JPH03165354A - Method and device for inspecting magneto-optical disk - Google Patents

Abstract

PURPOSE:To easily and speedily evaluate sensitivity by recording and reproducing two signals which have the same peak power and differ in frequency and making a decision based upon the amplitude ratio of both the playback signals. CONSTITUTION:A magneto-optical pickup 32 records the high-frequency signal and low-frequency signal from a recording signal source 33 which have the same peak power on the magneto-optical disk 31. They are reproduced by the pickup 32, the amplitude values of the playback signals from a voltmeter 36 are supplied through a memory 37, and an arithmetic circuit calculates the resolution of the ratio of both the amplitudes. A comparing circuit 39 which is applied with reference values 1 and 2 decides the resolution depending merely upon the rising recording power to easily and speedily evaluate whether or not the sensitivity is within a specific range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical disk testing method and apparatus for evaluating the sensitivity of a magneto-optical disk.

[Background Art] In recent years, with the development of information technology, optical information recording and reproducing devices have been attracting attention as human figure omega storage devices.

Among these optical information recording and reproducing devices, the magneto-optical recording method is attracting attention because it is rewritable.

In this magneto-optical recording, a magnetic thin film having perpendicular magnetic anisotropy is formed on a transparent substrate by sputtering etc. as a recording medium, and information is recorded by forming bits with different magnetization directions on the magnetic thin film. .

FIG. 12 shows an example of a cross section of a magneto-optical disk, which is the recording medium. This magneto-optical disk is mounted on a polycarbonate substrate 1 with a 1 m thin PLA2. For example, a magnetic thin film made of a rare earth transition metal alloy thin film 3. and a dielectric film 4 for protection are formed in the same manner. A laser beam 5 for recording and reproducing is transmitted through the polycarbonate substrate 1 and focused on the magnetic recording film 3. When recording bits are formed on this magnetic thin film 3, the magnetization direction of the magnetic thin film 3 is aligned in one direction in advance, and then the magnetic thin film 3 is prepared from the outside! While applying the ll field, the high power laser beam is applied to the 12th
As shown in the figure, light is focused on the magnetic 7a film 3 and the temperature of the magnetic thin film 3 is raised to near the Kichori point. Since the coercive force of the heated portion decreases, the magnetization is reversed in the direction of the external magnetic field, and as shown in FIG. 13, the bit 6 is formed as a magnetization reversal domain. By moving the recording medium and constantly rotating the magneto-optical disk, the power of the laser beam is increased in a pulsed manner at the position where bit 6 is to be formed, as shown in FIG. 13, information can be recorded. It will be done.

When reading out the information recorded by the recording bit 6, a magneto-optical effect called a magneto-optical effect is used as much as possible. That is, as shown in FIG. 14, depending on the magnetization direction of the magnetic thin film 3, the polarization plane of the incident linearly polarized light is slightly rotated and reflected. Since the direction of rotation of the plane of polarization is reversed depending on the direction of magnetization, this plane of polarization can be extracted as an electrical signal by a known differential magneto-optical pickup 20 as shown in FIG.

The magneto-optical pickup 20 is equipped with a semiconductor laser 10 as a light source, and the linearly polarized light emitted from the semiconductor laser 10 is made into parallel light by a collimator lens 9, transmitted through a beam splitter 8, and then converted into a parallel light by an objective lens 7. The light is focused on the magnetic thin film 3 of the magneto-optical disk 21. In the figure, reference numeral 15 indicates the linear polarization direction of the incident light. The light reflected by the magnetic thin film 3 is
It undergoes Kerr rotation according to the magnetization direction of the magnetic i[3, passes through the objective lens 7, is reflected by the beam splitter 8, and enters the 1/2 wavelength plate 11. The azimuth angle of the wavelength plate 11 is set to 22.5° so as to rotate the plane of polarization by 45°.The light that has passed through the 1/2 wavelength plate 11 is incident on the polarizing beam splitter 12, and the beams are perpendicular to each other. The two polarized light components are respectively focused by condenser lenses 13a and 13b and received by photodiodes 14a and 14t). Then, an information signal is obtained by using a differential amplifier 22 to calculate the difference between the outputs of the photodiodes 14a and 14b.

Incidentally, one of the performances of magneto-optical disks as described above is sensitivity, and due to variations during manufacturing, the sensitivities of produced magneto-optical disks are distributed within a certain range. Those located at the ends of this distribution, that is, those that have higher or lower sensitivity than the average sensitivity, may cause problems in actual use. For example, when writing a signal on a magneto-optical disk, the output power of the laser beam is set for an average disk, so when writing a magneto-optical signal on a magneto-optical disk with low sensitivity, the output power of the laser beam is set to In some cases, this may result in recording with poor signal quality. Furthermore, high-sensitivity devices often have poor durability, such as changes in magnetic properties when erased/written many times.

Therefore, we evaluated the sensitivity of all produced magneto-optical disks or a portion of them by removing them.
It is necessary to reject discs whose sensitivity exceeds a certain range as unsuitable for use.

Conventionally, the sensitivity of magneto-optical disks has been determined by, for example, the C/
It is evaluated by the laser power at which N rises. FIG. 16 shows the results of measuring the change in C/N as the recording power is increased. In this example, as indicated by reference numeral 26, the recording power value at which the C/N rises is 4. It becomes 62mW. Since this rising recording power pth differs depending on the sensitivity, the sensitivity of the magneto-optical disk can be evaluated by measuring it.

[Problem to be solved by the invention 2fil However, from such measurements, the rising recording power p
In order to determine th, recording and playback must be performed several times while changing the recording power, which poses the problem of time-consuming measurement and the need for a device that can vary the recording power within a certain range. There are some problems.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a magneto-optical disk inspection device that can quickly and easily evaluate the sensitivity of a magneto-optical disk.

[Means for Solving the Problems] The magneto-optical disk inspection method and apparatus of the present invention record two signals of different frequencies with the same peak power on the magneto-optical disk, and perform playback corresponding to each signal. The quality of the magneto-optical disk is determined based on the ratio of the amplitudes of the signals.

[Operation] In a magneto-optical disk, the amplitude of the reproduced signal differs depending on the frequency of the recorded signal. This is because, as shown in FIG. 4, the 28 rows of recorded bits are mainly read with a reproduction beam spot 27 having a certain size.

This will be explained with reference to FIGS. 5 to 8. Fig. 5 shows the pit string when recorded at high frequency, Fig. 6 shows the reproduced signal when recorded at high frequency, Fig. 7 shows the bit string when recorded at low frequency, and Fig. 8 shows the bit string when recorded at low frequency. Figures 6 and 8 show playback signals when recorded at low frequencies.
As shown in the figure, generally the higher the frequency, the smaller the amplitude.

This is because, as shown in Fig. 5, the higher the frequency, the narrower the interval between recording bits 28, and the beam spot 27 with a finite size overlaps the adjacent bit and is influenced by this adjacent bit. This is because when recording at 100 kHz, the bit becomes larger and is affected by the temperature of the previous bit. In addition, since it is affected by the temperature of the bit, the size of the pips 1~ formed also changes depending on the laser power during recording, so even if the laser power is changed, the reproduced signal amplitude changes. That is, the amplitude increases until the bit reaches a certain size, but when the bit becomes too large, the amplitude decreases due to the influence of adjacent bits.

For these reasons, the amplitudes of the reproduced waveforms of recording signals of different frequencies exhibit different dependencies on the laser power intensity during recording. FIG. 9 shows the results of actual measurements regarding the relationship between the recording laser power and the reproduction signal amplitude, where the X mark indicates the reproduction waveform amplitude of the low frequency signal and the cross mark indicates the reproduction waveform amplitude of the high frequency signal. As shown in this figure, by appropriately selecting the low frequency and high frequency, the ratio of the respective amplitudes [playback waveform amplitude for 6-frequency recording] / [playback waveform amplitude for low-frequency recording] x 100 (%) It has become clear that the defined resolution (indicated by J5 and * in FIG. 9) changes monotonically within a certain range of recording power. Furthermore, F
As shown in the Sio diagram, when such measurements were performed on a large number of recording media with varying sensitivities, it was found that there was a monotonous dependence between the resolution and the rising recording power at a certain peak recording power. I found out something.

Such a monotonous dependence generally holds true for sensitivity variations in magneto-optical disks with a fixed basic structure, such as a laminated structure.

In the present invention, by utilizing this property, we measure the resolution at a recording power of a certain peak power, and determine whether the value falls within a certain range, thereby detecting a disk whose sensitivity is significantly out of range. be able to.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

Figures 1 to 3 relate to the first embodiment of the present invention.
Figure 2 is a block diagram showing the configuration of a magneto-optical disk inspection device, Figure 2 is a histogram of the ratio of each reproduced signal amplitude for high-frequency recording and low-frequency recording, and Figure 3 is a histogram showing the measurement results of the sensitivity of the magneto-optical disk. It is.

As shown in FIG. 1, the magneto-optical disk inspection apparatus 30 includes a magneto-optical pickup 32 that records and reproduces information on a magneto-optical disk 31, and a magneto-optical pickup 32 that records and reproduces information on a magneto-optical disk 31.
2 is provided with a recording signal source 33 that sends recording signals for inspection. Furthermore, on the output side of the magneto-optical pickup 32,
Envelope detection circuit 34. Low-pass filter (hereinafter referred to as
Written as LPF. )35. A voltmeter 36 is provided in sequence. The output of the voltmeter 36 is stored in a memory 37 via a control circuit 40. This memory 37
The output of the arithmetic operation circuit 38 is inputted to the operator circuit 38, and the output of this arithmetic operation circuit 38 is inputted to the comparison circuit 39. Further, reference value 1 and reference value 2 are input to this comparison circuit 39. Further, the recording signal source 33.
The memory 37 and the arithmetic circuit 38 are controlled by a control circuit 40.

Next, the operation of this embodiment will be explained.

The recording signal source 33 sequentially generates two recording signals having the same peak power and different frequencies under the control of the control circuit 4o. The magneto-optical pickup 32 emits a laser pulse modulated by the signal from the recording signal source 33, and performs recording on, for example, the innermost track on the magneto-optical disk 31. For recording one signal, a magneto-optical pickup 32
The signal is then played back. The envelope of this reproduced signal is detected by an envelope detection circuit 34, and is inputted to a voltmeter 36 via an LPF 35, and the amplitude of the reproduced magneto-optical signal is measured by this voltmeter 36. This amplitude is stored in the memory 37 via the control circuit 40.

Next, after erasing the signal recorded on the magneto-optical disk 31, the frequency of the recording signal is changed and recording is performed on the same innermost track. Then, in the same manner as described above, the amplitude of the reproduced magneto-optical signal is measured, and this amplitude is stored in the memory 37.
I remember it.

The arithmetic circuit 38 calculates, from the amplitude of each reproduced signal corresponding to the two recording frequencies stored in the memory 37, the ratio of both amplitudes: reproduced waveform amplitude for high frequency recording]/[reproduced waveform amplitude for low frequency recording]X100(% ), that is, the resolution is calculated and sent to the comparison circuit 39. The comparison circuit 39 determines whether or not the resolution falls within a predetermined range set by the reference value 1 and the 19 value 2, and those that fall within that range are deemed to be acceptable products, and those that are outside of this range are rejected. Outputs the determination result that the product is considered to be a good product.

As an example, for a large number of magneto-optical disks 31, the recording power is 8.5 mW, the recording pulse width is 60 nsec,
At a disk rotation speed of 180 rpm, the magneto-optical disk 3
1, the frequencies 3.7MHz and 1.3
When 8MH2 recording and reproduction were performed sequentially and the amplitude ratio of the reproduced signals was determined, the histogram shown in FIG. 2 was obtained. Here, from another measurement of the sensitivity of the magneto-optical disk 31,
It was known that those with the ratio (resolution) exceeding 55% and those below 45% are unfavorable for practical use, so as shown in Figure 2, magneto-optical materials falling within the range other than these are shown. Disc 31 was determined to be a passed product.

Next, an example of measuring the sensitivity of the magneto-optical disk 31 for setting the reference value 1 and the reference value 2 will be described with reference to FIG.

At the beginning of the production of the magneto-optical disk 31, we measured the rising recording power of several hundred disks for the purpose of investigating the sensitivity distribution, and the results were obtained as shown in the histogram of FIG. Sample disks near the upper and lower limits of sensitivity are labeled H1 to H3, 11 to H3 in Figure 3.
I selected six L3 discs and used an actual drive to find out what sensitivity they could tolerate.

First, the limits of low sensitivity are Ll, L2. Regarding L3, it was determined by the following procedure.

Drives perform recording and erasing using a specified laser power depending on the medium, but due to variations in drive circuits and pickups, it is possible that a drive with a laser power that is 10% lower than the standard value may be used. be. Also,
Although the operating environment temperature is set within a certain range, in magneto-optical recording, when the Inn humidity temperature or the medium temperature is low, the laser power becomes insufficient for a low-sensitivity medium, which is a severe condition.

Therefore, we manufactured a test drive with the laser power intentionally lowered by 10% than the standard value, placed it in a constant temperature oven at 5℃, which is the lower limit of the operating environment temperature, and similarly maintained the yif temperature at 5℃.
The disks fl 1 to L3 were driven in a thermostatic oven, recorded and reproduced, and the jitter and C/N of the reproduced signal were measured.

For example, if the C/N and jitter allowed for the medium are specified as 45 dB or more and 5 n5ec or less, it is considered that up to L2 can be used, and L2 is considered to be usable.
2 was defined as the limit product on the low sensitivity side.

On the other hand, the limit on the high sensitivity side was selected from H1 to H3 as follows.

In this case, overpower becomes a problem, contrary to the case of low sensitivity. Therefore, we intentionally increased the laser power by 1
We made a test drive heated to 0%, put it in a thermostat at 50°C, which is the upper limit of the operating environment temperature, and similarly heated it to 50°C.
The disks H1 to H3 left at a temperature of 0.degree. C. were driven in a constant temperature bath, recording and reproduction were performed, and the jitter and C/N of the reproduction signal were measured. The results are as shown in the table below. From this table, it is thought that up to H2 can be used, as in the case of low sensitivity, and H2 is considered the limit product on the high sensitivity side.

Next, the resolution of the two disks L2 and H2 was measured. The resolution was measured using a recording power of 8 mW, a pulse width of 6 Qnsec, and a frequency of 3.7 MHz and 1
．． This was done by taking the amplitude ratio of each reproduced signal when a 38MH2 signal was recorded and reproduced. As a result, values of 65% for L2 and 45% for 1''2 were obtained. From the results described above, it was concluded that a disk with sensitivity between L2 and H2 can be used, but from the above resolution measurement results, the resolution is between 45% and 65%.
It was found that disks that fall between % are usable.

Therefore, during shipping inspection of actual manufactured products, the resolution of each disk is measured and the value is between 45% and 65%.
It was possible to judge whether the sensitivity was acceptable or not based on whether the sensitivity was within the range.

The above example of sensitivity measurement is different from the example shown in FIG. 2, and is not used to determine the sheath depression of the accepted product shown in FIG.

As described above, according to this embodiment, the sensitivity of a magneto-optical disk can be evaluated quickly and simply by recording and reproducing signals of different frequencies once at a low power.
Can be judged as unsuitable.

Note that after two signals of different frequencies are sequentially recorded on adjacent tracks, these two signals may be sequentially reproduced and evaluated.

FIG. 11 is a waveform diagram of a reproduced signal for explaining the amplitude measuring method in the second embodiment of the present invention.

In the first example, signals of different frequencies were recorded and reproduced once each, and the amplitudes of each were measured.
In this embodiment, as shown in FIG.
The recording signal frequency is switched during one rotation of the clock.

The amplitudes of the reproduced signals corresponding to the two frequencies are stored in the memory 37, and the ratio thereof is determined in the same manner as in the first actual droplet example.

According to this embodiment, the sensitivity of the magneto-optical disk can be evaluated more quickly.

The other functions and effects of Structure 2 are the same as those of the first embodiment.

Note that the present invention is not limited to the above-mentioned embodiments; for example, when measuring resolution, instead of recording and reproducing signals of different frequencies, the present invention is not limited to the above-mentioned embodiments. The signal may be recorded and reproduced.

In addition, the measurement of the sensitivity of the magneto-optical disk for setting the resolution of the pass/fail boundary of the magneto-optical disk is not limited to that shown in the example. The setting may be based on whether or not there is deterioration of the medium during recording and reproduction.

[Effects of the Invention] As explained above, according to the present invention, two signals having the same peak power and different frequencies are recorded on a magneto-optical disk, and the ratio of each amplitude of a reproduced signal corresponding to each signal is Since the quality of the magneto-optical disk is determined based on this, there is an effect that the sensitivity of the magneto-optical disk can be evaluated quickly and easily.

[Brief explanation of the drawing]

Figures 1 to 3 relate to the first embodiment of the present invention.
Figure 2 is a block diagram showing the configuration of a magneto-optical disk inspection device, Figure 2 is a histogram of the ratio of each reproduced signal amplitude for high-frequency recording and low-frequency recording, and Figure 3 is a histogram showing the measurement results of the sensitivity of the magneto-optical disk. , FIG. 4 is an explanatory diagram showing recording pits and reproduction beam spots, FIG. 5 is an explanatory diagram showing a bit string when recording at high frequency, and FIG. 6 is a waveform diagram showing a reproduction signal when recording at high frequency. Fig. 7 is an explanatory diagram showing a pit string when recording at low frequency, Fig. 8 is a waveform diagram showing a reproduced signal when recording at low frequency, and Fig. 9
The figure is a characteristic diagram showing the relationship between recording laser power and reproduction signal amplitude, Figure 10 is a characteristic diagram showing the relationship between resolution and rising recording power, and Figure 11 explains the amplitude measurement method in the second embodiment of the present invention. FIG. 12 is a cross-sectional view of the magneto-optical disk, FIG. 13 is a perspective view showing bits formed on the magnetic film, and FIG. 14 shows the rotation of the plane of polarization due to the Kerr effect. An explanatory diagram, FIG. 15 is an explanatory diagram showing the configuration of the magneto-optical pickup, and FIG. 16 is a characteristic diagram showing the relationship between recording laser power and C/N. 30... Inspection device 31... Magneto-optical disk 3
2... Magneto-optical pickup 33... Recording signal source 36... Voltmeter 37...
Memory 38...3 arithmetic circuits...Comparison circuit 40...Control circuit 1st section 2nd section 3rd section 4th section 27 28 @o o. -c-4 π-throat call vJ75i bacteria 5 Fig. 6 Fig. 11 Fig. 9 Fig. 9 - 1 Power Fig. 10 Standing 1 record puff - (mW) Fig. 12 Fig. 13 Fig. 14 Ctsu () (wo (ji Fig. 15 Fig. 16 Fig. 6 snoring)

Claims (2)

[Claims] (1) Recording two signals of different frequencies with the same peak power on a magneto-optical disk, and determining the quality of the magneto-optical disk based on the ratio of the amplitudes of the reproduced signals corresponding to the respective signals. A method for inspecting a magneto-optical disk, characterized by: (2) a recording means for recording two signals of different frequencies with the same peak power on a magneto-optical disk; a reproduction means for reproducing the signal recorded on the magneto-optical disk; and a signal reproduced by the reproduction means. An inspection apparatus for a magneto-optical disk, characterized in that it comprises a determining means for determining the quality of the magneto-optical disk based on the ratio of the amplitudes of reproduction signals corresponding to the two signals.