JPH02301046A - Magneto-optical head device - Google Patents

Abstract

PURPOSE:To attain the miniaturization and simplification of a device and to reproduce an optical recording medium by providing a Faraday rotator which rotates the polarizing plane of a laser beam only by a prescribed angle between a semiconductor laser and a magneto-optical recording body. CONSTITUTION:The semiconductor laser 1 for the irradiation of the laser beam, an optical detector 4 to detect the light output of the laser 1, and the Faraday rotator 2 provided between the semiconductor laser 1 and a magnetic recording medium 3 and which rotates the polarizing plane of the laser beam by the prescribed angle are provided on the medium 3. Emission light from the front plane of the laser 1 transmits the Faraday rotator 2, and with which the magneto-optical recording medium 3 is irradiated, and the reflected light transmits the rotator 2 in a reverse direction, then, is fed back again to the laser 1. The emission light from the rear plane of the laser 1 is received with the optical detector 4. The quantity of change of an oscillation threshold current corresponding to the magnitude of the quantity of coupling as feedback light can be increased by using the laser on the front plane of which nonreflective coating is applied as the laser 1. Therefore, the quantity of change of the light output when the device is driven with a constant bias current can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical head device for reproducing information recorded on a magneto-optical recording medium.

[Conventional technology]

FIG. 7 shows a configuration example of a conventional magneto-optical head device for reproducing information recorded on a magneto-optical recording medium.

The emitted light from the semiconductor laser 1 is collimated by the collimating lens 21, transmitted through the beam splinters 22 and 23, and then condensed by the objective lens 24 and irradiated onto the magneto-optical recording medium 3. A part of the reflected light from the magneto-optical recording medium 3 is reflected by the beam splitter 23, and is reflected by the lens 25. The light passes through the analyzer 26 and is received by the photodetector 27. The difference in the direction of rotation of the polarization plane of the reflected light, which corresponds to the direction of magnetization of the magneto-optical recording medium 3, is converted by the analyzer 26 into the magnitude of the amount of light received by the photodetector 27, and is recorded on the magneto-optical recording medium 3. The recorded information will be played back.

On the other hand, another part of the reflected light from the magneto-optical recording medium 3 is transmitted through the beam splitter 23, reflected by the beam splitter 22, transmitted through the lens 28, and then split into two by the half mirror 29. The transmitted light of the half mirror 29 is received by the photodetector 31 via the knife 30 and used for focus error detection using the knife method, and the reflected light of the half mirror 29 is received by the photodetector 32 and tracked using the push-pull method. Used for error detection.

In contrast to magneto-optical head devices that use a large number of optical components, write-once optical head devices that play back optical recording media on which information is recorded depending on the reflectance of the device are designed to take advantage of the self-coupling effect of semiconductor lasers. A method has been proposed that utilizes this method to significantly downsize and simplify optical head devices.

FIG. 8 shows an example of the configuration of a write-once optical head device using this method (for example, INTERNATIONAL SYMPO
5IUMON 0PTICAL MEMORY 198
7. (See TB4). According to this write-once optical head device, the light emitted from the front surface of the semiconductor laser l is transmitted to the optical recording medium 13.
The reflected light returns to the semiconductor laser l again. On the other hand, the light emitted from the rear surface of the semiconductor laser 1 is received by the photodetector 4. FIG. 9 shows the principle of signal reproduction by the write-once optical head device of FIG. The injection current vs. optical output characteristic of the semiconductor laser 1 is as shown in characteristic (1) when the reflectance of the optical recording medium 13 is high because the amount of coupling with the feedback light is large, and when the reflectance is low, the amount of coupling with the feedback light is as shown in characteristic (1). Since the amount of coupling is small, characteristic (2) is obtained. Therefore, if the bias current is set at point A in the figure, the optical output of the semiconductor laser 1 will change between point B and point 0 in the figure depending on the reflectance of the optical recording medium 13, and this change will be reflected in the light. Information can be reproduced by detecting it with the detector 4.

In this optical head device, the semiconductor laser 1 and the photodetector 4 are integrated and floated close to each other above the optical recording medium 13, thereby eliminating the need for a focus servo mechanism. Furthermore, by using a known sample servo method, the track error signal can be detected as a change in the optical output of the semiconductor laser 1 depending on the reflectance of the optical recording medium 13, so it is possible to perform a track servo operation. It is.

[Problem to be solved by the invention]

The magneto-optical head device shown in FIG. 7 has problems in that it uses a large number of optical components, which increases the cost and increases the weight, resulting in a longer access time.

Further, although the write-once type optical head device shown in FIG. 8 has the advantage of being small and simple, it cannot reproduce a magneto-optical recording medium in which information is recorded in the direction of magnetization.

SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional problems and provide a magneto-optical head device that is small, simple, and capable of reproducing a magneto-optical recording medium.

[Means to solve the problem]

The magneto-optical head device of the present invention includes a semiconductor laser for irradiating a laser beam onto a magneto-optical recording medium, and a means for detecting the optical output of the semiconductor laser, and includes a means for detecting a light output of the semiconductor laser and a magneto-optical recording medium. Between,
It is characterized by having at least a Faraday rotator that rotates the polarization plane of laser light by a predetermined angle.

[Effect]

The operation of the magneto-optical head device of the present invention will be explained below with reference to FIG. The arrows in (a) to (d) of the figures indicate the direction of the polarization plane of the laser light in each part of the magneto-optical head device. The light emitted from the semiconductor laser is shown in (a) in the normal diagram.
) is linearly polarized light parallel to the junction plane. When this light passes through the Faraday rotator, the plane of polarization is rotated by a predetermined angle θ, as shown in (b) in the figure, and is irradiated onto the magneto-optical recording medium. When this light is reflected by the magneto-optical recording medium, the plane of polarization is rotated by θ in the positive or negative direction in accordance with the direction of magnetization, as shown in (c) of the figure. When this light passes through the Faraday rotator in the opposite direction, the plane of polarization is roughly rotated by θ, as shown in (d) in the figure. This light returns to the semiconductor laser again, and as shown in the figure (a)
) Only the polarized light component parallel to the emitted light is combined with the emitted light.

As can be seen from figure (d), the magnitude of this polarization component differs depending on the direction of rotation of the polarization plane of the reflected light from the magneto-optical recording medium. Similarly, according to the principle shown in Figure 9, the difference in the direction of rotation of the plane of polarization is converted into the magnitude of the optical output of the semiconductor laser, and by detecting the magnitude of this optical output, information recorded on the magneto-optical recording medium is reproduced. can do.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a first embodiment of a magneto-optical head device of the present invention. This magneto-optical head device has a magneto-optical recording medium 3.
A semiconductor laser l for irradiating a laser beam to the semiconductor laser l, a photodetector 4 for detecting the optical output of the semiconductor laser l, and a photodetector 4 for detecting the optical output of the semiconductor laser l, which is provided between the semiconductor laser l and the magneto-optical recording medium 3, and a photodetector 4 for detecting the polarization plane of the laser beam. It has a Faraday rotator 2 that rotates by a predetermined angle.

The light emitted from the front surface of the semiconductor laser l passes through the Faraday rotator 2 and is irradiated onto the magneto-optical recording medium 3, and the reflected light passes through the Faraday rotator 2 in the opposite direction and returns to the semiconductor laser l again. . On the other hand, the light emitted from the rear surface of the semiconductor laser 1 is received by the photodetector 4. By using a semiconductor laser with an anti-reflection coating on the front surface, it is possible to increase the amount of change in the oscillation threshold current depending on the amount of coupling with the feedback light, and as a result, the amount of change in the oscillation threshold current can be increased. The amount of change in optical output when driven with bias current can also be increased.

The Faraday rotator 2 can be made much thinner than bulk materials by using a thick film material such as old substituted Garnet, making the overall size of the magneto-optical head device significantly smaller. can be converted into For example, the thickness of the Faraday rotator 2 is such that the rotation angle θ of the plane of polarization is 40
deg.

In this embodiment, the photodetector 4 is used to detect the semiconductor laser l.
However, it is also possible to detect changes in the optical output by observing the voltage between the electrodes of the semiconductor laser l.

FIG. 3 shows the configuration of a second embodiment of the magneto-optical head device of the present invention. In this embodiment, a semiconductor laser 1 is used which has a property that its optical output changes discontinuously with a certain injection current. FIG. 4 shows the principle of signal reproduction by the magneto-optical head device of FIG. Injection current of semiconductor laser l-
When the amount of coupling with the feedback light is large, the optical output characteristics are
1), when the amount of coupling with the feedback light is small, the characteristic (2) is obtained, and the optical output changes discontinuously with the injection currents at points D and E in the figure, respectively. Therefore, if a noise current is set at point A in the figure, the optical output of the semiconductor laser 1 will change between point B and point 0 in the figure depending on the amount of coupling with the feedback light, and this change will be detected by photodetection. By detecting the information with the device 4, the information recorded on the magneto-optical recording medium 3 can be reproduced.

As the semiconductor laser 1 in this embodiment, for example, one in which one electrode is divided into two regions, an excitation region 11 and an absorption region 12 in the direction of light propagation, can be used. If a current is injected only into the excitation region 11 and the absorption region 12 is left open, the absorption region 12 will function as a saturable absorber, and the optical output will change discontinuously with a certain injection current. At this time, optical bistability may be exhibited in that the current that changes the optical output from a low level to a high level is different from the current that changes from a high level to a low level, but the interval between these currents is shown in Figure 4. A similar effect can be obtained if the interval is smaller than the interval between the injection currents at points D and E.

Since the amount of discontinuity in the optical output of the semiconductor laser 1 depends on the lengths of the excitation region 11 and the absorption region 12, by optimizing the length of each region and increasing the amount of discontinuity in the optical output, a constant amount of discontinuity can be achieved. When driven with a bias current, the amount of change in optical output depending on the amount of coupling with feedback light can also be increased.

In the embodiment shown in FIG. 3, the excitation region 11 is on the front side of the semiconductor laser l, but similar characteristics can be obtained even if the absorption region 12 is on the front side.

FIG. 5 shows the configuration of a third embodiment of the magneto-optical head device of the present invention. In this embodiment, a lens 5 is provided between the Faraday rotator 2 and the magneto-optical recording medium 3 in the magneto-optical head device shown in FIG.

The light emitted from the semiconductor laser 1 is normally a diverging light, but
By condensing this light with the lens 5, the diameter of the spot formed on the magneto-optical recording medium 3 can be made smaller than when the lens 5 is not used.

FIG. 6 shows the configuration of a fourth embodiment of the magneto-optical head device of the present invention. In this embodiment, in addition to the embodiment shown in FIG. 6
is provided. The optical axis of the polarizer 6 is set so that all polarized light components parallel to the cemented surface of the semiconductor laser 1 are transmitted. 6 The light emitted from the semiconductor laser 1 is normally linearly polarized light parallel to the cemented surface. , a slight polarization component perpendicular to the bonding surface is also included. Since this light becomes completely linearly polarized light by passing through the polarizer 6, the extinction ratio is improved compared to the case where the polarizer 6 is not used, and the S/N during reproduction is improved.
will improve. At this time, in the reflected light from the magneto-optical recording medium 3, only the polarized light component parallel to the cemented surface of the semiconductor laser l passes through the polarizer 6 in the opposite direction and returns to the semiconductor laser 1, and the polarized light component perpendicular to the cemented surface is blocked by the polarizer 6, but even if this polarized light component returns to the semiconductor laser I, it is not combined with the emitted light, so the effect is the same as when the polarizer 6 is not used.

By using a birefringent diffraction grating or a high-density grating as a material, the polarizer 6 can be made much thinner than a bulk type polarizing beam splitter or a Glan-Thompson prism.

In the magneto-optical head device of the present invention, similarly to the write-once optical head device shown in FIG. , the focus servo mechanism becomes unnecessary. In addition, by using the well-known sample servo method, the track error signal can be detected as a change in the optical output of the semiconductor laser depending on the reflectance of the magneto-optical recording medium, so it is possible to perform track servo operation. be.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a small and simple magneto-optical head device capable of reproducing a magneto-optical recording medium in which information is recorded in the direction of magnetization.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of the magneto-optical head device of the present invention, FIG. 2 is a diagram showing the direction of the polarization plane of laser light in each part of the magneto-optical head device of the present invention, and FIG. 4 is a diagram showing the structure of a second embodiment of the magneto-optical head device of the present invention, FIG. 4 is a diagram showing the principle of signal reproduction by the magneto-optical head device of FIG. 3, and FIG. FIG. 6 is a diagram showing the configuration of a fourth embodiment of the magneto-optical head device of the present invention; FIG. 7 is a diagram showing the configuration of a conventional magneto-optical head device. Figure 8 is a diagram showing an example of the configuration of a write-once optical head device that utilizes the self-coupling effect of a semiconductor laser, and Figure 9 is a diagram showing the principle of signal reproduction by the write-once optical head device shown in Figure 8. It is a diagram. l...Semiconductor laser 2...Faraday rotator 3...Magneto-optical recording medium 4...Photodetector 5...Lens 6...Polarized light Child 11...Excitation region 12...Absorption region 13...Optical recording medium 21...Collimating lenses 22, 23...Beam splitter 24...Objective lens 25... Lens 26... Analyzer 27... Photodetector 28... Lens 29... Half mirror 30... Naifetsuji 31, 32... ... Photodetector agent Patent attorney Yoshiyuki Iwasa 1: Semiconductor laser 2: Faraday rotator 3' magneto-optical recording vX 4: Photodetector Figure 1 (o) (b) (C)
(d) Fig. 2 1 Half-width rectangle 2 Faraday rotator 3 Magneto-optical recording medium 4, photodetector 11 Excitation region 1 or 120 q or 10 π rotation 3rd section 1 Hair shaft 1 Faraday rotation ± 3 Magneto-optical recording medium 4 Photodetector 5I/cis. Fig. 5 1 , Semiconductor laser 2 Faraday rotation j 3 Magneto-optical recording medium 4 Optical receiver 5 Reflector 6 Polarizer Fig. 6 1 Semiconductor laser 26 Preparation for analysis 3 Magneto-optical recording medium 27 Light Detector FIG. 7 1 Semiconductor laser 4 Photodetector I3. Optical recording medium Figure 8

Claims (1)

[Claims] (1) A semiconductor laser for irradiating a laser beam onto a magneto-optical recording medium, and a means for detecting the optical output of the semiconductor laser, the laser beam being emitted between the semiconductor laser and the magneto-optical recording medium. A magneto-optical head device comprising at least a Faraday rotator that rotates a plane of polarization by a predetermined angle.