JPH04278242A - Magnetooptical recording and reproducing apparatus - Google Patents

Abstract

PURPOSE:To achieve the high degree of recording density in a magnetic-field modulation type magnetooptical recording and reproducing apparatus by improving the shape of an arrow-feather-shaped magnetic domain, and improving the SN ratio of the regenerated signal. CONSTITUTION:The light beam is applied to a magnetooptical recording medium from a light source. The temperature of a magnetized film is increased to the temperature higher than a Curie-point temperature or to the vicinity of the Curie-point temperature. A magnetic filed which is modulated in response to record data is applied to the part where the temperature is increased. In a magnetooptical recording and reproducing apparatus wherein the data are recorded on the medium, the diameter of the recording optical spot which is applied to the recording medium in data recording is made larger than the diameter of the light spot in regeneration.

Description

[Detailed description of the invention]

0001

2. Description of the Related Art Conventionally, optical modulation systems and magnetic field modulation systems are known as magneto-optical recording and reproducing systems of this type. Figure 4
FIG. 2 is an explanatory diagram showing the information recording and reproducing process of the optical modulation method. In this optical modulation method, erasing is performed prior to information recording, as shown in FIG. 4(a). That is, information is erased by applying a magnetic field in a fixed direction from a magnet 29 to the film surface of the magneto-optical recording medium 25 and irradiating a strong unmodulated light beam 28 from the optical head 27. When recording information, as shown in FIG. 4(b), a magnetic field is applied from the magnet 29 in the opposite direction to that for erasing, and at the same time, a light beam 28 whose intensity is modulated according to the recording signal is emitted from the optical head 27.
is irradiated. As a result, information magnetic domains are formed on the film surface with different directions corresponding to recording signals, as shown by arrows 26. On the other hand, when performing reproduction, a weaker light beam is emitted from the optical head 27 than during recording, as shown in FIG. 4(c). Information is then reproduced by detecting a change in the polarization direction of the reflected light from the magneto-optical recording medium due to the magnetic Kerr effect.

FIG. 5 is a time chart showing information recording operation using the magnetic field modulation method. In the magnetic field modulation method, when recording information, a light beam with a constant intensity as shown in Figure 5(a) is irradiated onto the magneto-optical recording medium, and at the same time the polarity is changed according to the recording signal (Figure 5(b)). A modulated bias magnetic field (FIG. 6(c)) is applied. FIG. 2D shows a light spot of a recording light beam. This light spot scans an information track, and in combination with the application of a bias magnetic field, information is recorded. As a result of this recording operation, arrow-shaped recording magnetic domains 35 and 36 are formed on the information track as shown in FIG. 3(e). On the other hand, when reproducing information, the information track is scanned with a reproduction light spot 37 having a weaker intensity than the light intensity during recording, and the change in the polarization direction of the reflected light is detected, similar to the optical modulation method. , information reproduction is performed.

0003

However, with the above-mentioned optical modulation method, it is not possible to directly overwrite the magneto-optical recording medium, and it is necessary to erase the area to be recorded before recording information. Therefore, extra time is required for the erasing process, which is disadvantageous in terms of increasing the recording speed. On the other hand, the magnetic field modulation method is advantageous in terms of recording speed because overwriting is possible, but as mentioned above, since the recording magnetic domain is feather-shaped, there is a problem that the S/N ratio deteriorates. . That is, when the recording mark length is short, the reproduction light beam is irradiated to both magnetic domains corresponding to information "1" and "0", and the ratio of reflected light from both magnetic domains is 1:1. As the distance approaches the SN ratio of the reproduced signal, the SN ratio of the reproduced signal deteriorates. Since the recording density of information is determined by the S/N ratio, the magnetic field modulation method has the problem that the recording density cannot be increased compared to the optical modulation method.

The present invention was made to solve these problems, and its purpose is to improve the shape of the feather-shaped magnetic domain and improve the S/N ratio of the reproduced signal, thereby achieving higher density recording. The object of the present invention is to provide a magneto-optical recording and reproducing device that enables the following.

[0005]

[Means for Solving the Problems] Such an object of the present invention is to irradiate a magneto-optical recording medium with a light beam from a light source to heat a magnetized film to a temperature higher than or near the Curie point temperature, and In a magneto-optical recording and reproducing apparatus that records information on the medium by applying a magnetic field modulated according to the recorded information to this heated region, the recording light spot irradiated onto the recording medium during information recording is This is achieved by a magneto-optical recording/reproducing device characterized in that the diameter of the optical spot is larger than the diameter of the optical spot during reproduction.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the magneto-optical recording/reproducing apparatus of the present invention.

In FIG. 1, reference numeral 1 denotes a magneto-optical disk which is a magneto-optical information recording medium, and has a magneto-optical recording film 3 formed on a transparent substrate 2. The magneto-optical disk 1 is rotated about a central axis 0 by driving a spindle motor (not shown). On the upper surface of the magneto-optical disk 1, there is an optical head 7 composed of optical components such as a two-wavelength semiconductor laser element (hereinafter simply referred to as a semiconductor laser) 4 and an objective lens 5.
is installed. The optical head 7 is also equipped with a servo mechanism and a reproducing system (not shown). Further, on the lower surface of the magneto-optical disk 1, an electromagnet 8 is arranged opposite to the optical head 7 for generating a recording magnetic field. In addition,
10 is a modulation circuit that generates a modulation signal according to recorded information;
A drive circuit 9 drives the electromagnet 8 according to its modulated output, and the electromagnet 8 generates a bias magnetic field whose polarity is modulated according to recorded information. Further, the electromagnet 8 has an air floating type magnetic head configuration in order to increase the reversal speed of the magnetic field.

In this embodiment, the output of the semiconductor laser 4 during recording is 10 mw after exiting from the objective lens, and is 1.5 mw during reproduction.
mw, and its wavelength is 790 nm during recording and 780 nm during reproduction. In addition, in the optical head 7, the optical system including the objective lens 5 connects the smallest light spot on the magneto-optical recording film 3 when the semiconductor laser 4 emits light at 780 nm during reproduction, and emits light at 790 nm during recording. They are designed to connect as large a light spot as possible. That is, the diameter of the light spot is determined by the NA, aberration, and wavelength of the objective lens, and in this example, the spot diameter of the light beam is 1.5 μm (1/e2) during recording and 1.5 μm (1/e2) during playback.
．． It is 2 μm (1/e2).

Next, FIG. 2 shows the information recording and reproducing operation of this embodiment.
Explain with reference to. First, when recording information, as in the conventional magnetic field modulation method, a
) is irradiated with a light beam of constant intensity as shown in (). In this case, the diameter of the optical spot is larger than that during reproduction as described above, and the diameter of the optical spot 16 for recording (FIG. 2(d)) is set larger than the width of the information track 18 (FIG. 2(e)). has been done. By irradiating this laser beam, the temperature of the magneto-optical recording film 3 is raised to above or near the Curie point temperature. On the other hand, a bias magnetic field (
2(c)) is applied, and in combination with the temperature raising operation, a recording pattern as shown in FIG. 2(e) is formed on the information track. In Fig. 2(e), 19 is a magnetic domain due to a positive magnetic field, 20
is a magnetic domain due to a negative magnetic field. Further, 17 is a tracking track, and 18 is an information track.

Since the diameter of the optical spot 16 is larger than the width of the information track 18, as is clear from FIG. 2(e), the magnetic domains 19 and 20 have remarkable fletching compared to the conventional magnetic domains shown in FIG. It can be seen that the shape was improved. When reproducing this recording pattern, as shown in FIG. 2(e), the information track 18 is
Information is reproduced by scanning the top and detecting changes in the polarization direction of the reflected light. In this case, the diameter of the reproduction light spot 21 is smaller than the recording light spot 16,
Here, the width is set to be approximately the same as the width of the information track 18. When the recording pattern is read using the reproduction optical spot in this way, the reproduction optical spot 21 is sufficiently smaller than the recording optical spot 16, so even when the mark length is short as in the recording pattern shown in FIG. 2(e), , a good reproduction signal can be obtained.

[0011] The inventor of the present invention conducted an experiment and found that in the conventional magnetic field modulation method, the S/N ratio of the reproduced signal drops to 48 dB when the mark length is 1.8 μm. On the other hand, in the present invention, the SN ratio decreases to 48 dB when the mark length is 1.5 μm, and it was confirmed that the present invention is more effective than the conventional method. The conditions for this experiment are as follows:
As in the example, the diameter of the optical spot during recording was set to 1.5 μm.
, and 1.2 μm during reproduction.

FIG. 3 is a block diagram showing another embodiment of the present invention. In FIG. 3, 41 is a laser light source unit for reproduction, 42 is a laser light source unit for recording, 43 is a beam splitter for passing a recording light beam and a reproduction light beam through the same optical path, and 44 is a magneto-optical a polarizing beam splitter 4 for guiding the reflected light from the disk 1 to the detection system;
5 is a detection system for detecting magneto-optical reproduction signals and servo signals;
Reference numeral 46 denotes an optical system for focusing the light beam 47 onto the magneto-optical recording film 3. Note that the other configurations are the same as the embodiment shown in FIG.

A semiconductor laser with an emission wavelength of 780 nm was used as a laser light source for reproduction, and a semiconductor laser with an emission wavelength of 820 nm was used as a laser light source for recording. The size of the light spot is 1.2 μm (1/e2) during reproduction and 1.5 μm during recording, as in the previous example.
(1/e2). In this embodiment, since the optical beam wavelength during recording and the recording beam wavelength during reproduction are different from each other than in the previous embodiment, the design of the optical system is easier than in the previous embodiment.

In this embodiment, by providing recording and reproducing light sources with different wavelengths, the diameter of the optical spot during recording is made larger than the spot diameter during reproducing.
Even in this example, the shape of the magnetic domain can be improved as in the previous embodiment, and the S/N ratio of the reproduced signal can be improved. In addition, generally speaking, the shorter the wavelength of a semiconductor laser, the more difficult it is to obtain high output, so by having dedicated light sources for recording and playback, as in this example, you are not limited to the light beam output necessary for recording. Since a light source with a short wavelength can be used for reproduction, it becomes possible to record information with even higher density. Furthermore, in this embodiment, the light beam is emitted continuously during recording, but it is also possible to emit the light beam during recording in pulses at a sufficiently higher frequency than the recording signal, or in synchronization with the clock of the recording signal. Pulse lighting is also possible.

[0015] For example, a two-wavelength or multi-wavelength laser that can have a large difference in emission wavelength, such as the ADQW semiconductor laser reported at the 37th Applied Physics Conference (Lecture No. 28a-SA-13), If used in the light source of the embodiment shown in FIG. 1, it is possible to record information at a higher density as in the embodiment shown in FIG. In addition, the diameter of the optical spot can be increased during recording by correcting aberrations well at the light beam wavelength during playback, but by making the aberrations insufficiently corrected at the light beam wavelength during recording. The signal-to-noise ratio of the signal can be improved.

[0016]

As explained above, according to the present invention, since the optical spot during recording is made larger than the optical spot during reproduction, the shape of the feather-shaped recording magnetic domain can be improved, and the SN ratio of the reproduced signal can be improved. It has the effect of improving the Therefore, S
It is possible to increase the recording density determined by the N ratio,
A larger capacity magneto-optical recording/reproducing device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a magneto-optical recording/reproducing apparatus of the present invention.

FIG. 2 is a time chart showing information recording and reproducing operations in the embodiment of FIG. 1;

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the information recording and reproducing principle of a conventional optical modulation method.

FIG. 5 is an explanatory diagram showing the information recording and reproducing principle of a conventional magnetic field modulation method.

[Explanation of symbols]

1 Magneto-optical disk 2　　　　Substrate 3 Magneto-optical recording film 4 Two-wavelength semiconductor laser device 7 Optical head 8 Electromagnet 9 Drive circuit 10 Modulation circuit 16 Light spot for recording 18 Information track 19,20 Magnetic domain 21 Light spot for playback

Claims (4)

[Claims] Claim 1: A light beam is irradiated from a light source onto a magneto-optical recording medium to raise the temperature of the magnetized film to a temperature higher than or near the Curie point temperature, and the heated portion is modulated in accordance with recorded information. In a magneto-optical recording and reproducing apparatus that records information on the medium by applying a magnetic field, the diameter of the recording light spot irradiated onto the recording medium during information recording is set to be smaller than the diameter of the light spot during reproduction. A magneto-optical recording and reproducing device characterized by being enlarged. [Claim 2] The light source according to claim 1 is a single light source that emits light of different wavelengths during recording and reproduction, and emits a longer wavelength during recording than during reproduction. Item 1. Magneto-optical recording and reproducing device. 3. The magneto-optical recording according to claim 1, wherein the light source comprises two light sources for recording and reproduction, and the wavelength of the recording light source is longer than the wavelength of the reproduction light source. playback device. 4. The magneto-optical device according to claim 1, wherein aberrations are well corrected at a light beam wavelength during reproduction, and aberrations are less adequately corrected at a light beam wavelength during recording than during reproduction. Recording and playback device.