JPH0247017B2 - JIKIKOGAKUHETSUDO - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to an optical storage device that uses a magnetic film as a storage medium and records, reproduces, and erases information by irradiating the storage 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 at the pit portion to reproduce light, or a device that forms bit-shaped regions 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 above devices only have the function of being read-only or capable of additionally recording information, and there remains the problem that they do not have an erasing function, which is a major feature of memory devices.

Incidentally, among optical storage devices, a magneto-optical storage device using a magnetic material as a storage medium has three functions of recording, reproducing, and erasing, and can be 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.

<Objective> In view of the above-mentioned current situation, it is an object of the present invention to simplify the reproduction optical system of a magneto-optical storage device and improve the reliability of optical reproduction signals.

<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 is GdTbFe, GdDyFe, GdTbDyFe,
A storage disk formed by sputtering a substrate with an amorphous magnetic thin film such as TbFe.
The magnetic thin film is formed on an uneven guide track (not shown) for obtaining tracing error information. 2 is a laser device capable of emitting a laser beam of a predetermined intensity; 3 is a polarizer; 4 guides the reflected information light from the storage disk 1 to the detection system side;
It is a half prism that has a function of increasing the magneto-optical rotation angle that occurs depending on the magnetization state of the storage medium, and 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 connects 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 splitter) that divides the reflected information light into two at right angles. It has the optical properties that the transmittance and reflectance of S waves and P waves are close to 1:1, and the phase shift of P waves and S waves is small. As this half prism 7, a prism whose inclined surface is coated with Ag can be used. 8 and 9 are half-wave plates (8 and 9) that can change the rotation angle displacement of the reflected information light in a predetermined direction
is a first 1/2 wavelength plate, and 9 is a second 1/2 wavelength plate).

The action of the 1/2 wavelength plate will be explained using FIG. 2.
FIG. 2 shows the polarization state of the reflected information light after passing through the half prism 7 using vectors.
However, the polarization state of the laser beam incident on the storage disk 1 is assumed to be in the 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. However, M ⁺ and M ^- in the same figure
is the light that is the result of the magneto-optic rotation angle of the light reflected by the optical storage disk 1 being increased by the half prism 4 which has the function of increasing the magneto-optic effect. These reflected information beams M ⁺ and M ^- pass through the half prism 7 (as mentioned above, this half prism 7 has a transmittance of S and P waves close to 1:1, and a phase shift between P and S waves. It is small. Therefore, it does not have the function of increasing the magneto-optical rotation angle, but simply divides the light into two.)
The light is split into approximately two halves by the light beam and enters the rear half-wave plates 8 and 9. The structure of the 1/2 wavelength plates 8 and 9 is a quartz plate or a mica plate cut parallel to the optical axis and finished to a predetermined thickness. It can be shifted by up to 180°. Therefore, it is possible to change only the orientation of the incident polarized light.

Now, for the reflected information light M ⁺ and M ^- , the 1/2 wavelength plate 8,
The directions of the axes with delayed phase of 9 are shown in Fig. 2A and 9, respectively.
When set as shown in B, the polarized light passing through the half-wave plates 8 and 9 is expressed as M ^+A , M ^-A , M ^+B , and M ^-B in the figure. That is, in the half-wave plate 8, the direction of the delay axis is set to A, and M ⁺ and M ^- change counterclockwise by twice the angle between the A direction and the (S) axis, and M ^{+ A} becomes a vector of M ^-A . In addition, the direction of the delay axis of the 1/2 wavelength plate 9 is set to B;
M ⁺ and M ^- change clockwise by twice the angle between the azimuth and the (S) axis, becoming vectors M ^+B and M ^-B .
As is clear from FIG. 2, the difference in polarization information corresponding to the magnetization information of the storage medium of the light beam passing through the half-wave plate is emphasized. Note that the orientations A and B of the delay axes of the half-wave plates 8 and 9 are usually one (n/4π-π/8) and the other (n/4π+π/8) with respect to the orientation of the incident polarized light. Set to value. Here, n is an integer of 0, 1, 2,... As a result, the angle between the A direction and the B direction is set to 45 degrees.

Polarizing beam splitters 10 and 11 that divide light having mutually orthogonal polarization planes into two with the above settings.
(10 is the first polarizing beam splitter, 11 is the second polarizing beam splitter).
Light with polarization direction is transmitted. ), the light passing through the polarizing beam splitter is intensity-modulated according to the magnetization state of the storage disk 1. Therefore, the photodetectors 12 and 13 (12 is the first photodetector, 13 is the second photodetector) installed on the reflective side of each of the polarizing beam splitters receive light with opposite phases to each other. It will be done. By inputting the output signals of the photodetectors 12 and 13 to a differential amplifier (not shown), only information (recorded information) whose plane of polarization changes can be obtained.

On the other hand, one of the photodetectors 14 and 15 (third photodetector) arranged on the transmission side of the polarizing beam splitters 10 and 11 detects a change in the relative distance between the storage disk 1 and the objective lens 5. In other words, a photodetector for focus servo (for example, a 4-split detector is used, and the splitting center of the photodetector is aligned in the direction of one dividing line with respect to the optical axis center of the reflected light. A focus servo signal can be easily obtained by shifting the focus servo by a small distance.This configuration is specified in the previously filed Japanese Patent Application No. 56-173975. (Of course, an optical system for obtaining servo signals may be provided.), and the other is a track servo system that detects the relative positional deviation between the guide track provided on the storage disk 1 and the laser beam spot. photodetector (this photodetector is
For example, by using a two-part detector having a dividing line in the track direction, a track servo signal can be easily obtained by the well-known push-pull method. ). The error signals obtained by the photodetectors 14 and 15 are fed back to a drive mechanism (not shown) via an amplification circuit and a phase compensation circuit (not shown), and drive the objective lens 5 or the entire optical head in the focus direction and track direction. It is configured to drive and control the laser beam spot to connect it to a predetermined position.

Note that the photodetectors 14 and 15 are for focus,
Although they are not necessarily separated for tracking, it may be configured to obtain both control signals using one photodetector. For example, one photodetector may be used to obtain focus and track error signals, while the other photodetector may be used to obtain focus and track error signals. The inclination of the storage disk 1 and the optical head is detected by a photodetector,
It is also possible to provide feedback to the control signal.

Or the aforementioned polarizing beam splitter 10,1
The recording information signal is obtained from the signal obtained by the photodetectors 14 and 15 placed on the transmission side of the polarizing beam splitters 10 and 11.
A configuration may be adopted in which a control signal such as a focus servo signal or a track servo signal is obtained from the signals obtained in steps 2 and 13.

<Effects> According to the present invention described in detail above, it is possible to actively utilize the reflected information light, which was conventionally discarded after detection, as control signal light. Therefore, the optical system can be simplified. Also, 1/2 for setting the polarization direction of the reflected information light.
By using a wavelength 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 drawings]

FIG. 1 is a block diagram of an embodiment of a 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: Polarizer, 4: Half prism, 5: Objective lens, 6: Spot lens, 7: Half prism,
8, 9: 1/2 wavelength plate, 10, 11: polarizing beam splitter, 12, 13, 14, 15: photodetector.

Claims (1)

[Scope of Claims] 1. In a magneto-optical head of a magneto-optical storage device that uses a magnetic thin film as a storage medium and records, reproduces, and erases information by irradiating the storage medium with a laser beam, there is provided the following: comprising: a beam splitter that splits a light beam into two; and first and second half-wave plates disposed on the optical axis of each light beam separated by the beam splitter; and the azimuth angles of the delay axes of the second 1/2 wavelength plate are made different from each other so as to emphasize the difference in the polarization state corresponding to the magnetization information of the storage medium of the light beam that has passed through the 1/2 wavelength plate, first and second polarizing beam splitters having planes of polarization perpendicular to each other on the optical axis of the light that has passed therethrough; and light reflected (or transmitted) by the first and second polarizing beam splitters. at least one third photodetector that detects the light transmitted (or reflected) by the two polarizing beam splitters; and at least one third photodetector that detects the light transmitted (or reflected) by the two polarizing beam splitters. and circuit means for obtaining recorded information by differentially outputting the output of the second photodetector; and circuit means for obtaining a servo signal from the output of the third photodetector. magneto-optical head.