JPH0210546A - Recording method for optical information - Google Patents

Abstract

PURPOSE:To obtain a good quality regenerative signal by using a laser beam for heating a medium with such power as larger than regenerative laser beam power but smaller than laser beam power by which a pit is formed. CONSTITUTION:A laser beam pulse for forming the pit, a regenerative laser beam and the laser beam for heating medium with the power as larger than the regenerative laser beam power but smaller than the laser beam by which the pit is formed are applied to this method. Consequently, the recording medium is irradiated by the laser beam which does not form the pit prior to an irradiating time of a recording laser beam, and hence the irradiating time of the recording laser beam as of the laser beam pulse for recording after raising the temperature of the medium not to exceed its write-enable temperature limit can be shortened, thus obtaining the good quality regenerative signal with less peak shift.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method of recording digital or analog signals on an optical information recording medium that moves at high speed, and particularly relates to a method of recording a digital or analog signal on an optical information recording medium that moves at high speed. The present invention relates to a method for recording optical information signals suitable for obtaining data.

(Prior art) As a method of recording information on an optical information recording medium, a laser beam of constant intensity is moved at high speed in a small diameter medium.
A method has been developed in which pits are formed by irradiating for a predetermined time (also called pulse width) depending on the desired pit length and using the heat generated thereby. For example, (1) the medium is melted or sublimated by heat to create a depression, and the depression becomes a pit; (2) the heat causes a phase transition, and optical properties such as refractive index and reflectance return to their original state. Create an area different from , and use this area as a pit, (3
) The coercive force of the perpendicular magnetization aligned upward or downward in the medium is reduced by heat, and at the same time a reversal magnetic field is applied to reverse the direction of magnetization, creating a region where the direction of magnetization is opposite to the original state. Information recording methods such as one in which this region is used as pits (magneto-optical recording) have already been proposed, and some of them have been put into practical use.

The information recorded in this way is recorded by irradiating a laser beam onto a medium that is moving at high speed, taking advantage of the fact that the optical properties of the formed pits are different from the surroundings, and then using the laser beam that is reflected by the medium or It is reproduced by detecting optical changes in the transmitted beam. In addition, here, the case where a pit is simply a "dent" and causes diffraction or interference because of the "dent", but would not cause such diffraction or interference without the "dent" is also included in the difference in optical properties. .

(Problem to be solved by the invention) However, in this method of recording information using heat generated by laser beam irradiation, by reducing the pit interval, the peak of the reproduced signal after recording and reproduction is reduced. (The position of the value changes (also called peak shift)), making it impossible to obtain a high-quality playback signal. Further, sufficient consideration has not been given to the optimal recording method for obtaining high-quality reproduction signals.

An object of the present invention is to provide an information recording method suitable for obtaining a high-quality reproduction signal.

(Means for solving the problem) The above purpose is to heat a medium using a laser beam pulse for forming pits, a laser beam for reproduction, and a power greater than the laser beam power for reproduction but less than the laser beam power for forming pits. This is achieved by using a laser beam.

(Function) Generally, when pits are formed using heat, the medium has a minimum critical temperature (writable temperature T) required for pit formation.
w) is determined, and pits are formed only when Tw or more is reached. As a result of research on the relationship between the laser beam emission timing (which can also be referred to as the start time of energization to the laser light source or the rise time of a pulse - an electric signal pulse for laser beam emission) and Tw, the inventor found that ( 1) Even if the laser light source is energized, the temperature of the medium will not instantaneously rise above Tw; (2)
2) The spot that reaches rTw or higher in the medium surface irradiation area of the laser beam (usually circular and called a spot) is small immediately after the spot is formed, then gradually increases in size, and then becomes constant. It was found that there was a slight delay between the light emission timing and the pit formation start time due to this.

This delay is referred to as "F time lag" here, but in order to investigate this time lag, we calculated the relationship between recording laser beam power and time lag at a linear velocity of 5.6 m/s in a Tw200'C recording medium by computer simulation. did. As a result, it was found that the time lag increases as the irradiation laser beam power decreases, as shown in FIG.

Furthermore, if the time lag is large, it is necessary to increase the laser beam irradiation time required to form pits with a constant pit length. For this reason, in a recorded signal with a small pit interval, there is a shift in the pit formation time due to the influence of heat from the previous pit formation, making it impossible to obtain a high-quality reproduction signal.

Therefore, the time lag can be reduced by irradiating the recording medium with a laser beam that does not form pits before irradiating the recording laser beam and raising the medium temperature to a temperature that does not exceed the writable temperature Tw. Further, since the time lag can be reduced, the recording laser beam irradiation time can be shortened, and when recording is performed continuously with small pit intervals, it is possible to reduce the shift in pit formation time due to the influence of heat of a pit before a subsequent pit.

Figure 3 shows a simulation in which a recording medium is irradiated with a laser beam that does not form pits before the irradiation time of the recording laser beam, and the medium temperature is raised to a temperature that does not exceed the writable temperature Tw to perform recording and reproduction. Show the calculation results. The recording medium was irradiated with a medium heating laser beam power of 1 mW in addition to a reproduction laser beam power of 1 mW at a linear velocity of 5.6 m/s. This can reduce the time lag.

In Fig. 4 (a) and (b), at a linear velocity of 5.6 m/s,
A calculation diagram of the maximum temperature reached when recording is performed by irradiating a recording laser beam power of 10 mW for 100 ns is shown. Laser beam pulse P1 that irradiates a reproduction laser beam power of 1 mW before the recording laser beam irradiation time
and a laser beam pulse P2 that irradiates a laser beam power of 2 mW, including a laser beam power of 1 mW for reproduction and a laser beam power of 1 mW to raise the temperature of the recording medium to a temperature not exceeding the writable temperature Tw.
In this case, larger pits are formed in the pulse P2 having a smaller time lag. From this, the recording medium is irradiated with a laser beam that does not form pits before the irradiation time of the recording laser beam, and the recording laser beam is irradiated with a laser beam pulse that performs recording by raising the medium temperature to a temperature that does not exceed the writable temperature Tw. You can shorten the time. Therefore, a high quality reproduction signal with less peak shift can be obtained.

(Example) Examples of the present invention will be described below.

FIG. 5 shows a cross-sectional view of the recording medium used in the experiment. 1 is a transparent substrate made of PC, 2 is a protective film made of SiN,
3 is a magneto-optical recording film made of TbFeCo.

A recording/reproducing experiment was conducted using the recording medium using an apparatus as shown in FIG.

In FIG. 6, a magneto-optical recording head 4 is installed with respect to a magneto-optical disk 5. As shown in FIG. Here, 7 is a magnetic field applying device,
6 is a current source, 8 is an actuator, 9 is a lens, 10
, 11.12 is a beam splitter, 13 is a polarizing filter, 14 is a light receiving element for detecting reproduced signals, 15.16 is a light receiving element for error detection, 17 is a laser light source, 20.21 is a servo control circuit, 22 is an amplifier circuit It is. Pulses for the laser beam are generated by the laser light source modulation circuit 18 and the medium heating laser light source circuit 19, and the reversal magnetic field is applied by the magnetic field application device 7, and the recording and reproduction of pits is performed by the magneto-optical recording circuit 4. I went with the head.

The linear velocity was 5.6 m/s, the laser beam pulse waveform shown in FIG. 1(a) was used as a comparative example, the recording laser beam power was 10 mW, the recording laser beam irradiation time was 60 ns,
The peak shift of the reproduced signal at a reproduction laser beam power of 1 mW was 16 ns.

Next, before irradiation with the recording laser beam, a recording experiment was conducted by irradiating the recording medium with a laser beam that does not form pits and raising the medium temperature to a level that does not exceed the writable temperature Tw. The laser beam pulse waveform is
Shown in Figure (b). Linear velocity 5.6m/s, recording laser beam power 10mW, recording laser beam irradiation time 20n
s, 1 mW in addition to the reproduction laser beam power of 1 mW.
The recording medium was irradiated with a medium heating laser beam power of W, and the recorded signal was reproduced with a reproduction laser beam power of 1 mW. By irradiating the medium heating laser beam, the peak shift could be halved from 16 ns to 8 ns.

(Effects of the Invention) According to the present invention, a medium moving at high speed is irradiated with a laser beam of constant intensity narrowed to a minute diameter for a predetermined time (also called pulse width) according to a desired pit length, A method of forming pits using the heat generated by this, for example,
(1) A method in which the medium is melted or sublimated by heat to create a depression, and this depression becomes a pit.(2) A phase transition is caused by heat, and engineering properties such as refractive index and reflectance change from the original state. (3) Using heat to reduce the coercive force of the perpendicular magnetization aligned upward or downward in the medium, and at the same time applying a reversing magnetic field to reverse the direction of magnetization. To record information on an optical information recording medium and obtain an optimal reproduction signal in information recording methods such as those that create an area whose direction is opposite to the original state and pit this area (magneto-optical recording). Therefore, the reliability of recording/reproducing signals can be improved.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are explanatory diagrams of laser beam pulse waveforms, Figures 2 and 3 are calculation diagrams of recording laser beam power and time lag, and Figures 4 (a) and (b) are recording media. Figure 5 is a schematic cross-sectional view of the optical recording medium used in the present invention, and Figure 6 explains the method for recording and reproducing information on the optical recording medium. This is a diagram. Figure 3: Magneto-optical recording film 4: Magneto-optical recording head 5: Magneto-optical disk 7: Magnetic field application device 18: Loser light source modulation circuit.

Claims (1)

[Claims] A laser beam is emitted for a predetermined period of time depending on the desired pit length, and is irradiated onto a recording medium moving at a constant speed. In a recording method that forms pits with a fixed pit length or different pit lengths on a medium and records information depending on the presence or absence of these pits, a laser beam pulse for forming the pits, a laser beam for reproduction, and a laser for reproduction are used. 1. A method for recording optical information, the method comprising recording by using a medium heating laser beam having a power greater than that of the beam and a laser beam having a power less than the laser beam power at which pits are formed.