JPH03248353A - Inspection method for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To detect all the defects without missing by performing inspection by deciding the differential signal of an optical signal with a comparator after magnetizing a magneto-optical disk. CONSTITUTION:The magneto optical disk 22 is magnetized on the application device of an electromagnet on the N and S poles for which a coil 23 is wound by inserting the disk 22 perpendicularly into a magnetic field. A signal outputted from the photodiode 10 of a pickup for disk is fetched in a differential amplifier 14, and the differential signal 13 of a magneto-optical signal outputted from the amplifier is decided with the comparator 17, and an OR 16 is outputted from an OR circuit 15. In such a case, the OR 16 shows the flaw signal of the disk, and the decision level of the defect of the comparator 17 is set by variable resistors 11, 12. Thereby, it is possible to detect all the defects without missing.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for inspecting a magneto-optical recording medium.

[Summary of the Invention] The present invention is a method for inspecting a magneto-optical recording medium capable of recording, reproducing, or erasing, which involves magnetizing a magneto-optical disk in one direction and then using a pickup for the magneto-optical disk to By determining and inspecting the differential signals of the magnetic signals using a comparator, all defects can be detected without being overlooked, and high-quality magneto-optical disks can be manufactured.

[Prior Art] A conventional method for inspecting a magneto-optical recording medium is to shine light onto a magneto-optical disk and detect defects based on the amount of reflected light, as shown in FIG.

In FIG. 5, 32 is an object to be measured, 24 is a laser beam irradiation device, and 25 is a laser beam irradiated from this laser beam irradiation device 24. 26 is a collimating lens that makes the laser beam 25 parallel, 27 is a half mirror, and 28 is an objective lens that focuses the collimated laser beam 25 on the surface of the object 320 to be measured. Measured object 3
If there is no defect on the surface of the mirror 2, the reflected light returns to the objective lens 28 as it is and passes through the half mirror 27 and the condenser lens 3.
0 to the photodetector 31.

[Problem to be solved by the invention] However, when we investigated the defects in actual magneto-optical disks, we found that there were defects in the magneto-optical signal even when there was no large variation in the amount of reflected light. Therefore, we recorded data on both sides. It was necessary to conduct a remanufacturing test.

In other words, even if a laser beam hits a minute defect, it may not be scattered and may be overlooked, which is a fatal and serious problem for a defect inspection device.

Furthermore, if data is recorded on the entire surface and then reproduced for inspection, no defects will be missed, but there is a problem in that the inspection takes a very long time.

The present invention is intended to solve these problems, and its purpose is to provide a method for inspecting a magneto-optical recording medium that can be inspected at high speed without overlooking any defects such as minute scratches on the magneto-optical disk. There it is.

[Means for Solving the Problems] The method for inspecting a magneto-optical recording medium of the present invention uses a pickup for the magneto-optical disk after magnetizing the magneto-optical disk in one direction, and compares the differential signal of the magneto-optical signal with a comparator. It is characterized by the determination and inspection.

[Embodiment Fig. 3 shows a magnetizing device in an embodiment of the present invention, with N,
This is an electromagnet application device with a coil 23 wound around S. By inserting the magneto-optical disk 22 perpendicularly to the magnetic field, the magneto-optical disk can be magnetized.

The magnetic recording film before magnetization has different magnetization directions, but after magnetization by the apparatus shown in FIG. 3, the magnetization directions of the magnetic recording film all face the same direction.

FIG. 1 is a schematic diagram of a defect inspection apparatus according to the present invention.

Photodiode 1 of pickup for magneto-optical disk
The signal output from 0 is taken into the differential amplifier 14. And the differential signal 13 of the magneto-optical signal that came out from there
is determined by the comparator 17, and the logical sum 16 is outputted by the 15 OR circuits.

The logical sum 16 is a disc scratch signal.

The variable resistors 11 and 12 are used to set the defect determination level of the comparator 17.

FIG. 2 explains the determination operation of the signal output from the comparator of FIG. 1.

18 is a reproduction signal from the disk, and 19 and 20 are judgment levels of the comparator 17 set by variable resistors 11 and 12. 21 is a disc flaw signal output from the OR circuit 15 after being compared at the determination level 19.20.

FIG. 4 is a graph in which the horizontal axis represents the number of tracks on the disk and the vertical axis represents the pit error rate.

From this graph, it can be seen that defects that cannot be found using the inspection method using only reflected light can be found when the signal is recorded and then reproduced and when using the method according to the present invention. I would like to add here that the method according to the invention requires no signal recording during the testing stage and is therefore very time consuming.

By uniformly magnetizing the magneto-optical disk, a reproduced signal at a constant level can be obtained when there are no defects, and a reproduced signal that deviates from the constant level can be obtained when there is an abnormality in the recording layer.

In other words, by detecting this, it is possible to find all defects that cause abnormalities in the magneto-optical signal.

Therefore, all defects on the magneto-optical disk can be detected without recording signals, and inspection can be performed at high speed.

[Effects of the Invention] As described above, according to the present invention, since the magneto-optical disk is magnetized and then inspected by determining the differential signal of the optical signal using a comparator, it is possible to overlook all defects. It has the advantage of being able to detect without any problems and being able to perform inspections at high speed. In addition, the inspection method can improve quality and reliability as a magneto-optical recording medium, and even provide excellent characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a defect inspection apparatus according to the present invention. FIG. 2 is an operational waveform diagram of a signal output from the comparator of FIG. 1. Fig. 3 shows a magnetizing device which is an embodiment of the present invention;
The figure is a comparison graph of BER between the method of the present invention and the conventional method. FIG. 5 is a schematic diagram of a conventional defect inspection device. 1 ・ 2 ・ 3 ・ 4 ・ 5 ・ 6 ・ 7 ・ 8 ・ 9 ・ 0 1 2 3 4 5 6 7 8 9 0 ・Magneto-optical disk・Objective lens・Reflector・Beam splitter・Collimating lens・Laser diode・Wavelength Plate, polarizing beam splitter, lens, photodiode, variable resistor, variable resistor, differential signal, differential amplifier, OR circuit, disc flaw signal output from the comparator, comparator, reproduced signal from the disc, defect determination level・Defect determination level 1 2 3 4 5 6 7 8 9 0 1 2 ・Disk scratch signal ・Magneto-optical disk ・Coil laser beam irradiation device Laser light ・Collimating lens ・Half mirror ・Objective lens ・Scattered light ・Condensing lens ・Photodetector/Measurement object

Claims (1)

[Claims] In a method for inspecting magneto-optical recording media that uses a transparent substrate to irradiate light to perform recording, reproduction, or erasing, a magneto-optical disk is magnetized in one direction, and then a pickup for the magneto-optical disk is used to perform magneto-optical recording. A method for inspecting a magneto-optical recording medium, characterized in that differential signals of signals are determined and inspected using a comparator.