JPH03181045A - Optical disk device - Google Patents

Abstract

PURPOSE:To arrange an optical disk device apart from a recording medium by forming a magnetic core into a board or a column and magnetizing it and giving a light-transmissive property to it and providing a winding around the side face of the magnetic core. CONSTITUTION:The device consists of a supporting substrate 1, a recording medium 2, an electromagnet 4, a magnetic core 41, and a winding 42. The magnetic core 41 is formed into a board or a column and is magnetized and is light-transmissive. The winding 42 is wound around the side face of the magnetic core 41. In this manner, the magnetic core 41 is made of transparent and magnetized materials having a garnet type structure, and the recording media 2 is irradiated with light through the magnetic core 41, and the winding 42 is wound around the magnetic core 41 to obtain a magnetic field stronger than that of a hollow coil as the electromagnet 4. Thus, the device allows the light to pass through and obtains a stronger magnetic field and can be arranged apart from the recording medium.

Description

[Detailed Description of the Invention] [Summary] This invention relates to an electromagnet related to an optical disk device, and is intended to be used in such an electromagnet to allow light to pass therethrough and to obtain a large magnetic field, so that it can be placed away from a recording medium. The magnetic core has a disc-like or columnar shape, has magnetism, and is transparent to light, and the winding is wound on the side surface of the magnetic core. Configure.

[Industrial application field]

The present invention relates to an optical disk device, and particularly to an electromagnet that allows light to pass through the magnet and generates a large magnetic field, so that it can be placed away from a recording medium provided on an optical disk.

In recent years, optical disks and their devices have made remarkable progress, and have begun to be widely used in applications ranging from consumer use to information processing.

Because it has a very large capacity to store information, it is resistant to noise by digitizing vast amounts of analog information such as color images and high-quality music, as seen in LDs (laser discs) and CDs (compact discs). This is because it can be packed in as information.

Of course, in the field of information processing as well, the large storage capacity is the reason why it is attracting attention as a large-capacity file memory comparable to, for example, magnetic disks.

Optical disks can be broadly classified into three types, for example, read-only types, write-once types, and rewritable types, and each type is put into practical use using unique optical principles.

Among these, rewritable optical disks have great potential in the future, especially in the field of information processing.

This rewritable optical disk includes a magneto-optical disk (hereinafter, a rewritable magneto-optical disk is abbreviated as an optical disk).
is well known. Conventionally, this optical disk employs an optical modulation method in which light is irradiated from both sides with a substrate in between and a magnetic field is applied by an electromagnet.

However, since the transfer rate is slow due to the inductance of the electromagnet, there is a desire to develop optical disks using a magnetic field modulation method using floating magnetic heads, such as those found in magnetic disks, and devices related thereto.

[Conventional technology]

The principle of magneto-optical recording is that recording is performed by correlating the presence or absence of magnetization and the direction of magnetization to 1 or 0. During writing, light heats the magnetic film, so it is a type of so-called thermomagnetic recording. .

In other words, if a magnetic film is magnetized in a negative direction and a part of the film is heated by irradiating a beam of, for example, infrared laser light, until it exceeds the cue temperature, the heated part loses its magnetization in spots. Alternatively, if an external magnetic field is applied in the opposite direction to the magnetization direction of the magnetic film, only the heated portions will be magnetized in the opposite direction in a spot-like manner.

There are two methods for reading out the presence or absence of magnetization of this magnetized magnetic film and the direction of magnetization.

First, there is a readout method that applies the so-called Faraday effect, which detects the rotation of the plane of polarization of light passing through the magnetic film with respect to the direction of magnetization of the magnetic film, and a readout method that applies the so-called Faraday effect, which detects the rotation of the plane of polarization of the light that passes through the magnetic film, and a readout method that uses the so-called Faraday effect, which detects the rotation of the polarization plane of light that passes through the magnetic film. There is a readout method that applies the so-called Kerr effect, which results in elliptically polarized light.

Optical discs currently in use mainly utilize the latter Kerr effect for reading.

There are two methods for reading out optical discs: an optical modulation method in which light is modulated according to information, and a magnetic field modulation method in which a magnetic field applied by an electromagnet is modulated in accordance with information.

In the optical modulation method, a magnetic field is constantly applied to the recording medium of an optical disk using an electromagnet, and light is irradiated with contrasting strengths of light depending on information.

On the other hand, in the magnetic field modulation method, while constantly irradiating light, a magnetic field whose direction is reversed according to information is applied to the recording medium of the optical disk.

FIG. 5 is a cross-sectional view of the structure of a conventional optical modulation type optical disc.

In the figure, 1 is a support substrate, 2 is a recording medium, 3 is a light, 4 is an electromagnet, and 5 is a protective film.

The support substrate 1 is a disk with a thickness of 1.2 wa+. A transparent material is used for the support substrate 1, and for example, in the case of glass, Na on the surface of soda glass is replaced with K.
For example, in the case of plastic, polycarbonate or acrylic PMMA (polymethyl methacrylate) are used.

The recording medium 2 includes, for example, TbF with a film thickness of about 1100 nm.
An eCo-based magnetic thin film is used, and is provided by, for example, sputtering. More specifically, it is sandwiched with a thin film of Tb 5iOz, for example, to prevent oxidation.

A protective film 5 made of, for example, an ultraviolet curing resin is provided on the recording medium 2 .

By the way, in order to protect the recording medium 2 from dust and scratches,
Light 3 is irradiated through transparent support substrate 1. Therefore, the protective film 5 does not need to be transparent, but only needs to have the function of protecting the recording medium 2 from, for example, tentacles.

Recently, a semiconductor laser is used for this light 3, and for example, near infrared rays of 830 nm are used.

It is easy to directly modulate such a laser beam at a speed of several MHz, for example, depending on the presence or absence of information.

On the other hand, the electromagnet 4 is, for example, a so-called coil made by winding an electric wire around an iron core.
A magnetic field of about 5000e is obtained.

This electromagnet 4 is arranged on the side where the recording medium 2 is provided, opposite to the side of the support substrate 1 to which the light 3 is irradiated. However, since the electromagnet 4 can be arranged without contacting the recording medium 2, it does not touch the recording medium 2 directly. From this point of view, the protective film 5 does not need to be a very strong film.

In this way, although there is a restriction that the support substrate 1 must be made of a transparent material, the light modulation type optical disc is capable of being irradiated with sufficiently fast modulated light 3 while applying a sufficiently large magnetic field by the electromagnet 4. Recording, erasure, and playback are then performed.

However, the electromagnet 4 used here is suitable for constantly applying a magnetic field. However, because the inductance of the coil is large, it is difficult to reverse the magnetic field quickly.

Therefore, for example, if you want to erase once before rewriting and then record, two rotations are required, first erasing in the first rotation and then recording in the second rotation. The disadvantage is that the transfer rate is slow.

Therefore, in order to improve the transfer rate, various override techniques have been proposed using, for example, a magnetic field modulation method using a floating magnetic head.

FIG. 6 is a sectional view of one configuration of a magnetic field modulation type optical disk.

In the figure, 1 is a support substrate, 2 is a recording medium, 3 is a light, 4 is an electromagnet, and 5 is a protective film.

The magnetic field modulation method shown in the figure has the same basic structure as in Figure 4, but the light 3 is constantly transmitted to the support substrate.
In this method, the direction of the magnetic field applied to the recording medium 2 of the optical disk is reversed by the electromagnet 4 while the magnetic field is irradiated through the optical disk.

Therefore, overriding becomes possible if the reversal speed of the magnetic field can be increased.

However, in order to increase the reversal speed of the magnetic field, it is necessary to make the inductance of the electromagnet 4 as small as possible.

Therefore, as the IIT magnet 4, a magnet such as a magnetic head with small inductance used in magnetic recording such as a magnetic disk is used.

In this case, since the magnetic field can be reversed at high speed, there is no need for an erasing process, and rewriting can be performed in one rotation, so-called override.

However, since the inductance of the electromagnet 4 has become smaller, the generated magnetic field is also smaller. So, inevitably the electromagnet 4
It is necessary to arrange the recording medium 2 close to the recording medium 2, for example, by a distance of several μm.

With respect to the proximity of the electromagnet 4, the flying magnetic head is controlled in the same manner as that used for magnetic disks and the like.

To control this floating magnetic head, CSS (
(Contact Start S top) control, that is, when the optical disc is stopped, the electromagnet is in contact with the substrate, and when the optical disc starts rotating, it is required to float up.

Therefore, in case a head crash occurs, the recording medium 2 needs to have the ability to withstand it.

On the other hand, in this configuration, while the light 3 is irradiated through the support substrate 1, the electromagnet 4 must be placed close to the recording medium 2.

Therefore, it is not possible to easily create a double-sided structure by attaching two discs, such as optical modulation type optical discs, back to back.

FIG. 7 is a sectional view of another configuration of a magnetic field modulation type optical disk.

In the figure, 1 is a support substrate, 2 is a recording medium, 3 is a light, 4 is an electromagnet, and 5 is a protective film.

In the figure, light irradiation is performed from the same direction as the magnetic field application.

That is, the electromagnet 4 here is configured as a hollow coil from which a magnetic core such as an iron core is removed, and the light 3 is irradiated through the hollow hole.

With this configuration, a double-sided configuration in which the recording medium 2 is provided on both sides of the support substrate 1 is possible.

However, although the hollow coil-shaped electromagnet 4 without a magnetic core is somewhat effective in reducing inductance, it is difficult to obtain a large magnetic field.

[Problem to be solved by the invention]

As mentioned above, the delay in transfer rate that occurs in optical modulation type optical discs is due to the small inductance.
This problem can be solved by using a magnetic field modulation optical disc that uses electromagnets that can reverse magnetic poles at high speed.

However, the electromagnet requires C5S control.

Moreover, in order to enable double-sided recording on this magnetic field modulation type optical disk, it is necessary to perform both light irradiation and magnetic field application from the side where the recording medium is provided.

Therefore, unlike magnetic disk recording media, the recording medium has a problem in that it cannot tolerate minute damage caused by contact with an electromagnet, for example.

Furthermore, even if a protective film is provided on a recording medium, there is a problem in that the protective film cannot be damaged.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical disk device having a t-magnet that can generate a large magnetic field, can be placed away from a recording medium, and can also irradiate light through the electromagnet.

[Means to solve the problem]

The problem described above includes a magnetic core and a winding, the magnetic core is disk-shaped or columnar, has magnetism, and is transparent to light, and the winding has a magnetic core and a winding. teeth,
The problem is solved by an optical disk device having an electromagnet arranged so as to be wound around the side surface of a magnetic core.

(Function) As mentioned above, conventional electromagnets are placed close to the recording medium, which poses a risk of head crash, and hollow coils without magnetic centers are used to allow light to pass through from the electromagnet side and allow double-sided recording. In contrast to the case where it is difficult to obtain a strong magnetic field due to the magnetic field, the electromagnet used in the optical disk device according to the present invention allows light to pass through while producing a strong magnetic field.

That is, in the electromagnet used in the present invention, a transparent, magnetic material having a garnet type structure is used for the magnetic core.

Light can then be irradiated onto the recording medium through the magnetic core.

Furthermore, this magnetic core is made into an electromagnet by winding a winding around it in the same way as, for example, an iron core, so that a stronger magnetic field can be obtained than with a hollow coil.

In this way, light can be irradiated from the same direction as when a magnetic field is applied by the electromagnet.

Moreover, since the magnetic field obtained is stronger than that of a hollow coil, the electromagnet can be placed apart from the support substrate.

Therefore, the troublesome control such as C3S of the flying magnetic head, which is performed on magnetic disks, and the particularly tough protective film of the recording medium required for this are not necessary.

According to the optical disc device having the electromagnet of the present invention, by providing recording media on both sides of the support substrate, it is possible to obtain an optical disc capable of double-sided recording, which is composed of a single substrate.

〔Example〕

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
FIG. 3 is a sectional view showing another embodiment of the present invention, and FIG. 4 is a diagram showing the performance of the present invention.

In the figure, ■ is a support substrate, 2 is a recording medium, 3 is a light beam 3, 4 is an electromagnet, 41 is a magnetic core, 42 is a winding, and 5 is a protective film.

The magnetic core 41 constituting the IT electromagnet is made of yttrium iron garnet, abbreviated as YIG (3Y20
:l-5Fezo,,,) is used.

The single crystal of YIG is processed into a disk shape with a diameter of 21nflIφ and a thickness of 1.81 mm, and the opposing upper and lower surfaces are coated with an antireflection film. Then, the electromagnet 4 was manufactured by winding the winding wire 42 with 20 turns around the side surface thereof.

Example: 1 The optical disk used to evaluate the electromagnet 4 has the following configuration.

That is, a pre-group is formed on the surface of an Af plate having a thickness of 1.21 mm and a diameter of 5 inches φ, and the recording medium 2 is provided on the pre-group. For this recording medium 2, a magnetic thin film of GdFeCo type or TbFeCo type is used, for example.

In this example, a TbFeCo thin film is formed by sputtering to a thickness of, for example, 90 nm, and in order to prevent this film from oxidizing, it is sandwiched with a Tb-3in film having a thickness of, for example, 1100 nm. It becomes.

Using the optical disc produced in this way, the electromagnet 4 used in the optical disc device of the present invention will be evaluated.

In the evaluation system, light 3 emitted from an optical system (not shown) consisting of an electromagnet 4, a laser light source, a lens, etc. passes through a magnetic core 41 and is focused on a recording medium 2 on a support substrate 1. The structure is such that the support substrate 1 is arranged with a fixed gap of 0.5 mm+ from the support substrate 1.

The conditions for evaluation are that the recording method is a magnetic field modulation method, the modulation frequency of the electromagnet 4 is 2 MHz, and the rotation speed of the support substrate 1 is 18 per minute.
00 rotation, the wavelength of light 3 is 830 nm, and the output is 8 mW. Moreover, a hollow coil with a 20-turn winding and no magnetic core is used as an electromagnet for comparison.

In the evaluation results, the horizontal axis represents the applied current (mA) to the electromagnet 4 and the conventional coil, and the vertical axis represents the quality of the output signal (C/N).
(Carrier/No.1se, dB) as shown in FIG.

As a result, the electromagnet 4 of the optical disk device according to the present invention is
Compared to conventional hollow coils, recording can be performed with a current that is 1/10 or less, and a magnetic field can be efficiently obtained even if the coil is disposed with a fixed gap relative to the support substrate 1.

Example: 2 Using the support substrate 1 having the same specifications as in Example 1, pre-groups are formed on both sides.

Then, a recording medium 2 and a protective film 5 are formed on each surface of the pregrouped support substrate 1 according to the same specifications as in Example 1, thereby forming a double-sided recordable optical disc.

In this disc, a protective film 5 is provided on the recording medium 2.

This protective film 5 has a film thickness of 10 μm, and is formed on the recording medium 2 by spin-coding, for example, a transparent acrylic ultraviolet curable resin.

The evaluation system for this disk has a configuration in which an optical system with the same specifications as in Example 1 and electromagnets 4 are arranged on both sides of the optical disk.

Then, when the light 3 was focused on the recording medium 2 through the protective film 5 and simultaneous recording and playback was performed from both sides, the recording and playback performance obtained on each side was as follows. There was no difference from the single-sided optical disc of Example 1.

The size of the gap between the electromagnet and the optical disk, the material and shape of the magnetic core of the electromagnet, the number of turns of the winding, etc. described in this embodiment can be modified in various ways within the range that satisfies the conditions.

Also, here's the double-sided I! ! Although a protective film is provided on the above optical disc, it does not need to be a strong film such as is provided to realize C3S, and therefore, the configuration of the optical disc does not limit the essence of the present invention. .

〔Effect of the invention〕

As described above, since the electromagnet of the optical disk device according to the present invention uses a light-transmitting magnetic material for the magnetic core, light can be irradiated through the magnetic core from the same direction as the application of the magnetic field.

As a result, it has become possible to obtain a magnetic field that is orders of magnitude larger than that of conventional hollow coil electromagnets.
It is now possible to arrange the electromagnet with a fixed gap between it and the disk.

In addition, since there is no need to irradiate light through a support substrate as in conventional light modulation methods, it is possible to create a double-sided recordable optical disc in which recording media are provided on both sides of a single support substrate, which is not limited by transparency. It is now possible to configure easily.

Therefore, the present invention can greatly contribute to the development of rewritable optical disk systems, which are expected to further develop in the future.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
FIG. 3 is a cross-sectional view showing another embodiment of the present invention; FIG. 4 is a diagram showing the performance of the present invention; FIG. 5 is a cross-sectional view of a conventional optical modulation type optical disc. 6 is a sectional view of one structure of an optical disk using a magnetic field modulation method, and FIG. 7 is a sectional view of another structure of an optical disk using a magnetic field modulation method. In the figure, 1 is a support substrate, 3 is a light, 41 is a magnetic core, and 5 is a protective film. 2 is a recording medium; 4 is an electromagnet; 42 is a winding; Cross-sectional diagram band 3 Figure current (mA) The performance of the heather invention and the diagram T figure % 4 Figure 5 Figure 7: A cross-sectional view of one beak claw of a magnetic field adjustment system.

Claims (1)

[Scope of Claims] 1) It has a magnetic core (41) and a winding (42), and the magnetic core (41) is disk-shaped or columnar, has magnetism, and has a light (3) An optical disk device characterized in that the winding (42) is wound around a side surface of the magnetic core (41). 2) The optical disk device according to claim 1, wherein the magnetic core (41) is made of a material with a garnet structure.