JPH07192338A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To stably perform the formation recording and reproducing by changing the intensity of reproducing light in accordance with information recording position and adjusting the temperature of a medium caused by the difference in relative speed between the reproducing beam and the medium at the information recording position. CONSTITUTION:A CPU 1 sets data to a reproducing power setting DA converter 3, drives a laser driving circuit 5 in accordance with the set value and turns on the laser diode in an optical head 6. The light beam emitted from the laser diode is converged on an optical disk 10 by the head 6 and the reflected beam is modulated in accordance with the recorded information on the disk. The light beam received by the sensor in the head 6 is converted into a voltage by a preamplifier 7 and becomes a reproduced signal. The signal is demodulated by a demodulating circuit and the information recorded on the disk 10 is reproduced.

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 an enhancement layer 21, a reproduction layer 22, a recording layer 2 are formed on the substrate 20.
3 and the protective layer 24 are laminated in this order. 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 magnetic film having such a structure is irradiated with information reproducing light from the substrate side, a temperature gradient as shown in FIG. 5C is formed at the center of the data track. As shown in (b), the predetermined temperature Tth is set in the spot.
There will be an isotherm of. Then, as described above, the reproducing layer 22 becomes an in-plane magnetized film at a temperature equal to or lower than the predetermined temperature Tth, and therefore does not contribute to the polar Kerr effect.
The information of 3 is masked and becomes invisible. On the other hand, the predetermined temperature T
Although the reproducing layer 22 becomes a perpendicularly magnetized film in the portion of th or more, the magnetization direction at this time is the same as that of the recorded information due to exchange coupling from the recording layer 23. As a result, the information of the recording layer 23 is transferred only to the aperture portion which is smaller than the spot size, so that 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, a RAD (Rear Apert) is formed.
ure 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.

When recording / reproducing information on / from an ordinary optical disk,
Two methods are known for rotating a disc. One is CLV (Constant Lean Veloc)
The other is CAV (Constant An)
(guler Velocity). The former is a method that keeps the relative linear velocity between the recording / reproducing beam and the disk constant, and recording / reproducing can be performed under the condition of the highest density over the entire area of the disk, which is advantageous for increasing the total capacity.
Since it is necessary to change the number of rotations of the disk according to the information recording position, it is disadvantageous in response speed. On the other hand, the latter is advantageous in response speed because it keeps the number of revolutions of the disk constant, but has a problem that the capacity does not increase so much and the recording / reproducing conditions change depending on the information recording position.

On the other hand, the recording area on the disc is divided into several zones, and the zones are treated in the same manner as CAV, and the minimum recording pit for each zone is set to ZCAV ( A method called Zone CAV) has also been proposed, which solves the problem of capacity. However, in the case of ZCAV as well, since the number of rotations of the disk is constant, the problem that the recording / reproducing conditions change depending on the information recording position remains.

FIG. 8 shows the temperature distribution near the spot when the inner circumference, the middle circumference, and the outer circumference of the disk are scanned with the same reproducing light intensity, taking the case of RAD as an example. In the case of FIG.
In the vicinity of the middle circumference (FIG. 8B), the isotherm of the predetermined temperature Tth extends up to the center of the spot, which is at the optimum level for the super-resolution effect. However, when the inner circumference is reproduced with the same light intensity, the linear velocity is slow, so the maximum temperature becomes high as shown in FIG. 8A, and 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 middle lap. On the other hand, in the case of the outer circumference, since the linear velocity is high, the medium temperature does not rise as much as in the case of the middle circumference.
As shown in (c), the aperture is too small to reproduce information.

[0013]

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 an optical information recording / reproducing apparatus that reproduces recorded information by irradiating the optical information recording medium with reproduction light, using an optical information recording medium in which at least a reproducing layer for It is characterized in that the intensity of the reproduction light is changed.

[0014]

According to the present invention, the intensity of the reproducing light is changed according to the information recording position of the optical information recording medium, so that the medium temperature difference due to the relative velocity difference between the reproducing beam and the medium at the information recording position is eliminated. It adjusts and provides stable information recording / reproduction over the entire information area.

In the present invention, the reproducing light intensity is adjusted and linearly interpolated or polynomial approximated at a plurality of positions on the optical information recording medium to determine and change the reproducing light intensity over the entire range. You can

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram for explaining a 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, and 10 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 focused on the optical disk 10 by the optical head 6, and the reflected light is modulated according to the recorded information on the disk. The light received by the sensor in the optical head 6 is converted into a voltage by the preamplifier 7 and becomes a reproduction signal. This signal is demodulated by a demodulation circuit (not shown) to reproduce the information recorded on the optical disc 10.

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 according to the data of the recording signal to record on the optical disc 10.

Next, the concept of reproducing power setting will be described. FIG. 2 is a diagram showing the state of spots and the temperature distribution in the disc traveling direction when the present embodiment is applied to RAD. FIG. 2B shows the state of the middle circumference of the disk. The same super-resolution effect as shown in FIG. 8B is obtained, and only the high temperature portion of the spot above the predetermined temperature Tth is the aperture. Contributes to the reproduction of information pits. On the other hand, when the inner circumference of the disc is reproduced, the aperture is too large in FIG. 8A to obtain the optimum super-resolution effect, whereas in FIG. 2A, the reproduction is performed in accordance with the decrease of the linear velocity. By reducing the power, the temperature of the disc is prevented from rising too much, and the aperture size is optimized. On the contrary, in the case of reproducing the outer peripheral portion, the aperture is too small in FIG. 8C, while the reproducing power is increased as the linear velocity is increased in FIG. And the optimum aperture shape is obtained.

When actually performing the reproducing operation, the relationship between the radial position and the optimum reproducing power is recorded in advance as information about the disc, and when the disc is inserted, this data is first read and then the reproducing power is set based on that value. By doing so, optimum reproduction conditions can always be obtained. That is, the optimum super-resolution effect can be obtained over the entire data area of the disc, and it becomes possible to reproduce high-density pits having a higher optical resolution than the spot. By the way, even when reproducing information about this disc, it is necessary to set the reproduction power to a certain value, but since this portion occupies a small proportion of the entire disc capacity, there is no super-resolution effect. However, if you record in a pit that is large enough to be reproduced, the reproduction power margin will be large, and you can reproduce without problems even if it deviates slightly from the actual optimum power.

Further, although the present embodiment has been described by taking the RAD as an example, it goes without saying that the same effect can be obtained also when reproducing a disc of the FAD type. 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, also in the case of FIG. 7, it is needless to say that the same effect can be obtained by changing the reproduction power according to the information signal reproduction position on the disc as described in this embodiment.

The enhance layer of the disk shown in FIGS. 5 to 7 enhances the Kerr effect, and the protective layer is used to protect the magnetic layer and is omitted because it is irrelevant to the essence of the present invention. It doesn't matter. (Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG.
Will be described in detail. 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 members added to FIG. 1 are a peak hold circuit 8a, a bottom hold circuit 8b, and a differential amplifier 8
c, the AD converter 9. As in the case of FIG. 1, the CPU 1 sets data in the DA converters 2 and 3 for recording power and reproduction power, respectively, and outputs the output of the preamplifier 7 to a peak hold circuit 8a, a bottom hold circuit 8b, and a differential amplifier 8c. It is configured to monitor through the AD converter 9 and detect the amplitude of the information signal.
That is, when the optimum reproduction power corresponding to the information recording position is not known in advance, the CPU 1 can adjust the optimum reproduction power each time by monitoring the amplitude of the information signal.

FIG. 4 shows an example of the structure of the information area in a general optical disc. Each part of FIG. 4 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).

Of these, the test zones (b) and (f) are usually used only for testing the recording power. That is, in this area, reproduction is performed while varying the recording power in several steps (reproduction power is constant), and the recording power with the largest reproduction signal amplitude is set as the optimum recording power.

Therefore, in this embodiment, first, the Inne
After the optimum recording power Pwi at a certain reproduction power is obtained by r Test Zone, the signal recorded at Pwi is reproduced at the reproduction power of several steps to obtain the reproduction power Pri having the largest signal amplitude. Then turn the optical head out
er Test Zone and obtain the optimum reproduction power Pro by the same procedure. As described above, since the linear velocities are different between the inner circumference and the outer circumference, there is a difference in the super-resolution effect, and Pri and Pro have different values. Here, when the linear velocity is constant, the reproduction power and the temperature rise of the disc (the temperature difference between the maximum temperature of the laser-irradiated portion and the non-irradiated portion)
Is considered to be almost proportional to each other, and the linear velocity and the reproducing power change almost linearly when the maximum temperature of the laser irradiation portion is constant. Therefore, for example, In at the radial position Ri
The reproduction power obtained by the ner Test Zone is set to Pr.
i, Outer Test Zone at radius Ro
The reproduction power Pr in the case of reproducing the data at the position of the radial position R is Pro
You can ask at.

[0026]

[Equation 1] Or

[0027]

[Equation 2] That is, in the data area, the radial position R is calculated from the track number to be reproduced, and the optimum reproduction power is calculated and set from this value, so that optimum reproduction conditions can always be obtained. When Pwi (Pwo) and Pri (Pro) are obtained, Pwi (Pwo) at the obtained Pri (Pro)
It is possible to improve the measurement accuracy by repeatedly performing the work of obtaining

In the present embodiment, the optimum reproduction power is obtained from the track number. However, in the case where the optical head has a radial position sensor and the radial position can be obtained from the sensor output, the sensor output And P
It goes without saying that the reproduction power can be determined from ri and Pro. (Embodiment 3) As described above, a general optical disc uses a format called ZCAV, which is advantageous in terms of total capacity and high speed. As shown in FIG. 4, the data area has several zones (area 0 to area 0). It is divided into regions N). Within each zone, it is handled in the same manner as CAV, and the recording pit length at the innermost circumference of each zone is set to the limit size determined by the spot size of the reproducing beam or the super-resolution effect of the disc. Therefore, when arranging each zone in succession, the pit length and the clock frequency of tracks adjacent to each other are different from each other. Since the arrangement is also different, problems may occur in the signal leakage from the adjacent tracks and the access method. Therefore, normally, a buffer area of several tracks is provided between each zone so as not to be used for recording information for the user. However, this buffer area can withstand test recording and reproduction.

In the present embodiment, in addition to the test zones for the inner and outer circumferences described in the second embodiment, the same test recording / reproducing is performed in some buffer areas between the zones to obtain the optimum recording power and the optimum reproducing power. Keep it. However,
This does not necessarily have to be performed in the buffer areas of all zones, and may be minimized to obtain the required reproduction signal quality. This is because even if the number of measurement points is increased more than necessary, the rise time for each disk insertion will only increase.

As described above, the test is performed for an appropriate number of points, and the relation such as the formula 3 between the radial position R and the optimum reproduction power Pr is obtained by using a generally known approximation method such as the least square method. derive.

[0031]

## EQU3 ## Pr = a.R + b (3) where a and b are constants, and even if this formula 3 is used instead of the above formula 1, a stable signal is obtained over the entire area of the disk. Playback is possible. (Fourth Embodiment) In the third embodiment, linear interpolation is performed between the measurement points, but as a more accurate method, the radial position R
There is a method of calculating the relationship between the optimum reproduction power Pr and the optimum reproduction power Pr with a polynomial. FIG. 2 shows the change in temperature distribution when the linear velocity is changed. In this case, the maximum temperature reached by laser irradiation is made constant by changing the reproducing power according to the linear velocity,
The position of the predetermined temperature Tth at the center of the track was adjusted. However, the optimum aperture may not be obtained even if only the maximum temperature is adjusted due to the difference in thermal conductivity of the disk. That is, the aperture shape may change due to the difference in temperature distribution within the spot due to the linear velocity, and the optimum reproduction power may not change linearly. Therefore, the optimum reproduction power can be measured in several buffer areas as in the third embodiment, and the relationship between the radial position R and the optimum reproduction power Pr can be obtained by a polynomial. That is, the measured radial positions are R1, R2, ..., Rn, and the optimum reproduction powers at the respective positions are Pr1, Pr2 ,.
If rn, then the reproduction power Pr can be expressed by Equation 4 as a function of the radial position R.

[0032]

## EQU00004 ## Pr (R) = a _n- 1.R ^n-1 + a _n-2 .R ^n-2 + ... + a ₁ .R + a ₀ .. R1) = Pr1, Pr (R2) = Pr2, ..., Pr (R
n) = Prn Since Equation 4 is the equation of (n-1) and the measurement points are n points, each coefficient a ₀ , a ₁ , ..., A _n-1 can be uniquely obtained.

Therefore, as in the third embodiment, after obtaining the optimum reproduction power at three or more measurement points, the reproduction at each radial position is performed in the form of (n-1) the following equation for the number n of measurement points. Seeking power. As a result, the reliability during reproduction can be further increased. (Fifth Embodiment) In the third embodiment, the number of measurement points is n, and the relationship between the radial position R and the reproduction power Pr is a polynomial of (n-1) order. However, the relational expression is simplified and the measurement accuracy is improved. An approximation may be used to achieve That is, when the number of measurement points is n, the relationship between the radial position R and the reproduction power Pr is approximated to a polynomial of degree k (n-1> k) by using a method such as the least squares method or Lagrange interpolation. You can do it.

In practice, it is considered that a polynomial of 2 to 3 order is sufficient. Therefore, in order to improve the accuracy of approximation, it is necessary to take 4 to 5 or more measurement points. (Embodiment 6) In Embodiments 3 to 5, the test recording / reproduction for obtaining the relationship between the radial position R and the reproduction power Pr is performed in the buffer area between the zones. Since this information is not included, it may be difficult to perform the recording operation as a problem on the recording / reproducing apparatus side.

Therefore, in one or more zones, one or more tracks on the innermost circumference (outermost circumference) side are used as test tracks, and at the time of power check, the optimum reproduction power of these test tracks is determined. Try to ask. According to this method, the number of tracks provided for the test is only a few tracks in the entire disc, so that the recording / reproducing test can be easily performed with almost no reduction in capacity.

[0036]

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 with temperature, the information recording position is changed. Since the optimum reproduction light power is set accordingly, there is an effect that stable information recording / reproduction can be realized over the entire information area.

[Brief description of drawings]

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

FIG. 2 is a principle view of the present invention.

FIG. 3 is a configuration diagram for explaining a second embodiment of the present invention.

FIG. 4 is a format diagram on a disc in the second and third embodiments 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 conventional RAD type disk using a perpendicular magnetization film.

FIG. 8 is a diagram illustrating 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 Peak detector 9 A / D converter

Claims (3)

[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 reproducing the recorded information by irradiating the optical information recording medium with the reproducing light, the intensity of the reproducing light is changed according to the information recording position. Information recording / reproducing apparatus. 2. The optical system according to claim 1, wherein the intensity of the reproduction light is adjusted at a plurality of positions on the optical information recording medium, and the reproduction light intensity over the entire recording range is determined by linear interpolation. Information recording / reproducing apparatus. 3. The optical system according to claim 1, wherein the intensity of the reproduction light is adjusted at a plurality of positions on the optical information recording medium, and the reproduction light intensity over the entire recording range is determined by polynomial approximation. Information recording / reproducing apparatus.