JPH02278544A - Magneto-optical recording method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording method in which information is erased and recorded using a laser beam and an external magnetic field, and information is reproduced using a laser beam. [Conventional technology 1] Magneto-optical recording methods include an optical modulation recording method in which recording is performed by continuously applying an external magnetic field and changing the intensity of light as needed, and a method in which recording is performed by continuously applying a laser beam and changing the polarity of the external magnetic field at any time. There is a magnetic field modulation recording method that records by changing the magnetic field. (Magnetic domain length is 0.5μ
When performing high-density recording (less than m), with the optical modulation recording method, the magnetic domain length of the circular magnetic domain fluctuates greatly with respect to fluctuations in optical power, making it difficult to perform stable recording. On the other hand, in the magnetic field modulation recording method, the variation in the magnetic domain length of the crescent-shaped magnetic domain is much smaller than in the optical modulation recording method, and stable high-density recording is possible. Incidentally, regarding the magnetic field modulation recording method, there is, for example, Japanese Patent Laid-Open No. 60-4.8806. However, in the conventional magnetic field modulation recording method, wavelengths of 780 to 83
Since recording and reproduction are performed using a 0 nm laser beam, even though recording is possible, it is difficult to reproduce densely recorded magnetic domains with a good S/N ratio due to optical resolution. Furthermore, as the disk rotation speed increases, the curvature of the crescent-shaped magnetic domain increases, which causes deterioration of the S/N ratio. [Problems to be solved by the invention] In the conventional magnetic field modulation recording method, wavelengths of 780 to 830 nm
Recording and reproduction are performed using laser beams, so although stable high-density recording is possible, it is difficult to reproduce densely recorded magnetic domains with a good signal-to-noise ratio due to optical resolution. there were. Furthermore, as the disk rotation speed increases, the curvature of the crescent-shaped magnetic domain increases, which causes deterioration of the S/N ratio. An object of the present invention is to read out information recorded at high density using a magnetic field modulation recording method with a good signal-to-noise ratio, and to further improve the signal-to-noise ratio in high-speed recording. [Means for solving the problem 1 The problem of optical resolution when reading information can be solved by making the wavelength of light during reading smaller than the wavelength of light during recording, especially 6
This can be achieved by reducing the thickness to 00 nm or less. Furthermore, the problem that the curvature of the crescent-shaped magnetic domain becomes large in the case of high-speed recording can be solved by making the shape of the light spot during recording oblong or elliptical, and making the light intensity distribution trapezoidal. At this time, the oval or elliptical light spot shape can be formed using a diffraction grating or an acousto-optic effect. In addition to this, there is also a method of using a mask pattern of a desired shape and imaging the shape onto a recording medium through a lens. In this method,
Not only can the shape of the beam spot be controlled, but the intensity of light removal is not reduced. That is, the feature of the present invention is that a magnetic field modulation magneto-optical recording method that simultaneously erases and records information by continuously irradiating a magnetic material with a laser beam and changing the polarity of an externally applied magnetic field at any time, is capable of recording information. The present invention relates to a magneto-optical recording method in which the size of a light spot during reading and time is changed, or the shape of a light spot during recording and/or reading is made into a shape other than circular. It is desirable to make the diameter of the circular light spot during reading smaller than during recording by making the wavelength of the light during reading shorter than during recording. In this case, it is desirable to read information using light with a wavelength of 600 nm or less. Further, it is desirable that the wavelength during recording is 600 nm or more, and the wavelength during reading is 600 nm or less. It is desirable that the shape of the light spot during recording and/or reading is oval or elliptical. The oval and elliptical light spot shapes can be formed using a diffraction grating or an acousto-optic effect. To control the shape of a light spot during recording and/or readout, light is passed through a patterned mask having an arbitrary shape, and then the shape of the patterned mask is imaged at a desired location through a lens. The shape of the light spot can be controlled. The shape of the spot may be controlled by using a patterned mask on a glass substrate as the pattern mask. [Effect 1 The shaded area in Fig. 4 shows the edge shift (edge position during recording) when bit edge detection is performed using optical spora 1~ focused on the magneto-optical disk by a lens with a numerical aperture of 0.55. This shows the minimum magnetic domain length (the length of the magnetic domain in the direction of disk rotation) that does not cause the edge position during readout to occur. Since the diameter of the optical spot is proportional to the laser wavelength, if a wavelength of 600 nm or less is used, magnetic domains with a magnetic domain length of 0.5 μm or less can be read out without entering the edge shifter 1 or with a good signal-to-noise ratio. Furthermore, in the case of high-speed recording (linear velocity of 15 m/sec or higher), the curvature of the crescent-shaped magnetic domain is large, as shown in Figure 5. This is because the temperature rise at the center of the light spot is large. At this time, the amplitude of the reproduced signal becomes small and the SN ratio deteriorates. Therefore, by creating an oval or elliptical light spot with a trapezoidal intensity distribution in the radial direction of the disk, the temperature distribution in the radial direction of the disk becomes almost constant, and magnetic domains with small curvature can be recorded. At this time, the amplitude of the reproduced signal increases, and the SN ratio improves. Embodiments Embodiment 1 FIG. 1 shows an embodiment of the magneto-optical recording system according to the present invention. Light 3 with a wavelength of 830 nm and light with a wavelength of 4.
Light 4 of 20 nm was irradiated simultaneously. At this time, autofocus and tracking were performed using 830 nm light. The external magnetic field generation source 5 is located on the opposite side of the optical head across the disk. During recording, crescent-shaped magnetic domains 6 were recorded by modulating the intensity of the external magnetic field, using 830 nm light with the intensity necessary to form magnetic domains and 420 nm light with the intensity necessary to read information. When reading, 8
The 30 nm light had the intensity necessary for autofocus and tracking, and the information was read out using the 420 nm light. At this time, the diameter of the circular light spot 7 of 420 nm is:
This is about half of the circular light spot 8 of 830 nm. 420
The CN ratio when reading with nm light is approximately 5 dB higher than the CN ratio when reading with 830 nm light, and the S/N ratio is improved by making the optical wavelength during reading smaller than the optical wavelength during recording. It was confirmed that Embodiment 2 FIG. 2 shows the case where recording and reproducing were performed with only 420 nm of light irradiated onto the magneto-optical disk. In this case as well, the SN ratio was better than when recording and reproducing were performed using 830 nm light. Example 3 FIG. 3 shows a case where light with a wavelength of 420 nm is formed into a large number of circular sporaters 1 to 1 using an acousto-optic element 9, and these are superimposed to form an oval spot 10. When recording with this light spot, the curvature of the crescent-shaped magnetic domain became smaller. Furthermore, when this magnetic domain is read out with a circular light spot or an oval spot with a wavelength of 420 nm,
The signal-to-noise ratio was better than when recording with a circular spot. In addition to an acousto-optic element, a diffraction grating can be considered as a means for producing an oval light spot. Note that when using a diffraction grating, the optical system is simpler if the recording spot and the reading spot have the same oval shape. Embodiment 4 FIG. 6 is a schematic diagram showing the principle of magneto-optical recording using the magnetic field modulation recording method used in this embodiment. The disk had a magneto-optical recording medium (12) formed on a substrate (13). Then, the recording medium is continuously irradiated with laser light (15) through the lens (14), and the floating magnetic head (11) is
) and recorded by applying a switching magnetic field. A schematic diagram of the obtained recording magnetic domain is shown in FIG. This is 7 mW in the disk rotation direction (Figure 6 below), the wavelength of the laser beam is 500 nm, the frequency is 30 M,
This is a schematic M of a recording magnetic domain obtained when recording at Hz. An attempt was made to reproduce this using the conventional circular optical spoiler 1, but the noise level was high and the reproduction output was extremely small. What's more, the recorded information could not be played back at all. The reason for this is that the optical spot is significantly thicker than the recording magnetic domain. Therefore, reproduction was performed using the optical system of the present invention. First, a schematic diagram showing the principle is shown in FIG. As mentioned above, the shape of the recording magnetic domain is crescent-shaped (FIG. 8). Then, a laser beam (15) is irradiated through a slit (6) having a slightly larger crescent-shaped hole. The light that has passed through Surin 1 passes through the lens (14) to the recording medium (]2 formed on the disk substrate (13) J2.
) on which the image (17) is formed. The size relationship between the image (17) and the recording magnetic domain (18) at that time is shown as an enlarged view in the upper left of FIG. In this case, care must be taken because if the size of the image is too large than the recording magnetic domain (18), it will overlap with the adjacent magnetic domain, causing cross-storage and causing errors. Further, the focusing of the image may be performed using an AF circuit similar to that used for tracking signals. By using the light whose spot shape was controlled in this way, it was possible to reproduce the recorded signal without error. The maximum C/N (carrier-to-noise ratio) at that time was 4.3
dB (NA=0.60). This means that recorded minute magnetic domains can be read out with high resolution without crosstalk. In this example, a case was shown in which a method for controlling the shape of a light spot is applied to magneto-optical recording using a magnetic field modulation recording method. However, write-once optical recording with minute pits and I-eye variable type (
Needless to say, the present invention can be applied not only to optical recording (phase change type) but also to all kinds of optical recording such as CD-ROMs, compact discs, and laser discs. Furthermore, a similar effect was obtained using a light and dark pattern formed as slits on a glass plate. The above was an example using one wavelength, but next, an example using two types of light sources with different wavelengths will be described. That is, this is a case where the wavelength of light for recording or erasing is different from the wavelength of light for reproducing. Here, the wavelength of the light used for reproduction is shorter than that of the light used for recording and erasing. That is, the reproduction light was 500 nm, and the recording or erasing light was 780 nm. In this case, two optical systems may be used, or two light sources may be prepared and switched appropriately, or the two light sources may be mixed. In either case, what is important is to use the light whose shape of the light spot is controlled at least in the reproduction system of the optical disc. In addition, by controlling the shape of the optical spot of the present invention with respect to the recording laser beam, it was possible to control the shape of the recording magnetic domain formed. This made it possible to further increase the recording density. For comparison, when a light source of the same power was used for recording using light that controlled the shape of the beam spots 1 to 1 by combining two types of conventional beams, recording could not be performed due to insufficient recording laser power. This is because the light intensity near the peak of the light intensity that can be approximated to a Gaussian distribution is discarded during synthesis, and the weak light intensity near the base of the distribution is used. As described above, the present invention does not cause a decrease in light utilization efficiency. (Effects of the Invention) By using the magneto-optical recording method according to the present invention, crescent-shaped magnetic domains recorded at high density by magnetic field modulation can be read out with a good signal-to-noise ratio. Furthermore, since the curvature of the magnetic domain becomes smaller when recording at high speed, the S/N ratio improves.

[Brief explanation of drawings]

1st. Second. FIG. 3 shows an embodiment of the invention. A diagram showing the magnetic field modulation magneto-optical recording method, Figure 4 is a diagram showing the wavelength dependence of the minimum detectable magnetic domain length in the case of bit edge detection, and Figure 5 is a diagram showing the relationship between the shape of the light spot and the shape of the recorded magnetic domain. , FIG. 6 is a schematic diagram showing the principle of magneto-optical recording using the magnetic field modulation recording method according to this embodiment, FIG. 7 is a schematic diagram of the recorded magnetic domain obtained in this embodiment, and FIG. FIG. 2 is a schematic diagram showing the principle of reproduction using an optical system. 1. Magneto-optical disk, 2. Aperture lens, 3.
Light with a wavelength of 830 nm, 4... Light with a wavelength of 420 nm, 5
・External magnetic field source, 6 Recording magnetic domain, 7 ・Wavelength 420
nm optical spora 1, 8...light spot with wavelength 830 n rn, 9. acousto-optic element, 1o. oval light spot, 11.. levitated magnetic spatula 1, 12.. optical recording medium, 13... Disk substrate, 14 Lens, 15 Laser light, 16... Slit, 17... Image, 18... Recording magnetic domain. \N ”'+ s False\ \ \ \ \ \ Saddle ←, Ya experience

Claims (1)

[Claims] 1. In a magnetic field modulation magneto-optical recording method in which information is simultaneously erased and recorded by continuously irradiating a magnetic material with a laser beam and changing the polarity of an externally applied magnetic field as needed, A magneto-optical recording method characterized by changing the size of a light spot during time and readout, or making the shape of a light spot during recording and/or readout a shape other than a circle. 2. The magneto-optical recording method according to claim 1, wherein the diameter of the circular light spot during reading is made smaller than that during recording by making the wavelength of the light during reading shorter than during recording. 3. The magneto-optical recording method according to claim 2, wherein information is read using light having a wavelength of 600 nm or less. 4. The magneto-optical recording method according to claim 1, wherein the wavelength during recording is 600 nm or more, and the wavelength during reading is 600 nm or less. 5. The magneto-optical recording method according to claim 1, wherein the shape of the light spot during recording and/or reading is oval or elliptical. 6. The magneto-optical recording method according to claim 5, wherein the oval and elliptical light spot shapes are formed using a diffraction grating or an acousto-optic effect. 7. To control the shape of the light spot during recording and/or readout, light is passed through a pattern mask having an arbitrary shape, and then the shape of the pattern mask is imaged at a desired location through a lens. 2. The magneto-optical recording method according to claim 1, wherein the shape of the light spot is controlled by 8. The magneto-optical recording method according to claim 7, wherein a mask patterned on a glass substrate is used as the pattern mask to control the shape of the light spot.