the pulse duration period 
(11T and 4T shown in FIG. 4(a)), the modulated signal has narrow pulses 
which vary between peak power level Pp and playback power level Pr, and 
furthermore, during the pulse spacing period (6T shown in FIG. 4(a)), the 
modulated signal has narrow pulses which vary between erase power level Pb 
and playback power level Pr. 
Referring to FIG. 4(c) the fourth modulated signal which fulfills the above 
given criteria (1) to (5) is shown. 
According to the fourth modulated signal, during the pulse duration period 
(11T and 4T shown in FIG. 4)), the modulated signal has narrow pulses 
which vary between peak power level Pp and erase power level Pb, and 
furthermore, during the pulse spacing period (6T shown in FIG. 4(a)), the 
modulated signal has narrow pulses which vary between erase power level Pb 
and playback power level Pr. 
According to the third and fourth modulated signals, the modulation pattern 
is provided not only during the pulse duration periods but also during the 
pulse spacing periods at which the erase laser beam is produced. Such a 
modulation pattern provided in the pulse spacing periods is referred to as 
pulsating pattern. The merit for making the pulsating pattern even during 
the pulse spacing periods is to distinctly form the recording marks 
particularly at their edges. Such a merit further described hereinbelow in 
connection with FIGS. 5(a)-5(d). 
FIGS. 5(a) and 5(c) show the second and third modulated signals, 
respectively, which are formed, without and with erase laser beam 
modulation. Also, FIGS. 5(b) and 5(d) show the achieved temperature at the 
recording film resulted from the second and third modulated signals, 
respectively. By holding the recording film at a temperature greater than 
or equal to a crystallization temperature Tx, which is greater than room 
temperature To, the amorphous area crystallizes, and by increasing the 
temperature greater than melting point Tm, the recording film cools 
rapidly after melting and converts to an amorphous state. What is 
important in this is that (1) the achieved temperature of the recording 
film is held constant during recording mark formation and erasure, and (2) 
the temperature change can be completed in a short period of time during 
the transition from recording to erasing and from erasing to recording. 
With (1), shape distortion of the recording mark can be minimized and the 
rate at which the old signal is erased can be held constant, and with (2), 
the edge position of the beginning and end of the recording mark can be 
made distinct, thereby reducing jitter in the playback waveform. It is 
particularly important to rapidly cool at the end of the recording mark to 
clearly define the edge position. 
By pulse modulation of the erase laser beam, a playback power level Pr (or 
power off level) can be easily provided during the transition from the 
erase power level Pb to the record power level Pp, and conversely during 
the transition from the record power level Pp to the erase power level Pb, 
and the gradual increase in the achieved temperature during erasing can be 
minimized. It is to be noted that the time period for providing level Pr 
at the end of the recording mark can be made longer with this recording 
method than with the method shown in FIG. 3(a). Therefore, rapid cooling 
can be achieved. 
First Embodiment 
Referring to FIG. 6, an optical information recording apparatus for 
producing the first modulated signal according to a first embodiment of 
the present invention is shown. The recording apparatus comprises: a 
multipulse generation circuit (hereinafter referred to as MP circuit) 8 
for receiving an input signal s1, such as shown in FIG. 2(a) and clock 
signal cl at a rate of T from a signal generator 1; a reference voltage 
setting circuit 9 which upon receipt of a gate signal Wg produces a bias 
current Ia corresponding to power Pp-Pb, a bias current Ib corresponding 
to power Pb-Pr and a bias current Ic corresponding to power Pr-0; a switch 
4 inserted in a line for sending the bias current Ia; an optical head 5 
containing a semiconductor laser generator for producing a laser beam 
having a power relative to the sum of bias currents; and an optical disk 7 
driven by a spindle motor 6. The MP circuit 8 includes a modulator 2 and a 
pattern setting circuit 3 for producing a basic pattern. 
Referring to FIG. 7a, a detail of the modulator 2 is shown, which comprises 
a leading edge detector 10 and trailing edge detector 11 for detecting, 
respectively, the leading and trailing edges of the pulse duration period 
in the input signal s1. Modulator 2 also includes a pattern generator 12 
which is coupled with pattern setting circuit 3. Pattern setting circuit 3 
generates a predetermined basic pattern of full length 11T changing 
between "1" and "0", which is substantially the same as the longest 
modulation pattern such as shown in FIG. 7b(b), bottom row, and applies 
the basic pattern to the pattern generator 12 in which the basic pattern 
is used fully partially from its leading edge to produce the modulation 
pattern. 
In response to the detection of the leading edge of the pulse duration 
period, the leading edge detector 10 produces a start signal to pattern 
generator 12. The start signal causes the pattern generator 12 to read the 
full basic pattern (11T long) from pattern setting circuit 3 through line 
s3, and in turn begins to produce the basic pattern from the beginning 
along line s4, in synchronized manner with clock cl. Thereafter, when the 
trailing edge detector 11 detects the trailing edge of the pulse duration 
period, the trailing edge detector 11 produces a stop signal to the 
pattern generator 12. This stop signal causes the pattern generator 12 to 
interrupt the output of the basic pattern. 
For example, as shown in FIG. 7b(b), first row, if the stop signal is 
produced after time period 3T from the start signal, the pattern generator 
12 produces only a portion (3T) of the full basic pattern from the 
beginning. Similarly, as shown in FIG. 7b(b), fourth row, if the stop 
signal is produced after time period 6T from the start signal, the pattern 
generator 12 produces only a portion (6T) of the full basic pattern from 
the beginning. Furthermore, as shown in FIG. 7b(b), bottom row, if the 
stop signal is produced after time period 11T from the start signal, the 
pattern generator 12 produces the full basic pattern (11T). 
Thus, the basic pattern is produced from pattern generator 12 fully or 
partially depending on the length of the pulse duration period. The full 
or partial basic pattern as produced from the pattern generator 12 is 
referred to as a modulation pattern. 
In operation of the optical information recording apparatus of FIG. 6, 
during the signal recording mode and when recording gate signal Wg is 
input to reference voltage setting circuit 9, bias currents Ic and Ib 
required to obtain bias power (i.e., erase power) Pb at optical head 5 are 
produced and supplied to the semiconductor laser. Also, bias current Ia is 
produced, but is cut off at switch 4. Then, when a recording signal s1, 
particularly the pulse duration period, is produced from signal generator 
1, MP circuit 8 produces the modulation pattern, i.e., a full or a portion 
of the basic pattern, such as shown in FIG. 7b(b) in a manner described 
above. The modulation pattern is applied through line s4 to switch 4 which 
is turned on and off in response to "1" and "0" of the modulation pattern. 
Thus, the bias current Ia corresponding to power Pp-Pb is intermittently 
transmitted through switch 4 relative to the modulation pattern, and is 
superimposed on bias currents Ib+Ir, thereby producing a first modulated 
signal. The semiconductor laser built in the optical head 5 is driven by 
the first modulated signal, and the optical disk 7 turned by the spindle 
motor 6 is irradiated by the laser beam produced by the first modulated 
signal, thereby effecting the overwriting with the first modulated signal. 
Since the leading and trailing edge detectors 10 and 11, and pattern 
generator 12 operate in synchronism to clock Cl, jitter can be suppressed 
in the modulation pattern, thus in the first modulated signal. 
The major feature of this device is the modulation of input signal s1 to 
form the first modulated signal. The input signal s1 to be recorded is 
first input from the signal generator 1 to the modulator 2. At this stage, 
the input signal s1 is processed through pulse width modulation (PWM) to 
obtain a modulation pattern. 
As has been described above, according to the first embodiment, the first 
basic pattern of full length (11T) is previously stored in the pattern 
setting circuit 3. The modulator 2 detects the pulse width of each pulse 
duration period in input signal s1, and permits only the necessary length 
from the beginning of the basic pattern according to the length of the 
detected pulse width to be outputted as the modulation pattern, and 
outputs the modulation pattern from the modulator 2 to operate switch 4. 
Therefore, all patterns having different lengths 3T, 4T, 5T, 6T, 7T, 8T, 
9T, 10T and 11T determined by the input signal s1 can be presented in a 
form of a modulation pattern by using only one basic pattern. In addition, 
the basic pattern can be easily changed, if necessary, to an appropriate 
basic pattern so that distortion in the playback waveform is minimized. 
The reference voltage setting circuit 9 may be so arranged that it 
generates the voltage required to obtain bias currents Ib and Ia when the 
recording gate signal Wg is input. When the recording gate signal Wg is 
off, the semiconductor laser is emitting at the playback power level Pr, 
and therefor current Ir is supplied. 
Referring to FIG. 8, an example of MP circuit 8 used in the circuit of FIG. 
7a is shown. In this embodiment, the input signal s1-a is the EFM (8-14 
modulation) signal which is usually used for recording the Cds of the 
read-only type. The EFM signal is a PWM signal comprising pulses of nine 
different pulse widths varying from 3T to 11T where T (=230 nsec) is the 
clock cycle controlled by clock. The modulation pattern s4-a is used for 
operating switch 4 to drive the laser as described above in connection 
with FIG. 6, and the signal is written to the optical disk. The optical 
disk used is a phase-change type rewritable medium with a structure as 
shown in FIG. 9. 
Referring to FIG. 9, an optical disk substrate 21 is formed by a 5" 
polycarbonate substrate to which the signal recording track is previously 
formed. A recording film 23 is made of TeGeSb having a film thickness of 
400 angstroms. The recording film is sandwiched between ZnS protective 
layers 22, and a Au reflective layer 24 is provided on the side opposite 
that of laser beam incidence. A back cover 26 is provided to protect these 
thin layers. The signal recorded and erased states correspond to the 
amorphous and crystalline states, respectively, of the recording film. In 
signal recording tests, a signal is prerecorded to the recording track, 
and a new signal is recorded by single beam overwriting while erasing the 
old signal. The relative velocity of the optical disk and the recording 
spot where the focused laser beam impinges is 1.25 m/sec. 
Measurement of jitter in the reproduced signal is used to evaluate the 
recorded signal. Jitter is defined by using the zero crossing or the 
playback waveform as the evaluation level, repeatedly measuring the time 
from one zero crossing to the next zero crossing at each pulse of the nine 
differing pulse widths to obtain the standard deviation. 
Referring back to FIG. 8, the MP circuit includes: D flip-flops 13 and 14 
and NAND gates 15 and 16 which constitutes the leading and trailing edge 
detectors 10 and 11 shown in FIG. 7a; 44 switches SW1-SW44 defining the 
pattern setting circuit 3 so as to make the basic pattern of 11T length; 
and a parallel-in/serial-out shift register 17 defining the pattern 
generator 12 which receives the basic pattern as stored in switches 
SW1-SW44. In this example, switches SW9, SW13, SW17, SW21, SW25, SW29, 
SW33, SW37, SW41 are off, and the remaining switches are on to form the 
basic pattern. Any other desired pattern can therefore be created by 
turning these switches on and off in different pattern. 
The operation of the MP circuit shown in FIG. 8 is described hereinbelow 
with reference to the timing chart in FIG. 10. 
The clock cl-a is one-fourth (T/4) the clock cycle T of the EFM input 
signal s1-a. The timing chart shown in FIG. 10 shows a case in which pulse 
duration period of 4T long is applied as the input signal. 
First, in response to the leading edge of the EFM input signal s1-a of 4T 
long, a start signal s9 is produced by the D flip-flops 13 and 14, the and 
NAND 15 in synchronized manner with clock c1-a. Thus, 
parallel-in/serial-out shift register 17 reads the basic pattern from the 
pattern setting circuit 3, and starts outputting the basic pattern from 
its leading edge in synchronized with clock cl-a. 
Thereafter, in response to the trailing edge of the EFM input signal s1-a 
of 4T long, a stop signal s10 is produced in a synchronized manner with 
16th clock cl-a, corresponding to 4T long. This stop signal causes the 
parallel-in/serial-out shift register 17 to stop sending out the basic 
pattern stored in the register 17. Thus, up to this time, data 
corresponding to SW1-SW16 are sent out from register 17 through D 
flip-flop 20 as modulation pattern S4-a. It is to be noted that since the 
D flip-flop 20 is synchronized with clock cl-a, the jitter is reduced. 
Accordingly, it is possible to create modulation patterns of different 
lengths 3T to 11T using one basic pattern of length 11T. 
In the tests, the device as described above is used to produce the first 
modulated signal. The EFM input signal is converted to the modulated 
signal as shown in FIG. 2(b), so as to drive the laser. The overwritten 
signal is read and the jitter in the playback signal is measured. The bias 
power Pb used for overwriting is 4 mW. 
The test results are obtained by measuring relationship between recording 
peak power Pp (the value at the surface of the optical disk) and jitter, 
and are shown in FIG. 11. In FIG. 11, the results of jitter measurements 
of signals overwritten according to the present invention and the prior 
art are compared under such condition that the EFM signal is used to 
directly modulate the laser during signal overwriting. Jitter is measured 
by the amount of shifting of the zero crossing point. As will be 
understood from FIG. 11, jitter in the playback waveform according to the 
present invention is reduced because of the reduced recording mark shape 
distortion, and there is a reduction in the playback signal error rate and 
improvement in recording density in the case of the present invention. 
In FIG. 8, pattern setting circuit 3 is formed by a plurality of switches 
SW1-SW44, but alternatively, it can be formed by the use of a ROM or RAM 
device wherein the predetermined basic patterns are stored. If a 
semiconductor storage device is used, this circuit will contain no delay 
elements, thus enabling circuit integration and a more compact device. 
An important feature of a recording apparatus according to the present 
invention is that whether the pattern setting circuit is a switch bank or 
semiconductor storage device, the optimal patterns for optical disks of 
different varieties can be selected by simply changing the basic pattern. 
Possible Basic Patterns 
Next, different basic patterns are described. 
The relationship between the basic pattern and jitter is obtained using the 
device described in the first embodiment with the basic pattern being 
varied. The input signal, optical disk, relative velocity of the optical 
disk and the recording spot, bias power, and jitter measurement method are 
the same as those described in the above embodiment. The shapes of the 
tested basic patterns are shown in FIGS. 12(a)-12(o) and the values of the 
jitter measured in the playback signal resulting from the signal recorded 
according to each pattern are shown in Table 1. The jitter values as 
obtained are the minimum values when the recording peak power was varied. 
The recording peak power is also shown in Table 1 as obtained at the time 
of the measured jitter value. 
TABLE 1 
______________________________________ 
Pattern Jitter (nsec) 
Recording peak power (mw) 
______________________________________ 
FIG. 12 (a) 
50 7.0 
FIG. 12 (b) 
60 8.3 
FIG. 12 (c) 
60 10.0 
FIG. 12 (d) 
70 8.5 
FIG. 12 (e) 
60 6.8 
FIG. 12 (f) 
40 6.8 
FIG. 12 (g) 
40 6.9 
FIG. 12 (h) 
105 8.3 
FIG. 12 (i) 
65 6.9 
FIG. 12 (j) 
40 7.0 
FIG. 12 (k) 
130 7.3 
FIG. 12 (l) 
160 6.3 
FIG. 12 (m) 
40 7.3 
FIG. 12 (n) 
35 8.6 
FIG. 12 (o) 
35 10.5 
______________________________________ 
As apparent from Table 1, jitter is reduced to less, than 100 nsec with all 
patterns except FIG. 12(h), FIG. 12(k) and FIG. 12(i). Therefore, basic 
patterns other than 12(h), FIG. 12(k) and FIG. 12(i) are understood as 
being included in the present invention. 
In particular, jitter at the maximum 50 nsec or less is observed with basic 
patterns FIG. 12(a), FIG. 12(f), FIG. 12(g), FIG. 12(j) FIG. 12(m), FIG. 
12(n), and FIG. 12(o). The feature of these patterns is that the pulse 
width of the first or second pulse in the basic pattern of the pulse 
string is wide, the narrow pulses succeeding thereto are each of an equal 
pulse width and pulse interval, and the cycle of said narrow succeeding 
pulses is T such that for each one unit increase in the length of the 
recording mark, one narrow pulse of cycle T is added to the pulse string 
of the modulation pattern. 
In other words, according to the present invention, (I) the pulse width of 
the first or second, or first and second pulses at the beginning of the 
basic pattern is greater than the pulse width of each pulse in a 
successive narrow pulses succeeding thereto in the basic pattern and 
constant irrespective of the length of the recorded mark, (II) the pulse 
width and pulse cycle period of each pulse in said successive narrow 
pulses is equal to each other therein, and (III) when forming a recording 
mark of length nT (n is an integer between 3 and 11), the number of narrow 
pulses in the modulation pattern is {(n-2)a+b} pulses, wherein a and b are 
constants, a being a positive integer and b being an integer. 
It is to be noted that the values a and b of each pattern FIG. 12(a), FIG. 
12(f), FIG. 12(g), FIG. 12(j), FIG. 12(m), FIG. 12(n), and FIG. 12(o) 
described above are: a=1, b=0 for patterns FIG. 12(a), FIG. 12(j), and 
a=1, b=-1 for FIG. 12(f), FIG. 12(g), FIG. 12(m), FIG. 12(n), and FIG. 
12(o). 
From a broader aspect of the present invention, the above item (III) can be 
defined as such that, (III') when forming a recording mark of Mth shortest 
entry, the number of narrow pulses in the modulation pattern is {Ma+b} 
pulses, wherein a and b are constants, a being a positive integer and b 
being an integer. 
Furthermore, while the MP circuit used in this test divides the 11T signal 
pulse into 44 units, the pulse width of the successive pulses can be made 
T/8 if the signal pulse is further divided into 88 units. However, finer 
division will cause the clock frequency of the MP circuit to become too 
high, and circuit design will become difficult. Considering the results 
shown in Table 1 and the ease of circuit design, it is considered 
preferable that the pulse width of the successive pulses is between a 
minimum T/8 and a maximum T/2. 
Recording Speed 
The jitter levels resulting from signals recorded at different relative 
speeds of the optical disk to the recording spot are obtained using the 
same device as that described above using basic patterns FIG. 12(d) and 
FIG. 12(g). The input signal, optical disk, and jitter measurement method 
are the same as those in the above described embodiment. The relationship 
between relative speed and the jitter levels measured in the playback 
signal are shown in FIG. 13. The recorded jitter levels at the minimum 
points are obtained with respect to different combinations of the 
recording peak power and bias power. 
Jitter increased in both patterns FIG. 12(g) and FIG. 12(d) high relative 
speeds. The increase in jitter occurs at a lower relative speed with 
pattern FIG. 12(g) than with pattern FIG. 12(d). Such a lower relative 
speed is obtained at a point at which the repeat cycle .tau. {T=230 nsec 
in pattern (g), T/2=115 nsec in pattern (d)} of the succeeding pulses 
becomes greater than .lambda./L, wherein .lambda. is the wavelength of the 
laser (0.83 .mu. in the present embodiment) and L is the relative speed. 
This is considered due to the distortion occurring in a recording mark 
resulting from intermittent laser beam emissions reaching an order equal 
to that of the wavelength of the laser beam and thus being optically 
reproduced, thereby resulting in distortion in the playback waveform which 
causes an increase in the jitter level. Therefore, it is preferred that 
the repeat cycle of the successive pulses be set so that 
EQU .tau..ltoreq..lambda./L 
where 
.tau.: repeat cycle of the successive pulses 
.lambda.: wavelength of the laser beam 
L: relative velocity of the optical disk to the recording spot. 
Second Embodiment 
In the first embodiment described above, the recording apparatus for 
producing the first modulated signal which change between the bias power 
level Pb and the peak power level Pl such as shown in FIG. 1(b) is 
described. In the second embodiment, a recording apparatus for producing 
the second modulated signal which change between the peak power level Pp 
and the playback power level Pr such as shown in FIGS. 3(b) and 3(c) is 
described. 
Referring to FIG. 14, an optical information recording apparatus for 
producing the second modulated signal according to a second embodiment of 
the present invention is shown. When compared with the first embodiment, 
the recording apparatus of the second embodiment further comprises a data 
flip-flop 22 for receiving data from MP circuit 8, and a switch 25 
inserted in a line for sending the bias current Ib and is connected 
through an invertor 23 to D flip-flop 22. MP circuit 8 includes the 
circuit shown in FIG. 8 so as to use the Q output from D flip-flop 14 of 
FIG. 8 as the D input to D flip-flop 22 of FIG. 14. 
Furthermore, according to the second embodiment, the reference voltage 
setting circuit 26 produces bias current Ip instead of bias current Ia. In 
this embodiment, the bias current Ip corresponds to power Pp-Pr. 
In operation, when the signal generator 1 produces the input signal s1, 
such as shown in FIG. 15(a), MP circuit 8 produces on line s4 the 
modulation pattern such as shown in FIG. 15(b), and at the same time, 
invertor 23 produces on line s14 a control signal such as shown in FIG. 
15(c). 
Thus, during the pulse duration period, switch 4 is alternately turned on 
and off in accordance with FIG. 15(b) and at the same time, switch 25 is 
maintained off in accordance with FIG. 15(c). Thus, during the pulse 
duration period, the sum of pulse current Ip, corresponding to power 
Pp-Pr, and continuous current Ir, corresponding to power Pr-0, as best 
shown in FIGS. 3(a)-3(c) provided for driving the laser, thereby effecting 
the overwriting with the second modulated signal. 
During the pulse spacing period, switch 4 is maintained off and switch 25 
is maintained on. Thus, during the pulse spacing period, the sum of 
continuous current Ib, corresponding to power Pb-Pr, and continuous 
current Ir, corresponding to power Pr-0, is provided for driving the 
laser, thereby effecting the erasing. 
It is to be noted that if the reference voltage setting circuit 26 is set 
so that Ir is not supplied when the recording gate signal Wg is input, the 
modulation pattern is used for making a modulated signal which varies 
between Pp and the power off level. 
Tests are carried out to find out the effect of the second embodiment. In 
the tests, the basic patterns as shown in FIGS. 12(a), 12(f), and 12(m) 
are used. The input signal, optical disk, relative velocity of the optical 
disk and the recording spot, bias power, and jitter measurement method are 
the same as those used in the first embodiment. The test results showing 
the values of the jitter measured in the playback signal are shown in 
Table 2. The jitter values as obtained are the minimum values when the 
recording peak power was varied. The recording peak power is also shown in 
Table 2 as obtained at the time of the measured jitter value. 
TABLE 2 
______________________________________ 
Pattern Jitter (nsec) 
Recording peak power (mw) 
______________________________________ 
FIG. 12 (a) 
45 8.3 
FIG. 12 (f) 
35 8.0 
FIG. 12 (m) 
30 8.6 
______________________________________ 
These results show a jitter level that is less than that for each same 
pattern in Table 1. This is because the cooling rate after irradiation 
with a short pulse is high during recording mark formation, thereby making 
the amorphous phase change easy, and resulting in a large recording mark. 
The jitter reduction effect is particularly great with the basic pattern 
12(m). This is because in the transition from the bias power level Pb to 
the peak power level Pp, and conversely from the peak power to the bias 
power level, the playback power level Pr is passed through, thereby 
resulting in a rapid change in the recording film temperature before and 
after the recording mark, and thus causing the edge position of the 
recording mark to be clearly defined. 
Third Embodiment 
Referring to FIG. 16, an optical information recording apparatus for 
producing the third modulated signal (FIG. 4(b) according to a third 
embodiment of the present invention is shown. When compared with the first 
embodiment, the recording apparatus of the third embodiment further 
comprises a second MP circuit 28 which receives input signal S1 through an 
invertor 29 and clock C1 and produces a pulsating signal applied to a 
switch 25 inserted in a line for sending the bias current Ib. MP circuit 
28 has the same structure as MP circuit 8. Instead of the basic pattern, 
pattern setting circuit 3 used in MP circuit 28 is previously stored with 
a pulsating pattern, such as shown in FIG. 17(a). 
Furthermore, according to the third embodiment, reference voltage setting 
circuit 26' produces bias current Ip instead of bias current Ia, as in the 
second embodiment. In this embodiment, the bias current Ip corresponds to 
power Pp-Pr. 
In operation, when the signal generator 1 produces the input signal s1, 
such as shown in FIG. 17(b), MP circuit 8 produces on line s4 the 
modulation pattern such as shown in FIG. 17(c) and at the same time, MP 
circuit 28 produces on line s15 the pulsating pattern such as shown in 
FIG. 17(d). 
Thus, during the pulse duration period, switch 4 is alternately turned on 
and off in accordance with FIG. 17(c), and at the same time, switch 25 is 
maintained off in accordance with FIG. 17(d). Thus, during the pulse 
duration period, the sum of pulse current Ip, corresponding to power 
Pp-Pr, and continuous current Ir, corresponding to power Pr-0, as best 
shown in FIG. 4b is provided for driving the laser, thereby effecting the 
overwriting with the third modulated signal. 
During the pulse spacing period, switch 4 is maintained off and switch 25 
is alternately turned on and off in accordance with FIG. 17(d). Thus, 
during the pulse spacing period, the sum of pulsating current Ib, 
corresponding to power Pb-Pr, and continuous current Ir, corresponding to 
power Pr-0, is provided for driving the laser, thereby effecting the 
erasing. 
It is to be noted that if the reference voltage setting circuit 26' is set 
so that Ir is not supplied when the recording gate signal Wg is input, the 
modulation pattern is used for making a modulated signal which varies 
between Pp and the power off level. 
Tests are carried out to find out the effect of the third embodiment. In 
the tests, the basic patterns as shown in FIGS. 12(a), 12(f), and 12(m) 
are used. The input signal, optical disk, relative velocity of the optical 
disk and the recording spot, and jitter measurement method are each the 
same as the respective items in the first embodiment. The power level Pb 
used for the erase pulse string is 4.5 mW. The test results showing the 
values of the jitter measured in the playback signal are shown in Table 3. 
The jitter values as obtained are the minimum values when the recording 
peak power was varied. The recording peak power is also shown in Table 3 
as obtained at the time of the measured jitter value. 
TABLE 3 
______________________________________ 
Pattern Jitter (nsec) 
Recording peak power (mw) 
______________________________________ 
FIG. 12 (a) 
40 8.4 
FIG. 12 (f) 
25 8.0 
FIG. 12 (m) 
20 8.7 
______________________________________ 
These results show a jitter level that is less than that for each same 
pattern in Table 2. This is because by pulse modulation of the erase laser 
power, (1) the achieved temperature of the erase area becomes constant and 
the old recording mark is uniformly crystallized, and (2) the recording 
film at the end of the recording mark cools rapidly, and the edge position 
of the recording mark becomes clearly defined because the playback power 
level Pr is passed through in the transition from the recording pulse 
string to the erase pulse string. 
It is to be noted that according to the present invention, a wave-shaped 
short pulse P (dotted line) is eliminated at the beginning of the 
pulsating pattern for the erase pulse string set, as shown in FIG. 17(a). 
If such a short pulse P is not eliminated, the measured jitter would be 
undesirably increased to 30 nsec with the pattern of FIG. 12(f), because 
rapid cooling at the end of the recording mark may not be obtained. 
Furthermore, if the pulse cycle period in the erase pulse string is the 
same as the pulse cycle period of the successive narrow pulses in the 
recording pulse string, the MP circuits 8 and 28 can be formed to have the 
same construction as mentioned above. 
Fourth Embodiment 
Referring to FIG. 18, an optical information recording apparatus for 
producing the fourth modulated signal (FIG. 4(c) according to a fourth 
embodiment of the present invention is shown. When compared with the third 
embodiment, the recording apparatus of the fourth embodiment differs in 
the reference voltage setting circuit 9 which produces bias currents Ia 
(corresponding to power Pp-Pb), Ib (corresponding to power Pb-Pr) and Ir 
(corresponding to power Pr-0), which is the same as the first embodiment. 
Furthermore, an invertor 33 is inserted between MP circuit 28' and switch 
25. Also, MP circuit 28' produces the pulsating pattern such as shown in 
FIG. 19(a). 
In operation, when the signal generator 1 produces the input signal s1, 
such as shown in FIG. 19(b), MP circuit 8 produces on line s4 the 
modulation pattern such as shown in FIG. 17(c), and at the same time, MP 
circuit 28' produces on line s16 the pulsating pattern such as shown in 
FIG. 19(c). 
Thus, during the pulse duration period, switch 4 is alternately turned on 
and off in accordance with FIG. 17(c), and at the same time, switch 25 is 
maintained not off but on in accordance with waveform of FIG. 19. Thus, 
during the pulse duration period, the sum of pulse current Ia, 
corresponding to power Pp-Pb, continuous current Ib, corresponding to 
power Pb-Pr, and continuous current Ir, corresponding to power Pr-0, as 
best shown in FIG. 4(c), is provided for driving the laser, thereby 
effecting the overwriting with the fourth modulated signal. 
During the pulse spacing period, switch 4 is maintained off and switch 25 
is alternately turned on and off in accordance with FIG. 17(d). Thus, 
during the pulse spacing period, the sum of pulsating current Ib, 
corresponding to power Pb-Pr, and continuous current Ir, corresponding to 
power Pr-0, is provided for driving the laser, thereby effecting the 
erasing. 
It is to be noted that if the reference voltage setting circuit 9 is set so 
that Ir is not supplied when the recording gate signal Wg is input, the 
modulation pattern is used for making a modulated signal which varies 
between Pp and the power off level. 
Tests are carried out to find out the effect of the fourth embodiment. In 
the tests, the basic patterns as shown in FIGS. 12(a), 12(f), and 12(m) 
are used. The input signal, optical disk, relative velocity of the optical 
disk and the recording spot, and jitter measurement method are each the 
same as the respective items in the first embodiment. The power level Pb 
used for the erase pulse string is 4.5 mW. The test results showing the 
values of the jitter measured in the playback signal are shown in Table 4. 
The jitter values as obtained are the minimum values when the recording 
peak power was varied. The recording peak power is also shown in Table 4 
as obtained at the time of the measured jitter value. 
TABLE 4 
______________________________________ 
Pattern Jitter (nsec) 
Recording peak power (mw) 
______________________________________ 
FIG. 12 (a) 
40 7.2 
FIG. 12 (f) 
30 6.9 
FIG. 12 (m) 
25 7.4 
______________________________________ 
These results show that while the jitter levels are slightly greater than 
those shown in Table 3, the recording peak power can be reduced. This is 
because the bias power level Pb is present in the recording pulse string. 
Fifth Embodiment 
Referring to FIG. 20, an optical information recording apparatus according 
to a fifth embodiment of the present invention is shown. When compared 
with the first embodiment shown in FIG. 6, the recording apparatus of the 
fifth embodiment differs in the reference voltage setting circuit 36 which 
produces only bias currents Ia (corresponding to power Pp-Pb) and Ir 
(corresponding to power Pr-0). The bias current Ib (corresponding to power 
Pb-Pr) is not produced in this embodiment, because the recording apparatus 
according to this embodiment is particularly designed for 
write-once-read-many (WORM) media, as explained below. 
The erase power level Pb shown in the modulated waveform in FIG. 1(b) 
erases the old signal during an overwrite operation. However, this 
embodiment of the present invention is designed in accordance with the 
requirements of write-once-read-many (WORM) media. The distinguishing 
difference between this embodiment and the first embodiment shown in FIG. 
6 is the elimination of the means for generating a current Ib, which is 
unnecessary in write-once-read-many optical information recording 
apparatus wherein signal erasure is not required. 
In operation, during the pulse duration period, the input signal such as 
shown in FIG. 21(a), is converted to basic signal by MP circuit 8. The 
basic signal is used for switching the switch 4 inserted in a line for the 
current Ia. The modulated signal such as shown FIG. 21(b), is obtained by 
superimposing current Ia on current Ir, and is used for drive the 
semiconductor laser built in to the optical head 5. The laser beam is thus 
modulated between the peak power level Pp and the playback power level Pr 
as shown in FIG. 21(b), and emitted to the WORM disk 35. By using the 
modulation pattern, i.e., the full or portion from the beginning of the 
basic pattern, the recording mark can also be reduced when writing to WORM 
media by means of a recording apparatus of simple construction. 
During the pulse spacing period, switch 4 is maintained off so that only 
the continuous current Ir, corresponding to power Pr-0, is provided for 
driving the laser, thereby effecting no erasing. 
Tests are carried out to find out the effect of the fifth embodiment. In 
the tests, the recording medium such as shown in FIG. 22 is used, which 
comprises an optical disk substrate 37 made of 5" polycarbonate on to 
which the signal recording track is preformed. The recording film 38 is a 
TePdO material with a film thickness of 1000 angstroms. A back cover 40 to 
protect the recording film is applied by means of an adhesive 39. When 
nothing is written to this disk, i.e., the disk is blank, the recording 
film is in an amorphous state, and signals can be recorded by emitting a 
laser beam to this medium to effect a phase-change conversion from this 
amorphous state to a crystalline state. It is not possible to erase the 
signals once written to this media because it is not possible to change 
the recording film from a crystalline to an amorphous state. 
In the signal recording test, the recording apparatus shown in FIG. 20 is 
used. The relative speed of the optical disk and the recording spot is 
1.25 m/sec. Furthermore, the basic patterns as shown in FIG. 12(a), 12(f), 
12(l) and 12(m) are used. The playback power level Pr is set to 0.7 mW by 
tuning the reference voltage setting circuit 36. The values of the jitter 
measured in the playback signal resulting from the signal recorded 
according to each pattern are shown in Table 5. The test results showing 
the values of the jitter measured in the playback signal are shown in 
Table 5. The jitter values as obtained are the minimum values when the 
recording peak power was varied. The recording peak power is also shown in 
Table 5 as obtained at the time of the measured jitter value. 
TABLE 5 
______________________________________ 
Pattern Jitter (nsec) 
Recording peak power (mw) 
______________________________________ 
FIG. 12 (a) 
45 6.1 
FIG. 12 (f) 
35 6.0 
FIG. 12 (l) 
130 5.0 
FIG. 12 (m) 
35 6.3 
______________________________________ 
As apparent from Table 5, jitter is reduced to (1) is equivalent to a case 
in which the recording signal S1 is used to directly modulate the laser 
beam, and shows a high jitter level. This example is provided for 
comparison with the present invention. In other words, the recording 
apparatus according to the present invention as shown in FIG. 20 features 
a simple construction, and is able to produce a recording mark with low 
shape distortion in write-once-read-many optical disk media. 
As described hereinabove, a recording method and a recording apparatus for 
optical information according to the present invention are able to 
significantly reduce recording mark distortion and thereby reduce jitter 
in the playback signal to a low level by recording a new signal while 
erasing an old signal in a data overwrite operation by means of a device 
of extremely simple construction. 
In addition, a recording apparatus for optical information according to the 
present invention is also able to record a signal with very low jitter to 
a write-once-read-many optical information medium by means of a device of 
extremely simple construction. 
These achievements are directly related to a reduction in the error rate of 
the optical disk, and therefore to an increase in the storage capacity of 
the optical disk.