JPH07141713A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To stably record and reproduce information by adjusting a reproduction power by using the differential signal of reproduced signals at the time of mounting a disk. CONSTITUTION:A CPU 1 sets data in a DA converter 3 for setting the reproducing power and drives a laser driver circuit 5 to light the laser diode in an optical head 6 according to a set value at the time of reproduction operation. This exit light is condensed onto the optical disk 11 and the information is reproduced in accordance with this reflected light. The output A of a preamplifier 7 is sent to a reproducing system and is simultaneously differentiated by a differentiating circuit 8. The level of the output B is taken into the CPU 1 from the differential output B by using a peak detector 9 and an A/D converter 10. The reproducing power is so adjusted as to maximize the level of the output B in the CPU 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus, and more particularly to an optical information recording / reproducing apparatus for reproducing recorded information by utilizing magneto-optical interaction.

[0002]

2. Description of the Related Art Conventionally, there is known a method of recording / reproducing information on / from a disc-shaped information recording medium (hereinafter referred to as an optical disc) by utilizing magneto-optical interaction (polar Kerr effect). Among them, a medium configuration as shown in FIG. 5 has been proposed as a super-resolution technique for realizing a recording density higher than the optical resolution of reproduction light.

FIG. 5A shows a cross-sectional view of an optical disc, which is an example of the super-resolution technique. The substrate 20 is usually a transparent material such as glass or polycarbonate, and a first dielectric layer (enhancement layer) 21, a reproducing layer 22, a recording layer 23, and a second dielectric layer (protection layer) are formed on the substrate 20. Stack in the order of 24. The arrow in the magnetic material represents the direction of magnetization in the film.

The recording layer 23 is made of, for example, TbFeCo or DyF.
With a film having a high perpendicular magnetic anisotropy such as eCo, recorded information is held depending on whether the magnetic domain of this layer is upward or downward. Reproduction layer 2
No. 2 is made of a material having a large saturation magnetization Ms and a small perpendicular magnetic anisotropy, and is an in-plane magnetization film at room temperature, but becomes a perpendicular magnetization film because the saturation magnetization Ms becomes small when the temperature reaches a predetermined temperature Tth.

When the information reproducing light is irradiated from the substrate side to the magnetic film having such a structure, a temperature gradient as shown in FIG.
When viewed from the side, as shown in FIG.
There will be an isotherm of th. Then, the reproduction layer 2
As described above, No. 2 does not contribute to the polar Kerr effect because it becomes an in-plane magnetized film at a temperature equal to or lower than the predetermined temperature Tth, and the information of the recording layer 23 is masked and invisible from the reproducing light side. On the other hand, the reproducing layer 22 becomes a perpendicularly magnetized film at a portion having a temperature equal to or higher than the predetermined temperature Tth. As a result, the recording layer 2 is formed only in the aperture portion which is smaller than the spot size.
Since the information of 3 is transferred, super-resolution is realized. In such a configuration, since an aperture can be formed on the rear side with respect to the direction in which the spot advances on the disc, RAD (Rear Ap
This is called "Error Detection".

FIG. 6 shows an FAD (Front Apert) which has an aperture on the front side with respect to the direction in which the spot advances.
An example of the configuration of the ure Detection) is shown. In this case, the reproducing layer 22 has weaker in-plane anisotropy than RAD, and at room temperature, the magnetic domain of the recording layer 23 is transferred to the reproducing layer 22 through the intermediate layer 25 by exchange coupling. The Curie temperature of the intermediate layer 25 is set to around 100 ° C,
When the medium is heated by the reproducing light and reaches the Curie temperature of the intermediate layer 25, the exchange coupling is broken, so that the magnetization direction of the reproducing layer 22 becomes in-plane. Therefore, when the Curie temperature of the intermediate layer 25 is set to the predetermined temperature Tth, the magnetic domain of the recording layer 23 is transferred only on the front side of the spot with the isothermal line of the predetermined temperature Tth shown in FIG. .

Another method for performing super-resolution is shown in FIG.
A configuration as shown in is also proposed. The reproducing layer 22 in FIG. 7A is a perpendicular magnetization film having a low coercive force, and by applying the initialization magnetic field Hb at room temperature, the magnetization is aligned in the direction of the initialization magnetic field regardless of the orientation of the recording layer 23. That is, recording layer 2
A domain wall is generated in a portion where the magnetization direction of 3 and the direction of the initialization magnetic field are opposite. With the magnetization of the reproducing layer 22 thus initialized, reproducing light is emitted while applying a reproducing magnetic field Hr in the direction opposite to the initializing magnetic field. At this time, in the low temperature portion of the reproducing light spot, the reproducing magnetic field is so adjusted that the coercive force of the reproducing layer 22 is larger than the energy for reversing the magnetization of the reproducing layer 22 due to the exchange force from the recording layer 23 and the reproducing magnetic field. Set the size of. That is, since the magnetization of the reproducing layer 22 is oriented in the direction of the initializing magnetic field in the low temperature portion, the magnetization of the recording layer 23 is masked and does not contribute to signal reproduction. However, when the temperature of the reproducing layer 22 is gradually increased by the irradiation of the reproducing light, the coercive force of the reproducing layer 22 is lowered, and the magnetization of the reproducing layer 22 is reversed in the portion where the domain wall exists due to the exchange force from the recording layer 23 and the reproducing magnetic field. That is, the magnetization of the recording layer 23 is transferred to the reproducing layer 22. In this way, it is possible to realize super-resolution in FIG. 7B, in which only the portion in the spot where the temperature is equal to or higher than the predetermined temperature Tth contributes to signal reproduction.

In practice, an intermediate layer may be provided between the reproducing layer 22 and the recording layer 23 to control the domain wall energy, but the principle is the same as that shown in FIG.

[0009]

However, in the above-mentioned conventional example, the temperature distribution in the reproduction light spot contributes to the super-resolution, so that there are the following problems.

FIG. 8 shows the temperature distribution near the spot when the reproduction power is optimum, small, and large, taking the case of RAD as an example. In the case of FIG. 8, the isotherm of the predetermined temperature Tth extends to around the center of the spot at the optimum power (FIG. 8B), which is at the optimum level as the super-resolution effect. However, if the reproducing power is too small, the maximum temperature becomes low as shown in FIG. 8A, and the isotherm of the predetermined temperature Tth is close to the trailing edge side of the spot, so that the aperture is too small to reproduce information. On the other hand, if the reproducing power is too high, as shown in FIG.
Since the isotherm of the predetermined temperature Tth extends to the front side of the spot, as a result, the aperture becomes too large, and it becomes impossible to reproduce a smaller pit at the optimum power.

Therefore, there is a problem in that there are cases in which accurate reproduction of information cannot be performed due to differences in reproduction signal levels due to variations in disk temperature characteristics, operating temperatures, and errors in laser power control.

[0012]

According to the optical information recording / reproducing apparatus of the present invention, the magnetic coupling state between a recording layer made of a perpendicularly magnetized film for magnetically retaining information and the recording layer changes with temperature. In the optical information recording / reproducing apparatus, which reproduces recorded information by irradiating the optical information recording medium with a reproducing light, using the optical information recording medium having at least a reproducing layer for A sensor and a differentiating means for differentiating a signal from the sensor are provided, and the intensity of the reproduction light is changed according to the magnitude of the output of the differentiating means.

[0013]

According to the present invention, the sensor for receiving the reproduction light and the differentiating means for differentiating the signal from the sensor are provided, and the intensity of the reproduction light is changed according to the magnitude of the output of the differentiating means. Thus, stable information recording / reproducing is provided.

That is, the reproduction power is adjusted so that the level of the differential signal of the reproduction signal becomes large even if the reproduction power is not an appropriate value due to variations in the temperature characteristics of the disk, operating temperature, errors in laser power control, and the like. Thus, stable information recording / reproducing is performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram for explaining the first embodiment of the present invention. In the figure, 1 is a CPU, 2 and 3 are DA converters, 4 is a switch, 5 is a laser driver circuit, 6 is an information recording / reproducing optical head, 7 is a preamplifier, 8 is a differentiating circuit serving as differentiating means, and 9 is peak detection. A container, 10 is an A / D converter, and 11 is an optical disk.

When performing the reproducing operation, the CPU 1 sets data in the reproducing power setting DA converter 3 according to the procedure described later, and the laser driver circuit 5 according to the set value.
To turn on the laser diode in the optical head 6. The light emitted from the laser diode is condensed on the optical disk 11 by the optical head 6, and the reflected light is modulated according to the recorded information. The light received by the sensor in the optical head 6 is converted into a voltage by the preamplifier 7 and becomes an information signal. This signal is demodulated by a reproduction system demodulation circuit (not shown) to reproduce the information recorded on the optical disk 11.

When performing the recording operation, the CPU 1 sets data in the recording power setting DA converter 2 and controls the output of the DA converter 2 to the laser driver circuit 5 via the switch 4. A recording signal from a modulation circuit (not shown) is used as a control signal for the switch 4, and the laser is modulated in accordance with the data of the recording signal to record on the optical disc 11. Regarding the setting of the recording power, the following method is usually adopted in order to record information under the optimum recording conditions.

FIG. 3 shows an example of the structure of the information area in a general optical disc. Each part of FIG. 3 has the following roles. (A) Lead-in Zone (lead-in area)
An area for performing focus control, tracking control pull-in, and servo adjustment for making the reproduction beam follow the information track on the optical disk. (B) Inner Test Zone (inner circumference test area) ... A test area in which the recording power is adjusted on the inner circumference side. (C) Inner Control Zone (inner peripheral control area): An area in which information about the disk is recorded, in which servo information, maximum reproduction power, erasing conditions, etc. are written. (D) Data Zone: An area effective for data storage. (E) Outer Control Zone (outer peripheral control area) ... An area on the outer peripheral side in which the same information as in (c) is written. (F) Outer Test Zone (peripheral test area) ... A test area for recording power adjustment on the outer peripheral side. (G) Lead-out Zone (buffer area on the outer peripheral side).

As described above, the test zones (b) and (f) are used for the recording power test. That is, when the disc is loaded, the recording power is varied in several steps while keeping the reproducing power constant in this area, and the recording power with the highest reproducing signal level is set as the optimum recording power.

Next, a method of setting the reproducing power, which is a feature of the present invention, will be described. In the present invention, after adjusting the recording power in the test zone, the recording power is fixed to the optimum value, the shortest pit is recorded in the test zone, and the pit is reproduced while the reproducing power is varied in several steps. Then, the optimum reproducing power is obtained.
Further, the read power is readjusted according to the optimum read power, so that the adjustment accuracy can be further improved.

In FIG. 1, the output A of the preamplifier 7 is sent to the reproducing system and simultaneously differentiated by the differentiating circuit 8, and the level of the differential output B is converted from the differential output B by using the peak detector 9 and the A / D converter 10. It is configured to be taken into the CPU 1. FIG. 2 shows changes in the preamplifier output A and the differential output B when an isolated pit is recorded on the RAD disk and the same pit is reproduced by changing the power. FIG. 2B shows the preamplifier output A and the differential output B when the reproduction power is set to the optimum value. Here, the reason why the reproduced signal is asymmetrical at the rising and falling edges is as follows.

Since the intensity distribution of the reproducing light on the disc usually takes the form of a Gaussian distribution, the edge of the reproducing waveform on a general disc that is not super-resolution becomes gentle.
The aperture in the case of a RAD disc also becomes gentle because the fall side is considered to be the same as an ordinary disc, but as is clear from FIG. 8B, a sufficient amount of light is obtained at the aperture boundary on the rise side. The rising waveform sharply rises as shown in FIG. Therefore, the differential waveform is large on the positive side and small on the negative side.

Next, in the case where the reproduction power is small and the aperture as shown in FIG. 8A, the reproduction signal amplitude becomes small because the aperture is too small, and the rising becomes slow, so that the preamplifier output A and the differential output B become The level becomes small as shown in FIG.

On the contrary, when the reproducing power becomes large, the aperture becomes too large as shown in FIG. 8 (c), so that the resolution for the minimum pit decreases and the amplitude of the preamplifier output A does not increase as the light quantity increases. Further, the larger the aperture, the slower the rising edge, so the amplitude of the differential signal B decreases conversely. The reason why the shortest pit is used for adjusting the reproduction power is that the reduction in resolution with respect to the unnecessary expansion of the aperture is used.

From the above, when the recording power is adjusted in the test zone when the disc is mounted, the peak level of the differential signal B of the reproduction signal is taken into the CPU 1 by using the A / D converter 10 and the level is maximized. By adjusting the reproduction power so as to achieve stable information reproduction that is not affected by disc differences or laser power control errors.

Although the present embodiment has been described by taking the RAD as an example, when reproducing a disc of the FAD type,
Obviously, the same effect can be obtained by paying attention to the trailing edge of the reproduction signal and adjusting the differential signal so as to have the maximum level. Further, although the case where the in-plane magnetized film is used for the reproducing layer and the reproducing layer is the in-plane magnetized film in the mask portion has been described in the present embodiment, the present invention is not limited to such a film structure. it is obvious. Therefore, for example, as shown in FIG. 7, the magnetization direction of the reproducing layer made of a perpendicularly magnetized film is aligned in one direction by the initialization magnetic field to form a mask, and the magnetization of the recording layer is transferred and reproduced only in the high temperature portion. Even in such a case, it does not depart from the scope of the idea of performing information reproduction while changing the transfer state of magnetization depending on the temperature of the film, which is a feature of the present invention. That is, in the case of FIG. 7 as well, similar effects can be obtained by adjusting the reproduction power so that the differential signal level of the reproduction signal becomes maximum when the disc is mounted as described in the present embodiment. Needless to say.

The first dielectric layer as shown in FIGS. 5 to 7 enhances the Kerr effect, and the second dielectric layer is used to protect the magnetic layer. It is irrelevant to the essence of and can be omitted. [Second Embodiment] Next, a second embodiment of the present invention will be described in detail with reference to FIG. However, members having the same functions as those shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference from FIG. 1 is that the preamplifier output A is directly taken into the A / D converter 10 serving as differentiating means.

In recent years, some methods for digitally processing the reproduction signal have been proposed. In that case, signal processing is performed using an A / D converter having a conversion speed almost equal to the frequency of the reproduced signal (about 10 to 50 MHz). The power of a general A / D converter is several times higher than this (several hundred M
Since many of them have a speed of Hz), these high-speed A /
By using the D converter, it is possible to perform A / D conversion of several points on the shortest isolated pit. Therefore, since the data difference for each A / D conversion corresponds to the differential signal in the first embodiment, the same effect as in the first embodiment can be obtained by adjusting the reproduction power while monitoring the maximum value.

[0029]

As described in detail above, according to the present invention, when information is reproduced from an optical information recording medium in which the magnetic coupling state of the recording layer and the reproducing layer changes depending on the temperature, reproduction is carried out when the disc is mounted. Since the reproduction power is adjusted by using the differential signal of the signal, there is an effect that stable information recording / reproduction can be realized irrespective of disc difference and laser power control error.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is a waveform chart of each part in the first embodiment of the present invention.

FIG. 3 is a format diagram on a disc.

FIG. 4 is a configuration diagram for explaining a second embodiment of the present invention.

FIG. 5 is a principle diagram of a conventional RAD type disc.

FIG. 6 is a principle diagram of a conventional FAD type disc.

FIG. 7 is a principle diagram of a RAD type using a conventional perpendicular magnetization film.

FIG. 8 is a diagram for explaining a conventional problem.

[Explanation of symbols]

 1 CPU 2,3 D / A converter 4 Switch 5 Laser driver circuit 6 Optical head 7 Preamplifier 8 Differentiation circuit 9 Peak detector 10 A / D converter 11 Optical disk

Claims (1)

[Claims] 1. An optical information recording medium comprising at least a recording layer made of a perpendicular magnetization film for magnetically retaining information and a reproducing layer in which a magnetic coupling state with the recording layer changes with temperature. In the optical information recording / reproducing apparatus for irradiating the optical information recording medium with reproduction light to reproduce recorded information, a sensor for receiving the reproduction light and a differentiating means for differentiating a signal from the sensor are used. An optical information recording / reproducing apparatus, comprising: the intensity of the reproducing light is changed according to the magnitude of the output of the differentiating means.