JPH05342676A - Test device for magnetic-optical disk - Google Patents

Abstract

PURPOSE:To provide a small-sized test device for a magneto-optical disk which can easily test defects of the magneto-optical disk in a short time. CONSTITUTION:A test device for a magneto-optical disk irradiates a recording medium in which information is magnetically recorded with a light flux polarized in a prescribed direction, divides reflected or transmitted light flux from the above medium modulated in a polarized state in accordance with the above information by the magnetic optical effect into two light flux polarized in the direction of being orthogonally crossed each other, detects the divided two light flux with a detecting means respectively, and detects a magneto-optical signal with differential output of the detected signal. This device is provided with means 10, 15 which are provided in a light path through which the light flux passes through and causes two different variations of phase difference, and a means for detecting defects accompanying variation of phase difference in the recorded medium by processing arithmetically the magneto-optical signal corresponding to those two different variations of phase difference obtained by this means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a local birefringence abnormality existing in a magneto-optical disk for recording and reproducing information on a recording medium by utilizing a magneto-optical effect, and a change in reflected light quantity due to the presence of foreign matter. Regarding inspection equipment suitable for detecting,
In particular, the present invention relates to a magneto-optical disk inspection apparatus that detects defects from changes in phase difference.

[0002]

2. Description of the Related Art A disk drive device is used as a device for inspecting defects of a magneto-optical disk at a product level, and a recording area of a disk in which a signal is not recorded is traced to detect defects such as a change in reflectance of the disk. There is a method of detecting an abnormal portion, or a method of recording a magneto-optical signal on a disc and reproducing the recorded signal and binarizing the signal to determine whether or not there is an abnormality. Further, as a device for detecting a change in phase difference due to birefringence of a disk substrate or a local abnormality in a magneto-optical film, various phase difference measuring devices for detecting a change in polarization state are used.

FIG. 5 is a block diagram showing an example of a conventional phase difference measuring apparatus. In the figure, a linearly polarized light beam emitted from the semiconductor laser denoted by 61 is a collimator lens 62.
After being collimated by the laser beam, the beam is passed through the beam shaping prism 63, the beam splitter 64, and the beam splitter 65, and then narrowed down to the medium surface of the magneto-optical disk 67 by the objective lens 66.
The light flux reflected by the medium surface passes through the objective lens 66, a part of it is reflected by the beam splitter 65, and after passing through the ½ wavelength plate 68 and the phase compensation plate 69, the condenser lens 70.
Then, the polarized beam splitter 71 separates the two polarized light beams orthogonal to each other and enters the detectors 72 and 73, respectively. 1 /
The two-wave plate 68 is installed in a direction in which the plane of polarization of the linearly polarized light passing therethrough is rotated by 45 ° with respect to the plane of incidence of the polarization beam splitter 71. A Babinet Soleil compensator is generally used as the phase compensator 69. Of the light flux reflected by the medium surface, the light flux transmitted through the beam splitter 65 is reflected by the beam splitter 64, passes through the condenser lens 74, and then the detector 7
Up to 5. The detector 75 is a detector for detecting a servo signal, and uses the signal obtained from the detector 75 to focus the light flux narrowed down by the objective lens 66 on the medium surface of the magneto-optical disk 67 and to perform tracking control. To do.

In order to measure the phase difference of a magneto-optical disk using this device, the amplitude of the magneto-optical signal as the output of the differential amplifier 76 obtained from the disk under test on which a signal of a constant frequency is recorded is monitored. Meanwhile, the phase compensator 69
Use to change the phase. Since the amplitude of the magneto-optical signal is maximized when the phase difference generated by the measured disk is canceled by the phase compensator 69, the compensation amount of the phase compensator 69 at this time represents the phase difference of the measured disk.

FIG. 10 schematically shows a phase difference measuring device for a magneto-optical disk using a Babinet-Soleil phase compensator. As shown in FIG. 10, a Babinet-Soleil phase compensator 95 is inserted in the optical path of an optical system for reproducing a magneto-optical signal by irradiating the magneto-optical disk 82 on which the magneto-optical signal is recorded with laser light, Read the amplitude change of the magneto-optical signal while changing the phase difference given to the beam little by little,
The phase difference at the point where the amplitude is maximum is estimated by a numerical analysis means such as the least square method.

[0006]

In such a prior art, a device for detecting a defective portion only by changing the reflectance can detect a defect such as a foreign substance that reduces the amount of reflected light, but it does not seem to be an abnormality caused by birefringence. No change in the polarization state can be detected. Further, in the method of reproducing and binarizing the magneto-optical signal, it is impossible to distinguish between a simple change in the amount of reflected light and a change in the polarization state.

When detecting the change in the polarization state using the phase difference measuring device described in FIG. 5, both the normal part and the abnormal part are changed while changing the phase using the compensator to detect the compensation position. There is a problem that it is necessary to carry out the measurement a large number of times, which is troublesome.

Particularly, in the conventional example, since the Babinet-Soleil phase compensator is used, there are the following drawbacks.

(1) Since the magneto-optical signal amplitude is measured while slightly shifting the phase difference, the number of measurement points is large and the measurement time is long.

(2) Since the change in the phase difference is discontinuous, the true value is estimated by the method of least squares and the measurement error is large.

(3) Due to the large size of the Babinet-Soleil phase compensator, the entire apparatus has become large-scale.

Further, in the conventional detection method and apparatus, since there is only one means for giving the phase difference change, only one reproduced signal waveform can be obtained at the same time. Therefore, it is impossible to determine whether the deterioration of the signal amplitude is a decrease in reflectance caused by a foreign substance such as dust or a change in the polarization state accompanied by a phase difference change caused by an abnormality in birefringence. There was a task to be done.

[0013]

In order to solve the above problems, the present invention irradiates a recording medium on which information is magnetically recorded with a light beam polarized in a predetermined direction, and the information is recorded by a magneto-optical effect. The reflected or transmitted light beam from the medium whose polarization state has been modulated in accordance with the above is split into two light beams which are polarized in directions orthogonal to each other, and the two divided light beams are respectively detected by the detection means and detected. In the inspection device of the magneto-optical disk that detects the magneto-optical signal with the differential output of the signal,
In the recording medium, means for providing a plurality of different phase difference changes is provided in the optical path through which the light flux passes, and a magneto-optical signal corresponding to the plurality of different phase difference changes obtained through the means is arithmetically processed. The magneto-optical disk inspecting device is characterized by detecting the phase difference fluctuation and the defect.

Further, according to the present invention, by inserting a phase plate into the optical path of the magneto-optical signal recording / reproducing optical system and providing means for rotating the magneto-optical disk at the same time, the light beam is synchronized with the rotation of the disk. The continuous phase difference is continuously changed.

With respect to the above-mentioned state where a plurality of different phase differences are given, the amplitude of the magneto-optical signal increases and decreases at a portion having a local change in birefringence with a constant deviation from the surrounding normal portion. On the other hand, a defect that merely causes a decrease in reflection intensity has a constant decrease in amplitude with respect to the surrounding normal part. Therefore, the defect can be discriminated by comparing and calculating the signal amplitudes of these two states.

[0015]

【Example】

(Embodiment 1) FIG. 1 shows a configuration diagram of an optical system portion of an inspection apparatus used in the present invention. In the figure, 1 is a semiconductor laser, 2
Is a collimator lens, 3 is a beam shaping prism, 4 and 5 are beam splitters, 6 is an objective lens, 7 is a magneto-optical disk which is an object to be measured, 8 is a half-wave plate, 9 is a beam splitter, and 10 and 15. Are phase plates having different phase differences from each other, 11 and 16 are condenser lenses, and 12 and 17
Is a polarization beam splitter, 13, 14, 18, and 19 are photodetectors, and 20 and 21 are detectors.

In FIG. 1, the light flux emitted from the semiconductor laser 1 reaches the magneto-optical disk 7, and the light flux reflected by the medium surface of the magneto-optical disk is partially reflected by the beam splitter 5 to be 1/2. The light beam that has entered the wave plate 8 and transmitted through the beam splitter 5 is reflected by the beam splitter 4, passes through a condenser lens 22, and then enters a detector 23 for detecting a servo signal. The part described above has the same configuration and function as the conventional example of FIG.

The light beam that has passed through the half-wave plate 8 is split by the beam splitter 9 into two light beams that are reflected and transmitted substantially equally. The reflected light beam is given a constant phase difference, for example, a phase difference of 15 °, between polarization components orthogonal to each other by the action of the phase plate 10, and then passes through the condenser lens 11 and is polarized by the polarization beam splitter 12 to be orthogonal to each other. It is divided into two luminous fluxes each having a component
And 14 are incident. The outputs of the detectors 13 and 14 are differentially amplified by the differential amplifier 20, and the first magneto-optical signal RF-1
Becomes

Similarly, the light beam that has passed through the beam splitter 9 is given a phase difference different from that of the phase plate 10 by the phase plate 15, for example, −15 °, between polarization components orthogonal to each other, and then the condenser lens 16 is provided. The second magneto-optical signal RF-2 is given to the differential amplifier 21 via the polarization beam splitter 17 and the photo detectors 18 and 19.

2 (a) and 2 (b) respectively show a magneto-optical signal RF.
It is a figure showing the waveform of -1 and RF-2. If the magneto-optical signal is recorded beforehand on the magneto-optical disk 7 at a constant frequency, the amplitude of the reproduction signal will have a constant value, and therefore the envelope waveform shown by the broken line in the figure should also be constant. .. However, if the magneto-optical disk has a local defect or an abnormal portion of birefringence, it is 31, 3 in the figure.
As shown by 2 or 31 ', 32', local variations appear in the envelope waveform.

Since such defects and abnormalities in birefringence may deteriorate the quality of the signal and interfere with the binarization and reproduction of the signal in some cases, these harmful parts are detected and replacement processing is performed in advance. It is necessary to take action. In addition to detection, it is necessary to analyze at which stage in the manufacturing process these harmful parts occurred and take appropriate measures.

However, in the conventional detection method and apparatus, FIG.
(A) or (b), only the reproduced signal waveform can be obtained at the same time, and the deterioration of the signal amplitude from this is the decrease in reflectance caused by foreign matter such as dust, or the polarization state caused by abnormal birefringence. It was not possible to determine whether it was due to the change in.

FIG. 3 is an overall block diagram including a signal processing system of the inspection apparatus according to the present invention. The method of the present invention for solving the above problems will be described below with reference to FIG. 40 in the figure
Is a block diagram of the inspection device described in FIG.
Reference numeral 41 is a timing circuit for generating a trigger signal for signal processing, which will be described later, and 42 and 43 are RF smoothing circuits. After the magneto-optical signals RF-1 and RF-2 obtained from the inspection device 40 are AC-coupled, a smoothing circuit is provided. Has a function of converting into a low-frequency envelope signal for each of the plus side and the minus side. Four
Reference numerals 4 and 45 are A / D conversion circuits, which perform A / D conversion of the envelope signal at the timing of the trigger signal generated from the timing circuit and send it to the arithmetic circuit 46. The arithmetic circuit 46 performs the operation described later on the two types of envelope signals, and outputs the result to the CP.
Send to U47. The CPU 47 controls the entire signal processing system, and uses the information obtained from the arithmetic circuit 46 to perform processing such as local defect level determination and defect type determination.

FIG. 4 is a diagram showing output waveforms of the RF smoothing circuits 42 and 43 and the arithmetic circuit 46. In the figure, (a) is a single-wave envelope of the magneto-optical signal RF-1 shown in (a) of FIG.
Similarly, FIG. 2B shows a single-wave envelope of the magneto-optical signal RF-2 shown in FIG. These waveforms also include locations 51, 51 ', 52, 52' corresponding to the above-mentioned defective portions. The envelope of the part where there is no defect has constant outputs V1 and V2. When the phase of the optical system portion of FIG. 1 is 0, the transmitted light of the beam splitter 9 and the reflected light have the same division ratio, and the phase differences provided by the phase plates 10 and 15 are equal to each other with different signs as in the above example. In some cases V1 and V2 are proportional only to the phase difference of the magneto-optical disk. After the waveforms shown in (a) and (b) are A / D converted, respectively, the result of the following calculation by the calculation circuit 46 is shown in (c).

In the calculation performed by the calculation circuit 46, first, the average value of the A / D converted signals having the waveform of (a) is obtained, and this is used as the magneto-optical signal V10 of the normal portion. Similarly, the average value obtained from the waveform of (b) is set to V20, and for each data V1 and V2 of the A / D converted waveforms of (a) and (b), Is performed.

As a result, the calculation result of the normal part showing an average amplitude value becomes almost zero. On the other hand, FIG.
The abnormal portion of birefringence indicated by 51, 51 'in (b) shifts from the surrounding normal portion by a constant value and the amplitude increases or decreases, so a constant difference is generated by the above calculation (Fig. 4 ( 53) of c). Further, in the defect portion which is not accompanied by the phase difference change due to dust or the like, the reflectance is always reduced at a constant rate with respect to the average value, and therefore the above calculation result is almost zero.
(54 in FIG. 4 (c)). Therefore, by providing the determination level as shown by the broken line in FIG. 4C, it is possible to detect the defect that is always caused by the phase difference such as birefringence and the degree thereof. The defect without phase change is shown in Figure (a),
It can be detected by adding the waveforms shown in (b) or by directly monitoring the sum signal of the photodetector as is conventionally done.

In the arithmetic circuit described above, the average value V1
It is also possible to adopt a median value (median) or a maximum value (mode) instead of 0 and V20, and various arithmetic devices can be devised in accordance with the predicted defect type and frequency.

If the phase difference of the optical system of the apparatus shown in FIG. 1 excluding the phase plate is known (for example, 0 °), the average phase difference of the measured disk can be known from the amplitude of the signal. .. As in the above-mentioned example, when the plus and minus equal amounts of phase difference are given to the phase plate, if the signal average values are V10 and V20, the signal amplitude is proportional to the cosine of the phase difference. The average phase difference of the disk can be obtained by using the interpolation or the extrapolation.

The phase difference of the phase plate may be any value as long as it is known, and it is not always necessary to use two plates. If only one sheet is used, the optical path without the phase plate has a zero phase difference, and the other optical path has a known phase difference other than zero.

Further, in the apparatus of FIG. 1, the light beam is divided into two optical paths using two phase plates, but it may be divided into more optical paths.

Although a magneto-optical disk has been used in the description of this embodiment, the scope of the present invention is not limited to the magneto-optical disk, and a read-only disk such as a CD or a write-once type disk is not limited. The present invention can also be applied to the above optical discs and phase change type optical discs.

(Embodiment 2) FIG. 6 is a view showing another embodiment of the present invention, in which 81 is a phase plate having uniaxial anisotropy, 82 is a magneto-optical disk, and 83 is a phase plate 81.
And a spindle motor for simultaneously rotating the magneto-optical disk 82, a semiconductor laser 84, and a semiconductor laser 84.
The collimator lens for converting the emitted light emitted from the light into parallel rays, 86 is a polarization beam splitter for guiding the light reflected by the magneto-optical disk 82 and returned to the detection optical system, and 87 is the return light focused on the photodetector. A condensing lens, 88 is a polarization beam splitter that separates the P-polarized component and the S-polarized component of the return light, 89 and 90 are photodetectors, and 91 is a differential amplifier that outputs a magneto-optical signal from the difference between the polarized components. Reference numeral 92 designates an objective lens for condensing the laser light on the recording film of the magneto-optical disk 82, 93 designates a ½ wavelength plate for changing the polarization direction of the laser, 9
Reference numeral 4 denotes a total reflection mirror that changes the traveling direction of the laser.

The output power of the semiconductor laser 84 is fixed at the reproduction level by a control means (not shown), and the emitted laser light is collimated by a collimator lens 85.
After being converted into parallel rays by, the light passes through the polarization beam splitter 86 and the total reflection mirror 94, and is focused on the recording film of the rotating magneto-optical disk 82 by the objective lens 92. A magneto-optical signal is recorded in advance on the magneto-optical disk 82, and a reproduction signal can be obtained by focusing laser light on the magneto-optical signal by a focus and tracking control means (not shown).

The reproduced light thus obtained is guided to the phase plate 81 by the polarization beam splitter 86 via the objective lens 92 and the total reflection mirror 94. Phase plate 81
Is a structure in which two crystal plates with different optical rotation directions are attached so that their optical axes are orthogonal to each other. The diameter is about 8 cm and the phase difference is 90 °.
Got one. The phase plate 81 is rotated simultaneously with the magneto-optical disk 82 by the spindle motor 83, and gives the reproduction light a phase difference as shown in FIG. 8 according to the rotation angle. Thus, the reproduction light that has passed through the phase plate 81 is collected by the condenser lens 8.
7. The polarization beam splitter 88 divides the P-polarized component and the S-polarized component into light components, which are collected on the photodetectors 89 and 90 and converted into electric signals, which are then converted into magneto-optical signals by the differential amplifier 91.

When the phase difference of the magneto-optical disk is uniform in the circumferential direction and has a phase difference of, for example, -30 °, when the rotation angle of the phase plate 81 is about 20.6 °, P is independent of the Kerr rotation angle.
The polarized component and the S polarized component are only the direct current component, and the amplitude of the magneto-optical signal becomes minimum (zero). This state is shown in FIG.
On the contrary, by detecting the rotation angle θ of the phase plate at which the amplitude of the magneto-optical signal exhibits the minimum value, the phase difference δ of the magneto-optical disk can be calculated back by the following equation. δ = −tan ⁻¹ (sin ² 2θ / cos 2θ) A digital oscilloscope is used to measure the magneto-optical signal, and if the signal is taken in in synchronization with the rotation of the phase plate, the magneto-optical disk can be rotated once. Since the phase difference can be measured, the measurement time is greatly shortened. Moreover, since the change in phase difference is continuous, accurate measurement is possible.

Further, since the magneto-optical signal amplitude has four minimum values during one rotation of the magneto-optical disk, if the phase difference corresponding to the position of each minimum value does not match, the position in the circumferential direction of the disk. It can be seen that there are variations in the phase difference.

Furthermore, the size of the device can be reduced to half or less as compared with the case where the Babinet-Soleil phase compensator is used.

The phase plate 81 may be any substance that gives uniaxial anisotropy, and natural crystals and artificial crystals showing birefringence such as mica, or uniaxially stretched polymer film may be used. The applied phase difference is not limited to 90 ° and may be any value larger than the phase difference of the measurement target.

The half-wave plate 93 is inserted in the optical path when it is desired to change the polarization direction of the light incident on the magneto-optical disk, and is used when it is desired to separate the phase difference between the substrate and the film.

(Embodiment 3) FIG. 7 is a view showing another embodiment of the present invention. This is a modification of the above-described embodiment so as to be suitable for the measurement of the inner peripheral portion of the magneto-optical disk or the magneto-optical disk having a relatively small diameter.
The objective lens 92 is moved to the magneto-optical disk 82 by making the polarized beam splitter 86 of the above have a function of a reflection mirror.
It has become possible to locate it on the inner circumference of the. Except that the total reflection mirror 94 is omitted, the other structure is the same as that of the above-described embodiment.

[0040]

As described above, according to the inspection apparatus of the present invention, a defect accompanied by a phase difference change caused by birefringence or the like and a uniform reflection can be obtained by a relatively simple and compact structure. It becomes possible to easily discriminate defects that cause a decrease in
Furthermore, it is possible to obtain an effect that has not been obtained in the past such that the average phase difference can be known. Therefore, if the apparatus of the present invention is introduced into the magneto-optical disk inspection process, it has a great effect on the process control, the analysis of the cause of the defect, and the prevention.

By inserting a uniaxially anisotropic phase plate into the optical path of the magneto-optical signal recording / reproducing optical system and rotating it simultaneously with the magneto-optical disk, the phase difference of the magneto-optical disk can be accurately measured in a short time. Further, there is an effect that the device can be further downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system section of an inspection device according to the present invention,

2 is a diagram showing a waveform of a magneto-optical signal obtained by the apparatus of FIG.

FIG. 3 is a block diagram showing the entire inspection apparatus according to the present invention,

FIG. 4 is a diagram for explaining a calculation process of a signal waveform by the inspection device of the present invention;

FIG. 5 is a diagram showing a configuration of a conventional phase difference measuring device.

FIG. 6 is a view showing another embodiment of the present invention,

FIG. 7 is a view showing another embodiment of the present invention,

FIG. 8 is a diagram showing a phase difference of a light beam provided by a phase plate,

FIG. 9 is a diagram showing a signal amplitude of a magneto-optical disk,

FIG. 10 is a diagram for explaining a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser 5 beam splitter 7 magneto-optical disk 8 1/2 wavelength plate 9,17 polarization beam splitter 10, 16 phase plate 81 phase plate, 82 magneto-optical disk, 83 spindle motor, 84 semiconductor laser, 85 collimator lens, 86 polarization Beam splitter, 87 condensing lens, 88 polarizing beam splitter, 89, 90 photodetector, 91 differential amplifier, 92 objective lens, 93 1/2 wavelength plate, 94 total reflection mirror, 95 Babinet-Soleil phase compensator.

Claims (4)

[Claims] 1. A reflection from a medium, which is polarized in a predetermined direction, is irradiated onto a recording medium on which information is magnetically recorded, and the polarization state is modulated according to the information by a magneto-optical effect. Alternatively, the transmitted light flux is divided into two light fluxes polarized in directions orthogonal to each other, the two divided light fluxes are respectively detected by the detection means, and the magneto-optical signal is detected by the differential output of the detected signals. In a magnetic disk inspecting apparatus, means for providing two different phase difference changes provided in an optical path through which the light flux passes, and magneto-optical signals corresponding to the two different phase difference changes obtained through the means. A magneto-optical disk inspecting device, comprising means for detecting a defect accompanied by a phase difference variation in the recording medium by performing arithmetic processing. 2. An arithmetic mean of the A / D conversion signal of the waveform obtained by one of the means for giving the two different phase difference changes, and the waveform obtained by the other means. When V1 is the average value of V1 and V1 and V2 are constant outputs of the envelopes of the portions where there is no defect in each waveform, the calculation of V1− (V10 / V20) × V2 is performed on V1 and V2. The magneto-optical disk inspection apparatus according to claim 1, wherein 3. The magneto-optical disk inspection apparatus according to claim 1, wherein the means for applying the phase difference change provides a plurality of phase difference changes. 4. A magneto-optical disc inspection apparatus, a uniaxially anisotropic phase plate inserted in the optical path of a magneto-optical signal recording / reproducing optical system, means for rotating the phase plate simultaneously with the magneto-optical disc, A magneto-optical disk inspecting apparatus, comprising means for inspecting a defect of the magneto-optical disk from a signal whose phase has been changed by a phase plate.