JP2001023230A - Optical head and optical recording / reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head and an optical recording / reproducing apparatus capable of reducing a manufacturing cost while appropriately maintaining a separation distance between a solid immersion lens forming a condensing spot and a recording medium. . SOLUTION: A solid immersion lens 12 is provided on a magneto-optical disk 2 at a position close to a recording film 2a.
On the upper side of 2, an optical head 10 is provided by providing an objective lens 13 for condensing recording / reproducing light emitted from a light source on a solid immersion lens 12. Here, the bottom surface of the solid immersion lens 12 is
It is formed into a downwardly convex spherical shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for recording / reproducing information on / from a recording medium by light and an optical head used for the optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art Conventionally, as an apparatus for recording / reproducing information on a recording medium using light, there is an apparatus utilizing a magneto-optical change or a crystal phase change of a recording film provided on the recording medium. here,
In the case of utilizing the magneto-optical change of the recording film, recording is performed by applying a magnetic field from the outside to a portion of the recording film heated to a temperature above the Curie point by irradiating a laser beam and inverting the magnetization of the portion. Reproduction is performed by detecting the rotation of the polarization angle of the reflected light due to the Kerr effect. On the other hand, in the case of utilizing the crystalline phase change of the recording medium, recording is performed by causing the phase change of the recording film from a crystalline state to an amorphous state and vice versa by the heat of a laser to perform recording. Is performed utilizing the fact that the reflectances of the images are different.

In such an optical recording / reproducing apparatus, in order to increase the recording density and increase the recording capacity of a recording medium, it is necessary to reduce the diameter of a laser spot formed on a recording film. Here, the focused spot diameter is K ·
λ / NA (λ: light wavelength, NA: numerical aperture of objective lens,
It is known that the diameter of the condensed spot is reduced by decreasing the light wavelength λ or increasing the NA of the objective lens.
Here, the light wavelength λ is 400 nm with a small semiconductor laser.
Some of them are being put to practical use, but have shortcomings in terms of short life and productivity, and have not yet reached a level that can be incorporated into equipment at present.

On the other hand, there is a type in which a solid immersion lens (SIL: Solid Immersion Lens) is provided in a condensing portion of an objective lens to increase the synthetic NA. According to this, it is possible to increase NA, which is about 0.45 to 0.60 only with the objective lens, to about 1.2 to 1.6. FIG. 6A shows a configuration example of an optical head using a hemispherical solid immersion lens, and a slider 111 (shown as a driving mechanism of the slider 111) provided near the recording film 102 a of the recording medium 102. (Not shown), an objective lens 113 and a solid immersion lens 112 are provided in a gap 111a. Light emitted from the light source is condensed by the objective lens 113, and a condensed spot is formed on the bottom surface of the solid immersion lens 112. As described above, in the case of the hemispherical solid immersion lens 112, the synthetic NA is (NA of the objective lens) × (refractive index n of the solid immersion lens material). Thus, for example, NA = 0.6 and n =
If 2.0, the synthetic NA is 1.2, and the focused spot diameter is about 320 nm for a light wavelength of 630 nm and about 200 nm for a light wavelength of 400 nm, with a constant K of 0.6.
It can be.

FIG. 6B shows a super hemispherical solid immersion lens 21.
In this case, the composite NA is (NA of the objective lens) × (refractive index n of the solid immersion lens material) ² . Therefore, for example, if NA = 0.6 and n = 2.0, the synthetic NA is 2.4, and the focused spot diameter is a constant K.
Is set to 0.6, and about 160 n for an optical wavelength of 630 nm.
m, about 100 nm for a light wavelength of 400 nm.

[0006]

As described above, the synthetic NA
Although it is possible to increase the recording density by reducing the diameter of the condensed spot by increasing the diameter of light, when the combined NA exceeds 1, as in the above apparatus, the light condensed on the bottom surface of the solid immersion lens A part or most of the light is totally reflected inside the bottom surface of the solid immersion lens, and a so-called evanescent wave having weak energy is formed below the bottom surface of the solid immersion lens. For this reason, the separation distance between the solid immersion lens and the surface of the recording medium cannot be made too large, and is generally set to be shorter than the light wavelength. This separation distance is 50 n when the light wavelength is 630 nm or 400 nm as described above.
m or less.

However, in order to bring a solid immersion lens having a diameter of about 1 mm close to a recording medium at a very small interval of 50 nm or less and to hold the same even during a recording / reproducing operation, high-precision machining / assembly is required. Need to be done. Therefore, the parallelism between the solid immersion lens and the recording medium needs to be maintained such that the end of the lens does not contact the recording medium even when the distance between the center of the lens and the surface of the recording medium approaches 50 nm. Therefore, the relative inclination angle θ allowed for both members (the solid immersion lens and the recording medium) is approximately equal to or less than (the distance between the center of the solid immersion lens and the recording medium) / (the radius of the solid immersion lens) rad. Become. This means that, for example, when the diameter of the solid immersion lens is 1 mm, 50 nm / 0.
5 mm = 0.1 mrad or less. As described above, the optical head of the optical recording / reproducing apparatus using the solid immersion lens is required to have extremely high work / assembly accuracy, which causes an increase in cost.

The present invention has been made in view of such a problem, and it is possible to reduce the manufacturing cost while appropriately maintaining the distance between the solid immersion lens forming the condensed spot and the recording medium. It is an object to provide an optical head and an optical recording / reproducing device.

[0009]

In order to achieve the above object, an optical head according to the present invention comprises a light source for emitting recording / reproducing light (for example, a light irradiation device 5 in the embodiment),
A solid immersion lens disposed at a position close to a recording film of a recording medium (for example, the magneto-optical disk 2 in the embodiment); and a solid immersion lens disposed above the solid immersion lens to record and reproduce light from a light source. And a bottom surface of the solid immersion lens is formed in a downwardly convex spherical shape.

The solid immersion lens forming the converging spot is provided in parallel with and extremely close to the recording medium surface. In the present invention, the bottom surface of the solid immersion lens is located near the optical axis of the recording / reproducing light. (The center of the solid immersion lens) has a shape that protrudes downward, so that even when both members (the solid immersion lens and the recording medium) are in a non-parallel state, the peripheral portion of the lens remains on the recording medium surface. The two members are less likely to interfere with each other than in the conventional case where the bottom surface of the solid immersion lens is flat. For this reason, it is possible to increase the range in which the non-parallelism of the two members can be tolerated while appropriately maintaining the separation distance between the solid immersion lens and the recording medium, thereby reducing manufacturing costs in terms of machining and assembly accuracy. It becomes possible.

An optical recording / reproducing apparatus according to the present invention has a medium driving mechanism (for example, a spindle motor 1 in the embodiment) for holding and moving a recording medium in a plane, the optical head, and the optical head. It is configured to include a head arm and an arm driving mechanism (for example, the voice coil motor 3 in the embodiment) for driving the head arm so as to move the optical head in a direction intersecting the plane movement direction of the recording medium. By using the optical head, the manufacturing cost can be reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show an optical recording / reproducing apparatus provided with an optical head according to the present invention. The optical recording / reproducing apparatus is provided on a recording film 2a of a magneto-optical disk 2 driven to rotate by a spindle motor 1. An optical head 10 positioned close to the head, a head arm 4 for holding the optical head 10, a voice coil motor 3 for rotating the head arm 4, and a light irradiation device 5 for irradiating recording / reproducing laser light. Is configured.

The optical head 10 includes a slider 11. The slider 11 is located on the recording film 2a on the rotating magneto-optical disk 2 and floats by a certain minute distance from the recording film 2a by an air bearing effect. (Ie, constitute a flying head). Head arm 4
Is a rotary shaft 4a connected to the voice coil motor 3 and driven to rotate, an arm 4b extending horizontally from the upper end of the rotary shaft 4a, and an optical head 1 at the tip of the arm 4b.
And a suspension portion 4c that supports the vertical movement of the suspension portion 4c. Voice coil motor 3
When the rotation shaft 4a is driven to rotate, the arm portion 4b swings horizontally and moves the optical head 10 in a direction substantially perpendicular to the rotation direction of the magneto-optical disk 2 (the direction of arrow A in FIG. 2). The optical head 10 scans on the recording film 2a of the magneto-optical disk 2. That is, tracking control is performed by the voice coil motor 3.

A circular tapered space 11a extending upward is formed in the slider 11 of the optical head 10.
A solid immersion lens 12 made of a glass material is provided below the gap 11a, and an objective lens 13 also made of a glass material is provided above the gap 11a. A microprism 15 is provided above the slider 11 with a spacer 14 interposed therebetween, and a high reflection film 16 is provided on a reflection surface 15a thereof. This micro prism 1
Reference numeral 5 is connected to the suspension section 4c of the head arm 4 via the fine movement actuator 20. The space 11a may be filled with a transparent or light-transmitting material.

As shown in FIG. 3, the solid immersion lens 12 is formed in a shape obtained by shaping the bottom surface of a hemispherical member having an upwardly convex radius r into a downwardly convex spherical shape. Here, the spherical shape of the bottom surface is a perpendicular line L passing through the center P of the hemispherical member (this point P results in the lowest point of the solid immersion lens 12).
(This coincides with the optical axis of the hemispherical member.) The center is a point Q set above and a line segment PQ (= R. R>
It is given as part of a sphere with radius r). In addition,
This solid immersion lens 12 is manufactured by a mold.

FIG. 4 shows the fine movement actuator 20 in an enlarged manner. The fine movement actuator 20 is of a parallel plate type, and specifically has a fixed block 23 and a movable block 24 provided on a first substrate 21 joined to the suspension part 4c.
4 has a large number of parallel flat plates extending parallel to each other. By applying a voltage between these parallel flat plates to actuate electrostatic force, the movable block 24 is finely moved relative to the fixed block 23 in a direction perpendicular to the parallel flat plate (the direction of arrow B) to provide fine and highly accurate movement control. Is available.

The movable block 24 is further joined to the microprism 15 via the flat plate portion 22. Therefore, if a voltage is applied between the parallel flat plates to finely move the movable block 24, the movable block 24 is moved relative to the suspension portion 4c. The optical head 10 can be slightly moved in the direction of arrow B. The direction of the arrow B is the same as the moving direction A for scanning the optical head 10 by the voice coil motor 3.

A reflection mirror 6 is disposed on a rotating shaft 4a of the head arm 4 so as to be obliquely opposed to the light irradiation device 5.
The recording / reproducing laser beam emitted from the light irradiating device 5 is reflected by a reflecting mirror 6 as shown by chain lines R1 and R2 in FIGS.
And is guided to the microprism 15. The recording / reproducing laser light guided to the microprism 15 in this manner is reflected by the high reflection film 16 on the reflection surface 15a of the microprism 15, and then condensed by the objective lens 13 so as to be narrowed down to the diffraction limit. The light enters the immersion lens 12.

The operation of the optical recording / reproducing apparatus having the above configuration will be described. First, the magneto-optical disk 2 is rotated at a predetermined speed by the spindle motor 1. At this time, the optical head 10 supported by the suspension portion 4c of the head arm 4 and disposed on the recording film 2a on the upper surface of the magneto-optical disk 2
Means that the slider 11 has the recording film 2
It floats by a very small distance from a. When the recording / reproducing laser beam is irradiated from the light irradiation device 5 in this state, this light is reflected by the reflecting mirror 6 and enters the microprism 15 as indicated by chain lines R1 and R2. Then, after being reflected by the reflecting surface 15a of the microprism 15, the light is condensed by the objective lens 13 and enters the solid immersion lens 12 to be focused. As a result, a focused spot is formed on the bottom surface of the solid immersion lens 12 (see FIG. 3).

Here, since the magneto-optical disk 2 is driven at a constant speed, the flying height of the slider 11 is always constant. Therefore, the distance between the recording film 2a of the magneto-optical disk 2 and the bottom surface of the solid immersion lens 12 is high. The distance is always kept at an appropriate value. For this reason, the condensed spot can be always positioned on the recording film 2a of the magneto-optical disk 2, and it is not necessary to provide a focusing mechanism as in the conventional case.

The temperature of the portion of the recording film 2a where the condensed light spot is locally increased, but when a magnetic field is applied from the outside while the temperature is raised to a temperature higher than the Curie point, the magnetization of the portion is reversed. Then, the information is recorded (or erased). The application of the magnetic field is performed by energizing an electromagnetic coil (not shown) provided in the vicinity of the solid immersion lens 12, but the direction of the applied magnetic field can be switched by changing the direction of the energizing current. . The direction of the applied magnetic field (generated by the electromagnetic coil) is perpendicular to the recording film 2a. On the other hand, a device for detecting the magnetic Kerr effect is used for reproducing information, and such a device is also provided in the above-mentioned optical recording / reproducing device. .

The recording and reproduction of such information is performed by moving (scanning) the optical head 10 in the radial direction of the magneto-optical disk 2 in accordance with the rotation of the magneto-optical disk 2. Scanning or tracking is performed by rotating the head arm 4 by the voice coil motor 3 arranged at the root of the head arm 4. However, here, the voice coil motor 3 is used as a coarse movement servo, and controls a relatively low-speed component of the head arm 4. That is,
Since the precision of tracking control by the voice coil motor 3 is limited and fine tracking control is difficult, the tracking control is used for coarse movement servo control.
This is performed by applying a fine movement servo with 0.

Since the bottom surface of the solid immersion lens 12 is formed in a downwardly convex spherical shape as described above, the solid immersion lens 12 may be displaced from the magneto-optical disk 2 in parallelism. Even if there is, the periphery of the solid immersion lens 12 will not be extremely close to the disk 2. Hereinafter, this will be described with reference to FIG.

As shown in FIG. 5 (symbols common to FIG. 3 are used as is), a point on the bottom surface which is horizontally shifted by X from the lowermost point P of the solid immersion lens 12 is P1. , The angle θ between the line segment connecting the point Q and the point P1 and the perpendicular L is θ = sin ⁻¹ (X / R). Here, the difference Δ in the distance between the point P and the point P1 from the surface of the magneto-optical disk 2 is Δ = R (1−cos θ) as is clear from the drawing. This is approximately Δ ≒ Rθ ² when the angle θ is very small.
/ 2. Therefore, the solid immersion lens 12
The inclination angle θ1 of the magneto-optical disk 2 with respect to the solid immersion lens 12 is θ> 許 容 θ, where m> Δ, assuming that the predetermined distance m is maintained between the magneto-optical disk 2 and the optical disk 2.
More required. Here, for example, if the diameter of the solid immersion lens 12 is 1.0 mm (radius r = 0.5 mm) and the radius of curvature R of the bottom surface shape is 5.0 mm, θ1 when the predetermined separation distance m is 50 nm. <4.5 mrad. This means that there is a margin 45 times as large as 0.1 mrad when the bottom surface of the solid immersion lens is flat.

Here, since the bottom surface of the solid immersion lens 12 has a spherical shape, even if the solid immersion lens 12 and the surface of the magneto-optical disk 2 are perfectly parallel, the point P1 can be used. R (1-cos θ) = R (1-cos
s (sin ⁻¹ (X / R))) ≒ X ² / 2R away from the surface of the disk 2, but generally this effect is extremely large when considering a field of view (light spot diameter) of about several μm. small. For example, in the above example, the visual field is φ20 μm
(X = 10 μm), it is about 10 nm, and there is no particular problem. Furthermore, when the bottom surface is processed into a spherical surface, even if an error occurs during processing, the line connecting the centers of the two spherical surfaces is set as a new optical axis, as in the case where there was no processing error at all. Become.

As described above, in the present invention, since the bottom surface of the solid immersion lens 12 has a downwardly convex spherical shape,
Even when the solid immersion lens 12 and the magneto-optical disk 2 are in a non-parallel state, the periphery of the lens 12 is
There is no extreme closeness to the surface, and both members 12 and 12 are harder than in the conventional case where the bottom surface of the solid immersion lens 12 is flat.
2 is less likely to interfere. For this reason, it is possible to increase the allowable range of the non-parallelism of the two members 12 and 2 while appropriately maintaining the separation distance between the solid immersion lens 12 and the magneto-optical disk 2, and thus, it is possible to manufacture the device from the viewpoint of machining and assembly accuracy. Costs can be reduced. Therefore, an optical recording / reproducing apparatus including the optical head 10 according to the present invention can be manufactured at low cost.

Although the optical head and the optical recording / reproducing apparatus according to the present invention have been described above, the scope of the present invention is not limited to the above embodiment. For example, the shape of the solid immersion lens 12 is not limited to a hemispherical shape, and may be a super hemispherical shape or the like. Further, the optical head according to the present invention is not limited to the optical recording / reproducing apparatus having the above configuration, and can be mounted on an optical recording / reproducing apparatus having another configuration.

[0028]

As described above, in the optical head according to the present invention, the bottom surface of the solid immersion lens has a shape protruding downward as it approaches the optical axis of recording / reproducing light (the center of the solid immersion lens). Therefore, even when the solid immersion lens and the recording medium are in a non-parallel state, the peripheral portion of the lens does not become extremely close to the recording medium surface, and the solid immersion lens has a flat bottom surface. In this case, both members are less likely to interfere with each other. For this reason, it is possible to increase the range in which the non-parallelism of the two members can be tolerated while appropriately maintaining the separation distance between the solid immersion lens and the recording medium, thereby reducing manufacturing costs in terms of machining and assembly accuracy. It becomes possible.

Further, an optical recording / reproducing apparatus according to the present invention comprises a medium drive mechanism for holding a recording medium and moving it in a plane, the optical head, a head arm for holding the optical head,
An arm drive mechanism for driving the head arm to move the optical head in a direction intersecting with the plane movement direction of the recording medium is provided, but it is possible to manufacture the optical head at low cost by using the above optical head. it can.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a configuration of an optical recording / reproducing apparatus including an optical head according to the present invention.

FIG. 2 is a schematic plan view showing a configuration of the optical recording / reproducing apparatus.

FIG. 3 is an enlarged side view illustrating a shape of a solid immersion lens.

FIG. 4 is a perspective view showing a fine movement actuator constituting the optical recording / reproducing apparatus.

FIG. 5 is a side view showing the vicinity of a solid immersion lens for describing the effect of the present invention.

FIGS. 6A and 6B are schematic side views showing a part of the configuration of an optical head used in a conventional optical recording / reproducing apparatus. FIG. 6A shows a case where a hemispherical solid immersion lens is used, and FIG. This is an example in the case where a solid immersion lens is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spindle motor (medium drive mechanism) 2 Magneto-optical disk (recording medium) 2a Recording film 3 Voice coil motor (arm drive mechanism) 4 Head arm 5 Light irradiation device (light source) 10 Optical head 11 Slider 12 Solid immersion lens 13 Objective lens

Claims (2)

[Claims] A light source for emitting recording / reproducing light; a solid immersion lens disposed at a position close to a recording film of a recording medium; and a recording / reproduction from the light source disposed above the solid immersion lens. The optical head according to claim 1, further comprising: an objective lens for condensing light on the solid immersion lens, wherein a bottom surface of the solid immersion lens has a downwardly convex spherical shape. 2. A medium driving mechanism for holding a recording medium and moving the recording medium in a plane, the optical head according to claim 1, a head arm holding the optical head, and moving the optical head in a plane movement direction of the recording medium. And an arm driving mechanism for driving the head arm so as to move the head arm in a direction intersecting with the optical recording / reproducing apparatus.