JP2800391B2 - Magnetic field modulation coil for optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an optical storage device, and more particularly, to a magnetic field modulation recording optical head for performing recording by modulating a magnetic field, and more particularly to an optical head capable of efficiently extracting a large magnetic field from both surfaces of a medium. In order to provide a magnetic field modulation coil, a magnetic field modulation coil of an optical head that performs recording and erasing of information on a medium for a magneto-optical disk by a magnetic field modulation method. Along with providing a condensing optical path for forming a spot with laser light so as to penetrate in a non-contact manner with the air core of the coil,
At the moving position when the area of the medium heated by the spot formation reaches the vicinity of the Curie temperature while cooling,
A core made of a magnetic material for concentrating a magnetic flux is provided in a non-contact with the converging optical path in the air core of the coil.

[Industrial applications]

The present invention relates to an optical storage device, and more particularly, to a magnetic field modulation recording optical head that performs recording by modulating a magnetic field.

[Conventional technology]

FIG. 9 is a perspective view showing the arrangement of main parts of a conventional magneto-optical disk and optical head. In the figure, reference numeral 1 denotes a magneto-optical disk rotating in the direction of arrow A, and 2 denotes a magneto-optical disk 1 (hereinafter referred to as medium 1).
(Abbreviated as "abbreviated") is shown in an optical head in a non-contact state. The optical head 2 uses a built-in objective lens (not shown) to narrow the laser beam to a diameter of about 1 μm, and irradiates a predetermined track on the recording film of the medium 1. Recording / playback of information
This is for erasing. Conventional magnetic field modulation type medium 1
Has provided an electromagnet or a permanent magnet on the opposite side of the optical head 2 to record and erase data by applying a magnetic field. As an electromagnet that applies this magnetic field, a coil having an iron core was used, so that 200 to 500
Although a magnetic field of about Oe can be obtained sufficiently, the conductance of the coil is so large that high-speed reversal of the magnetic field is not possible.Erasing is performed in the first rotation, and the direction of the magnetic field is reversed in the second rotation to record. Thus, two rotations are required, and the transfer rate is slow. For this reason, various overwrite techniques have been devised as techniques for performing rewriting in one rotation.

FIG. 10 is an explanatory sectional view of a first example of the conventional overwriting method. In order to facilitate understanding of the description of the configuration and operation, the same portions are denoted by the same reference numerals throughout the drawings, and redundant description will be omitted.

In the drawing, a medium 1 is composed of a recording film 11 and a transparent substrate 12, and is a cross-sectional view rotating and moving in the direction of arrow A.
Reference numeral 3 denotes an objective lens mounted on an optical head (not shown), which narrows down the laser beam 4 and transmits a transparent substrate 12 to form a spot on the surface of the recording film 11. Reference numeral 5 denotes a floating type head which is arranged at a position facing the objective lens 3 with the medium 1 interposed therebetween and floats in a non-contact state with respect to the medium 1 (using the same principle as a floating type magnetic head), and 6 denotes a floating type head 5 is a magnetic head in which a coil is wound around a magnetic core mounted on the magnetic head 5. Recording is performed using a magnetic field generated from the magnetic head.

This is not to compare the intensity of light to the signal, but to record by comparing the direction of the magnetic field to the signal.
This is a magnetic field modulation method. In this case, an erasing step is not necessary, and rewriting can be performed in one rotation. However, if the magnetic head 6 flies above the surface of the medium 1, there is a danger of a head crash like a conventional magnetic disk, which is not preferable. Further, since the optical head and the flying head 5 are arranged with the medium 1 interposed therebetween, there is a disadvantage that only one side of the medium 1 can be used.

FIG. 11 is a sectional explanatory view of a second example of the conventional overwriting method. In the figure, reference numeral 1a denotes a medium having a structure in which recording films 11a and 11b are formed on the front and back surfaces of a substrate 12a, respectively. Numeral 7 denotes an air-core magnetic field modulation type coil (doughnut type coil), which irradiates the recording film 11a with a light beam narrowed by the objective lens 3 through the center space of the coil 7. In this case, a high-speed reversal magnetic field can be obtained as in the case of the magnetic head 6 in FIG. 10, and both surfaces of the medium 1a can be used. However, since the coil 7 is air-core, a large magnetic field cannot be obtained. is there.

Here, in order to increase the magnetic field, the magnetic flux density can be increased by using a magnetic material for the magnetic core (hereinafter abbreviated as the core) of the coil. However, when light is radiated through the interior of the coil, the core blocks the optical path, so it is necessary to make a hole so that light can pass through the portion where the core blocks the light.

FIG. 12 is an explanatory sectional view of a third example of the conventional overwriting method. In the figure, reference numeral 8 denotes a core provided with conical light so as not to block a convergent light path around the optical axis P of the laser light 4. The coil 7 is formed by winding concentrically around a core 8 around which the conical hole is wound. By applying a current to the coil 7, a pattern of the magnetic force lines 9 as shown is generated. Reference numeral 10 denotes a region where the recording film 11 formed on the medium 1 (the cross-sectional layers such as the substrate and the protective film are omitted; the same applies hereinafter).

As can be seen from the region 10 receiving the strong magnetic field, the magnetic flux distribution on the recording film 11 generated by the coil 7 is formed in a donut shape surrounding a spot forming portion of light when viewed in a plan view. And there is a disadvantage that the magnetization efficiency for the recording film 11 is not good.

FIG. 13 is a diagram showing the magnetic characteristics of the medium with respect to the temperature change. The horizontal axis shows the temperature, and the vertical axis shows the coercive force or the magnetization strength. A portion of a medium for a magneto-optical disk that has been irradiated with a laser beam spot is rapidly heated. When the temperature of the recording film becomes equal to or higher than the Curie temperature Tc, recording is performed by utilizing the fact that the coercive force is lost and the property of being magnetized by an external magnetic field is also lost.

FIG. 14 is a diagram showing a temperature change and a magnetization characteristic of the medium with respect to time, wherein the horizontal axis represents time, and the vertical axis represents temperature or magnetization intensity. Exceeded Curie temperature Tc in the time period of time t ₃ from the time t ₁ as shown to indicate over time the change in temperature of the portion of the upper medium, property of being magnetized in the time period is zero. That is, at a time point the temperature has reached the Curie temperature Tc at time t ₃ cold after but not magnetized even if an external magnetic field is applied to the time slot exceeds the Curie temperature Tc has elapsed the maximum temperature of the medium It becomes magnetized following the direction of the magnetic field.

At this time, a direction of cool middle field substantially time t ₃ when passing through the Curie point definitive for determining the magnetization direction,
It is not the magnetic field that is experienced when the medium is heated to its maximum temperature. In other words, the magnetic field necessary for recording the medium passes through the Curie temperature during the cooling process,
Greatest magnetic field needs to be provided to concentrate in the drawing time t _3. Therefore, it areas subjected to strong magnetic field is not efficient because it is distributed in a donut-shaped from time t ₁ to the time zone of the time t ₃ in Figure 14 is seen in the conventional example of Figure 12.

[Problems to be solved by the invention]

As described above, the conventional overwrite-type optical head that performs recording by comparing the direction of a magnetic field with a signal has a disadvantage that both sides of a medium cannot be used efficiently.

The present invention has been made in view of the above-mentioned conventional disadvantages, and has as its object to provide a magnetic field modulation coil of an optical head capable of efficiently extracting a large magnetic field from both surfaces of a magnetic field modulation type medium.

[Means for solving the problem]

FIG. 1 shows a basic configuration diagram of the present invention. In a magnetic field modulation coil 13 of an optical head that records and erases information on a medium 1 for a magneto-optical disk by a magnetic field modulation method,
A condensing optical path for forming a spot with a laser beam on the medium 1 on which the optical head rotates is provided so as to penetrate the coil 13 in a non-contact manner with the air core of the coil 13, and the heat generated by the spot forming is A core 14 made of a magnetic material for concentrating magnetic flux is moved to the coil 13 at a moving position when the area of the medium 1 reaches a temperature near the Curie temperature while cooling.
The core 13 is provided in a non-contact manner with the condensing optical path, but in order to further improve the efficiency, an external core 16 serving as a return path of the magnetic force lines generated from the core 14 is provided in the coil 13.
Annularly along the outer peripheral portion of the medium, or only a part of the annular front side in consideration of the relative movement between the medium 1 and the outer core 16 is provided partially, or the outer core 16 and the core 14 are It is constituted by being magnetically coupled with a magnetic material.

(Operation)

As described in FIG. 14, the direction of the magnetization of the medium is determined by the direction of the magnetic field almost passing through the Curie point during cooling, and it is necessary that the largest magnetic field be applied at that time. Therefore, when providing the core to an empty core of the coil, which corresponds to the air-core portion and the medium and in the moving direction of the rear relative movement with respect to the recording film 11 in the air-core region of the coil when considering (the time t ₃ of the coil By adopting a structure in which many cores are present at (position), the magnetic flux can be concentrated behind the inside of the coil, and a large magnetic field can be effectively given at the time of recording.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the principle of the present invention. FIG. 1 (a) is a sectional view taken along the line BB 'in FIG. 1 (b).
FIG. 1B is a plan view, and FIG. 1C is a perspective view of a core. In each of the figures, reference numeral 13 denotes a coil, and 14 denotes a core made of a magnetic material. The coil 13 is an air-core coil wound in an oval shape having a certain thickness in which the outer shape is shifted from the center of the great circle and the center of the small circle, and the outer periphery thereof is connected. A core 14 is arranged in the air core of the coil 13 on the small circle side which does not block the optical path of the laser light 4 through which the optical axis P of the light 4 passes and which is conically focused by an objective lens mounted on an optical head (not shown). ing.

The outer shape of the core 14 is, as shown in FIGS. 7A and 7C, along the conical outer surface of the laser beam 4, a surface having a required gap, and the inner surface of the coil 13 on the small circle side. A surface and a cubic shape surrounded by an upper surface and a lower surface parallel to the thickness of the coil 13, and the lower surface near the recording film 11 side is radially concentrated with respect to the optical axis P of the laser light 4. Is formed.

When an electric current is applied to the coil 13 in this arrangement shape, a pattern of the magnetic force lines 9 is formed as shown by an arrow, and the pattern of the magnetic force lines 9 forms a region 15 for receiving a strong magnetic field on the recording film 11 of the medium 1 facing the core 14. Is done. After the spot position formed on the recording film 11 by the laser beam 4 reaches the maximum temperature, the spot position moves while cooling in the direction of arrow A, and the time t _{3 in} FIG.
In the region 15 receiving the strong magnetic field at the position where the Curie temperature is reached, the portion of the recording film 11 that has reached the Curie temperature in the region 15 receiving the strong magnetic field is efficiently magnetized. become.

Accordingly, the coil 13 and the core 14 are adjusted so that the distance between the position of the core 14 facing the region 15 receiving the strong magnetic field and the optical axis P of the laser beam 4 becomes the optimum size corresponding to the rotation speed of the recording film 11. By setting the shape and arrangement dimensions, the recording film heated by the laser beam 4 to the Curie temperature or higher
A magnetic field modulation coil 13 of this optical head can be provided on both sides of the medium 1 when the heating point on the substrate 11 reaches the Curie point during cooling while rotating and moving. Accordingly, a large magnetic field can be efficiently extracted from both surfaces of the medium 1.

FIG. 2 is a view showing a first embodiment of the present invention. FIG. 2 (a) is a sectional view taken along the line CC 'in FIG. 2 (b), and FIG. 2 (b) is a plan view. Show. This figure is different from FIG. 1 in that the outer core 16 which is a return path of the magnetic force lines 9 generated from the core 14 is formed in an annular shape (an oval shape shown by a solid line and a broken line) along the outer periphery of the coil 13 or in the medium 1. The difference is that only the annular portion corresponding to the front side of the above, that is, only the annular front side in consideration of the relative motion between the medium 1 and the outer core 16 is partially provided as shown by a solid line in an arc shape. By providing the external core 16, the intensity of the magnetic field generated in the core 14 is further increased.

FIG. 3 is a view showing a second embodiment of the present invention. FIG. 3 (a) is a sectional view taken along the line DD 'in FIG. 3 (b), FIG. 3 (b) is a plan view, FIG. 3 (c) is a sectional view taken along the line EE 'in FIG. 3 (b). This drawing differs from FIG. 2 in that the core 14 and the outer core 16 are connected by a connecting core 17 made of a magnetic material, as shown in FIG. Magnetically coupled along the upper surface of
The difference is that the return path effect of the magnetic field lines 9 generated from the core 14 is further increased.

FIG. 4 is a view showing a third embodiment of the present invention. In this figure, the coil for modulating the magnetic field shown in FIG. 3 is fixed to the main body of the optical head. In the figure, 21 is the main body frame of the optical head, and 31 is the objective lens with respect to the main body frame 21 of the optical head. An actuator for finely controlling the positioning of the objective lens 3, comprising a permanent magnet and a drive coil which are arranged in a non-contact manner and facing each other, and has a focusing control function of a spot position where the objective lens 3 is connected to the medium 1; Has control function. Reference numeral 22 denotes a mounting plate for fixing the main body frame 21 of the optical head and the outer core 16. The mounting plate 22 may use a mounting member formed integrally with the outer core 16.

With this arrangement, the magnetic flux can be concentrated at a required position on the medium 1 without obstructing the movement of the objective lens 3 and the focusing optical path, and the same optical head can be used on both sides of the medium 1. it can. Also, the first
Needless to say, the coil having the configuration shown in FIGS. 2 and 3 can also be attached as in this example.

The core 14, the external core 16, and the connecting core 17 used in the magnetic field modulation coils of the optical heads of FIGS. 1 to 3 described above use Mn-Zn ferrite as members. The coil was wound 20 turns, and the signal quality of the optical head shown in FIG. 4 fixed to the main body frame was measured. For comparison, a result of manufacturing a coil having the same number of turns having the shape shown in FIG. 12 and performing measurement will be described.

The magneto-optical disk medium used was manufactured by sequentially laminating a protective film, a recording layer, and a protective film in this order on a substrate on which a pre-groove was formed, and then applying and curing a photo-curable resin as a protective film. did. The protective film is Tb
A material obtained by co-sputtering SiO ₂ is used. The recording film is TbFeCo, the composition is 21%, 71%, and 8%, respectively, and the film thickness is 100 μm for the lowermost protective film, 100 μm for the recording film, 100 μm for the next protective film, and 30 μm for the uppermost resin film. Formed.

FIG. 5 is a comparison diagram of the signal quality characteristics with respect to the coil drive current of the present invention and the conventional example. The drive current of the coil was shown in unit ampere (A), and the signal quality was shown in C / N in unit (dB).
The characteristic curve F shows the conventional coil 7 (air-core coil) of FIG.
A characteristic curve G shows the characteristic of the conventional coil 7 (with a magnetic core) in FIG. 12, a characteristic curve H shows the characteristic of the coil 13 of FIG. 1 of the present invention, and a characteristic curve I shows the characteristic of the coil 13 of FIG. Things.
As can be seen from this figure, it is understood that the use of the coil of the present invention improves the signal quality with a small driving current.

Although the characteristics of the coil shown in FIG. 2 of the present invention are not shown, they are located in the middle between the characteristic curves H and I, and the degree of improvement is gradually improved from FIG. 1 to FIG. In the example of FIG. 3, it can be seen that the efficiency is further improved by the return path structure. That is, when the optical head of each embodiment is used, recording can be performed with a current of about 1/5 or less as compared with an air-core coil, and a magnetic field can be applied efficiently.

FIG. 6 is a view showing a fourth embodiment of the present invention, and shows an example in which a magnetic field modulation coil provided opposite to the lower surface of a medium (not shown) is mounted on an optical head. Sixth
6 (a) is a perspective view, and FIG. 6 (b) is an enlarged view of an essential part taken along the line JJ 'in FIG. 6 (a). In both figures, reference numeral 18 denotes a linear positioner which linearly drives a positioner movable portion 19 in a radial direction (a direction traversing the track of the medium) of the medium (not shown). Built-in head. Reference numeral 20 denotes a main optical system fixing unit that optically transmits and receives laser light to and from an optical head built in a positioner movable unit 19, and 23 denotes a positioner 18
5 shows a medium drive unit formed integrally with the medium drive unit.

The positioner movable portion 19 includes voice coils 19a and 19b and a plurality of (four in the figure) ball bearings 19c on both sides, and has a front surface in a moving direction (a direction reciprocating in a laser beam transmitting direction indicated by an arrow K). Is provided with a light receiving window 19d for transmitting and receiving a laser beam from the main optical system fixing unit 20 facing the medium.
A coil 13 for modulating a magnetic field for transmitting and receiving laser light and the like are provided on the surface opposite to. Reference numerals 18a and 18b denote guide rails for linearly reciprocating the positioner movable portion 19 through a plurality of ball bearings 19c, and a permanent magnet 18c
And 18d, and together with the voice coils 19a and 19b, constitute a voice coil motor.

The medium drive unit 23 has a spindle mounting surface 23a formed integrally with the guide rail, and the spindle mounting surface 23a
Has one end connected to a spindle motor (not shown), and the other end has a mechanism for fitting and mounting the medium 1 (not shown). FIG. 6B is an enlarged view of a main part of the present invention.
A coil 13, a core 14, an external core 16 and the like shown in the figure are fixed to a frame of a positioner movable portion 19 in accordance with an optical axis of an objective lens 3 provided on a main body frame 21 of an optical head.

In the method for mounting the coil shown in FIG. 4 or FIG.
Alternatively, the objective lens 3 may come into contact with the core 14, the external core 16, and the like. Further, since the distance between the medium 1 and the coil 13 changes, the magnetic field applied to the medium 1 changes, which may affect the recording characteristics. The means for avoiding the influence will be described below.

FIG. 7 is a view showing a fifth embodiment of the present invention. 4 differs from FIG. 4 in that the core 14 including the coil 13 and the external core 16 are fixed integrally with the movable part of the actuator 31, that is, the objective lens 3. By this means, the components included in the movable part of the actuator 31 can solve both the contact problem and the magnetic field fluctuation problem. However, adding such components to the movable part of the actuator 31 increases the weight of the movable part. As a result, the weight of the coil becomes a burden when controlling the light spot of the objective lens 3 and the light spot servo performance is reduced. It may hinder high speed. The means for avoiding the influence will be described below.

FIG. 8 is a view showing a sixth embodiment of the present invention. This drawing differs from FIG. 7 in that the core 14 including the coil 13 and the external core 16 are integrally fixed with a magnetic field modulation actuator 24 that performs positioning control in synchronization with the movable part of the actuator 31. As shown in the figure, the magnetic field modulation actuator 24 has a fixed side provided at an end extending integrally with the fixed side of the actuator 31, and a coil 13 is provided on the movable side of the magnetic field modulation actuator 24 which is paired with the fixed side. The objective lens 3 and the core 14 including the coil 13 and the external core 16 are interlocked with each other independently of each other by this means. Can be held.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, a large magnetic field can be efficiently extracted from both sides of the medium, and the recording speed can be stably improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention, FIG. 2 is a diagram showing a first embodiment of the present invention, FIG. 3 is a diagram showing a second embodiment of the present invention, and FIG. FIG. 5 is a diagram showing a third embodiment of the present invention, FIG. 5 is a comparison diagram of signal quality characteristics with respect to a coil drive current of the present invention and a conventional example, FIG. 6 is a diagram showing a fourth embodiment of the present invention, FIG. Is a view showing a fifth embodiment of the present invention, FIG. 8 is a view showing a sixth embodiment of the present invention, FIG. 9 is a perspective view showing the arrangement of a main part of a conventional magneto-optical disk and optical head, FIG. FIG. 11 is a cross-sectional explanatory view of a first example of the conventional overwrite method, FIG. 11 is a cross-sectional explanatory view of a second example of the conventional overwrite method, and FIG. 12 is a third example of the conventional overwrite method. FIG. 13 is a diagram showing magnetic characteristics of the medium with respect to temperature changes, and FIG. 14 is a diagram showing a temperature change and magnetization characteristics of the medium with time. 1 to 2, 4 and 6 to 8, 1 is a medium (magneto-optical disk), 3 is an objective lens, 13 is a coil,
14 is a core, 16 is an external core, 19 is a positioner movable part, 21
Denotes a main body frame of the optical head, and 24 denotes a means for controlling positioning (magnetic field modulation actuator).

Continuation of the front page (72) Inventor Tsutomu Tanaka 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-63-276731 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 11/10

Claims (7)

(57) [Claims] 1. A magnetic field modulation coil (13) of an optical head for recording / erasing information on a medium (1) for a magneto-optical disk by a magnetic field modulation method, wherein the medium rotates the optical head. A converging optical path for forming a spot with a laser beam is provided so as to penetrate the coil (13) in a non-contact manner with respect to (1), and the medium (1) heated by the spot forming is provided.
The core (1) made of a magnetic material for concentrating the magnetic flux at the movement position when the area reaches near the Curie temperature while cooling
A coil for modulating a magnetic field of an optical head, wherein 4) is provided in non-contact with the converging optical path in the air core of the coil (13). 2. An outer core (16), which is a return path for magnetic lines of force generated from said core (14), is formed in an annular shape along the outer periphery of said coil (13), or only on the front side of said medium (1). 3. The coil for modulating a magnetic field of an optical head according to claim 1, wherein the coil is partially provided in the optical head. 3. A magnetic field modulation coil for an optical head according to claim 2, wherein said outer core and said core are magnetically coupled by a magnetic material. 4. A magnetic field modulation coil for an optical head according to claim 1, wherein each of said magnetic field modulation coils is fixed to a main body frame of said optical head. 5. A positioner (18) for moving said optical head in a direction transverse to a track of said medium (1).
4. The magnetic field modulation coil for an optical head according to claim 1, wherein each of the magnetic field modulation coils is fixed to a frame of the positioner movable section (19). 6. A magnetic field modulation coil for an optical head according to claim 1, wherein each of said magnetic field modulation coils is fixed integrally with an objective lens of each of said optical heads. . 7. A means (24) for positioning control of each of said magnetic field modulating coils in synchronization with the movement of an actuator for driving said objective lens (3). 4. A coil for modulating a magnetic field of the optical head according to 3.