JPS5938949A - Magneto-optical reproducer - Google Patents

Abstract

PURPOSE:To obtain a large output of reproduction, by providing an analyzer and a photodetector at both sides of a recording medium, and making use of both Kerr effect of reflected light and Faraday effect of transmitted light at a time to perform a magneto-optical reproduction. CONSTITUTION:The light sent from a laser light source 1 passes through a polarizer 2 and irradiated to a recording medium 4 after having its optical path bent by a half mirror 3. When the magnetization of the medium 4 is set upward, the polarized wave surface of the reflected light 6 turns by a Kerr revolving angle +thetaK to the polarized wave surface of the incident light 8. The light 7 transmitted through a substrate 5 turns by a Faraday revolving angle +thetaF. Then the light 6 passes through an optical detector 9 having its quenching direction turned by -thetaK and is detected by a photodetector 11. As the detector 10 has its quenching direction turned by -thetaF, no transmitted light 7 reaches a photodetector 12. Therefore, a reproduced signal having about doubled value of VR, where Vr is obtained when only the Faraday effect is used can be obtained by supplying outputs +VR and 0 which is applied with the photoelectric conversion by the detectors 11 and 12 to a differential amplifier 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a magneto-optic reproducing device that optically reproduces recorded information on a magneto-optic recording medium.

[Prior art]

So-called magneto-optical recording, in which recording is performed using the temperature rise of a recording medium due to absorption of light, is a type of optical recording, and because it uses a magnetic thin film as the recording medium, erasing and rewriting are possible. Furthermore, when a laser is used as a light source, light with excellent directivity and monochromaticity can be obtained, so it is possible to narrow down the light to about that wavelength and significantly improve the recording density. For these reasons, magneto-optical recording is attracting attention as a new magnetic recording method.

A magneto-optical effect is used to reproduce recorded information, and is called the Faraday effect or Kerr effect.

The Kerr effect is a rotation phenomenon of the plane of polarization that occurs when linearly polarized light is reflected by a recording medium, but the rotation angle at this time, that is, the Kerr rotation angle, is extremely small. For example, existing magneto-optical recording media MnB1゜Gd-Co, Gd-
Fe, Tb-Fe, Gd-Tb-Fe, etc. have a Kerr rotation angle of 0.7° or less in the visible light region. The signal-to-noise ratio during magneto-optical reproduction, that is, 8/N, strongly depends on the Kerr rotation angle, and since the Kerr rotation angle is small as described above, not only analog information but also tu 171. "°0"
Even when reproducing binary information, a sufficient 8/N ratio cannot be obtained.

On the other hand, the Faraday effect is a rotation phenomenon of the plane of polarization that occurs when linearly polarized light is transmitted through a recording medium, and the rotation angle at this time, that is, the shift Faraday rotation angle, is proportional to the film thickness of the recording medium. Therefore, by increasing the film thickness of the recording medium, a large Faraday rotation angle can be obtained. However, as the recording medium becomes thicker, the following drawbacks arise.

(1) Since the optical energy required during recording increases, a high output light source is required.

(2) The magnetization reversal region that can stably exist in the recording medium, ie, the minimum diameter of the recording bit, becomes large, making it difficult to significantly improve the recording density.

(3) Since the amount of light absorbed by the recording medium is large, the transmitted light intensity is very low, making it impossible to obtain a reproduced signal of sufficient intensity.

For the reasons mentioned above, there are restrictions on the film thickness of the recording medium, and as a result, the Faraday rotation angle becomes as large as the Kerr rotation angle, and a magneto-optical reproducing device that uses only transmitted light is no longer sufficient. The playback output cannot be desired.

[Purpose of the invention]

An object of the present invention is to provide a magneto-optical reproducing device for obtaining sufficient reproduction signal output.

[Summary of the invention]

In order to achieve the above object, the device of the present invention is characterized by disposing an analyzer and a light receiving element on both sides of the recording medium, and uses the Kerr effect of reflected light and the Faraday effect of transmitted light simultaneously to generate magnetic fields. Perform optical playback.

[Embodiments of the invention]

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

In FIG. 1, a laser beam emitted from a laser light source 1 passes through a polarizer 2 to become linearly polarized light, and the optical path is bent by a half mirror 3 before being irradiated onto a recording medium 4. When the magnetization of the irradiated area is upward, the recording medium 4
The plane of polarization of the reflected light 6 is rotated by the Kerr rotation angle +θ with respect to the plane of polarization of the incident light 8. On the other hand, the polarization plane of the transmitted light 7 transmitted through the recording medium 4 and the substrate 5 having sufficient light transmittance is rotated by the Faraday rotation angle +θF.

The reflected light 6 passes through an analyzer 9 rotated by one θ from the extinction direction with respect to the incident light 8, and is detected by a light receiving element 11. Further, the analyzer 10 placed on the transmitted light side
Because it is rotated by 10 degrees from the extinction direction,
The transmitted light 7 does not reach the light receiving element 12.

Therefore, each k photoelectrically converted by the light receiving elements 11 and 12
(7) If outputs 13 (=+VR) and 14 (=O) are input to the differential amplifier 15, +V! A positive output appears.

Conversely, when the incident light 8 is irradiated onto a region where the magnetization is downward, the plane of polarization of the reflected light rotates only partially, so it matches the extinction direction of the analyzer 9, and the reflected light 6 is directed toward the light receiving element 11. , and the output 13 becomes zero.

However, since the polarization direction of the transmitted light 7 is partly rotated by F, a part of it passes through the analyzer and is detected by the light receiving element 12, and an output 14 (=+V) is obtained. Therefore, the differential amplifier 15
gives a negative output of -v2.

The above magneto-optical reproduction principle is summarized in FIG.

Here, the differential amplifier outputs V+ and V2 are each VR.

The value of k in Figure 2 is set to 1 so that it is larger than VT.
Set above.

Now, a signal waveform 16 when a recording medium on which information "1010" is recorded is reproduced using the apparatus of the present invention is shown by a solid line in FIG. Here, upward magnetization corresponds to fi III, and downward magnetization corresponds to 0''.

Further, when only the Kerr effect or the Faraday effect is used as in a conventional magneto-optical reproducing device, a signal waveform 17 as shown by a dashed line is obtained.

When comparing the peak values of signal waveforms 16 and 17, the device of the present invention obtains a large value of IVll + l V2 l, and the peak value of the signal waveform obtained when only the Kerr effect (or Faraday effect) is used. It is approximately twice as large as the value VR(VT).

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a reproduced signal with a large output in magneto-optical reproduction.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the present invention, Fig. 2 is a table illustrating the regeneration principle of the inventive device, and Fig. 3 is a diagram illustrating a case in which the inventive device is used and a conventional device. This is the reproduced signal waveform at the time. 1... Laser light source, 3... Half mirror, 4...
・Recording medium, 9.10...Analyzer, 11.12...
Light receiving element, 15...Differential amplifier, 16...Positive image of one embodiment of the present invention 1 Figure O 2 Figure 269- 3 Figure O1Q

Claims (1)

[Claims] In an optical reproducing device that reproduces information recorded on a magneto-optical recording medium provided on a substrate using the magneto-optic effect, the reflected light and transmitted light of the light irradiated onto the recording medium during information reproduction are A magneto-optical reproducing device characterized in that it can be used simultaneously.