JPS5883348A - Optical magnetic memory - Google Patents

Abstract

PURPOSE:To simplify the whole constitution of an optical system and to perform stable signal reproduction by using an optical circulator which has at least three ports, and separating incident light to an information recording carrier from reflected light from the information recording carrier. CONSTITUTION:Laser light from a semiconductor laser SL3 is polarized by an acoustooptical polarizer 11 in three directions, and those components illuminate the 1st port PA of an optical circulator 12, emitted from the 2nd port PB, and focused on a magnetic disk surface 4 through an objective L12 to form three spots. Then while the reflected light from the magnetic disk surface 4 is emitted from the 2nd port PB of the optical circulator 12 through the 3rd port PC, the current plane of polarization is preserved, so a rotary component of the plane of polarization by magnetic Kerr effect is also transmitted with fidelity, and the reflected light from the magnetic disk surface 4 never returns to the semiconductor laser SL3 through the 1st port PA, thus preventing the operation from being unstable.

Description

[Detailed description of the invention] The present invention relates to an optical magnetic memory.

Optical magnetic memory, in which desired information is magnetically written into an optical magnetic memory having a Kerr effect and the written information is optically read out, has recently begun to attract attention as a rewritable large capacity memory. An example of a conventional optical magnetic memory is shown in FIG. First optical magnetic disk memory 1
The recording system will be explained. The laser beam emitted from the semiconductor laser 811 is turned into a parallel beam by the magnifying lens L1, and its optical path is converted by the total reflection mirror M1. Further, this laser light passes through a polarizing beam splitter 2 and a quarter wave plate 3, and is focused onto a magnetic disk 4 by an objective lens L2 to form a spot 5. The magnetic disk 4 is heated only at this spot 5, 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 magnetic disk 4 has an amorphous Gb Tb Fe alloy film layer 4b formed on a glass substrate 4a, and is rotated at a constant speed about a rotating shaft 4c.

The laser beam reflected from the surface of the magnetic 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, is converted into a focus error signal FE1 by the photodiode D1. This focus error signal FE
1, the objective lens L2 is tilted, and the spot 5 is always correctly formed on the magnetic 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 reproduction system B will be explained. The laser beam emitted from the semiconductor laser SL2 becomes a parallel beam by the magnifying lens L4, is divided into three laser beams by the diffraction grating 8, and is further divided by the polarizer 9.
becomes linearly polarized light. Here, in FIG. 1, the polarizer 9
The subsequent laser beams B1, B2, and B3 correspond to three laser beams divided by the diffraction grating 8. The laser beam B1 at the center is for an information signal and a focus error signal, and the laser beams B2 and B3 at both ends are 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 magnetic disk 4. Note that a total reflection mirror M2 for changing the optical path and a half mirror Hl for extracting the reflected light from the magnetic disk 4 are inserted behind the lens L5 and the objective lens L6. Information “ is stored on the magnetic disk 4 in accordance with the direction of magnetization.
OII or "1" is recorded. To read information on the magnetic 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 surface of the magnetic disk 4 differs depending on the direction of magnetization of the magnetic material. In order to detect only this polarization plane rotation component, the reflected light taken out from the half mirror Hl is split into two directions by the half mirror H2. For one laser beam, the analyzer A1 is
The analyzer A2 is configured to allow only the reflected polarized light of the recording pit "1" to pass through, and for the other laser beam, to pass only the reflected polarized light of "0". Therefore, both reflected polarized lights are transmitted to photodiodes D2 and B3, respectively.
By detecting the signal IS1 and extracting the information signal IS1 by the differential amplifier AMP1, the information of "0" or ha11+ can be reproduced. At the same time, by placing a cylindrical lens L7 after the analyzer A2, a focus error signal FE2 is obtained from the photodiode D3. In addition, laser beam B2
Detect the reflected light with silicon Plucell 81.82,
A tracking error signal TES1 is obtained by extracting the differential output using a differential amplifier AMP2. Tracking is performed by moving the objective lens L6 in the radial direction of the magnetic disk 4 using the tracking error signal TESI.

However, such a recording/reproducing device for an optical magnetic disk memory has the following drawbacks. There are many parts,
It takes a lot of time to adjust the optical axis, and errors are likely to occur due to misalignment of the optical system. Furthermore, there is also a large optical loss due to reflection of light in each optical component. In addition, in the reproduction system, the reflected light from the 4 surfaces of the magnetic disk passes through the half mirror Hl and returns to the semiconductor laser SL2, making the operation of the semiconductor laser 8m2 unstable, such as changes in optical output5-, resulting in errors and S/N ratio. resulting in deterioration of

An object of the present invention is to provide an optical magnetic memory that solves the above-mentioned conventional drawbacks, simplifies the configuration of the entire optical system, and allows stable signal reproduction by using an optical circulator. be.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 2 and 3.

FIG. 2 shows a schematic configuration of an optical system of an optical magnetic disk memory according to the present invention. The laser beam emitted from the semiconductor laser SL3 is turned into parallel beams by the magnifying lens 110, and further polarized in three directions by the acousto-optic light polarizer 11, and then passed through the lens L11 to the first beam of the optical circulator 12.
is incident on the boat PA.

This optical circulator 12 converts the light incident from the first boat PA into linearly polarized light and outputs it from the second boat PB.The light incident from the second boat Pa is transferred to the third boat while preserving its polarization plane. The light is emitted from the PC, and its configuration will be described in detail later. The laser beam emitted from the second boat PB is focused on the magnetic disk surface 4 by the objective lens L12 to form three spots.

The reflected light from the magnetic disk surface 4 passes through the objective lens L12, enters the second boat PB of the optical circulator 12, and exits from the third boat PC.

At this time, since the plane of polarization is preserved, the rotational component of the plane of polarization caused by the magnetic Kerr effect is also faithfully transmitted. Also, the magnetic disk surface 4 incident on the second boat PB
The reflected light from the semiconductor laser 1C does not directly exit from the boat PA of the cylinder 1 and return to the semiconductor laser SL3.
It is possible to prevent instability of the operation and deterioration of the S/N ratio. Three reflected lights emitted from the third boat PC of the optical circulator 12 are split into two directions by a half mirror H3.

Thereafter, signal reproduction is performed in the same manner as in the conventional example shown in FIG. A4 and the photodiode array D through the cylindrical lens L13 respectively.
4. The light is received by D5, and the information signal 182 is output from the differential amplifier AMP3, the focus error signal FE3 is output, and the tracking error signal TE is output from the differential amplifier AMP4.
S2 is obtained.

During reproduction, the laser output is controlled by the laser drive device 13 so that the temperature of the laser spot portion 15 on the magnetic disk surface 4 is below the recording temperature and the S/N ratio is large. In addition, ultrasonic waves are applied to the acousto-optic light polarizer 11 by an acousto-optic light polarizer driving device 114, and the laser light is polarized in three directions, and the central laser light B1 is an information signal IS2 and a focus error signal. Signal FE3
The laser beams 82 and 83 at both ends are used to detect the tracking error signal TES2. This information signal I
By reading S2, any address on the magnetic disk 4 can be accessed.

During recording, after the allocated 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 magnetic 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 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 the central laser Writing is performed using only the light B1. As soon as writing is completed, the playback state is entered and tracking continues. That is, in this recording/reproducing system, since writing is performed in a pulsed manner, the tracking error signal TES2 can be read out 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 boat PB is actually emitted from the front to the opposite side of the page, but for the sake of clarity, the laser light B1. B2゜B3. Lens L12. The coil 16 and the magnetic disk 4 are indicated by the dashed line A
-Illustrated in a developed state from line A.

Next, an example of the configuration of the optical circulator 12 will be described in detail. FIG. 3(a) is a schematic sectional view of the optical circulator 12, and FIG. 3(b) is a schematic view of FIG. 3(a) seen from below. This optical circulator 12 is a rutile prism 31, 32, 33, 34 for polarization separation and synthesis.
．． 35, a Faraday rotating glass 36.37, and a quartz crystal polarizer 38.
A DC magnetic field is applied to 7 from the outside. The rotation angles of the planes of polarization of the light in the Faraday rotation glasses 36 and 37 and the crystal polarizer 38 are each 45 degrees. Further, the direction of rotation of the plane of polarization is constant regardless of the direction in which the light travels in the crystal rotator 38, but is reversed depending on the direction in which the light travels in the Faraday rotation glasses 36 and 37. 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 cancels 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. Note that the Faraday rotary glasses 36 and 37 are of an optical path reflective type in order to be miniaturized, and their reflective surfaces are coated with a reflective film 39. Rutile is an optical crystal with -axis anisotropy, 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 Brewster angle condition and total internal reflection at the boundary between rutile and the air layer. In FIG. 3, the angle θ is the Brewster's angle with respect to ordinary light.

First, the light a incident from the first boat PA is divided into an ordinary light component a1 and an extraordinary light component a2 at the boundary between the rutile prisms 31 and 32. 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 Brewster's angle and thus passes through the rutile prism 32. This ordinary light component a1 passes through the Faraday rotating glass 36 and the crystal rotator 38, but 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 boat PB. Therefore, the light incident from the first boat PA is emitted from the second boat PB only as its ordinary light component a1, that is, as linearly polarized light.

Next, the light beam incident from the second boat 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. The ordinary light component b1 passes through the rutile prism 34 as it is, and the extraordinary light component b2 is totally reflected again within the rutile prism 35 and then passes through the crystal polarizer 38.
The plane of polarization is rotated by 90 degrees by passing through the Faraday rotating glass 37.

Similarly, the ordinary light component b1 passes through the crystal polarizer 38 and the Faraday rotating glass 36, so that the plane of polarization becomes 90
Rotate 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 b2
passes through the boundary between the rutile prisms 32 and 33 without reflection, so the rays b1 and b2 pass through the rutile prism 32.3.
It is synthesized again at the boundary of 3, and the polarization state when it enters the second boat PB remains rotated by 90 degrees.
is emitted from the boat PC. This optical circulator 1
2 is configured such that the optical paths of the ordinary light component 61 and the extraordinary light component b2 are equidistant.

In other words, in this embodiment, the configuration is simplified by using the laser device and optical system for the recording system and the reproducing system in common, and since the tracking signal can also be used in the recording system, random access is possible. Recording at the recording position can be performed accurately.

Note that the configuration of the optical system of this optical disk memory recording and reproducing apparatus is not limited to that shown in the above embodiments, but 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, by using an optically anisotropic crystal other than rutile for polarization separation and synthesis and changing the shape of the prism, the boat arrangement 13 can be made to any desired position. 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.

As described above, the optical magnetic memory according to the present invention has three boats, and after converting the laser light incident from the first boat into linearly polarized light, it is sent out from the second boat onto the magnetic disk surface. The optical axis can be adjusted by reducing the number of optical components by using an optical circulator that allows the reflected light from the magnetic disk surface to be emitted from the third boat to the detection system while preserving its polarization plane. In addition to reducing the occurrence of errors due to misalignment of the optical system, it also prevents the reflected light from the magnetic disk surface from returning to the semiconductor laser, thereby preventing operational instability and deterioration of the S/N ratio, making it extremely Provides stable and excellent playback.

[Brief explanation of the drawing]

14- Fig. 1 is a schematic diagram of a conventional optical magnetic memory, Fig. 2 is a schematic diagram of an optical magnetic memory according to the present invention, and Fig. 3 is a schematic diagram of a conventional optical magnetic memory.
The figure is a schematic configuration diagram of an optical circulator according to the present invention. In the figure, SL3 is a semiconductor laser, 4 is a magnetic disk, 12
is the optical circulator, PA is the first boat, and PB is the second boat.
boat, PC is the third boat, A3. A4 is an analyzer,
D4. D5 is a photodiode, and AMP3 is a differential amplifier. Patent applicant 15-

Claims (1)

[Scope of Claims] An information recording carrier having a magnetic Kerr effect, a light beam irradiation device for irradiating a light beam onto the information recording carrier, and detecting a rotation angle of a polarization plane of reflected light from the information recording carrier. a photodetection device for converting into an electrical signal; and at least three boats for separating light incident on the information recording carrier from light reflected from the information recording carrier; The present invention is characterized by comprising an optical circulator that converts the beam into linearly polarized light, emits it from a second boat, and emits the light that enters the second boat from a third boat while preserving the plane of polarization. Optical magnetic memory.