JPH06176417A - Magneto-optical recording medium for adjustment and adjustment method for magneto-optical recording device of magnetic field modulation system - Google Patents

Abstract

PURPOSE:To adjust the position and magnetic field strength of a magnetic field modulation head in a short time by using the magneto-optical recording medium having the smaller coercive force than the magnetic field to be applied by the magnetic field modulation head at the temp. sufficiently lower than a Curie temp. CONSTITUTION:The magnetic field modulation device is subjected to the position adjustment of the magnetic field modulation head under prescribed conditions by using the magneto-optical recording medium for adjustment having Tc deg.C Curie temp. and <=HcOe coercive force at a temp. t(t<Tc) deg.C on a substrate having optical guide grooves. The laser spot on the medium under these conditions has about t deg.C temp. and, therefore, when the magnetic field modulation head comes into the laser spot, the coercive force of the part is HcOe or below and is sufficiently before the Curie temp. Tc deg.C and, therefore, the magnetization inversion takes place and the observation of magneto-optical signals is possible as well. As a result, the relative alignment of the magnetic field modulation head and the optical head is easily executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field adjusting disk used for adjusting a magnetic field applying section of a magneto-optical recording device for recording information by irradiating a magneto-optical recording medium with a light beam and applying a magnetic field. The present invention relates to an adjusting method using the same, an optical head inspection disk for reading information written on an optical disk or a magneto-optical disk, and an inspection method using the disk.

[0002]

2. Description of the Related Art In recent years, as an information recording apparatus, an optical disk capable of increasing the capacity, particularly a magneto-optical disk capable of recording and reproducing, has been commercialized and used in various fields.

Conventionally, the relative alignment between the magnetic field modulation head and the optical head in a magnetic field modulation type magneto-optical recording device depends on the assembling accuracy, and the magnetic field intensity is adjusted using a Gauss meter.

Further, a magneto-optical disk uses a magnetic layer as a disk recording layer, holds recorded information in the direction of magnetization on this magnetic layer, and irradiates a linearly polarized laser beam on this recording layer at the time of reading to reflect light. The information is read out by utilizing the phenomenon (Kerr effect) in which the polarization direction of (3) rotates depending on the magnetization direction of the irradiation portion of the recording layer. Therefore, the optical head for reading out the magneto-optical disk has a polarization detecting optical system.

By the way, since the polarization detection is performed in this way, when there is a difference in the polarization characteristics of the optical components in the read head of the magneto-optical disk, especially, there is a phase difference between the two polarization components. If there is a cause for causing a phase difference in the magneto-optical disk, the reproduction signal from the optical head will change. More specifically, it is known that PC (polycarbonate), which is often used as a substrate for optical discs, has birefringence. Due to this birefringence, reflected light for reading has a polarization state, especially a signal reproduction in a phase difference. Receive a harmful disturbance. Further, some reflection parts are provided in the optical head in order to obtain small size and light weight, but the reflection at these parts also causes harmful disturbance to the polarization state (phase difference). The direction of the read signal changes depending on the combination of the phase differences of the optical head and the disk. In order to prevent this, in the magneto-optical disk system, it is necessary to manage the polarization component phase difference in each of the optical head and the disk. The phase difference of the optical head can be known by measuring the phase difference of each optical component forming the head.

[0006]

Among the above-mentioned conventional examples, the method of adjusting the magnetic field strength of a magnetic field modulation type magneto-optical recording apparatus using a Gauss meter is used when the magnetic field generation area of the magnetic field modulation head is large to some extent. This method can be applied only in. If the magnetic field modulation is driven at a high frequency in order to perform the adjustment quickly, the magnetic field generation area becomes small, which causes the following problems, which hinders the adjustment to be speeded up.

(1) There is a limit to the assembly accuracy of the magnetic field modulation head, and since the position is not checked directly, the yield is deteriorated due to the smaller magnetic field generation area.

(2) If the magnetic field generation area is not sufficiently large with respect to the sensor area of the Gauss meter, the measured value will fluctuate depending on the measuring position, and correct adjustment will not be possible.

The following method is used as an adjusting method for solving each of these problems.

(I) Position adjusting method Using a conventional magneto-optical recording medium, the magnetic field modulation head is moved in the XY directions at a constant rate relative to the optical head to perform magnetic field modulation recording / reproduction / erasing. Three operations are performed, and the magnetic field modulation head is moved to the center of the region where a constant CN ratio is obtained by looking at the map of the CN ratio of the reproduced signal obtained at this time.

(II) Method of adjusting magnetic field strength The magneto-optical recording medium used for the adjustment is adjusted by an optical modulation method using a bias magnet coil (this is calibrated with a Gauss meter) whose magnetic field strength in a wide magnetic field generation region is known. Data of the CN ratio of the magnetic field strength is saved, the magnetic field modulation head to be adjusted is driven by DC, the same magneto-optical recording medium is recorded / reproduced by the optical modulation method, and the magnetic field modulation head is compared with the above-mentioned CN ratio data. Calibrate the magnetic field generated by.

However, even if these methods are used, there is a limit to the positional accuracy and it takes much time for the adjustment, so that it is not practical.

Therefore, an attempt was made to determine whether or not the magnetic field modulation head is located above the recording beam spot by using a normal magneto-optical recording medium by observing the reflected light during recording in the recording process by direct magnetic field modulation. The recording at this time is recording in the vicinity of the Curie temperature, but at the Curie temperature, the Kerr rotation angle becomes 0, so that a sufficient magneto-optical signal could not be obtained. In addition, in a normal magneto-optical recording medium, the coercive force rapidly increases below the Curie temperature in order to improve the pit storage property, and the magnetization reversal itself does not occur at a recording power lower than the Curie temperature. It was found that it was difficult to determine with.

On the other hand, the magneto-optical disk system which manages the polarization component phase difference in each of the optical head and the optical disk has the following problems.

Generally, the phase difference of optical components can be measured by a measuring instrument such as an ellipsometer, but it is difficult to use a usual ellipsometer for an optical device having a complicated structure such as an optical head. Yes, you have to use very specific measuring equipment.

It is possible to measure the phase difference of each optical component constituting the optical head and estimate the phase difference of the assembled optical head, but the required phase difference is the combined total. In order to obtain this, (A) If setting and managing the phase difference of each part in anticipation of the worst, setting an unreasonably high demand for each part will reduce the yield.

(B) In order to manage the overall phase difference from the combination of the phase differences of each part, it is necessary to manage the phase difference of each component.

From these, a simple method for inspecting the phase difference of the entire optical head is required. Further, such a method of inspecting the phase difference of the entire optical head is also necessary for the inspection optical head for shipping the disk in order to guarantee the performance of the optical head.

As a simple method for such an inspection, several kinds of disks for inspection having known phase differences are applied to the optical heads to be inspected, and the magneto-optical signals obtained from these disks are compared to determine the optical head. A method of estimating the phase difference can be considered.

However, the above method is not only complicated with the use of several kinds of inspection disks, but also has the problem that the phase difference of the disks includes some uncertainty depending on the location. is there. Particularly, it is difficult to measure the phase difference of a disk having a normal guide groove using a normal ellipsometer, and the reliability of the measured value becomes low.

The present invention has been made in view of the problems of the above-described conventional technique, and it is an object of the present invention to realize a method capable of adjusting the position of the magnetic field modulation head and the magnetic field strength in a short time. To aim.

Another object of the present invention is to realize a method and apparatus which can easily carry out phase difference inspection of the entire optical head.

[0023]

An adjusting magneto-optical recording medium of a magnetic field modulation type magneto-optical recording apparatus of the present invention is a magnetic field modulation type magneto-optical recording apparatus including a magnetic field applying section and an optical head. An adjusting magneto-optical recording medium used when adjusting a position and a magnetic field strength with respect to an optical head, wherein the temperature of the medium irradiated with a light beam by a magnetic field modulation type magneto-optical recording device is the Curie temperature of the medium. The recording layer has a layer that has a coercive force sufficiently lower than the magnetic field strength applied by the magnetic field applying unit.

In this case, it is possible to use one in which the coercive force of the recording layer is very small, and the magnetization does not saturate in the range of the magnetic field strength to be adjusted and has a substantially proportional relationship.

As an adjusting method using the above-described magneto-optical recording medium, the relative position between the magnetic field applying section and the optical head is referred to by referring to the magneto-optical signal when the light beam is applied to the adjusting magneto-optical recording medium. The magnetic field strength of the magnetic field applying unit may be changed so that the amplitude of the magneto-optical signal is saturated.

An optical head inspection disk according to the second structure of the present invention comprises a substrate having no birefringence, a magneto-optical recording layer including at least one magnetic layer provided on the substrate, and a magneto-optical recording layer. An optical layer having a birefringence provided on the opposite side of the substrate is used, and an optical layer whose birefringence index radius distribution is generally known is used.

In this case, the radius distribution of the birefringence of the optical layer may be measured in advance.

The optical layer may be composed of an optical crystal.

At least one of the axes of birefringence of the optical layer is
One may be oriented radially and the birefringence may be arranged to change radially.

As an optical head inspection method using the optical head inspection disk as described above, the phase difference of the optical head may be obtained from the amplitudes of the reproduced magneto-optical signals at two points having different radii.

The optical head inspection disk may be constructed such that at least one of the birefringent axes of the optical layers is oriented in the same direction over the entire area of the optical disk. As a head inspection method, the phase of the optical head may be detected from the change in the amplitude of the reproduced magneto-optical signal with respect to the rotation of the disk.

Further, the phase difference of the optical head may be detected from the reproduction magneto-optical signal amplitude having a half cycle of the disk rotation in synchronization with the disk rotation and the DC component of the reproduction magneto-optical amplitude.

[0033]

According to the present invention, by using a magneto-optical recording medium having a coercive force smaller than the magnetic field applied by the magnetic field modulation head at a temperature sufficiently lower than the Curie temperature, the magnetic field is generated at a temperature (laser power) at which a magneto-optical signal is sufficiently generated. Since the magnetization is inverted according to the magnetic field applied by the modulation head, the relative position of the magnetic field modulation head and the optical head can be adjusted directly while monitoring the magneto-optical signal. Further, if a magneto-optical recording medium manufactured so as to have a magnetic field strength for which the magnetic field strength at which the magnetization at the temperature during adjustment is saturated is adjusted, the magneto-optical signal monitored after the position adjustment of the magnetic field modulation head is The magnetic field strength can be adjusted directly by setting the magnetic field modulation head at the point where saturation begins.

Further, the coercive force is very small and almost zero.
When using a magneto-optical recording medium having a layer in which the magnetization does not saturate in the range of the magnetic field strength to be adjusted and is almost proportional, the magnetic field strength and the magneto-optical signal output have a proportional relationship. The position can be adjusted more accurately, and the magnetic field intensity can be adjusted to an arbitrary value of the magnetic field intensity by establishing the relationship between the magnetic field intensity and the magneto-optical signal output in advance instead of one point as described above. Can be adjusted. Further, it is possible to measure the generated magnetic field intensity distribution of the magnetic field modulation head. In order to make the coercive force small and the magnetization proportional to the applied magnetic field as described above, it is possible to use a material having a large saturation magnetization including Gd or the like having an extremely small anisotropy energy.

[0035]

EXAMPLES The present invention will be described more specifically below with reference to examples.

[Example 1-1] The Curie temperature was 170 ° C on a polycarbonate substrate having an optical guide groove,
Also, TbFe having a coercive force of 300 Oe or less at 110 ° C.
Using a magneto-optical recording medium for adjustment in which a Co film is sandwiched by a silicon nitride protective film and an Al film is further formed, a wavelength of 7
80 nm, NA (numerical aperture) 0.55, generated magnetic field ± 300
The position of the magnetic field modulation head of the magnetic field modulation driving device of Oe or higher (1 MHz) was adjusted at a laser power of 2.5 mW and a linear velocity of 7.0 m / sec.

FIG. 1 is a graph showing temperature characteristics of coercive force of the adjusting magneto-optical recording medium used in this example. In the figure, 1 is T
The temperature dependence curve of the coercive force of the bFeCo film is shown by 2, the applied magnetic field strength of the magnetic field modulation head, 3 at room temperature (25 ° C.), and 4 at the Curie temperature (170 ° C.) of the TbFeCo film.

Under the above-mentioned conditions, the temperature of the laser spot on the medium is around 110 ° C. Therefore, when the magnetic field modulation head comes over the laser spot, the coercive force of that portion is 300.
Since it is less than Oe and well before the Curie temperature, magnetization reversal occurs, and a magneto-optical signal can be observed. This facilitates relative alignment between the magnetic field modulation head and the optical head. Furthermore, if the magnetic field intensity of the magnetic field modulation head is changed after alignment to adjust to a position where the magneto-optical signal amplitude is saturated, the magnetic field intensity at which the magnetization of the adjusting magneto-optical recording medium is saturated at about 110 ° C. ( The magnetic field modulation head can be adjusted (measured in advance).

[Embodiment 1-2] Tb having a Curie temperature of 170 ° C. on a polycarbonate substrate having an optical guide groove.
An exchange-coupling two-layer film in which a FeCo film and a GdFeCo film having a Curie temperature of 350 ° C. and a single layer having a small coercive force even at room temperature are laminated is sandwiched by a silicon nitride protective film, and
1 film was formed. Such an adjusting magneto-optical recording medium is
The coercive force of the GdFeCo film at 180 ° C., which is higher than the Curie temperature of the TbFeCo film, is very small because it is not exchange-coupled and is around 50 Oe. Using this medium, the same magnetic field modulation driving device as in Example 1-1 was used with a laser power of 6 m.
The magnetic field modulation head position was adjusted at W and a linear velocity of 7.0 m / sec.

FIG. 2 is a graph showing temperature characteristics of coercive force of the adjusting magneto-optical recording medium used in this example. In the figure, 2 is the applied magnetic field intensity of the magnetic field modulation head, 5 is the temperature dependence curve of the coercive force of the adjusting magneto-optical recording medium, and 6 is the Curie temperature (350 ° C.) of the GdFeCo film.

Under the above-mentioned conditions, the temperature of the laser spot on the medium is around 180 ° C. Therefore, when the magnetic field modulation head comes over the laser spot, the coercive force of that portion is 30.
Since it is less than Oe (50 Oe) and well before the Curie temperature (because it is higher than the Curie temperature of the TbFeCo film, it is a characteristic of the GdFeCo film single film), the magnetization reversal occurs and the magneto-optical signal can be observed. This facilitates relative alignment between the magnetic field modulation head and the optical head. Further, the magnetic field strength can be adjusted as in [Example 1-1]. However, in [Example 1-1], the coercive force greatly changes due to the temperature change on the medium (including the change in the laser power), and the coercive force at room temperature must be small, so that the pit storage stability is low. bad. Therefore, this medium cannot be used as an ordinary magneto-optical recording medium. On the other hand, the medium of this example has a high Curie temperature of the GdFeCo film and a small coercive force, and therefore is resistant to temperature changes during adjustment and can have a high coercive force at room temperature. Can be used as

[Embodiment 1-3] The adjusting magneto-optical recording medium of this embodiment has a Curie temperature of 350 ° C. on a polycarbonate substrate having an optical guide groove and a coercive force of almost 0 at room temperature. And the magnetic field strength at which the magnetization is saturated is 1
A GdFeCo film of about KOe was sandwiched with a silicon nitride protective film, and an Al film was further formed. In the adjusting magneto-optical recording medium having the above-described configuration, the magnetization has a substantially proportional relationship with the applied magnetic field.

Using this medium, the same magnetic field modulation driving device as in Example 1-1 was used with a laser power of 1.2 mW and a linear velocity of 7.0.
The magnetic field modulation head was aligned at m / sec.

FIG. 3 is a diagram showing the MH characteristic of the coercive force of the adjusting magneto-optical recording medium used in this example at room temperature. In the figure, 7 is the MH curve of the GdFeCo single layer film.

Since the adjusting magneto-optical recording medium of the present example has a coercive force of almost 0 at room temperature or higher, it has a small magnetic field strength at any value as long as the laser power does not exceed the Curie temperature of 350 ° C. or higher. Magnetization reversal also occurs, and a magneto-optical signal is also observed.

Since the applied magnetic field and the magnetization are proportional to each other, if the data of the magneto-optical signal with respect to the applied magnetic field is obtained by using a bias magnet (calibrated by a Gauss meter) whose magnetic field strength is known beforehand, After adjusting the mounting position of the modulation head, the magnetic field modulation head can be adjusted to an arbitrary magnetic field strength while observing the magneto-optical signal. (In addition, the intensity distribution of the magnetic field modulation head can be measured.) In the case of this embodiment, there is almost no dependence on the temperature of the medium (including the laser power) [Example 1-1], [Example 1]
-2] makes it easier to adjust the position and magnetic field strength.
However, since the coercive force is almost 0 even at room temperature, the pits cannot be stored and therefore cannot be used as a normal magneto-optical recording medium.

[Embodiment 2-1] Next, an embodiment according to the second configuration of the present invention will be described. FIG. 1 is a diagram showing the structure of an inspection disk according to the present invention.

In FIG. 1, 401 is an optical layer, 402 is a substrate,
403a is a protective upper layer, 403b is a magnetic recording layer, 40
3c is a protective underlayer. The protective layers 403a and 403c not only protect the magnetic material of 403b, but also control the heat conduction process in the photothermal writing process when writing the pits. Further, it has a function of amplifying the Kerr rotation of magneto-optical property due to multiple reflection, and various configurations other than this embodiment can be adopted. Here, 403a, 403b, 40
When 3c is collectively referred to as a magneto-optical layer 403, such a magneto-optical layer 403 is not limited to this example, but a single layer of magnetic material or a heat conductive layer having a heat conduction effect is added, for overwriting. For example (for other purposes), a magnetic layer having a multi-layered structure different in composition has been presented before.
The present invention is applicable to all these magneto-optical layer configurations.

Although not shown, a protective coat for protecting the magneto-optical film is provided under the magneto-optical layer 403, or a disk having the same structure as that shown in the figure is adhered with the optical layers facing each other. It is also possible to bond them via (light curing or thermoplastic) to form a double-sided disc.

The substrate 402 is made of an isotropic refractive index material such as glass and has a phase difference of almost zero. Also, the substrate 40
In No. 2, a pre-groove is formed so that tracking at the time of reading is possible.

The optical layer 401 is made of, for example, a polycarbonate material having birefringence by injection molding or the like, which is the same as an ordinary optical disk. The flat plate thus formed generally has a main axis in a radial direction or a direction perpendicular thereto, that is, an in-plane direction, and has birefringence. However, since the present optical layer does not have a pre-groove, the phase difference between the polarized light in the radial direction and the in-plane direction perpendicular to the radial direction, that is, the circumferential direction can be measured by a single unit by an ordinary ellipsometer or the like.
When the measurement of such an optical layer is performed, as is well known, the phase difference between the polarized light in the radial direction and that in the tangential direction is substantially equal on the same circumference, and the value changes depending on the radius.

The optical layer 401 for which the radial distribution of retardation has been measured as described above is bonded to the glass substrate 402 via an ultraviolet curing adhesive.

In the disc having such a structure, unlike the conventional disc, the birefringence of the substrate 402 is almost zero, and the phase difference distribution of the optical layer 401 is known by actual measurement.

Furthermore, the center value of the phase difference distribution in the radial direction of the disk can be set to a suitable value depending on the thickness of the optical layer. That is, the phase difference ψ of the optical layer 401 is the thickness of the optical layer 401 d, and the difference in birefringence Δn.
Then, it is represented by ψ = 2π × Δn / λ × d (where ψ is radical), and can be set in a form substantially proportional to the thickness d of the optical layer. The thickness d of the optical layer can be changed by the optical head within a range in which the imaging performance of the laser used is kept good when reading or writing. That is, it is desirable that the optical layer and the substrate have a total thickness of about 1.0 to 1.5 mm, and particularly preferably 1.2.
It is desirable that the thickness is ± 0.1 mm, and thus the thickness d of the optical layer is preferably about 0.3 to 1.0 mm. Within this range, the central value of the phase difference can be set in the range of nearly three times.

The phase center value at this time varies depending on the molding conditions of the polycarbonate material and the like, but is approximately −several degrees to −2.
It becomes possible to set the angle to about 0 °, which is a value at which the later-described phase difference detection is sufficiently possible. In addition, the change of the phase difference with respect to the radius also depends on the molding conditions of the polycarbonate material and the optical layer 401.
It is possible to change the phase difference by approximately several degrees to 20 degrees, although it changes depending on the thickness of the.

In this embodiment, the optical layer is integrally formed. However, as shown in FIG. 5, the optical layer has ring-shaped parts formed under different molding conditions and each part has a different phase difference. It is also possible to construct a disc with various optical layers.

If the disk shown in FIG. 5 is further explained, 501a, 501b and 501c are polycarbonate zonal optical layer portions formed on the substrate 501 under different forming conditions, each of which is measured by an ellipsometer or the like. After actually measuring the phase difference, the optical layer 501 is formed by adhering it on the substrate as described above (in addition, it is possible to divide the optical layer 501 more than this example). This optical layer 501 also has a distribution in the radial direction, and its phase difference is actually measured.

The disk thus formed has birefringence anisotropy on the surface of the substrate and has a known radial distribution of phase difference.

Next, a method of inspecting the phase difference of the optical head using the disk formed as described above will be described.

First, recording / reproducing of magneto-optical recording is performed on this disk by using a reference optical head. The reference optical head is an optical component with a known phase difference and is manufactured by using all the components, and it is particularly preferable that the optical component is selected so that the overall phase difference is zero. FIG. 6 shows the magneto-optical signal amplitude when the reference optical head reads each part in the radial direction of the optical disk.

In FIG. 6, the vertical axis represents the value of the magneto-optical signal amplitude (relative value), the upper horizontal axis represents the disk radius, and the lower horizontal axis represents the phase difference of the disk optical layer measured at each radius.

As is well known, the magneto-optical signal has the following dependence on the phase difference of each part.

Magneto-optical signal = cos (δ _H + δ _M + δ _S ) where δ _H is the phase difference of the optical head, δ _M is the phase difference of the magneto-optical layer δ _S is the phase difference from the other optical path of the disk.

In the case of the present disc, δ _S is almost determined by the phase difference of the optical layer measured previously. δ _H becomes 0 when the reference head is used. On the other hand, δ _M is the phase difference of the magneto-optical layer, and generally depends on the configuration of the magneto-optical layer because it depends on the multiple interference effect between the magneto-optical layers, but it is also possible to take a layer configuration that is set to almost 0 in advance.

From this, the amplitude of the magneto-optical signal changes in the form of cos with respect to the radial position of reading, that is, the phase difference of the optical layer.

The maximum value is calculated by applying the measured value shown in FIG. 6 to cos. The phase difference δ of the magneto-optical layer due to the maximum value
_M is given. The phase difference δ _{M of the} magneto-optical layer is added as a correction value to determine the phase difference distribution in the radial direction of the present inspection disk.

Next, FIG. 7 shows a result of measuring the magneto-optical signal amplitude for each radius by reproducing the present inspection disk with the optical head which is not measured.

In FIG. 7, the vertical axis represents the amplitude of the magneto-optical signal,
The horizontal axis represents the disk phase difference at the reading point obtained from the relationship between the radius and the phase difference of the inspection disk to which the correction value has been added. When the measured value is applied to cos in the same manner as in the above case to obtain the maximum phase difference of the disk, this becomes the value of the reverse sign of the head phase difference.

FIG. 8 is a diagram showing the structure of an inspection device for executing these inspections.

The optical head is usually formed integrally with an actuator for performing the tracking and focusing operations of the head, and this description adds a method for inspecting the actuator unit. However, this method is effective for inspection of a single unit including an actuator unit such as a drive unit, or inspection of a unit that optically configures an optical head.

In FIG. 8, 804 is an inspection disk, 805 is a spindle motor, 806 is a linear motor, 807 is an actuator head to be inspected, 808 is a controller, 8
09 is an AC coupler, 810 is a peak / bottom detector, 8
Reference numeral 11 is an A / D converter, and 812 is a computer.

An actuator head 807 including an optical head to be inspected is fixed on a linear motor 806. The magneto-optical signal S8 is output from the actuator head 807.
12, a servo error signal for focus and track is output. Further, the linear motor 806 is equipped with a linear encoder (not shown), and a position signal indicating the position of the actuator in the disk radial direction is output. The position signal and the servo error signal are input to the controller 808.
The controller 808 performs servo control using the servo error signal, and outputs an operation signal for the actuator head 807 to perform a predetermined operation.
Output to. The controller 808 also outputs a drive signal for driving the linear motor 806 and also inputs an actuator position signal from the linear motor 806 and outputs it to the personal computer 812.

The AC coupler 809 extracts only the vibration component of the magneto-optical signal, and the peak / bottom detector 810 detects the peak value and the bottom value. The peak value and the bottom value are A / D converted by the A / D converter 811 and input to the computer 812.

In the computer 812, the magneto-optical signal amplitude is calculated from the A / D converted peak / bottom values, and from this and the actuator position signal, cos is calculated in the same manner as in FIG.
Then, the phase difference of the optical head is obtained. As a result, the correction value δ _M of the optical disc phase difference is stored in the computer 812. Also, the optical head phase difference defining range is stored in the computer 812 in advance, and the obtained optical head phase difference is compared with the previously stored optical head phase difference defining range to determine whether the optical head phase difference performance is acceptable or not. It can also be configured to.

[Embodiment 2-2] The inspection disk of this embodiment is an inspection disk having a structure in which the characteristics of the optical layers are different from those shown in FIG. 1 in [Example 2-1]. The layer structure is the same as that shown in FIG. The structure of the inspection disk of this embodiment will be described below.

As the substrate in this embodiment (the substrate 402 in FIG. 4), an isotropic refractive index material such as glass, that is, a material that brings about an optical phase difference is used, and tracking is possible at the time of reading. A pre-groove is formed.

The optical layer (optical layer 401 in FIG. 4) is
Made of uniaxial optical liquid crystal material, liquid crystal material, organic film, etc.,
Optically has substantially uniaxial refractive index anisotropy, and
The main axis of the refractive index is the same in the entire optical layer and in the plane perpendicular to the laminating direction of the optical layers.

Such an optical layer can be obtained, for example, by cutting a single crystal of uniaxial crystal such as quartz into a plane parallel to the optical axis. Further, a liquid crystal material, particularly preferably a ferroelectric liquid crystal material, which is oriented in one direction by an electric field or tension, can be used as the optical layer. Similarly, an organic sheet such as polyvinyl chloride is spread. It is also possible to use the one. All of these are so-called refractive index materials that have substantially refractive index anisotropy, and the principal axis direction (optical axis direction) of the refractive index is aligned in the sheet (layer) plane and in the same direction. In addition, it has a characteristic that it is optically highly transparent. The present invention can be used for all materials having such conditions.

In the optical layer as described above, the polarized light traveling perpendicular to the layer surface has different refractive indexes in the direction of the optical refractive index principal axis and the direction perpendicular thereto. Therefore, a phase difference occurs in the polarized light after passing through. This phase difference ψ is given by ψ = [(n′-n), where d is the thickness of the optical layer, n ′ is the refractive index of the polarized light in the principal axis direction, and n is the refractive index of the polarized light in the principal axis vertical direction. Xd] / λ × 2π.

Here, assuming that the thickness of the optical layer is 10 μm, when λ = 830 nm, a phase difference of about 39 ° occurs in polarized light in the main axis and the polarized light in the direction perpendicular to the main axis.

The optical layer of this embodiment will be described in more detail. A circular quartz crystal plate cut out on a plane parallel to the principal axis is polished to produce two annular discs. The two discs are polished to have a thickness difference of 10 μm, and are laminated so that their principal axes are orthogonal to each other to form an optical layer. In general, crystal materials such as quartz crystal have their refractive index almost determined when the wavelength and cut-out surface orientation are determined, and the phase difference of polarized light (main axis and its vertical axis) incident perpendicularly to this is almost determined only by the thickness difference. Therefore, it is preferable in terms of uniformity and stability as compared with other polymer materials and the like. Such an optical layer has a uniaxial refractive index anisotropy substantially because the principal axes intersect perpendicularly.

When the phase difference of each part of the optical layer thus produced was measured using an ellipsometer, a phase difference of approximately 39 ° was observed.

The optical layer thus produced was laminated on the glass substrate on which the magneto-optical layer was formed in the same manner as in Example [2-1], and the inspection disk having the layer structure shown in FIG. 4 was obtained. It was made.

The main difference between this example and Example [2-1] lies in the direction of the principal axis of the substantial uniaxial refractive index anisotropy in the optical layer. In the example [2-1], the main axis faces the radial direction, whereas in the present example, the main axis faces the same one direction in the plane.

The effect of this difference on the optical head is shown in FIG.
Will be described with reference to.

In the figure, 907 is an optical head (or actuator unit), 904 is an inspection disk, and 914 is an information track formed on the inspection disk. The optical head 907 reads the magneto-optical pit signal on the track 914 with a laser beam while tracing the track 914 on the disk 904. The laser light at this time is linearly polarized light, and its polarization direction always forms a constant angle with respect to the track radial direction. Although this angle differs depending on the configuration of the optical head, for example, the polarization direction and the radial direction coincide with each other in this embodiment, and this direction is shown as a laser light polarization direction 913 by an arrow in FIG.

The axis of the refractive index anisotropy of the optical layer of the disc 904 for inspection is oriented in a fixed direction over the entire plane of the disc, and the direction with respect to the optical head changes as the disc rotates. FIG. 9 shows the relationship between the axis of anisotropic refractive index of the disc optical layer and the direction of laser polarization at a certain moment.

Reference numeral 913 is the above-mentioned laser light polarization direction for reading, 915 is the direction of the refractive index anisotropy axis of the disk optical layer at the moment of the illustrated state, and 916 is the disk rotation axis direction. As is apparent from FIG. 9, as the inspection disk 904 rotates in the disk rotation axis direction 916, the angle formed by the reading laser beam polarization direction 913 and the disk optical layer refractive index anisotropic axis direction 915 makes the disk rotation. Changes synchronously (at the same cycle).

As described above, the amplitude of the magneto-optical signal detected through the optical layer having the phase difference between the orthogonal polarization components and the axis of which is rotated is represented by the following formula. A {cos δ _S cos (δ _H + δ _M ) -cos Z θ sin
δ _S sin (δ _H + δ _M )} where A is the disc reflectivity, a constant due to the magneto-optical performance of the magneto-optical layer, δ _S is the phase difference of the optical layer, and θ is the optical layer refractive index anisotropy axis. Angle formed by the polarization direction of the laser light for
δ _H is the phase difference of the head, and δ _M is the phase due to the magneto-optical layer.

As is apparent from FIG. 9, θ becomes the same as the disc rotation angle by synchronizing the disc rotation with the disc and making the start point of the disc rotation proper.

An example of the magneto-optical signal amplitude detected in this way is shown in FIG. In FIG. 10, the horizontal axis represents the rotation angle of the disk and the vertical axis represents the magneto-optical signal amplitude.

As is apparent from the above equation, the amplitude of the magneto-optical signal changes in cos as the disk rotates, and the cycle becomes half of the disk rotation cycle. Taking the ratio of the amplitude of this magneto-optical signal amplitude change (portion indicated by A in FIG. 10) and the DC component (portion indicated by D in FIG. 10), from the above equation, D / A = tan δ _S tan (δ _H + Δ _M ).

Here, δ _S is determined by the thickness T of the two crystal plates forming the optical layer described above. Moreover,
By measuring this optical layer with an ellipsometer, it can be obtained or confirmed by actual measurement. In this embodiment, it is 39 ° ± 0.5 °.

Next, the magneto-optical signal is recorded / reproduced in the reference optical head having the phase difference of 0 as a whole on the present inspection disk. The recording pits are preferably repetitive signals with a constant pit length in order to measure the amplitude of the magneto-optical reproduction signal, and a pit length of 1 to 2 μm is particularly preferable.
When this magneto-optical recording signal was reproduced by using the same head and the amplitude of the magneto-optical reproduction signal was detected, it was observed that the magneto-optical recording signal fluctuated cos with respect to the disk rotation as shown in FIG.
When the amplitude A of this fluctuation and the DC component D are obtained and the ratio between them is taken, the phase difference of this reference head is 0, so that D / A = tan δ _S tan δ _M. δ _M is determined from δ _S = 39 °.

Next, when this disc is reproduced by the inspection head and D and A are obtained in the same manner as described above, δ _H is obtained from the relationship of D / A = tan δ _S tan (δ _H + δ _M ).

The method for detecting D and A will be described in more detail. FIG. 11 is a diagram showing an embodiment of the detection method of D and A described above, and the same reference numerals as those in FIG. 8 indicate the same. The magneto-optical reproduction signal S812 read out in substantially the same manner as the embodiment shown in FIG.
After only the vibration component is taken out, the vibration component is input to the peak hold circuit 1117 and the bottom hold circuit 1118.
The peak hold circuit 1117 controls the magneto-optical reproduction signal S812.
Hold the peak of the vibration part of. This hold time is set to several to several tens of magneto-optical recording signal pits on the disc. Similarly, the bottom hold circuit 1117
Holds and outputs the bottom of the amplitude of the magneto-optical reproduction signal for several to several tens of pits. These hold times are long for the pits on the disc, but short enough for one cycle of the disc rotation, giving the envelope waveform of the magneto-optical reproduction signal and The amplitude variation as shown in 10 can be reproduced almost faithfully.

The outputs from the peak hold circuit 1117 and the bottom hold circuit 1118 are differentiated by the differential circuit 1119. The output from the differential circuit 1119 has the magneto-optical reproduction signal amplitude as shown in FIG. This differential circuit 1
The output from 119, that is, the amplitude of the magneto-optical reproduction signal is
It is input to the integrating circuit 1120 and the lock-in amplifier 1121.

On the other hand, the rotation of the spindle motor 805 is
It is detected by a rotation detector such as a rotary encoder (not shown). The output of the rotation detector is the rotation synchronization signal generator 1
It is input to 124, and based on this, the rotation synchronization signal generator 1
A rotation synchronizing signal is generated from 124. This rotation synchronization signal is output from the rotation synchronization signal generator 1124 and input to the lock-in amplifier 1121. Lock-in amplifier 11
21 uses the rotation synchronizing signal to output the differential circuit 111 described above.
Of the amplitude of the magneto-optical reproduction signal from No. 9, a frequency component that is synchronized with rotation and has a rotation cycle and a 1/2 cycle is output to the A / D converter 1123.

The magneto-optical reproducing signal amplitude inputted from the differential circuit 1119 to the integrating circuit 1120 is integrated in the integrating circuit 1120 for a time sufficiently longer than the rotation cycle, and the magneto-optical reproducing signal amplitude corresponding to D in FIG. , And outputs it to the A / D converter 1122.

The A / D converters 1123 and 1124 are A
/ D conversion is performed and the output is output to the computer 812. In the computer 812, D. A is obtained, and at the same time, the phase difference of the optical head is calculated from the information of δ _S and δ _M stored in advance.

This embodiment has the following advantages.

Since the inspection can be performed in one track on the disk, the area of the optical layer is limited to a ring-shaped limited area, particularly a small area near the minimum readable radius of the drive equipped with the optical head to be tested. This not only requires a small crystal area when a uniform optical crystal is used, but also requires a small area that requires uniformity in thickness, etc. , Easy to make.

The radial variation with respect to the characteristics of the optical layers and the like can be almost ignored. In particular, since there is no variation in the characteristics, phase difference, reflectance, Kerr rotation index, etc. of the magneto-optical layer, the influence of these on the magneto-optical reproduction signal can be ignored, and the head phase difference measurement error caused by the variation does not occur. Further, due to the reproduction characteristics of the optical head, workability is excellent because only one track is required for measurement regardless of the inner and outer track ratios.

This embodiment has the following advantages by synchronizing the amplitude of the magneto-optical reproduction signal with the disk rotation and extracting the 1/2 cycle component of the rotation. That is, even with respect to the variation in the circumferential direction of the inspection disk, 1/2 of the rotation speed
Since only the periodic component (and DC component) is used, 1/2
Variations other than the period can be removed.

Especially, the fluctuation of the reproduction signal due to the influence of the disc eccentricity has a period of the number of revolutions, so that it can be eliminated.

In this embodiment, the lock-in amplifier 1121 is used to synchronize with the rotation speed based on the rotation cycle signal from the spindle motor. However, if the spindle rotation speed is stable, this rotation speed signal is used. Lock-in amplifier 1121 with a bandpass filter centered at twice the frequency
Can be used instead of the above to simplify the structure of the inspection method. Also,
It is also possible to use a suitable low pass filter instead of the integrator 1120.

[0107]

Since the present invention is constructed as described above, it has the following effects.

According to the first and third aspects and methods, there is an effect that the position of the magnetic field modulation head and the magnetic field intensity can be adjusted in a short time while directly watching the magneto-optical signal. Also, the coercive force is almost 0 from around room temperature.
If the medium of is used, it is possible to measure the magnetic field intensity distribution of the magnetic field modulation head.

According to the fourth and eleventh aspects and the method, there is an effect that the phase difference inspection of the optical head can be easily performed by using one inspection disk whose phase difference distribution is known. .

[Brief description of drawings]

FIG. 1 is a temperature characteristic diagram of coercive force in Example [1-1].

FIG. 2 is a temperature characteristic diagram of coercive force in Example [1-2].

FIG. 3 is an MH characteristic diagram at room temperature in Example [1-3].

FIG. 4 is a diagram showing a layer structure of Example [2-1].

FIG. 5 is a diagram showing a configuration of an optical layer in Example [2-1].

FIG. 6 is a diagram showing a radius of a disc and a magneto-optical reproduction signal amplitude according to an example [2-1].

FIG. 7 is a diagram showing a relationship between a magneto-optical reproduction signal and an optical head phase difference at the time of inspection in Example [2-1].

FIG. 8 is a diagram showing a configuration of an inspection device using the embodiment [2-1].

FIG. 9 is a diagram showing the refractive index main axis of the disk and the polarization direction of the reading laser in Example [2-2].

FIG. 10 is a diagram showing a relationship between a disk rotation angle and a magneto-optical signal amplitude at the time of inspection in Example [2-2].

FIG. 11 is a diagram showing a configuration of an inspection apparatus using Example [2-2].

[Explanation of symbols]

 1 Temperature dependence curve of coercive force of TbFeCo film 2 Applied magnetic field strength of magnetic field modulation head 3 Room temperature (25 ° C) 4 Curie temperature of TbFeCo film (170 ° C) 5 Temperature dependence curve of coercive force of Example 6 GdFeCo film Curie temperature (350 ° C.) 7 MH curve of GdFeCo single layer film 401, 501 Optical layer 402, 502 Substrate 403 Magneto-optical layer 403a Protective upper layer 403b Magnetic recording layer 403c Protective underlayer 501a-501c Optical layer portion 804 Inspection disk 805 Spindle motor 806 Linear motor 807 Actuator head 808 Controller 809 AC coupler 810 Peak / bottom detector 811, 1122, 1123 A / D converter 812 Computer 904 Inspection disk 907 Optical head 913 Laser beam polarization method 914 tracks 915 the refractive index anisotropy axis direction 916 disk rotational direction 1117 peak hold circuit 1118 bottom hold circuit 1119 differential circuit 1120 integrated circuit 1121 lock-in amplifier 1124 rotation synchronizing signal generator

Claims (11)

[Claims] 1. A magneto-optical recording medium for adjustment used for adjusting the position and magnetic field strength of a magnetic field applying section with respect to an optical head in a magnetic field modulation type magneto-optical recording apparatus having a magnetic field applying section and an optical head. Then, the temperature of the medium in the portion irradiated with the light beam by the magnetic field modulation type magneto-optical recording device is sufficiently before the Curie temperature of the medium, and the coercive force at that temperature is sufficiently smaller than the magnetic field intensity applied by the magnetic field applying section. An adjusting magneto-optical recording medium having a recording layer. 2. The adjusting magneto-optical recording medium according to claim 1, wherein the coercive force of the recording layer is very small, and the magnetization does not saturate in a range of the magnetic field strength to be adjusted, but has a substantially proportional relationship. A characteristic magneto-optical recording medium for adjustment. 3. An adjusting method for a magnetic field modulation type magneto-optical recording device using the adjusting magneto-optical recording medium according to claim 1 or 2, wherein a light beam is applied to the adjusting magneto-optical recording medium. The magnetic field applying unit and the optical head are relatively aligned with reference to the magneto-optical signal at the time, and thereafter, the magnetic field strength of the magnetic field applying unit is changed so that the amplitude of the magneto-optical signal is saturated. Method for adjusting magnetic field modulation type magneto-optical recording device. 4. A substrate having no birefringence, a magneto-optical recording layer including at least one magnetic layer provided on the substrate, and a magneto-optical recording layer provided on the opposite side of the magneto-optical recording layer from the substrate. An optical head inspection disk, comprising: an optical layer having a refraction, wherein the optical layer has a birefringence index whose radius distribution is generally known. 5. The optical head inspecting disk according to claim 4, wherein the optical layer inspecting disk has a radius distribution of birefringence that can be measured in advance. 6. The optical head inspection disk according to claim 4 or 5, wherein the optical layer comprises an optical crystal. 7. The optical head inspection disk according to claim 4, wherein at least one of the birefringence axes of the optical layer is directed in the radial direction, and the birefringence is changed in the radial direction. An optical head inspection disk characterized in that 8. A phase difference of an optical head is obtained from the amplitudes of reproduced magneto-optical signals at two points having different radii by using the optical head inspection disk according to any one of claims 4 to 7. Characteristic optical head inspection method. 9. The optical head inspection disk according to claim 4, wherein at least one of birefringence axes of the optical layer is oriented in the same direction over the entire area of the disk. Optical head inspection disk. 10. A phase difference detection method for an optical head, wherein the optical head inspection disk according to claim 9 is used to detect the phase of the optical head from an amplitude change of a reproduction magneto-optical signal with respect to disk rotation. 11. The optical disk for optical head inspection according to claim 9, wherein the reproduction magneto-optical signal amplitude and the DC component of the reproduction magneto-optical amplitude are synchronized with the disk rotation and have a half cycle of the disk rotation. A method of detecting a phase difference of an optical head, which is characterized by detecting a phase difference of the optical head.