JPH0329781Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a reading device that reads magnetic recording on a magnetic recording medium using magneto-optical effect.

<Prior Art> As a magnetic recording readout device for reading magnetic records on a magnetic recording medium, a magnetic recording readout method has been proposed that uses magneto-optical effects to read out data in place of a conventional readout device using a magnetic head. This magnetic recording readout method that utilizes the magneto-optical effect places a soft magnetic film in contact with the magnetic recording medium, and transfers the perpendicular component of the magnetic recording signal on the magnetic recording medium to the soft magnetic film. It is an optical readout method that utilizes Faraday optical rotation depending on the magnetization direction of the domains of the soft magnetic film.

FIG. 1 is a diagram showing the configuration of a conventional magnetic recording/reading device. In the figure, it is assumed that 1 is a magnetic recording medium such as a magnetic tape, and its magnetic layer 1a is provided with magnetic recording by a modulation method such as pulse code modulation, frequency modulation, or pulse width modulation.

A read head 2 that utilizes the magneto-optical effect of a soft magnetic film is provided in contact with the magnetic layer 1a of the magnetic recording medium 1. For example, as shown in FIG. 2, the read head 2 includes a soft magnetic film 2b coated on the side facing the magnetic recording medium 1 of an optically transparent GdGa garnet substrate 2a with a thickness of 0.2 to 0.5 mm. However, it has a structure in which a reflective film 2c is deposited on the soft magnetic film 2b. The soft magnetic film 2b is made of an optically transparent and soft magnetic material, such as YSmCaFeGe garnet such as Y ₁ . ₉₂ Sm ₀ . ₁ Ca ₀ . ₉₈ Fe ₄ . ₀₂ Ge ₀ . ₉₈ O ₁₂ . The film is formed to have a thickness of approximately 6 μm and has an axis of easy magnetization in a direction perpendicular to the surface. A protective film 2d made of, for example, silicon dioxide is provided on the surface of the reflective film 2c.

When the read head 2 is brought into contact with the magnetic recording medium 1, the domains of the soft magnetic film 2b are brought into contact with the magnetic recording medium 1.
The film is magnetized in a direction perpendicular to the film surface by the perpendicular component of the leakage magnetic flux generated from the magnetic recording signal. To read out this domain signal, a laser beam or the like generated from a light source generator 3 is linearly polarized through a polarizer 4 and supplied to a beam splitter 5. The light is focused onto the soft magnetic film 2b. Reflecting film 2
The beam is reflected by C, passes through the objective lens 6 again, is bent at a right angle by the beam splitter 5, and is supplied to the analyzer 7. During this time, the light undergoes Faraday rotation to the right or left depending on the magnetization direction of the domains of the soft magnetic film 2b. The light that has undergone Faraday optical rotation is guided through an analyzer 7 to a light receiving system 8, where it is converted into an electrical signal. The signal converted into an electric signal by the light receiving system 8 is reproduced by a reproducing device (not shown).

<Problem to be solved by the invention> However, the conventional optical system described above has a structure in which the polarizer 4 and the analyzer 7 are arranged before and after the beam splitter 5 independently of the beam splitter 5. As a result, the optical path length becomes long, it is susceptible to optical disturbances, and there are drawbacks such as a decrease in the S/N ratio due to a halo phenomenon and the like.

Therefore, an object of the present invention is to provide a magnetic recording/reading device in which the optical path length is made as short as possible, optical disturbances and halo phenomena are prevented, and the S/N ratio is improved.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention utilizes the magneto-optical effect of a soft magnetic film having an axis of easy magnetization perpendicular to its surface to perform magnetic recording on a magnetic recording medium. In the reading device, a polarizing beam splitter is provided on the optical path from the light source to the soft magnetic film and the light receiving system, and the polarizing plane is attached to the light source side and the light receiving system side of the polarizing beam splitter. Polarizers matched to the plane of polarization of the soft magnetic film are arranged respectively, and an optical rotator having an optical rotation angle substantially equal to the optical rotation angle of the soft magnetic film is provided on the other side of the substrate on which the soft magnetic film is formed on one side. Features.

<Function> Since a polarizing beam splitter is installed on the optical path from the light source to the soft magnetic film and the light receiving system, the optical system that conventionally consists of a polarizer and analyzer can be replaced with a single component, the polarizing beam splitter. The optical path length can be significantly shorter than that of the conventional method.

Polarizers whose polarization planes match those of the polarizing beam splitter are placed on the light source side and the light receiving system side of the polarizing beam splitter, so that the light entering the polarizing beam splitter from the light source device and the polarizing beam splitter are The light that enters the light receiving system through the polarization beam splitter is only linearly polarized light that is polarized in the direction that it should be received by the polarization beam splitter. Therefore, optical disturbance to the optical system, halo phenomenon, etc. are prevented, and the S/N ratio is improved.

On the other side of the substrate with a soft magnetic film formed on one side,
Since it is equipped with an optical rotator that has an optical rotation angle that is approximately equal to the optical rotation angle of the soft magnetic film, the light that has been Faraday-rotated to the right or left by the soft magnetic film is further rotated by the optical rotator, increasing the amount of change in optical rotation of the receiving target. can be done. Therefore, the maximum contrast can be obtained with respect to reversed magnetization information of the magnetic recording medium, and the S/N ratio is improved.

<Embodiment> FIG. 3 is a diagram showing the configuration of a magnetic recording/reading device according to the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same components. In the figure, 9 is a polarizing beam splitter. Polarizing beam splitter 9 on the light source device 3 side and light receiving system 8
Polarizers 10 and 11 whose polarization planes are matched to the polarization plane of the polarizing beam splitter 9 are respectively arranged. Further, in this embodiment, the positions of the light source device 3 and the light receiving system 8 with respect to the polarizing beam splitter 9 are arranged in a relationship opposite to that shown in FIG. 12 is a condensing lens, and 13 is an imaging lens.

As mentioned above, in the present invention, the light source device 3
Since the polarizing beam splitter 9 is arranged in the optical path from the reading head 2 having the soft magnetic film 2b to the light receiving system 8, the light from the light source device 3 is split into a straight line by the polarizing beam splitter 9. While polarizing the light and reflecting it in the direction of the read head 2,
The light reflected by the reflective film 2c of the read head 2 and subjected to Faraday optical rotation by the soft magnetic film 2b can be supplied again to the polarizing beam splitter 9 to extract only the optically rotated component, and can be supplied to the light receiving system 8. . In this way, in the present invention, the optical system, which was conventionally composed of a polarizer and an analyzer, is composed of a single component, the polarizing beam splitter 9, so that the optical path length is significantly shorter than that of the conventional one. . Moreover, since the polarizers 10 and 11 whose polarization planes match the polarization planes of the polarization beam splitter 9 are arranged on the light source device 3 side and the light receiving system 8 side of the polarization beam splitter 9,
The light entering the polarizing beam splitter 9 from the light source device 3 and the light entering the light receiving system 8 through the polarizing beam splitter 9 are polarized by the polarizers 10 and 11 in the direction in which they should originally be received by the polarizing beam splitter 9. It becomes only linearly polarized light. Therefore, optical disturbance to the optical system, halo phenomenon, etc. are prevented, and S/N
ratio is improved.

In this embodiment, as shown in an enlarged view in FIG. 4, the read head 2 is a GdGa garnet substrate 2a which has a soft magnetic film 2b for reading on one side, and has a soft magnetic film 2b similar to the soft magnetic film 2b on the other side. It has a structure in which another soft magnetic film 2e having the composition is deposited. 2c
is a reflective film, and 2d is a protective film.

As already mentioned, the soft magnetic films 2b and 2e are
Using a material that is optically transparent and has soft magnetic properties, such as YSmCaFeGe garnet such as Y ₁ . ₉₂ Sm ₀ . ₁ Ca ₀ . ₉₈ Fe _{4 . 02 Ge 0} . The film is formed to have a thickness of approximately 6 μm and has an easy axis of magnetization. The soft magnetic film 2 is attached to the substrate 2a.
A liquid phase epitaxial growth method (hereinafter referred to as LPE method) is used to deposit layers b and 2e.
That is, by immersing the non-magnetic garnet single crystal, which will become the substrate 2a, in a liquid phase in which the above-mentioned magnetic garnet component is dissolved at high temperature using flux,
A magnetic garnet single crystal film, which will become the soft magnetic films 2b and 2e, is formed on the surface thereof. Since the conventional structure was such that the soft magnetic film 2b was provided only on one surface of the substrate 2a, it was necessary to remove the magnetic garnet single crystal film on the other surface formed by the LPE method by polishing or other means. However, in the case of this embodiment, this work is not necessary, and the advantage is that the number of steps is small.

Further, a magnet 14 such as a permanent magnet or an electromagnet is provided on the soft magnetic film 2b, and the magnet 14 moves the domain of the soft magnetic film 2e in a direction having an optical rotation angle that is approximately equal to the optical rotation angle of the soft magnetic film 2b. magnetize. With such a configuration, the soft magnetic film 2b responds to light Faraday-rotated to the right or left by the soft magnetic film 2b.
e can further rotate the light and increase the amount of change in optical rotation of the light receiving target. For example, the soft magnetic film 2b
When trying to receive light when the domain of the film is magnetized in a direction with the N pole on the lower surface side and the S pole on the upper surface side (hereinafter referred to as NS direction magnetization), the magnet 14
The polarity is arranged such that the north pole side faces the soft magnetic film 2e. Then, as shown in FIG.
The light rotated by an angle θ to the left in b is further rotated by an angle θ to the left by the soft magnetic film 2e,
The optical rotation corresponding to the SN direction magnetization, which is a reversed magnetization state, has an optical rotation angle of 0. Therefore, as is clear from FIG. 5, the optical rotation change corresponding to the NS direction magnetization, which is the receiving target, increases from the conventional Ksinθ to Ksin2θ, and the maximum contrast can be obtained in relation to the SN direction magnetization. Furthermore, since the amount of change in optical rotation to be received is increased, the S/N ratio is improved.

Similar effects can be obtained by arranging an independent optical rotator between the read head 2 and the polarizing beam splitter 9 instead of the soft magnetic film 2e and the magnet 14.

In the case of the conventional example shown in FIG. 1, the objective lens focuses light into a spot on the soft magnetic film 2b, and magnetic recording on the magnetic recording medium 1 is performed bit by bit, that is, bit by bit. by. However, in this embodiment, there is no objective lens, and a plurality of magnetic recording signals distributed within a certain plane area of the magnetic recording medium 1 are simultaneously sent to the light receiving system 8 as one information group. can be transmitted. Therefore, by configuring the light receiving system 8 with a surface imaging device such as a charge transfer device, it is possible to configure a magnetic recording/reading device that simultaneously reads out information groups and to significantly improve the readout speed.

Furthermore, the polarizing beam splitter 9 is connected to the read head 2.
Since the structure is such that the light beam is placed directly on the polarizing beam splitter 9, the optical path length from the read head 2 to the polarizing beam splitter 9 is shortened, and effects such as an improvement in the S/N ratio can also be obtained.

Regarding the optical processing, various embodiments can be taken in addition to those shown in the examples.

<Effects of the invention> As described above, according to the present invention, the following effects can be obtained.

(a) In a device that reads magnetic records of a magnetic recording medium using the magneto-optical effect of a soft magnetic film having an axis of easy magnetization perpendicular to the surface, the optical path from the light source to the soft magnetic film and the light receiving system is A polarizing beam splitter is installed in the , and polarizers whose polarization planes match those of the polarizing beam splitter are placed on the light source side and the light receiving system side of the polarizing beam splitter, so the optical path length can be maximized. It is possible to prevent optical disturbances, halo phenomena, etc., improve the S/N ratio, and provide a magnetic recording/reading device.

(b) Since the other side of the substrate with the soft magnetic film formed on one side is equipped with an optical rotator having an optical rotation angle approximately equal to the optical rotation angle of the soft magnetic film, the maximum contrast can be achieved with respect to reversed magnetization information of the magnetic recording medium. obtained,
A magnetic recording/reading device with a high S/N ratio can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional magnetic recording/reading device, FIG. 2 is a sectional view of its reading head, FIG. 3 is a diagram showing the configuration of a magnetic recording/reading device according to the present invention, and FIG. FIG. 5, which is an enlarged sectional view of the main part of the magnetic recording/reading device according to the present invention, is also a diagram showing the Faraday optical rotation thereof. 1...Magnetic recording medium, 2...Reading head, 2a
... Substrate, 2b ... Soft magnetic film, 2e ... Soft magnetic film, 9 ... Polarizing beam splitter, 10 ... Polarizer, 12 ... Polarizer.

Claims (1)

[Claims for Utility Model Registration] (1) In an apparatus for reading magnetic recording of a magnetic recording medium using the magneto-optical effect of a soft magnetic film having an axis of easy magnetization in a direction perpendicular to the surface, A polarizing beam splitter is provided on the optical path leading to the film and the light receiving system, and polarizers whose polarization planes are aligned with the polarization plane of the polarizing beam splitter are provided on the light source side and the light receiving system side of the polarizing beam splitter, respectively. A magnetic recording/reading device comprising: a substrate having the soft magnetic film formed on one side thereof and an optical rotator having an optical rotation angle substantially equal to the optical rotation angle of the soft magnetic film on the other side of the substrate. (2) The utility model registration claim 1 is characterized in that the optical rotator is constructed by forming a soft magnetic film on the other surface of the substrate and arranging a magnet on the soft magnetic film. The magnetic recording/reading device described above. (3) The magnetic recording/reading device according to claim 2, wherein the polarizing beam splitter is placed on the magnet.