JP4601867B2 - Near-field optical head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a near-field optical head that uses near-field light to perform high-density recording and reproduction of information.
[0002]
[Prior art]
An optical microscope as a means for observing a micro area on the surface of a sample has an advantage that the sample is hardly damaged, but has a disadvantage that a resolution exceeding the diffraction limit of light to be used cannot be obtained in principle. In recent years, the sample surface is scanned with a probe having an optical aperture of a size equal to or smaller than the incident light wavelength, and high-resolution observation of the sample is performed by utilizing the interaction between the near-field light generated from the aperture and a micro area on the sample surface. The realized near-field optical microscope is attracting attention. A near-field optical information recording apparatus applies this principle to a high-density information recording apparatus.
[0003]
In the near-field optical information recording apparatus, instead of the near-field probe described above, a substantially planar near-field optical head having a minute optical aperture is used. This near-field optical head is arranged in place of the conventional magnetic recording device head, and information recorded on the surface of the disk-shaped recording medium is reproduced, and recording is performed by changing the optical characteristics of the surface of the recording medium. It is. The near-field optical head has, for example, a waveguide formed on a Si substrate and a minute opening formed on the bottom surface. The minute opening is formed by covering the entire cone formed by isotropic etching of the SiO ₂ layer on the Si substrate with an Al vapor deposition film and cutting the tip portion with FIB (Focused Ion Beam). This head is floated in the same manner as the magnetic recording apparatus, and the minute aperture is brought close to the surface of the recording medium from several tens to several hundreds of nanometers. Light from the laser is guided to the minute aperture through the waveguide, the near-field light generated from the minute aperture is scattered by the data mark on the surface of the recording medium, and the scattered light is detected to recognize the data mark.
[0004]
[Problems to be solved by the invention]
However, the conventional near-field optical head has a problem of low light efficiency. That is, since the light is absorbed or scattered by the light shielding film before reaching the minute aperture, the energy of the generated near-field light is extremely minute. The absorbed light energy is converted into heat in the vicinity of the minute opening, and the Al film near the opening is damaged. The scattered light is further reflected by the suspension arm and other parts, and part of the light enters the detector and becomes stray light noise. When the near-field light energy is weak, the interaction with the data mark is also small, and the output signal of the detector is also weak. For this reason, the C / N ratio of the information recording apparatus deteriorates, and there is a problem that high-speed data transfer is impossible.
[0005]
In order to increase the light efficiency, inserting a condensing function such as a microlens between the waveguide exit surface and the microscopic aperture increases the number of parts, which increases the manufacturing cost and increases the overall head size. There is a problem that the light efficiency is abruptly deteriorated when the focus of the collected light is not exactly coincident with the minute aperture.
[0006]
In addition, in order to increase the generated near-field light energy, there is a method of using a high-power laser, but this causes problems such as increasing power consumption and damaging the Al film near the opening by absorbed energy. have.
[0007]
In order to increase the light efficiency, a two-stage taper structure in which the inclination of the taper portion inside the minute aperture is two-staged has been proposed. This leads to an increase.
[0008]
There is also a method of condensing the light from the laser directly with a lens without going through a waveguide and guiding it to a microscopic aperture, but this leads to an increase in the size of the entire device, and it is optically applied to a head that performs microscopic tracking at high speed. There are problems such as the need to follow the system.
[0009]
[Means for Solving the Problems]
The present invention solves the above conventional problems. The near-field optical head according to the present invention is
A slider formed on the substrate;
An optical aperture formed on the substrate and having a size equal to or smaller than the incident light wavelength;
Levitated at a certain distance from the surface of the recording medium by the levitating force generated by the relative movement of the slider and the surface of the recording medium
In the near-field optical head for recording or reproducing information or both by interacting with the recording medium surface via near-field light generated from the optical aperture,
A concavo-convex structure made of metal periodically exists around the optical aperture on the substrate,
The optical aperture is located approximately in a plane defined by the bottom surface of the slider;
The near-field optical head is characterized in that the convex portion of the concavo-convex structure is located on the light incident side with respect to a plane defined by the slider bottom surface.
[0010]
According to the near-field optical head having such a structure, most of the light energy incident on the periphery of the microscopic aperture is converted into plasmon energy on the surface of the periodic concavo-convex structure of the metal. Therefore, the minute aperture serves as a minute light source to generate near-field light. Thereby, a dramatic improvement in light efficiency is realized as compared with the conventional near-field optical head.
[0011]
The near-field optical head according to the present invention is
In the near-field optical head, the metal is made of gold, silver, or copper.
[0012]
Thereby, plasmons can be generated with high efficiency in the optical wavelength range to be used. Further, a near-field optical head can be easily manufactured using a conventional process technique such as patterning by vapor deposition.
[0013]
The near-field optical head according to the present invention is
In the near-field optical head, a period of the concavo-convex structure is any one of 50 nanometers to 500 nanometers.
[0014]
As a result, the near-field optical head of the present invention can be manufactured only by existing technologies such as conventional semiconductor processes and electron beam exposure, and the near-field with high light efficiency can be obtained by efficiently converting incident light energy into plasmon energy. An optical head is realized.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a conceptual diagram showing a state in which a near-field optical head 2 according to Embodiment 1 of the present invention is mounted on an information recording apparatus. The near-field optical head 2 is bonded to the suspension arm 3 and is close to the surface of the recording medium 1 by the balance between the air levitation force generated by the high-speed rotation of the recording medium 1 in the direction of the arrow and the load applied to the suspension arm 3. The distance of the bottom surface of the field optical head 2 is kept constant. This distance is typically several tens of nm, but is designed to an appropriate value in the range of several to several hundreds of nm depending on the required recording density. Although not shown, an optical fiber is bonded to the suspension arm 3 to guide light having a wavelength of 405 nm from a laser light source (not shown). The size of the near-field optical head 2 is 1.5 mm in length, 1.2 mm in width, and 0.8 mm in thickness.
[0016]
FIG. 2 is a cross-sectional view of the near-field optical head 2 according to Embodiment 1 of the present invention. The near-field optical head 2 includes a mirror substrate 4, an aperture substrate 5, and an optical fiber 7. The mirror substrate 4 has a mirror surface 6 on which Al is vapor-deposited on a slope formed by anisotropic etching on a Si substrate. A V-groove (not shown) is also formed in the mirror substrate 4 by etching, and an optical fiber 7 is fixedly bonded thereto. The aperture substrate 5 is made of SiO ₂ , and a micro lens 9 having a diameter of 0.2 mm is formed on the upper surface. On the bottom surface of the opening substrate 5, a slider 8 for air levitation and a substantially rectangular parallelepiped near-field light generating microstructure 10 are formed therebetween. The height of the slider 8 is about 2 microns, and the tip of the microstructure 10 is located on a plane defined by the bottom surface of the slider. The outgoing light 11 from the optical fiber 7 is reflected by the mirror surface 6, condensed by the microlens 9 as indicated by the arrow in the figure, and irradiated to the near-field light generating microstructure 10.
[0017]
FIG. 3 is a bottom view of the opening substrate 5. There is a near-field light generating microstructure 10 between the two sliders 8, and a microlens 9 is disposed thereon. FIG. 4 is a cross-sectional view of the near-field light generating microstructure 10. The near-field light generating microstructure 10 is made of SiO ₂ and incident light 11 is transmitted through it. FIG. 5 is an enlarged view of the portion indicated by the region A. In FIG. 5, the portion of the SiO ₂ layer irradiated with the incident light 11 has a periodic uneven structure, and the region other than the minute openings 13 is coated with the Au film 12. These irregularities have a period of about 500 nm and a depth of 20 nm, and are arranged in a lattice form as shown in FIG. FIG. 6 shows the region A in FIG. 4 as viewed from the bottom side. An Au film 12 is coated on the entire surface of the concavo-convex structure with a thickness of about 20 nm, and a square minute opening 13 having a side of 100 nm is opened in the center thereof. The minute opening 13 does not have to be at the center of the Au film 12 and may be at the end or near the corner. In FIG. 5 again, the energy of the incident light 11 is converted into surface plasmons of the Au film 12 having an uneven shape. The surface plasmon propagates on the surface of the Au film 12, but is scattered by the microscopic aperture 13 that becomes a defect of the concavo-convex structure, becomes near-field light 50, and is localized near the microscopic aperture 13.
[0018]
The generation of surface plasmons by the incidence of light on the Au film having a periodic uneven shape is described, for example, by Thio et al. (Tineke Thio, HJ Lezec, TW Ebesen, Physica B, vol. 279, 90 (2000)). Here, by processing the tip of the optical fiber to form a periodic uneven structure of Au and measuring the light emission from the minute aperture, extremely high light efficiency was realized. Although there are many unclear points regarding this mechanism, the fact that it is due to surface plasmon is described, for example, in a paper by Sonnicsen et al. Feldmann, Appl.Phys.Lett., Vol.76, 140 (2000)). Also in the present embodiment, the light efficiency is improved by an order of magnitude or more as compared with the minute opening formed in the Al planar film.
[0019]
FIG. 7 shows a manufacturing process of the near-field optical head according to the present embodiment. In step S701, the microlens 9 is formed on the lower surface of the 400 micron thick SiO ₂ substrate by etching. This may be a grating or a Fresnel lens. In step S702, two sliders 8 and a rectangular parallelepiped shape 14 having a lattice pattern are formed on the upper surface of the substrate by etching. At this time, the height of the rectangular parallelepiped shape 14 is slightly lower than the height of the slider 8, and specifically, the etching is performed so as to be 40 nm lower by the sum of the thickness of the Au film 12 to be deposited in the next step and the thickness of the uneven structure. In step S703, the Au film 12 is formed on the upper surface of the rectangular parallelepiped shape 14 by vapor deposition. Finally, in step S704, the minute opening 13 is formed by FIB (Focused Ion Beam). The convex portion of the concavo-convex structure is substantially located in a plane defined by the bottom surface of the slider 8. Even if the convex part protrudes in the direction of the recording medium if it is small from this plane, there is no problem as long as the protruding amount is smaller than the flying height of the slider from the surface of the recording medium. In this manner, a near-field optical head could be easily manufactured only by a combination of ordinary process techniques.
[0020]
The near-field optical head having such a structure can also be manufactured by applying an optical disk manufacturing method in which a plastic is formed on a glass surface.
[0021]
The near-field optical head according to the present invention does not have a tapered shape as in a near-field optical probe manufactured from a conventional fiber or a head having a shape obtained by cutting the tip of a cone tip made of SiO ₂ . Therefore, incident light is irradiated to the near-field light generating microstructure 10 without loss. Dozens of percent of the incident light energy is converted into surface plasmon energy generated at the interface between SiO ₂ and Au. In addition, incident light is collected by the microlens 9, but its focal point does not necessarily coincide with the minute aperture 13. This is because the component of the incident light that is not directly irradiated onto the microscopic aperture 13 is irradiated onto the surface (upper surface) of the Au film, so that the light energy is once converted into plasmon energy, and the microscopic aperture is propagated after the plasmon propagates through the Au surface. This is because the light is scattered by 13 and becomes near-field light.
(Embodiment 2)
8A and 8B are a bottom view of the near-field optical head according to Embodiment 2 of the present invention and a sectional view taken along line BB ′ in the upper view. In the present invention, since the main point is to form a periodic concavo-convex structure made of metal around a microstructure that generates near-field light, there is no limitation on a method for guiding light to this microstructure. In the first embodiment, light from a laser is guided by an optical fiber, reflected by a mirror, and then condensed by a microlens. In the second embodiment, light is guided using a waveguide formed on the bottom surface of the head made of the Si substrate 15. In FIG. 8, the upper figure is the bottom surface of the near-field optical head. A waveguide 19 is formed in a portion sandwiched between two sliders 8, and an Au film is formed in a shape having a periodic concavo-convex structure at the tip thereof. 12 is coated, and a minute opening 13 is formed near the center. The figure below shows a cross section. The waveguide 19 is composed of a clad 16 and a core 17, and the light propagated in the core 17 is reflected by the mirror surface 18 and applied to the Au film 12.
[0022]
FIG. 9 shows a method for manufacturing a near-field optical head according to the present embodiment. The upper diagram is a bottom view of the head, and the lower diagram is a cross-sectional view taken along the line CC ′. In step S901, the slope 20 is formed by anisotropically etching the Si substrate. In step S902, a waveguide is formed, and the upper surface is polished and flattened. In step S903, the two sliders 8 and the periodic uneven shape 21 are formed by etching. In step S904, the Au film 12 is deposited. Finally, in step S905, the minute opening 13 is formed by FIB.
[0023]
In the near-field optical head manufactured in this way, incident light is guided inside the head by the waveguide 19 and is stably irradiated with high intensity onto the Au film 12 that generates surface plasmons. Compared to the first embodiment, the optical efficiency is higher because the distance from the waveguide to the minute aperture is shorter. Furthermore, since the optical waveguide structure is provided on the bottom surface side of the head, the entire head can be made thin. In this embodiment, a head having a thickness of about 200 microns can be realized. As in the case of the first embodiment, even if light is not accurately irradiated to the minute aperture, the light energy is converted into plasmon energy on the surface of the Au film, and then becomes near-field light from the minute aperture 13. Since it appears, a sufficiently high light efficiency was realized.
(Embodiment 3)
FIG. 10 shows the structure of a near-field optical head according to Embodiment 3 of the present invention. The upper figure shows the bottom, and the lower figure shows the cross section along line DD ′. Similar to the first and second embodiments, a waveguide 19 is formed in a portion sandwiched between the two sliders 8. The Au film 12 is coated on the periodic concavo-convex shape, and the minute opening 13 is formed. In the present embodiment, as a method of bending light propagating through the waveguide 19 in the direction of the minute opening 13, the grating structure 22 is formed at the interface with the cladding on the lower surface of the core of the waveguide 19. Such a structure can be produced by etching the SiO ₂ layer using a normal photolithography technique. The light bent by the grating 22 is applied to the Au film 12 and excites plasmons on the surface of the Au film 12. The surface plasmon propagates on the Au film 12 and is scattered by the minute opening 13 to appear as near-field light and appear outside the minute opening 13.
[0024]
The near-field optical head having such a structure has realized a dramatic improvement in light efficiency. Further, the size of the entire head could be reduced as in the second embodiment.
[0025]
In the embodiment introduced above, light is incident on an optical microscopic aperture having a size equal to or smaller than the wavelength of light as a means for generating near-field light. The near-field light can also be generated by this method, and in this case, the same effect can be obtained by forming a metal film having a periodic concavo-convex structure around the protrusion shape.
[0026]
【The invention's effect】
As described above, by forming a periodic concavo-convex structure made of a metal film that generates plasmons around a microstructure that generates near-field light in a near-field optical head, incident light energy is temporarily reduced to the surface plasmon of the metal. A near-field optical head with high light efficiency, which was impossible in the past, was realized by a mechanism that converts it into energy and generates near-field light from a microstructure. Moreover, high light efficiency was realized even if the incident light irradiation site did not match the microstructure. These structures could be easily manufactured by ordinary process technology, and a near-field optical head excellent in mass productivity and low cost could be realized. This head can be incorporated into an apparatus having substantially the same structure as an existing magnetic recording apparatus, and the manufacturing cost of the entire information recording apparatus can be kept low. Even when the microscopic aperture is further miniaturized in order to increase the information recording density, the head can be manufactured by the same manufacturing method, and since there is no taper structure like the conventional near-field optical head, the light efficiency is also reduced. Can be minimized.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a state in which a near-field optical head 2 according to Embodiment 1 of the present invention is mounted on an information recording apparatus.
FIG. 2 is a cross-sectional view of a near-field optical head 2 according to Embodiment 1 of the present invention.
FIG. 3 is a bottom view of the opening substrate 5;
4 is a cross-sectional view of the near-field light generating microstructure 10. FIG.
5 is an enlarged view of a portion indicated by a region A in FIG.
6 is a view of a region A in FIG. 4 as seen from the bottom surface side.
7 shows a manufacturing process of the near-field optical head according to Embodiment 1. FIG.
FIGS. 8A and 8B are a bottom view and a sectional view of a near-field optical head according to a second embodiment of the invention. FIGS.
9 shows a method for manufacturing a near-field optical head according to Embodiment 2. FIG.
FIG. 10 shows a structure of a near-field optical head according to a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Recording medium 2 Near-field optical head 3 Suspension arm 4 Mirror board | substrate 5 Aperture board 6 Mirror surface 7 Optical fiber 8 Slider 9 Micro lens 10 Near-field light generation microstructure 11 Incident light 12 Au film 13 Micro-aperture 14 Cuboid shape 15 Si substrate 16 Cladding 17 Core 18 Mirror surface 19 Waveguide 20 Slope 21 Periodic uneven shape 22 Grating structure 50 Near-field light S701 to S704 Manufacturing process steps S901 to S905 Manufacturing process steps

Claims (3)

A slider formed on the substrate;
An optical aperture formed on the substrate and having a size equal to or smaller than the incident light wavelength;
Levitated at a certain distance from the surface of the recording medium by the levitating force generated by the relative movement of the slider and the surface of the recording medium
In a near-field optical head for recording or reproducing information or both by interacting with the recording medium surface via near-field light generated from the optical aperture,
A concavo-convex structure made of metal periodically exists around the optical aperture on the substrate,
The convex portion of the concavo-convex structure, the near-field optical head characterized that you located substantially in the plane defined by the bottom surface of the slider.   The substrate includes a facing surface facing the recording medium, an optical waveguide formed along the facing surface, and a grating structure that guides incident light propagating through the optical waveguide toward the concavo-convex structure. The near-field optical head according to claim 1, comprising: a near-field optical head according to claim 1.   3. The near-field optical head according to claim 1, wherein the metal is made of gold.

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