JPH06203383A - Method for determining heat blocking condition for optical recording, apparatus for determining the same, optical recording method and optical recording apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] To avoid deterioration of data discrimination. A light source 2 for emitting a laser beam, an irradiation unit 5 for irradiating the optical recording medium D with the laser beam, and a medium D
The moving means 6 for changing the irradiation position of the laser beam above, and the intensity Ppre for maintaining the laser beam intensity for irradiating the optical recording medium to form a mark in a preheated state where the temperature of the medium D surface becomes a certain temperature. To PW1 which is higher than Ppre, PW1 is maintained for the time TW1 and then lowered to PW2 which is lower than PW1 and the preheating state within the time until it is raised to PW1 again to form the next mark. Therefore, the control means controls at least one of Ppre, Toff, and PLB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of determining a heat-shielding condition for optical recording, an apparatus for determining the same, an optical recording method and an optical recording apparatus.

[0002]

2. Description of the Related Art At present, optical recording is performed by making full use of the thermal property of a laser beam, and a recording medium (optical disk) is (1) a write-once type optical disk (1) capable of recording only once. Perforated type), for example, an optical disc having a thin metal film or a cermet film as a recording layer,
(2) An optical disk that can be repeatedly recorded, reproduced, and erased, such as a magneto-optical disk that uses a magnetic thin film as a recording layer, or a metal film or a cermet film that changes phase between a crystalline phase and an amorphous phase. Examples thereof include a phase change optical disk having a layer.

On the optical disk, tens of thousands of tracks for recording information are spirally or concentrically formed. Two types of information units corresponding to 0 and 1 are formed on this track and information is recorded. Actually, the track itself (that is, the ground portion) indicates the first information unit corresponding to one of 0 and 1, and the second information corresponding to the other of 0 or 1 in dots or islands on the track. A unit (recently called a mark) is formed. In this case, the presence or absence of a mark, the mark interval, the length of the mark, the mark formation start position (that is, the front edge position of the mark), the mark formation end position (that is, the rear edge position of the mark) and the like represent information.
Particularly, a method in which the edge position of the mark represents information is called mark length recording.

The optical recording device mainly comprises a laser beam light source, an irradiation optical system for irradiating a laser beam from the light source onto the optical disk, a modulating means for modulating the laser beam intensity according to information to be recorded, and a rotating means for the optical disk. In the case of the magneto-optical recording device, magnetic means for applying a bias magnetic field is further added to the beam irradiation position. Since optical recording exclusively uses the thermal properties of the laser beam (heat mode), in principle the laser beam intensity is between a relatively high first level and a relatively low base level (second level). It is sufficient to carry out pulse modulation with, and a mark is formed at the first level, and no mark is formed at the second level. That is, one pulse forms one mark. The second level does not form a mark, so the second level
The level can be zero. However, when a mark is to be formed, in other words, when the front edge of the mark is to be formed, it is preferable that the disk temperature state immediately before formation is always positively maintained at a constant temperature state. If I do not,
The front edge position changes depending on the temperature state immediately before the formation. The fluctuation becomes an obstacle when trying to record at high density. Therefore, it is preferable to preheat the optical disk to a preheated state by preheating it to a predetermined temperature Θpre.
The level is generally set to the strength Ppre that maintains this preheated state (temperature Θpre). The temperature Θpre is a constant temperature regardless of the information (data) pattern recorded at the peak temperature position of the beam or the spot center position of the disk immediately before the mark formation, and Ppre is represented by the following formula.

Θpre = A × Ppre × {1-exp (−∞ / τ)} + ΘA (2) where A (° C./mW) is determined by the disc, spot and recording linear velocity. It is the thermal efficiency of the laser beam intensity, and Θ A (° C) is the disk temperature without any beam irradiation. The first method of forming marks is
This is a method of simply forming one mark with one pulse. FIG. 11 is a waveform diagram of the laser beam intensity when one mark is formed by the first method. As shown in FIG. 11, the laser beam intensity is raised from the base level (second level) Ppre to start the mark formation, and the raised intensity (first level) PW1 is maintained at the full width at half maximum for the time TW1. It becomes a pulse waveform that falls to. In this case, when the mark length becomes long, there is an adverse effect due to heat accumulation. The adverse effect is that even if the laser beam intensity is lowered to Ppre in order to finish the mark formation, the medium temperature does not easily fall below the mark formation start temperature because of the accumulated heat. Therefore, the mark length becomes carelessly long or the mark width becomes carelessly thick. This adverse effect is referred to as "recording data pattern dependency of the mark formation end position, that is, the mark trailing edge position". This dependency becomes an obstacle to high-density recording and reduces the discriminability of data.

The second mark forming method solves this problem to some extent. FIG. 12 shows that this second method
FIG. 6 is a waveform diagram of laser beam intensity when forming two marks. As shown in FIG. 12, the intensity of the laser beam applied to the optical recording medium to form the mark is changed from Ppre to P
The intensity is raised to PW1 higher than pre, PW1 is maintained for a time TW1 and then lowered to PLT lower than PW1, and then intensity is modulated between PLT and intensity PW2 higher than PLT. The time for which PW2 is maintained is TW2, and the modulation cycle for intensity modulation between PLT and PW2 is Tp. This method
The waveform that should be originally one pulse (see FIG. 11) is a waveform consisting of the first small pulse and one or more subsequent small pulses.
Called the scheme. In this case, the temperature of the laser beam irradiation position on the optical disc during mark formation generally fluctuates up and down near a high temperature.

On the other hand, in the case of high density recording, there is a problem that the start position of the next mark fluctuates depending on the end position of the previous mark. This is referred to as the "recording data pattern dependency of the mark formation start position, that is, the mark front edge position". In order to solve this problem, when the laser beam intensity is lowered to complete the mark formation, the laser beam intensity is once lowered to PLB lower than Ppre, and Ppre after the time Toff.
An optical recording system was proposed to be launched at. 9 and 10
FIG. 4 is a waveform diagram of laser beam intensity when one mark is formed by this method. FIG. 9 shows a case of forming one mark with one pulse, and FIG. 10 shows a case of forming a mark by the pulse train method. In this method, the formation of the next mark is started from a predetermined position regardless of the length of the previous mark. In other words, the thermal effect from the previous mark is blocked for the next mark. The condition in which the thermal influence is cut off in this way is called "heat cut-off condition", which is indicated by Ppre, PLB and Toff. Conventionally, the heat insulation condition has been the European Computer Manufacturers Union (EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION
(Abbreviated as ECMA), as shown in page 87 of the ECMA / TC31 / 92/36 document (see FIG. 13), PLB is the laser beam intensity Pr during reproduction, and Toff is the write clock cycle ( write clock period) T was fixed.

[0008]

In the prior art as described above, in the case of high density recording, there is a problem that the discriminability of data is carelessly lowered depending on the optical disc used. The object of the present invention is to solve this problem.

[0009]

According to the research conducted by the present inventors, the laser beam intensity decreases from PW1 or PW2, and PLB
When it becomes Ppre after passing through, the temperature of the optical disk is lowered from a high temperature (hereinafter referred to as Θtop) at which a mark can be formed, and then becomes constant at the preheated temperature Θpre.
In this case, there are two cooling profiles.

The first is a monotonic decrease from Θ top to Θ pre
The temperature drop profile is that the temperature reaches a certain level and then remains unchanged (constant). The second is a temperature decrease profile in which the temperature decreases from Θ top to once below Θ pre, then starts to increase the temperature, reaches Θ pre, and then remains flat (constant). In any case, if the temperature of the optical disk is not constant at Θ pre, the start position of the next mark formation, that is, the front edge position of the mark will not be as desired. In either case,
Ttc is the time it takes for Θ top to decrease and Θ pre to become constant.
Call.

If the next mark is formed before the time Ttc elapses in order to increase the recording density, the front edge position of the mark has a recording data pattern dependency, and the data discrimination is deteriorated. Therefore, the next mark is formed after the time Ttc has passed, but if this Ttc is long, the interval between the mark and the next mark must be lengthened, and the recording density becomes coarse.

It can be said that the condition for shortening Ttc is the heat cutoff condition. As a result of diligent research, the inventors of the present invention have found that the cause of the problem is a fixed heat-shielding condition regardless of the optical disc, and therefore the optimum heat-shielding condition is not established depending on the optical disc. It was 14
FIG. 4 is a graph of the temperature of the spot center of the laser beam at each time or the peak temperature at each time when the mark is formed by the pulse train and the heat cutoff method. Insufficient thermal insulation results in the temperature drop profile shown in Figure 14 by the dash-dotted line, resulting in a long Ttc. Further, when the heat is cut off, the temperature drop profile shown by the chain double-dashed line in FIG. 14 is obtained, which also results in a long Ttc. Under optimal heat insulation conditions,
The cooling profile shown by the solid line in FIG. 14 is obtained, which results in the shortest Ttc. Due to the fact that it is not the optimum heat cutoff condition, when higher density recording is performed, there is a dependency of the leading edge position on the recording data pattern, and the discriminability of data decreases.

As a result of further research, the inventors of the present invention have invented a method for determining the optimum heat cutoff condition for each optical disk. Further, the invention also invented a method and a magneto-optical device for optical recording using the determined heat blocking condition. That is, the present invention is the first
"The laser beam intensity for irradiating the optical recording medium is raised from an intensity Ppre that maintains a preheated state where the temperature on the medium surface is a certain temperature Θpre to an intensity PW1 higher than Ppre to form a mark on the medium surface. An optical recording method in which the mark is formed, then lowered to an intensity PLB lower than Ppre, and raised to Ppre after a time Toff, and the next mark is formed by controlling at least one of Ppre, Toff, and PLB. Therefore, the optical recording method (claim 1) is provided in which the preheated state is set within a period of time until the PW1 is restarted.

The present invention secondly provides the "optical recording method according to claim 1 (claim 2), wherein the thermal response characteristics of the optical recording medium can be approximated by an exponential function". In the third aspect of the present invention, "the intensity of the laser beam applied to the optical recording medium is kept from a preheated state Ppre to Ppr for maintaining a preheated state where the temperature on the medium surface becomes a certain temperature Θpre.
An optical recording method of raising the intensity to PW1 higher than e to form a mark on the medium surface, maintaining PW1 for time TW1 and then lowering to intensity PLB lower than Ppre, and raising to Ppre after time Toff. An optical recording method (claim 3) is provided in which each value is obtained as a combination satisfying the following expression (1). Toff = τ × ln [{(PW1-PLB)-(PW1-Ppre) × exp (-TW1 / τ)} ÷ (Ppre-PLB)] Equation (1) (τ is the optical recording medium (4) The present invention, fourthly, "the strength PLB is set to zero.
The optical recording method (claim 4) described above is provided.

In the fifth aspect of the present invention, "the time Tof
5. The optical recording method according to claim 1, wherein the write clock period T is m / n times (m and n are natural numbers) or a value close thereto. (Claim 5) "is provided. The present invention also provides a sixth aspect.
"A light source for emitting a laser beam, an irradiation means for irradiating the optical recording medium with the laser beam, a moving means for changing the irradiation position of the laser beam on the medium, and the medium for forming marks. The intensity of the laser beam applied to the
It rises from the strength Ppre that maintains the preheated state of e to the strength PW1 higher than Ppre, and then the strength PL lower than Ppre.
The modulation means is lowered to B and raised to Ppre after the time Toff, and Ppr is set so that the preheat state is reached within the time until it is raised to PW1 again to form the next mark.
An optical recording device (claim 6) is provided, which comprises a control means for controlling at least one of e, Toff and PLB.

In a seventh aspect of the present invention, "a light source for emitting a laser beam, an irradiation unit for irradiating the optical recording medium with the laser beam, and an irradiation position of the laser beam on the recording medium are changed. The moving means and the laser beam intensity for irradiating the medium in order to form a mark are raised from the intensity Ppre that maintains a preheated state where the temperature on the medium surface is a certain temperature Θpre to an intensity PW1 higher than Ppre, and PW1 Strength PL lower than Ppre after maintaining TW1 for time
An optical recording apparatus comprising: a modulation unit that falls to B and rises to Ppre after a time Toff, and a condition determination unit that obtains each value as a combination that satisfies equation (1) (claim 7). "I will provide a.

In the eighth aspect of the present invention, "the strength PLB is
Is set to zero.
And an optical recording device (claim 8). The ninth aspect of the present invention is that the time Toff is set to m / n times the write clock period T (m and n are natural numbers) or a value close thereto. Alternatively, the optical recording device according to claim 8 is provided.

In the tenth aspect of the present invention, "the intensity Pp for maintaining the intensity of the laser beam applied to the optical recording medium in a preheated state where the temperature on the medium surface is a certain temperature Θpre.
A method of deciding the conditions of the optical recording method of raising from re to a strength PW1 higher than Ppre to form a mark on the medium surface, then lowering to a strength PLB lower than Ppre, and rising to Ppre after a time Toff. , A method for determining a heat-shielding condition for optical recording, characterized in that a combination of Ppre, Toff, and PLB is obtained so that the preheated state is achieved within a time period until the mark is formed again to PW1. Item 10) ”is provided.

In the eleventh aspect of the present invention, "the intensity Pp for maintaining the intensity of the laser beam applied to the optical recording medium in a preheated state where the temperature on the medium surface is a certain temperature Θpre.
A mark is formed on the medium surface by raising the strength from re to Pw1 higher than Ppre, and after maintaining PW1 for a time TW1, Ppre
A method of determining the condition of an optical recording method of falling to a lower intensity PLB and rising to Ppre after a time Toff, characterized in that each value is obtained as a combination satisfying the expression (1). Method for deciding heat insulation condition (Claim 1
1) ”is provided.

In the twelfth aspect of the present invention, "the strength P is
12. The method for determining the heat blocking condition for optical recording according to claim 10 or 11, wherein LB is set to zero (claim 1
2) ”is provided. The thirteenth aspect of the present invention is that the time Toff is set to m / n times the write clock cycle T (m and n are natural numbers) or a value close thereto. Alternatively, the method for determining the heat blocking condition for optical recording according to claim 12 is provided.

In the fourteenth aspect of the present invention, "the intensity Pp for maintaining the intensity of the laser beam applied to the optical recording medium in a preheated state in which the temperature on the medium surface is a certain temperature Θpre.
A device for determining the condition of an optical recording method in which a mark is formed on the medium surface by raising from re to a higher intensity PW1 than Ppre, then lowering to a lower intensity PLB than Ppre, and rising to Ppre after a time Toff. , A calculation unit that obtains a combination of Ppre, Toff, and PLB so that the preheat state is reached within the time until the mark is formed again to PW1 to form the next mark, and the value calculated by the calculation unit is output. An optical recording heat-shielding condition determining device (claim 14) "is provided.

In the fifteenth aspect of the present invention, "the intensity Pp for maintaining the intensity of the laser beam applied to the optical recording medium in a preheated state in which the temperature on the medium surface becomes a certain temperature Θpre.
A mark is formed on the medium surface by raising the strength from re to Pw1 higher than Ppre, and after maintaining PW1 for a time TW1, Ppre
An apparatus for determining the conditions of an optical recording method of falling to a lower intensity PLB and rising to Ppre after a time Toff, comprising: an arithmetic unit that obtains each value as a combination that satisfies Expression (1); An optical recording thermal cutoff condition determining device (claim 15) "is provided.

The sixteenth aspect of the present invention is that "the strength P is
The apparatus for determining the heat-shielding condition for optical recording according to claim 14 or 15, characterized in that LB is set to zero.
6) ”is provided. The seventeenth aspect of the present invention is that the time Toff is set to m / n times the write clock period T (m and n are natural numbers) or a value close thereto. Alternatively, there is provided an optical recording heat-shielding condition determining device (claim 17).

[0024]

First, the thermal time constant τ will be described. Figure 3
An example of the pattern (waveform) of the data signal to be recorded (FIG. 3
(1)), a chart showing emission and extinction of the laser beam at that time (chart of power input to the light source) (Fig. 3
(2)), a temperature profile of the disk at that time (heating profile) (FIG. 3 (3)), and an explanatory diagram showing the relationship between the marks formed (FIG. 3 (4)).

When optical recording is performed on an optical disk by using a recording laser beam (pulse), there are two types of disks, an adiabatic disk and a thermal diffusion disk, from the viewpoint of thermal diffusion. It is assumed that the laser beam is activated stepwise (like a rectangular wave) from extinction to emission as shown in FIG. 3 (2) according to the data signal (FIG. 3 (1)). Since the adiabatic disk is more likely to retain heat than the thermal diffusion disk, the temperature rise per unit intensity of the laser beam [° C./mW], that is, A in the formula (2) is large. That is, when irradiated with the same intensity for a long time, the adiabatic disk has a higher temperature saturation level. on the other hand,
An adiabatic disc is a temperature-increasing profile or an instantaneous (elevated) temperature profile.
e] takes a long time to reach saturation as compared with the heat diffusion disk. FIG. 4 is a graph of a temperature profile showing the time required for the temperature to reach saturation (tsat). That is, the adiabatic disc is tsat in FIG.
However, it is longer than a heat diffusion disk. This is easy to understand if you think that clay pots are harder to heat and cool than iron pots. The thermal time constant τ corresponds to this tsat. That is,
It can be said that a disk with a long tsat has a large τ.

As a result of earnest research, one of the inventors of the present invention invented a method of measuring the thermal time constant of the disk by first measuring the optical disk itself. Next, this measuring method will be described. <Measurement method of thermal time constant> An optical disc which is an object to be measured,
An optical recording / reproducing device (hereinafter, also referred to as an evaluation drive) for evaluating an optical disk, which is a measurement tool (measuring means), is prepared. Laser beam has NA = 0.55, wavelength = 830 nm
And the rise and fall times are both about 5ns.
ec. Set the optical disk in the evaluation drive, and measure the track speed of the disk (V = 11.3 m / sec).
Rotate the disc so that Then, the spot of the laser beam of the evaluation drive is servo-on on the track. That is, the focusing and tracking servo devices are activated. Then, the laser beam is pulse-modulated. Although the temperature of the disk is raised by the irradiation of the laser beam, the pulse modulation is performed in a duty cycle such that a sufficient time interval is opened to consider that the heat generated by heating each pulse does not interfere with each other. And various pulse duration (hereinafter PD)
Each PDT is radiated to the disc with a pulse
The "minimum power (Pth) capable of recording on the disk" is calculated for each. Figure 5 shows the pulse duration (PD
It is a waveform diagram explaining T.). "Minimum power (Pth) capable of recording on disk" during time PDT
Shows that the laser beam pulse is applied to the disk. FIG. 6 is a graph in which data is plotted with Pth being the vertical axis and PDT being the horizontal axis. As shown in FIG.
th decreases as PDT becomes longer and converges to a certain level P0.

Next, as shown in FIG. 7, Pth is the reciprocal of the value normalized by P0, that is, P0 / Pth is the vertical axis and PD is the PD.
Plot the data on the horizontal axis of T. This represents a graph of the thermal response function at the time of temperature rise when the disk is irradiated with the laser beam. Further, as shown in FIG. 8, the vertical axis represents 1-P.
If 0 / Pth is taken, it represents a graph of the thermal response function at the time of cooling when the laser beam is turned off. When the thermal response function of FIG. 8 can be approximated to an exponential function exp (−t / τ), τ is the temperature of the measured optical disc at the measured linear velocity (V) when the temperature rises and falls due to the measured laser beam. Represents a constant.

Conventional fixed thermal cutoff condition (PLB = Pr
, Toff = T), the optimum condition for minimizing Ttc shown in FIG. 14 cannot be obtained, so that the preheated state takes a long time to reach the normal state. In particular, in the case of a disc having a large thermal time constant τ, the influence is remarkable, and therefore, the position where the next mark is formed tends to depend on the previous mark. However, if the thermal cutoff condition determined by substituting τ into the following (1) according to the present invention is used, Ttc shown in FIG. Toff = τ × ln [{(PW1-PLB)-(PW1-Ppre) × exp (-TW1 / τ)} ÷ (Ppre-PLB)] (1) (τ is the optical recording medium Thermal time constant) This was first discovered by the present inventors. for that reason,
By using the determined heat insulation conditions, even during high-density recording,
The next mark formation position (in other words, the front edge position of the mark) is always the predetermined position regardless of the previous mark. This means that there is no dependence on the recording data pattern, that high-density recording can be performed accurately, and that the discriminability of data is not inadvertently reduced.

Furthermore, the present inventors have found that under the heat cutoff condition where PLB is zero in the equation (1), Ttc shown in FIG. 14 becomes the minimum absolute value. Therefore, PLB
Is preferably zero. Further, it is preferable that Toff is set to a value that is m / n times the write clock period T (m and n are natural numbers) or a value close thereto.

The present invention is particularly useful for an optical disc having a thermal time constant τ of 30 nsec or more at V = 11.3 m / sec. Also,
The present invention is useful for optical discs with τ> T. By the way, the heat cutoff condition of the equation (1) can be applied only when the thermal response characteristic of the disk can be approximated by a simple exponential function exp (-t / τ). When it cannot be approximated by a simple exponential function, the thermal response function is regarded as a function of time f (t) and considered as follows.

When the heat is cut off for Toff time and the temperature is raised to Ppre again, t = 0, and the temperature of the disk at that time (temperature is proportional to the intensity of the laser beam.
Hereafter, when expressed as a time function of intensity) is F0, F0
Can be expressed as F0 = Ppre · f (TW1 + Toff) + PW1 · {f (Toff) −f (TW1 + Toff)} + PLB · {1-f (Toff)} Further, the disk temperature after t = nx (x is arbitrary) time Fnx
Is as follows.

Fnx = Ppre · f (TW1 + Toff + nx) + PW1 · {f (Toff + nx) −f (TW1 + Toff + nx)} + PLB · {f (nx) −f (Toff + nx)} + Ppre・ {1-f (nx)} The condition for the disk temperature to be constant after heat cutoff is F0
= F1x = F2x = ... Fnx. That is, Fnx = F (n + 1) x
When formulating as (n = 0,1,2, ...), the following formula (3)
Becomes

Ppre · [f {TW1 + Toff + (n + 1) x} -f (TW1 + Toff + nx) -f {(n + 1) x} + f (nx)] + PW1 · [f {Toff + (n +1) x} -f {TW1 + Toff + (n + 1) x} -f (Toff + nx) + f (TW1 + Toff + nx)] + PLB [f {(n + 1) x} -f {Toff + (n + 1) x} -f (nx) + f (Toff + nx)] = 0 (3) Equation (3) cannot be solved any further. Therefore, assume that f (t) satisfies the following condition.

F (a) · f (b) = f (a + b), f (a) / f (b) = f (a−b) (4) Then, the equation (3) can be further decomposed. , Becomes the following formula. f (nx) {f (x) -1} [f (Toff). {(PW1-PLB)-(PW1-Ppre) .f (TW1)}-(Ppre-PLB)] = 0 (5 ) It is clear that f (x) -1 ≠ 0. Therefore, in equation (5), if f (Toff) · {(PW1-PLB)-(PW1-Ppre) · f (TW1)}-(Ppre-PLB) = 0, then Fnx = F for any n The condition that (n + 1) x holds is determined. That is, the condition is f (Toff) = (Ppre−PLB) / {(PW1−PLB) − (PW1−Ppre) · f (TW1)} (6) Equation (6) is the condition for heat cutoff. In expression (1), exp (-t
/ Τ) = f (t).

From the above, when the thermal response function f (t) satisfies the condition of the equation (4), the condition that the disk temperature becomes constant after the heat is shut off can be determined. If the thermal response function f (t) does not satisfy the condition of the equation (4), the condition that the disk temperature is constant cannot be determined. Therefore, FA is defined as the average of F0 to Fnx.

[0036]

[Equation 1]

The condition that minimizes is to be searched. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0038]

FIG. 1 is a conceptual diagram showing the main structure of a magneto-optical recording apparatus according to this embodiment. This device also serves as a reproducing device, and mainly has a motor (rotating means 6) for rotating the magneto-optical recording medium D, the laser beam light source 2, and the intensity of the laser beam at a high level according to the binary information to be recorded. Source driving circuit 1 that performs pulse modulation between high and low levels,
The recording magnetic field applying unit (permanent magnet 11), the pulse waveform shaping circuit 10, and the condition determining unit 12 are included. Here, the pulse waveform shaping circuit 10 changes the pulse waveform as shown in FIG.
Shape the waveform as shown in.

The condition deciding means 12 is provided with an arithmetic section for deciding a combination of the respective values (Ppre, PW1, PLB, TW1, Toff) based on the equation (1), and an output section for outputting the decided values. ing. The calculation unit determines each value based on the equation (1). Then, the determined value is output from the output unit. The pulse waveform shaping circuit 10 shapes the pulse waveform based on this output value.

A magneto-optical disk is set as the medium D. The medium D is rotated by the rotating means 6 so that the linear velocity of the track of the medium D becomes a predetermined value. The spot of the laser beam from the light source 2 is turned on on the track.
That is, a focusing and tracking servo device (not shown) is activated. Then, the laser beam emitted from the light source 2 should be recorded by the light source drive circuit 1.
Pulse modulation is performed according to the digitized information. After the beam emitted from the light source 2 is collimated through the collimator lens 3,
It is reflected by the beam splitter 4. The reflected beam is condensed by the objective lens 5 and focused on the medium D.
The record is basically over.

In the case of reproduction, the medium-D is irradiated with a DC-lighted laser beam which is not intensity-modulated as in recording. Then, the light reflected from the medium is made incident on the beam splitter 4 through the objective lens 5, and the light transmitted therethrough is condensed by the condenser lens 7 and then made incident on the detector 9.
At this time, the rotation state of the polarization plane is converted into a change in the intensity of light through an analyzer (polarizer) placed between the condenser lens 7 and the detector 9. As a result, the recorded information of the medium D, which is read as the rotation of the polarization plane, is converted into a change in the intensity of light. The change in light intensity is converted by the detector 9 into the intensity of an electric signal. This is reproduction.

In the apparatus as described above, a magneto-optical disk having τ = 55 nsec (V = 11.3 m / sec) by the measuring method of τ explained in the section of action was prepared. After the initialization of the entire surface, this magneto-optical disk was rotated at a measurement linear velocity of V = 11.3 m / sec, while NA = 0.55, wavelength = 830 nm, and the rise and fall times of the laser pulse were both about 5 ns.
Using a recording / reproducing laser beam of ec, 2/3 (1,7) RLL, 0.56 μm / bit, T (write
NRZI mark length recording random signal of clock period) = 33 nsec was recorded. As the pulse waveform, a pulse train method and a heat insulation method as shown in FIG. 2 were used. There are 7 types of marks, 2T mark to 8T mark. FIG. 2 is a waveform diagram of the laser beam intensity when forming 2T marks to 8T marks. Here, the nT mark is
When the recorded mark is reproduced, the width of the reproduction pulse corresponding to the mark is n times the clock cycle T (for example, 2T).
In the case of a mark, the mark is doubled.

The pulse train condition is PW1 = 11 mW, T
p = 33nsec (= T), TW1 = 50nsec (= T × 3/2),
PLT = Ppre, full width at half maximum of subsequent pulse TW2 = 16.5nsec (=
T × 1/2), PW2 = 11.2 mW (value at which the recording data pattern dependency of the mark formation end position, that is, the mark rear edge position is minimized). [Example 1] PLB and Toff were calculated as follows: PLB = Pr = 1.5 m
W and Toff were fixed at 33 nsec (= T).

After that, recording was performed while changing Ppre variously.
Reproduction was carried out with the reproduction laser beam intensity Pr = 1.5 mW, and "the mark formation start position, that is, the front edge position of the mark
"Recorded data pattern dependence" was measured, and Ppre
= 5.5 mW, the dependency became the minimum. [Example 2] PLB and Toff were calculated as follows: PLB = 0 mW, Toff
It was fixed at 33 nsec (= T).

After that, recording was performed while changing Ppre variously.
Reproduction was carried out with the reproduction laser beam intensity Pr = 1.5 mW, and "the mark formation start position, that is, the front edge position of the mark
"Recorded data pattern dependence" was measured, and Ppre
= 4.6 mW, the dependence became the minimum. [Embodiment 3] PLB and Ppre are expressed as PLB = Pr = 1.5 m
W and Ppre were fixed at 4.2 mW.

After that, recording was performed while changing Toff variously.
Reproduction was carried out with the reproduction laser beam intensity Pr = 1.5 mW, and "the mark formation start position, that is, the front edge position of the mark
When the "recording data pattern dependency" was measured,
At 50 nsec, the dependency was minimized. [Embodiment 4] PLB and Ppre were obtained by using PLB = Pr = 1.5 m
W and Ppre were fixed at 4.2 mW.

When Toff was calculated from the equation (1), Toff was 50 nsec. This value was equal to the value that minimizes the "recording data pattern dependency of the mark formation start position, that is, the front edge position of the mark", that is, the value obtained in [Example 3].

[0048]

[Comparative Example] Recording and reproduction were performed in exactly the same conditions as in [Example 3] except that Toff = 33 nsec (= T). As a result, the front edge position of the next mark after 2T interval (the interval between the previous mark and the rear mark) is about 1 nsec as compared with the front edge position of the next mark after 3T interval to 8T interval, It was out of the way. "Dependence on the recording data pattern of the mark formation start position, that is, the front edge position of the mark" still remains. It seems that Ttc is greater than the 2T interval.

[0049]

As described above, according to the present invention, the optimum heat-shielding condition is required for the optical disk. Therefore, when optical recording is performed using this, the "mark formation start position, that is, mark Of the recording data pattern of the front edge position of ". As a result, it is possible to always record at a high density, and yet it is always possible to avoid the deterioration of data discrimination.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a main configuration of a magneto-optical recording device according to an embodiment of the invention.

FIG. 2 is a waveform diagram of laser beam intensity when forming 2T marks to 8T marks used in the examples.

FIG. 3 is an example of a pattern (waveform) of a data signal to be recorded, a chart showing emission and extinction of a laser beam at that time (chart of power input to a light source), a temperature profile of a disk at that time (heating profile) ) And an explanatory diagram showing the relationship between the formed marks.

[Fig. 4] Time required for temperature to reach saturation (tsat)
Of temperature profile showing

FIG. 5 is a waveform diagram illustrating a pulse time length (P.D.T.).

FIG. 6 is a graph in which data is plotted with Pth as the vertical axis and PDT as the horizontal axis.

FIG. 7 is a graph in which data is plotted with P0 / Pth as the vertical axis and PDT as the horizontal axis (representing the temperature rise profile of the disk).

FIG. 8 is a graph in which data is plotted with 1-P0 / Pth as the vertical axis and PDT as the horizontal axis (representing the cooling profile of the disk).

FIG. 9 is a waveform diagram of a laser beam intensity when one mark is formed by using heat blocking.

FIG. 10: 1 with pulse train method using heat cut-off
FIG. 6 is a waveform diagram of laser beam intensity when two marks are formed.

FIG. 11 is a waveform diagram of the laser beam intensity when one mark is formed by the conventional method.

FIG. 12 is a waveform diagram of the laser beam intensity when one mark is formed by the pulse train method.

FIG. 13 is a waveform chart described on page 87 of the standard ECMA / TC31 / 92/36 document.

FIG. 14 is a graph of the temperature of the spot center of the laser beam at each time point or the peak temperature at each time point when a mark is formed by the pulse train and the heat blocking method.

[Explanation of symbols]

 1; Light source drive circuit 2; Laser beam light source 3; Collimator lens 4; Beam splitter 5; Objective lens 6; Motor (rotating means) 7; Focusing lens 8; Analyzer (polarizer) 9; Detector 10; Pulse waveform shaping circuit 11: recording magnetic field applying means (permanent magnet) 12: condition determining means D: recording medium

Claims (17)

[Claims] 1. An intensity Ppre to a laser beam intensity applied to an optical recording medium, which is maintained in a preheated state where the temperature on the medium surface becomes a certain temperature Θpre, and an intensity P higher than Ppre.
A mark is formed on the medium surface by raising to W1 and then lowering to an intensity PLB lower than Ppre, and after a time Toff, Ppre
An optical recording method for starting up to PW1, wherein at least one of Ppre, Toff, and PLB is controlled so that the preheated state is achieved within a time period until starting up to PW1 again to form the next mark. An optical recording method characterized by. 2. The optical recording method according to claim 1, wherein the thermal response characteristics of the optical recording medium can be approximated by an exponential function. 3. The intensity Ppre to Ppre higher than Ppre for maintaining the laser beam intensity for irradiating the optical recording medium in a preheated state in which the temperature on the medium surface becomes a certain temperature Θpre.
An optical recording method of rising to W1 to form a mark on the medium surface, maintaining PW1 for a time TW1 and then lowering to an intensity PLB lower than Ppre, and rising to Ppre after a time Toff, wherein each of the above values is An optical recording method, characterized in that a combination satisfying formula (1) is obtained. Toff = τ × ln [{(PW1-PLB)-(PW1-Ppre) × exp (-TW1 / τ)} ÷ (Ppre-PLB)] Equation (1) (τ is the optical recording medium Thermal time constant) 4. The optical recording method according to claim 1, 2 or 3, wherein the intensity PLB is set to zero. 5. The time Toff is set to m / n times the write clock cycle T (m and n are natural numbers) or a value close to it, as claimed in claim 1, claim 2 or claim 3.
Alternatively, the optical recording method according to claim 4. 6. A light source for emitting a laser beam, an irradiation means for irradiating the optical recording medium with the laser beam, a moving means for changing an irradiation position of the laser beam on the medium, and a mark for forming a mark. The laser beam intensity for irradiating the medium is raised from an intensity Ppre that maintains a preheated state where the temperature on the medium surface is a certain temperature Θpre to an intensity PW1 higher than Ppre, and then is lowered to an intensity PLB lower than Ppre, Modulating means for raising to Ppre after Toff, and Ppre and Toff so that the preheat state is reached within a time period until raising to PW1 again to form the next mark.
And a control means for controlling at least one of PLB. 7. A light source for emitting a laser beam, an irradiation means for irradiating the optical recording medium with the laser beam, a moving means for changing the irradiation position of the laser beam on the recording medium, and a mark for forming the mark. The intensity of the laser beam applied to the medium is raised from the intensity Ppre that maintains a preheated state where the temperature on the medium surface becomes a certain temperature Θpre to an intensity PW1 higher than Ppre, and after PW1 is maintained for a time TW1 it is lower than Ppre. An optical recording apparatus comprising: a modulation unit that lowers the intensity to PLB and that rises to Ppre after a time Toff, and a condition determination unit that determines each value as a combination that satisfies the following expression (1). Toff = τ × ln [{(PW1-PLB)-(PW1-Ppre) × exp (-TW1 / τ)} ÷ (Ppre-PLB)] Equation (1) (τ is the optical recording medium Thermal time constant) 8. The optical recording apparatus according to claim 6 or 7, wherein the intensity PLB is set to zero. 9. The method according to claim 6, wherein the time Toff is set to m / n times the write clock period T (m and n are natural numbers) or a value close thereto.
The optical recording device described. 10. The intensity Ppre of the laser beam applied to the optical recording medium is higher than the intensity Ppre to maintain a preheated state where the temperature on the medium surface is a certain temperature Θpre.
A mark is formed on the medium surface by raising to W1 and then lowering to an intensity PLB lower than Ppre, and after a time Toff, Ppre
A method for determining the condition of the optical recording method for starting up to Pw, Ppre, Toff, in which the preheat state is reached within the time until the next mark is formed again to PW1.
And a method for determining a thermal cutoff condition for optical recording, characterized in that a combination of PLB is obtained. 11. An intensity P of a laser beam for irradiating an optical recording medium, which is maintained in a preheated state in which the temperature on the medium surface is a certain temperature Θpre, and an intensity P higher than Ppre.
A method for determining the conditions of an optical recording method in which a mark is formed on the surface of the medium by rising to W1 and PW1 is maintained for a time TW1 and then decreased to an intensity PLB lower than Ppre, and then increased to Ppre after a time Toff. A method for determining a heat blocking condition for optical recording, characterized in that each of the above values is obtained as a combination satisfying the following expression (1). Toff = τ × ln [{(PW1-PLB)-(PW1-Ppre) × exp (-TW1 / τ)} ÷ (Ppre-PLB)] Equation (1) (τ is the optical recording medium Thermal time constant) 12. The method for determining the heat blocking condition of optical recording according to claim 10, wherein the intensity PLB is set to zero. 13. The time Toff is set to m / n times the write clock cycle T (m and n are natural numbers) or a value close thereto, according to claim 10, 11, or 12. Method for determining heat-blocking conditions for optical recording. 14. An intensity P of a laser beam for irradiating an optical recording medium, which is maintained in a preheated state where the temperature on the medium surface becomes a certain temperature Θpre, and an intensity P higher than Ppre.
A mark is formed on the medium surface by raising to W1 and then lowering to an intensity PLB lower than Ppre, and after a time Toff, Ppre
A device for deciding the conditions of the optical recording method to be started up to Pw, which is in the preheat state within the time until it is restarted to PW1 to form the next mark.
An optical recording heat-shielding condition determining device, comprising: an arithmetic unit for obtaining a combination of PLB and PLB; and an output unit for outputting the value obtained by the arithmetic unit. 15. An intensity P of a laser beam for irradiating an optical recording medium from Ppre to Ppre higher than Ppre for maintaining a preheated state where the temperature on the medium surface is a certain temperature Θpre.
A device for determining the conditions of the optical recording method of raising to W1 to form a mark on the medium surface, maintaining PW1 for a time TW1 and then lowering to an intensity PLB lower than Ppre, and raising to Ppre after a time Toff. An optical recording heat-shielding condition determination device, comprising: an arithmetic unit that obtains each value as a combination that satisfies the following formula (1); and an output unit that outputs the value calculated by the arithmetic unit. . Toff = τ × ln [{(PW1-PLB)-(PW1-Ppre) × exp (-TW1 / τ)} ÷ (Ppre-PLB)] Equation (1) (τ is the optical recording medium Thermal time constant) 16. An apparatus according to claim 14 or 15, wherein the intensity PLB is set to zero. 17. The method according to claim 14, wherein the time Toff is set to m / n times the write clock cycle T (m and n are natural numbers) or a value close thereto. Device for determining heat-shielding conditions for optical recording.