JP2001256664A - Recording/reproducing head using plasmon and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform optical recording of super-high density. SOLUTION: Light is made incident on a flat substrate, into which a fine metal body is embedded, localized plasmon is excited to locally reinforce photoelectric field in the vicinity of the fine body, and information is recorded/ reproduced to/from a fine area exceeding the diffraction limit by using the light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical recording using plasmons.

[0002]

2. Description of the Related Art In optical recording, a method is used in which a laser beam is focused on a small spot on a medium by a lens, and the characteristics of a minute area of the medium are changed by heat or photoreaction generated thereby to perform recording. I have. When this method is used, the size of the spot diameter that can be focused is limited by the wavelength of the laser beam used for recording. Therefore, in order to write a smaller spot, a light source having a shorter wavelength had to be used.

Further, Applied Physics Letter 65 (1994), p. 388 (Appl. Phys. Lett.
Vol. 65, pp 388 (1994)) and JP-A-5-189796.
lens). When this lens is used, the numerical aperture of the lens can be increased in proportion to the square of the refractive index, so that light can be narrowed to a region smaller than a normal lens.

As another ultra-high density recording, there is a near-field optical recording method using a probe having a minute aperture. For example, Journal of Applied Physics 79 (19
1996) p.8082 (J. Appl. Phys. Vol. 79, p.
As described in p8082 (1996), there is a method in which the temperature of a very small region of a medium is increased by light near a minute opening to cause a phase change. When these methods are used, a region where light is localized is about the size of an aperture, regardless of the wavelength used, so that a minute spot exceeding the diffraction limit can be written or read.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to realize a minute light source exceeding the diffraction limit in order to achieve ultra-high density optical recording and reproduction.

By shortening the wavelength, the diameter of the condensed spot can be reduced. However, when the wavelength is shortened to the ultraviolet region, inexpensive optical systems such as inexpensive lenses that have been used absorb ultraviolet light. It cannot be used. In addition, the light source itself with such a short wavelength also has
Compact and stable things have not yet been realized.
Therefore, it can be said that increasing the density by optimizing the wavelength of the light source is not practical. The same applies to the solid immersion lens in that the wavelength is limited.

Further, in the case of recording using a probe having a small aperture, light throughput is poor due to the small aperture, a laser with a large power is required for writing, and it takes time to write and read. There was a problem.

[0008]

Even if ordinary laser light is condensed by a lens or the like, it can be narrowed down to only about half the wavelength of the laser used (diffraction limit). Therefore, the size of the recording spot also remains at that level. There is also a recording method using near-field light leaking from a minute aperture in order to concentrate the light intensity in a narrower area, but there is a problem with the weak power of the available light.

It is known that irradiating metal fine particles with light excites plasmons. If a plasmon generated near a metal body smaller than half the wavelength is used, the electric field intensity near the metal body is enhanced by the excitation of the plasmon, so that a strong electric field exceeding the diffraction limit can be concentrated. If this electric field is used for writing, a smaller spot than before can be written, and high-density recording becomes possible.

Here, the electric field intensity in which the shape of the fine metal particles is excited in an ellipsoidal sphere than in a true sphere is further enhanced (Surface Science 156 (1985) No. 67).
8 pages (Surface Science, Vol.156, pp678 (198
Five))). In the case of an elongated shape such as an ellipsoidal sphere, plasmons can be efficiently excited by irradiating light polarized in the longitudinal direction, and the enhanced electric field intensity becomes several tens times.

In the case of a true sphere, when p-polarized light is incident,
It has been reported that the degree of enhancement is further enhanced (Optical Review 6 (1999), p. 211 (Op.
tical Review, Vol. 6, 211 (1999)).

As described above, when an electric field due to plasmons excited near a metal body is used for writing an optical record, the spatial spread is about the size of the metal body, and the electric field strength increases by jumping only in the vicinity of the metal body. . When light is condensed on a metal body by a lens, the light is also irradiated to other parts of the recording medium, but the threshold of the electric field intensity at which recording occurs,
What is necessary is just to be between the plasmon electric field intensity and the electric field intensity by the light condensed by the lens. For example, if it is a phase change disk,
A phase change occurs with the electric field strength enhanced by the plasmon,
The relationship between the material of the recording medium and the intensity of the incident light may be adjusted so that the light collected by the lens does not change.

When a solid immersion lens is used as a focusing lens, the focusing can be performed efficiently. This lens has a shape in which a part of a spherical lens is cut out, and light is condensed on an end face thereof. Since the numerical aperture is very high, the light collection efficiency is higher than that of a normal lens.

Further, when this lens is combined with an elongated metal minute body such as an ellipsoidal sphere or a cylinder, the longitudinal direction of the minute body is perpendicular to the flat surface of the head, that is, the flat surface of the solid immersion lens. The arrangement can be expected to further increase the electric field strength. Because, with a normal lens, the wave vector of the light condensed by the lens is oblique to the end face, and the electric field strength oscillating in the direction that can excite plasmons (the direction perpendicular to the flat surface) is originally And the cosine of the incident angle multiplied by the electric field strength of the light source, and the incident light intensity cannot be fully utilized. When light is narrowed down by the solid immersion lens, the condensed light enters the end face at a higher angle. This means that the cosine of the incident angle increases, so that the light intensity that can contribute to excitation increases. In addition, light incident at an angle larger than the critical angle for total reflection becomes an evanescent wave and has a wave vector parallel to the end face. Can be.

[0015] Further, if the flat substrate is formed into a shape in which metal micro-objects are embedded, it can be mounted on a slider when an optical head is formed. Recording and reproduction can be performed on a rotating disk at high speed without any obstacle and without collision.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing a configuration of a basic portion of the optical head of the embodiment. Helium-cadmium laser 5
A light 101 having a wavelength of 33 nm is narrowed down through a lens 102 and focused on a minute metal body 104 formed on a substrate 103 made of a material transparent to the light from the back side. The laser beam 101 is vertically incident on the flat surface of the substrate 103,
02 is located just above the substrate to provide a compact structure. The metal body 104 moves on a recording medium (not shown here) so that it does not hinder the substrate 103.
It is created to be embedded in.

Although a method of forming the substrate 103 will be described in detail later, here, a cylindrical hole having a diameter of 50 nm and a depth of about 100 nm was formed, and gold was embedded as a minute metal body 104 therein. The lens 102 has a structure capable of finely moving up, down, left, and right with respect to the substrate 103, and the position of the lens 102 is adjusted and fixed so that the minute metal body 104 is located exactly at the center of the focal point. When used as a head, they may be integrated into a structure, and an automatic focusing mechanism may be added.

When a laser beam 101 is incident on this head, localized plasmons are excited in the metal body 104, and the electric field intensity near the metal body 104 is increased. In this case, since the minute metal body 104 is cylindrical and its bottom surface is on the flat surface of the head facing the medium, the spread of the enhanced electric field is about the diameter of the circle on the bottom surface, that is, about 50 nm.
When this head is mounted on a recording / reproducing apparatus having a function of controlling the distance to a recording medium, and is brought close to the recording medium by a certain distance, information can be recorded with a spot diameter that is about equal to the spread of light.

Here, in the above embodiment, the minute metal body 104
Is a cylindrical shape, but may be an elliptic cylinder, a spheroid, a cone, a prism, a pyramid, or the like as long as the shape is asymmetric. What is necessary is just to arrange | position so that a longitudinal direction may become perpendicular to a head flat surface.

As a recording medium at this time, the same material as that used so far can be used in the same manner, but the threshold value to be recorded is increased in the vicinity of the minute metal body 104. It is necessary to be smaller than the intensity and larger than the light intensity of the portion focused by the other lenses. Therefore, it is necessary to adjust the sensitivity of the medium and the incident light intensity in advance. Also, since the light intensity is higher near the head,
It is considered that the recording becomes more efficient if there is no protective layer on the medium.

For reproduction, the reflected or transmitted signal is detected using light whose incident light intensity is weaker than during recording. The detection threshold is set between the signal intensity from the electric field enhanced by the plasmon and the signal intensity from the part focused by the other lens, and the signal other than the signal from the light enhanced by the plasmon is set. Do not take off. This makes it possible to reproduce information written in a minute area below the diffraction limit.

FIG. 2 is a diagram showing a main part of a head using a solid immersion lens as a lens. A laser beam 101 is narrowed down through a solid immersion lens 105 and irradiated on a minute metal body 104 in a substrate 103 similar to that shown in FIG. The minute metal body 104 may be formed directly on the end face of the solid immersion lens 105. However, it is difficult to manufacture the metal body at a position where light is condensed. Then, a thin layer of UV-curable optical adhesive was sandwiched between them. While measuring the light intensity, the substrate and the lens were arranged at the position where the intensity became the strongest, and the entire surface was irradiated with ultraviolet light and cured to integrate the lens 105 and the substrate 103, thereby forming a basic part of the head. In the figure, parallel light is illustrated as being incident, but light that has been previously focused by a lens may be incident.

FIG. 3 is a graph showing the light intensity near the optical head shown in FIG. A flat surface with respect to the medium under the head was scanned by a near-field optical microscope so as to pass over the metal micro-object, and the generated light was picked up by a probe and its intensity was measured. A place where the light intensity was amplified and which had a width approximately equal to the size of the formed metal microparticles was observed.

FIG. 4 is a diagram showing a main part of another head using a solid immersion lens. In this embodiment, the laser light 10
A light-shielding portion 106 is provided at a central portion of the solid immersion lens 105 to which 1 is irradiated. Here, metal chromium was deposited. The light blocking mechanism may be configured to irradiate the lens with ring-shaped light by inserting something like a pupil filter into the optical path of the incident laser without directly providing the lens with a light.

The range of light shielding is determined so that the angle θ at which the light blocked by the light enters the substrate is smaller than the critical angle for total reflection. With such a structure, the light irradiated to the minute metal body mainly has an incident angle larger than the critical angle for total reflection. Such light causes total reflection at the lower part of the head, and generates an evanescent wave near the interface.

Since the evanescent wave near the interface has a wave vector in a direction parallel to the interface, its polarization plane is perpendicular to the interface. Therefore, it is possible to efficiently excite localized plasmons of a minute metal body elongated in a direction perpendicular to the interface.

By blocking light that does not cause total reflection,
Although the intensity of the entire incident light decreases, the excitation efficiency of the plasmon increases, so that the contrast between the electric field intensity enhanced by the plasmon and the electric field intensity of the other portion focused by the lens can be increased. Therefore, it is possible to suppress occurrence of an error such that a spot having a large diameter is erroneously recorded in a portion focused by a lens other than the electric field enhanced by plasmon excitation. Further, there is an advantage that the range which can be taken as a threshold value of the light intensity required for recording is widened, and the design becomes easy.

FIG. 5 shows still another embodiment. Laser light is incident on the substrate 103 provided with the minute metal body 104 formed in the above-described embodiment through the prism 107 so as to be totally reflected at the lower part of the substrate. At this time, the polarization direction of the incident laser light was p-polarization, that is, the direction in which the polarization direction was included in the incident plane. Also in this case, the plasmon can be efficiently excited because it is excited by an evanescent wave generated by total reflection. In the figure, parallel light is illustrated as being incident, but light focused by a lens may be incident.

Hereinafter, a method of manufacturing a substrate having a structure like an optical head in which the fine metal body shown in FIGS. 1, 2, and 4 is embedded will be described. A flat dielectric substrate that is transparent at the wavelength to be used is processed with a focused ion beam and has a diameter of about 50 nm.
Drill a hole with a depth of about 100 nm. Metal is deposited here,
After that, the surface is polished so that the whole is at the same height.
As a result, a structure in which a part of the minute region on the surface of the dielectric is replaced with metal can be obtained.

The method of making the holes is not limited to a focused ion beam, but may be lithography or a stamp method for transferring a microstructure onto a substrate. The type of metal depends on the wavelength to be used and the optical characteristics of the substrate to be embedded. However, it is preferable to use gold in terms of stability and plasmon excitation efficiency.

When a high refractive index glass is used for the substrate, 50
Because localized plasmons can be excited at wavelengths around 0 nm, the second harmonic of helium neon laser or neodymium yag laser,
Green light such as a semiconductor laser can be used. In the case of localized plasmons, the conditions for excitation are relatively mild as compared with surface plasmons, and thus there are no strict restrictions on the incident angle, wavelength, and the like.

[0032]

According to the present invention, in optical recording, a spot smaller than the spot diameter, which is limited to about half a wavelength at the diffraction limit, can be written on an optical recording medium.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a basic configuration of another embodiment of the present invention.

FIG. 3 is a graph showing a spatial distribution of light intensity emitted from the head shown in FIG.

FIG. 4 is a longitudinal sectional view showing a basic configuration of another embodiment of the present invention.

FIG. 5 is a longitudinal sectional view showing a basic configuration of another embodiment of the present invention.

[Explanation of symbols]

101 laser light, 102 lens, 103 substrate, 1
04 ... minute metal body, 105 ... solid immersion lens, 106 ...
Light shielding part, 107 ... prism.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G11B 7/22 G11B 7/22 G12B 21/06 G12B 1/00 601C F-term (Reference) 2H087 KA13 LA01 NA00 RA00 5D119 AA11 AA22 AA43 BA01 CA06 DA01 DA05 EC27 JA44 JA70 9A001 KK16

Claims (7)

[Claims] A recording / reproducing head for recording / reproducing information on / from a medium by light has a portion which is transparent to light used for recording / reproduction and has a flat surface with respect to the medium, and the flat surface has a wavelength equal to or less than the wavelength of light used for recording / reproduction. A recording / reproducing head, wherein a recording / reproducing head is embedded with a small metal body having a size of, and performs recording or reproduction using an electromagnetic field enhanced by plasmons generated near the small metal body. 2. The recording / reproducing head according to claim 1, wherein the shape of the minute metal body is longer in one direction than in the other direction, and the direction is perpendicular to the flat surface of the head. Recording / playback head. 3. A recording / reproducing head according to claim 1, further comprising a lens at an upper portion of the head for condensing light perpendicularly incident on a flat surface of the head onto a minute metal body. Playhead. 4. The recording / reproducing head according to claim 3, wherein the lens that focuses on the minute metal body is a solid immersion lens. 5. A recording / reproducing head according to claim 4, wherein light having an incident angle on the surface in which the minute metal body is embedded is smaller than the critical angle for total reflection, that is, light incident on the central portion of the lens is partially shielded. A recording / reproducing head characterized by having a structure to perform. 6. The recording / reproducing head according to claim 1, wherein the polarization direction of the incident light is a direction included in the incident surface. 7. A method for manufacturing a recording / reproducing head according to claim 1, wherein a fine hole is dug in the substrate by using a focused ion beam or lithography technique, and a metal is deposited to fill the hole. A method for manufacturing a recording / reproducing head, characterized in that the entire surface is polished and made flat.