JPS6360451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information recording/reproducing apparatus using a so-called magneto-optical disk memory, and particularly to a writing/reading apparatus used in such an information recording/reproducing apparatus.

A so-called magneto-optical disk memory consists of a disk-shaped base made of glass, plastic, etc., and a perpendicularly magnetized film, usually several microns thick, provided on the base. The perpendicularly magnetized film is made of an amorphous alloy or the like and has the property of being magnetized only in the direction perpendicular to the film surface.

To record information on such a magneto-optical disk memory, first, the magnetization direction of the perpendicular magnetization film of the magneto-optical disk memory is aligned in one direction, and then a relatively weak bias magnetic field is applied in the opposite direction. A laser beam spot applied to the perpendicularly magnetized film and digitally modulated by an information signal is irradiated onto the perpendicularly magnetized film to bring the temperature of the perpendicularly magnetized film close to the so-called Curie temperature. Then, the part irradiated by the laser beam spot will be
The magnetization direction of the irradiated portion is reversed according to the direction of the bias magnetic field, and a logic "1" (or "0") is recorded. The recorded information is not changed by the bias magnetic field at room temperature.

Examples of alloy materials for the perpendicular magnetization film mentioned above include amorphous alloys such as gadolinium cobalt (GdCo) and gadolinium-terbium-iron (GdTbFe). In particular, it has been found that GdTbFe alloys have excellent properties, such that information can be recorded at a density of about 5 million bits per cm ² with an optical power of only a few mW.

In order to read the information recorded in the magneto-optical disk memory in this way, a reading beam spot is irradiated onto the perpendicularly magnetized film, and the difference in the direction of magnetization of the perpendicularly magnetized film causes a difference in the slope of the polarization plane of the reflected beam. It uses the Kerr effect phenomenon.

Development of a magneto-optical disk recording and reproducing apparatus for recording and reproducing video or audio information using the above-mentioned magneto-optical disk memory is progressing. The writing/reading device used in such a magneto-optical disk recording/reproducing device is relatively expensive and may be large because it includes both a recording optical system and a reading optical system.

Therefore, an object of the present invention is to provide a writing/reading device that is inexpensive and compact.

The writing/reading device according to the present invention uses a single laser light source as both a writing optical system and a reading optical system using a switching means.

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

In FIG. 1, a laser beam emitted from a laser light source 1 passes through a plane mirror 2, a polarizer 3, and a focusing lens 4, and then enters an optical modulator 5. The optical modulator 5 is
For example, an acoustic optical modulator (Acoustic Optical Modulator)
modulator), which modulates the intensity of the incident beam by a drive signal from the driver 6 in accordance with the input signal to be written. The modulated beam is λ/2 carried on a movable carrier member 7.
The light passes through the plate 8 and enters the polarizing prism 9. When a beam polarized by an angle α with respect to the crystal axis direction is incident on a λ/2 plate, the transmitted beam has an angle
It has the property of giving a polarization plane of 2α.
Therefore, by appropriately setting the polarization plane of the beam from the light source 1 or the polarization direction of the polarizer 3 with respect to the crystal axis of the λ/2 plate 8, the incident beam on the polarization plane 9a of the polarizing prism 9 becomes λ/2. If it passes through plate 8, it becomes S polarized light, and if it does not pass through λ/2 plate 8, it becomes P polarized light.
It can be made to be polarized light. Now, λ/2
If the plate 8 is located outside the optical path of the beam that has passed through the optical modulator 5, the beam incident on the polarizing prism 9 is P-polarized light, passes through the polarization plane 9a, and enters the plane mirror 11 of the writing optical system 10. do. The beam reflected by the plane mirror 11 passes through a polarizing prism 12 having a polarizing plane 12a, and further passes through a λ/4 plate 13,
The light is irradiated as a spot onto the perpendicularly magnetized film surface of the magneto-optical disk memory 16 through the plane mirror 14 and the objective lens 15. Magneto-optical disk memory 16
is placed on the turntable 17 and the clamper 1
8. turntable 19
is rotated at a predetermined speed by a drive motor 21 via a spindle 20. Drive motor 2
1 is movable in the direction of arrow A, and the writing beam writes information in a spiral track. A bias magnetic field generating coil 22 is provided on the opposite side of the objective lens 15 with the magneto-optical disk memory 16 in between. The bias magnetic field generating coil 22 generates a bias magnetic field in a direction corresponding to the bias current supplied through the terminals 22a and 22b, and cooperates with the writing beam to apply a magnetic change to the magneto-optical disk memory 16 to perform writing. It has an embedding effect. On the other hand, the reflected beam of the writing beam is reflected by the polarizing prism 12.
a and enters the photodetector 23, and the output of the photodetector 23 is used as a servo signal.

Next, when the λ/2 plate 8 is in the optical path of the beam that has passed through the optical modulator 5, the beam that has passed through the λ/2 plate 8 becomes S-polarized light, and the polarization plane 9a of the polarizing prism 9
After being reflected by another λ/2 plate 24 and having its polarization plane corrected by a predetermined angle, the plane mirrors 25 and 26
The light then enters the half mirror 27. The beam transmitted through the half mirror 27 passes through a plane mirror 28 and an objective lens 29, and is projected onto the perpendicularly magnetized film surface of the magneto-optical disk 16 as a reading beam. When the projected reading beam is reflected by the surface of the perpendicularly magnetized film, the plane of polarization rotates depending on the magnetization direction of the perpendicularly magnetized film (Kerr effect). This reflected beam passes through the objective lens 29 and the plane mirror 28 again, and then passes through the half mirror 27.
half of the reflected beam is incident on another half mirror 30. The beam split into two by the half mirror 30 passes through analyzers 31 and 32 and enters photodetectors 33 and 34. The transmission characteristics of the analyzers 31 and 32 are determined by the solid line a in FIG.
b, and a signal with an intensity corresponding to the inclination of the plane of polarization of the returned beam after passing through the half mirrors 27 and 30 is outputted from the differential amplifier 34 as a read signal.

The reason why the differential amplifier 35 is used to detect the displacement of the tilt of the plane of polarization is to cancel the noise component originally contained in the laser beam from the laser light source.

It goes without saying that the reading optical system is also provided with a servo optical system (not shown) to perform focusing and tracking servo of the reading beam, and since various servo systems are already known, they will not be described in detail here.

In the above-mentioned writing/reading device using the magneto-optical disk memory according to the present invention, the laser beam from a single laser light source is used as both the writing optical system and the reading optical system by a simple switching means. It is becoming easier to reduce the cost and size of the entire device.

Further, in the above embodiment, a λ/2 plate is used as the polarization plane rotation means, but a so-called Faraday rotation element whose polarization characteristics change depending on the applied electric field can also be used.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing the output characteristics of the analyzer used in FIG. 1. Explanation of symbols of main parts, 1... Laser light source, 3
...Polarizer, 5...Optical modulator, 6...Driver,
8, 24...λ/2 plate, 9...Polarizing prism, 1
0...Writing optical system, 12...Polarizing prism, 16
... magneto-optical disk memory, 19 ... turntable, 21 ... drive motor, 22 ... bias magnetic field generating coil, 23, 34 ... photodetector, 2
7, 30... Half mirror, 31, 32... Analyzer, 35... Differential amplifier.

Claims (1)

[Scope of Claims] 1. A turntable means rotatably supporting a magneto-optical recording disk having perpendicular magnetization characteristics, a writing optical system that emits a writing beam toward the magneto-optical recording disk, and a magneto-optical recording disk. a reading optical system that irradiates a reading beam onto the disk and detects the displacement of the polarization plane of the reflected beam to read information; a single laser light source; a polarization plane rotation means, comprising a switching means for selectively supplying the polarized light beam to the writing optical system and the reading optical system, the switching means rotating the polarization plane of the polarized beam by a predetermined angle in accordance with the switching command signal; A writing/reading device comprising: a polarizing prism having a polarizing plane onto which the polarized beam that has passed through the polarization plane rotating means is incident. 2. The polarization plane rotating means comprises a λ/2 plate and a driving means for selectively arranging the λ/2 plate on the optical path of the polarized beam according to the switching signal. The writing/reading device according to scope 1. 3. The writing according to claim 1, wherein the polarization plane rotation means includes a Faraday rotation element and a control means for changing the polarization characteristics of the Faraday rotation element according to the switching signal. reading device.