JP4481243B2 - Electromagnetic field conversion element, electromagnetic field generating unit, and recording apparatus - Google Patents

Description

  The present invention relates to an electromagnetic field conversion element that converts light into an electromagnetic field.

  Optical disks such as CD and DVD, and magneto-optical disks such as MD and MO are used as information recording media for recording images, videos, text data, and the like. In such optical disks and magneto-optical disks, it is desired to increase the recording density as the amount of data to be recorded increases. Also, optical assist technology has been developed for improving the recording density of magnetic recording media such as hard disks.

  In optical recording apparatuses that record information on these recording media, the size of the light spot irradiated on the recording medium determines the recording density, and the intensity of the light determines the transfer rate. Therefore, in an optical recording apparatus, it is desired to irradiate a recording medium with a stronger intensity with a smaller spot in order to improve the recording density. However, with normal light (propagating light), the spot size can only be reduced to the diffraction limit and is limited to about the wavelength.

  Therefore, the use of a local electromagnetic field called near-field light has attracted attention as a method for forming a small spot exceeding the diffraction limit. This local electromagnetic field is obtained, for example, by allowing propagating light to enter an opening having a diameter smaller than the wavelength, and is localized only in the vicinity of the opening and does not propagate. In this case, since the light localization method is determined by the diameter of the aperture, if the aperture diameter is reduced, a small spot that greatly exceeds the diffraction limit can be obtained.

  However, in this method, light that cannot be focused on a spot having a diameter of less than the wavelength is incident on the aperture of the wavelength or less, so that the light utilization efficiency is deteriorated. That is, if the light source is set to the same intensity as the conventional one, the obtained electromagnetic field intensity becomes weaker by the size of the opening relative 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, and the intensity on the recording surface further decreases.

  In order to solve this, there is a method in which an opening is made of a metal film, surface plasmon polaritons are generated, and strong near-field light is generated by amplifying the surface plasmon polaritons.

  Hereinafter, an element that converts normal light into a local electromagnetic field is referred to as an electromagnetic field conversion element, and a ratio of the intensity of the local electromagnetic field to the incident light intensity is referred to as incident light-electromagnetic field conversion efficiency.

  For example, in Patent Document 1, as shown in FIG. 21, light is emitted using an electromagnetic field conversion element 200 that irradiates a metal film 107 provided with a minute opening 100 and a periodic topography 108 to generate a local electromagnetic field. A recording / reproducing method has been proposed.

In the electromagnetic field conversion element 200, surface plasmon polariton is excited on the surface of the metal film 107 when light is incident on the opening 100 having a size equal to or smaller than the wavelength of light. At this time, the surface plasmon polaritons are amplified by the periodic topography 108 around the opening 100. Thereby, the near-field light intensity generated in the opening 100 is increased, and the transfer rate can be increased.
JP 2001-291265 A (released on October 19, 2001) Surface Plasmons on smooth and rough surfaces and on gratings, Heinz Raether, Springer-Verlag, 1988 p.118-p.123

  However, such periodic topography must be formed over many periods with a submicron width. Also, if the topography is not formed on the light incident side and the light emission side of the surface of the metal film, the effect is weak, but since a substrate supporting the metal film is required on the light incident side, the incident surface is periodically It was difficult to make a simple topography. Further, when dust or the like accumulates in the periodic topography, there is a problem that the intensity of the surface plasmon polariton that is excited and amplified is attenuated and changes with time occur.

  The present invention has been made in view of the above-mentioned conventional problems, and has an electromagnetic field conversion element that generates a local electromagnetic field with a simple configuration and a large strength, and a high recording density and high transfer using the electromagnetic field conversion element. It is an object of the present invention to provide a recording apparatus or recording / reproducing apparatus having a rate.

In order to solve the above problems, an electromagnetic field conversion element according to the present invention is an electromagnetic field conversion element that converts incident light into surface plasmon polariton and extracts the surface plasmon polariton as an electromagnetic field, and a transparent substrate having translucency, A first metal film and a second metal film are provided on the surface of the transparent substrate, and the first metal film and the second metal film are formed of different materials , and the first metal film or the second metal is formed. At least one of the films converts light incident from the transparent substrate side into the surface plasmon polariton so that the first metal film and the second metal film are in contact with different regions on the surface of the transparent substrate. It is provided in.

  According to the above configuration, the surface plasmon polariton generated by light in the first metal film and / or the second metal film is reflected at the boundary between the first metal film and the second metal film, and the surface plasmon polariton is generated. Amplified surface plasmon polaritons are generated on the surface of the metal film.

  This phenomenon is reflected when the surface plasmon polariton that has propagated and traveled through the first metal film in contact with the second metal film reaches the second metal film, and is reflected by the second metal film. One factor is considered to be strengthening each other by superimposing with surface plasmon polariton that has progressed on the surface.

  Thus, the electromagnetic field conversion element of the present invention amplifies the surface plasmon polariton while having a simple configuration in which at least two kinds of metal films, a first metal film and a second metal film, are arranged on a transparent substrate. A strong local electromagnetic field can be obtained.

  The electromagnetic field conversion element having the above-described periodic topography has a problem that the intensity of the surface plasmon polariton to be excited and amplified is attenuated when dust or the like accumulates in the topography. However, the electromagnetic field conversion element of the present invention can amplify the intensity of the surface plasmon polariton while having a flat surface, and therefore has the effect that dust and the like are less likely to collect and the above-described problems are less likely to occur.

  Of the first metal film and the second metal film, the metal film that converts light incident from the transparent substrate side into surface plasmon polaritons preferably has a higher dielectric constant than one of the metal films. In other words, the electromagnetic field conversion element according to the present invention is configured to excite surface plasmons on a metal film having a large dielectric constant in the first metal film or the second metal film and to proceed to a metal film having a small dielectric constant. It is preferable that

  According to the above configuration, when the surface plasmon polariton generated by light in the first metal film or the second metal film is transmitted to the other metal film, the electric field strength is enhanced due to the difference in dielectric constant. Such enhancement occurs when, for example, surface plasmon polaritons are generated in the first metal film, and in the surface plasmon polaritons that have progressed to the second metal film, they are parallel to the surface of the electric field on the surface of the second metal film. One factor is that the intensity of the component perpendicular to the boundary line increases due to the difference in dielectric constant between the first metal film and the second metal film.

  The first metal film is preferably formed between at least two second metal films and has at least two boundary lines.

  According to the above configuration, the surface plasmon polariton generated in the first metal film propagates on the surface of the first metal film, reaches the second metal film, and is reflected. The reflected surface plasmon polariton propagates on the surface of the first metal film, and is reflected again by a second metal film different from the first metal film reflected first. As described above, the surface plasmon polaritons reflected by the separate second metal films overlap on the first metal film formed between the second metal films, thereby amplifying the surface plasmon polaritons. According to the above configuration, the surface plasmon polariton generated in the second metal film also propagates to the surface of the first metal film and is reflected by the two second metal films, thereby overlapping and amplifying. To do.

  As described above, with the above configuration, the surface plasmon polariton is superposed, and the amplification effect is further increased.

  Moreover, it is preferable that the refractive index of the material of the metal film in contact with at least the second metal film is smaller than the refractive index of the material of the second metal film.

  According to the above configuration, since the refractive index of the metal film in contact with the second metal film is smaller than the refractive index of the second metal film, the surface plasmon polariton at the boundary between the second metal film and the metal film in contact with the second metal film. Since the reflection efficiency is increased, the amplification effect of the surface plasmon polariton can be further enhanced.

  Furthermore, when the refractive index of the metal film in contact with the second metal film is smaller than the refractive index of the second metal film, the dielectric constant of the metal film in contact with the second metal film is greater than the dielectric constant of the second metal film. Becomes smaller. Therefore, when surface plasmon polaritons are excited by the second metal film, when the surface plasmon polaritons proceed from the second metal film to the metal film in contact with the second metal film, the electric field on the surface of the second metal film is increased. The intensity of the component parallel to the surface and perpendicular to the boundary line is increased.

  The boundary lines between the first metal film and the second metal film are preferably linear and parallel to each other.

  According to the above configuration, since the superposition efficiency of the surface plasmon polaritons on the surface of the metal film in contact with the second metal film is good, there is an effect that the amplification effect of the surface plasmon polaritons can be further enhanced.

  In addition, a dielectric layer having a refractive index smaller than that of the transparent substrate is formed between the transparent substrate and the first metal film and / or between the transparent substrate and the second metal film. It may be.

  According to the above configuration, the surface plasmon polariton is generated on the surface of the first metal film in contact with the dielectric layer, and propagates and travels on the surface of the first metal film in contact with the dielectric layer. That is, since the metal surface on which surface plasmon polaritons are generated and propagated is protected by the substrate and the dielectric layer, there is an effect that scratches and dirt can be prevented.

  In addition, it is desirable that at least one local electromagnetic field generation unit that scatters the surface plasmon polariton is provided on the surface of the first metal film and / or the second metal film.

  According to the above configuration, in order to generate a local electromagnetic field by scattering surface plasmon polaritons by the local electromagnetic field generator, the position where the local electromagnetic field is generated can be selected depending on the position where the local electromagnetic field generator is provided. it can. Further, the spot size of the local electromagnetic field can be adjusted according to the shape of the local electromagnetic field generator.

  In addition, the local electromagnetic field generation unit is formed within a range of the propagation length of the surface plasmon polariton from the boundary line between the first metal film and the second metal film. Is desirable.

  According to the above configuration, since the surface plasmon polariton is reflected at the boundary between the second metal film and the metal film in contact with the second metal film, the distance to propagate to the local electromagnetic field generation unit is sufficiently short. Attenuation due to propagation and progression of plasmon polaritons is small. That is, a surface plasmon polariton having a high intensity can be extracted as a local electromagnetic field.

  The local electromagnetic field generator may be at least one edge of the first metal film and / or the second metal film.

  According to the above configuration, since the local electromagnetic field can be generated without providing a special member, the configuration of the electromagnetic field conversion element can be simplified.

  Further, a part of the first metal film in contact with the second metal film is formed so as to divide the first metal film from a boundary with the second metal film, and is in contact with the second metal film. The edge of a part of the first metal film may be the local electromagnetic field generator.

  According to the above configuration, the local electromagnetic field can be generated without providing a special member, and the spot size of the generated local electromagnetic field can be reduced by changing the width of the metal film that divides the second metal film. Can be changed. Furthermore, the direction of approach to the recording medium can be freely selected.

  The local electromagnetic field generation unit may be an opening or an edge of a slit provided in the first metal film and / or the second metal film.

  According to the above configuration, the shape of the generated local electromagnetic field can be adjusted by changing the shapes of the opening and the slit.

  The local electromagnetic field generation unit may be a protrusion provided on the first metal film and / or the second metal film.

  According to the said structure, the generation | occurrence | production position of a local electromagnetic field can be selected by the position which forms the said metal protrusion. In addition, the shape of the local electromagnetic field can be changed depending on the shape of the metal protrusion, and the degree of freedom in designing the electromagnetic field conversion element is increased. Furthermore, the surface plasmon polariton on the surface of the metal film can be prevented from overlapping the local electromagnetic field as a background by the distance between the metal film on which the metal protrusion is formed and the tip of the metal protrusion. Also, when bringing the local electromagnetic field closer to the local electromagnetic field irradiation target, the required adjustment accuracy such as adjustment of the parallelism between the irradiation target and the electromagnetic field conversion element is eased, so a recording apparatus with fewer members is manufactured. Manufacturing costs can be reduced.

  In the electromagnetic field generating unit including the electromagnetic field conversion element according to the present invention, the incident light irradiated from the light source is the first metal film and / or the second metal film with respect to the first metal film and / or the second metal film. It is preferable that the incident light is incident at an angle at which the reflected light intensity from the two metal films becomes a minimum value.

  With the above-described configuration, there is an effect that utilization efficiency of incident light increases and incident light-electromagnetic field conversion efficiency increases.

  The polarization direction of the incident light is preferably p-polarized light.

  According to the said structure, since the conversion efficiency from incident light to surface plasmon polariton increases, there exists an effect that incident light-electromagnetic field conversion efficiency becomes high.

  Further, the incident light irradiating part irradiated with the incident light may be a surface of the first metal film and / or the second metal film on the transparent substrate side, and the first metal film and / or the above-mentioned It may be the edge of the second metal film. In this case, since no special member is provided as the incident light irradiation part, the surface plasmon polariton can be excited with a simple configuration.

  The incident light irradiation unit may be an opening or a slit provided in the first metal film and / or the second metal film.

  According to the above configuration, since the shape of the surface plasmon polariton generated from the opening or slit can be changed depending on the shape of the opening or slit, the degree of freedom in designing the electromagnetic field conversion element is increased. Furthermore, according to the above configuration, the position where the surface plasmon polariton is generated can be selected by selecting the position of the opening or the slit.

  In the above configuration, the incident light is irradiated perpendicularly to the first metal film and / or the second metal film, and the polarization direction of the incident light is perpendicular to the edge of the opening or slit. It is preferable.

  According to the above configuration, incident light can be efficiently converted into surface plasmon polariton.

  Moreover, the electromagnetic field generation unit of the present invention is an electromagnetic field generation unit including the electromagnetic field conversion element and the light source, and the electromagnetic field conversion element and the light source may be provided at positions separated from each other.

  According to the above configuration, since the light source and the electromagnetic field conversion element are spatially separated from each other, the light source is not affected by the heat generated by the electromagnetic field conversion element, and the light oscillation is stabilized. Play.

  In the electromagnetic field generation unit of the present invention, the electromagnetic field conversion element may be provided in a light output portion of the light source.

  According to the above configuration, since the electromagnetic field conversion element is integrated with the light source, the number of components is small, the assembly accuracy is increased, and the reliability is improved.

  The electromagnetic field generating unit is preferably provided with means for minimizing light from the light source, and the means may be a lens or a beam expander.

  According to the above configuration, when a lens is used, the irradiation area of incident light is reduced. Therefore, the incident light is a range in the vicinity of the boundary between the metal films, that is, the surface plasmon polariton excited by the incident light. It becomes easy to irradiate the range below the propagation length.

  In addition, when a beam expander is used, light having an optimum angle for exciting the surface plasmon polariton can be irradiated with a small irradiation area, although not as much as a lens.

  The recording apparatus of the present invention is an apparatus that includes the electromagnetic field generating unit and records or reproduces information on a recording medium, and the distance between the electromagnetic field conversion element and the recording surface of the recording medium is the electromagnetic field. It is preferable that the wavelength is controlled to a quarter or less of the wavelength of the local electromagnetic field generated in the conversion element.

  With the above configuration, since the recording medium can be irradiated before the local electromagnetic field generated by the electromagnetic field conversion element is significantly attenuated, the transfer rate can be improved.

  In addition, the recording apparatus can efficiently perform recording and reproduction with respect to a magneto-optical recording medium by using a local electromagnetic field generated from the electromagnetic field conversion element by mounting a magnetic recording / reproducing head. It becomes possible.

  The electromagnetic field conversion element of the present invention includes a first metal film and a second metal film that amplifies the surface plasmon polariton on the surface of the transparent substrate, and the light incident from the transparent substrate side is the first metal film. Either the first metal film and / or the second metal film is converted into the surface plasmon polariton, and the second metal film is provided in contact with the first metal film, and the first metal film The material of at least the region in contact with the second metal film is different from the material of the second metal film.

  Therefore, the surface plasmon polariton generated in the first metal film can be amplified by another metal film, and a large local electromagnetic field can be obtained.

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

  First, a method for exciting surface plasmon polaritons in an electromagnetic field conversion element, which is a premise of the present embodiment, will be described with reference to FIGS.

  The electromagnetic field conversion element of the present invention includes at least a first metal film and a second metal film on a transparent substrate. The first and second metal films are formed of different materials, that is, different metal materials. The surface plasmon polariton is generated in at least one of the first metal film and the second metal film. Hereinafter, in the electromagnetic field conversion element of the present invention, when there is no particular distinction between the first metal film and the second metal film, these metal films are simply referred to as “metal films”.

  In general, there are two methods described below for exciting surface plasmon polaritons with an electromagnetic field conversion element including a substrate, a metal film, and a dielectric, namely, a first excitation method and a second excitation method.

  The first excitation method is a method in which incident light enters an electromagnetic field conversion element including a substrate, a metal film, and a dielectric layer at an appropriate angle from the substrate side.

  The configuration of the electromagnetic field conversion element 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 Otto arrangement will be described with reference to FIGS.

  FIG. 1 shows a perspective view of an electromagnetic field conversion element 2 configured by a Kretchmann arrangement. In the Kretchmann arrangement, as shown in the figure, a metal film 17 is formed on the transparent substrate 9, and the side opposite to the surface of the metal film 17 in contact with the transparent substrate 9 (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 9 (corresponding to air in the structure shown in FIG. 1). When the surface plasmon polariton 12 is excited by the electromagnetic field conversion element 2, the incident light 11 is incident at an appropriate angle from the transparent substrate 9 side toward the interface between the transparent substrate 9 and the metal film 17. Then, as shown by the arrow 12 in FIG. 1, the wave vector of the incident light 11 is applied to the side opposite to the transparent substrate 9 of the metal film 17 (the side opposite to the surface on which light is incident), that is, the surface in contact with the dielectric layer. A surface plasmon polariton 12 is generated as a surface wave traveling in the direction of the component parallel to the metal film 17 (indicated by an arrow 12 in FIG. 1).

  In FIG. 2, the perspective view of the electromagnetic field conversion element 22 comprised by Otto arrangement | positioning is shown. In the Otto arrangement, as shown in the figure, a dielectric layer 13 having a refractive index smaller than that of the transparent substrate 9 is formed on the transparent substrate 9, and a metal film 17 is formed on the dielectric 13. When the surface plasmon polariton 12 is excited by the electromagnetic field conversion element 22, the incident light 11 is incident from the transparent substrate 9 side toward the interface between the transparent substrate 9 and the metal film 17 at an appropriate angle with respect to the interface. . Then, a surface plasmon polariton (not shown) is generated as a surface wave traveling in the direction of the component parallel to the metal film 17 of the wave vector of the incident light 11 as in the Kretchmann arrangement, but unlike the Kretchmann arrangement, The surface plasmon polariton is generated at the interface between the metal film 17 and the dielectric layer 13. As described above, in the Otto arrangement, the surface where the surface plasmon polariton is generated is not exposed, so that dust or scratches are not easily attached to the surface, and the conversion efficiency of the surface plasmon polariton due to dust or scratches is not easily lost.

  In these first excitation methods, the most efficient when the polarization direction of the incident light 11 is p-polarized with respect to the interface between the transparent substrate 9 and the metal film 17 in any of the Kretchmann arrangement and the Ototo arrangement. The surface plasmon polariton 12 can be excited.

  The incident angle of the incident light 11 with respect to the interface between the transparent substrate 9 and the metal film 17 is not particularly limited as long as it is an angle that can excite the surface plasmon polariton 12. However, since the surface plasmon polariton 12 converts the energy of the incident light 11, the incident angle is preferably an angle at which the energy of the incident light 11 is converted into the surface plasmon polariton 12 most efficiently. That is, the incident angle is preferably an angle at which the reflectance of the incident light 11 with respect to the metal film 17 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 9 and the metal film 17. The optimum incident angle is realized by making the transparent substrate 9 itself a prism, or by bonding the transparent substrate 9 to the prism.

  Next, the second excitation method will be described with reference to FIG. FIG. 3 is a perspective view of the electromagnetic field conversion element 23 using the second excitation method. The second excitation method is a method of irradiating the edge of the metal film 17 with the incident light 11 as shown in FIG. In this method, the surface plasmon polariton 12 can be excited most efficiently when the polarization direction of incident light is perpendicular to the edge. When light is applied to the edge of the metal film 17, free electrons at the edge are shaken by the electric field of the light, and this vibration is transmitted to the electrons on the surface of the metal film 17, thereby generating surface plasmon polaritons 12. The surface plasmon polariton 12 travels in a direction substantially perpendicular to the edge of the metal film 17.

  According to the second excitation method, the surface plasmon polariton 12 can be excited if a component having a polarization direction perpendicular to the edge is included in the incident light. 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 11 is incident on the edge may be perpendicular to the metal film 17, and an appropriate angle with respect to the interface between the transparent substrate 9 and the metal film 17 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 11 is incident on the metal film 17 perpendicularly, the transparent substrate 9 may be a parallel plane substrate, which is easier to design than the case of using a prism or the like 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 11 is incident on the interface between the transparent substrate 9 and the metal film 17 at an angle suitable for exciting the surface plasmon polariton 12, the surface plasmon polariton 12 is incident by light incident on a portion other than the edge. Is excited, and the surface plasmon polariton 12 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 12 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.

  When the surface plasmon polariton 12 is generated using the electromagnetic field conversion element according to the embodiment of the present invention, the first excitation method or the second excitation method 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 11 is reduced by a lens or a beam expander or the like, the area irradiated with the incident light can be narrowed down to an area where the distance to the local electromagnetic field generator is less than the propagation length of the surface plasmon polariton. As a result, the utilization efficiency of the incident light 11 is increased. When the incident light 11 is narrowed by a lens, the incident light 11 includes light beams having various incident angles, and also 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 use efficiency of the incident light 11 is high, and the generation area of the generated surface plasmon polariton can be reduced to a desired area.

  On the other hand, in order to reduce the irradiation area of the incident light 11, the beam diameter of the incident light 11 may be narrowed using a beam expander or the like. When the beam expander is used, the irradiation area cannot be reduced as much as the lens is squeezed. However, since the incident angle can be set to the optimum incident angle for exciting the surface plasmon polariton 12, the incident light is converted into the surface plasmon polariton 12. There is an advantage that the utilization efficiency of the light 11 is increased.

  Next, amplification of surface plasmon polaritons in the electromagnetic field conversion element of the present invention will be described.

  As already described, the electromagnetic field conversion element of the present invention includes at least a first metal film and a second metal film on a transparent substrate.

  The first metal film and the second metal film are formed so as to contact each other, and the surface plasmon polariton is generated and propagated at a boundary line between the first metal film and the second metal film. Exists on the surface.

  In the electromagnetic field conversion element of the present invention, when surface plasmon polaritons are generated on the surface of the first metal film, the surface plasmon polaritons propagate on the surface of the first metal film and reach the second metal film. Therefore, the surface plasmon polariton is reflected by the second metal film. The reflected surface plasmon polariton overlaps the surface plasmon polariton that has propagated through the first metal film. That is, superposition of the surface plasmon polaritons occurs, and as a result, the surface plasmon polaritons are amplified. When surface plasmon polariton is generated on the surface of the second metal film, the surface plasmon polariton is reflected by the first metal film, and the surface plasmon polariton is amplified as described above.

  Furthermore, in the electromagnetic field conversion element of the present invention, it is preferable that the first metal film and the second metal film have different dielectric constants. At this time, when surface plasmon polariton is generated on the surface of the second metal film, the surface plasmon polariton propagates on the surface of the second metal film and proceeds to the first metal film. At this time, when the dielectric constant of the second metal film is larger than the dielectric constant of the first metal film, the intensity of the component parallel to the surface of the electric field in the surface plasmon polariton and perpendicular to the boundary line is large on the surface of the first metal film. Become.

  In the electromagnetic field conversion element of the present invention, surface plasmon polaritons are generated on the surface of the metal film as described above by irradiating the metal film with incident light. That is, incident light is converted into surface plasmon polariton. Then, the surface plasmon polariton is amplified, and the amplified surface plasmon polariton is extracted as a local electromagnetic field. That is, in the electromagnetic field conversion element of the present invention, incident light is converted into an electromagnetic field (local electromagnetic field). As described above, the electromagnetic field conversion element of the present invention efficiently amplifies the surface plasmon polariton, and thus has an effect of high incident light-electromagnetic field conversion efficiency. That is, an electromagnetic field can be generated with energy efficiency.

  The electromagnetic field conversion element of the present invention may be configured such that the first metal film is formed between at least two second metal films and has at least two boundary lines. In this specification, the phrase “the first metal film is formed between at least two second metal films and has at least two boundary lines” means that at least a part of the periphery of the first metal film is the first. 2 or more boundary lines between the first metal film and the second metal film are in contact with each other (discontinuously), or the boundary line is connected continuously, Means that the boundary lines extend. That is, the above-mentioned wording is a case where the boundary line is a straight line and one, that is, a case where one first metal film and one second metal film are in contact via a straight boundary line. means. Therefore, the metal film may be formed in parallel in the order of the second metal film-the first metal film-the second metal film, or the entire periphery of the first metal film is surrounded by the second metal film. May be. The electromagnetic field conversion element of the present invention has a metal film (first metal film) made of a material different from the metal film in contact with the metal film (second metal film) by two or more boundary lines. Surface plasmon polaritons are more efficiently amplified at the surface of

  More specifically, with the above configuration, the surface plasmon polariton generated on the surface of the metal film of the electromagnetic field conversion element of the present invention propagates through the first metal film and reaches the second metal film. At this time, the surface plasmon polariton reflected by the second metal film at the boundary line propagates again on the surface of the first metal film and is reflected again by the second metal film. In this way, the surface plasmon polaritons are superposed to cause amplification of the surface plasmon polaritons. In other words, it is considered that when the mirrors face each other, a phenomenon similar to the fact that the light reflected by the mirrors reciprocates and overlaps between the mirrors occurs, and the surface plasmon polariton is strengthened. At this time, the second metal film that forms a boundary line with the first metal film, that is, is in contact with the first metal film, may be one kind, or two or more kinds of metal films may be used as the second metal film.

  In addition, the boundary line between the first metal film and the second metal film is a straight line and is parallel to each other, which is suitable for efficient superposition of surface plasmon polaritons, that is, amplification of surface plasmon polaritons.

  As described above, the electromagnetic field conversion element of the present invention is configured such that the surface plasmon polaritons reflected by the second metal film overlap each other at the boundary between the first metal film and the second metal film. Preferably it is.

  The electromagnetic field conversion element of the present invention includes a metal film made of at least two different metal materials, and the surface plasmon polariton is generated in at least one of the metal films.

  That is, at least one metal film (a metal film in which surface plasmon polaritons are generated) among the metal films is irradiated with incident light from the transparent substrate side. That is, at least one metal film (metal film in which surface plasmon polariton is generated) is formed so as to be in contact with the transparent substrate, or a light-transmitting dielectric layer is formed on the transparent substrate. May be formed so as to be in contact with the dielectric layer. In addition, since at least a part of the metal film (metal film that generates surface plasmon polaritons) can be irradiated with incident light that excites the surface plasmon polaritons, at least the metal film (metal film that generates surface plasmon polaritons) can be irradiated. It is only necessary that a part thereof is in contact with the transparent substrate or in contact with the translucent dielectric layer.

  Furthermore, in the electromagnetic field conversion element of the present invention, it is preferable that at least two different metal films are formed along the direction in which the surface plasmon polariton propagates.

  Further, in the electromagnetic field conversion element of the present invention, the surface plasmon polariton is generated on the surface of the metal film and then propagates on the surface of the two or more metal films, and then reaches the second metal film and the first metal film. It may be amplified at the surface.

  Further, in order to generate surface plasmon polaritons on the surface of the metal film, each parameter in surface plasmon polariton excitation in the electromagnetic field conversion element, that is, the film thickness and refractive index of the metal film that generates surface plasmon polaritons, and the transparent substrate The refractive index, the refractive index of the dielectric layer (air in this embodiment) that is in contact with the surface opposite to the metal film that generates the surface plasmon polariton, and the incident light The incident angles must be in an optimum range. Since the relationship between these parameters, the generation intensity of the surface plasmon polariton at that time, and the propagation length are known, they may be set according to this (for example, see Non-Patent Document 1). The propagation length is a distance at which the intensity of the surface plasmon polariton is 1 / e. The propagation length depends on the incident light and the metal material, but is about several tens of microns to several hundreds of microns in an ideal system.

  In order to efficiently amplify the excited surface plasmon polariton, the metal material constituting these metal films is preferably a material having high electrical conductivity. Typical examples of these metal materials include noble metals such as gold (Au), silver (Ag), and platinum (Pt), aluminum (Al), copper (Cu), and chromium (Cr). The thickness of the metal film according to the present invention is preferably several nm to several tens of nm.

  The surface plasmon polariton attenuates in intensity as it progresses. Therefore, if the distance that the surface plasmon polariton propagates on the metal surface is too long, the strength of the surface plasmon polariton is attenuated and the amplification effect is reduced. Therefore, the distance from the occurrence of surface plasmon polaritons to the arrival of the next metal film, the distance from the arrival of one metal film to the arrival of another metal film, and the metal film having a local electromagnetic field generator The distance from reaching to the local electromagnetic field generator is preferably equal to or less than the propagation length.

  When the surface plasmon polariton amplified as described above is taken out as a local electromagnetic field and irradiated to a recording medium (local electromagnetic field irradiation target), there are the following two methods, that is, two local electromagnetic field generation methods. .

  The first local electromagnetic field generation method is a method of using the local electromagnetic field of the surface plasmon polariton itself by bringing the recording medium close to the amplified surface plasmon polariton. At this time, the recording medium may be brought closer to the range within one-fourth of the wavelength of the surface plasmon polariton from the electromagnetic field conversion element.

  The second local electromagnetic field generation method is a method in which surface plasmon polaritons are scattered by a scatterer (local electromagnetic field generation unit) formed on a metal film and extracted as another local electromagnetic field. In the second local electromagnetic field generating method, the shape of the generated local electromagnetic field can be changed by changing the shape of the local electromagnetic field generating unit.

  There are the following two methods for generating the second local electromagnetic field.

  The first method is to scatter at the edge of the metal film of the electromagnetic field conversion element. The edge may be an end portion that is an outer peripheral portion of the metal film, or may be an end portion of the opening or the like when the opening is provided in the metal film. Further, as will be described later, these edges can also serve as an incident light irradiation unit that excites surface plasmon polaritons by the second excitation method and a local electromagnetic field generation unit.

  As a second method, there is a method of forming a scatterer (projection) such as a minute projection on a metal film. As this protrusion, for example, metal fine particles may be provided on a metal film to form a protrusion.

In addition, since surface plasmon polariton attenuates in strength as it progresses, the distance from the local electromagnetic field generation part such as these edges and protrusions to the boundary between metal films is less than the propagation length of surface plasmon polariton. In order to obtain a strong local electromagnetic field, an example in which an opening formed on a metal film or the like is used for excitation and / or extraction of surface plasmon polaritons will be described below. The opening or the like may be used for exciting the surface plasmon polariton, may be used for scattering the surface plasmon polariton, or may have both of these functions.

  First, an electromagnetic field conversion element whose opening and the like are used only for excitation of surface plasmon polaritons, that is, an electromagnetic field conversion element used only as an incident light irradiation part will be described. In such an electromagnetic field conversion element, an incident light irradiation part (in this case, an opening or the like) and a local electromagnetic field generation part are provided separately. As described above, when the recording medium (local electromagnetic field irradiation target) is irradiated with a local electromagnetic field, when the recording medium (local electromagnetic field irradiation target) is irradiated, the incident light and the local electromagnetic field are It becomes difficult to overlap. In other words, since it is possible to prevent incident light from being applied to the recording medium as a background, the S / N (Signal to Noise ratio) of the recording data can be improved when used in a recording apparatus.

  In addition, when an opening or the like is provided in the same metal film as the metal film provided with the local electromagnetic field generation unit, and this opening or the like is used as the incident light irradiation unit, the surface plasmon polariton does not travel the boundary of the metal film. Therefore, the loss of the surface plasmon polariton caused by the reflection or scattering of the surface plasmon polariton at the boundary of the metal film can be prevented.

  In addition, each opening or the like may be formed across two different metal films.

  Next, an electromagnetic field conversion element that uses an opening or the like only as a local electromagnetic field generator for scattering surface plasmon polaritons will be described. In such an electromagnetic field conversion element, as described in the case where the opening or the like is already used only for exciting the surface plasmon polariton, the S / N of the recording data can be improved when used in the recording apparatus.

  In the case where the opening or the like is used for both the surface plasmon polariton excitation and the scattering, the opening for exciting the surface plasmon polariton 12 and the local electromagnetic field generation unit may not be separately manufactured. Manufacture is easy, and both manufacturing time and cost can be reduced. The opening or the like is preferably smaller than the wavelength of incident light. As a result, it is possible to suppress the rate at which incident light passes through the opening and the like as it is and irradiates the recording medium as background, so that the S / N of the recording data is improved when used in a recording apparatus. Can do. In addition, when using an opening or the like as a local electromagnetic field generator in this way, the size of the spot of light irradiated on the recording medium determines the recording density, so that the opening is set to the target spot size. What is necessary is just to decide the size of a part etc.

  Combining the excitation method, amplification method, and local electromagnetic field extraction method for the surface plasmon polariton 12 described above, several specific examples of electromagnetic field conversion elements are given, and a local electromagnetic field amplified in a minute region can be obtained. Is verified by simulation using the FDTD method (finite-difference time-domain method).

[Embodiment 1]
One embodiment of the present invention is described below with reference to FIGS.

  The electromagnetic field conversion element 24 of the present embodiment excites the surface plasmon polaritons by the first excitation method (Kretchmann arrangement) described above and takes it out as an electromagnetic field. In FIG. 4, the perspective view of the electromagnetic field conversion element 24 of this embodiment is shown.

  In the following first to fifth embodiments, as shown in FIG. 4, the longitudinal direction of the transparent substrate 9 is the x-axis direction, the short direction is the y-axis direction, and the transparent substrate 9 has a metal film (metal film 5. The direction on the side where 6.7) is formed is taken as the z direction.

  As shown in the figure, the electromagnetic field conversion element 24 includes a transparent substrate 9, a metal film 5 (second metal film) formed on the transparent substrate 9, a metal film 6 (first metal film), and a metal film 7 ( A second metal film). The metal films 5, 6, and 7 are formed in substantially the same film thickness in different regions on the transparent substrate 9 so as to be in contact with the transparent substrate 9. In addition, the boundaries between the metal films are straight lines and parallel to each other. That is, the metal films 5, 6, and 7 are arranged in this order in the x-axis direction, and the boundary line of each metal film is parallel to the y-axis direction.

  The width w1 of the metal film 6, that is, the distance from the boundary between the metal film 5 and the metal film 6 to the boundary between the metal film 6 and the metal film 7 is equal to or less than the propagation length of the surface plasmon polariton as described above. The effect of the width w1 of the metal film 6 on the amplification effect of the surface plasmon polariton, that is, the incident light-electromagnetic field conversion efficiency, will be described later in the simulation.

  When exciting the surface plasmon polariton, any of the metal films 5, 6, and 7 may be irradiated with the incident light 11. In the present embodiment, as shown in FIG. 4, incident light 11 is incident on the first metal film 5 from the transparent substrate 9 side. As described above, the surface light plasmon polariton 12 is generated by the incident light 11 on the surface opposite to the surface of the metal film 5 in contact with the transparent substrate 9 (the surface opposite to the surface on which the light is incident). The surface plasmon polariton 12 is a surface wave that travels in the same direction as the component parallel to the metal film of the wave number vector of the incident light 11.

  The surface plasmon polariton 12 generated on the surface of the metal film 5 proceeds to the surface of the metal film 6 as indicated by an arrow in FIG. 4, and the surface plasmon polariton 12 proceeds on the surface of the metal film 6 to form a metal. When the film 7 is reached, the surface plasmon polariton 12 is reflected and returns to the metal film 6. The reflected surface plasmon polariton is further reflected by the metal film 5, whereby the surface plasmon polariton is amplified on the surface of the metal film 6.

  Thus, since the electromagnetic field conversion element 24 includes the metal films 5, 6, and 7, the surface plasmon polariton 12 can be amplified.

  At this time, as will be described later, the metal film 6 and the metal films 5 and 7 are preferably made of different materials, and the metal film 6 is made of a material having a smaller refractive index than the metal films 5 and 7. It is preferable. The metal films 5 and 7 may be made of the same material or different materials.

  When the dielectric constant of the metal film 5 is larger than the dielectric constant of the metal film 6, when the surface plasmon polariton 12 proceeds from the metal film 5 to the metal film 6, the dielectric constant is parallel to the surface of the electric field in the surface plasmon polariton 12. The intensity of the component perpendicular to the boundary line is increased. Therefore, there is an effect that the surface plasmon polariton 12 is amplified. Note that the ratio of the dielectric constant of the metal film 5 to the metal film 6 is preferably large.

  The surface plasmon polariton 12 amplified as described above is scattered when the recording medium is brought close to the electromagnetic field conversion element 24 and taken out as a local electromagnetic field. That is, in the present embodiment, the surface of the metal film 6 serves as a local electromagnetic field generator.

  In order to generate the surface plasmon polariton 12 on the surface of the metal film 5, the incident angle of the incident light 11 may be an appropriate angle with respect to the boundary surface between the substrate 9 and the metal film 5 as described above. desirable. The polarization direction of the incident light is preferably p-polarized light in order to increase the incident light-electromagnetic field conversion efficiency.

  When the excitation method of the surface plasmon polariton 12 in the electromagnetic field conversion element 24 is the first excitation method already described, as shown in FIG. 4, the wave vector of the incident light 11 of the wave vector of the incident light 11. The component parallel to the surface of the metal film and the boundary line of the metal film on the surface of the metal film are preferably perpendicular. The second excitation method may be used as the excitation method in the electromagnetic field conversion element 24. In this case, the edge of the metal film that generates the surface plasmon polariton and the metal film boundary on the surface are made parallel. It is preferable. At this time, since the traveling direction of the generated surface plasmon polariton 12 is perpendicular to the boundary of the metal film, the superposition with the incident surface plasmon polariton 12 when reflected by reaching another metal film is the most. Done efficiently.

  Further, when the surface plasmon polariton proceeds from a metal film having a large dielectric constant to a metal film having a small dielectric constant, the amplification effect of the surface plasmon polariton becomes large. When the surface plasmon polariton advances from the metal film having a low refractive index to the large metal film and is reflected, the amplification effect of the surface plasmon polariton is further increased. In order to increase the amplification effect of the surface plasmon polariton 12, a combination of metal films may be appropriately selected based on the traveling direction of the surface plasmon polariton 12.

  Further, the position of the metal film where the incident light 11 is irradiated (the position of the incident light irradiation portion) is not particularly limited, but is preferably in the vicinity of the boundary between the metal film 5 and the metal film 6. This is because, if the distance from the generation of the surface plasmon polariton 12 of the metal film 5 to the arrival of the metal film 6 after the generation of the surface plasmon polariton 12 on the metal film 5 is too long, as described above, the surface plasmon polariton 12 is attenuated. This is because the incident light-electromagnetic field conversion efficiency is lowered.

  The width w1 of the metal film 6 in the x-axis direction, that is, the distance between the metal film 5 and the metal film 7 is preferably equal to or less than the propagation length of the generated surface plasmon polariton 12.

  In the present embodiment, the surface plasmon polariton 12 generated in the metal film 5 is propagated through the metal film 6, and the boundary between the metal film 7 and the metal film 6, and the metal film 5 and the metal film 6. It is amplified at the boundary. However, the surface plasmon polariton 12 may be generated directly on the metal film 6.

  Further, the incident light 11 may be a plane wave light, or may be light that is narrowed by a lens or the like. The advantages and disadvantages of using a lens and using a plane wave are as described above.

  The case where the method called the Kretchmann arrangement is used in the first excitation method has been described above, but the method called the Ototo arrangement of the first excitation method described above can also be used.

  In the present embodiment, a scatterer that scatters the surface plasmon polariton 12 is not provided. When such an electromagnetic field conversion element is used in a recording apparatus, the distance from the electromagnetic field conversion element to the recording medium (local electromagnetic field irradiation object) is within a range of ¼ or less of the wavelength of the surface plasmon polariton 12. It is preferable to make it. Further, as will be described later, the surface plasmon polariton 12 can be scattered by forming slits or openings or protrusions such as fine metals. When these scatterers are used, the surface plasmon polariton 12 can be amplified and more localized. On the other hand, when the shape of these scatterers changes over time due to heat, collision with the recording medium, or the like, There is a problem that characteristics change. In particular, when an opening or a slit is used, not only near-field light but also propagation light is generated, which causes a problem of background noise. These problems can be prevented in a configuration that does not use a scatterer.

  Next, the result of simulation by the FDTD method using the configuration of the electromagnetic field conversion element 24 will be described with reference to FIGS. 5 and 6. In this simulation, the metal film 5 and the metal film 7 are made of the same material in order to simplify the configuration.

  In FIG. 4, the metal film 6 was made Ag, the metal film 5 and the metal film 7 were made Al, and the thickness of each metal film was 11 nm to produce the electromagnetic field conversion element 24. The incident light 11 is a plane wave having a wavelength of 600 nm, and is located near the boundary between the metal film 5 (Al) and the metal film 6 (Ag) in the metal film 5 (Al) and at the interface between the transparent substrate 9 and the metal film 5. On the other hand, the incident angle was 45 degrees and the incident light was p-polarized light.

  First, the influence of the width w1 of the metal film 6 (Ag) on the amplification effect of the surface plasmon polariton was examined. FIG. 5 is a graph showing incident light-electromagnetic field conversion efficiency with respect to the width w1 of the metal film 6 (Ag). In the graph of the figure, the horizontal axis indicates the width w1 (nm) of the metal film 6 (Ag), and the vertical axis indicates the incident light-electromagnetic field conversion efficiency. The width w1 of the metal film 6 (Ag) film of 0 nm indicates that only the Al film is formed as the metal film on the transparent substrate 9. From the figure, when the width w1 of the metal film 6 (Ag) was changed from 0 to 600 nm, the metal film 6 (Ag), the metal film 5 (Al), and the second second metal film ( Amplification of the surface plasmon polariton 12 was observed because the two types of metals (Al) 7 were formed on the transparent substrate 9. Note that when only the Ag film was provided on the substrate, the strength was almost the same as when only the Al film was provided (not shown). Further, it was found that the amplification effect of the surface plasmon polariton was maximized when the metal film 6 (Ag) width w1 was around 200 nm.

  Next, the incident light-electromagnetic field conversion efficiency with respect to the ratio (n ratio) between the refractive index of the metal material of the metal film 5 and the metal film 7 in FIG. 4 and the refractive index of the metal material of the metal film 6 was examined.

  FIG. 6 is a graph showing incident light-electromagnetic field conversion efficiency when the metal material of the metal film 6 is changed. The metal film 5 and the metal film 7 are fixed to Al, and the metal material of the metal film 6 is silver (Ag), gold (Au), copper (Cu), nickel (Ni), titanium as shown in FIG. (Ti), platinum (Pt) or manganese (Mn) was used. The horizontal axis of the graph is the refractive index ratio (n ratio) of the metal material of the metal film 6 to the metal film 7 (Al), that is, [refractive index of the metal material of the metal film 6 / refractive index of Al]. The vertical axis represents the incident light-electromagnetic field conversion efficiency. Further, the case where only the Al film is formed on the transparent substrate 9 is also shown in the graph.

  As shown in FIG. 6, compared to the case where only the Al film is formed, the incident light-electromagnetic field conversion can be achieved when the metal film made of another metal material is formed together, regardless of which other metal material is used. The efficiency was high. That is, the amplification effect of the surface plasmon polariton 12 was obtained by using a metal material different from the metal film 5 and the metal film 7 as the metal film 6.

  Further, the amplification effect increased as the refractive index of the metal material of the metal film 5 and the metal film 7 increased with respect to the refractive index of the metal material of the metal film 6. That is, in the electromagnetic field conversion element 24 of the present embodiment, the refractive index of the metal material of the metal film 6 is preferably smaller than the refractive index of the metal material of the metal film 5 and the metal film 7. In this simulation, it is preferable to use any one of Ag, Au, and Cu as the metal film 6 with respect to the Al of the metal film 5 and the metal film 7.

[Embodiment 2]
Another embodiment of the electromagnetic field conversion element according to the present invention will be described with reference to FIG.

  FIG. 7 is a perspective view of the electromagnetic field conversion element 25 according to the present embodiment.

  However, in the following description, members having the same functions as those of the electromagnetic field conversion element 24 in FIG.

  As shown in the figure, in the electromagnetic field conversion element 25, metal films 5, 6, and 7 are formed on the transparent substrate 9 in the same manner as the electromagnetic field conversion element 24 in FIG. 4.

  However, unlike FIG. 4, a region (region 60) of a part of the metal film 6 extending from the midpoint of the boundary line with the metal film 7 to the width d extends to the metal film 7 side perpendicularly to the boundary. The metal film 7 is divided into two regions (metal films 7a and 7b) by the region 60. The width d of the region 60, that is, the distance between the boundary line between the metal film 7a and the region 60 and the boundary line between the region 60 and the metal film 7b determines the length of the region where the local electromagnetic field is generated.

  The electromagnetic field conversion element 25 has the Kretchmann arrangement as in the first embodiment, and when the surface plasmon polariton 12 is excited, as shown in the drawing, the incident light enters the vicinity of the boundary between the metal film 5 and the metal film 6. Light 11 is incident. As described above, the incident light 11 can excite the surface plasmon polariton 12 most efficiently when the polarization direction is p-polarized light. As described above, the surface plasmon polariton 12 generated on the surface of the metal film 5 by the incidence of the incident light 11 proceeds to the surface of the metal film 6 and is amplified at the boundary with the metal film 7 (metal films 7a and 7b). The

  In the electromagnetic field conversion element 25 according to the present embodiment, as will be described later, scattering of surface plasmon polariton occurs at the end of the region 60, that is, the edge 8 (see FIG. 8). That is, in the electromagnetic field conversion element 25, the edge 8 of the region 60 becomes a local electromagnetic field generating part. Therefore, the vicinity of the plane including the side surface on the edge side of the region 60 of the electromagnetic field conversion element 25, that is, the vicinity of the plane indicated by the dotted line 4A, or the vicinity of the plane including the surface opposite to the transparent substrate 9 side of the electromagnetic field conversion element 25. That is, by placing the recording medium in the vicinity of the plane indicated by the dotted line 4B, the recording medium can be irradiated with a local electromagnetic field. When the recording medium is placed in the vicinity of the plane indicated by the dotted line 4B, the surface plasmon polariton 12 on the surfaces of the metal film 5 and the metal film 6 overlaps with the local electromagnetic field scattered at the edge of the region 60, and the recording medium is used as the background. May be irradiated. However, when the recording medium is placed in the vicinity of the plane indicated by the dotted line 4A, this is unlikely to occur, so that the S / N of the recording data can be improved when used in a recording apparatus.

  A result of simulation by the FDTD method using the configuration of the electromagnetic field conversion element 25 will be described with reference to FIG.

  In this simulation, the transparent substrate 9 shown in FIG. 7 is made of glass, the metal film 6 is made of Ag, and the metal film 5 and the metal films 7 (metal films 7a and 7b) are made of Al. The thickness of each metal film is 11 nm, and the width w2 of the metal film 6 (see FIG. 7), that is, from the boundary line between the metal film 5 and the metal film 6 to the boundary line between the metal film 6 and the metal film 7. The distance d is 300 nm, and the width d of the region 60 (see FIG. 7), that is, the distance from the boundary between the metal film 7a and the region 60 to the boundary between the region 60 and the metal film 7b is 100 nm. The incident light 11 is a plane wave having a wavelength of 600 nm and is p-polarized light having an incident angle of about 45 degrees with respect to the metal film 5.

  FIG. 8 shows an electromagnetic field distribution of the electromagnetic field conversion element 25 configured as described above. As shown in FIG. 8, a strong local electromagnetic field was obtained at the edge portion of the region 60. This is because a part of the surface plasmon polariton 12 amplified on the surface of the metal film 6 between the metal films 7a and 7b and the metal film 5 shown in FIG. It is because it was scattered.

[Embodiment 3]
Hereinafter, an electromagnetic field conversion element 26 according to another embodiment of the present invention will be described with reference to FIG.

  FIG. 9 is a perspective view of the electromagnetic field conversion element 26 of the present embodiment.

However, in the following description, members having the same functions as those of the electromagnetic field conversion element 24 in FIG.
In the electromagnetic field conversion element 26, the metal film 5, the metal film 6, and the metal film 7 are formed in the same manner as the electromagnetic field conversion element 24 of FIG.

  However, unlike the above-described first embodiment, in the electromagnetic field conversion element 26 according to the present embodiment, as shown in FIG. 9, a slit is formed in the metal film 6 and the metal film 7 as a local electromagnetic field generator. Is formed. The slit is formed so as to bisect the metal film 7 from the end of the metal film 7 opposite to the surface in contact with the metal film 6, and the boundary line between the metal film 6 and the metal film 7. And reaches the center of the metal film 6 perpendicular to the boundary line.

  In the present embodiment, the slit bisects the metal film 7. However, in the electromagnetic field conversion element of the present invention, the shape of the slit is not limited to this, and may be formed so as to be biased in the y-axis direction. However, it is preferable that the intensity center of the incident light is irradiated on the extension of the center line of the slit.

  The electromagnetic field conversion element 26 has a Kretchmann arrangement as in the first embodiment, and when exciting the surface plasmon polariton, as shown in FIG. 9, incident light is incident in the vicinity of the boundary between the metal film 5 and the metal film 6. 11 is incident. As described above, the incident light 11 can excite the surface plasmon polariton most efficiently when the polarization direction is p-polarized light. As described above, the surface plasmon polariton 12 generated on the surface of the metal film 5 by the incidence of the incident light 11 proceeds to the surface of the metal film 6 and is amplified at the boundary with the metal film 7.

  The amplified surface plasmon polariton is scattered at the edge of the slit in the electromagnetic field conversion element 26 and taken out as a local electromagnetic field.

  As described above, when the local electromagnetic field is extracted by the first excitation method, that is, when the incident electromagnetic wave 11 is extracted from the transparent substrate 9 side by the slit, the incident light 11 directly hits the slit which is the local electromagnetic field generator. There is no. Therefore, when irradiating the recording medium with a local electromagnetic field, the incident light and the local electromagnetic field are unlikely to overlap. That is, since the incident light 11 is not irradiated on the recording medium as a background, the S / N of the recording data can be improved when the electromagnetic field conversion element of the present embodiment is used in the recording apparatus.

  Next, the results of simulation using the electromagnetic field conversion element 26 with the following specific configuration will be described with reference to FIG. The transparent substrate 9 was made of glass, the metal film 6 was made of Ag, and the metal film 5 and the metal film 7 were made of Al. The thickness of each metal film is 11 nm, the width w3 of the metal film 6 (Ag), that is, the boundary line between the metal film 5 (Al) and the metal film 6 (Ag), the metal film 6 (Ag), and the metal film. The distance from the boundary line with 7 (Al) was 300 nm, and the width in the short direction of the slit was 100 nm. The incident light 11 was a plane wave having a wavelength of 600 nm, and was incident on the interface between the transparent substrate 9 and the metal film 5 as p-polarized light having an incident angle of about 45 degrees. The incident angle and the film thickness of the metal film 5 (Al) were selected so that the surface plasmon polariton 12 was generated in the metal film 5 (Al).

  FIG. 10 is a graph showing the distribution of the electromagnetic field in the electromagnetic field conversion element 26 configured as described above. In the graph, the intensity distribution of the electromagnetic field on the chain line in FIG. 9, that is, the line parallel to the slit and passing through the center of the slit is shown by a solid line. The horizontal axis indicates the distance from the center of the metal film 6 (Ag), that is, the end of the slit on the metal film 6 side. The vertical axis represents the ratio of the local electric field intensity to the incident light intensity, that is, the incident light-electromagnetic field conversion efficiency. For comparison, only the Al film was formed on the transparent substrate 9, and the result of simulating the local electromagnetic field under the same conditions is indicated by a dotted line.

  From the graph, a peak of incident light-electromagnetic field conversion efficiency was obtained near the end of the slit on the metal film 6 side. In addition, when the metal film 6 (Ag) is formed (solid line), the incident light-electromagnetic field conversion efficiency at the peak is larger and the surface plasmon polariton is amplified than when the metal film is only an Al film (dotted line). Can be seen.

[Embodiment 4]
Below, the electromagnetic field conversion element 27 which concerns on embodiment of this invention is demonstrated based on FIG.

  In FIG. 11, the perspective view of the electromagnetic field conversion element 27 of this Embodiment is shown.

  However, in the following description, members having the same functions as those of the electromagnetic field conversion element 24 in FIG.

As shown in the figure, in the electromagnetic field conversion element 27, the metal film 5, the metal film 6, and the metal film 7 are formed in the same manner as the electromagnetic field conversion element 24 in FIG. However, unlike the electromagnetic field conversion element 24, the electromagnetic projection 27 is provided with the metal protrusion 10 on the metal film 6 as a local electromagnetic field generation unit, and has a Kretchmann arrangement as in the first embodiment, and has a surface plasmon. When exciting the polaritons, as shown in FIG. 11, incident light 11 is made incident near the boundary between the metal film 5 and the metal film 6. As described above, the incident light 11 can excite the surface plasmon polariton most efficiently when the polarization direction is p-polarized light. As described above, the surface plasmon polariton 12 generated on the surface of the metal film 5 by the incidence of the incident light 11 is reflected and superimposed on the metal film 5 and the metal film 7 and amplified on the surface of the metal film 6.

  In the electromagnetic field conversion element 27, as described above, the metal protrusion (protrusion part) 10 is provided on the metal film 6. Therefore, the amplified surface plasmon polariton is scattered by the metal protrusion 10, and a local electromagnetic field is generated. As taken out. That is, in the electromagnetic field conversion element 27, the metal protrusion 10 serves as a local electromagnetic field generating part.

  As described above, in the present embodiment, the surface plasmon polariton 12 is excited by the first excitation method, that is, by irradiating the metal film 5 with the incident light 11 from the transparent substrate 9 side, and on the metal film 6. The local electromagnetic field is taken out by the metal protrusion 10. Therefore, the incident light 11 is not directly applied to the metal protrusion 10 (local electromagnetic field generating portion). Therefore, when the recording medium is irradiated with the local electromagnetic field scattered by the metal protrusion 10, the incident light 11 is not irradiated to the local electromagnetic field and the recording medium. As a result, the S / N ratio of the recording data can be improved.

  The incident light 11 may be applied to the metal film 6. In this case, the incident angle and the thickness of the metal film are brought into an optimal state. However, since the boundary between the metal films is desirably sufficiently shorter than the propagation length of the surface plasmon polariton 12 as described above, the area of the metal film 6 is smaller than the light diffraction limit. Therefore, it is desirable to reduce the irradiation area of the incident light 11 and prevent the light use efficiency from being lowered by irradiating a large amount of light on the metal film 5 or the metal film 7 in which the generation conditions of the surface plasmon polariton 12 are different.

  In the electromagnetic field conversion element 27 according to the present embodiment, the local electromagnetic field of the surface plasmon polariton 12 and the local electromagnetic field scattered by the metal protrusion 10 are not easily overlapped by the height of the metal protrusion 10, so the surface plasmon polariton 12. Is difficult to irradiate the recording medium. That is, when the electromagnetic field conversion element 27 is used in a recording apparatus, the S / N ratio of recording data can be improved.

  Further, when the local electromagnetic field is brought closer to the recording medium, the local electromagnetic field generating portion is in the same plane as the metal film (metal film 5, metal film 6, and metal film 7) of the electromagnetic field conversion element. Although high accuracy is required for the parallelism and the like, the electromagnetic field conversion element 27 relaxes the required accuracy.

  Further, the material of the metal protrusion 10 may be the same as or different from the metal film on which the metal protrusion 10 is formed (the metal film 6 in the present embodiment). Changing the shape and material of the metal protrusion 10 also changes the scattering efficiency for extracting the surface plasmon polariton 12 as a local electromagnetic field.

  Next, the results of simulation by the FDTD method using the electromagnetic field conversion element 27 will be described with reference to FIG.

  In this simulation, the transparent substrate 9 of FIG. 11 is made of glass, the metal film 6 is made of Ag, and the metal film 5 and the metal film 7 are made of Al. The thickness of each metal film is 11 nm, the width w4 of the metal film 6 (Ag), that is, the boundary line between the metal film 5 (Al) and the metal film 6 (Ag), the metal film 6 (Ag), and the metal film 7. The distance between the boundary line with (Al) was 300 nm. Further, the metal protrusion 10 is provided in the center of the metal film 6 as a cone made of Ag, having a diameter of 100 nm and a height of 50 nm. The incident light 11 was a plane wave having a wavelength of 600 nm, and was incident on the interface between the transparent substrate 9 and the metal film 5 (Al) as p-polarized light having an incident angle of about 45 degrees. The incident angle and the thickness of each metal film were selected so that the surface plasmon polariton 12 was generated in the metal film 5 (Al).

  FIG. 12 shows a graph of the incident light-electromagnetic field conversion efficiency distribution on the chain line in FIG. 11, that is, on the line parallel to the x-axis direction and passing through the tip of the metal protrusion 10. In this graph, the horizontal axis is the distance from the metal protrusion 10. The vertical axis represents incident light-electromagnetic field conversion efficiency. For comparison, the result when the metal film is only an Ag film is shown by a dotted line. From FIG. 12, it can be seen that the electric field concentration is amplified by using two types of metal films as compared to the case of using one type of metal film.

[Embodiment 5]
Below, other embodiment of the electromagnetic field conversion element which concerns on this invention is described based on FIG.

  In FIG. 13, the perspective view of the electromagnetic field conversion element 28 of this Embodiment is shown.

  However, in the following description, members having the same functions as those of the electromagnetic field conversion element 24 in FIG.

  The electromagnetic field conversion element 28 excites the surface plasmon polariton by the second excitation method. On the transparent substrate 9, a metal film 7c, a metal film 6a, a metal film 6b, and a metal film 7d are formed in this order along the x-axis direction. Further, the metal film 7a and the metal film 6a are formed in contact with each other, the metal film 6b and the metal film 7b are formed in contact with each other, and a slit is formed between the metal film 6a and the metal film 6b. ing. The boundary lines and slits of each metal film are straight and parallel. That is, the boundary line and slit of each metal film are parallel to the y-axis direction.

  In the present embodiment, when exciting the surface plasmon polariton, the incident light 11 uses the second excitation method described above, and the metal film 6 (metal films 6a and 6b) and the transparent substrate 9 are directed toward the slit. Incident in a direction perpendicular to the interface. Thereby, the surface plasmon polariton 12 generated on the surface of the metal film 6 proceeds from the edge of the slit toward the outside of the slit, reaches the metal film 7 (metal films 7a and 7b), and is amplified on the surface of the metal film 6. Happens. The amplified surface plasmon polariton 12 is scattered at the same slit edge as that used for excitation, and is extracted as a local electromagnetic field.

  Next, the results of simulation by the FDTD method using the electromagnetic field conversion element 28 will be described with reference to FIGS.

  In the electromagnetic field conversion element configured as described above, when Ag is used as the metal film 6 and Al is used as the metal film 7, the metal film 6 (Ag) is formed from the slit end of the metal film 6 (Ag). The effect of the width to the boundary between the metal film 7 (Al) and the incident light-electromagnetic field conversion efficiency was examined.

  FIG. 14 shows the distance from the slit end (edge) to the boundary between the metal film 6a (metal film 6b) and the metal film 7a (metal film 7b), that is, incident light with respect to the width w5 of the metal film 6a (metal film 6b). A graph of electromagnetic field conversion efficiency is shown. The horizontal axis of FIG. 14 indicates w5 (nm), and the vertical axis indicates incident light-electromagnetic field conversion efficiency. For convenience of explanation, 0 on the horizontal axis indicates a case where only the metal film 6a (metal film 6b) is formed on the transparent substrate 9 and a slit is formed. Here, the incident light-electromagnetic field conversion efficiency is the intensity of the electromagnetic field on the edge of the slit with respect to the intensity of the incident light.

  The incident light 11 is a plane wave having a wavelength of 600 nm, and is incident on the interface between the transparent substrate 9 and the metal film 6 (Ag) at an incident angle of 90 degrees. As shown in FIG. 14, only Ag is formed (w5 = 0 nm) Incident light-electromagnetic field conversion efficiency was higher when two types of metal Ag and Al were formed. This is because the surface plasmon polariton was amplified on the surface of the metal film 6a (Ag) as described above by arranging two kinds of metals. This amplification effect was observed regardless of the value of w5 other than 0 nm, but there is w5 where the amplification effect reaches a peak, which is around 300 nm, which is about half the wavelength of the surface plasmon polariton 12 (594 nm). Met.

  Next, by fixing the widths of the two metal films 6 (metal films 6a and 6b) (Ag) shown in FIG. 13 to 300 nm and changing the metal materials of the metal films 7a and 7b, the metal films 6 (Ag) The effect of the ratio (n ratio) of the refractive index of the metal material of the metal film 7 on the incident light-electromagnetic field conversion efficiency was examined. As the metal film 7, Au, Cu, Al, Ni, Ti, Pt, and Mn were used as shown in FIG. In addition, simulation was also performed for incident light-electromagnetic field conversion efficiency when only Ag was used as the metal film and the metal film 7 was not formed.

  FIG. 15 shows the ratio of the refractive index of the metal film 6 (Ag) to the metal film 7 (n ratio), that is, the incident light-electromagnetic field conversion efficiency with respect to the value obtained by dividing the refractive index of the metal film 7 by the refractive index of the metal film 6. The graph is shown. Here, the incident light-electromagnetic field conversion efficiency is the intensity of the electromagnetic field on the edge of the slit with respect to the intensity of the incident light.

  As shown in FIG. 15, the incident light-electromagnetic field conversion efficiency was higher when another metal film was formed as the metal film 7 regardless of the type of metal, compared to the case where only Ag was used. That is, by arranging two types of metals, as described above, amplification of surface plasmon polaritons occurred on the surface of the metal film 6 (Ag). Further, as shown in FIG. 15, the amplification effect tends to increase as the refractive index of the metal material of the metal film 7 with respect to the metal film 6 increases.

  Next, the width of the metal film 6 (Ag) shown in FIG. 13 is set to 300 nm, the metal films 7a and 7b are made of Al, and the incidence on the straight line (the chain line shown in FIG. 13) equally dividing the slit vertically. The distribution of light-electromagnetic field conversion efficiency was investigated.

  FIG. 16 is a diagram showing the distribution of the incident light-electromagnetic field conversion efficiency. The horizontal axis indicates the distance (nm) from the center of the slit, and the vertical axis indicates the incident light-electromagnetic field conversion efficiency. For comparison, the distribution when the metal film 7 (Al) is not formed and only the metal film 6 (Ag) is used is indicated by a dotted line.

  From FIG. 5, a sharp peak of the electromagnetic field was obtained at ± 50 nm from the center of the slit, that is, at the edge portion of the metal film 6 (Ag). This is because the surface plasmon polariton is scattered at the edge of the metal film 6 (Ag). In addition, the incident light-electromagnetic field conversion efficiency was greater when the metal film 6 (Ag) and the metal film 7 (Al) were formed than when only the Ag film was used as the metal film. This is because the surface plasmon polariton was amplified by providing two types of metal films.

  In the electromagnetic field conversion element of the present invention, the metal film whose surface plasmon polariton is excited by light may be in contact with the transparent substrate, and the other metal film does not need to be in contact with the transparent substrate. FIG. 17 shows a configuration in which the metal film 7 of FIG. 13 is not in contact with the transparent substrate 9. In the electromagnetic field conversion element 29 shown in FIG. 17, surface plasmon polaritons are excited by the metal film 6. In FIG. 17, the metal film 7 is formed by being embedded in the metal film 6 and is not in contact with the transparent substrate 9, but the surface plasmon polariton excited by the metal film 6 propagates through the surface of the metal film 6. Since it reaches the metal film 7 and is reflected and amplified there, there is no change in the amplification effect.

[Embodiment 6]
Below, other embodiment of the electromagnetic field conversion element which concerns on this invention is described based on FIG.

  The electromagnetic field conversion element 30 of the present embodiment excites the surface plasmon polaritons by the first excitation method (Kretchmann arrangement) described above, and takes it out as an electromagnetic field. In FIG. 22, the perspective view of the electromagnetic field conversion element 30 of this embodiment is shown.

  Also in this embodiment, as shown in FIG. 22, the transparent substrate 9 is formed with a metal film (metal films 5 and 6) on the transparent substrate 9 in the x-axis direction and the short-side direction in the y-axis direction. The direction on the side to be performed is the z direction.

  As shown in the figure, the electromagnetic field conversion element 30 includes a transparent substrate 9, a metal film 5 (second metal film) formed on the transparent substrate 9, and a metal film 6 (first metal film). The metal films 5 and 6 are formed in substantially the same film thickness in different regions on the transparent substrate 9 so as to be in contact with the transparent substrate 9. In addition, the boundaries between the metal films are straight lines and parallel to each other. That is, the metal films 5 and 6 are arranged in this order in the x-axis direction, and the boundary line of each metal film is parallel to the y-axis direction.

  In the present embodiment, as shown in FIG. 22, incident light 11 is incident on the metal film 5 from the transparent substrate 9 side. As described above, the surface light plasmon polariton 12 is generated by the incident light 11 on the surface opposite to the surface of the metal film 5 in contact with the transparent substrate 9 (the surface opposite to the surface on which the light is incident). The surface plasmon polariton 12 is a surface wave that travels in the same direction as the component parallel to the metal film of the wave number vector of the incident light 11.

  The surface plasmon polariton 12 generated on the surface of the metal film 5 proceeds to the surface of the metal film 6 as indicated by an arrow in FIG. When the dielectric constant of the metal film 5 is larger than the dielectric constant of the metal film 6, the surface plasmon polariton 12 traveling from the metal film 5 to the metal film 6 is parallel to the electric field surface and perpendicular to the boundary line of the metal films 5 and 6. Increases the strength of various components.

  Thus, since the electromagnetic field conversion element 30 includes the metal films 5 and 6, the surface plasmon polariton 12 can be amplified. Note that the ratio of the dielectric constant of the metal film 5 to the metal film 6 is preferably large.

  The surface plasmon polariton 12 amplified as described above is scattered when the recording medium is brought close to the electromagnetic field conversion element 30 and taken out as a local electromagnetic field. That is, in the present embodiment, the surface of the metal film 6 serves as a local electromagnetic field generator.

  In order to generate the surface plasmon polariton 12 on the surface of the metal film 5, the incident angle of the incident light 11 may be an appropriate angle with respect to the boundary surface between the substrate 9 and the metal film 5 as described above. desirable. The polarization direction of the incident light is preferably p-polarized light in order to increase the incident light-electromagnetic field conversion efficiency.

  When the excitation method of the surface plasmon polariton 12 in the electromagnetic field conversion element 30 is the first excitation method already described, as shown in FIG. 22, the wave vector of the incident light 11 of the wave vector of the incident light 11 The component parallel to the surface of the metal film and the boundary line between the metal films on the metal film surface are preferably perpendicular.

  The second excitation method may be used as the excitation method in the electromagnetic field conversion element 30. In this case, the edge of the metal film 5 that generates the surface plasmon polariton and the metal film 5 on the metal film surface. It is preferable to make the boundary line between 6 parallel. At this time, the traveling direction of the surface plasmon polariton 12 generated in the metal film 5 is perpendicular to the boundary line between the metal films 5 and 6. Therefore, when the surface plasmon polariton 12 reaches the metal film 6, the component parallel to the surface of the electric field and perpendicular to the boundary line is most efficiently amplified. That is, at this time, the intensity amplification of the surface plasmon polariton due to the different dielectric constants is most efficiently performed. In order to increase the amplification effect of the surface plasmon polariton 12, a combination of metal films may be appropriately selected based on the traveling direction of the surface plasmon polariton 12.

  Further, the position of the metal film where the incident light 11 is irradiated (the position of the incident light irradiation portion) is not particularly limited, but is preferably in the vicinity of the boundary between the metal film 5 and the metal film 6. This is because, if the distance from the generation of the surface plasmon polariton 12 of the metal film 5 to the arrival of the metal film 6 after the generation of the surface plasmon polariton 12 on the metal film 5 is too long, as described above, the surface plasmon polariton 12 is attenuated. This is because the incident light-electromagnetic field conversion efficiency is lowered.

  Further, the incident light 11 may be a plane wave light, or may be light that is narrowed by a lens or the like. The advantages and disadvantages of using a lens and using a plane wave are as described above.

  The case where the method called the Kretchmann arrangement is used in the first excitation method has been described above, but the method called the Ototo arrangement of the first excitation method described above can also be used.

  In the present embodiment, a scatterer that scatters the surface plasmon polariton 12 is not provided. When such an electromagnetic field conversion element is used in a recording apparatus, the distance from the electromagnetic field conversion element to the recording medium (local electromagnetic field irradiation object) is within a range of ¼ or less of the wavelength of the surface plasmon polariton 12. It is preferable to make it. In addition, the surface plasmon polariton 12 can be scattered by forming slits or openings, or protrusions such as fine metals. When these scatterers are used, the surface plasmon polariton 12 can be amplified and more localized. On the other hand, when the shape of these scatterers changes over time due to heat, collision with the recording medium, or the like, There is a problem that characteristics change. In particular, when an opening or a slit is used, not only near-field light but also propagating light is generated, which causes a problem of background noise. These problems can be prevented in a configuration that does not use a scatterer.

  Next, the result of simulation by the FDTD method using the configuration of the electromagnetic field conversion element 30 will be described with reference to FIG.

  The incident light-electromagnetic field conversion efficiency with respect to the dielectric constant of the metal material of the metal film 6 in FIG. 22 was examined.

  FIG. 23 is a graph showing incident light-electromagnetic field conversion efficiency when the metal material of the metal film 6 is changed. As shown in the figure, the metal film 5 is fixed to Al and the metal material of the metal film 6 is silver (Ag), gold (Au), copper (Cu), nickel (Ni), titanium (Ti), Platinum (Pt) or manganese (Mn) was used. The horizontal axis of the graph is the magnitude of the dielectric constant of the metal material of the metal film 6, and the vertical axis is the incident light-electromagnetic field conversion efficiency. Further, the case where only the Al film is formed on the transparent substrate 9 is also shown in the graph.

  As shown in FIG. 23, compared to the case where only the Al film is formed, incident light-electromagnetic field conversion is achieved when the metal film made of another metal material is used together, regardless of which other metal material is used. The efficiency was high. That is, the amplification effect of the surface plasmon polariton 12 was obtained by using a metal material different from the metal film 5 as the metal film 6.

  In addition, the amplification effect increased as the dielectric constant of the metal material of the metal film 5 increased with respect to the dielectric constant of the metal material of the metal film 6. That is, in the electromagnetic field conversion element 30 of the present embodiment, the dielectric constant of the metal material of the metal film 6 is preferably smaller than the dielectric constant of the metal material of the metal film 5. In this simulation, it is preferable to use either Au or Cu as the metal film 6 with respect to Al of the metal film 5.

  In the present embodiment, since only two metal films are used, it is not necessary to create a very thin metal film 6 as in the first to fifth embodiments. There is an advantage that the accuracy required for alignment of the metal film is reduced.

[Method of manufacturing electromagnetic field conversion element]
The manufacturing method of the electromagnetic field conversion element of the present invention described above will be described based on FIGS. 18 (a) to 18 (f).

  18 (a) to 18 (f) are diagrams showing a method for manufacturing the electromagnetic field conversion element 28 shown in FIG. The electromagnetic field conversion element 28 can be manufactured as follows by a dry etching process such as RIE (reactive ion etching).

  First, the metal film 7 is formed on the transparent substrate 9 by sputtering or vapor deposition. A photoresist 15 is applied thereon by a spin coater or the like. At this time, if the photoresist 15 is a positive type, the portion other than the portion where the metal film 6 is to be formed is covered with the mask 14 (FIG. 18A). By exposing and developing in the state covered with the mask 14, the portion of the photoresist 15 not covered with the mask 14 is removed (FIG. 18B). Next, RIE is performed to etch the portion of the metal film 7 from which the photoresist 15 has been removed (FIG. 18C). In the course of this etching, all the metal film 7 not covered with the photoresist 15 is removed, so that the metal film 6 is in contact with the transparent substrate 9 as in the electromagnetic field conversion element 28 of FIG. it can.

  After the etching, the metal film 6 is formed by vapor deposition (FIG. 18D), and when the remaining photoresist 15 covered with the mask 14 is removed, the metal film 6 and the metal film 7 are adjacent to each other. (FIG. 18 (e)). If there are burrs on the surface of the metal film, the surface may be polished.

  The opening and the slit can be obtained by removing a desired portion with FIB (focus in beam) (FIG. 18 (f)).

  On the other hand, when the metal film 6 is formed first and then removed by etching, the amount of etching, that is, the depth of digging of the metal film 6 is changed to change between the metal film 7 and the transparent substrate 9. The thickness of the metal film 6 can be adjusted. That is, by making the digging shallow, a structure in which the metal film 7 does not contact the transparent substrate 9 as in the electromagnetic field conversion element 29 of FIG.

  Further, the metal film 7, the metal film 6, and the metal film 7 are formed in this order on another substrate, a transparent substrate 9 is attached to the side surface, and the side surface opposite to the side where the transparent substrate 9 is attached is polished. Alternatively, the metal film 6 and the metal film 7 can be formed on the transparent substrate 9 by cutting with FIB.

  When the metal protrusion 10 is provided as in the electromagnetic field conversion element 27 shown in FIG. 11, the protrusion may be formed at a desired location on the metal film.

[Recording device]
Hereinafter, a recording apparatus using the electromagnetic field conversion element of the present invention will be described with reference to FIG.

  FIG. 19 is a perspective view of a recording apparatus 30 using the electromagnetic field conversion element according to the present embodiment. The recording device 30 includes at least an electromagnetic field conversion element 2, a light source 31, a drive unit 32, a spindle 33, and a control unit 40. The electromagnetic field conversion element 2 may be any of the electromagnetic field conversion elements 21, 22, 23, 24, 25, 26, 27, 28, and 29 described above.

  The drive unit 32 includes an arm 37, a rotation shaft 35, and a slider 36. The electromagnetic field conversion element 2 and the light source 31 are mounted on the slider 36. The light source 31 irradiates the electromagnetic field conversion element 2 with light. The electromagnetic field conversion element 2 converts the light from the light source 31 into an electromagnetic field and irradiates the recording medium 50, thereby recording on the recording medium 50. And / or play. The slider 36 controls the distance between the disk-shaped recording medium 50 and the electromagnetic field conversion element 2. The arm 37 is a support portion of a swing arm structure that moves the slider 36 in a substantially radial direction of the disk-shaped recording medium 50. The arm 37 can rotate around the rotation shaft 35. The spindle 33 corresponds to a spindle motor that rotates the recording medium 50.

  Since the intensity of the local electromagnetic field generated by the electromagnetic field conversion element 2 decreases with increasing distance from the generation position, the recording medium 5 and the electromagnetic field conversion element are used to irradiate the recording layer of the recording medium 5 with sufficient intensity. The distance from 2 should be as short as possible. Therefore, the electromagnetic field conversion element 2 is mounted on the slider 36, and the distance from the electromagnetic field conversion element 2 to the recording surface of the recording medium 5 is controlled by the structure of the slider 36. Currently, this distance is generally several nanometers. In the present embodiment, it is preferable that the distance between the electromagnetic field conversion element 2 and the recording surface of the recording medium 5 is controlled to be ¼ or less of the wavelength of the local electromagnetic field generated by the electromagnetic field conversion element 2.

  In FIG. 19, a light source 31 is provided on the arm 37 as a light source for irradiating the electromagnetic field conversion element 2 with light.

  The control unit 40 scans the slider 36 and the electromagnetic field conversion element 2 to a desired position on the recording medium 50, and an access circuit 42 that controls the rotational position of the arm 37 in the drive unit 32, and a local in the electromagnetic field conversion element 2. A laser drive circuit 43 for controlling the intensity of the electromagnetic field and the irradiation time of the laser light from the light source 3, a spindle drive circuit 44 for controlling the rotational drive of the recording medium 50, and a control circuit 41 for comprehensively controlling them. I have.

  The light source 31 of the recording apparatus 30 is not particularly limited, but a semiconductor laser is preferable when downsizing is a priority, and a gas laser, solid laser, or pulse laser is used when light intensity is required. That's fine.

  In FIG. 19, the light source 31 is a semiconductor laser and is integrated with the electromagnetic field conversion element 2 and mounted on the drive unit 32. However, the electromagnetic field conversion element 2 and the light source 31 may be provided separately.

  In the case where the electromagnetic field conversion element 2 and the light source 31 are integrated, the electromagnetic field conversion element 2 may be installed immediately after the light source 31, or an electromagnetic field conversion element is formed by directly depositing and processing a metal film on the emission port of the light source 3. 2 may be configured. In this case, the integrated light source 31 and electromagnetic field conversion element 2 are both mounted on the drive unit 32. When integrated in this way, the number of parts is small and the assembly accuracy is improved, so that the reliability is improved. In addition, there is an advantage of being small.

  When the light source 3 and the electromagnetic field conversion element 2 are provided separately, a means for guiding the light from the light source 3 to the electromagnetic field conversion element 2 is separately provided. FIG. 20 shows an example of means for guiding light from the light source 31 to the electromagnetic field conversion element 2. In this example, the arm 37 is provided with a mirror 38 whose reflection surface has an upper side angle of 45 degrees with respect to the axis of the arm 37. The mirror 38 is irradiated with light from the light source 3 from a direction 90 degrees directly above the axis of the arm 37. The light reflected by the mirror 38 travels in the direction of the tip of the arm 37 parallel to the axis of the arm 37 and is irradiated to the mirror 39 disposed near the tip of the arm 37. The mirror 39 is installed such that its reflection surface is at an angle of 45 degrees on the lower side with respect to the axis of the arm 37, and the mirror 39 transmits the light reflected by the mirror 38 to the electromagnetic field conversion element 2. Lead. In the arm 37, an opening is provided in a region serving as an optical path of light from the mirror 39 to the electromagnetic field conversion element 2 so that light can be transmitted. Even if the arm 37 rotates, if the light from the light source 31 is incident on the mirror 38 of the arm 37 from directly above, the direction reflected by the mirror 38 is the direction along the axis of the arm 37. That is, the light reflected by the mirror 38 is reflected by the mirror 39 at the tip of the arm 37 and is always applied to the electromagnetic field conversion element 2.

  As a means for guiding light to the electromagnetic field conversion element 2, 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. Moreover, the light source 3 may be installed away from the arm 37 as shown in FIG. Further, by installing the light source 31 at the position of the mirror 38 in the arm 37 and emitting the light in the direction of the mirror 39, the electromagnetic field conversion element 2 is irradiated with the light by the mirror 39, similarly to the configuration shown in FIG. be able to.

  When the light source 31 and the electromagnetic field conversion element 2 are separately provided as described above, the light source 3 and the electromagnetic field conversion element 2 are installed spatially separated from each other, so that the light source 3 generates heat generated by the electromagnetic field conversion element 2. There is an advantage that light oscillation is stabilized without being affected.

  Next, the operation of the recording apparatus 1 will be described.

  When the recording device 30 records or reproduces information on the recording medium 50, that is, during operation, the spindle drive circuit 44 in the control unit 40 rotates the spindle 33 on which the recording medium 50 is installed at an appropriate rotational speed. . The access circuit 42 in the control unit 40 scans the electromagnetic field conversion element 2 to a desired location on the recording medium 50 by moving the drive unit 32. The laser drive circuit 43 causes the light source 31 to emit light at a predetermined intensity and time interval. By irradiating the electromagnetic field conversion element 2 with this light (incident light), the surface plasmon polariton is excited and a local electromagnetic field is generated.

  As described above, the mark is recorded on the recording medium 50 by the local electromagnetic field generated at the intensity and time interval corresponding to the light emission of the light source 31. In the control circuit 35, the light emission of the light source 3, the operation of the drive unit 4, and the rotation of the spindle are summarized and an instruction is given to each circuit so that desired recording can be performed at a desired location.

  The recording medium 5 may be a recording medium on which data is recorded or reproduced using light. For example, the recording medium 5 is a CD (Compact Disc), DVD (Digital versatile Disc), BD (Blu-ray Disc) ROM, -R, ± RW, an organic structure change medium such as a RAM, and a phase change medium. The information may be recorded only by light (optical recording medium). In this case, the local electromagnetic field generated from the electromagnetic field conversion element 2 causes a structural change or phase change in the recording layer of the optical recording medium, and this changed portion becomes a recording mark. Since the size of the recording mark is determined by the spot size of the local electromagnetic field, the spot size can be reduced by using the local electromagnetic field generated only in the minute region generated from the electromagnetic field conversion element 2 of the present invention. Recording density can be improved. Further, the formation speed of the recording mark, that is, the speed at which the structural change or phase change occurs in the recording medium 5 depends on the applied energy, that is, the strength of the electromagnetic field. That is, since the electromagnetic field conversion element 2 of the present invention generates a strong local electromagnetic field, the transfer rate can be improved.

  The recording medium 5 may be a magneto-optical recording medium that is recorded by light and magnetism, such as MD, MO, and optically assisted magnetic recording medium. In this case, the slider 36 at the tip of the arm 21 of the drive unit 4 of the recording medium is provided with a magnetic head (not shown) together with the electromagnetic field conversion element 2. At the time of information recording, the recording layer of the recording medium 5 is heated by a local electromagnetic field generated from the electromagnetic field conversion element 2, and a magnetic field generated from the magnetic head is applied to reverse the direction of the magnetic moment inside the recording layer. The The portion where the magnetic moment is reversed becomes a recording mark. In particular, when optically assisted magnetic recording / reproduction is performed, a reproducing element (not shown) is mounted on the slider 36 of the drive unit 4 together with the magnetic head. As the reproducing element, GMR (Giant Magneto Resistive), TMR (Tunneling Magneto Resistive), or the like may be used.

  In addition, a protective layer made of a mold resin or the like is provided between the light source 3 and the electromagnetic field conversion element 2 and the magnetic head and the reproducing element so as not to destroy the magnetic head and the reproducing element due to heat generated by the light source 3 and the electromagnetic field conversion element 2. May be provided.

  The size of the recording mark of the magneto-optical recording medium is determined by the overlap between the region sufficiently heated by the local electromagnetic field and the region irradiated with the magnetic field from the magnetic head. Therefore, the recording density can be improved by using the electromagnetic field conversion element 2 of the present invention that generates a local electromagnetic field having a small spot diameter. Further, the recording mark formation speed of the magneto-optical recording medium, that is, the recording speed depends on the heating rate of the recording layer, and this heating rate depends on the strength of the applied local electromagnetic field. That is, as in the case of the electromagnetic field conversion element 2 of the present invention, when the intensity of the local electromagnetic field applied to the recording layer is strong, the time for raising the temperature of the recording medium 5 to the required temperature is shortened, so that the transfer rate is improved. be able to.

  Furthermore, the recording apparatus 1 can record a fine structure by using a substrate coated with a resist as the recording medium 5. In this case, the wavelength of light incident on the electromagnetic field conversion element 2 may be selected from the resist photosensitive region. Usually, wavelengths near the ultraviolet region are used so that they are not easily exposed to ambient illumination or sunlight.

  If the resist is a positive type, a portion exposed by a local electromagnetic field generated from the electromagnetic field conversion element 2 is removed during development. If it is a negative type, parts other than the exposed part are removed during development. Since the minimum size of this shape is determined by the irradiation region of the local electromagnetic field, if the local electromagnetic field is generated only in the minute region as in the present case, fine processing becomes possible. In addition, since the resist can be exposed in a shorter time as the intensity of the local electromagnetic field generated from the electromagnetic field conversion element 2 increases, the exposure rate increases.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of 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 information recording apparatus that records or reproduces information by light.

It is the perspective view shown about the 1st excitation method of the surface plasmon polariton in the electromagnetic field conversion element which concerns on embodiment of this invention (Kretchmann arrangement | positioning). It is the perspective view shown about the 1st excitation method of the surface plasmon polariton in the electromagnetic field conversion element which concerns on embodiment of this invention (Otto arrangement | positioning). It is the perspective view shown about the 2nd excitation method of the surface plasmon polariton concerning embodiment of this invention. It is the perspective view which showed the electromagnetic field conversion element which concerns on embodiment of this invention. It is a graph showing the simulation result of the electromagnetic field conversion element shown in FIG. It is a graph showing the simulation result of the electromagnetic field conversion element shown in FIG. It is the perspective view which showed the electromagnetic field conversion element which concerns on other embodiment of this invention. It is drawing showing the distribution of the electromagnetic field intensity of the electromagnetic field conversion element shown in FIG. It is the perspective view which showed the electromagnetic field conversion element which concerns on other embodiment of this invention. It is the graph which showed the simulation result of the electromagnetic field conversion element shown in FIG. It is the perspective view which showed the electromagnetic field conversion element which concerns on other embodiment of this invention. It is drawing which showed the simulation result of the electromagnetic field conversion element shown in FIG. It is the perspective view which showed the electromagnetic field conversion element which concerns on other embodiment of this invention. It is a graph showing the simulation result of the electromagnetic field conversion element shown in FIG. It is a graph showing the simulation result of the electromagnetic field conversion element shown in FIG. It is a graph showing the simulation result of the electromagnetic field conversion element shown in FIG. It is the perspective view which showed the electromagnetic field conversion element which concerns on other embodiment of this invention. It is drawing which showed the manufacturing method of the electromagnetic field conversion element shown in FIG. 1 is a block diagram showing an optical recording apparatus according to an embodiment of the present invention. It is drawing which shows the electromagnetic field generation | occurrence | production unit which concerns on embodiment of this invention. It is a perspective view which shows the prior art and shows the electromagnetic field conversion element which formed periodic topography on the metal film surface. It is the perspective view which showed the electromagnetic field conversion element which concerns on other embodiment of this invention. It is drawing which showed the simulation result of the electromagnetic field conversion element shown in FIG.

Explanation of symbols

2, 21-30 Electromagnetic field conversion element 5 Metal film (second metal film)
6 Metal film (first metal film)
7 Metal film (second metal film)
9 Transparent substrate 10 Metal protrusion (protrusion)
DESCRIPTION OF SYMBOLS 11 Incident light 12 Surface plasmon polariton 13 Dielectric layer 17 Metal film 200 Electromagnetic field conversion element

Claims (26)

An electromagnetic field conversion element that converts incident light into surface plasmon polaritons and extracts the surface plasmon polaritons as an electromagnetic field,
A transparent substrate having translucency;
A first metal film and a second metal film are provided on the surface of the transparent substrate,
The above first metal film and the second metal film is formed of different materials,
At least one of the first metal film or the second metal film converts light incident from the transparent substrate side into the surface plasmon polariton,
The electromagnetic field conversion element , wherein the first metal film and the second metal film are provided in contact with each other in different regions on the surface of the transparent substrate .   The metal film that converts light incident from the transparent substrate side into a surface plasmon polariton out of the first metal film and the second metal film has a dielectric constant larger than one of the metal films. Electromagnetic field conversion element.   3. The electromagnetic field conversion element according to claim 1, wherein the first metal film is formed between at least two of the second metal films and has at least two boundary lines.   4. The electromagnetic field conversion element according to claim 3, wherein the refractive index of the material of the metal film in contact with at least the second metal film is smaller than the refractive index of the material of the second metal film.   5. The electromagnetic field conversion element according to claim 3, wherein boundaries between the first metal film and the second metal film are linear and parallel to each other. 6.   A dielectric layer having a refractive index smaller than that of the transparent substrate is formed between the transparent substrate and the first metal film and / or between the transparent substrate and the second metal film. The electromagnetic field conversion element according to claim 1, wherein:   The local electromagnetic field generating part for scattering the surface plasmon polariton is provided on at least one surface of the first metal film and / or the second metal film, according to any one of claims 1 to 6. The electromagnetic field conversion element described in 1.   The local electromagnetic field generating part is formed in a range not more than a propagation length of a surface plasmon polariton from a boundary line between the first metal film and the second metal film. Electromagnetic field conversion element.   The electromagnetic field conversion element according to claim 7 or 8, wherein the local electromagnetic field generation unit is at least one edge of the first metal film or the second metal film.   A part of the first metal film in contact with the second metal film is formed so as to separate the first metal film from a boundary with the second metal film, and the first metal film in contact with the second metal film. The electromagnetic field conversion element according to claim 7, wherein an edge of a part of the metal film is the local electromagnetic field generation unit.   9. The electromagnetic field conversion element according to claim 7, wherein the local electromagnetic field generation unit is an opening or an edge of a slit provided in the first metal film and / or the second metal film.   9. The electromagnetic field conversion element according to claim 7, wherein the local electromagnetic field generation unit is a protrusion provided on the first metal film and / or the second metal film. 10.   The electromagnetic field generation unit provided with the electromagnetic field conversion element and light source of any one of Claims 1-11 at least.   Incident light irradiated from the light source is at an angle at which the intensity of reflected light from the first metal film and / or the second metal film is a minimum value with respect to the first metal film and / or the second metal film. The electromagnetic field generation unit according to claim 13, wherein the electromagnetic field generation unit is incident.   The electromagnetic field generating unit according to claim 13 or 14, wherein the polarization direction of incident light emitted from the light source is p-polarized light.   16. The incident light irradiation unit irradiated with incident light from the light source is an edge of the first metal film and / or the second metal film, according to any one of claims 13 to 15. Electromagnetic field generation unit.   The incident light irradiating portion irradiated with the incident light from the light source is an opening or slit provided in the first metal film and / or the second metal film. The electromagnetic field generating unit according to item 1.   The electromagnetic field generating unit according to claim 17, wherein the incident light is irradiated in a direction perpendicular to the first metal film and / or the second metal film.   The electromagnetic field generating unit according to claim 17 or 18, wherein a polarization direction of the incident light is perpendicular to an edge of the opening or the slit.   The electromagnetic field generation unit according to any one of claims 13 to 19, wherein the electromagnetic field conversion element and the light source are provided at positions separated from each other.   The electromagnetic field generating unit according to any one of claims 13 to 19, wherein the electromagnetic field conversion element is provided in a light output portion of the light source.   The electromagnetic field generating unit according to any one of claims 13 to 21, further comprising means for minimizing light from the light source.   The electromagnetic field generating unit according to claim 22, wherein the means for minimizing the light is a lens.   The electromagnetic field generating unit according to claim 22, wherein the means for miniaturizing the light is a beam expander. An apparatus for recording or reproducing information on a recording medium, comprising the electromagnetic field generating unit according to any one of claims 13 to 24,
A recording apparatus, wherein a distance between the electromagnetic field conversion element and a recording surface of the recording medium is controlled to be equal to or less than a quarter of a wavelength of a local electromagnetic field generated by the electromagnetic field conversion element.   26. The recording apparatus according to claim 25, comprising a magnetic recording and reproducing head.

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