JPS5954054A - Magneto-optical head - Google Patents

Abstract

PURPOSE:To improve reliability of an optically reproduced signal, by dividing a reflected light beam sent from a storing medium into two parts by a beam splitter and distributing successively a 1/2 wavelength plate, a polarized beam splitter and a photodetector on the optical axis of each split beam. CONSTITUTION:For a storing disk 1 obtained by sputtering an amorphous magnetic thin film of CdTbFe, etc., a magnetic thin film is formed on a recessing/ projecting guide track in order to obtain the trace error information. The light given from a laser device 2 is transmitted via a polarizer 3, a half prism 4 which increases the magneto-optical revolving angle produced in response to the state of magnetization of a storing medium, an objective lens 5 which forms a micro-spot on the magnetic thin film, a spot lens 6, a beam splitter 7, etc. Then about 1:1 correspondence is secured between the transmittance and reflection factor of S and P waves. In addition, 1/2 wavelength plates 8 and 9 are provided to change the replacement of revolving angle of the reflection information light in the prescribed direction.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to an optical storage device that uses a magnetic film as a recording medium and records, reproduces, and erases information by irradiating the recording medium with a light beam such as a laser beam. , particularly regarding its optical device.

<Prior Art> In recent years, optical storage devices have been widely studied as memory devices capable of higher density, larger capacity, and faster access.

Among these, there is a device that forms a fine pit row on a storage medium and uses the diffraction phenomenon of a light beam in the pit portion to reproduce light, or a device that forms bit-shaped areas with different refractive indexes on the storage medium and Alternatively, some devices for reproducing light using changes in transmittance are being put into practical use. However, the memory device only has the function of being read-only or capable of additionally recording information, and the problem remains that it does not have an erasing function, which is a major feature of the memory device.

Incidentally, among optical storage devices, a magneto-optical storage device that uses a magnetic material as a storage medium has three functions of recording, reproduction, and erasing, making it a useful optical storage device.

However, this magneto-optical storage device has problems such as its reproducing optical system being more complicated than other optical storage devices and the quality of the optical reproduction signal being poor, and its practical application has been delayed.

<Purpose> In view of the current situation as described in item 1, the present invention aims to simplify the reproduction optical system of a magneto-optical storage device and improve the reliability of the optical reproduction signal.

<Embodiments> Examples of the magneto-optical head according to the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment according to the present invention. 1
are GdTbFe, GdDyFe, GdTbDyFe
, TbFe, etc. (3) is coated on a substrate by sputtering. is formed.

2 is a laser device capable of emitting a laser beam of a predetermined intensity; 3
4 is a polarizer, 4 is a half prism that has the function of guiding the reflected information light from the storage disk 1 to the detection system side (B) and increasing the magneto-optical rotation angle that occurs depending on the magnetization state of the storage medium; - For example Rp=0.3, Tp=0
．． 7, Rs=0.99. When the polarization characteristic is Ts-0,01, the magneto-optic rotation angle can be increased by about 1.6 times. 5 is an objective lens that forms a minute spot on the magnetic thin film, 6 is a spot lens that focuses the reflected information light onto a photodetector, which will be described later, and 7 is a half prism (beam) that splits the reflected information light into two parts at right angles. splitter),
It has optical properties such that the transmittance and reflectance of S waves and P waves are close to 1:1, and the phase shift between P waves and S waves is small. As the half prism 7, a prism whose slanted surface is coated with Ag can be used.

(4) 8.9 shows the rotation angle displacement of the reflected information light in a predetermined direction. FIG. 2 shows the polarization state of the reflected information light after passing through the half prism 7 as a vector.

However, the polarization state of the laser beam incident on the storage disk 1 is P
direction. In FIG. 2, M+ and M- indicate the polarization state of the reflected information light corresponding to the magnetization information on the storage disk 1. In FIG. The reflected information lights M+ and M- are cut parallel to the optical axis and finished to a predetermined thickness through a crystal plate or a mica plate, and the phases of the polarized lights having planes of polarization perpendicular to each other are set to 180 degrees. It can be shifted. Therefore, it is possible to change only the orientation of the incident polarized light.

A in Fig. 2 indicates the direction of the axis where the phase lags.

expressed. Note that the direction A of the delay axis of the one-wavelength plates 8 and 9 is
, B are usually oriented on one side with respect to the direction ' of the incident polarized light.

With the above settings, the polarizing beam splitter 10 splits light with mutually orthogonal polarization planes into two. If the respective polarization axes of the polarization beams II are S and P in the figure, the light that has passed through the polarization beam splitter is intensity-modulated according to the magnetization state of the storage disk 1. Therefore, a photodetector 12 is installed on each reflective side of the polarizing beam splitter. At +3, lights with mutually opposite phases are obtained. The photodetector 12 is connected to a differential amplifier (not shown). By inputting the output signal of the IS, only information (recorded information) whose plane of polarization changes can be obtained.

On the other hand, the polarizing beam splitter 10. Of the photodetectors 14 and 15 arranged on the transmission side of the II, one detects a change in the relative distance to the storage disk 1 (!: objective lens 5, that is, detects the amount of light detected for focus servo), and the other detects the amount of light detected for the focus servo. This is a photodetector for track servo that detects the relative positional deviation between the guide track provided on the storage disk 1 and the laser beam spot.The error signals obtained by the photodetectors 14 and 15 are shown in the figure. The laser beam is fed through an amplification circuit and a phase compensation circuit (not shown) to a drive mechanism (not shown), and drives and controls the objective lens 5 or the entire optical head in the focus direction and track direction to focus the laser beam spot at a predetermined position. It is configured so that it can be used.

Note that the photodetector+4. , ] 5 is for focus.

Although they are not necessarily separated for the track, they may be configured to obtain both control signals with - photodetectors,
For example, it is also possible to obtain focus and tracking error signals from one photodetector, and detect the inclination of the storage disk 1 and the optical head from the other photodetector, and feed them back to the control signal.

Alternatively, a recording information signal is obtained from the (IJ) obtained by the photodetector 14.15 placed on the transmission side of the polarization beam splitters 10, 11 described above, and a photodetector placed on the reflection side of the polarization beam splitter 10.11 is used. A control signal such as a focus servo signal or a track servo signal may be obtained from the signal obtained in step 3.

<Effects> According to the present invention described in detail above, it is possible to actively utilize reflected information light, which was conventionally discarded after analysis, as control signal light. Although the optical system can be simplified, by using a long plate, reflected information light of any polarization direction can be obtained, thereby providing an extremely excellent optical head constituting a differential optical system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the magneto-optical head according to the present invention, and FIG. 2 is a vector diagram showing the polarization state of reflected information light. In the figure, 1: storage disk, 2: laser device, 3: 9:1
Wave plate, 10, 11: Polarization beam splitter, 12, 1
8, 14, 15: Photodetector.

Claims (1)

[Claims] 1. A magnetic thin film having perpendicular magnetic anisotropy is used as a storage medium,
In a magneto-optical head of a magneto-optical storage device that records, reproduces and erases information by irradiating the storage medium with a laser beam, a beam splitter divides a reflected light beam from the storage medium into two; A magneto-optical head characterized in that each of the splitters and the photodetector are arranged in this order. 2. A light beam separated by the beam splitter and incident on one side and a light beam incident on the polarization beam splitter of the beam splitter are connected to the P axis or S of the one polarization beam splitter and the other polarization beam splitter. 2. The magneto-optic heald according to claim 1, wherein phase delay directions are set such that polarization directions are opposite to each other with respect to the axis.