JPS58169358A - Optical reproducing device - Google Patents

Abstract

PURPOSE:To obtain detection sensitivity having high accuracy, by detecting a state variation of light which repeats reflection by a photomagnetic disk plural times, and reading the information. CONSTITUTION:A reflecting device R having a total reflector 8 is provided on the upper part of an objective lens 6. Laser light passes through a hole 10 of the reflecting device R, is condensed to one point 9 of a magnetic recording medium 1, is reflected, passes through the lens 6, passes through a reverse optical path again by the total reflector 8, and is returned from the hole 10, by which information is read. In this case, the laser light is influenced by a magnetic field 2 times from the medium 1, therefore, by a magnetooptic Kerr effect, the polarizing face is rotated on a comparatively large scale. Therefore, detection sensitivity having high accuracy can be obtained, and an S/N ratio is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a device for optically reproducing information on a medium, and particularly relates to a device for optically reproducing information on a medium, and in particular, it relates to a device for optically reproducing information on a medium, and in particular, it relates to a device for optically reproducing information on a medium, and in particular, it relates to a device for optically reproducing information on a medium, and in particular, it relates to a device for optically reproducing information on a medium. The present invention relates to an information reproducing method that reads information by detecting changes. By the way, the magneto-optical Kerr effect, as is well known, refers to a phenomenon in which the plane of polarization rotates when light is reflected by a substance or magnetic material in a magnetic field.

(2) Background of the Technology The development of optoelectronics has been remarkable in recent years, and in particular, optical disks or magneto-optical disks using lasers or the like have recently been attracting particular attention. Various playback devices have been proposed for optical disk devices, which have already been put into practical use, and there is therefore an increasing demand for high-performance devices.

(3) Prior art and problems - In the information reproducing method using the magneto-optical Kerr effect, in the conventional reproducing method, due to the interaction between light and magnetism, the polarization plane i inversion angle of light is
Since the angle is extremely small (0.5° in the case of Fe), it has the disadvantage that the detection sensitivity is relatively low due to the noise generated at the same time.

(4) Purpose of the Invention The purpose of the present invention is to make the light beam incident on the same spot on the magnetic medium multiple times using a reflector, etc. when reproducing information on a magneto-optical disk. An object of the present invention is to provide an optical reproducing device that can obtain highly accurate detection sensitivity by generating a relatively large change in the polarization state in the polarization plane and the polarization plane of light reflected by a magnetic medium multiple times.

(5) Structure of the Invention A feature of the present invention is that in an optical reproduction method for optically reproducing information from a medium on which information is recorded in an optically readable manner, reflection on the medium is prevented. The shape of light repeated multiple times! l! This is achieved by providing an optical playback device that reads information from the medium by detecting changes.

(6) Embodiments of the Invention First, the magneto-optical Kerr effect will be explained with reference to FIG.

Figure 1 shows that due to the magneto-optic Kerr effect, which is an interaction between light and magnetism, the polarization state of an incident light beam changes when reflected by a magneto-optical recording medium, causing rotation in the plane of polarization. It is an explanatory diagram.

In other words, as shown in FIG. 3(a), the direction of the magnetic field between the incident light beam and the beam irradiation part of the magneto-optical recording medium 1 is the same, +1
In the case of 1.-, the polarization plane of the light after being reflected by the magneto-optical recording medium 1 rotates 0 around the hour hand in θ. ((1) and (2) in the same figure) When the directions of the incident light beam and the magnetic field of the beam irradiation part on the magneto-optical recording medium 1 are opposite, the magneto-optical recording medium 1 The plane of polarization of the reflected light is also rotated counterclockwise by θ. ((3) and (4)
)) Therefore, it is possible to reproduce information on the medium by detecting the difference in the amount of light caused by the change in the polarization state between the incident light of the laser light on the magneto-optical recording medium 1 and the reflected light. However, since this change in polarization state is very small, there is a problem in that the signal-to-noise ratio is poor.

Next, one embodiment of the present invention will be explained with reference to the second WJ and FIG. 3.

FIG. 2 is an optical path diagram showing the reproduction method for the magneto-optical medium of the present invention. As for the path along which light travels, for example, light generated from a laser diode (LD) 2 is collected by a focusing lens (coupling lens) 3, and further becomes a parallel beam of light and passes through a polarizer 4. By the way, a polarizer is, for example, as well known as a Glan-Thompson prism.
This is a device that extracts only light with a specific polarization plane or state.

The plane of polarization is called the plane of optical vibration, and when this plane of polarization is limited to one plane, it is called linearly polarized light.

The laser light that passes through the polarizer 4 and becomes linearly polarized light is half reflected by the half mirror 5 and enters the objective lens 6, and is further reflected by the magneto-optical medium 1, so that the polarization plane is changed to, for example, θ. '(θK''<<1'''') rotation occurs, and the light reflected by the magneto-optical medium ! enters reflection #8, is reflected again, and re-enters the magneto-optical medium 1, and the reflected light is The light passes through the half mirror 5 again, and half of it is transmitted, that is, the original amount of light A enters the analyzer 4'.

Thereafter, only the light having the polarized component determined by the analyzer 4' is focused by the lens 3'. The optical reproducing apparatus of the present invention attempts to reproduce information using this method.

Here, a series of optical path diagrams related to the objective lens 6 and the magnetic medium 1 of the optical reproducing apparatus of the present invention for obtaining high detection sensitivity are shown in FIG. 3 and will be explained. In the figure, (a) is a front view showing the optical path, and (a) is a plan view.

The laser beam that passes through the hole lO provided in the reflective bag WR at the upper part of the objective lens 6 and enters the objective lens 6 is focused on a point 9 on the magnetic recording medium 1, passes through the objective lens 6, and then passes through the reflection device. The laser beam returns from the hole 10 again through the opposite optical path at the total reflection mirror 8 provided at R, but in the above path, the laser beam is twice influenced by the magnetic field from the magnetic recording medium 1. As a result, the plane of polarization rotates counterclockwise by 2θ for every θ. Therefore, the detection sensitivity for changes in the plane of polarization is increased, and the S/N ratio is improved.

FIG. 4 shows another embodiment using the reflecting mirror of the present invention, and the same parts as in FIG. 3 are given the same numbers.

As described above, the optical reproducing apparatus according to the present invention was implemented by installing a total reflection mirror above the objective lens, but as shown in the figure, total reflection mirror 8 was installed at three locations at appropriate angles with respect to the optical axis. Of course, by arranging the light beam and reflecting it four times in total, the plane of polarization can be rotated even more, and the detection sensitivity can be further increased. Further, the reflecting device R may be constituted by a reflecting mirror, and the hole 10 may be provided in this reflecting mirror.

In addition, this method is not only intended for reproduction of magneto-optical recording media, but can also improve the sensitivity when reproducing information from media recorded in bit format or with changes in reflectance. Needless to say.

(7) Effects of the Invention According to the present invention, detection sensitivity can be increased by increasing the number of reflections on the medium surface, and the S/N ratio can be improved.

[Brief explanation of the drawing]

Figure 1 shows the magneto-optical Kerr effect used in the present invention, Figure 2 is an optical path diagram showing the reproduction method using a magneto-optical medium, and Figures 3 (a) and (b) show the light in the vicinity of the magneto-optical medium. A front view and a plan view of the device of the present invention showing the path, and FIG. 4 are diagrams for explaining another embodiment of the present invention using four reflections. 1... Magnetic recording medium, 4... Polarizer, 4゛...
Detector, 6... Objective lens, 8... Total reflection mirror,
10...hole, R...reflector. (1) C2 No. C3 No. F4 No. 1 Figure 2 Figure 4

Claims (1)

[Claims] In an optical reproduction method that optically reproduces information from a medium on which information is recorded in an optically readable manner, a state table of light that is reflected multiple times on the medium is created. An optical playback device characterized in that information is read from the medium by detection.