JP2000171611A - Solid immersion lens and optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid immersion lens which is lightweight and easily fitted to a lens barrel and which can be accurately molded out of glass. SOLUTION: This solid immersion lens 1 is constituted of a spherical surface 1a being the incident surface of light and a.plane surface 1b being the emitting surface of proximity-field light. Then, both side surfaces of the surface 1a in a sagittal direction Y are formed as the cut surfaces 1c and 1c and the dimension of incident width W is set so as to become about 40-60% of the diameter D of the surface 1a. By constituting an arrayed optical head, not only recording density can be enhanced by the lens 1 but also an effect for making the individual lenses lightweight and compact can be synergistically demonstrated by the lens 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid immersion lens used for high density optical memory (recording / reading) and an optical head provided with the solid immersion lens.

[0002]

2. Description of the Related Art In recent years, in the field of optical memory for optically recording / reading information, a larger amount of information can be recorded, that is, recording density is remarkably improved with the increase in speed of computers and development of multimedia. Device is desired,
Near-field optical recording technology has been proposed. In a conventional optical memory using a laser beam, the upper limit of the recording density is determined by the diffraction limit of light, and recording / reading can be performed only for marks of about the wavelength of light (several 100 nm).

In an optical memory using a near-field phenomenon of light recently proposed, a fiber probe or a solid immersion lens (solid immersion lens) having a minute aperture smaller than the wavelength of light is used.
By irradiating recording / reading light to a recording medium (optical disc) with the distance between the optical head and the recording medium approaching several tens of nm using a laser beam, the light exceeds the diffraction limit of light to reach several tens of nm. A small mark can be written and read as a signal.

[0004]

2. Description of the Related Art Conventionally, as a solid immersion lens, a hemispherical solid immersion lens 41 shown in FIG. 10 and a super hemispherical solid immersion lens 42 having a stigma below the hemisphere shown in FIG. Had been produced. The solid immersion lenses 41 and 42 have spherical surfaces 41a and 42a, which are light incident surfaces, and flat surfaces 41b, which are light emitting surfaces.
42b. In FIGS. 10 and 11,
43 is a normal objective (light collecting) lens, and 44 is a recording medium (optical disk).

In the hemispherical solid immersion lens 41, the light beam LB is perpendicularly incident on the spherical surface 41a and is condensed on the center of the plane 41b. Assuming that the refractive index of the solid immersion lens 41 is n, the wavelength in the lens 41 is 1 / n, and as a result, the numerical aperture NA of the condenser lens 43 is n times. The spot size of the light beam LB is reduced to 1 / n, and the resolution becomes n times. That is, the numerical aperture NA of the condensing lens 43 is 0.1.
5. The refractive index n of the solid immersion lens 41 is 1.8, and the light beam LB
Is 780 nm, the spot size S is determined by the following equation (1): S = λ / (2 nsin θ) (1) 430 nm Here, θ is の of the aperture angle of the focused beam.

In the super hemispherical solid immersion lens 42, the effective optical path is larger than the radius. In this case, the spot size S of the light beam LB is obtained by the following equation (2), and S = λ / (2n ² sin θ) (2) 240 nm.

As described above, by using the solid immersion lenses 41 and 42, it is possible to obtain a condensed spot whose wavelength is equal to or less than the wavelength of light to be used. To use this method, the recording medium 44
The distance (air gap) between the lens and the solid immersion lenses 41 and 42 must be sufficiently small so as to maintain a value of about 100 nm or less. In order to maintain and control the air gap, it has been proposed to mount a solid immersion lens on a flying slider by applying the technology of a magnetic hard disk.

[0008]

The conventional solid immersion lenses 41 and 42 are composed of only spherical surfaces 41a and 42a and flat surfaces 41b and 42b. ) Was difficult to position. Also, when molding the lens with glass,
Due to the large difference in thickness between the central part and the peripheral part, there is a problem that "sink" occurs during cooling and deformation occurs. Further, the lenses 41 and 42 are required to be further reduced in weight when mounted on the flying slider. This is because if the optical head is heavier, high-speed movement is restricted or a drive system needs to be enlarged. In particular, in an optical head in which a plurality of solid immersion lenses are juxtaposed and arrayed, it is important to reduce the weight of each lens.

Accordingly, an object of the present invention is to provide a solid immersion lens which is lightweight, can be easily attached to a lens barrel, and can be formed with high precision glass. Still another object of the present invention is to provide a lightweight optical head provided with a plurality of solid immersion lenses.

[0010]

In order to achieve the above object, a solid immersion lens according to the present invention comprises a plane which is a light exit surface and a light incident surface having a point at a predetermined distance from the plane. The spherical surface was a surface, and the incident width of the spherical surface in the sagittal direction was set to about 40 to 60% of the diameter of the spherical surface.

That is, in the solid immersion lens according to the present invention, both side surfaces of the spherical surface are cut into parallel surfaces, wedge-shaped inclined surfaces, or other shapes. Lightened by the cut amount,
The weight of the flying slider itself is reduced, which is advantageous in terms of high-speed movement and reduction of the load on the drive system. In addition, since the thin peripheral part of the hemispherical shape or super hemispherical shape is cut, the difference in thickness is reduced, and when molding with glass, "sinking" during cooling hardly occurs, enabling high precision molding Becomes Furthermore, if the lens is attached to a lens barrel or the like using the cut surface, positioning can be performed reliably and easily.

The recording medium is usually disc-shaped, and recording / reading / erasing is performed during rotation. Since the solid immersion lens according to the present invention has an incident width of about 40 to 60% of the spherical diameter, the resolution is reduced. However, the incident width is narrowed in the sagittal direction, and the resolution in the sagittal direction is not required to be so strict as to the resolution in the recording pit forming direction. However, there is a limit to the resolution in the sagittal direction. When the diameter is reduced by 40% with respect to the diameter, the reduction of the resolution is about 40%, and the numerical value around the lower limit is the lower limit.

Further, when a plurality of solid immersion lenses according to the present invention are arranged side by side to constitute a lens array, an optical head having a great advantage of light weight can be obtained. If a diffraction grating array (for example, a Fresnel lens array) is used as an optical member for condensing light on each solid immersion lens, a more compact and lightweight optical head can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a solid immersion lens and an optical head according to the present invention will be described below with reference to the accompanying drawings.

(First Embodiment of Solid Immersion Lens, FIGS. 1 and 2)
FIG. 1 shows a solid immersion lens 1 according to a first embodiment. The solid immersion lens 1 includes a hemispherical spherical surface 1a which is an incident surface of a condensed light beam LB, and a flat surface 1b which is a light emitting surface. 1a has a diameter D centered on the focal point S of the plane 1b. This spherical surface 1a has both sides cut into parallel surfaces 1c, 1c perpendicular to the emission plane 1b, and has a width W.

As shown in FIG. 2, such a solid immersion lens 1 has a cut surface 1 in a sagittal direction Y orthogonal to a direction X in which recording pits 7 are formed on a disk-shaped recording medium 6.
Recording / reading / erasing is performed with c and 1c positioned. In this case, the light beam LB condensed by the condensing lens 5 is
a, and is condensed at the center of the plane 1b. At this time, near-field light seeps out of the converging point S in a region of １ ／ or less of the wavelength, and forms a recording pit 7.

As described above, in the solid immersion lens 1 in which both sides are cut, the weight is reduced as the cut amount, that is, the width dimension W is reduced. When W = 0.8D, a weight reduction of about 6% can be realized. Although not much effect can be expected only by this weight reduction, the holding frame (not shown) can be reduced by 20%, which greatly contributes to the weight reduction of the holding frame. Also,
When W = 0.7D, a weight reduction of about 12% can be realized.
= 0.6D, weight reduction of about 20% can be realized, and W =
In the case of 0.4D, a weight reduction of about 43% can be realized.

On the other hand, regarding the resolution, the cut surfaces 1c,
Since the incident width of the light beam LB is limited in the sagittal direction Y where 1c is located, the reduction in resolution is inevitable. The numerical aperture NA of the condenser lens 5 is 0.7, and the solid immersion lens 1 is
Has a refractive index n of 1.83375 and a radius of the spherical surface 1a of 0.5
mm, sagittal direction Y when W = 0.7D
Does not decrease, the resolution decreases by about 10% when W = 0.6D, and the resolution decreases by about 2 when W = 0.5D.
When W = 0.4D, the resolution is reduced by about 40%, and when W = 0.3D, the resolution is reduced by about 55%.

As shown in FIG. 2, the recording pit 7
Is about 1/3 of the circumferential direction X with respect to the sagittal direction Y, and the resolution in the sagittal direction Y is not required to be stricter than that in the circumferential direction X. No problem occurs. Therefore, it is preferable that the width W of the spherical surface 1a is about 40 to 60% of the diameter D in consideration of weight reduction and reduction in resolution. Further, the lens 1 having both sides cut has a small difference in thickness, and when molded from a glass material, "sink" is unlikely to occur, and can be molded with high precision as designed.

(Second Embodiment of Solid Immersion Lens, FIGS. 3 and 4)
FIG. 3 shows a solid immersion lens 2 according to a second embodiment, which comprises a super hemispherical spherical surface 2a which is an incident surface of a converged light beam LB, and a plane 2b which is a light emitting surface. The condensed light beam LB is obliquely incident on the spherical surface 2a, is refracted, and condenses at the center of the plane 2b. At this time, near-field light seeps out of the converging point S in a region of １ ／ of the wavelength to form the recording pit 7 (see FIG. 4).

Also in this solid immersion lens 2, both sides in the sagittal direction Y are planes 2c, 2c perpendicular to the emission plane 2b.
2c, and has a width W smaller than the diameter D of the spherical surface 2a.

As in the first embodiment, the weight can be reduced as the width W decreases. Regarding the resolution in the sagittal direction Y, the numerical aperture NA of the condenser lens 5 is 0.466, and the refractive index n of the solid immersion lens 2 is 1.83.
375, when the radius of the spherical surface 2a is 0.5 mm, W =
The reduction is about 13% for 0.7D, about 32% for W = 0.6D, and about 39% for W = 0.5D. Further, in the case of W = 0.4D, it is reduced by about 47%,
In the case of W = 0.3D, it is reduced by about 57%.

As in the first embodiment, also in the second embodiment, considering the reduction in weight and the reduction in resolution,
The width W of the spherical surface 2a is preferably about 40 to 60% of the diameter D.

(Attaching Structure and Attaching Method of Solid Immersion Lens, see FIGS. 5, 6 and 7) Next, an attaching structure of the solid immersion lens to the lens barrel will be described. FIG. 5 shows a mounting structure and a mounting method of the solid immersion lens 1. First, the solid immersion lens 1 is inserted with the cut surfaces 1c, 1c aligned with the parallel surfaces 11, 11 of the ball frame 10 shown in FIG.
The solid immersion lens 1 is fixed to the ball frame 10 by injecting an adhesive from the substrate.

When the solid immersion lens 1 is inserted into the lens frame 10, as shown in FIG.
5 is used. That is, the lens frame 10 is placed on the jig 15, and the solid immersion lens 1 is inserted until the apex of the spherical surface 1 a contacts the concave portion 16. Thus, the solid immersion lens 1 is fixed to the ball frame 10 while maintaining a predetermined relationship.

Next, as shown in FIG.
The ball frame 10 is fitted into the front end opening 18 of the lens, and the collar 13 is fixed to the lens barrel 17 with an adhesive 19. The condenser lens 5 is also fixed to a predetermined position in the lens barrel 17. The fixing structure is the same as the conventional one, and the illustration is omitted.

FIG. 6 shows another mounting structure. The solid immersion lens 1 is inserted into the distal end opening 21 of the lens barrel 20 from the direction of arrow B, and the edge of the spherical surface 1a is brought into contact with the claw portion 22 for positioning. After that, the adhesive 23 is filled in the periphery of the distal end opening 21 and fixed. In the solid immersion lens 1, corners of the emission plane 1b and the cut surface 1c are chamfered to prevent chipping of the corners.

FIG. 7 shows another mounting structure. The solid immersion lens 1 used here has the cut surfaces 1c, 1c formed as wedge-shaped inclined surfaces. In this case, the inclined cut surfaces 1c, 1c are connected to the inclined inner side surface 27 of the distal end opening 26 of the lens barrel 25.
And position it. Next, an elastic ring 28 is attached to a concave portion formed by the edge of the spherical surface 1a and the inner surface of the distal end opening 26. In this example, it is preferable that the emission plane 1b be fixed at a position slightly protruding from the tip of the lens barrel 25. This is because the clearance between the lens barrel 25 and the recording medium can be increased by the amount of the protrusion.

In the solid immersion lens 1 according to the first embodiment, since the cut surfaces 1c, 1c are formed on both sides, the solid immersion lens is interposed by using the cut surfaces 1c, 1c via the ball frame 10. Alternatively, as compared with a conventional solid immersion lens 41 (see FIG. 10) which can be directly attached to the lens barrel 17, 20, or 25 and has no cut surface 1c, 1c.
Handling is easy, and the positioning accuracy with respect to the barrel 17, 20, or 25 is also improved.

Although the above description has been made with reference to the solid immersion lens 1 according to the first embodiment, the solid immersion lens 2 according to the second embodiment can be attached with a similar structure.

(Arrangement of solid immersion lens, see FIG. 8) By utilizing near-field light leaching from the solid immersion lens, recording / reading at high density can be performed. However, with near-field light, the SN ratio of the read signal is not so large, so that the rotation speed of the recording medium cannot be set high. To improve the data transfer rate in this state, a method of arraying a plurality of solid immersion lenses and reading data in parallel can be considered.

FIG. 8 shows a lens array 35 or 3 with solid immersion lenses 1 arranged side by side to improve the data transfer rate.
6 is constituted. (Although not shown, the solid immersion lens 2 can of course be similarly arrayed.)

FIG. 8A shows an example in which the solid immersion lenses 1 are arranged in a row so that their cut surfaces 1c are adjacent to each other, and mounted on a slider (not shown) in parallel with the sagittal direction Y orthogonal to the locus L of the recording pits. Is shown. FIG. 8B shows a lens array 35.
Is mounted on a slider (not shown) with a slight inclination angle with respect to the sagittal direction Y. In this case, the density of the locus of the recording pit can be increased in the sagittal direction Y. FIG. 8C shows a lens array 36 in which a plurality of rows of the solid immersion lenses 1 are arranged. By providing an appropriate inclination angle with respect to the sagittal direction Y, the recording density can be further increased.

In the solid immersion lens according to the present invention, by forming an optical head in an array, not only the recording density can be increased, but also the effect of reducing the weight and size of each lens is synergistically exhibited. .

(Combination of solid immersion lens and diffraction grating,
The above-mentioned condenser lens 5 (see FIGS. 2 and 4) is the same as the conventional one. By cutting both sides of the condenser lens 5, the weight and size of the optical head can be reduced.

Further, in order to reduce the weight and size of the optical head, it is preferable to use an array 30 composed of a diffraction grating 31 having a function of condensing light as shown in FIG. 9 as a condenser lens. . It is preferable to use a Fresnel lens as the diffraction grating 31. The diffraction grating 31 can be easily manufactured by a lithography method or an etching method.

(Other Embodiments) The solid immersion lens and the optical head according to the present invention are not limited to the above embodiments, but can be variously modified within the scope of the invention. In particular, the shape of the cut surfaces on both sides of the solid immersion lens is not limited to a parallel surface or an inclined surface, and may be a stepped surface.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a solid immersion lens, wherein (A) is a plan view, (B) is a front view, and (C) is a side view.

FIG. 2 is a perspective view showing a state of recording / reading by the solid immersion lens shown in FIG.

3A and 3B show a second embodiment of the solid immersion lens, wherein FIG. 3A is a plan view, FIG. 3B is a front view, and FIG. 3C is a side view.

FIG. 4 is a perspective view showing a state of recording / reading by the solid immersion lens shown in FIG. 3;

FIG. 5 is an explanatory view showing an example of a structure for attaching a solid immersion lens to a lens barrel and a process of attaching the same.

FIG. 6 is a sectional view showing another example of the mounting structure of the solid immersion lens.

FIG. 7 is a sectional view showing still another example of the mounting structure of the solid immersion lens.

FIG. 8 is an explanatory view showing a solid immersion lens array and its installation direction.

9A and 9B show a diffraction grating array, wherein FIG. 9A is a plan view of the diffraction grating array, and FIG. 9B is a side view showing a state where the diffraction grating array and the solid immersion lens array are combined.

FIG. 10 is an elevation view of an optical system including a conventional solid immersion lens (hemispherical shape).

FIG. 11 is an elevation view of an optical system including a conventional solid immersion lens (super hemispherical shape).

[Explanation of symbols]

 1, 2 ... solid immersion lens 1a, 2a ... spherical surface (incident surface) 1b, 2b ... plane (exit surface) 1c, 2c ... cut surface 30 ... diffraction grating array 35, 36 ... lens array Y ... sagittal direction

Claims (5)

[Claims] 1. A flat surface which is a light emitting surface and a spherical surface which is a light incident surface centered on a point separated by a predetermined distance from the plane, and an incident width of the spherical surface in a sagittal direction is equal to a diameter of the spherical surface. A solid immersion lens characterized by being about 40-60%. 2. The solid immersion lens according to claim 1, wherein both side surfaces in the sagittal direction are parallel surfaces perpendicular to the emission plane. 3. The solid immersion lens according to claim 1, wherein both side surfaces in the sagittal direction are wedge-shaped inclined surfaces. 4. An optical head comprising a lens array in which a plurality of the solid immersion lenses according to claim 1, 2 or 3 are arranged in parallel. 5. The optical head according to claim 4, further comprising a diffraction grating array for condensing light on each of the solid immersion lenses.