JPH0437491B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is characterized in that information is recorded magnetically, and a rotational component of the plane of polarization of an irradiated light beam produces different reflected light depending on the information. The present invention relates to a recording/reproducing device for a magneto-optical memory.

[Prior Art] In general, an optical magnetic memory (hereinafter also referred to as a magneto-optical disk) having a magnetic Kerr effect is capable of magnetically writing desired information and reading the written information optically. Recently, it has started to attract attention as a rewritable large-capacity memory.

An example of a conventional optical magnetic memory and its recording/reproducing device is shown in FIG. First, the recording device A of the optical magnetic memory recording and reproducing device 1 will be explained.

The laser light emitted from the semiconductor laser SL1 is
The magnifying lens L1 converts the light into parallel light, and the total reflection mirror M1 converts the optical path. Further, this laser light passes through a polarizing beam splitter 2 and a quarter wave plate 3, and is focused onto a magneto-optical disk 4 by an objective lens L2 to form a spot 5.
In the magneto-optical disk 4, only this spot 5 is heated by condensing light, and the previously recorded magnetization is erased. Thereafter, only the spot 5 is remagnetized in the direction of the magnetic field applied by the coil 6 and new information is recorded.

The magneto-optical disk 4 has an amorphous GbTbFe alloy film layer 4b laminated on a glass substrate 4a, and is rotated at a constant speed about a rotation axis 4c. The laser beam reflected by the magneto-optical disk 4 passes through the quarter wave plate 3 again, so that its plane of polarization is rotated by 90 degrees with respect to the incident light. Therefore, the reflected light is separated from the incident light by the polarizing beam splitter 2, and after passing through the cylindrical lens L3,
It is converted into a focus error signal FE1 by the photodiode D1. The objective lens L2 is controlled by this focus error signal FE1, and the spot 5 is always formed correctly on the magneto-optical disk 4. Note that the semiconductor laser SL1 is controlled by the laser driving device 7 so as to emit light only during writing.

Next, the playback device B of this recording and playback device 1 will be explained. The laser beam emitted from the semiconductor laser SL2 is made into parallel beams by a magnifying lens L4, divided into three laser beams by a diffraction grating 8, and further converted into linearly polarized beams by a polarizer 9. Here, in FIG. 1, the laser beam B after the polarizer 9 is
1, B2, and B3 correspond to three laser beams divided by the diffraction grating 8. The center laser beam B1 is used for an information signal and a focus error signal, and the laser beams B2 and B3 on both sides are used for a tracking signal.

The three laser beams are focused by a lens L5 and an objective lens L6 to form three spots on the magneto-optical disk 4. Furthermore, between the lens L5 and the objective lens L6, there is a total reflection mirror M2 for optical path conversion.
A half mirror H1 for taking out the reflected light from the magneto-optical disk 4 is arranged.

Information "0" or "1" is recorded on the magneto-optical disk 4 in accordance with the direction of magnetization. To read information recorded on the magneto-optical disk 4, the so-called Kerr effect is used, in which the direction of rotation of the polarization plane of the reflected light from the four surfaces of the magneto-optical disk differs depending on the direction of magnetization of the magnetic material. . In order to detect only the rotational component of this plane of polarization, the half mirror H1
The reflected light taken out from the mirror is split into two directions by a half mirror H2. For one laser beam, analyzer A1 passes only the reflected light with information "1", and for the other laser beam, analyzer A2 passes only the reflected light with information "0". It is allowed to pass through.

Therefore, both of these reflected lights are detected by photodiodes D2 and D3, respectively, and an information signal IS1 is generated.
“0” or “1” stored in the magneto-optical disk 4 is extracted by the differential amplifier AMP1.
information can be reproduced. At the same time, by placing a cylindrical lens L7 after the analyzer A2, a focus error signal FE is generated from the photodiode D3.
2 is obtained. Further, the tracking error signal TES1 is obtained by detecting the reflected light of the laser beam B2 by the silicon blue cells S1 and S2 and extracting the difference in output by the differential amplifier AMP2. Tracking uses this tracking error signal TES
1, the objective lens L16 is connected to the magneto-optical disk 4.
This is done by moving it in the radial direction.

[Problems to be Solved by the Invention] However, such an optical magnetic memory reproducing device has the following drawbacks. That is, the optical system has a large number of parts, and it takes a lot of time to adjust the optical axis, and errors are likely to occur due to misalignment of the optical system parts. Furthermore, optical loss due to reflection of light in each optical system component is also large. Also,
In the reproducing device, the reflected light from the four surfaces of the magneto-optical disk passes through the half mirror H1 and is transmitted to the semiconductor laser.
Because it returns to SL2, the operation of semiconductor laser SL2 becomes unstable due to changes in optical output, resulting in errors and S/N.
This results in a deterioration of the ratio.

[Object of the Invention] An object of the present invention is to solve the above-mentioned conventional drawbacks, to simplify the configuration of the entire optical system by using an optical circulator, and to provide a magneto-optical memory recording capable of stable signal reproduction. The purpose of the present invention is to provide a playback device.

[Example] Hereinafter, a second example embodying the present invention will be described.
This will be explained in detail with reference to FIGS. 3 to 3.

FIG. 2 shows a schematic configuration of a magneto-optical memory and a recording/reproducing device thereof according to the embodiment. Semiconductor laser SL
The laser beam emitted from the laser beam 3 becomes a parallel beam by the magnifying lens L10, and is further changed into three directions by the acousto-optic light polarizer 11. The first port PA of the optical circulator 12 through the lens L11
is incident on the This optical circuit 12 converts the laser light irradiated by the semiconductor laser SL3 and entered through the first port PA into linearly polarized light and outputs it to the magneto-optical disk 4 through the second port PB.
The laser light emitted from the second port PB is focused on the magneto-optical disk surface 4 by the objective lens L12 to form three spots.

The light reflected by the magneto-optical disk surface 4 passes through the objective lens L12, enters the second port PB of the optical circulator 12, and exits from the third port PC. At this time, since the polarization plane of the reflected light is preserved, the rotational component of the polarization plane caused by the magnetic Kerr effect is also faithfully transmitted. In addition, since the reflected light from the magneto-optical disk surface 4 that is incident on the second port PB does not directly exit from the first port PA and return to the semiconductor laser SL3, the operation of the semiconductor laser SL3 may become unstable and the S /N ratio deterioration can be prevented. Three reflected lights emitted from the third port PC of the optical circulator 12 are split into two directions by a half mirror H3.

Hereinafter, signal reproduction is performed in the same manner as in the conventional example shown in FIG.
The light is received by photodiode arrays C4 and D5 through A4 and cylindrical lens L13, respectively, and an information signal IS2 and a focus error signal FE3 are obtained as the output of the differential amplifier AMP3, and a tracking error signal TES2 is obtained as the output of the differential amplifier AMP4.

During reproduction, the laser output is controlled by the laser driving device 13 so that the temperature of the laser spot portion 15 on the magneto-optical disk surface 4 is below the recording temperature and the S/N ratio is large. Further, ultrasonic waves are applied to the acousto-optic light polarizer 11 by the acousto-optic light polarizer driving device 14, and the laser beam is
The laser beam B1 at the center is used for detecting the information signal IS2 and the focus error signal FE3, and the laser beams B2 and B3 at both ends are used for detecting the tracking error signal TES2. By reading this information signal IS2, any address on the magneto-optical disk 4 can be accessed.

During recording, after the recording address is accessed, the laser output is increased in a pulsed manner by the laser driving device 13, and the laser spot portion 15 on the magneto-optical disk 4 is heated to a temperature higher than the recording temperature. At the same time, a magnetic field is applied in the direction corresponding to the information being written by the coil 16, and new information is written. At this time, since no ultrasonic waves are applied to the acousto-optic light polarizer 11, the laser light is not polarized and writing is performed only with the central laser light B1. As soon as writing is completed, the playback state is entered and tracking continues. In other words, in this recording/reproducing device, writing is performed in a pulsed manner, so
The tracking error signal TES2 can be read between writes, and stable tracking can be performed. Note that since focusing is performed using the central laser beam B1, it is constantly performed throughout recording and reproduction.

In Fig. 2, the laser light emitted from the second port PB is actually emitted from the front side of the page to the opposite side, but for the sake of clarity, the laser beams B1, B2, B3, lens L12, coil 16, and magneto-optical The disk 4 is shown unfolded from the dashed line A--A.

Next, the configuration of the optical circulator 12 will be explained in detail. FIG. 3a is a schematic sectional view of the optical circulator 12, and FIG. 3b is a schematic view of FIG. 3a viewed from below.

This optical circulator 12 includes rutile prisms 31, 32, 33, 34, 35 for polarization separation and synthesis;
The Faraday rotating glass 3 is composed of Faraday rotating glasses 36, 37 and a crystal rotator 38.
A DC magnetic field is applied to 6 and 37 from the outside. The rotation angles of the planes of polarization of the light in the Faraday rotary glasses 36, 37 and the crystal rotator 38 are respectively
It is 45 degrees. Furthermore, the direction of rotation of the plane of polarization is constant regardless of the direction in which the light travels in the crystal polarizer 38, but is reversed in the Faraday rotation glasses 36 and 37 depending on the direction in which the light travels. Therefore, in FIG. 3, for light passing from left to right, the rotation of the plane of polarization by the Faraday rotation glasses 36, 37 and the crystal rotator 38 cancel each other out, and no rotation of the plane of polarization occurs. However, for light passing from right to left, the rotation of the plane of polarization is added, resulting in a rotation of the plane of polarization of 90 degrees. In addition, Faraday rotating glass 36, 37
In order to reduce the size, it is of an optical path reflection type, and the reflection surface is coated with a reflection film 39. The rutile prism is a uniaxially anisotropic optical crystal, and the optical axes of the rutile prisms 31 to 35 are all in the same direction, which is perpendicular to the plane of the paper in FIG. Further, the rutile prisms 31 to 35 are fixed to each other with an air layer of about 10 to 30 μm in between. Polarization separation utilizes the Brilleusta angle condition and total internal reflection at the boundary between the rutile prism and the air layer. In FIG. 3, the angle θ is the Brilleusta angle with respect to ordinary light.

First, the light a incident from the first port PA is
At the boundary between the rutile prisms 31 and 32, the light is divided into an ordinary component a1 and an abnormal component a2. That is, the extraordinary light component a2 is totally reflected at the boundary without any reflection and is absorbed by the light absorber 40, whereas the ordinary light component a1 is incident at the Brieuster angle and therefore passes through the rutile prism 32. Although this ordinary light component a1 passes through the Faraday rotation glass 36 and the crystal optical rotator 38, the plane of polarization does not rotate as described above. Further, the ordinary light component a1 passes through the boundary between the rutile prisms 34 and 35 without reflection, has its optical path bent by 90 degrees by the rutile prism 35, and exits from the second port PB. Therefore,
The light incident from the first port PA becomes only its ordinary light component a1, that is, linearly polarized light, and is emitted from the second port PB.

Next, the light b which is reflected by the magneto-optical disk 4 and enters through the second port PB is divided into an ordinary light component b1 and an extraordinary light component b2 at the boundary between the rutile prisms 34 and 35. ordinary light component
b1 passes through the rutile prism 34 as it is,
The extraordinary light component b2 is totally reflected again within the rutile prism 35, and then passes through the crystal polarizer 38 and the Faraday rotating glass 37, so that the plane of polarization becomes 90°.
Rotate degrees. Similarly, the ordinary light component b1 passes through the crystal polarizer 38 and the Faraday rotation glass 36, so that the plane of polarization is rotated by 90 degrees. Therefore, the light ray b1 is converted into extraordinary light, and the light ray b2 is converted into ordinary light. Therefore, the light beam b1 is totally reflected at the boundary between the rutile prisms 31 and 32, and further totally reflected at the boundary between the rutile prisms 32 and 33. On the other hand, ray b
2 passes through the boundary between the rutile prisms 32 and 33 without reflection, so the rays b1 and b2 are combined again at the boundary between the rutile prisms 32 and 33, and the polarization state when entering the second port PB is rotated by 90 degrees. It is emitted from the third port PC while maintaining the same state. This optical circulator 12 is configured so that the optical paths of the ordinary light component b1 and the extraordinary light component b2 are equidistant.

That is, in this embodiment, the configuration is simplified by using the laser device and optical system of the recording device and the reproducing device in common, but the present invention may be applied to each of the recording device and the reproducing device. Furthermore, in the recording apparatus of this embodiment, since the tracking signal of the reproduction apparatus can be used, random access is possible, and recording at an arbitrary recording position can be performed accurately.

Note that the configuration of this magneto-optical memory recording/reproducing device is not limited to that shown in the above embodiments, and it is also possible to use a diffraction grating or a beam splitter in place of the acousto-optic light polarizer. In the optical circulator as well, an optically anisotropic crystal other than a rutile prism can be used for polarization separation and synthesis, and by changing the shape of the prism, the ports can be arranged at arbitrary positions. Further, the Faraday rotating glass may have a shape other than the optical path reflecting type, and it is also possible to use a magneto-optic crystal such as YIG instead of the Faraday rotating glass, and it is also possible to use a half-wave plate instead of the crystal polarizer.

[Effects of the Invention] As described above, the magneto-optical memory recording and reproducing device according to the present invention has three ports and is irradiated by a light beam irradiation device, and converts the light beam incident through the first port into linearly polarized light. The reflected light from the magneto-optical memory is emitted as light through the second port onto the magneto-optical memory and is incident through the second port.
By using an optical circulator that outputs light from the third port to the photodetector while preserving the rotational component of the polarization plane corresponding to the information stored in the magneto-optical memory, the number of optical components can be reduced. , facilitates optical axis adjustment, reduces errors caused by misalignment of the optical system, and prevents reflected light from the magneto-optical memory surface from returning to the semiconductor laser, thereby reducing operational instability and deterioration of the S/N ratio. This ensures extremely stable and excellent playback.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a conventional optical magnetic memory and its recording and reproducing device, FIG. 2 is a schematic configuration diagram of an optical magnetic memory and recording and reproducing device according to an embodiment of the present invention, and FIG. 3 is a schematic diagram of the present invention. FIG. 1 is a schematic configuration diagram of an optical circulator according to the invention. In the figure, SL3 is a semiconductor laser, 4 is a magneto-optical disk, 12 is an optical circulator, PA is the first port, PB is the second port, PC is the third port,
A3 and A4 are analyzers, D4 and D5 are fat diodes, and AMP3 is a differential amplifier.

Claims (1)

[Scope of Claims] 1. A magneto-optical memory in which information is magnetically recorded and a rotational component of a plane of polarization of an irradiated light beam produces reflected light that differs depending on the information; and on the magneto-optical memory. a light beam irradiation device that irradiates the light beam to the magneto-optical memory; a photodetection device that detects a rotational component of the polarization plane of the reflected light reflected by the magneto-optical memory and converts it into a corresponding electric signal; and a photodetection device that irradiates the magneto-optical memory. In order to separate the light beam and the reflected light from the magneto-optical memory, it has at least three ports, and converts the light beam irradiated from the light beam irradiation device and incident through the first port into a linearly polarized light beam. The reflected light from the magneto-optical memory, which is emitted from the second port to the magneto-optical disk memory and entered through the second port, retains the rotational component of the plane of polarization,
A magneto-optical memory recording/reproducing device comprising: an optical circulator that emits light from a third port to the photodetecting device.