JP4837521B2 - Surface plasmon polariton concentrator, information recording head, and recording apparatus - Google Patents

Description

  The present invention relates to a surface plasmon polariton concentrator that focuses surface plasmon polariton, which is a kind of near-field light, and an information recording head and a recording apparatus using the surface plasmon polariton concentrator.

  By reducing the diameter of the focal point where light is collected, the so-called light spot, various densities can be achieved in various fields. For example, in the optical recording field in which data is recorded / reproduced on / from a recording medium using laser light, high-density recording / reproduction is possible. Further, in the field of optical processing in which processing of resin, glass or the like is performed using laser light, finer processing can be performed. Furthermore, in the measurement field using a microscope or the like, the measurement resolution can be improved.

  Therefore, in each field using light such as optical recording, optical processing, and measurement using a microscope, it has been desired to reduce the diameter of the light spot. However, the size of the light spot is limited to the light wavelength by the diffraction limit of light in ordinary light, and it is difficult to further reduce the diameter. Therefore, the use of locally existing near-field light has attracted attention as a method for forming a light spot smaller than the diffraction limit of light using ordinary light.

  Near-field light is light (electromagnetic field) that is generated when light is incident on a minute structure smaller than the wavelength of light, for example, a structure such as an opening, and is localized only in the vicinity of the opening. is there. Near-field light generated in the vicinity of the opening remains in the vicinity of the opening and does not propagate to other parts.

  When light is incident on the opening from the light source, when the diameter of the opening is larger than the wavelength of the light, the light is partially blocked by the opening, but without generating near-field light, As it is, the light passes through the opening as propagating light. However, when the diameter of the opening is smaller than the wavelength of the incident light, the light hardly transmits through the opening, and near-field light is generated in the vicinity of the opening. Since the generated near-field light has an intensity distribution having a size substantially the same as the diameter of the opening, a light spot having a diameter smaller than the diffraction limit of the light is obtained around the opening.

  The diameter-reduced light spot obtained in this manner is suitably used for the light-assisted magnetic recording method. The optically assisted magnetic recording method is attracting attention as a promising technology for next-generation high-density magnetic recording in the optical recording field, and performs magnetic recording on a magnetic recording medium having a high coercive force that is resistant to thermal fluctuations. is there. Specifically, the coercive force of the magnetic recording medium is reduced by condensing light on the surface of the magnetic recording medium and locally raising the temperature of the magnetic recording medium. This makes it possible to perform magnetic recording on the magnetic recording medium using a normal magnetic head.

  However, since the light spot having a reduced diameter obtained by the above-described method causes light that cannot be focused to a spot having a diameter equal to or smaller than the wavelength to be incident on an opening having a wavelength equal to or smaller than the wavelength, the light use efficiency is deteriorated. That is, if the light source is set to the same intensity as the conventional one, the obtained near-field light intensity becomes weaker by the size of the opening with respect to the size of the light irradiated to the opening. Further, since the light is localized, the intensity rapidly decreases as the distance from the light generation position increases.

  For this reason, a method is used in which openings are formed in a metal film, surface plasmon polaritons are generated in the metal film, and strong near-field light is generated by amplifying the surface plasmon polaritons. However, it is very difficult to create a minute opening with a size of about several tens of nanometers in a metal film, and surface plasmon polaritons generated on the metal film propagate from the opening to the periphery of the opening. End up. As a result, the available spot size is larger than the size of the opening formed in the metal film.

  Therefore, Patent Document 1, Patent Document 2, and Non-Patent Document 1 describe techniques for focusing the generated surface plasmon polaritons more locally to obtain higher density energy. The technique described in Patent Document 1 will be described below with reference to FIG. FIG. 24 is a perspective view showing a conventional concentrator 101 that focuses surface plasmon polaritons.

  As shown in FIG. 24, the concentrator 101 described in Patent Document 1 includes a plurality of lens microstructures 103 arranged in a circular arc according to a predetermined rule on a metal film 102. The surface plasmon polariton 4 is collected by the structure 103. When the surface plasmon polariton 4 is propagated from the direction opposite to the center of the circular arc formed by the lens microstructure 103, the surface plasmon polariton 4 is diffracted by the lens microstructure 103 and condensed at the center of the circle. To do. Thus, the concentrator 101 can focus the surface plasmon polariton 4 with a high NA.

  Further, the technique described in Patent Document 2 will be described with reference to FIGS. 25 and 26. FIG. FIG. 25 is a perspective view showing a schematic configuration of a conventional metal film 201 having two kinds of film thickness for propagating and bending a surface plasmon polariton wave. FIG. 26 is a perspective view showing a surface plasmon lens 211 for condensing the surface plasmon polariton.

  The metal film 201 includes a first metal film 202 and a second metal film 203 having different film thicknesses. By using the fact that the effective refractive index of the surface plasmon polariton is different when the film thickness is different, the first metal film 201 is used. In this configuration, the surface plasmon polariton 4 excited in the film 202 is bent at the boundary formed between the first metal film 202 and the second metal film 203.

  Here, the effective refractive index n of the metal film is

It is represented by Β represents the wave vector in the traveling direction of the surface plasmon polariton, c represents the speed of light, and ω represents the angular frequency of the surface plasmon polariton.

  The surface plasmon polariton is attenuated in strength as it travels on the metal film, and the distance at which the intensity of the surface plasmon polariton becomes 1 / e is called the propagation length. The propagation length L, which is a parameter representing the intensity attenuation of such surface plasmon polaritons, is

It is represented by

  Β, which is the wave vector in the traveling direction of the surface plasmon polariton, depends on the frequency of the surface plasmon polariton, the mode of the surface plasmon polariton, the metal material composing the metal film, the film thickness of the metal film, and the material in contact with the metal film Yes.

  The surface plasmon polariton mode will be described below. Surface plasmon polaritons propagating on a metal film generally have two modes. One mode is a symmetry mode in which the surface plasmon polaritons on both surfaces of the metal film are coupled symmetrically, and can be excited in the Kretchmann configuration described later. The other mode is an asymmetric mode in which surface plasmon polaritons on both surfaces of the metal film are asymmetrically coupled, and can be excited in the Otto configuration described later.

  Therefore, β, which is the wave vector in the traveling direction of the surface plasmon polariton, has two values corresponding to the two modes of the surface plasmon polariton in each configuration. These details are introduced in detail in Non-Patent Document 1.

  In the surface plasmon lens 211, as shown in FIG. 26, a metal film 215 is provided on the upper surface of the dielectric layer 216, and the surface of the metal film 215 opposite to the surface in contact with the dielectric layer 216 is provided. In addition, a first dielectric layer 213 having a low refractive index and a second dielectric layer 214 having a higher refractive index than the first dielectric layer 213 are provided. The first dielectric layer 213 is not shown in FIG. 26 because it may be air.

In the surface plasmon lens 211, when the laser beam 212 is irradiated between the metal film 215 on the side where the first dielectric layer 213 is provided and the dielectric layer 216, the metal film 215 and the first dielectric layer are irradiated. Surface plasmon polariton 204 is excited between 213 and 213. Since the effective refractive index in the metal film 215 varies depending on the medium with which the metal film 215 is in contact, the surface plasmon polariton 204 propagates in the direction of the second dielectric layer 214, and the first dielectric layer 213 and the second dielectric layer 214 Refracts and converges at the boundary formed between the two.
Japanese Patent Laying-Open No. 2006-23410 (released on January 26, 2006) US2003 / 0137772 (published January 24, 2003) “Nanodot coupler with a surface plasmon polariton condenser for optical far / near-field conversion”, Wataru Nomura, Motoichi Ohtsu, Takashi Yatsui, Applied Physics Letters, 86, 181108 (2005) ”Surface-polariton-like waves guided by thin, lossy metal film” JJ Burke and GIStegeman, Physical Review B, 33, 5186, (1986)

  Among the above-described technologies, in the technology described in Patent Document 1, the concentrator 101 must form a plurality of lens microstructures 103 on the metal film 102 at submicron intervals. It is very difficult. Furthermore, if the number of lens microstructures 103 is small, the focusing effect of the surface plasmon polariton becomes small. Therefore, in order to increase the focusing effect, it must be manufactured more precisely.

  Moreover, in the metal film 201 described in Patent Document 2, the propagation direction of the surface plasmon polariton 4 is changed at the boundary formed between the first metal film 202 and the second metal film 203 having different film thicknesses. It is possible to propagate the surface plasmon polariton to an arbitrary position with a simple configuration. Therefore, by applying the configuration of the metal film 201 to the metal film 215 of the surface plasmon lens 211, it is possible to focus the surface plasmon polariton 4 at an arbitrary position with a simple configuration.

  In order to sufficiently focus the surface plasmon polariton 4 at the boundary formed between the first metal film 202 and the second metal film 203, the effective refractive index ratio between the first metal film 202 and the second metal film 203 is sufficient. Need to be considered. However, in order to realize the effective refractive index ratio between the first metal film 202 and the second metal film 203 for causing sufficient focusing of the surface plasmon polariton 4, the first metal film 202 and the second metal film 203 are The difference in film thickness becomes very large.

  Therefore, when the surface plasmon polariton 4 propagates on the surfaces of the first metal film 202 and the second metal film 203, the surface plasmon polariton 4 is scattered at the edge of the first metal film 202, and the background due to the scattered light. Noise is generated. Further, when there is such a step, for example, when the metal film 201 is applied to an optically assisted magnetic recording apparatus, it is difficult to cause physical interference with other members or to form a film on the metal film 201. There was a problem.

  In the surface plasmon lens 211 described in Patent Document 2, the surface is formed at the boundary formed between the first dielectric layer 213 and the second dielectric layer 214 having different refractive indexes provided on the metal film 215. The propagation direction of the plasmon polariton 4 can be changed, and the surface plasmon polariton can be propagated to an arbitrary position with a simple configuration.

  However, the effective refractive index in the surface plasmon lens 211 depends not only on the refractive indexes of the first dielectric layer 213 and the second dielectric layer 214 but also on the thickness of the metal film 215. In the surface plasmon lens 211, since the surface plasmon polariton 4 is excited in an Otto arrangement described later, the surface plasmon polariton 4 is in an asymmetry mode.

  Therefore, as described in Non-Patent Document 1, the thinner the metal film 215 is, the larger the effective refractive index and the shorter the propagation length. As a result, when the thickness of the metal film 215 is reduced in order to sufficiently refract the surface plasmon polariton 4 at the boundary formed between the first dielectric layer 213 and the second dielectric layer 214, the surface plasmon lens The propagation length in 211 is about several times the wavelength of the surface plasmon polariton 4 or less than the wavelength.

  However, in the surface plasmon lens 211, when the effective refractive index is increased by the refractive index of the dielectric, the propagation length is shortened, the focusing effect is reduced, and a lens having a particularly long focal length cannot be produced. In particular, the refractive index introduced in Patent Document 2 is of the asymmetry mode, and as described in Non-Patent Document 2, the effective refractive index increases as the film thickness decreases. However, according to Non-Patent Document 2, the propagation length is also shortened at this time, which is about several times the wavelength of the surface plasmon polariton. This means that the intensity will be weak unless the focal length is set to the surface plasmon polariton wavelength, but it is not practical to set the focal length to the wavelength.

  As described above, in the surface plasmon lens 211, in order to sufficiently refract the surface plasmon polariton 4 at the boundary formed between the first dielectric layer 213 and the second dielectric layer 214, the propagation length is short. There was a problem of becoming.

  Further, if one of the first dielectric layer 213 and the second dielectric layer 214 is air having a low dielectric constant in order to increase the refraction angle, the first dielectric layer 213 or the second dielectric layer 214 Since an edge appears, when the surface plasmon polariton 4 propagates on the surface of the metal film 215, the surface plasmon polariton 4 is scattered at the edge, and background noise due to scattered light is generated.

  Further, when there is such a step, for example, when the surface plasmon lens 211 is applied to an optically assisted magnetic recording apparatus, it is difficult to cause physical interference with other members or to form a film on the metal film 215. There was a problem. In addition, when near-field light is used from a direction perpendicular to the surface of the metal film 215 on which the first dielectric layer 213 and the second dielectric layer 214 are provided, the thickness of the second dielectric layer 214 is increased. There was a problem that only near-field light of weak intensity could be obtained.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a surface plasmon polariton concentrator that suppresses scattering of surface plasmon polariton at an edge with a simple configuration.

  In order to solve the above problems, a surface plasmon polariton concentrator of the present invention is a surface plasmon polariton concentrator that focuses surface plasmon polaritons, and includes a metal film support member and a predetermined surface of the metal film support member. At least two metal films formed adjacent to each other and having an effective refractive index different from that of the adjacent metal films, and each metal film has at least a part of a boundary line between the adjacent metal films The surface that is curved and is opposite to the surface that is in contact with the metal film support member is flush with the surface of the adjacent metal film that is opposite to the surface that is in contact with the metal film support member. It is characterized by being.

  With the above configuration, each metal film formed on a predetermined surface of the metal film supporting member and having an effective refractive index different from each other adjacent to each other is a boundary line formed between the metal films. Since at least a part of the curve is a curve, the propagation direction of the surface plasmon polariton can be changed at the boundary line, and the surface plasmon polariton can be focused. At this time, the surface of the metal film opposite to the surface in contact with the metal film support member and the surface of the adjacent metal film opposite to the surface in contact with the metal film support member should be flush with each other. Thus, when the surface plasmon polariton propagates to the adjacent metal films, it is possible to suppress scattering at the edges between the adjacent metal films.

  Thus, in the surface plasmon polariton concentrator of the present invention, for example, the effective refractive index of adjacent metal films can be varied by varying the metal material, film thickness, and the like. For this reason, the surface plasmon polariton concentrator of the present invention varies the effective refractive index of the metal film 215 depending on the film thickness of the metal film 215 and the refractive indexes of the first dielectric layer 213 and the second dielectric layer 214. As compared with the configuration of the surface plasmon lens 211, the degree of freedom in design is increased, and the propagation direction of the surface plasmon polariton can be easily controlled. Furthermore, since there is no need to provide a dielectric on the metal film, the surface plasmon polariton on the surface of the metal film can be used directly, and the strength is not attenuated by the dielectric. As a result, the surface plasmon polariton concentrator of the present invention can obtain a strong near-field light.

  Further, when the concentrator 101 described in Patent Document 2 is used as a recording / reproducing element for optical recording, for example, when the lens microstructure 103 faces the recording medium, When the recording medium collides with the recording medium, the shape of the lens microstructure 103 changes, and the concentrator 101 changes with time in intensity of the focused surface plasmon polariton. However, the surface plasmon polariton concentrator of the present invention is applied to a recording / reproducing element for optical recording because the surface plasmon polariton of the adjacent metal film propagates on the same surface. Even if the propagation surface and the recording medium come into contact with each other, a change with time is unlikely to occur.

  As a result, the surface plasmon polariton concentrator of the present invention increases the intensity of the focused surface plasmon polariton and can suppress the generation of background noise due to scattered light. In addition, when any film is formed on the surface plasmon polariton concentrator, there is no need to worry about the film thickness difference.

  In the surface plasmon polariton concentrator according to the present invention, the metal films may have the same film thickness.

  Each metal film can be made to have the same film thickness because the effective refractive index can be made different by using different materials. With the above configuration, in the surface plasmon polariton concentrator of the present invention, since no edge appears between the metal films, the surface plasmon polariton scattering at the edge can be suppressed, and the surface propagates to the adjacent metal film The intensity of the plasmon polariton is increased and the influence of background noise due to scattered light can be suppressed.

  In the surface plasmon polariton concentrator according to the present invention, the curved portion of the boundary line is formed between the first metal film and the second metal film of each of the metal films, and the effective of the first metal film. When the relationship between the refractive index na and the effective refractive index nb of the second metal film is na <nb, the curve portion of the boundary line has a convex shape with respect to the first metal film. It may be formed as follows.

  With the above configuration, when surface plasmon polariton is propagated from the first metal film to the second metal film having an effective refractive index larger than that of the first metal film, or when propagated from the second metal film to the first metal film The surface plasmon polariton can be efficiently focused with a simple configuration by adjusting the convex shape of the curved portion of the boundary line formed between the first metal film and the second metal film. . Further, by adjusting the convex shape of the curved portion of the boundary line, it is possible to change the focusing position, focusing size, etc. of the surface plasmon polariton.

  Therefore, for example, the surface plasmon polariton concentrator of the present invention can be suitably used for various applications by appropriately adjusting according to the use as in the case of applying the surface plasmon polariton concentrator to a recording apparatus.

  In the surface plasmon polariton concentrator of the present invention, when the surface plasmon polariton propagates from the first metal film to the second metal film, the curved portion of the boundary line may be an elliptical arc.

  With the above configuration, when the surface plasmon polariton propagates from the first metal film to the second metal film having an effective refractive index larger than that of the first metal film, the surface plasmon polariton is interposed between the first metal film and the second metal film. By making the curved portion of the formed boundary line into an elliptical arc, it becomes possible to efficiently focus the surface plasmon polaritons in the second metal film, and the focusing size of the surface plasmon polaritons in the second metal film is made very small. be able to. In addition, since the focusing size of the surface plasmon polariton is reduced, the intensity of the focused electric field is increased, so that near-field light having a high intensity can be obtained.

  Therefore, for example, when the surface plasmon polariton concentrator having the above-described configuration is applied to a recording apparatus, it is possible to record a minute mark on a recording medium because the converging size is very small.

  In the surface plasmon polariton concentrator of the present invention, the propagation direction of the surface plasmon polariton may be parallel to a line connecting two focal points of the elliptic arc.

  With the above configuration, the surface plasmon polariton can be efficiently refracted at the boundary line of the elliptic arc formed between the first metal film and the second metal film, and can be focused at the focal point of the elliptic arc.

  In the surface plasmon polariton concentrator according to the present invention, when the surface plasmon polariton propagates from the second metal film to the first metal film, the curved portion of the boundary line may be a hyperbola.

  When the surface plasmon polariton propagates from the second metal film to the first metal film having an effective refractive index smaller than that of the second metal film, the boundary line formed between the first metal film and the second metal film When the curved portion is an elliptical arc, the surface plasmon polariton diffuses in the first metal film. Therefore, by making the curved portion of the boundary line formed between the first metal film and the second metal film a hyperbola, it becomes possible to focus surface plasmon polaritons in the first metal film, and the first metal film The focusing size of the surface plasmon polariton at can be made very small. In addition, since the focusing size of the surface plasmon polariton is reduced, the intensity of the focused electric field is increased, so that near-field light having a high intensity can be obtained.

  Therefore, for example, when the surface plasmon polariton concentrator having the above-described configuration is applied to a recording apparatus, it is possible to record a minute mark on a recording medium because the converging size is very small.

  In the surface plasmon polariton concentrator of the present invention, the propagation direction of the surface plasmon polariton may be parallel to a line connecting the two focal points of the hyperbola.

  With the above configuration, the surface plasmon polariton can be efficiently refracted at the boundary line of the hyperbola formed between the first metal film and the second metal film, and can be focused at the focal point of the hyperbola.

  In the surface plasmon polariton concentrator of the present invention, at least two boundary lines may be formed so as to block the propagation direction of the surface plasmon polariton.

  When there is only one boundary line between adjacent metal films through which the surface plasmon polaritons pass, the surface plasmon polariton is converged by only one change in the propagation direction of the surface plasmon polariton because the change in the propagation direction of the surface plasmon polariton occurs only once. It is necessary to design the propagation direction of the surface plasmon polariton and each metal film as possible. For example, in the concentrator 101 described in Patent Document 2, the position where the surface plasmon polaritons are focused is the center of a circle formed by the lens microstructure 103. The radius of the circle formed by the fine structure 103 becomes large, and the entire concentrator 101 becomes large.

  Therefore, according to the above configuration of the present invention, the boundary line can be formed without changing the size of the surface plasmon polariton concentrator by forming at least two boundary lines between adjacent metal films in the propagation direction of the surface plasmon polariton. The surface plasmon polariton can be focused more steeply than in the case of one. Further, by changing the distance between at least two boundary lines in the propagation direction of the surface plasmon polariton, it is possible to change the distance until the surface plasmon polariton is focused or the focusing size.

  In the surface plasmon polariton concentrator of the present invention, the distance from the surface plasmon polariton propagation start position or the excitation position to the position where the surface plasmon polariton converges may be shorter than the propagation length of the surface plasmon polariton.

  With the above configuration, the intensity of the surface plasmon polariton is attenuated when the surface plasmon polariton propagates from the position where the surface plasmon polariton is propagated or the position where the surface plasmon polariton converges from the excitation position in the surface plasmon polariton concentrator of the present invention. This makes it possible to obtain near-field light having a high intensity.

  Further, the surface plasmon polariton concentrator of the present invention may be a combination of two or more of the above-described surface plasmon polariton concentrators, and each surface plasmon polariton concentrator may focus the surface plasmon polariton at one point.

  With the above configuration, the surface plasmon polariton can be focused at one point using a plurality of surface plasmon polariton concentrators, so that near-field light with high intensity can be obtained. Further, the distance until the surface plasmon polariton converges and the converging size can be changed depending on the combination of the metal materials and the shape of the boundary line.

  In the surface plasmon polariton concentrator according to the present invention, it is preferable that an incident beam diameter of the surface plasmon polariton with respect to the curved portion of the boundary line is shorter than a length of the curved portion of the boundary line.

  When the length of the curved portion of the boundary line formed between adjacent metal films is shorter than the incident beam diameter of the surface plasmon polariton, a part of the surface plasmon polariton propagating through the metal film is a curved portion of the boundary line. Since the propagation direction of the surface plasmon polariton is not changed, the intensity of the focused near-field light is reduced. Therefore, with the above-described configuration of the present invention, the surface plasmon polariton propagating on the metal film can pass through the curved portion of the boundary line formed between the adjacent metal films. Light can be obtained.

  An information recording head of the present invention is an information recording head provided in a recording apparatus for recording on a recording medium, the surface plasmon polariton concentrator described above, a light source, and light emitted from the light source. A near-field light excitation means for converting the surface plasmon polariton to a recording medium; and a near-field light output means for irradiating the recording medium with the near-field light, wherein the surface plasmon polariton concentrator is configured to convert the surface plasmon polariton from the near-field light excitation means. The light is focused on the near-field light output means.

  With the above configuration, the surface plasmon polariton converted from the light of the light source in the near-field light excitation unit can be propagated and focused on the near-field light output means for irradiating the recording medium with the near-field light. As described above, the surface plasmon polariton is focused on the near-field light output means by using the surface plasmon polariton concentrator, so that the near-field light output means has a very small size and strong near-field light. Can be irradiated. As a result, the information recording head of the present invention can record very small marks on the recording medium, and the recording density on the recording medium increases. In addition, the information recording head of the present invention has a very strong near-field light emitted from the near-field light output means, so it is possible to increase the transfer rate with respect to the recording medium and have a sufficient distance from the recording medium. Can be made. Therefore, the position where the light source and the near-field light output means are arranged can be set relatively freely.

  In the information recording head of the present invention, the near-field light output means may be provided on a metal film on which the surface plasmon polaritons are focused, among the metal films of the surface plasmon polariton concentrator.

  With the above configuration, the information recording head of the present invention does not need to propagate the surface plasmon polariton focused by the surface plasmon polariton concentrator to other members or the like. The recording medium can be irradiated. As a result, the information recording head of the present invention can increase the transfer rate with respect to the recording medium, and can provide a sufficient distance from the recording medium.

  In the information recording head of the present invention, the near-field light output means may be provided at a position where the surface plasmon polariton of the metal film where the surface plasmon polariton is focused.

  With the above configuration, the surface plasmon polariton focused at the surface plasmon polariton concentrator is extracted as near-field light by the near-field light output means at the focus position, and the near-field light output means is located at a position different from the focus position. Compared with the case where it is provided, it is not necessary to propagate the focused surface plasmon polariton on the metal film, and the surface plasmon polariton is not attenuated, and it is possible to extract near-field light having a high intensity. As a result, the information recording head of the present invention can increase the transfer rate with respect to the recording medium, and can provide a sufficient distance from the recording medium.

  In the information recording head of the present invention, the near-field light output means may be a metal end of the metal film or an opening, slit, or metal protrusion provided in the metal film.

  With the above configuration, it is possible to provide an appropriate near-field light output unit according to the use of the information recording head of the present invention.

  In the information recording head of the present invention, among the metal films, the metal film on which the surface plasmon polariton is focused may have a long propagation length of the surface plasmon polariton.

  In order to extract strong near-field light from the surface plasmon polariton concentrator of the present invention, it is preferable that a near-field light output means is provided at the focusing position of the surface plasmon polariton as described above. However, if the propagation length of the surface plasmon polariton in the metal film where the surface plasmon polariton is focused is short, the surface plasmon polariton is attenuated until the near-field light output means. Therefore, with the above-described configuration of the present invention, strong near-field light can be obtained even when the distance between the boundary line formed between adjacent metal films and the focusing position of the surface plasmon polariton is designed to be relatively long. Can do. As a result, the information recording head of the present invention can install the light source and the near-field light output means sufficiently separated, and can suppress the background noise.

  In the information recording head of the present invention, the metal film supporting member of the surface plasmon polariton concentrator is a substrate having translucency, the near-field light excitation means is the substrate, and the surface plasmon polariton focusing is performed. Surface plasmon polaritons may be excited on at least one of the metal films by obliquely entering light from the side where the substrate is provided with respect to the vessel.

  With the above configuration, since the metal film support member, which is a component of the surface plasmon polariton concentrator, can be used as the near-field light excitation means, other members are used as the surface plasmon polariton concentrator to generate the surface plasmon polariton. There is no need to provide it. Therefore, it is possible to easily generate the surface plasmon polariton in the surface plasmon polariton concentrator, and the surface plasmon polariton concentrator can be easily processed.

  In the information recording head of the present invention, the predetermined surface of the metal film support member in the surface plasmon polariton concentrator is an emission surface that emits light of the light source, and the near-field light excitation means includes It may be provided on at least one of the membranes.

  With the above configuration, since the predetermined surface of the metal film support member in the surface plasmon polariton concentrator is an exit surface that emits light from the light source, each metal film of the surface plasmon polariton concentrator is formed on the exit surface of the light source. ing. Therefore, the surface plasmon polariton concentrator of the present invention can suppress background noise due to propagating light emitted from the light source, and by providing near-field light excitation means on at least one of the metal films, Surface plasmon polaritons can be excited from the light of the light source on the metal film.

  As described above, since each metal film of the surface plasmon polariton concentrator is provided on the emission surface of the light source, there is no need for parts for introducing light from the light source to the surface plasmon polariton concentrator, thereby reducing the manufacturing cost. be able to. In addition, as the number of parts is small, the assembly accuracy increases. Furthermore, since there are few adhesion | attachment locations after an assembly, a time-dependent change decreases and reliability improves. Moreover, since there are few assembly processes, manufacturing time can also be shortened. Further, the light emitted from the light source is small and can be used efficiently.

  The recording apparatus of the present invention is a recording apparatus for recording on a recording medium, and is characterized by including the above-described information recording head.

  With the above configuration, it is possible to obtain a recording apparatus with high degree of design freedom while suppressing scattering of surface plasmon polariton at the edge.

  The recording apparatus of the present invention further includes a control unit that controls the position of the information recording head and the recording medium, and the control unit determines the distance between the near-field light output unit and the recording medium as a surface. You may control below the wavelength of a plasmon polariton.

  The surface plasmon polariton focused by the surface plasmon polariton concentrator is converted into near-field light by the near-field light output means. However, the intensity of the near-field light decreases as the distance from the near-field light output means increases. Therefore, according to the above configuration of the present invention, the near-field light irradiated from the near-field light output means converts the surface plasmon polariton focused by the surface plasmon polariton concentrator so as to reach the recording medium before the intensity is attenuated. The near-field light can be used more efficiently. Therefore, the recording apparatus of the present invention can irradiate the recording medium with near-intensity light with sufficient intensity, so that not only recording can be performed sufficiently, but also the transfer rate can be increased.

  In the recording apparatus, the recording medium is a magnetic recording medium having a high coercive force that is resistant to thermal fluctuation, and includes a magnetic field generation unit that applies a magnetic field to the recording medium, and the magnetic field generation unit A magnetic field may be applied to the recording medium at the same time that the recording medium is irradiated with the near-field light from the light output means.

  With the above configuration, near-field light is irradiated to the recording medium from the near-field light output means of the surface plasmon polariton concentrator, and the near-field light and the magnetic field are irradiated by applying a magnetic field to the recording medium by the magnetic field generator. Only the region thus formed becomes a mark in a magnetic recording medium having a high coercive force that is resistant to thermal fluctuations. Since the surface plasmon polariton concentrator of the present invention can make the surface plasmon polariton a small focusing size, a smaller mark can be recorded on the magnetic recording medium, and the recording density can be increased.

  Further, the near-field light obtained by converting the surface plasmon polariton focused by the surface plasmon polariton concentrator of the present invention by the near-field light output means has a high intensity, so that the transfer rate can be increased. The intensity of near-field light attenuates with increasing distance from the generation position, but the surface plasmon polariton concentrator of this recording device has a sufficiently strong intensity at the generation position. it can.

  The recording apparatus of the present invention may include a reproducing element that reads information recorded on the recording medium, and the reproducing element may be provided at a position away from the light source.

  A reproducing element that reads information recorded on a recording medium is easily affected by heat. If a reproducing element is provided close to a heat source such as a light source, the reproducing element may be deteriorated or destroyed. The reliability of the element decreases. For this reason, in the recording apparatus of the present invention, by providing the reproducing element at a position away from the light source, information recorded on the recording medium can be read and the reproducing element can be prevented from being affected by the heat emitted from the light source. Thus, the reliability of the reproducing element can be improved.

  In the recording apparatus of the present invention, the recording medium has photosensitivity, and the recording medium is exposed to the near-field light irradiated from the surface plasmon polariton concentrator and information is recorded. Good.

  With the above configuration, a fine structure can be recorded by irradiating a recording medium having photosensitivity with near-field light from a surface plasmon polariton concentrator.

  As described above, the surface plasmon polariton concentrator of the present invention is a surface plasmon polariton concentrator that focuses the surface plasmon polariton, and is formed on a metal film support member and a predetermined surface of the metal film support member. At least two metal films that are adjacent to each other and have an effective refractive index different from that of the adjacent metal films, and each metal film has a curved line at least part of a boundary line between the adjacent metal films And the surface on the opposite side to the surface in contact with the metal film support member and the surface on the opposite side to the surface in contact with the metal film support member in the adjacent metal film are flush with each other. It is characterized by.

  With the above configuration, at least a part of the boundary line of each metal film that is adjacent to each other and has an effective refractive index different from that of the adjacent metal film is a curved line, so that the propagation direction of the surface plasmon polariton is changed at the boundary line. It can be transformed to focus the surface plasmon polaritons. At this time, the surface plasmon polariton of the metal film propagates to the adjacent metal film by making the surface of the metal film that propagates the surface plasmon polariton and the surface of the adjacent metal film that the surface plasmon polariton propagates flush with each other. When this is done, scattering at the edges between the adjacent metal films can be suppressed.

  As a result, the surface plasmon polariton concentrator of the present invention increases the intensity of the focused surface plasmon polariton and can suppress the generation of background noise due to scattered light. In addition, when any film is formed on the surface plasmon polariton concentrator, there is no need to worry about the film thickness difference.

  An embodiment of the present invention will be described below with reference to FIGS.

  The surface plasmon polariton concentrator of the present invention has a metal film supporting member and at least 2 which are formed on a predetermined surface of the metal film supporting member and have effective refractive indexes different from each other adjacent to each other. Each metal film has a curved surface at least a part of a boundary line between the adjacent metal films, and a surface opposite to the surface in contact with the metal film support member; The surface of the adjacent metal film is flush with the surface opposite to the surface in contact with the metal film support member.

  The surface plasmon polariton concentrator of the present invention has a role equivalent to a lens for light with respect to the surface plasmon polariton. The shape of the lens with respect to light is determined by the shape of the entrance surface, the shape of the exit surface, and the center thickness. Similarly, the shape of the surface plasmon polariton concentrator is determined by the shape of the incident boundary line, the shape of the output boundary line, and the center distance.

  The incident boundary line is a boundary line between adjacent metal films through which the surface plasmon polariton passes for the first time in the surface plasmon polariton concentrator. Further, the emission boundary line is a boundary line between adjacent metal films through which the surface plasmon polariton passes after passing through the incident boundary line in the surface plasmon polariton concentrator. There is only one incident boundary in the surface plasmon polariton concentrator, but there may be more than one exit boundary. However, in the case of the surface plasmon polariton concentrator of the present invention, a configuration having only an incident boundary line may be used.

  Even if it has only the incident boundary line, or has the incident boundary line and the output boundary line, the shape of the curved portion at the boundary line of each adjacent metal film only needs to be able to focus the surface plasmon polariton. In addition to arcs, elliptical arcs, hyperbolic curves, parabolas, shapes obtained by modulating them with higher-order functions may be used. Note that the focal point refers to the focal point of the original arc, elliptical arc, hyperbola, parabola, even in the case of the shape of the curved part at the boundary line of each adjacent metal film, even if the shape is modulated by a higher-order function. To do.

[First Embodiment]
First, a surface plasmon polariton concentrator 1 according to a first embodiment of the present invention having only an incident boundary will be described with reference to FIGS. FIG. 1 is a top view and a perspective view showing a schematic configuration of a surface plasmon polariton concentrator 1 of the present embodiment. In addition, the arrow in a figure has shown the propagation direction of the surface plasmon polariton 4. FIG.

  As shown in FIG. 1, the surface plasmon polariton concentrator 1 of the present embodiment includes a metal film support member 5, a first metal film 2, and a second metal film 3.

  The surface plasmon polariton concentrator 1 of the present embodiment propagates the surface plasmon polariton 4 from the first metal film 2 to the second metal film 3, so that the first metal film 2 and the second metal film 3 This is for changing the propagation direction of the surface plasmon polariton 4 at the boundary line formed between them and focusing the surface plasmon polariton 4 on the second metal film 3, and is used for optical recording, optically assisted magnetic recording, and the like. It can be suitably used for a recording apparatus.

  In the surface plasmon polariton concentrator 1 of the present embodiment, the surface plasmon polariton 4 may be configured to propagate from the first metal film 2 to the second metal film 3, and the surface plasmon polariton 4 may be used as the first metal film 2. May be used, or may be used as part of a surface plasmon polariton waveguide. Since a method for generating the surface plasmon polariton 4 on the first metal film 2 will be described later, description thereof is omitted here.

  The metal film support member 5 serves as a base for forming the first metal film 2 and the second metal film 3. In FIG. 1, the metal film support member 5 is described as a plate having a predetermined thickness, but the present invention is not limited to this. For example, the light-emitting surface of the light source may be the metal film support member 5 and the first metal film 2 and the second metal film 3 may be formed on the light-emitting surface. That is, the metal film support member 5 is not limited to a shape or a configuration, and may be any configuration as long as the first metal film 2 and the second metal film 3 can be formed.

  Further, by using the metal film support member 5, it is possible to generate the surface plasmon polariton 4 on the first metal film 2, and in this case, a transparent substrate as the metal film support member 5. Is used.

In this case, as a material constituting the metal film support member 5, for example, crown glass such as fused silica or BK7 (Schott Glass), flint glass such as F2 or SF11, and Lumicera (Murata Manufacturing Co., Ltd.) are used. A suitable ceramic or optical crystal such as SiO ₂ or sapphire is preferably used. In addition to the above-mentioned materials, optical resins such as acrylonitrile butadiene styrene, polycarbonate, polystyrene, polypropylene, polyoxymethylene, polyester acrylate, epoxy acrylate, urethane acrylate, polyether acrylate, acrylic resin, and polyolefin resin are suitable. Used. Moreover, the structure which has translucency with respect to only a specific wavelength like a silicon substrate may be sufficient as the metal film support member 5. FIG.

Further, when the surface plasmon polariton 4 is generated on the first metal film 2 by using the metal film support member 5, in addition to using a light-transmitting substrate as the metal film support member 5, for example, A dielectric film formed on another support such as an emission surface of the light source may be used. The dielectric material constituting the dielectric film may be a material having translucency, and in addition to the substrate material, MgF ₂ , TiO ₂ , Ta ₂ O ₃ , ZnO, Al ₂ O ₃ , SiN And AlN.

  The first metal film 2 and the second metal film 3 have the same thickness and are formed so as to be in contact with each other. Moreover, although the 1st metal film 2 and the 2nd metal film 3 are the same film thickness, since each is comprised with a different kind of metal, an effective refractive index differs. In the surface plasmon polariton concentrator 1, when the effective refractive index of the first metal film 2 is n1 and the effective refractive index of the second metal film 3 is n2, the relationship is n1 <n2. In addition, it is desirable that the film thicknesses of the first metal film 2 and the second metal film 3 of the present embodiment are in the range of several nm to several hundred nm.

  The boundary line formed between the first metal film 2 and the second metal film 3 is a curve, and has a convex shape from the second metal film 3 toward the first metal film 2. The focusing of the surface plasmon polariton 4 is in principle the same concept as the focusing of light. In the present embodiment, the convex shape is an elliptical arc in order to provide high focusing performance by reducing wavefront aberration. (See Lens design fundamentals, Rudolf Kingslake, Academic Press). Note that the boundary line formed between the first metal film 2 and the second metal film 3 only needs to be formed on at least the surface on which the surface plasmon polariton 4 propagates.

  In addition, the boundary line formed between the first metal film 2 and the second metal film 3 is a case where two kinds of metals forming the boundary line are mixed with each other with a width within the wavelength of the surface plasmon polariton 4. Shall also be included. In this case, the boundary line takes the center of the width where two kinds of metals are mixed.

  The refraction by the boundary line formed between the first metal film 2 and the second metal film 3 of the surface plasmon polariton 4 is in principle the same concept as the refraction of light, and the refraction angle is the first metal film. 2 and the effective refractive index ratio between the second metal film 3 and the incident angle of the surface plasmon polariton 4 with respect to the boundary line formed between the first metal film 2 and the second metal film 3.

  The incident angle means that the surface plasmon polariton 4 propagates on the surface of the first metal film 2 with respect to the boundary line formed between the first metal film 2 and the second metal film 3. The angle θ1 (θ) formed by the propagation direction of the surface plasmon polariton 4 with respect to the normal of the boundary line is defined as 0 ° <θ1 <90 °. The refraction angle is formed between the first metal film 2 and the second metal film 3 when the surface plasmon polariton 4 propagates from the first metal film 2 onto the surface of the second metal film 3. The angle θ2 formed by the propagation direction of the surface plasmon polariton 4 on the surface of the second metal film 3 with respect to the normal of the boundary line is defined as 0 ° <θ2 <90 °.

  Here, the ratio of the effective refractive index between the first metal film 2 and the second metal film 3 and the incidence of the surface plasmon polariton 4 on the boundary line formed between the first metal film 2 and the second metal film 3. The relationship between the angle and the refraction angle will be described.

  The relationship between the incident angle and the refraction angle of the surface plasmon polariton 4 with respect to the boundary line formed between the first metal film 2 and the second metal film 3, that is, the magnitude of the conversion of the propagation direction of the surface plasmon polariton 4 is By the same principle as light refraction (Snell's law),

It is expressed.

  In the present embodiment, the propagation direction of the surface plasmon polariton 4 is parallel to the line connecting the two focal points of the elliptic arc with respect to the boundary line of the elliptic arc formed between the first metal film 2 and the second metal film 3. It is desirable that

  When the surface plasmon polariton 4 propagates in parallel to the line connecting the two focal points of the elliptic arc with respect to the boundary line of the elliptic arc formed between the first metal film 2 and the second metal film 3, the first metal film 2 The boundary line formed between the first metal film 3 and the second metal film 3 is an elliptical arc from the second metal film 3 toward the first metal film 2, and the effective refractive index of the first metal film 2 is Is smaller than the effective refractive index of the second metal film 3, the surface plasmon polariton 4 is greatly refracted at the outer part of the boundary line, hardly refracted at the center part of the boundary line, and the surface plasmon polariton 4 at the focal point of the elliptic arc. 4 converge.

  That is, in the surface plasmon polariton concentrator 1, the surface plasmon polariton 4 is focused on the second metal film 3 because the refraction angle of the surface plasmon polariton 4 at each position on the boundary line is different.

  According to the above configuration, the surface plasmon polaritons can be focused well with a simple configuration, and the distance until the surface plasmon polaritons are focused and the focusing size can be changed by changing the shape of the curved portion. .

  Further, the eccentricity e of the ellipse in the elliptical arc of the boundary line formed between the first metal film 2 and the second metal film 3 is the effective refractive index n1 of the first metal film 2 and the effective efficiency of the second metal film 3. Refractive index n2,

It is preferable that the relationship be

  Further, the focal length f of the ellipse is given by assuming that the half major axis of the ellipse is a.

It becomes.

  In order to focus all the surface plasmon polaritons 4 reaching the boundary line formed between the first metal film 2 and the second metal film 3 in the second metal film 3, the surface reaching the boundary line is used. It is desirable to design the configuration of the first metal film 2 and the second metal film 3 so that all the plasmon polaritons 4 pass through the boundary line.

  Further, as described above, the effective refractive index of the first metal film 2 and the second metal film 3 is not limited to the constituent metal material, but the mode of the surface plasmon polariton 4, the thickness of the metal film, or the medium in contact with the metal film Depends on the refractive index. That is, even if the materials constituting the first metal film 2 and the second metal film 3 are the same, the mode and film thickness of the surface plasmon polariton 4 or the medium with which the first metal film 2 or the second metal film 3 is in contact By making the refractive indexes different, the effective refractive indexes of the first metal film 2 and the second metal film 3 can be made different.

  Therefore, in the surface plasmon polariton concentrator 1 of the present embodiment, the effective refractive index of the first metal film 2 and the effective refractive index of the second metal film 3 are made different by making the film thicknesses different from each other. There may be. In this case, the surface of the first metal film 2 opposite to the surface in contact with the metal film support member 5 and the surface of the second metal film 3 opposite to the surface in contact with the metal film support member 5 are provided. It is desirable to be in the same plane. As a result, the surface plasmon polariton 4 propagating from the first metal film 2 to the second metal film 3 is prevented from being scattered by the edge formed between the first metal film 2 and the second metal film 3. be able to. As a result, the surface plasmon polariton concentrator 1 increases the intensity of the focused surface plasmon polariton 4 and can suppress the generation of background noise due to scattered light.

  The surface plasmon polariton 4 propagating on the surfaces of the first metal film 2 and the second metal film 3 is attenuated in strength as it travels. The distance at which the intensity of the surface plasmon polariton 4 is 1 / e is called the propagation length, and the propagation length depends on the metal materials and film thicknesses of the first metal film 2 and the second metal film 3 through which the surface plasmon polariton 4 propagates. The propagation length varies greatly from several tens of nanometers to several tens of micrometers depending on the metal materials and film thicknesses of the first metal film 2 and the second metal film 3, so that the first metal film does not become too short. It is necessary to consider the configuration of the second and second metal films 3.

  If the distance that the surface plasmon polariton 4 propagates on the surfaces of the first metal film 2 and the second metal film 3 is too long, the intensity of the focused surface plasmon polariton 4 is attenuated. Therefore, when the surface plasmon polariton 4 is excited in the first metal film 2, the distance (focal length) from the position where the surface plasmon polariton 4 is excited to the position where the surface plasmon polariton 4 is focused is also different from that other than the surface plasmon polariton concentrator 1. When the excited surface plasmon polariton 4 is propagated to the first metal film 2, the distance from the propagation start position of the first metal film 2 to the focusing position (focal length) is preferably less than the propagation length. . Thereby, before the intensity | strength of the surface plasmon polariton 4 attenuate | damps, since the surface plasmon polariton 4 can be converged, strong near-field light can be obtained.

  In the surface plasmon polariton concentrator 1 of this embodiment, it is desirable that the propagation length in the second metal film 3 is longer than the propagation length in the first metal film 2. In particular, the propagation length of the surface plasmon polariton 4 in the second metal film 3 is the focal length of the surface plasmon polariton 4 in the surface plasmon polariton concentrator 1, the surface plasmon polariton 4 is the first metal film 2, the second metal film 3, In consideration of the fact that the incident beam width incident on the boundary line formed between the layers must be sufficiently larger than the diffraction limit, and obtaining a sufficient interference effect, it is about 5 times the wavelength of the surface plasmon polariton 4. It is desirable that

  Thereby, even if the distance from the surface plasmon polariton 4 passing through the boundary line formed between the first metal film 2 and the second metal film 3 to the focusing position is designed to be relatively long, the strength is increased. Strong near-field light. Therefore, when the surface plasmon polariton concentrator 1 of the present embodiment is applied to a recording apparatus or the like, the light source can be installed sufficiently separated from the near-field light output unit (near-field light output means).

  By the way, in order to shorten the focal length, the ratio of the effective refractive index between the first metal film 2 and the second metal film 3 or another metal film must be large to some extent. It is preferable that the propagation length is sufficiently longer than the wavelength of the surface plasmon polariton in each metal film.

  However, if the metal material and the film thickness are changed so that the propagation length in the first metal film 2 and the second metal film 3 is not too short, the effective refractive index of the first metal film 2 and the second metal film 3 is also increased. Change. Therefore, the first metal film 2 and the second metal film 2 and the second metal film 3 do not become too short and the surface plasmon polariton 4 can achieve a desired focal length. It is desirable to consider the configuration of the membrane 3.

  How the effective refractive index and the propagation length in the metal film change when the metal material and the film thickness constituting the metal film are changed will be described below with reference to FIG. FIG. 2 is a graph showing changes in effective refractive index and propagation length of each metal film when the film thickness of the metal film composed of Al and the metal film composed of Ag is changed.

In FIG. 2, the metal film composed of Al and the metal film composed of Ag are in contact with air on both sides, and propagate the surface plasmon polariton 4 in the symmetry mode having a frequency of 7.5 × 10 ¹⁴ Hz. Are simulating. The solid line in the figure indicates the effective refractive index of each metal film, and the dotted line indicates how many times the propagation length of the surface plasmon polariton 4 in each metal film is relative to the wavelength of the surface plasmon polariton 4.

  Referring to FIG. 2, the metal film composed of Al and the metal film composed of Ag both increase in effective refractive index and decrease in propagation length as the film thickness increases. Specifically, the metal film composed of Al and the metal film composed of Ag both have a propagation length that is shorter than the wavelength of the surface plasmon polariton 4 when the film thickness is greater than about 50 nm. . In addition, in the case of a metal film composed of Ag, the effective refractive index becomes almost constant when the film thickness is greater than about 50 nm. However, in a metal film composed of Al, the effective refractive index increases as the film thickness increases. Become.

  Thus, when the materials constituting the metal film are different, the propagation length and the effective refractive index change when the thickness of each metal film is changed. Therefore, when designing the configuration of the first metal film 2 and the second metal film 3, the propagation length and effective refractive index in the metal film depend on the material constituting the metal film and the film thickness of the metal film, Considering that the change in propagation length and effective refractive index when the thickness of the metal film is changed depends on the material constituting the metal film, the thickness of the metal material constituting the metal film and the thickness of the metal film are determined. It is desirable to decide.

  Here, the surface plasmon polariton concentrator 1 of the present embodiment has an effective refractive index by making the film thicknesses of the first metal film 202 and the second metal film 203 different as in the metal film 201 shown in FIG. The effective refractive index is made different by making the thickness of the first metal film 2 and the second metal film 3 the same and making the metal material constituting each metal film different. The advantages will be described below.

  In the metal film 201 shown in FIG. 25, for example, the first metal film 202 and the second metal film 203 are each made of Ag, the film thickness of the first metal film 202 is 100 nm, and the film thickness of the second metal film 203 is In the case of 20 nm, referring to FIG. 2, the effective refractive index ratio between the first metal film 202 and the second metal film 203 is 1.13.

  On the other hand, when the first metal film 2 and the second metal film 3 are configured with the same film thickness using different metal materials as in the surface plasmon polariton concentrator 1 of the present embodiment, for example, the first metal film 2 is composed of Al and the second metal film 3 is made of Ag and the film thickness is 100 nm, and referring to FIG. 2, the ratio of the effective refractive index of the first metal film 2 and the second metal film 3 is 1 .12.

  Therefore, the effective refractive index ratio between the first metal film 2 and the second metal film 3 of the surface plasmon polariton concentrator 1 of the present embodiment is the same as that of the metal film 201 and the first metal film 202 and the second metal film 203. The effective refractive index ratio between the first metal film 202 and the second metal film 203 of the metal film 201 can be made substantially the same without changing the film thickness of the first metal film 201.

  Further, the propagation lengths of the first metal film 202 of the metal film 201 and the first metal film 2 and the second metal film 3 of the surface plasmon polariton concentrator 1 are shorter than the propagation length of the metal film 201 in the second metal film 203. However, since it has a sufficient length of about 18 times the wavelength of the surface plasmon polariton 4, it does not significantly affect the attenuation of the surface plasmon polariton 4.

Next, scattering of the surface plasmon polariton 4 caused by the edge of the first metal film 202 of the metal film 201 shown in FIG. 25 will be described with reference to FIG. In FIG. 3, the metal film 201 includes, for example, a first metal film 202 and a second metal film 203 each made of Ag. The film thickness of the first metal film 202 is 100 nm, and the film thickness of the second metal film 203. Is 100 nm or less, the edge intensity at the edge of the first metal film 202 when the surface plasmon polariton 4 in the symmetry mode having a frequency of 7.5 × 10 ¹⁴ Hz propagates from the first metal film 202 to the second metal film 203. It is a figure which shows ratio and coupling efficiency.

  The edge strength ratio is indicated by a solid line in the drawing, and there is no difference in film thickness between the electric field strength at the edge of the first metal film 202 and the first metal film 202 and the second metal film 203. In this case, the ratio is the ratio of the electric field strength at the boundary line formed between the first metal film 202 and the second metal film 203.

  The coupling efficiency is indicated by a dotted line in the figure. The electric field strength after the surface plasmon polariton 4 passes through the edge of the first metal film 202, the first metal film 202, the second metal film 203, When the surface plasmon polariton 4 passes through the boundary line formed between the first metal film 202 and the second metal film 203 in the case where there is no difference in film thickness,

  As shown in FIG. 3, the edge intensity ratio becomes the maximum value when the film thickness difference between the first metal film 202 and the second metal film 203 is about 20 nm. The edge strength ratio decreases as the thickness decreases and the difference in film thickness increases. Thus, the amount of scattering of the surface plasmon polariton 4 at the edge of the first metal film 202 is maximized when the film thickness difference between the first metal film 202 and the second metal film 203 is a predetermined thickness. Note that the amount of scattering of the surface plasmon polariton 4 at the edge of the first metal film 202 varies depending on the wavelength of the surface plasmon polariton 4 or the materials constituting the first metal film 202 and the second metal film 203.

  The coupling efficiency tends to be opposite to the edge intensity ratio because the surface plasmon polariton 4 incident on the edge of the first metal film 202 is scattered at the edge and loses energy. That is, the minimum value is obtained when the difference in film thickness between the first metal film 202 and the second metal film 203 is about 20 nm. The coupling efficiency increases with increasing. Therefore, for example, the first metal film 202 and the second metal film 203 of the metal film 201 are each composed of Ag, the film thickness of the first metal film 202 is 100 nm, and the film thickness of the second metal film 203 is 20 nm ( That is, when the film thickness difference is 80 nm, the surface plasmon polariton 4 is scattered at the edge of the first metal film 202 at 3.1 times the intensity propagating through the first metal film 202 as shown in FIG. The coupling efficiency is 0.45.

  As described above, in the configuration of the metal film 201 shown in FIG. 25, the surface plasmon polariton 4 is scattered in a large amount at the edge of the first metal film 202, and the strength of the usable surface plasmon polariton 4 is lowered. Therefore, it is preferable that there is no difference in film thickness between the first metal film 2 and the second metal film 3 as in the surface plasmon polariton concentrator 1 of the present embodiment. As described above, even if the film thicknesses of the first metal film 2 and the second metal film 3 are the same, the effective refractive index of the first metal film 2 and the second metal film 2 are made different by changing the constituent metal materials. It is possible to make a difference from the effective refractive index of the metal film 3. Further, as shown in FIG. 3, by making the first metal film 2 and the second metal film 3 have the same thickness, the surface plasmon polariton 4 is formed between the first metal film 2 and the second metal film 3. It propagates without scattering at the boundary formed between them.

  In order to make the effective refractive index of the metal film different, the first dielectric layer 213 and the second dielectric layer having different refractive indexes are formed on one surface of the metal film 215 as in the surface plasmon lens 211 shown in FIG. By providing the body layer 214, the effective refractive index on the side where the first dielectric layer 213 is provided can be made different from the effective refractive index on the side where the second dielectric layer 214 is provided.

  Here, the surface plasmon polariton concentrator 1 of the present embodiment makes the refractive index of the dielectric layer provided on one surface of the metal film 215 different as in the surface plasmon lens 211 shown in FIG. The effective refractive index is not changed by making the first metal film 2 and the second metal film 3 have the same film thickness and different metal materials constituting each metal film. The advantages of this are described below with reference to FIG. FIG. 4 shows the effect of each metal film when the refractive index of the dielectric film provided on the metal film composed of Au, the metal film composed of Al, and the metal film composed of Ag is changed. It is a graph which shows the change of a refractive index and propagation length.

In FIG. 4, a metal film composed of Au, a metal film composed of Al, and a metal film composed of Ag are provided on a substrate having a refractive index of 2.0 with a film thickness of 100 nm, respectively. Is simulated by propagating the surface plasmon polariton 4 in a symmetry mode of 5.5 × 10 ¹⁴ Hz. The solid line in the figure indicates the effective refractive index of each metal film, and the dotted line indicates how many times the propagation length of the surface plasmon polariton 4 in each metal film is relative to the wavelength of the surface plasmon polariton 4.

  In the surface plasmon lens 211 shown in FIG. 26, for example, the metal film 215 is made of Al, the refractive index of the first dielectric layer 213 is 1 (air), and the refractive index of the second dielectric layer 214 is 2. In this case, as shown in FIG. 4, the effective refractive index ratio between the side of the metal film 215 where the first dielectric layer 213 is provided and the side where the second dielectric layer 214 is provided is very large. Become. For example, when the metal film 215 is made of Ag, the refractive index of the first dielectric layer 213 is 1 (air) and the second dielectric layer 214 is the same as when the metal film 215 is made of Al. 4, the effective refraction between the side of the metal film 215 on which the first dielectric layer 213 is provided and the side on which the second dielectric layer 214 is provided is shown in FIG. The rate ratio is very large. However, when the refractive index of the second dielectric layer 214 is 2, the propagation length becomes as short as several times the wavelength of the surface plasmon polariton 4.

  As described above, in the configuration of the surface plasmon lens 211 shown in FIG. 26, the effective refraction between the side on which the first dielectric layer 213 of the metal film 215 is provided and the side on which the second dielectric layer 214 is provided. In order to realize a sufficient ratio of the surface plasmon polariton 4 to the ratio of the ratio, it is necessary to increase the refractive index of the second dielectric layer 214, and the second dielectric layer 214 of the metal film 215 is provided. Propagation length on the side of the wire is very short. Therefore, as in the surface plasmon polariton concentrator 1 of the present embodiment, the effective refractive index may be different by making the metal materials of the first metal film 2 and the second metal film 3 different. preferable.

  As shown in FIGS. 2 to 4, the effective refractive index and propagation length in the metal film are as follows: the metal material constituting the metal film, the film thickness of the metal film, the material in contact with the metal film, the surface plasmon polariton frequency, and the surface plasmon Although it depends on the polariton mode, the first metal film 2 and the second metal film 3 are made of different metal materials as in the surface plasmon polariton concentrator 1 of the present embodiment, so that the degree of design freedom is further increased. Obviously it will be higher.

  The material constituting the first metal film 2 and the second metal film 3 may be any metal capable of propagating the surface plasmon polariton 4, but a metal having high electrical conductivity is used because the propagation length becomes long. It is preferable. Examples of the material suitably used for the first metal film 2 and the second metal film 3 include noble metals such as gold (Au), silver (Ag), and platinum (Pt), aluminum (Al), and copper (Cu). And chromium (Cr).

  In the surface plasmon polariton concentrator 1 of this embodiment, a boundary line is formed between the first metal film 2 and the second metal film 3 having the same film thickness. That is, the surface of the first metal film 2 opposite to the surface in contact with the metal film support member 5 and the surface of the second metal film 3 opposite to the surface in contact with the metal film support member 5 are surfaces. It is one. However, in reality, when producing a surface plasmon polariton concentrator, it is difficult to make a film thickness difference completely in the boundary line. In the current film forming apparatus, the film thickness control is about ± 5% of the film thickness although it depends on the size of the region. Therefore, in the present embodiment, “same film thickness” and “same surface” include a film thickness difference of up to 5% of the film thickness.

  In FIG. 8, for example, when the film thickness of the first metal film 2 and the second metal film 3 is 100 nm, the film thickness difference between the first metal film 2 and the second metal film 3 is 5 nm. At this time, as shown in FIG. 23, the edge intensity ratio is about 1.9 and the coupling efficiency is about 0.6. However, this value does not greatly affect the scattering of the surface plasmon polariton 4. Further, unevenness called surface roughness is generated on the surface of the metal film. The size of the unevenness depends on the material under the metal film, the compatibility between the surface state of the material below and the material of the metal film, and the film thickness. When there is such surface roughness, the average value of the film thickness at several positions of the metal film is taken as the film thickness of the metal film. Therefore, when the film thickness at the position (x, y) is h (x, y) and the area of the metal film is S, the average film thickness ha is

It becomes.

  Next, a method for extracting the surface plasmon polariton 4 focused on the second metal film 3 as near-field light for use in optical recording or optically assisted magnetic recording by the surface plasmon polariton concentrator 1 of the present embodiment will be described below. Explained.

  In order to extract the surface plasmon polariton 4 as near-field light, there are two methods of using near-field light. Two methods for using near-field light will be described below.

  For example, when the surface plasmon polariton 4 is used for optical recording or optically assisted magnetic recording, the first method of using near-field light is an object such as a recording medium with respect to the surface plasmon polariton 4 focused on the second metal film 3. In this method, the near-field light of the surface plasmon polariton 4 itself is used by bringing an object closer. At this time, the object and the surface plasmon polariton concentrator 1 may be brought close to a range within a quarter of the wavelength of the surface plasmon polariton 4. However, this method cannot generate a spot smaller than the diffraction limit of the focused surface plasmon polariton 4.

  The second method of using near-field light is to scatter the surface plasmon polariton 4 focused on the second metal film 3 by a near-field light output unit (near-field light output means) formed on the metal film. There are the following two methods.

  The first method is to scatter at the edge of the second metal film 3 of the surface plasmon polariton concentrator 1. The edge of the second metal film 3 may be an end portion that is an outer peripheral portion of the second metal film 3, and when the opening is provided in the second metal film 3, the edge of the opening is Also good.

  The second method is a method of forming a protrusion such as a minute protrusion on the second metal film 3. The protrusion may be, for example, metal fine particles provided on the second metal film 3.

  Thus, in the second near-field light utilization method, the near-field light output unit is provided at the metal end of the metal film or the metal film according to the use of the surface plasmon polariton concentrator 1 of the present embodiment. It is preferable to use open openings, slits or metal protrusions.

  Since the surface plasmon polariton 4 is attenuated in intensity as it travels, in order to obtain strong near-field light, from the boundary line formed between the first metal film 2 and the second metal film 3, The distance to the edge or protrusion of the second metal film 3 is preferably shorter than the propagation length of the surface plasmon polariton 4.

  In the second method and the second method using the second near-field light, it is desirable to provide a scatterer at the focal position of the surface plasmon polariton 4. As a result, the surface plasmon polariton 4 focused by the surface plasmon polariton concentrator 1 can be efficiently extracted as near-field light.

[Second Embodiment]
Next, a surface plasmon polariton concentrator 11 according to a second embodiment of the present invention having only an incident boundary will be described with reference to FIG. FIG. 5 is a top view and a perspective view showing a schematic configuration of the surface plasmon polariton concentrator 11 of the second embodiment. In addition, the arrow in a figure has shown the propagation direction of the surface plasmon polariton 4. FIG. Moreover, the same code | symbol is attached | subjected about the component in the surface plasmon polariton focusing device 1 of 1st Embodiment, and the component which has an equivalent function.

  As shown in FIG. 5, the surface plasmon polariton concentrator 11 of the present embodiment includes a metal film support member 5, a first metal film 12, and a second metal film 13. In the surface plasmon polariton concentrator 11 of this embodiment, when the effective refractive index of the first metal film 12 is n10 and the effective refractive index of the second metal film 13 is n20, the relationship is n10> n20.

  In the surface plasmon polariton concentrator 11, the surface plasmon polariton 4 is configured to propagate from the second metal film 13 to the first metal film 12, and the surface plasmon polariton 4 is focused on the first metal film 12. That is, the surface plasmon polariton 4 propagates from the first metal film 2 to the second metal film 3 having an effective refractive index larger than that of the first metal film 2 in the first embodiment. The surface plasmon polariton 4 propagates from the metal film 13 to the first metal film 12 having an effective refractive index smaller than that of the second metal film 13.

  In the surface plasmon polariton concentrator 11, the surface plasmon polariton 4 propagates from the second metal film 13 to the first metal film 12 having an effective refractive index smaller than that of the second metal film 13, so that the surface plasmon polariton 4 is the same as in the first embodiment. If the boundary line formed between the first metal film 12 and the second metal film 13 is an elliptical arc, the surface plasmon polariton 4 is diffused in the first metal film 12.

  Therefore, the boundary line formed between the first metal film 12 and the second metal film 13 is a curve, and has a convex shape from the second metal film 13 toward the first metal film 12. In the present embodiment, the convex shape is a hyperbola in order to provide high focusing performance by reducing wavefront aberration. With the above configuration, the surface plasmon polariton concentrator 11 of the present embodiment has a small focused size of the surface plasmon polariton 4, and thus the focused electric field strength is high, and strong near-field light can be obtained. Therefore, for example, when the surface plasmon polariton concentrator having the above-described configuration is applied to a recording apparatus, it is possible to record a minute mark on a recording medium because the converging size is very small.

  Further, the eccentricity e of the hyperbola of the boundary line formed between the first metal film 12 and the second metal film 13 is the effective refractive index n10 of the first metal film 12 and the effective refractive index of the second metal film 13. n20,

It is preferable that the relationship be

  The focal length f of the hyperbola is 2a, where the difference in distance from the two hyperbolas to the hyperbola is 2a.

It becomes.

  In this embodiment, the propagation direction of the surface plasmon polariton 4 is parallel to the line connecting the two focal points of the hyperbola with respect to the boundary line of the hyperbola formed between the first metal film 12 and the second metal film 13. It is desirable that

  When the surface plasmon polariton 4 propagates in parallel to the line connecting the two focal points of the hyperbola with respect to the boundary line of the hyperbola formed between the first metal film 12 and the second metal film 13, the first metal film 12 The boundary line formed between the second metal film 13 and the second metal film 13 has a hyperbolic convex shape from the second metal film 13 toward the first metal film 12, and the effective refractive index of the first metal film 12 Is smaller than the effective refractive index of the second metal film 13, the surface plasmon polariton 4 is greatly refracted in the outer part of the boundary line, hardly refracts in the central part of the boundary line, and the surface plasmon polariton 4 at the hyperbolic focus. 4 converge.

  The first metal film 12 and the second metal film 13 of the present embodiment are different from each other in that the boundary line formed between the first metal film 12 and the second metal film 13 is a hyperbola, that is, each metal The metal material constituting the film, the film thickness of each metal film, the material in contact with each metal film, the wavelength of the surface plasmon polariton 4, the mode of the surface plasmon polariton 4 and the like are the first metal film 2 of the first embodiment. Since it can be set in the same manner as the second metal film 3, the description thereof is omitted here.

[Third Embodiment]
Next, a surface plasmon polariton concentrator 21 according to a third embodiment of the present invention having an entrance boundary and an exit boundary will be described with reference to FIG. FIG. 6 is a top view and a perspective view showing a schematic configuration of the surface plasmon polariton concentrator of the third embodiment. In addition, the arrow in a figure has shown the propagation direction of the surface plasmon polariton 4. FIG. Moreover, the same code | symbol is attached | subjected about the component in the surface plasmon polariton focusing device 1 of 1st Embodiment, and the component which has an equivalent function.

  As shown in FIG. 6, the surface plasmon polariton concentrator 21 of the present embodiment includes a metal film support member 5, a first metal film 22, and a second metal film 23 surrounded by the first metal film 22. Has been.

  Note that the first metal film 22 and the second metal film 23 of the present embodiment are other than the configuration in which the second metal film 23 is surrounded by the first metal film 22, that is, the metals constituting each metal film. The first metal film 2 and the second metal film according to the first embodiment have different degrees of freedom such as the material, the film thickness of each metal film, the material in contact with each metal film, the wavelength of the surface plasmon polariton 4, the mode of the surface plasmon polariton 4. Since it can be set in the same manner as in FIG. 3, the description thereof is omitted here.

  In the surface plasmon polariton concentrator 21 of the present embodiment, since the second metal film 23 is surrounded by the first metal film 22, the surface plasmon polariton 4 propagates from the first metal film 22 to the second metal film 23. Then, the surface plasmon polariton 4 passes through the second metal film 23 and is propagated again to the first metal film 22. Therefore, the surface plasmon polariton 4 passes through the boundary line formed between the first metal film 22 and the second metal film 23 twice. That is, the surface plasmon polariton 4 passes through the incident boundary line and the outgoing boundary line. In the surface plasmon polariton concentrator 21 of the present embodiment, the line connecting the two focal points of the incident boundary line and the line connecting the two focal points of the output boundary line are parallel to each other.

  For this reason, the surface plasmon polariton 4 is converged more steeply by changing the propagation direction twice in the boundary line formed between the first metal film 22 and the second metal film 23.

  In the present embodiment, by surrounding the second metal film 23 with the first metal film 22, the boundary line where the surface plasmon polariton 4 is formed between the first metal film 22 and the second metal film 23 is formed twice. Although it is designed to pass, the present invention is not limited to this. That is, the first metal film 22 and the second metal film 23 may be provided adjacent to each other in the order of the first metal film 22, the second metal film 23, and the first metal film 22. Further, using the third metal film, a boundary line formed between the first metal film 22 and the second metal film 23 is used as an incident boundary line, and between the second metal film 23 and the third metal film. The formed boundary line may be used as the output boundary line. In this case, it is desirable that n2> n3, where n2 is the effective refractive index of the second metal film and n3 is the effective refractive index of the third metal film.

[Fourth Embodiment]
Next, a surface plasmon polariton concentrator 31 according to a fourth embodiment of the present invention having an entrance boundary and two exit boundaries will be described with reference to FIG. FIG. 7 is a top view and a perspective view showing a schematic configuration of the surface plasmon polariton concentrator 31 of the fourth embodiment. In addition, the arrow in a figure has shown the propagation direction of the surface plasmon polariton 4. FIG. Moreover, the same code | symbol is attached | subjected about the component in the surface plasmon polariton focusing device 1 of 1st Embodiment, and the component which has an equivalent function.

  As shown in FIG. 7, the surface plasmon polariton concentrator 31 of this embodiment includes a metal film support member 5, a first metal film 32, a second metal film 33 and a third metal film 33 surrounded by the first metal film 32. And a metal film 34. Since the first metal film 32 and the second metal film 33 of the present embodiment have the same configuration as the first metal film 22 and the second metal film 23 of the third embodiment, description thereof is omitted here.

  The structure in which the surface plasmon polariton concentrator 31 of the present embodiment is different from the surface plasmon polariton concentrator 21 of the third embodiment is that a third metal film 34 is provided. The third metal film 34 is made of a metal material different from that of the first metal film 32 and the second metal film 33 and has a different effective refractive index.

  In addition, as shown in FIG. 7, the surface plasmon polariton concentrator 31 has a boundary line formed between the first metal film 32 and the third metal film 34 and the first metal film 22 of the third embodiment. The boundary line formed between the second metal film 23 and the output boundary line of the surface plasmon polariton 4 is parallel to the boundary line.

  Therefore, the surface plasmon polariton 4 propagating through the surface plasmon polariton concentrator 31 of the present embodiment is a boundary line formed between the first metal film 32 and the second metal film 33, the second metal film 33 and the third metal film 33. The light is emitted to the first metal film 32 via the boundary line formed between the metal film 34 and the boundary line formed between the third metal film 34 and the first metal film 32. That is, the surface plasmon polariton 4 passes through the two output boundary lines, and the propagation direction can be changed three times at the incident boundary line and the two output boundary lines.

  Therefore, the surface plasmon polariton concentrator 31 of the present embodiment has the same configuration as the achromatic lens in the case of light, and the focusing performance of the surface plasmon polariton 4 is improved.

[Fifth Embodiment]
Next, a surface plasmon polariton concentrator 41 according to a fifth embodiment of the present invention having an entrance boundary and an exit boundary will be described with reference to FIGS. FIG. 8 is a perspective view showing a schematic configuration of the surface plasmon polariton concentrator 41 of the fifth embodiment. In addition, the arrow in a figure has shown the propagation direction of the surface plasmon polariton 4. FIG. In FIG. 8, the shape of the first metal film 42 when viewed from above is a rectangle. In the following description, the longitudinal direction of the first metal film 42 is perpendicular to the x-axis direction and the longitudinal direction. One direction is the y-axis direction, and the film thickness directions of the first metal film 42 and the second metal film 43 are the z direction. Moreover, the same code | symbol is attached | subjected about the component in the surface plasmon polariton focusing device 1 of 1st Embodiment, and the component which has an equivalent function.

  As shown in FIG. 8, the surface plasmon polariton concentrator 41 of the present embodiment includes a metal film support member 5, a first metal film 42, and a second metal film 43 surrounded by the first metal film 42. Has been. The second metal film 43 has a shape surrounded by an elliptic arc and a straight line, and the straight line portion is provided perpendicular to a line connecting the two focal points of the ellipse in the elliptic arc portion.

  The first metal film 42 and the second metal film 43 of the present embodiment are the first metal of the third embodiment except that the shape of the second metal film 43 is a shape surrounded by an elliptical arc and a straight line. Since it is the same as the film | membrane 22 and the 2nd metal film | membrane 23, description is abbreviate | omitted here. In FIG. 8, the shape of the first metal film 42 when viewed from the top is rectangular, but the present invention is not limited to this. What is necessary is just to set suitably as shapes of the 1st metal film | membrane 42 according to the objective, such as circular and a polygon.

  In the surface plasmon polariton concentrator 41, the surface plasmon polariton 4 is a line connecting the two focal points of the ellipse of the elliptic arc part from the elliptical arc part side of the second metal film 43 of the first metal film 42 toward the linear part side. Propagate in parallel.

  Therefore, in the surface plasmon polariton concentrator 41, when the surface plasmon polariton 4 is propagated from the elliptical arc portion side of the second metal film 43 of the first metal film 42 toward the linear portion side, the first metal film 42 and the second metal A boundary line formed between the second metal film 43 and the first metal film 42 is convex in an elliptical arc, and the effective refractive index of the first metal film 42 is the second metal. Since it is smaller than the effective refractive index of the film 43, the surface plasmon polariton 4 is largely refracted in the outer portion of the boundary line and hardly refracted in the central portion of the boundary line.

  Further, the surface plasmon polariton 4 is further refracted in the linear portion of the boundary line formed between the first metal film 42 and the second metal film 43, and the surface plasmon polariton 4 is focused on the surface of the first metal film 42. Happens. If the ratio of the effective refractive index of the second metal film 43 to the first metal film 42 is large, the focal length is shortened and the focusing effect is increased.

  In order to increase the focusing effect of the surface plasmon polariton 4, the effective refractive index ratio and boundary shape of the metal film may be appropriately designed. The effective refractive index of the metal film can be changed depending on the combination of the metal film materials, the film thickness, and the material in contact with the metal film.

  The center distance d1 of the second metal film 43 in the x-axis direction is preferably equal to or shorter than the propagation length of the generated surface plasmon polariton 4. This is because when the surface plasmon polariton 4 is excited in the first metal film 42, the distance (focal length) from the position where the surface plasmon polariton 4 is excited to the position where the surface plasmon polariton 4 is focused, or other than the surface plasmon polariton concentrator 41. When propagating the excited surface plasmon polariton 4 to the first metal film 42, if the distance (focal length) from the propagation start position of the first metal film 42 to the focusing position is too long, the surface plasmon polariton 4 is This is because the intensity of the surface plasmon polariton 4 is attenuated before focusing.

  Here, the focusing of the surface plasmon polariton 4 in the surface plasmon polariton concentrator 41 of this embodiment will be confirmed with reference to FIG. 9 by simulation using the FDTD method (finite-difference time-domain method). FIG. 9 is a diagram showing the electric field intensity distribution of the surface plasmon polariton 4 on the surfaces of the first metal film 42 and the second metal film 43 of the surface plasmon polariton concentrator 41.

In the surface plasmon polariton concentrator 41 used for the FDTD method, the first metal film 42 and the second metal film 43 are each made of Al and Ag to a film thickness of 100 nm. At this time, referring to FIG. 2, the effective refractive index of the first metal film 42 is 1.02, and the effective refractive index of the second metal film 43 is 1.14. The elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43 has a center distance of 2 μm, a semi-major axis of 4.3 μm, and a semi-minor axis of 2.1 μm. As shown in FIG. 9, when the surface plasmon polariton 4 having a frequency of 7.5 × 10 ¹⁴ Hz is propagated from the first metal film 42 of the surface plasmon polariton concentrator 41 to the second metal film 43, the second metal It was confirmed that the surface plasmon polariton 4 converges in the film 43.

  Next, the focusing of the surface plasmon polariton 4 in the surface plasmon polariton concentrator 41 is confirmed by the phase distribution of the electric field with reference to FIGS. 10 (a) and 10 (b). 10A is a diagram showing the phase distribution of the electric field component in the traveling direction of the surface plasmon polariton 4 in the surface plasmon polariton concentrator 41, and FIG. 10B is the first metal in the surface plasmon polariton concentrator 41. FIG. 4 is a diagram showing a phase distribution of electric field components perpendicular to the surfaces of a film 42 and a second metal film 43. It can be seen that the phase distributions in FIGS. 10A and 10B once converge and diverge after passing through the second metal film 43. The transition from convergence to divergence is at substantially the same position as the location where the electric field converges in FIG.

  Next, the influence of the curvature of the incident boundary line on the focusing effect of the surface plasmon polariton will be described with reference to FIG. 11 and FIG.

  First, the relationship between the semi-major axis of the second metal film 43 of the surface plasmon polariton concentrator 41 and the focal position of the surface plasmon polariton 4 will be described with reference to FIG. FIG. 11 is a graph showing the relationship between the focal length and the half major axis of the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43 in the surface plasmon polariton concentrator 41. In the graph of FIG. 11, the horizontal axis indicates the half major axis (μm) in the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43, and the vertical axis indicates the boundary line. The focal length (μm), which is the distance from the straight line portion to the position where the surface plasmon polariton 4 converges, is shown.

  Here, the second metal film 43 of the surface plasmon polariton concentrator 41 is made of Ag, and the x-axis in the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43. The center distance d1 in the direction is 2 μm, and the eccentricity is 0.87. As shown in FIG. 11, when the semi-major axis of the elliptical arc part is changed from 4.3 μm to 6.6 μm, the focal length gradually increases as the semi-major axis increases. It can be confirmed that the surface plasmon polariton 4 is focused.

  Next, the semi-major axis in the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43 is 4.3 μm, the eccentricity is 0.87, and the center distance d1 in the x-axis direction is set. FIG. 12 shows the simulation result when the value is changed. FIG. 12 is a graph showing the relationship between the focal length and the center distance of the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43 in the surface plasmon polariton concentrator 41. In the graph of FIG. 12, the horizontal axis indicates the center distance d1 in the x-axis direction in the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43, and the vertical axis indicates the boundary. The focal length which is the distance from the straight line part of a line to the position where the surface plasmon polariton 4 converges is shown.

  As shown in FIG. 12, the center distance d1 in the x-axis direction in the elliptical arc portion of the boundary line formed between the first metal film 42 and the second metal film 43 was changed from 1.8 μm to 2.2 μm. However, as the center distance d1 increases, the focal distance greatly decreases, but it can be confirmed that the surface plasmon polariton 4 is focused regardless of the center distance d1.

  Even if the configuration of the metal film support member 5 changes, it is easily predicted that the same result corresponding to the effective refractive index ratio between the first metal film 42 and the second metal film 43 can be obtained. Non-Patent Document 1 specifically describes the effective refractive index when a metal film is provided on a substrate.

  When the surface plasmon polariton 4 focused by the surface plasmon polariton concentrator 41 of the present embodiment is scattered and used, a slit 44 may be provided on the first metal film 42 as shown in FIG. . The slit 44 extends from the converging position of the surface plasmon polariton 4 of the first metal film 42 in the direction perpendicular to the straight line portion of the boundary line formed between the first metal film 42 and the second metal film 43. A cut is provided in the thickness direction of the first metal film 42 up to the end of the film 42. As a result, the surface plasmon polariton 4 focused by the surface plasmon polariton concentrator 41 is scattered at the edge of the slit 44 and extracted as near-field light. In the present embodiment, the slit 44 is provided in order to scatter the surface plasmon polariton 4, but the present invention is not limited to this and may be a metal end or an opening or a metal protrusion.

[Sixth Embodiment]
Next, a surface plasmon polariton concentrator 51 according to a sixth embodiment of the present invention, which is a modification of the surface plasmon polariton concentrator 41 of the fifth embodiment, will be described with reference to FIG. FIG. 14 is a perspective view showing a schematic configuration of the surface plasmon polariton concentrator 51 of the sixth embodiment. In addition, the arrow in a figure has shown the propagation direction of the surface plasmon polariton 4. FIG. Moreover, the same code | symbol is attached | subjected about the component in the surface plasmon polariton focusing device 1 of 1st Embodiment, and the component which has an equivalent function.

  As shown in FIG. 14, the surface plasmon polariton concentrator 51 of the present embodiment includes an objective lens 55 (metal film support member), a first metal film 52, and two second metal films surrounded by the first metal film 52. The metal film 53 includes a near-field light output unit 54 (near-field light output means).

  The surface plasmon polariton concentrator 51 of this embodiment has a configuration in which two surface plasmon polariton concentrators 41 of the fifth embodiment are combined on an objective lens 55. Therefore, the configurations of the first metal film 52 and the second metal film 53 of the present embodiment are the same as the configurations of the first metal film 42 and the second metal film 43 of the fifth embodiment, and thus description thereof is omitted here. To do. In the present embodiment, an objective lens 55 is used instead of the metal film support member 5 as a base on which the first metal film 52 and the second metal film 53 are formed.

  The objective lens 55 is configured such that one surface is a flat surface and the other surface is a convex surface. The first metal film 52 and the second metal film 53 of the surface plasmon polariton concentrator 51 of the present embodiment are provided on the plane of the objective lens 55, and the two second metal films 53 are the first metal film 52. And a linear portion of the boundary line formed between the second metal film 53 and the second metal film 53 are provided so as to face each other symmetrically with respect to the optical axis of the objective lens 55. A near-field light output unit 54 made of a metal protrusion is provided at an intermediate position between the two second metal films 53. That is, the near-field light output unit 54 is provided at a position where the optical axis of the objective lens 55 and the first metal film 52 intersect.

  When the incident light 56 is irradiated from the convex surface side of the objective lens 55, the first metal film 52 is p-polarized light and has a predetermined angle at the objective lens 55 by the Kretchmann arrangement described later. The surface plasmon polariton 4 is excited on the first metal film 52 from the elliptical arc portion side of the two metal film 53 toward the center of the first metal film 52. The surface plasmon polariton 4 is focused at the near-field light output portion 54 of the first metal film 52 by passing from the elliptical arc portion of each second metal film 53 to the straight line portion.

  As described above, the surface plasmon polariton concentrator 51 of the present embodiment is configured by combining two surface plasmon polariton concentrators 41 of the fifth embodiment, and the surface plasmon polariton 4 is adjacent to each other in each second metal film 53. Since the light can be focused on one point of the field light output unit 54, near-field light having high intensity can be obtained. Further, the distance until the surface plasmon polariton converges and the converging size can be changed depending on the combination of the metal materials and the shape of the boundary line.

  In this embodiment, a configuration in which two surface plasmon polariton concentrators 41 according to the fifth embodiment are combined is described, but the present invention is not limited to this, and two or more surface plasmon polariton concentrators 41 are provided. A combined configuration may also be used.

  In the surface plasmon polariton concentrator 51 of the present embodiment, the focused surface plasmon polariton 4 is extracted as near-field light by providing a metal protrusion as the near-field light output unit 54. However, the present invention is not limited to this. I can't. That is, the first metal film 52 may be provided with a minute opening as the near-field light output unit 54. In this case, the near-field light is generated even when the incident light 56 is directly applied to the minute opening. To do.

  In the surface plasmon polariton concentrators of the first to sixth embodiments described above, the adjacent metal films are all the same film thickness, and all the metal films are air. The thickness of each metal film may be changed, or another dielectric may be provided on each metal film.

[Method of manufacturing surface plasmon polariton concentrator]
Here, the manufacturing method of the surface plasmon polariton concentrator of this invention is demonstrated based on Fig.15 (a)-FIG.15 (e). 15 (a) to 15 (e) are cross-sectional views showing a method for manufacturing the surface plasmon polariton concentrator of the present invention. In addition, the manufacturing method of the surface plasmon polariton concentrator of this invention is applicable to the surface plasmon polariton concentrator 1, 11, 21, 31, 41, 51 mentioned above. In the following description, a method for manufacturing the surface plasmon polariton concentrator 1 will be described.

  First, as shown in FIG. 15A, the first metal film 2 is formed on the metal film support member 5 by sputtering or vapor deposition. Then, a photoresist 7 is applied to the entire surface of the first metal film 2 by a spin coater or the like. At this time, when the photoresist 7 is a positive type, the photoresist 7 other than the portion where the second metal film 3 is formed is covered with the mask 6. As shown in FIG. 15A, the mask 6 and the photoresist 7 may be set apart from each other, or may be exposed in close contact with each other. Further, the shape of the mask 6 may be transferred to the photoresist 7 at the same magnification or may be reduced.

  Next, by exposing and developing the metal film supporting member 5 in a state where the photoresist 7 is covered with the mask 6, as shown in FIG. 15B, a portion of the photoresist not covered with the mask 6 is exposed. 7 is removed.

  Next, as shown in FIG. 15C, the first metal film 2 is etched by etching the first metal film 2 where the photoresist 7 has been removed, that is, where the second metal film 3 is to be formed. Remove. During this etching process, all of the first metal film 2 that is not covered with the photoresist 7 is removed.

  Next, as shown in FIG. 15D, when the second metal film 3 is formed by sputtering or vapor deposition, and the remaining photoresist 7 covered with the mask 6 is removed, as shown in FIG. 15E. In addition, the first metal film 2 and the second metal film 3 are adjacent to each other. If there are burrs on the surface of the metal film, the surface may be polished.

  For manufacturing the surface plasmon polariton concentrator, a wet etching process and a dry etching process such as ion etching or reactive ion etching (RIE) are used.

  In the method for manufacturing the surface plasmon polariton concentrator 1 described above, an aligner or a stepper is mainly used for exposure. Further, instead of etching, a process by FIB (Focused Ion Beam) or nanoimprint may be used.

  Further, when a slit is provided on the first metal film 42 as in the surface plasmon polariton concentrator 41 of the fifth embodiment shown in FIG. 13, as shown in FIG. 15 (f), etching, FIB, It is possible to provide slits and openings by a method such as nanoimprinting. Further, when a metal protrusion such as the near-field light output unit 54 in the surface plasmon polariton concentrator 51 of the sixth embodiment shown in FIG. 14 is provided on the first metal film 52, A protrusion may be formed at a desired position.

[Excitation method of surface plasmon polariton]
Here, the surface plasmon polariton excitation method in the surface plasmon polariton concentrator of the present invention will be described with reference to FIGS. 20-23 (Surface Plasmons on smooth and rough surfaces and on gratings, Heinz Raether, Springer-Verlag, 1988 p. .118-p.123). In the following description, in order to simplify the description, a description will be given using a surface plasmon polariton excitation unit including a substrate, a metal film, and a dielectric.

  In general, in order to excite surface plasmon polaritons in the surface plasmon polariton excitation unit, there are three methods described below, namely, a first excitation method, a second excitation method, and a third excitation method.

  The first excitation method is a method in which incident light is incident on the surface plasmon polariton excitation unit including a substrate, a metal film, and a dielectric layer at an appropriate angle from the substrate side.

  The configuration of the surface plasmon polariton excitation unit using the first excitation method includes a Kretchmann arrangement and an Ototo arrangement depending on the arrangement of the substrate, the metal film, and the dielectric layer. Hereinafter, the Kretchmann arrangement and the Ototo arrangement will be described with reference to FIGS. 20 and 21. FIG.

  FIG. 20 is a perspective view of the surface plasmon polariton excitation unit 301 configured by the Kretchmann arrangement. In the Kretchmann arrangement, as shown in FIG. 20, a metal film 303 is formed on a transparent substrate 302, and the side opposite to the surface of the metal film 303 in contact with the transparent substrate 302 (the side opposite to the surface on which light is incident). This surface is in contact with a dielectric layer having a refractive index smaller than that of the transparent substrate 302 (corresponding to air in the structure shown in FIG. 20). When the surface plasmon polariton excitation unit 301 excites the surface plasmon polariton, incident light 304 is incident from the transparent substrate 302 side toward the interface between the transparent substrate 302 and the metal film 303 at an appropriate angle. Then, as indicated by an arrow 305 in FIG. 20, plasmon resonance occurs in the metal film 303, and both surfaces of the metal film 303, that is, the surface in contact with the transparent substrate 302 (the surface on which light is incident) and the opposite surface. Furthermore, surface plasmon polaritons are generated as surface waves that travel in the direction of the component parallel to the metal film 303 of the wave number vector of the incident light 304 (indicated by the arrow 305 in FIG. 20).

  FIG. 21 is a perspective view of the surface plasmon polariton excitation unit 311 configured by the Otto arrangement. In the Otto arrangement, as shown in FIG. 21, a dielectric layer 306 having a refractive index lower than that of the transparent substrate 302 is formed on the transparent substrate 302, and a metal film 303 is formed on the dielectric layer 306. When the surface plasmon polariton excitation unit 311 excites the surface plasmon polariton 305, incident light 304 is directed from the transparent substrate 302 side toward the interface between the transparent substrate 302 and the metal film 303 at an appropriate angle with respect to the interface. Make it incident. Then, the surface plasmon polariton 305 is generated as a surface wave traveling in the direction of the component parallel to the metal film 303 of the wave number vector of the incident light 304, as in the Kretchmann arrangement. The difference from the Kretchmann arrangement is that the Otto arrangement excites a surface plasmon polariton in a mode having a higher effective refractive index and a shorter propagation length. For this reason, when the surface plasmon polariton 305 is excited by the Kretchmann arrangement, the refraction angle at the boundary line of the adjacent metal film of the surface plasmon polariton concentrator of the present invention cannot be increased so much, but the propagation length after refraction becomes sufficiently long. On the other hand, when the surface plasmon polariton 305 is excited by the Otto arrangement, the refraction angle at the boundary line between adjacent metal films of the surface plasmon polariton concentrator of the present invention can be increased, but the propagation length after refraction is shortened.

  In these first excitation methods, the most efficient when the polarization direction of the incident light 304 is p-polarized with respect to the interface between the transparent substrate 302 and the metal film 303 in either the Kretchmann arrangement or the Ototo arrangement. The surface plasmon polariton 305 can be excited.

  The incident angle of the incident light 304 with respect to the interface between the transparent substrate 302 and the metal film 303 is not particularly limited as long as it is an angle that can excite the surface plasmon polariton 305. However, since the surface plasmon polariton 305 converts the energy of the incident light 304, the incident angle is preferably an angle at which the energy of the incident light 304 is converted into the surface plasmon polariton 305 most efficiently. That is, the incident angle is preferably an angle at which the reflectance of the incident light 304 with respect to the metal film 303 becomes a minimum value. Thus, the optimum incident angle with the highest light utilization efficiency is around 45 degrees, although it depends on the materials of the transparent substrate 302 and the metal film 303. The optimum incident angle is realized by making the transparent substrate 302 itself a prism or by bonding the transparent substrate 302 to the prism.

  Next, the second excitation method will be described with reference to FIG. FIG. 22 is a perspective view of the surface plasmon polariton excitation unit 321 using the second excitation method. The second excitation method is a method of irradiating the edge of the metal film 303 with incident light 304 as shown in FIG. In this method, the surface plasmon polariton 305 can be excited most efficiently when the polarization direction of incident light is perpendicular to the edge. When the edge of the metal film 303 is irradiated with light, the free electrons at the edge portion are shaken by the electric field of the light, and this vibration is transmitted to the electrons on the surface of the metal film 303, thereby generating surface plasmon polaritons 305. The surface plasmon polariton 305 travels in a direction substantially perpendicular to the edge of the metal film 303.

  According to the second excitation method, the surface plasmon polariton 305 can be excited if the incident light contains a component having a polarization direction perpendicular to the edge. That is, the degree of freedom in selecting the refractive index and film thickness of the metal material is increased.

  The angle at which the incident light 304 is incident on the edge may be perpendicular to the metal film 303, and an appropriate angle with respect to the interface between the transparent substrate 302 and the metal film 303 as in the first excitation method. That is, it may be incident at an appropriate angle in order to generate surface plasmon polaritons.

  When the incident light 304 is incident on the metal film 303 perpendicularly, the transparent substrate 302 may be a parallel plane substrate, which is easier to design than a case where a prism or the like is used, and is suitable for miniaturization. Further, since the allowable range of the incident angle error is wider than that of the first excitation method, assembly is easy, and both the manufacturing time and cost can be reduced.

  On the other hand, when the incident light 304 is incident on the interface between the transparent substrate 302 and the metal film 303 at an angle suitable for exciting the surface plasmon polariton 305, the surface plasmon polariton 305 is incident on the part other than the edge. And the surface plasmon polariton 305 generated from the vibration of free electrons is excited at the edge portion. Therefore, in this case, the light utilization efficiency is higher than when the surface plasmon polariton 305 is excited using only the edge portion.

  Further, the edge, which is the incident light irradiation part in the second excitation method, can be produced at a desired position by providing an opening or a slit (hereinafter referred to as an opening or the like) in the metal film.

  Next, the third excitation method will be described with reference to FIG. FIG. 23 is a perspective view of the surface plasmon polariton excitation unit 331 using the third excitation method. As shown in FIG. 23, the third excitation method is a method of irradiating incident light 304 onto the diffraction grating 307 of the metal film 303 at an appropriate angle. When the wave number of light diffracted by the diffraction grating 307 matches the wave number of the surface plasmon polariton, the surface plasmon polariton can be excited. The incident angle is not particularly limited as long as the surface plasmon polariton 305 can be excited. However, since the surface plasmon polariton 305 converts the energy of the incident light 304, the incident angle is preferably an angle at which the energy of the incident light 304 is converted into the surface plasmon polariton 305 most efficiently. That is, the incident angle is preferably an angle at which the reflectance of the incident light 304 with respect to the metal film 303 becomes a minimum value. The grating interval of the diffraction grating 307 is about the wavelength although it depends on the incident angle and the wave number of the surface plasmon polariton.

  In the embodiment of the surface plasmon polariton concentrator of the present invention described below, when generating the surface plasmon polariton, the first excitation method may be used, and the second excitation method or the third excitation method may be used. It may be used. Further, the arrangement of the substrate, the metal film, and the dielectric layer may be a Kretchmann arrangement or an Ototo arrangement.

  Further, when the irradiation area of the incident light 304 is reduced by a lens or a beam expander, the area irradiated with the incident light can be narrowed down to an area where the distance to the near-field light output unit is less than the propagation length of the surface plasmon polariton. As a result, the utilization efficiency of the incident light 304 is increased. When the incident light 304 is narrowed by a lens, the incident light 304 includes light beams having various incident angles, and includes light beams that do not meet the optimum conditions for exciting the surface plasmon polariton. However, since the irradiation area can be reduced, there is an advantage that the utilization efficiency of the incident light 304 is high, and the generation area of the generated surface plasmon polariton can be reduced to a desired area.

[Optical assisted magnetic recording device]
Next, an optically assisted magnetic recording apparatus 60 (recording apparatus) that performs optically assisted magnetic recording using the surface plasmon polariton concentrator of the present invention will be described with reference to FIG. FIG. 16 is a perspective view of an optically assisted magnetic recording apparatus 60 using the surface plasmon polariton concentrator of the present invention.

  As shown in FIG. 16, the optically assisted magnetic recording device 60 includes a spindle 61, a drive unit 62, and a control unit 63. The optically assisted magnetic recording device 60 is for recording information on the magnetic recording medium 64 by light and magnetism.

  The spindle 61 corresponds to a spindle motor that rotates the magnetic recording medium 64.

  The drive unit 62 includes an arm 65, a rotation shaft 66, and a slider unit (information recording head) 57. The arm 65 is for moving the slider portion 57 in the substantially radial direction of the disk-shaped magnetic recording medium 64, and is a support portion of a swing arm structure. The arm 65 is supported by a rotating shaft 66 and can rotate around the rotating shaft 66. The slider portion 57 is for irradiating the magnetic recording medium 64 with near-field light and a magnetic field, and includes the surface plasmon polariton concentrator of the present invention.

  The control unit 63 includes an access circuit 69, a recording circuit 70, a spindle drive circuit 71, and a control circuit 68. The access circuit 69 is for controlling the rotational position of the arm 65 in the drive unit 62 in order to scan the slider unit 57 to a desired position on the magnetic recording medium 64. The recording circuit 70 is for controlling the intensity of near-field light and the laser beam irradiation time in the slider portion 57. The spindle drive circuit 71 is for controlling the rotational drive of the magnetic recording medium 64. The control circuit 68 controls the access circuit 69, the recording circuit 70, and the spindle drive circuit 71 in an integrated manner.

[Slider part comparison example]
As described above, in the optically assisted magnetic recording apparatus 60, the surface plasmon polariton concentrator of the present invention is provided on the slider portion 57. Therefore, first, a slider portion in which the surface plasmon polariton concentrator of the present invention is not provided will be described as a comparative example with reference to FIG. FIG. 17 is a plan view of a slider 97, which is a comparative example of the slider 57, as viewed from the magnetic recording medium 64 side.

  The slider unit 97 includes a light source 80, a near-field light excitation unit (near-field light excitation unit) 81, a magnetic field generation unit 83, a magnetic shield layer 84, a reproducing element 85, and a slider 86.

  The light source 80 is preferably small in consideration of being mounted on the slider portion 97, and a semiconductor laser is preferable.

  The near-field light excitation unit 81 is for exciting near-field light with light (propagation light) from the light source 80. The near-field light excitation unit 81 is provided in the vicinity of the center of the metal film formed on the emission surface side of the light source 80 and is a minute opening having a diameter smaller than the wavelength of light from the light source 80. Therefore, near-field light is generated in the near-field light excitation unit 81 when light is emitted from the light source 80.

  In addition, although the near-field light excitation part 81 is made into the minute opening in this embodiment, this invention is not limited to this. That is, the near-field light excitation unit 81 may be metal fine particles provided on the metal film. In addition, as a method for irradiating the near-field light excitation unit 81 with light from the light source 80, the light from the light source 80 may be obliquely incident on a grating, a prism, or the like. In the present embodiment, the light source 80 and the near-field light excitation unit 81 are integrated and mounted on the drive unit 62, but may be provided separately.

  For example, in the case where the light source 80 and the near-field light excitation unit 81 are integrated, as described above, a near-field is formed by forming a metal film directly on the emission surface of the light source 80 and performing a process such as creating a minute opening. The photoexcitation unit 81 may be created. In this case, the integrated light source 80 and near-field light excitation unit 81 are both mounted on the slider 86. As described above, when the light source 80 and the near-field light excitation unit 81 are integrated, the number of parts constituting the slider unit 97 is reduced and the assembly accuracy is increased, so that the reliability is improved. Further, there is an advantage that the slider portion 97 becomes small.

  Further, when the light source 80 and the near-field light excitation unit 81 are individually provided, it is necessary to separately provide a means for guiding the light from the light source 80 to the near-field light excitation unit 81. As a means for guiding light to the near-field light excitation unit 81, a combination of optical components such as a lens or a mirror may be used, or a waveguide such as an optical fiber may be used.

  Thus, when the light source 80 and the near-field light excitation unit 81 are individually provided, the light source 80 and the near-field light excitation unit 81 are spatially separated from each other. There is an advantage that light oscillation is stabilized without being affected by the generated heat.

  The magnetic field generator 83 is for applying a magnetic field to the magnetic recording medium 64 to record a recording mark, and is made of a magnetic material such as NiFe or NiFeTa. In general, a coil is wound around a part of the magnetic field generator 83, and the direction of the recording magnetic field is controlled by the direction of the current flowing through the coil.

  The magnetic shield layer 84 is for shielding the magnetic field of the magnetic field generator 83 so that the reproducing element 85 does not read the magnetic field of the magnetic field generator 83. The magnetic shield layer 84 may be configured using a magnetic material such as NiFe or NiFeTa, for example, similarly to the magnetic field generator 83. The magnetic shield layer 84 is provided adjacent to the slider 86 and surrounds the reproducing element 85. The magnetic shield layer 84 is provided with a magnetic field generator 83 on the side opposite to the side to which the slider 86 is connected.

  The reproducing element 85 is for reading a recording mark recorded on the magnetic recording medium 64 and for tracking at the time of recording. For example, GMR (Giant Magneto Resistive) or TMR (Tunneling Magneto Resistive) may be used as the reproducing element 85. In addition, the reproducing element 85 is provided with a magnetic shield layer 84 around it so as to prevent a magnetic field from the magnetic field generator 83 in order to detect a leakage magnetic field from the magnetic recording medium 64. Furthermore, since the slider unit 97 includes the light source 80 in addition to the magnetic field generation unit 83 and the reproducing element 85, the light source 80, which is a heat source, is used to suppress the reproducing element 85 from being deteriorated and destroyed by heat. Further, it is necessary to separate from the near-field light excitation unit 81. Therefore, the light source 80 is provided on the side opposite to the side where the magnetic shield layer 84 of the magnetic field generation unit 83 is provided. Further, the reproducing element 85 is provided on the slider 86 side in the magnetic shield layer 84.

  The slider 86 is for controlling the distance between the slider portion 97 and the magnetic recording medium 64. The slider 86 is provided with an uneven structure for controlling the flying height of the slider portion 97 from the magnetic recording medium 64 on the surface facing the magnetic recording medium 64. In FIG. 17, the uneven structure for controlling the flying height created on the slider 86 is omitted.

The near-field light excited by the near-field light excitation unit 81 and the magnetic field generated by the magnetic field generation unit 83 decrease in intensity as the distance from the generation position, and the intensity distribution widens, so the near-field light excitation unit 81 and the magnetic field generation unit 83. Is preferably as close to the magnetic recording medium 64 as possible. Furthermore, it is preferable that the reproducing element 85 be as close as possible to the magnetic recording medium 64 in order to reduce the influence of the leakage magnetic field from the adjacent mark when reading the leakage magnetic field from the magnetic recording medium 64. That is, it is preferable that the slider portion 97 be as close to the magnetic recording medium 64 as possible by the slider 86, and is generally about several nanometers. As a material constituting the slider 86, an AlTiC substrate or a ZrO ₂ substrate is preferably used. Further, in order to integrally form the semiconductor laser as the light source 80 with the slider 86, the slider 86 may be made of a semiconductor laser material.

  In the slider unit 97 of the comparative example, the surface plasmon polariton excited in the near-field light excitation unit 81 proceeds in a direction parallel to the polarization direction of the excited light (arrow in the figure), that is, in a direction parallel to the active layer. . For this reason, the near-field light is generated at a position away from the magnetic field generator 83, which is not preferable for applying the slider 97 to the optically assisted magnetic recording apparatus.

  In the slider portion 97, it is possible to excite the surface plasmon polariton 4 so as to advance to the magnetic field generating portion 83 by rotating the light source 80 by 90 °. In this case, the light source 80 is integrated with the slider portion. Since it is difficult to form, the components other than the light source 80 are integrally formed and then attached to the side surface of the magnetic field generator 83. However, when the light source 80 is attached later, unless the position of the light source 80 is precisely adjusted with respect to the position of the magnetic field generating unit 83, the positions of the near-field light and the recording magnetic field are shifted, and the recording mark spreads. cause.

[First Example of Slider]
Therefore, in order to propagate the surface plasmon polariton 4 excited in the near-field light excitation unit 81 to the vicinity of the magnetic field generation unit 83, the configuration of the slider unit 57 using the surface plasmon polariton concentrator of the present invention will be described with reference to FIG. I will explain. FIG. 18 is a plan view of the slider portion 57 according to the first embodiment of the slider portion as viewed from the magnetic recording medium 64 side. In FIG. 18, the uneven structure for controlling the flying height provided on the slider 86 is omitted. Further, constituent elements having the same functions as constituent elements in the slider portion 97 of the comparative example are denoted by the same reference numerals and description thereof is omitted.

  The slider unit 57 of this embodiment includes a surface plasmon polariton concentrator 1, a light source 80, a near-field light excitation unit 81, a near-field light output unit (near-field light output means) 82, a magnetic field generation unit 83, A magnetic shield layer 84, a reproducing element 85, and a slider 86 are mounted. Note that any of the above-described surface plasmon polariton concentrators 1, 11, 1311, 41, and 51 may be mounted on the slider portion 57 of the present embodiment, but here, the surface plasmon polariton concentrator 1 will be described.

  In the surface plasmon polariton concentrator 1, the first metal film 2 and the second metal film 3 are directly formed on the emission surface of the light source 80, and a minute opening is provided in the first metal film 2 as the near-field light excitation unit 81. That is, in the slider part 57 of this embodiment, the emission surface of the light source 80 has a role as the metal film support member 5 of the surface plasmon polariton concentrator 1. Note that the configuration of the surface plasmon polariton concentrator 1 formed on the emission surface of the light source 80 is not limited to the above-described configuration, and the emission surface of the light source 80 is made of a material having translucency as the metal film support member 5. The first metal film 2 and the second metal film 3 may be formed on the dielectric layer after forming the dielectric layer.

  The near-field light output unit 82 is a metal protrusion provided on the surface of the surface plasmon polariton concentrator 1 facing the magnetic recording medium 64 and in the vicinity of the magnetic field generation unit 83. The near-field light output unit 82 converts the surface plasmon polariton 4 propagated and focused by the surface plasmon polariton concentrator 1 into near-field light (local surface plasmon polariton), and records the near-field light on the magnetic recording medium 64. By irradiating the surface, the magnetic recording medium 64 is locally heated, and a recording mark is recorded only on the local portion.

  By providing a metal protrusion as the near-field light output unit 82, the surface on which the surface plasmon polariton 4 propagates is disposed to face the magnetic recording medium 64, and the near-field light generated at the minute aperture of the near-field light excitation unit 81 is magnetic. Even when the recording medium 64 is irradiated, the strength is attenuated by the height of the metal protrusion, and the influence on the magnetic recording medium 64 can be reduced.

  Further, the near-field light output unit 82 may be an opening, a slit, or an edge of the metal film itself. Further, it is preferable that the near-field light output unit 82 has a configuration in which the propagation distance of the surface plasmon polariton 4 from the near-field light excitation unit 81 is shorter than the propagation length of the surface plasmon polariton 4. As a result, the near-field light output unit 82 can generate near-field light having a high intensity because the intensity attenuation of the surface plasmon polariton 4 is small.

  When the surface plasmon polariton concentrator 41 of the fifth embodiment or the surface plasmon polariton concentrator 51 of the sixth embodiment is mounted on the slider unit 57, the slit 44 or the near-field light output unit 54 is the near-field light output unit. 82 is used.

  Since the constituent elements other than those described above have the same configuration and arrangement as the slider portion 97 of the comparative example, description thereof is omitted here.

  With the above configuration, the surface plasmon polariton 4 excited in the near-field light excitation unit 81 can be propagated to the vicinity of the magnetic field generation unit 83 with a simple configuration.

  Further, by using the surface plasmon polariton concentrator of the present invention, even when the light source 80 is rotated by 90 °, after the light source 80 other than the light source 80 is integrally formed, it is attached to the side surface of the magnetic field generator 83. In addition, the position of the near-field light excitation unit 81 can be precisely adjusted with respect to the position of the magnetic field generation unit 83.

[Second Embodiment of Slider]
Next, a slider portion 67 according to a second embodiment of the slider portion will be described with reference to FIG. FIG. 19 is a plan view of the slider portion 67 according to the second embodiment of the slider portion as viewed from the magnetic recording medium 64 side. In FIG. 19, the uneven structure for controlling the flying height provided on the slider 86 is omitted.

  Each component of the slider portion 67 according to the second embodiment has the same function as each component of the slider portion 57 of the first embodiment, and only the arrangement is different. Hereinafter, the arrangement of the slider portion 67 will be described.

  As shown in FIG. 19, after the slider 86 and the magnetic field generator 83 are integrally formed, the light source 80 is attached to the side wall of the slider 86. At this time, the emission surface of the light source 80 is provided so as to be perpendicular to the magnetic recording medium 64. The surface plasmon polariton concentrator 1 is formed from the emission surface of the light source 80 to the magnetic field generator 83. Further, the magnetic shield layer 84 and the reproducing element 85 are formed on the side opposite to the side on which the slider 86 of the magnetic field generator 83 is provided.

  With the above configuration, the light emitted from the emission surface of the light source 80 is converted into the surface plasmon polariton 4 in the near-field light excitation unit 81 provided in the surface plasmon polariton concentrator 1, and the surface plasmon polariton 4 is converted into the magnetic recording medium 64. On the other hand, the light propagates to the near-field light output unit 82 in a plane perpendicular to the surface.

  As described above, since the emission surface of the light source 80 is in a plane perpendicular to the magnetic recording medium 64, it is possible to suppress the propagation light from the light source 80 from being applied to the magnetic recording medium 64. Therefore, background noise can be suppressed.

  Further, since the surface on which the surface plasmon polariton 4 of the surface plasmon polariton concentrator 1 propagates does not face the magnetic recording medium 64, a near-field light excitation unit 81 is provided in advance by providing a metal protrusion as the near-field light output unit 82. Even if the height of the near-field light output unit 82 is not changed, the height from the magnetic recording medium 64 to the near-field light output unit 82 and the magnetic field generation unit 83 can be made equal. In addition, since the surface on which the surface plasmon polariton 4 of the surface plasmon polariton concentrator 1 propagates is not directed to the magnetic recording medium 64, the slider 67 of this embodiment is close to the edge part of the surface plasmon polariton concentrator 1 The field light output unit 82 can also suppress the surface plasmon polariton 4 propagating through the surface plasmon polariton concentrator 1 from being irradiated to the magnetic recording medium 64. Therefore, background noise can be suppressed.

  Here, the configuration in which the surface plasmon polariton concentrator of the present invention is applied to an optically assisted magnetic recording apparatus has been described, but the application example of the surface plasmon polariton concentrator of the present invention is not limited thereto. In other words, the slider portion on which the surface plasmon polariton concentrator of the present invention is mounted does not include the magnetic field generator 83 and the reproducing element 85, and is an optical recording medium only with near-field light irradiated from the near-field light output portion 82. Alternatively, the recording may be performed on a photosensitive recording medium.

  When recording is performed only with the near-field light irradiated from the near-field light output unit 82, a small mark can be recorded with the near-field light generated by the surface plasmon polariton concentrator of the present invention, and the recording density can be increased. Moreover, since the near-field light obtained by converting the surface plasmon polariton 4 focused by the surface plasmon polariton concentrator of the present invention by the near-field light output unit 82 has a high intensity, the transfer rate can be increased. In addition, although the intensity of near-field light attenuates as it moves away from the generation position, the surface plasmon polariton concentrator of the recording apparatus has a sufficiently strong intensity at the generation position, so that it is possible to give a margin to the distance from the recording target. .

[Operation of Optically Assisted Magnetic Recording Device 60]
Next, the operation of the optically assisted magnetic recording device 60 will be described with reference to FIG.

  When the optically assisted magnetic recording device 60 records or reproduces information on the magnetic recording medium 64, that is, during operation, the spindle drive circuit 71 in the control unit 63 moves the spindle 61 on which the magnetic recording medium 64 is installed. Rotate at an appropriate speed. Further, the access circuit 69 in the control unit 63 scans the slider units 57 and 67 described above to a desired location on the magnetic recording medium 64 by moving the drive unit 62.

  The recording circuit 70 causes the light source 80 to emit light at a predetermined intensity and time interval, and causes the magnetic field generator 83 to generate a magnetic field. Specifically, the recording circuit 70 emits light from the light source 80 to irradiate the near-field light excitation unit 81 with light, and the near-field light excitation unit 81 excites the surface plasmon polariton 4. The excited surface plasmon polariton 4 is propagated and focused from the near-field light excitation unit 81 to the near-field light output unit 82 by the surface plasmon polariton concentrators 1, 11, 21, 31, 41, 51, and the near-field light output unit 82. , The magnetic recording medium 64 is irradiated as local surface plasmon polaritons. At substantially the same time, the recording circuit 70 can irradiate the magnetic recording medium 64 with the near-field light and the magnetic field at the same time by causing the magnetic field generator 83 to generate a magnetic field.

  Even if the light source 80 always emits light, if the direction of the magnetic field generated by the magnetic field generator 83 is modulated, recording can be performed on the magnetic recording medium 64 corresponding to the direction of the magnetic field.

  When the position of the near-field light and the magnetic field is deviated, it is preferable that the magnetic recording medium 64 be irradiated with the near-field light before the magnetic field.

  As described above, the mark is recorded on the magnetic recording medium 64 by the intensity corresponding to the light emission of the light source 80 and the local magnetic field generated at time intervals. In the control circuit 68, the light emission of the light source 80, the operation of the drive unit 62, and the rotation of the spindle 61 are summarized, and instructions are given to each circuit so that desired recording can be performed at a desired location.

  The magnetic recording medium 64 is a magneto-optical recording medium that is recorded by light and magnetism. At the time of recording, the recording layer of the magnetic recording medium 64 is heated by near-field light generated from the near-field light output unit 82 to generate a magnetic field. By applying a magnetic field generated from the portion 83, the direction of the magnetic moment inside the recording layer is reversed. The portion where the magnetic moment is reversed becomes a recording mark.

  The size of the recording mark on the magnetic recording medium 64 is determined by the overlap between the region sufficiently heated by the near-field light and the region irradiated with the magnetic field. Therefore, the recording density can be improved by using the near-field light output unit 82 that generates near-field light having a small spot diameter. Further, the recording mark formation speed of the magnetic recording medium 64, that is, the recording speed depends on the heating rate of the recording layer, and this heating rate depends on the intensity of the near-field light applied. That is, when the intensity of the irradiated near-field light is strong, the time for heating the magnetic recording medium 64 to the required temperature is shortened, so that the transfer rate can be improved.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be suitably used for an optical recording apparatus or an optically assisted magnetic recording apparatus that records on a recording medium by optical recording or optically assisted magnetic recording.

It is the top view and perspective view which show schematic structure of the surface plasmon polariton focusing device of 1st Embodiment of this invention. It is a graph which shows the change of the effective refractive index and propagation length of each metal film at the time of changing the film thickness of the metal film comprised with Al, and the metal film comprised with Ag. 25, for example, when the first metal film and the second metal film are each composed of Ag, the thickness of the first metal film is 100 nm, and the thickness of the second metal film is 100 nm or less. FIG. 5 is a diagram showing edge intensity ratios and coupling efficiencies at the edges of the first metal film when surface plasmon polaritons in a symmetry mode with a frequency of 7.5 × 10 ¹⁴ Hz propagate from the first metal film to the second metal film. . Effective refractive index and propagation of each metal film when the refractive index of the dielectric provided on the metal film composed of Au, the metal film composed of Al, and the metal film composed of Ag is changed It is a graph which shows change of length. It is the top view and perspective view which show schematic structure of the surface plasmon polariton focusing device of 2nd Embodiment of this invention. It is the top view and perspective view which show schematic structure of the surface plasmon polariton focusing device of 3rd Embodiment of this invention. It is the top view and perspective view which show schematic structure of the surface plasmon polariton focusing device of 4th Embodiment of this invention. It is a perspective view which shows schematic structure of the surface plasmon polariton focusing device of 5th Embodiment of this invention. It is a figure which shows electric field strength distribution of the surface plasmon polariton 4 on the surface of the 1st metal film and 2nd metal film of the surface plasmon polariton focusing device of 5th Embodiment. (A) is a figure which shows phase distribution of the electric field component of the advancing direction of surface plasmon polariton in a surface plasmon polariton concentrator, (b) is a figure of the 1st metal film and 2nd metal film in a surface plasmon polariton concentrator. It is a figure which shows phase distribution of an electric field component perpendicular | vertical to the surface. It is a graph which shows the relationship between the half major axis of the elliptical arc part of the boundary line formed between the 1st metal film and the 2nd metal film in the surface plasmon polariton focusing device of 5th Embodiment, and a focal distance. It is a graph which shows the relationship between the center distance of the elliptical arc part of the boundary line formed between the 1st metal film and the 2nd metal film in the surface plasmon polariton focusing device of 5th Embodiment, and a focal distance. In the surface plasmon polariton concentrator of 5th Embodiment, it is the perspective view which showed providing the slit in order to scatter surface plasmon polariton. It is a perspective view which shows schematic structure of the surface plasmon polariton focusing device of 6th Embodiment of this invention. (A)-(e) is sectional drawing which shows the manufacturing method of the surface plasmon polariton focusing device of this invention. 1 is a perspective view of an optically assisted magnetic recording apparatus using a surface plasmon polariton concentrator of the present invention. It is the top view which looked at the slider part which is a comparative example of a slider part from the magnetic recording medium side. It is the top view which looked at the slider part which concerns on 1st Example of a slider part from the magnetic recording medium side. It is the top view which looked at the slider part which concerns on 2nd Example of a slider part from the magnetic recording medium side. It is a perspective view of the surface plasmon polariton excitation part comprised by Kretchmann arrangement | positioning. It is a perspective view of the surface plasmon polariton excitation part 311 comprised by Otto arrangement | positioning. It is a perspective view of the surface plasmon polariton focusing device using the 2nd excitation method. It is a perspective view of the surface plasmon polariton focusing device using the 3rd excitation method. It is a perspective view which shows the conventional concentrator which focuses surface plasmon polariton. It is a perspective view which shows schematic structure of the conventional metal film which has two types of film thickness which propagates and bends a surface plasmon polariton wave. It is a perspective view which shows the surface plasmon lens for condensing surface plasmon polariton.

Explanation of symbols

1, 11, 21, 31, 41, 51 Surface plasmon polariton concentrator 2, 12, 22, 32, 42, 52 First metal film 3, 13, 23, 33, 43, 53 Second metal film 4 Surface plasmon polariton 5 Metal film support member 6 Mask 7 Photoresist 44 Slit 54 Near-field light output section (Near-field light output means)
55 Objective lens (metal film support member)
57, 67, 97 Slider section (information recording head)
60 Optically assisted magnetic recording device (recording device)
61 Spindle 62 Drive unit 63 Control unit 64 Magnetic recording medium 65 Arm 66 Rotating shaft 68 Control circuit 69 Access circuit 70 Recording circuit 71 Spindle drive circuit 81 Near-field light excitation unit (near-field light excitation means)
82 Near-field light output section (Near-field light output means)
83 Magnetic field generator 84 Magnetic shield layer 85 Reproducing element 86 Slider 301, 311, 321 Surface plasmon polariton excitation unit 302 Substrate 303 Metal film 304 Incident light 306 Dielectric layer 307 Diffraction grating

Claims (23)

In a surface plasmon polariton concentrator that focuses surface plasmon polaritons,
A metal film support member;
At least two metal films formed on a predetermined surface of the metal film support member, adjacent to each other and having an effective refractive index different from the adjacent metal films,
In each of the metal films, at least a part of the boundary line between the adjacent metal films is a curve, and the surface opposite to the surface in contact with the metal film support member and the adjacent metal film A surface plasmon polariton concentrator characterized in that a surface opposite to a surface in contact with the metal film support member is flush with the surface.   2. The surface plasmon polariton concentrator according to claim 1, wherein each of the metal films has the same thickness. The curved portion of the boundary line is formed between the first metal film and the second metal film of each metal film,
When the relationship between the effective refractive index na of the first metal film and the effective refractive index nb of the second metal film is na <nb, the curved line portion of the boundary line is that the second metal film is the first metal film. The surface plasmon polariton concentrator according to claim 1, wherein the surface plasmon polariton concentrator is formed to have a convex shape.   The surface plasmon polariton concentrator according to claim 3, wherein when the surface plasmon polariton propagates from the first metal film to the second metal film, a curved portion of the boundary line is an elliptical arc.   5. The surface plasmon polariton concentrator according to claim 4, wherein the propagation direction of the surface plasmon polariton is parallel to a line connecting two focal points of the elliptical arc.   The surface plasmon polariton concentrator according to claim 3, wherein when the surface plasmon polariton propagates from the second metal film to the first metal film, a curved portion of the boundary line is a hyperbola.   The surface plasmon polariton concentrator according to claim 6, wherein the propagation direction of the surface plasmon polariton is parallel to a line connecting two focal points of the hyperbola.   The surface plasmon polariton concentrator according to any one of claims 1 to 7, wherein at least two boundary lines are formed so as to block a propagation direction of the surface plasmon polariton.   The surface plasmon polariton focusing according to claim 1, wherein a distance from a propagation start position or excitation position of the surface plasmon polariton to a position where the surface plasmon polariton is focused is shorter than a propagation length of the surface plasmon polariton. vessel. Two or more surface plasmon polariton concentrators according to any one of claims 1 to 9 are combined,
The surface plasmon polariton concentrator focuses the surface plasmon polariton at one point by the surface plasmon polariton concentrator.   The surface plasmon polariton concentrator according to any one of claims 1 to 10, wherein an incident beam diameter of the surface plasmon polariton with respect to the curved part of the boundary line is shorter than a length of the curved part of the boundary line. . In an information recording head provided in a recording apparatus for recording on a recording medium,
A surface plasmon polariton concentrator according to claims 1-11;
A light source;
Near-field light excitation means for converting light emitted from the light source into surface plasmon polaritons;
A near-field light output means for irradiating the recording medium with near-field light,
The information recording head, wherein the surface plasmon polariton concentrator focuses the surface plasmon polariton from the near-field light excitation unit to the near-field light output unit.   13. The information recording head according to claim 12, wherein the near-field light output means is provided on a metal film on which the surface plasmon polariton is focused, among the metal films of the surface plasmon polariton concentrator.   14. The information recording head according to claim 13, wherein the near-field light output means is provided at a position where the surface plasmon polariton of the metal film is focused by the surface plasmon polariton.   15. The information recording head according to claim 13, wherein the near-field light output means is a metal end of the metal film or an opening, slit, or metal protrusion provided in the metal film.   16. The information recording head according to claim 14, wherein the metal film on which the surface plasmon polariton is focused among the metal films has a long propagation length of the surface plasmon polariton. The metal film support member of the surface plasmon polariton concentrator is a substrate having translucency,
The near-field light excitation means is the substrate, and surface plasmon polaritons are applied to at least one of the metal films by obliquely incident light from the side on which the substrate is provided with respect to the surface plasmon polariton concentrator. The information recording head according to claim 12, wherein the information recording head is excited. The predetermined surface of the metal film support member in the surface plasmon polariton concentrator is an emission surface that emits light of the light source,
The information recording head according to claim 12, wherein the near-field light excitation unit is provided on at least one of the metal films. In a recording apparatus for recording on a recording medium,
A recording apparatus comprising the information recording head according to claim 12. A control unit for controlling the position of the information recording head and the recording medium;
The recording apparatus according to claim 19, wherein the control unit controls a distance between the near-field light output unit and the recording medium to be equal to or less than a wavelength of a surface plasmon polariton. The recording medium is a magnetic recording medium having a high coercive force that is resistant to thermal fluctuations,
A magnetic field generator for applying a magnetic field to the recording medium;
21. The magnetic field generation unit according to claim 19 or 20, wherein the magnetic field generator applies a magnetic field to the recording medium at the same time as the recording medium is irradiated with the near-field light from the near-light output unit. Recording device. Comprising a reproducing element for reading information recorded on the recording medium,
The recording apparatus according to any one of claims 19 to 21, wherein the reproducing element is provided at a position distant from the light source. The recording medium has photosensitivity,
The recording apparatus according to claim 19, wherein the recording medium is sensitized by near-field light irradiated from the surface plasmon polariton concentrator and information is recorded.