JPH01118248A - Magneto-optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To stabilize a laser beam source and to improve a C/N by providing a polarizing means which eliminates S polarization to be returned to the laser beam source of reflected light in an irradiation optical system which projects a laser beam in spot shape on a magneto-optical disk. CONSTITUTION:In the reflected light by the magneto-optical disk D, its polarizing plane is rotated in a direction of magnetization by a light spot, and the light is made incident on a first polarizing beam splitter 4 after passing an objective lens 6 and a mirror 5. An S polarized component in a direction of X out of incident reflected light on the first polarizing beam splitter 4 is made incident on a polarizing filter 21 after around 1% of it transmits the polarizing beam splitter 4, however, since the polarizing filter 21 shields the S polarized component in the direction of X, no S polarized component in the direction of X of the reflected light is made incident on the laser beam source 1. Thereby, the fluctuation of the S polarization of the laser beam due to the fluctuation of the light emitting component of the laser beam source 1 itself can be eliminated, then, the C/N can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a magneto-optical recording and reproducing apparatus that uses laser light to reproduce information recorded on a magneto-optical disk.

[Prior Art] In general, the magneto-optical recording method is used to record information by first irradiating a magneto-optical disk with laser light in the form of a spot, and creating a cue in which the recording medium loses magnetization only in the areas irradiated with the laser light. The temperature rises to the temperature above the scene. At this time, when the laser beam irradiation is stopped while an external magnetic field is applied, the temperature of the part that was irradiated with the laser beam decreases to that of a cuirass encyclopedia, and at the same time, it becomes magnetized in the direction of the external magnetic field. Even if the external magnetic field is removed in this state, the part that was irradiated with the laser beam will remain magnetized in the same direction as the external magnetic field that was applied earlier, so information can be recorded.

To reproduce information from a magnetic disk that has been recorded in this way, a spot of weak laser light that does not heat the recording medium to the temperature above the cue is irradiated. This results in the Kerr effect, in which the direction of rotation of the polarization plane of reflected laser light changes according to the direction of magnetization of the part irradiated with laser light, and the Faraday effect, in which the direction of rotation of the polarization plane of transmitted laser light changes. Therefore, the direction of magnetization of the portion irradiated with the laser beam can be detected from the rotation direction of the polarization plane of the laser beam, and information can be reproduced.

FIG. 4 shows the optical configuration of a conventional magneto-optical recording/reproducing device, with (a) being a side view and (b) being a plan view. A collimator lens 2, an anamorphic prism 3, a first polarizing beam splitter 4, and a mirror 5 are arranged along the optical path of the laser light source 1, and an objective lens 6 and a magneto-optical disk D are provided in the reflection direction of the mirror 5. . In addition, in the direction of reflection of light from the mirror 5 side of the first polarizing beam splitter 4, there is a 1/2 wavelength plate 7, a second polarizing beam splitter 8. A condenser lens 9, a first photodiode 10 are arranged, and a 172 wavelength plate 7 of a second polarizing beam splitter 8 is arranged.
A condenser lens 11 and a second photodiode 12 are installed in the direction in which light from the side is reflected. Furthermore, the output of the photodiode 10.12 is connected to a differential amplifier 13.

Note that the laser light source 1 is, for example, a laser diode, and the emitted laser light has elliptical radiation characteristics,
The anamorphic prism 3 has a function of correcting the cross-sectional shape of the laser beam described above from an ellipse to a circular shape. In addition, the first polarization beam splitter 4 has 60% of the P polarization component.
It transmits 40% of the light, reflects 40% of the light, and 1% of the S-polarized light component.
The 1/2 wavelength plate 7
rotates the plane of polarization of incident linearly polarized light by 45°.

The direction of the 1/2 wavelength plate 7 is 2 from the X direction which is the P polarization direction.
The half-wave plate 7 rotates the linearly polarized light in the X direction by 45'' across the optical axis.

Light configured like this? In a recording and reproducing device,
A laser beam irradiated from a laser light source 1 is turned into a parallel beam having a circular cross section by a collimator lens 2 and an anamorphic prism 3, and is incident on a first polarizing beam splitter 4. As described above, this first polarizing beam splitter 4 reflects 99% of the S polarized light component in the X direction and transmits 60% of the P polarized light component in the Y direction. Most of the laser light that passes through is the P-polarized light component in the Y direction, and this P-polarized light component is reflected by the mirror 5 and passes through the objective lens 6 to image a light spot on the magneto-optical disk D. And magneto-optical disk D
The laser beam irradiated is reflected, passes through the objective lens 6 and the mirror 5, and enters the first polarizing beam splitter 4 again. When the laser beam incident on the first polarizing beam splitter 4 is reflected by the magneto-optical disk D, the plane of polarization rotates from the Y direction by an angle δ or −δ according to the direction of magnetization of the optical spot portion. It has an S-polarized light component in the X-direction in addition to a P-polarized light component in the X-direction. As described above, the first polarizing beam splitter 4 receives most of the S-polarized component in the X direction and 40% of the P-polarized component in the Y direction of the incident laser beam.
The half-wave plate 7 rotates the polarization plane of the incident laser light by 45 degrees, and then irradiates the laser light onto the second polarization beam splitter 8 . And a second polarizing beam splitter 8
Of the laser light incident on the
The light passes through the polarizing beam splitter 8 and enters the photodiode 10 via the condenser lens 9. The S-polarized light component in the
incident on . The laser light incident on the photodiodes 10 and 12 is converted into an electrical signal, and the differential amplifier 1
3 to a control circuit (not shown) as a reproduction signal.

By the way, if the laser light incident on the 1/2 wavelength plate 7 is polarized in the X direction and does not have a P polarized component, the 1/2 wavelength plate 7 will convert the linearly polarized light in the Since the polarization plane of the laser beam incident on the second polarization beam splitter 8 forms an angle of 45 degrees with the X direction, the P polarization components in the two directions and the S polarization components in the X direction are equal. Laser light is magneto-optical disk D
Since the plane of polarization is rotated by the angle δ or -δ when reflected by the The polarization plane of the laser beam irradiated to the polarizing beam splitter 8 of No. 2 has an angle of 45° + δ or 45° − δ with the X direction, and
The P-polarized light component in the X-direction and the S-polarized light component in the X-direction are not equal, and one of the P-polarized light component in the X-direction and the S-polarized light component in the becomes larger than As a result, one of the electrical signals from the photodiodes 10 and 12 becomes stronger than the other, so the output of the differential amplifier 13 takes a positive or negative value according to the direction of magnetization of the optical spot portion of the optical disc D, and the information is transmitted. Can be played. Furthermore, if the differential amplifier 13 is used, changes in the intensity of the laser beam can be canceled out, making it possible to detect only the polarization angle of the laser beam. However, in general, the rotation angle of the polarization plane of the reflected light due to the magnetization of the magneto-optical disk D is a small amount of 1° or less, so C/
N (carrier to noise
o) It is difficult to perform reproduction with good ratio.

In addition, when using a magneto-optical recording/reproducing device, noise can be generated at the photodiode, regenerative amplifier tube laser light source, magneto-optical disk, etc.
When a laser diode is used as
Jump in the oscillation mode of the laser diode itself (C) Emphasis on fluctuations in the oscillation mode and jumps in the oscillation mode due to the P-polarized light returning to the laser diode (d) S-polarization longitudinal due to the S-polarization component of the return light from the magneto-optical disk This may be due to instantaneous oscillation of the mode or an increase in super radiance, but in the case of the conventional example mentioned above, the reproduced signal is detected differentially, so the influence of fluctuations in the light intensity of the laser beam is eliminated. be done. However, since a small amount of the S-polarized component of the laser beam output from the laser light source 1 is also irradiated onto the magneto-optical disk D, fluctuations occur in the S-polarized component of the laser beam as shown in (a) and (d). The fluctuation makes the reproduced signal unstable because the S polarization component indicates the rotation direction of the polarization plane by the magneto-optical disk D, and the Kerr rotation angle by the magneto-optical disk D is a small amount of 1 degree or less. There is a problem.

[Object of the Invention] An object of the present invention is to provide a magneto-optical recording and reproducing device that stabilizes a laser light source by suppressing the S-polarized component of the return light from a magneto-optical disk.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is to provide a laser light source that emits laser light, an irradiation optical system that projects the laser light from the laser light source in a spot shape onto a magneto-optical disk, a detection optical system that detects reflected light from the magneto-optical disk;

a reproducing circuit that outputs a reproducing signal based on a detection signal from the detection optical system, and a polarizing means for removing an S-polarized component of the reflected light that returns to the laser light source in the irradiation optical system. This is a magneto-optical recording and reproducing device characterized by:

[Embodiments of the Invention] The present invention will be described in detail based on embodiments illustrated in FIGS. 1 to 3.

FIG. 1 shows a first embodiment, (a) is a side view, (b)
is a plan view. This first embodiment has a configuration in which a polarizing filter 21 is disposed between the conventional 7-nanohik prism 3 shown in FIG. 4 and the first polarizing beam splitter 4. Note that the same reference numerals as in FIG. 4 indicate the same members, and the polarizing filter 21 has a function of removing the S-polarized light component in the X direction.

In the magneto-optical recording and reproducing apparatus configured as described above, the laser light emitted from the laser light source 1 is transmitted through the collimator lens 2. The anamorphic prism 3 turns the beam into a parallel beam with a circular cross section, and the polarizing filter 21 turns it into a parallel beam of light in the X direction.
After the polarized light component is removed, the light beam enters the first polarized beam splitter 4 and forms a light spot on the magneto-optical disk D via the mirror 5 and the objective lens 6. magneto-optical disk D
The reflected light has a polarization plane rotated by the direction of magnetization by the light spot, and enters the first polarizing beam splitter 4 through the objective lens 6 and mirror 5. Of the reflected light incident on the first polarizing beam splitter 4, S in the X direction
Approximately 1% of the polarized light component passes through the first polarizing beam splitter 4 and enters the polarizing filter 21;
1 blocks the S-polarized light component in the X direction, so the S-polarized light component in the X direction of the reflected light does not enter the laser light source 1 .

Therefore, the laser light source 1 does not cause instantaneous oscillation of the S-polarized longitudinal mode due to the S-polarized light component of the return light from the magneto-optical disk D, and does not cause an increase in superradiance. Fluctuations in the S-polarized light of the laser beam due to fluctuations in the S-polarized light are removed by the polarizing filter 21, so it is possible to obtain a reproduced signal with a good C/N ratio.

Of the light reflected by the magneto-optical disk D, the laser light reflected by the first polarizing beam splitter 4 is detected in the same manner as in the conventional example shown in FIG. Output.

FIG. 2 is a characteristic diagram of the C/N ratio comparing the first embodiment and the conventional example, where the horizontal axis is the output of the laser light from the laser light source 1, and the vertical axis is the C/N ratio. Characteristic A is polarizing filter 2
1 is inserted, and B shows the case where it is not inserted. From this characteristic diagram, it can be seen that when the polarizing filter 21 is inserted as in the first embodiment, the C/N is higher than when it is not inserted.
It was found that the C/N ratio was significantly improved, and the improvement in the C/N ratio was particularly remarkable when the laser oscillation of the laser light source 1 was unstable and low output.

FIG. 3 shows the second embodiment, (a) is a side view, (-b
) is a plan view, in which a third polarized beam having the same characteristics as the first polarized beam splitter 4 is inserted between the conventional anamorphic prism 3 shown in FIG. 4 and the first polarized beam splitter 4. A splitter 22 is provided, and a condenser lens 2 is provided along the optical path in the direction of reflection of the reflected light from the mirror 5 side of the third polarizing beam splitter 22.
3. Cylindrical lens 24, photodiode 25
are arranged sequentially.

In this case, the laser beam emitted from the laser light source 1 becomes a parallel beam with a circular cross section by the collimator lens 2 and the anamorphic prism 3, and enters the third polarizing beam splitter 22 and the first polarizing beam splitter 4 sequentially. However, as mentioned above, the polarizing beam splitter 4.2
2 transmits 1% of the S-polarized light component and reflects 99%, so
There is almost no S-polarized component in the laser beam that has passed through the third and first polarizing beam splitters 22.4. This first
A laser beam emitted from a polarizing beam splitter 4 is reflected by a mirror 5 and forms a light spot on a magneto-optical disc via an objective lens 6. The light reflected by the magneto-optical disk D has its polarization plane rotated by the direction of magnetization by the light spot, and passes through the objective lens 6 and mirror 5 to the first
The light enters the polarizing beam splitter 4 and the third polarizing beam splitter 22 sequentially, but as mentioned above, the polarizing beam splitter 4.22 transmits only 1% of the S-polarized component, so the third polarizing beam splitter 22 0 of the S polarization component of the reflected light incident on the first polarization beam splitter 4
．． Even if the laser light source 1 is irradiated, there is almost no effect on the laser light source 1. Therefore, the first
Similarly to the embodiment described above, it is possible to obtain a reproduced signal with a good C/N ratio.

In addition, 60% of the P-polarized light component of the reflected light from the magneto-optical disk D is transmitted through the first polarization beam splitter 4, and 10% of it is reflected from the magneto-optical disk D by the third polarization beam splitter 22. 6% of the P-polarized component of the light is reflected, and the condenser lens 23 and the cylindrical trical lens 24
The photodiode 25 is irradiated through the photodiode 25. and,
Focusing control and tracking control are performed by a control circuit (not shown) based on the output from the photodiode 25.

Further, of the light reflected by the magneto-optical disk D, the laser light reflected by the first polarizing beam splitter 4 is detected in the same way as in the conventional example shown in FIG. 4, and a reproduced signal is output from the differential amplifier 13. do.

In this way, a reproduced signal with a good C/N ratio can be obtained by removing the S-polarized component of the light returned to the laser light source 1, but the polarization used to remove the S-polarized component Filter 21 and third polarizing beam splitter 2
Although the polarization ratio of 2 largely depends on the characteristics of the laser light source 1, it is considered that a value of 30 or more is sufficient, for example.

[Effects of the Invention] As explained above, the magneto-optical recording and reproducing apparatus according to the present invention suppresses the S-polarized component of the return light from the magneto-optical disk to the laser light source by providing the polarization means in the irradiation optical system. As a result, the laser light source is stabilized and C
A reproduced signal with a good /N ratio can be obtained.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the magneto-optical recording and reproducing apparatus according to the present invention, FIG. 1(a) is a side view of the first embodiment, FIG. 2(b) is a plan view, and FIG. is the first embodiment, C of the conventional example
/N ratio characteristic diagram, FIG. 3(a) is a side view of the second embodiment, FIG. 3(b) is a plan view, FIG. 4(a) is a side view of the conventional example, and FIG. 4(b) is a plan view. It is a diagram. 1 is a laser light source, 2 is a collimator lens, 3 is an anamorphic prism, 4.8.22 is a polarizing beam splitter, 5 is a mirror, 6 is an objective lens, 7 is a 172 wavelength plate, 9.11 is a condenser lens, 10 .12.25 is a photodiode, 13 is a differential amplifier, and 21 is a polarizing filter. . Patent applicant: Shibasoku CD Co., Ltd.

Claims (1)

[Claims] 1. A laser light source that emits laser light, an irradiation optical system that projects the laser light from the laser light source in a spot shape onto a magneto-optical disk, and detects reflected light from the magneto-optical disk. Polarized light that includes a detection optical system and a regeneration circuit that outputs a reproduction signal based on a detection signal from the detection optical system, and that removes an S-polarized component of the reflected light that returns to the laser light source in the irradiation optical system. 1. A magneto-optical recording and reproducing device characterized by comprising means. 2. The magneto-optical recording and reproducing apparatus according to claim 1, wherein the polarizing means is a polarizing filter. 3. The magneto-optical recording and reproducing apparatus according to claim 1, wherein the polarizing means is a polarizing beam splitter.