JPH09297944A - Information reproduction control method for optical magnetic information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a scanning direction diameter so as to improve apparent resolution by reducing a Kerr rotational angle by head produced by light spot irradiation and making a reproducing signal to respond to a part formed by eliminating a response limit region from an irradiation part in order to form the response limit region. SOLUTION: The strength and scanning speed of a light spot 102 are set in a magneto-optical disk having a plurality of marks magnetized on a recording surface, and this spot is irradiated with a light. Because of the irradiation, a temperature distribution protruded in the center is formed inside the light spot 102. A Kerr rotational angle is reduced by heat produced thereby, and a response limit region 101 is formed. Thus, after a recording layer 105 is cooled to a room temperature after scanning of the light spot, the magnetization of the recording layer 105 is recovered to a state before the scanning and the shape of a mark 104 is read. Thus, since a reproducing signal reflects the response of a part formed by eliminating the response limit region 101 from the irradiation part of the light spot 102, the scanning direction diameter of the light spot 102 is shortened to the diameter of an effective spot 103 and seeming resolution is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reproduction control method for reproducing information from a magneto-optical information recording medium capable of increasing the information recording density.

[0002]

2. Description of the Related Art Generally, a magneto-optical information recording medium (hereinafter referred to as a magneto-optical disk) irradiates a laser beam onto a magneto-optical recording film to raise the temperature of an irradiated portion of the magneto-optical recording film to a Curie temperature. Information is recorded by changing the magnetization direction from the other part. At the time of reproduction, by utilizing the fact that the reflected light of the laser light irradiated by this magnetization displacement is deflected by the Kerr effect (Kerr effect), it is read out through the polarization state of the reflected light from this medium, and after being converted into an electric signal by a photoelectric conversion element, It is electrically processed and restored as information. A recording portion recorded as a magnetic domain on the magnetic layer by the irradiation of the laser light is called a mark, and the laser light irradiated to detect the mark is called a light spot.

In order to read the mark on the magneto-optical information recording medium and restore it to the recorded information, a signal-to-noise ratio of a predetermined value or more depending on the error rate / modulation method / signal detection method of the recording medium and the reproducing apparatus. (S / N ratio) is required. However, due to the recent demand for higher recording density, finer marks and higher recording linear density in the light spot scanning direction are being used, and the mark length and the mark interval are shortened. The reproduced signal strength decreases in the part that is continuous with an interval, and the local S
There is a problem that the / N ratio deteriorates and the error rate at the time of restoring information increases.

For example, when the wavelength of the light source is λ, the numerical aperture of the objective lens is NA, and the diameter of the light spot is λ / NA, for example, an optical system with λ = 680 nm and NA = 0.55 can be obtained. Sufficient intensity to accurately determine the presence / absence of a mark even when scanning a portion where marks having a diameter of 0.40 μm are continuously formed every 0.80 μm using a light spot having a diameter of 1.2 μm. The reproduction signal of is the precision that cannot be obtained.

To solve this problem, a magnetic super-resolution recording medium composed of a plurality of magnetic layers is used, and the magneto-optical super-resolution magnetic film is scanned with a light spot so that a part of the magnetic layer in the light spot is scanned. A method of forming a mask magnetic domain and thereby obtaining an effect equivalent to that of reducing a spot and improving the apparent resolution of an optical system is disclosed in JP-A-3-93056 and JP-A-3-93.
It is disclosed in Japanese Patent Publication No. 058.

[0006]

In the technique of using the magnetic super-resolution recording medium composed of a plurality of magnetic layers according to the prior art, the reproduced signal waveform from the magnetic super-resolution recording medium is asymmetric in the longitudinal direction. However, complicated signal processing is required, which is disadvantageous in terms of the scale of the signal processing circuit.

Further, in the prior art, the S / N ratio in the reproduced signal is lowered and the error rate at the time of restoring the information is increased with the occurrence of the operation noise due to the deformation of the mask magnetic domain.
There is also a problem that there is a limit to the increase in recording density.

Further, in the prior art, the optical spot for recording and reproducing is distorted due to the variation of the optical system and the variation of the mechanical system,
As a result, there has been a problem that the transfer characteristics of the reproduced signal vary or deteriorate. In order to solve these problems, a waveform equalization circuit may be provided to electrically improve the transfer characteristic. However, this method also reduces the interference between codes and improves the signal amplitude. Although it can be done, it causes a problem that noise is also increased. In addition, because the characteristics of the device vary from device to device / magneto-optical disk, it is necessary to set the waveform equalization circuit for each device, and also to set the equalization circuit for each magneto-optical disk, and also for the inner and outer disks. There was also a problem that it was necessary to switch.

An object of the present invention is to eliminate the above-mentioned problems caused by the prior art, and when the recording density of an information recording / reproducing apparatus using a magneto-optical recording medium is increased, the recording linear density limit mentioned above is exceeded. An object of the present invention is to provide an information reproduction method for a magneto-optical recording medium and an information reproduction control method for a magneto-optical information recording medium that absorbs variations in signal characteristics due to various factors.

[0010]

In order to achieve the above object, an information reproducing control method for a magneto-optical information recording medium according to the present invention records and reproduces information on a magneto-optical information recording medium by irradiation of laser light by a magneto-optical effect. A magneto-optical reproduction system
The carrier intensity in the reproduction signal obtained by scanning the mark formed with the linear density substantially equal to the cut-off spatial frequency of the magneto-optical reproduction system is ++ 1 with respect to the increase of the reproduction light amount by +1 dB.
The magneto-optical information recording medium uses a magneto-optical information recording medium in which the noise intensity in the reproduced signal increases at a rate of change of +1 dB or less with respect to an increase in the amount of reproduction light of +1 dB when increasing at a rate of change of 1 dB or more. With respect to the recording medium, the carrier intensity is +1 dB and the reproduction light amount is increased by +1 dB.
It is characterized in that the output value of the optical head is controlled so that the mark is scanned with the reproduction light amount in the range increasing with the above change rate.

Further, the information reproducing control method for a magneto-optical information recording medium according to the present invention comprises a magneto-optical reproducing system for recording and reproducing information on the magneto-optical information recording medium by a magneto-optical effect by irradiation of a laser beam, and the magneto-optical reproducing system. Scan a mark formed with a linear density substantially equal to the cut-off spatial frequency and the carrier intensity in the reproduced signal obtained by scanning a mark formed with a linear density sufficiently lower than the cut-off spatial frequency of the system. By using a magneto-optical information recording medium in which the difference in carrier intensity in the reproduced signal obtained by decreasing with the increase of the reproducing light amount, the magneto-optical reproducing system to the cut-off spatial frequency for the magneto-optical information recording medium A range in which the carrier intensity in a reproduction signal obtained by scanning marks formed with substantially equal linear density increases at a rate of change of +1 dB or more with respect to an increase of the reproduction light amount of +1 dB. The second feature scanning a mark reproducing light quantity.

Further, the present invention is characterized in that, in the information reproduction control method according to the above feature, the amplitude of the reproduction signal or the differential amplitude thereof when controlling the output value of the optical head is detected and the reproduction light amount is reset. And

[0013]

DETAILED DESCRIPTION OF THE INVENTION An information reproduction control method for a magneto-optical information recording medium according to an embodiment of the present invention will be described below with reference to the drawings. 1 is a diagram for explaining an equalization method of an information reproduction control method according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of a recording medium used in this embodiment, and FIG. 3 is this embodiment. FIG. 4 is a diagram for explaining an example of the structure of a recording medium used, FIG. 4 is a diagram for explaining temperature characteristics of a magnetic layer in the recording medium used in this embodiment, and FIG. 5 is a response limitation of the recording medium of this embodiment. FIG. 6 is a diagram for explaining a change in resolution due to formation of a region, FIG. 6 is a diagram for explaining a change in a signal level according to the reproduction light amount and a method for setting the reproduction light amount according to the present embodiment, and FIG. 7 is a waveform equalization according to a conventional technique. FIG. 8 is a diagram showing an example of a circuit, FIG. 8 is a diagram showing a circuit for learning and controlling the equalization characteristic according to the present invention, FIG. 9 is a diagram for explaining the principle of a method for learning the reproduction characteristic, and FIG. It is a figure which shows an example of the reproduction signal from which a characteristic differs.

First, the concept of the present invention will be described. As described in the section of the means for solving the above-mentioned problems, the present invention provides carrier strength in a reproduced signal obtained by scanning a mark formed with a linear density substantially equal to the cut-off spatial frequency of the reproducing optical system. Is + 1d with respect to an increase in the reproduction light amount of +1 dB
A recording medium in which the noise intensity in the reproduced signal increases at a rate of change of +1 dB or less with respect to an increase of the amount of reproduction light of +1 dB when increasing at a rate of change of B or more is used. The feature is that the range is set to increase at a change rate of +1 dB or more with respect to the increase.

Further, according to the present invention, the carrier intensity in a reproduced signal obtained by scanning a mark formed with a line density sufficiently lower than the cut-off spatial frequency of the reproduction optical system and the cut-off spatial frequency are substantially the same. Using a recording medium in which the difference in carrier intensity in a reproduction signal obtained by scanning marks formed with equal linear density decreases with an increase in reproduction light amount,
The reproduction light quantity is + 1d with respect to the increase of the reproduction light quantity in which the carrier intensity in the reproduction signal obtained by scanning the mark formed with the linear density substantially equal to the cut-off spatial frequency is +1 dB.
The feature is that it is set in a range that increases at a change rate of B or more. Further, in the magneto-optical reproduction system having the above characteristics, the present invention provides an optimum transfer characteristic based on the phase information detected by the signal amplitude of the reproduction signal under a certain amount of reproduction light or the slice level. It is characterized by controlling the reproduction power.

The reason for using the above-mentioned recording medium in the present invention is as follows.
By appropriately setting the intensity of the light spot and the scanning speed of these media, a region in which the Kerr rotation angle is reduced by being heated by irradiation in the light spot (hereinafter, this region in which the Kerr rotation angle is lowered is referred to as This is to form a “response restriction area”).

That is, in magneto-optical recording, since the reproduction signal is obtained by detecting the rotation of the plane of polarization of the reflected light from the magneto-optical recording medium, the region where the Kerr rotation angle is decreased in the temperature rising portion becomes the reproduction signal. Taking advantage of not contributing much,
The playback signal is configured to be obtained from the part where the response limit area is excluded from the light spot irradiation part, and as a result, the same effect as when the diameter of the light spot in the scanning direction is shortened is obtained, and the apparent resolution of the optical system is obtained. Is to improve.

This response-limited region has a Ke due to temperature rise.
Since it is a region where the rr rotation angle is reduced, it is not necessary to apply a magnetic field to form the response limiting region.
Since the rr rotation angle changes continuously with respect to the temperature of the recording film, there is no clear boundary portion such as a domain wall unlike the mask area due to the magnetic domain, so that the formation of the response limiting area is spatially continuous. It is possible to continuously change the transfer characteristic together with the reproduction light amount. Further, for the same reason, it is possible to prevent the occurrence of operation noise peculiar to the conventional magnetic super-resolution operation caused by the domain wall movement during scanning. At the same time, the reproduced signal has good symmetry between the front edge and the rear edge of the mark, which is advantageous in terms of the scale of the signal processing circuit. Even when the marks are formed adjacent to each other, unlike the mask region formed by the magnetic domains, the response limited area has less nonlinearity of the magneto-optical reproduction signal due to the magnetic interaction with the mark magnetic domains. That is, the response when a plurality of marks are adjacent to each other can be accurately approximated by adding the responses when the respective marks are individually present. Further, as described above, the amplitude of the reproduction signal when controlling the output value of the optical head or the differential amplitude thereof is detected, and the reproduction light amount is reset, so that there is a variation in each device / magneto-optical disk and the inner and outer circumferences of the disk. Can be easily corrected. The above is the basic concept of the present invention.

Now, an example of the structure of the magneto-optical disk (magneto-optical information recording medium) used in this embodiment will be described with reference to FIG. FIG. 3A shows a sectional structure of a magneto-optical disk composed of one magnetic layer, and FIG. 3B shows a sectional structure of a magneto-optical disk composed of two magnetic layers.

The magneto-optical disk shown in FIG. 3A has a light-transmissive first protective layer 203a on a light-transmissive substrate 202.
And the recording layer 105 is formed on the first protective layer 203a.
And a second protective layer 203 on the recording layer 105.
b and the reflective layer 204 are sequentially stacked. This reflective layer 20
4 if necessary, further UV resin protective film layer 205
May be formed.

The first protective layer 203a also serves as an interference layer for increasing the apparent Kerr rotation angle of the recording layer due to multiple interference. The recording layer 105 has a room temperature T
_It is a ferrimagnetic film having a finite coercive force Hc and a Kerr rotation angle θ _K near _ROOM , and has a temperature characteristic as shown in FIG. This temperature characteristic shows that when the temperature T is raised, the holding force Hc diverges at a compensation temperature T _COMP = 170 ° C.
The characteristic is zero near the Curie temperature Tc = 240 ° C. On the other hand, the rotation angle θ _K decreases as the temperature T rises, and represents the characteristic that at T = Tc, Hc = 0 and the rotation angle θ _K = 0 and the paramagnetic state occurs.

The magneto-optical disk shown in FIG. 3B has a light-transmissive first protective layer 203a on a light-transmissive substrate 202.
And the reproducing layer 106 is formed on the first protective layer 203a.
The recording layer 105 and the second protective layer 203b.
Are sequentially stacked. If necessary, a UV resin protective film layer 205 may be further formed on the second protective layer 203b.

The first protective layer 203a also has a function as an interference layer for increasing the apparent Kerr rotation angle of the reproducing layer 106 due to multiple interference. As shown in FIG. 4B, the compensation temperatures of the recording layer 105 and the reproduction layer 106 are T _COMP1 = 0 ° C., T _COMP2 = 200 ° C., and Cu.
A ferrimagnetic film having a rie temperature of Tc1 = 150 ° C and Tc2 = 260 ° C is preferable. Also, T _COMP1 is T
Before and after _ROOM , T _COMP2 has a value around Tc1, and the relations of T _COMP1 <T _COMP2 and T _ROOM <Tc1 <Tc2 are established.

When the magneto-optical disk thus formed is irradiated with a light spot, the temperature of the recording film at the irradiated portion locally rises and the Kerr rotation angle changes. This state will be described next with reference to FIG.

First, FIG. 2A shows the magnetic domain distribution on the surface of the recording film on the surface of the magneto-optical disk shown in FIG. 3A, the magnetic domain distribution seen from the cross section of the magneto-optical disk, and the recording on the magneto-optical disk. It is a figure showing the temperature and Kerr rotation angle distribution of a film. The length and direction of the arrow in the magnetic layer indicate the magnitude and direction of magnetization, respectively.

In the magneto-optical disk according to the present embodiment, the recording layer 105 is a ferrimagnetic material, and as shown in FIG. 4A, when the temperature T is increased, the Kerr rotation angle θ _K becomes the temperature T.
Has a characteristic that it decreases with an increase in temperature and becomes a paramagnetic state with a Kerr rotation angle θ _K = 0 at a temperature T = Tc. Therefore, as shown in FIG. 2A, when a magneto-optical disk having a plurality of marks magnetized in advance on the recording surface is irradiated with the intensity and scanning speed of the light spot 102 set appropriately, the light spot 1
The inside of 02 has a temperature distribution of a curve whose center protrudes due to irradiation, and this heating forms a response limiting region 101 (shown by crossed diagonal lines in the figure) in which the Kerr rotation angle is reduced. The maximum temperature T _RD of the response limiting area 101 is C
It is set lower than the urie temperature Tc, and is selected so that the coercive force Hc of the recording layer 105 at the maximum temperature T _RD is sufficiently larger than the demagnetizing field and the like.

As a result, if the recording layer 105 is cooled to the room temperature T _ROOM after the scanning of the light spot, the magnetization of the recording layer 105 is restored to the state before the scanning, so that the shape of the mark 104 is not affected by the reading operation. .

In magneto-optical recording, since the reproduction signal is obtained by detecting the rotation of the plane of polarization of the reflected light from the magneto-optical recording medium 100, the region where the Kerr rotation angle in the temperature rising portion is greatly reduced is not much in the reproduction signal. It will not contribute. That is, in the present embodiment, the response of the reproduced signal is the portion of the portion irradiated with the light spot 102 excluding the response limiting area 101 (the modified crescent moon portion of the circle of the light spot 102 excluding the shaded inner circle portion of the response limiting area 101). As a result, the same effect as that when the diameter of the light spot 102 in the scanning direction is shortened to the diameter of the effective spot 103 (corresponding to the width on the right side of the modified crescent moon portion) is obtained, and the apparent appearance of the optical system is obtained. The resolution of can be improved.

Also in the magneto-optical disk shown in FIG. 3B, the apparent resolution of the optical system can be similarly improved. That is, the present magneto-optical disk is as shown in FIG.
The holding force Hc2 diverges once around the compensation temperature T _COMP2 , and C
a recording layer 105 of a ferrimagnetic material having a characteristic of becoming zero at the urie temperature Tc2, and a compensation temperature around the temperature T = T _ROOM ,
The Kerr rotation angle θ _K decreases as the temperature T increases, and
= Tc2, a reproduction layer 106 of a ferrimagnetic material having a paramagnetic state with a rotation angle θ _K = 0 is laminated.
The recording layer 10 is formed on the reproducing layer 106 in a state around the temperature T = T _ROOM.
5 has a characteristic that the magnetic domain distribution shapes of the reproducing layer 106 and the recording layer 105 are the same, by transferring the magnetic domains, ie, marks.

A light spot 1 is applied to this magneto-optical disk.
When the intensity of 02 and the scanning speed are appropriately set and the irradiation is performed, a response limiting region 101, which is heated by the irradiation and has a reduced Kerr rotation angle, is formed in the light spot 102 as shown in FIG. 2B. The maximum temperature T _RD of the response limiting region 101 is set lower than Tc2, and Hc2 of the recording layer 105 at T _RD is selected to be sufficiently larger than the demagnetizing field or the like.

As a result, the shape of the mark 104 in the recording layer 105 at the time of scanning by the light spot 102 is not affected by the temperature increase at the time of scanning, and the reproducing layer 106 in the response limiting area 101 is affected by the temperature increase. K
The err rotation angle θ _K decreases.

In magneto-optical recording, the rotation of the plane of polarization of the reflected light from the magneto-optical recording medium 100 is detected to obtain a reproduction signal. Therefore, the response-decreasing region in which the Kerr rotation angle in the temperature-raising portion of the reproduction layer is greatly reduced is It does not contribute much to the reproduction signal. That is, as in the above embodiment, the reproduction signal mainly reflects the response of the portion excluding the response limited region 101 from the irradiated portion of the light spot 102, so that the diameter of the light spot 102 in the scanning direction is shortened to the width of the effective spot 103. The same effect as described above can be obtained and the apparent resolution of the optical system can be improved. 2B is similar to FIG. 2A, the magnetic domain distribution on the surface of the recording film on the surface of the magneto-optical disk, the magnetic domain distribution seen from the cross-sectional direction of the magneto-optical disk, the temperature of the recording film on the magneto-optical disk, and It is a figure showing Kerr rotation angle distribution. The length and direction of the arrow in the magnetic layer indicate the magnitude and direction of magnetization, respectively.

An example of a change in resolution when the response limiting area 101 is formed by scanning a light spot having an appropriate amount of light on the magneto-optical disk thus constructed at an appropriate speed is shown in FIG.
Shown in In FIG. 5, an optical head having a characteristic of wavelength λ = 0.68 μm and aperture lens numerical aperture NA = 0.55 is used, and the vertical axis indicates the spectrum intensity of the magneto-optical reproduction signal and the cut-off of the reproduction optical system. It is normalized by the spectrum intensity in the vicinity of direct current (1/10 of cut-off spatial frequency) sufficiently lower than the spatial frequency.

The diameter of the light spot in this example is 0.8.
9 μm, cut-off spatial frequency 2.3 × 10 ^
It is equal to the length of two cycles of ³¹ p / mm (“^” is an operator representing a power). In the figure, the recording film is not sufficiently heated in the range of the reproducing light amount P _RD = 1.0 mW, and the response limiting region 101 is hardly formed while the response is lowered. On the other hand, in the state of P _RD = 3.0 mW, the response limiting region 101 is formed, and the response of the mark formed at the spatial frequency about 1/2 times or more the cut-off spatial frequency of the optical system is particularly large. You can see that it has been improved.

Next, the change in the signal level of the magneto-optical reproduction signal with respect to the reproduction light amount according to the above-described embodiment will be described with reference to FIG. 6 using the spatial frequency of the mark as a parameter.

First, in an ideal case where the decrease in carrier strength due to the decrease in Kerr rotation angle due to the increase in temperature of the magnetic film can be generally ignored, the carrier strength in a normal magneto-optical reproducing system is proportional to the reproducing light quantity, The amount of increase in carrier intensity with respect to the increase in light intensity of +1 dB is +1 dB. However, as shown in FIG. 5, a magneto-optical reproduction signal (carrier shown by a solid line) obtained from a mark having a spatial frequency of 2.3 × 10 ^ ³¹ p / mm equal to the cut-off spatial frequency of the reproduction optical system is reproduced. By forming the response limiting region in the range of the light amount of 1.0 mW or more, the Ke due to the temperature rise of the magnetic film
The apparent resolution of the reproducing optical system can be remarkably improved more than the decrease of the rr rotation angle, and the carrier intensity can be increased by +1 dB or more while the reproducing light amount is increased by +1 dB.

Therefore, in the present embodiment, when a mark having a density equal to the cut-off spatial frequency of the reproducing optical system is reproduced, the reproduction light amount is set within a range in which the increase of the carrier intensity with respect to the increase of the reproduction light amount by +1 dB exceeds +1 dB. As a result, it is possible to obtain a magneto-optical reproduction signal with an improved response especially at a high spatial frequency.

As described above, the response limiting region in the present invention is due to the region where the Kerr rotation angle decreases due to the temperature rise, and it is not necessary to apply a magnetic field specially to form the mask region. Further, since these responses continuously change with respect to temperature, there is no clear boundary portion such as a domain wall unlike the mask region due to magnetic domains, and the formation of the response limiting region is spatially continuous. Therefore, it is possible to prevent the occurrence of operation noise peculiar to the conventional magnetic super-resolution operation caused by the movement of the magnetic domain wall during scanning.

[0039] in the case of reproducing the mark of equal spatial frequency 2.3 × 10 ^ ³¹ p / mm cut-off spatial frequency of the reproducing optical system in FIG. 6, the spatial frequency 2.3 × 10 ^ ³¹ p /
The noise intensity around mm is also shown in the lower part of the figure. In the case of the magnetic super-resolution medium disclosed in Japanese Patent Application Laid-Open No. 3-93058, the noise intensity in the reproduced signal is +1 dB with respect to the increase of the reproduction light amount of +1 dB in the reproduction light amount before and after the formation of the mask magnetic domain. There is a region that increases at a rate of change that greatly exceeds it. On the other hand, in the present embodiment, the noise intensity in the reproduction signal monotonically increases as the reproduction light amount increases, but the increase rate of the noise intensity with respect to the reproduction light amount is always + 1d.
It can be B / dB or less.

Further, in this embodiment, even if the marks are formed adjacent to each other, the non-linearity of the magneto-optical reproduction signal due to the magnetic interaction between the mark magnetic domain and the response limiting region is small in principle. That is, the response when a plurality of marks are adjacent to each other can be accurately approximated as an addition of responses when each mark is individually present.

In the reproduction light amount setting range shown in FIG.
FIG. 1 shows an example of realizing the optimum equalization characteristic for the actual modulation method. In FIG. 1A, an optical head having a wavelength λ = 0.68 μm and a numerical aperture of a focusing lens NA = 0.55 is used, and the linear velocity of the optical head at this time is V = 10 (m / s),
This is an example in which the present embodiment is applied to an NRZ (non-return-zero) modulation method. The horizontal axis in the figure is the frequency f (MHz) obtained by multiplying the spatial frequency on the horizontal axis shown in FIG. 5 by the linear velocity V.

In this case, the spot diameter Ws narrowed down on the disc is generally given by (λ / NA), and Ws =
It becomes 1.2 μm. Here, in FIG. 1, the original signal characteristic 301 is obtained at a low reproduction light amount of 1 mW. As described in FIG. 5, the cutoff frequency fc is 1 / (λ / (2 ×
NA)) × v = 16.3 (MHz). Here, when the recording linear density is 0.40 μm / bit, in the NRZ method, the shortest mark length is 0.4 μm and the period is 0.8 μm.
And the frequency is 12.5 (MHz). In order to realize this linear density, it is understood that the original signal characteristic 301 cannot be sufficiently reproduced at the shortest mark repetition frequency of 12.5 (MHz) 316, because the signal level is significantly lowered as shown in the figure. . The original reproduction signal 310 at this time is shown in FIG. In the original reproduction signal 310 as shown in the figure, it can be seen that the opening showing the reliability of detection is not opened.

On the other hand, if the ideal characteristic 302 (FIG. 1) in which the signal level is sufficient can be obtained, the NR of the above-mentioned condition is obtained.
A desired linear density can be realized by the Z method. At this time, the reproduction signal 311 has a sufficiently opened opening as shown in FIG. In order to obtain such a reproduced signal waveform, waveform equalization processing is generally performed as signal processing. For example, a waveform equalization circuit as shown in FIG. 7 is used to generate an equalization characteristic 303 that raises the signal level in a required band, in this example, around 12.5 (MHz), and the original signal characteristic 301 is set. This is a method of improving the ideal characteristic 302.

The circuit shown in FIG. 7 is called a 3-tap transversal type equalizer circuit, and has two delay circuits 40.
1 and 402, gain circuits 403 and 404, and an addition circuit 405. This circuit divides the reproduction signal output 406 which is an input signal into three. The divided signal 407 is input to the delay circuit 401 of the delay amount τ, the signal 408 is input to the delay circuit 402 of the delay amount 2 × τ, and the other signals 410 are the gain amount of (−K1). Gain circuit 40
Gain is adjusted at 3. The delay circuits 401 and 402
And the output of the gain circuit 403 are added by the adder 405 to obtain a reproduction signal 409 after equalization.

The delay amount τ in this example is generally set to about ½ of the shortest mark repetition period, and the gain amount K
1 and K2 are set so that the signal of the mark at a certain data detection point leaks to the detection points distant at intervals of 1/2 of the shortest mark repetition period before and after (inter-code interference) becomes zero. This corresponds to the equalization characteristic 303 of FIG.
Generally, the gain K1 and the gain K2 are equal values,
If the leak is asymmetrical before and after, it is set to a different value.

The method using this general waveform equalization circuit is as follows.
Although there is an advantage that intersymbol interference from adjacent marks is suppressed and the signal level is improved, there is a limit for the following reasons.
One is that if the equalization gain is high, there is a problem of increasing the noise component contained in the reproduced signal.
It is a 3-tap type that processes with three signals before and after, and there is a problem that equalization residual noise occurs due to the fluctuation of the signal level of the next two signals.

Therefore, in the present embodiment, the reproduction light amount is set as shown in FIG.
The reproducing light amount setting range shown on the right side was set to 2.5 mW. As a result, the response as shown in FIG.
The response characteristic 30 shown in FIG. 1A increases in the high frequency region.
I was able to get 4. In this power region, the signal level is improved without increasing noise as shown in FIG. However, in a higher frequency region, unnecessary high-frequency emphasis includes only noise components, and therefore, in the present embodiment, the ideal characteristic 303 is obtained through the low-pass filter 308 of FIG.
Decided to get. As a result, as shown in the right end of FIG. 10A, the reproduction signal obtained by the present embodiment was able to obtain a reproduction signal (waveform) 312 in which the influence of noise was sufficiently small and the aperture was sufficiently opened.

On the other hand, FIG. 1B is a diagram showing an embodiment in which the partial response method is applied. This partial response method is a method in which leakage from an adjacent mark is allowed, and the reproduced signal waveform is shown in FIG.
In the case of PR (1, 1) as shown in FIG. 3, ternary multi-value level detection is performed. In this example, the linear density is 0.35 μm / bit.
Therefore, the required equalization characteristic 305 needs to raise the signal level in the middle range. On the other hand, in the present embodiment, the transfer characteristic 306 is obtained by setting the reproduction light amount to 2.0 mW, and the equalization characteristic 305 for the ideal PR (1,1) and the ideal PR (1,1) are set by setting the low-pass filter 308. PR
The (1,1) characteristic 307 was obtained. As a result, as compared with the reproduction signal 313 before the reproduction power is controlled, FIG.
A highly reliable reproduction signal (waveform) 31 as shown in (b)
4 was obtained.

Next, a method of setting a reproduction power and a low-pass filter to obtain the ideal equalization characteristic shown in FIG. 1, a method of learning the equalization characteristic, and a circuit for realizing the method will be described below with reference to FIGS. It demonstrates using. FIG. 8 shows an example of a reproduction characteristic learning and reproduction power control circuit, and FIGS. 9A and 9B are diagrams showing two examples of the learning method. FIG. 9A shows a repetitive mark row 51 having different recording frequencies, which appears in the modulation method used in the apparatus as a learning area, in front of the data area on the magneto-optical disk.
7 is recorded and reproduced later to be used for learning described later. This learning area is preferably provided in a part of each zone on the disc, which is divided into the inner circumference / outer circumference / or the radial direction.

The frequency of the reproduction learning is before shipment of the drive device from the factory / when the user inserts the disc / when the discs are continuously inserted, every 30 minutes / every time recording data is recorded on the disc. It is conceivable to do it as necessary. For a rewritable recording medium, it may also be used as an area for learning the recording power, and in this case, the learning area may be rewritten and used many times. Of course, the replay learning area is recorded in advance before shipping,
Only the reproduction learning may be performed if necessary.

The principle of learning shown in FIG.
By setting the ratio of the reproduction signal amplitude 511 corresponding to the high frequency region detected by the gate 515 to a certain target value with reference to the reproduction signal amplitude 512 in the longest pattern sequence corresponding to the low frequency region detected by By controlling the reproduction power so that the signal amplitudes at the longest mark repetition frequency 315 and the shortest mark repetition frequency 316 match so that the target reproduction characteristic 302 after equalization shown in FIG. 1A is obtained. Done. In the present embodiment, learning is performed only with two frequencies, that is, the shortest pattern and the longest pattern, but it is also possible to perform learning so that the ideal characteristic 302 is more completely obtained by using a repeating pattern having a pattern length between them. .

Next, a second embodiment of learning will be described with reference to FIG. This learning utilizes the fact that the fluctuation of the reproduction characteristic shown in FIG. 1 appears at the rising or falling of the original waveform 517 of the reproduced signal. For example, when the reproduction power is 1 mW, the reproduction signal rises and falls like the pre-control characteristic 518, which reflects that the amplitude cannot be taken in the high frequency region like the original signal characteristic 301 of FIG. 1A. It can be seen that the slope is lower than the ideal characteristic 519. Here, the ideal characteristic is a reproduction signal at a reproduction power of 2.5 mW, and shows the reproduction characteristic 302 after the target equalization. Further, since the gradient of the reproduction signal is obtained by the amplitude 513 of the first-order differential signal 520 of the original waveform, the differential signal amplitude which gives the optimum reproduction characteristic is set as the slice level value 514, and the reproduction power is controlled so as to obtain this value. You may learn as you do. However, since the differential amplitude also changes with the value of the amount of light received for reproduction due to changes in the reflectance of the medium and the reproduction power, more accurate control is possible by detecting and standardizing the amount of reflected light received in the unrecorded area in advance. Becomes

Next, a circuit embodiment for realizing the learning method of FIG. 9 will be described with reference to FIG. The circuit shown in the figure receives the reproduction signal 500, which is a differential signal standardized by the amount of reflected light received in the unrecorded portion, for the learning example of FIG. A reproduced signal response learning circuit 501 for performing learning, a power setting address corresponding to the response learned by the learning circuit 501 as an input, a ROM 502 for outputting power setting digital data corresponding to the address, and the digital The learning circuit that has a D / A converter 503 that receives data as input, converts the data into analog data, and outputs the analog data, and a laser drive current source 504 that drives the semiconductor laser 505 based on the analog data, and inputs the reproduction signal 500. 501 outputs a power setting address corresponding to a response described later, and inputs this address R M50
2 outputs digital data for power setting corresponding to the input address, and the D / A converter 503 at the next stage, which has input this, performs D / A conversion, whereby the analog input by the laser drive current source 504. The output is controlled based on the voltage setting, and the semiconductor laser 505 is driven to operate so as to control the reproduction output of the semiconductor laser (optical head).

Next, the reproduction signal response learning circuit 501 described above will be described in detail. This circuit 501 includes a preamplifier 506 that amplifies the reproduction signal 500, and FIG.
A pair of peak detectors 507 for detecting the peak detection signals 511 and 512 of the amplitudes of the gate signals 515 and 516 shown in FIG. Operation to input the output signal of the divider 509 for calculating the amplitude ratio 1 / K (= B / A) of the length and the longest mark length, the peak detection signal 511 and the calculator 509, and to output the error signal of these input signals An amplifier 508 and an A / D converter 5 for converting the output of the operation amplifier 508 into digital data and outputting the digital data.
10 and is configured to output the power setting digital signal from the output of the A / D converter 510 so that the error signal from the differential amplifier 508 becomes zero.
On the other hand, in the case of the learning method of FIG. 9B, the differential amplifier 508
The slice level setting value 514 shown in FIG. 9B is input to one input of the above, and a differential is obtained with the detected differential amplitude value 513 to obtain an error signal.

As described above, by using the learning function according to the present embodiment, it is possible to absorb the fluctuation of the reproduction characteristics which varies depending on each device or when the disc is replaced. Further, although FIG. 8 does not include the electrical equalization circuit shown in FIG. 7,
The present method can also be applied to the reproduction signal 500 that has passed through the equalization circuit of FIG. 7. In this case, the nominal reproduction power is set to the intermediate value of the reproduction light amount setting range shown in FIG. 6, for example, 2.0 mW before shipment, and the reproduction characteristics of the reproduction characteristics which vary before and after the device or when the disc is replaced are changed. It should be set to a value that can increase or decrease the response to fluctuations. In this power setting, the constants of the equalization circuit shown in FIG. 7 (delay amount τ, gains K1, K
2) is set so as to have an ideal equalization characteristic 303 in the example of FIG. By doing this,
By detecting the fluctuation of the reproduction characteristic which occurs after shipment from device to device or when the disc is replaced by the above-mentioned method and adaptively controlling the reproduction power, a circuit-complex adaptive equalization (A
Optimal equalization can be performed without using daptive Equalization).

[0056]

As described above, according to the present invention, the reproduction of the carrier intensity of +1 dB in the reproduction signal obtained by scanning the mark formed with the linear density substantially equal to the cut-off spatial frequency of the reproduction optical system. The noise intensity in the reproduced signal is + when increasing with a change rate of +1 dB or more with respect to the increase of the light amount.
A recording medium that increases at a rate of change of +1 dB or less with respect to an increase of the amount of reproduction light of 1 dB is used, and the amount of reproduction light is set in a range that increases at a rate of change of +1 dB or more with respect to an increase in the amount of reproduction light having a carrier intensity of +1 dB. By utilizing the fact that the region where the Kerr rotation angle of the temperature rising part is reduced does not contribute much to the reproduction signal, the reproduction signal is obtained from the part where the response limit region is excluded from the light spot irradiation part. As a result, the same effect as that of reducing the diameter of the light spot in the scanning direction can be obtained, and the apparent resolution of the optical system can be improved.

Further, according to the present invention, the carrier intensity in a reproduction signal obtained by scanning a mark formed with a line density sufficiently lower than the cut-off spatial frequency of the reproduction optical system and the cut-off spatial frequency are substantially equal to each other. Using a recording medium in which the difference in carrier intensity in a reproduction signal obtained by scanning marks formed with equal linear density decreases with an increase in reproduction light amount,
The reproduction light quantity is + 1d with respect to the increase of the reproduction light quantity in which the carrier intensity in the reproduction signal obtained by scanning the mark formed with the linear density substantially equal to the cut-off spatial frequency is +1 dB.
By setting the range in which the rate of change increases at B or higher, the region where the Kerr rotation angle of the temperature rising portion is reduced does not contribute much to the reproduction signal, and the response limiting region is removed from the light spot irradiation portion. The reproduction signal is obtained from the portion, and as a result, the same effect as that of reducing the diameter of the light spot in the scanning direction is obtained, and the apparent resolution of the optical system can be improved. Therefore, according to the present invention, it is possible to obtain the optimum equalization characteristic for the high-density modulation system in the information reproducing apparatus regardless of the fluctuation of the optical system or the medium, and it is possible to increase the information recording density. This has a great effect on the increase of the recording information amount and the transfer rate.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an equalization method of an information reproduction control method according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation / action of the recording medium used in this embodiment.

FIG. 3 is a diagram for explaining an example of the structure of a recording medium used in this embodiment.

FIG. 4 is a diagram for explaining temperature characteristics of a magnetic layer in a recording medium used in this embodiment.

FIG. 5 is a diagram for explaining a change in resolution due to formation of a response limited area of the recording medium of the present embodiment.

6A and 6B are views for explaining a change in signal level according to the reproduction light amount and a method for setting the reproduction light amount according to the present embodiment.

FIG. 7 is a diagram showing an example of a waveform equalization circuit according to a conventional technique.

FIG. 8 is a diagram showing a circuit for learning and controlling reproduction characteristics according to an embodiment of the present invention.

FIG. 9 is a diagram for explaining the principle of the method for learning the reproduction characteristic according to the present embodiment.

FIG. 10 is a diagram showing an example of reproduced signals having different equalization characteristics according to the present embodiment.

[Explanation of symbols]

100 ... Magneto-optical recording medium, 101 ... Response limited area, 10
2 ... Optical spot, 103 ... Effective spot, 104 ... Mark, 105 ... Recording layer, 106 ... Reproducing layer, 201 ... Recording film, 202 ... Substrate, 203a, b ... Protective layer, 204 ... Reflective layer, 205 ... Protective coating layer , 301 ... Original signal characteristics, 30
3, 305, 301 ... Necessary equalization characteristics, 501 ... Reproduction signal response learning circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Awano 1-280, Higashi Koigakubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. A magneto-optical reproducing system for recording / reproducing information on / from a magneto-optical information recording medium by irradiating a laser beam, and a linear density substantially equal to a cut-off spatial frequency of the magneto-optical reproducing system. When the carrier intensity in the reproduction signal obtained by scanning the formed mark increases at a rate of change of +1 dB or more with respect to the increase in the reproduction light amount of +1 dB, the noise intensity in the reproduction signal increases with respect to the increase of the reproduction light amount of +1 dB. +
A magneto-optical information recording medium that increases at a rate of change of 1 dB or less is used, and the magneto-optical reproduction system has a rate of change of +1 dB or more with respect to the magneto-optical information recording medium with respect to an increase in the reproduction light amount when the carrier intensity is +1 dB. An information reproducing control method for a magneto-optical information recording medium, characterized in that an output value of an optical head is controlled so that a mark is scanned with a reproducing light amount in an increasing range. 2. A magneto-optical reproducing system for recording / reproducing information on / from a magneto-optical information recording medium by irradiation of laser light, and a linear density sufficiently lower than a cut-off spatial frequency of the magneto-optical reproducing system. The difference between the carrier intensity in the reproduced signal obtained by scanning the mark formed by and the carrier intensity in the reproduced signal obtained by scanning the mark formed with a linear density approximately equal to the cut-off spatial frequency is reproduced. Using a magneto-optical information recording medium that decreases with an increase in the amount of light, the magneto-optical reproducing system scans the magneto-optical information recording medium with marks formed at a linear density substantially equal to the cut-off spatial frequency. The carrier intensity in the reproduced signal is +1
Information reproduction control of a magneto-optical information recording medium characterized by controlling an output value of an optical head so that a mark is scanned with a reproduction light amount in a range increasing at a change rate of +1 dB or more with respect to an increase of a reproduction light amount of dB. Method. 3. The magneto-optical information according to claim 1, wherein the amplitude of the reproduction signal or the differential amplitude thereof when controlling the output value of the optical head is detected and the reproduction light amount is reset. Information reproduction control method for recording medium.