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WO2019039551A1 - Metamaterial structure and refractive index sensor - Google Patents

Metamaterial structure and refractive index sensor Download PDF

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Publication number
WO2019039551A1
WO2019039551A1 PCT/JP2018/031180 JP2018031180W WO2019039551A1 WO 2019039551 A1 WO2019039551 A1 WO 2019039551A1 JP 2018031180 W JP2018031180 W JP 2018031180W WO 2019039551 A1 WO2019039551 A1 WO 2019039551A1
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Prior art keywords
refractive index
metamaterial structure
index sensor
detection
metamaterial
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PCT/JP2018/031180
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French (fr)
Japanese (ja)
Inventor
義明 金森
羽根　一博
友己 清水
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Tohoku University NUC
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Tohoku University NUC
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Priority to JP2019537682A priority Critical patent/JP7202661B2/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length

Definitions

  • the present invention relates to a metamaterial structure and a refractive index sensor.
  • Non-Patent Documents 1 and 2 Although a refractive index sensor using propagating surface plasmons on a glass prism on which a gold (Au) thin film is formed as described in Non-Patent Documents 1 and 2 can perform precise measurement, the device There was a problem that it was complicated and expensive. In addition, although a refractive index sensor using localized surface plasmons of Au colloid, as described in Non-Patent Document 3, is inexpensive and simple measurement is possible, compared to a refractive index sensor using propagating surface plasmons There is a problem that the detection accuracy is inferior.
  • the present invention has been made in view of such problems, and an object of the present invention is to provide a metamaterial structure and a refractive index sensor capable of performing inexpensive measurement with high precision.
  • the metamaterial is sensitive to changes in the refractive index of its surroundings, and that it is possible to design the shape with a high degree of freedom.
  • a high performance refractive index sensor can be realized. This makes it possible to provide a refractive index sensor that enables inexpensive and accurate measurement.
  • the metamaterial structure according to the present invention has a fine structure equal to or less than the wavelength of incident light, and the optical coupling between the incident light and the surface plasmon mode depending on the fine structure has a resonance condition
  • the fine structure is characterized by comprising a unit structure in which a two-dimensional periodic arrangement is rotationally symmetrical.
  • the refractive index sensor according to the present invention is characterized by having the metamaterial structure according to the present invention.
  • the metamaterial structure according to the present invention can adjust the selected wavelength of the light response by the size of the microstructure.
  • the selected wavelength is sensitively changed by the surrounding medium. Therefore, the metamaterial structure and the refractive index sensor according to the present invention detect the refractive index of the surrounding medium from the change of the selected wavelength or the change of the reflectance at a specific wavelength by the medium around the metamaterial structure.
  • the metamaterial structure and the refractive index sensor according to the present invention have a simple structure and can be manufactured at low cost, as compared with a conventional refractive index sensor using propagating surface plasmons.
  • the conventional refractive index sensor using surface plasmons is configured by randomly arranging a thin film of gold or fine particles of gold, the degree of enhancement of surface plasmons has not been optimized. In addition, optimization is difficult because it is made bottom up.
  • the shape of the metamaterial structure can be arbitrarily designed according to the concept of the metamaterial, so that the plasmon enhancement can be optimized. Therefore, the sensitivity can be made higher than that of the conventional case, and accurate measurement can be performed.
  • the refractive index sensor according to the present invention preferably has a refractive index sensitivity of 300 to 1000 nm / RIU.
  • the metamaterial structure according to the present invention can be made polarization independent because the fine structure is composed of a unit structure in which the two-dimensional periodic arrangement is rotationally symmetric.
  • the metamaterial structure according to the present invention may use any technique for shape processing of a fine structure, for example, using a semiconductor fine processing technique or nanoimprint capable of mass-producing nanostructures inexpensively. it can.
  • the incident light may have any wavelength depending on the object to be detected.
  • the metamaterial structure according to the present invention can be miniaturized by reducing the size of the fine structure, in which case, for example, the wavelength of incident light may be 2500 nm or less.
  • the fine structure is formed by arranging a plurality of the unit structures regularly in the longitudinal direction and / or the lateral direction along the two-dimensional array plane of the unit structures. It may be
  • the microstructure may be made of any material depending on the wavelength of incident light, for example, made of gold, silver, copper, aluminum or transition metal nitride. It is also good.
  • transition metal nitrides include TiN, ZrN, HfN, and TaN.
  • the refractive index sensor according to the present invention may have any configuration as long as the medium around the metamaterial structure can be detected according to the refractive index.
  • the refractive index sensor according to the present invention may include an optical fiber, and the metamaterial structure may be provided at the tip of the optical fiber.
  • in-situ measurement can be performed rather than invasive measurement in which the sample is cut out. For this reason, precise measurement is possible even for a measurement target that is environment-dependent, such as a living body.
  • an optical fiber thinner than the injection needle measurement with less damage to a living body or the like becomes possible.
  • the measurement range is determined by the diameter of the optical fiber, the physical quantity of the minute area can be measured by using a thin optical fiber. Also, by moving the optical fiber, spatial mapping of measurement results can be performed.
  • the refractive index sensor according to the present invention may have a glass plate, and the metamaterial structure may be provided on the surface of the glass plate.
  • the metamaterial structure may be provided on the surface of the glass plate.
  • the refractive index sensor according to the present invention may have a detecting agent attached to the surface of the fine structure, and the detecting agent may be capable of interacting with the object to be detected.
  • the agent for detection and the object to be detected are such that the agent for detection can interact with the object to be detected and the change in refractive index that can be measured is recognized before and after the interaction, It may be
  • the interaction between the agent for detection and the object to be detected may be any interaction such as binding of the object to be detected to the agent for detection.
  • the combination of a detection agent and a detection target includes, for example, a detection DNA and a complementary DNA, a detection RNA and a complementary RNA, biotin and avidin or streptavidin, an antigen and an antibody, various proteins and substances acting on the protein, These include various amino acids and substances acting on the amino acids, ligands and receptors.
  • the agent for detection comprises DNA for detection or RNA for detection, it can form a complementary strand with the DNA or RNA to be detected, and by measuring the change in refractive index due to the formation of the complementary strand, the desired DNA or RNA to be detected can be detected.
  • the fine structure is preferably made of a material capable of binding the detection DNA or the detection RNA.
  • the metamaterial structure according to the present invention is not limited to a refractive index sensor, for example, a chemical sensor, a biosensor, an in situ analysis device, a medical device integrated with a catheter or an endoscope, high refractive index and chemical / biomaterial It may be applied to a resolution spatial mapping device.
  • the chemical sensor is a sensor intended for gas and organic chemical substances, and is applied to, for example, taste, food, chemicals, alcohol check and the like.
  • the biosensor is a sensor intended for a living body or the like, and is applied to, for example, a toxicity sensor, a blood glucose sensor, a DNA sensor, a medical sensor or the like.
  • the measurement results spatially mappable, for example, in the case of a biosensor, it is possible to identify the shape, size, and type of cells and DNA, and in the case of a chemical sensor, Concentration distribution analysis etc. can be performed.
  • spatial mapping can not be performed, for example, when the object to be measured is a mixed substance, only one point can be measured, so it is not known whether they are mixed or not, and they have spatial distribution and shape. I do not know it.
  • the refractive index sensor according to the embodiment of the present invention has (a) reflection spectrum when the refractive index n around the metamaterial structure is 1.0 to 1.5, (b) reflection peak wavelength (Peak wavelength) It is a graph which shows ambient refractive index (Refractive index) dependence.
  • FIG. 10 is an electric field intensity distribution map of the upper part of the metamaterial structure. It is a scanning electron microscope (SEM) image of the metamaterial structure of embodiment of this invention.
  • SEM scanning electron microscope
  • A Reflection Spectrum Measured in Four Types of Media of Air (Air), Pure Water (DIW), Isopropanol (IPA), and Glycerin
  • Fig. 7 is a graph showing the refractive index (Refractive index) dependency of the reflection peak wavelength (Peak wavelength).
  • FIG. 14 is a plan view showing a modification in which the arrangement shown in (c) is reversed, (e) another modification, and a modification in which the arrangement shown in (f) and (e) is reversed.
  • A Other Modifications of the Microstructure
  • FIG. 14 is a plan view showing a modification in which the arrangement shown in (c) is reversed, (e) another modification, and a modification in which the arrangement shown in (f) and (e) is reversed.
  • connection state between the metamaterial structure and the light source and the optical detector (optical detector), (b) a variation of the connection state, (c) the connection state
  • FIG. 16 is a perspective view showing another modified example of (d) and another modified example of the connected state. It is a graph which shows the optical response of the refractive index sensor shown in FIG. a) to f) are cross-sectional views showing a method of manufacturing the refractive index sensor shown in FIG. (A) an electron micrograph showing a metamaterial structure of the tip end face of the optical fiber manufactured by the method for producing a refractive index sensor shown in FIG.
  • center part of the tip end face of the optical fiber shown in (a) 6 is an electron micrograph (a perspective view) obtained by enlarging the central portion of the tip surface of the optical fiber shown in (c) (a). It is a reflection spectrum in the air (Air) and in ethanol (Ethanol) of the refractive index sensor shown in FIG. It is a top view which shows the modification at the time of reducing the dimensional parameter of the metamaterial structure of embodiment of this invention. 24 is a transmission spectrum and a reflection spectrum of the metamaterial structure shown in FIG. 24 when the surrounding refractive index n is 1.0 to 1.2.
  • FIG. 1 to 25 show a metamaterial structure and a refractive index sensor according to an embodiment of the present invention.
  • the refractive index sensor 10 includes a metamaterial structure 11, a transparent substrate 12, a light source 13, a half mirror 14, and a spectroscope 15.
  • the metamaterial structure 11 has a microstructure 11 a composed of a plurality of cut wires, and is provided on a transparent substrate 12.
  • the fine structure 11a has a structure similar to or less than the wavelength of incident light, and is composed of a unit structure in which a two-dimensional periodic arrangement is made in rotational symmetry.
  • the metamaterial structure 11 is configured to exhibit a wavelength-selective light response by the optical coupling between incident light and the surface plasmon mode depending on the microstructure 11a becoming stronger under resonance conditions.
  • the metamaterial structure 11 is rotationally symmetric in unit structure and polarization independent.
  • the fine structure 11 a is made of gold (Au) having a high reflectance in the near infrared region.
  • the microstructure 11a may be made of silver, copper, aluminum, or TiN, ZrN, HfN, or TaN transition metal nitride having high carrier concentration and exhibiting plasmon characteristics.
  • the microstructure 11a is formed of a cut wire, and has a structure in which two rectangles arranged in parallel are arranged in four-fold symmetry.
  • the light source 13 is provided to cause incident light to be incident on the metamaterial structure 11 from the side of the transparent substrate 12 through the half mirror 14.
  • the half mirror 14 transmits incident light from the light source 13 and reflects reflected light from the metamaterial structure 11 so as to bend it 90 degrees.
  • a two-branch optical fiber may be used instead of the half mirror 14.
  • the spectroscope 15 receives the reflected light from the metamaterial structure 11 reflected by the half mirror 14 and is provided so as to detect its spectrum.
  • a combination of a wavelength variable light source and a photodetector may be used.
  • the metamaterial structure 11 can adjust the selected wavelength of the light response by the size of the microstructure 11a. Also, in the metamaterial structure 11, the selection wavelength is sensitively changed by the surrounding medium. For this reason, the refractive index sensor 10 can detect the refractive index of the surrounding medium from the change in the selected wavelength by the medium around the metamaterial structure 11 or the change in the reflectance at a specific wavelength. In addition, the refractive index sensor 10 has a simple structure as compared to a conventional refractive index sensor using propagating surface plasmons, and can be manufactured at low cost.
  • the shape of the metamaterial structure 11 can be arbitrarily designed according to the concept of the metamaterial, so that the plasmon enhancement can be optimized. Therefore, the sensitivity can be made higher than that of the conventional case, and accurate measurement can be performed.
  • any technique may be used for shape processing of the microstructure 11a. For example, semiconductor microfabrication technology or nanoimprint capable of mass-producing nanostructures inexpensively can be used. it can.
  • the metamaterial structure 11 was manufactured, and sensitivity measurement of refractive index was performed. First, optical design of the metamaterial structure 11 was performed. The Rigorous Coupled-Wave Analysis method was used for optical design.
  • a plurality of unit structures of the fine structure 11a shown in FIG. 1B are regularly arranged in the longitudinal direction and the lateral direction.
  • the metamaterial structure 11 has a w (width of cut wire) of 90 nm, a g (gap between cut wires disposed in parallel) of 150 nm, and a d (gap between cut wires disposed in vertical) in the figure.
  • the microstructure 11a is formed of a rectangular cut wire as shown in FIG. 1 (b)
  • the aspect ratio (l / w) is 3 to 4 and the surface has a unit structure in order to enhance the refractive index sensitivity.
  • the ratio (fill factor) occupied by the cut wire is preferably 0.08 to 0.12.
  • the reflection spectrum at each refractive index when the refractive index n around the metamaterial structure 11 is changed from 1.0 to 1.5 is obtained by design calculation, and the calculation result is shown in FIG. .
  • the harmonics at the time of calculation was set to 6. Further, the relationship between the peak wavelength (Peak wavelength) of the reflection spectrum and the refractive index (Refractive index) is obtained from FIG. 2 (a), and is shown in FIG. As shown in FIG. 2 (b), it was confirmed that the peak wavelength of the reflection spectrum changes linearly in accordance with the change of the refractive index around the metamaterial structure 11.
  • the refractive index sensitivity of the refractive index sensor 10 determined from FIG. 2B is 593 nm / refractive index unit (RIU).
  • the electric field intensity distribution on the upper portion of the metamaterial structure 11 when light is perpendicularly incident on the metamaterial structure 11 designed to design polarized light in the X direction and 45 ° inclined from the X direction at a resonance wavelength of 1250 nm It shows in FIG. 3 (a) and (b), respectively.
  • the direction of polarization is indicated by arrows in FIGS. 3 (a) and 3 (b).
  • the refractive index around the metamaterial structure 11 is 1.0.
  • the vicinity of 1250 nm of the resonance wavelength is called "the optical window of the second living body", and it is known that absorption and scattering by the living body are small.
  • FIG. 3A it has been confirmed that the electric field is amplified at both ends of the cut wire in the longitudinal direction which is the X direction, and exhibits resonance characteristics in the X direction. Further, in FIG. 3 (b), the electric field was amplified at both ends of all the cut wires, and it was confirmed that the resonance characteristics were exhibited in any polarization direction.
  • the metamaterial structure 11 was manufactured on a quartz substrate by a lift-off process. That is, first, an EB (Electron Beam) resist was spin-coated on a substrate, and then a resist pattern was produced by EB lithography. On top of that, Ti (film thickness: 1 nm) and Au (film thickness: 40 nm) were formed into a film by EB evaporation, and then the EB resist was peeled off to produce metamaterial structure 11. Note that other semiconductor microfabrication techniques or nanoimprinting may be used to manufacture the metamaterial structure 11.
  • EB Electro Beam
  • the scanning electron microscope (SEM) image of the manufactured metamaterial structure 11 is shown in FIG.
  • the dimensions of the manufactured metamaterial structure 11 are 84 nm for w (cut wire width), 156 nm for g (gap between cut wires arranged in parallel), and 162 nm for d (gap between cut wires arranged in perpendicular)
  • L cut wire length
  • ⁇ cycle
  • t thickness
  • the width (w) and the length (l) were slightly smaller than in the design and the gaps (g, d) were slightly increased, it could be manufactured almost accurately.
  • rounding of the edge of each cut wire affects the Q value of resonance, it is desirable to make the edge as sharp as possible.
  • the side surfaces of the cut wire are preferably non-tapered and substantially perpendicular to the surface of the substrate.
  • the reflection spectrum measurement by the spectrometer 15 was performed in four types of media of air (Air), pure water (DIW), isopropanol (IPA), and glycerin (Glycerin) using the manufactured metamaterial structure 11.
  • the measured reflection spectrum is shown in FIG. 5A, and the relationship between the peak wavelength of the reflection spectrum (Peak wavelength) and the refractive index of the surrounding medium (Refractive index) is shown in FIG. 5B.
  • the refractive index of each medium is 1.000 for air, 1.321 for DIW, 1.368 for IPA, and 1.461 for glycerin.
  • the sensitivity of the refractive index was 605 nm / RIU, and a value close to the measured value was obtained.
  • the result is that the refractive index sensitivity of a conventional refractive index sensor using surface plasmons is 60 to 190 nm / RIU (Takashi Yoshida, "Plasmonics", NTS Inc., August 24, 2011, p.
  • the sensitivity is more than three times higher than that at the maximum.
  • the difference between the calculated value and the measured value is the measurement error due to the signal noise component due to the reattachment of a part of the Au piece peeled off at the time of lift-off in the vicinity of the metamaterial structure 11 and disturbing the surface plasmon mode. Is considered to be a cause.
  • FIGS. 7 (b) and (c) The measurement results of the reflection spectra before and after the binding of the complementary DNA 22 in the dry state and the wet state are shown in FIGS. 7 (b) and (c), respectively.
  • FIG. 7 (b) it was confirmed that the reflection peak wavelength is shifted 8.5 nm to the long wavelength side in the dry state due to the binding of the complementary DNA 22.
  • FIG. 7 (c) it was confirmed that in the wet state, the wavelength was shifted by 1.7 nm to the short wavelength side.
  • the refractive index of the complementary DNA 22 is calculated from the measurement results, the refractive index in the dry state is 1.13 and the refractive index in the wet state is 1.30.
  • the agent for detection and the object to be detected are not limited to the detection DNA 21 and the complementary DNA 22, respectively, and the agent for detection can interact with the object to be detected, and the change in measurable refractive index before and after the interaction. As long as it is recognized, it may be anything.
  • the interaction between the agent for detection and the object to be detected may be any interaction such as binding of the object to be detected to the agent for detection.
  • the combination of a detection agent and a detection target includes, for example, biotin and avidin or streptavidin, an antigen and an antibody, various proteins and substances acting on the proteins, various amino acids and substances acting on the amino acids, ligands and receptors Etc.
  • the two-dimensional arrangement of the metamaterial structures 11 is not particularly limited as long as the fine structures 11 a composed of a plurality of cut wires are rotationally symmetric and two-dimensionally arranged. 8 to 14 show examples of arrangement variations of the metamaterial structure 11. FIG.
  • the metamaterial structure 11 is formed into, for example, a microstructure 11a (see FIG. 8) in which four or more rectangular cut wires arranged in parallel are arranged in four-fold symmetry, a lattice, a circle, or a cross A microstructure 11a (see FIG. 9) in which the cut wires are arranged in four-fold symmetry, and a microstructure 11a in which a cut wire formed in a shape in which a bowl shape and an I shape are crossed are arranged four-fold ), An annular ring, a square frame shape, and a cut wire formed into a doubled shape thereof, a microstructure 11a (see FIG.
  • microstructure 11 disposed in four-fold symmetry, a cruciform, and a central portion of a bowl shape are removed.
  • the cut wire formed in the shape is arranged in four-fold symmetry, the microstructure 11a (see FIG. 12) arranged in four-fold symmetry, and the cut wire formed in the shape excluding a ring-shaped, square frame-like part Microstructure 11a (FIG. 1) (Refer to Fig. 14), there is a microstructure 11a in which cut wires formed in a triangular frame are arranged in six-fold symmetry, and a microstructure 11a in which cut wires formed in a triangle are arranged four-fold (see FIG. 14) doing.
  • the metamaterial structure 11 may be one in which a portion constituted by cut wires of each variation and a portion without cut wires are inverted (complementary) .
  • the metamaterial structures 11 are not limited to the arrangement of four-fold symmetry or six-fold symmetry shown in FIGS. 8 to 14, and may be of n-fold symmetry (n is an integer of 2 or more).
  • the metamaterial structures 11 used in the simulation are those of the fine structures 11a of the arrangement and size shown in FIGS. 15 (a), 16 (a) and 17 (a), respectively.
  • the transparent substrate 12 is made of SiO 2
  • the microstructure 11 a is made of Au.
  • the thickness of the microstructure 11a is 40 nm.
  • the reflection spectrum at each refractive index is determined, and the calculation results are shown in FIG. (B), it shows in FIG.17 (b). Further, the relationship between the peak wavelength of the reflection spectrum and the refractive index is determined from FIGS. 15 (b), 16 (b) and 17 (b), and FIGS. 15 (c), 16 (c) and 17 (b), respectively. It shows in (c). As shown in FIGS. 15 (c), 16 (c) and 17 (c), the peak wavelength of the reflection spectrum changes almost linearly according to the change of the refractive index around the metamaterial structure 11. Was confirmed.
  • the refractive index sensitivities of the refractive index sensor 10 determined from FIGS. 15 (c), 16 (c), and 17 (c) were 368 nm / RIU, 458 nm / RIU, and 824 nm / RIU, respectively.
  • the refractive index sensor 10 may include an optical fiber 31, and the metamaterial structure 11 may be provided on the tip surface 31 a of the optical fiber 31.
  • the metamaterial structure 11, the light source 13, and the optical detector 32 are connected via the optical fiber 31.
  • the photodetector 32 includes the spectroscope 15 and a power meter.
  • the refractive index sensor 10 introduces the incident light from the light source 13 from the rear end face of the optical fiber 31, reflects the light by the metamaterial structure 11, and returns the light It is read by the detector 32.
  • the refractive index sensor 10 may be configured as shown in FIGS. 19 (b) to 19 (d) instead of the configuration shown in FIG. 19 (a).
  • incident light is introduced from the rear end face of the optical fiber 31, and light transmitted through the metamaterial structure 11 is read by the light detector 32.
  • FIG. 19C light is irradiated from the sample side, and the light passing through the metamaterial structure 11 and the optical fiber 31 is read by the light detector 32.
  • FIG. 19D light is emitted from the sample side, and the reflected light of the light that has hit the metamaterial structure 11 is read by the light detector 32.
  • the refractive index sensor 10 in which the metamaterial structure 11 is provided on the front end surface 31a of the optical fiber 31 is not an invasive measurement for cutting out the sample, as long as the front end of the optical fiber 31 can reach. It becomes possible to measure in). For this reason, precise measurement is possible even for a measurement target that is environment-dependent, such as a living body. Further, by using the optical fiber 31 thinner than the injection needle, measurement with less damage to a living body or the like becomes possible. Further, since the measurement range is determined by the diameter of the optical fiber 31, the physical quantity of the fine region can be measured by using the thin optical fiber 31. Also, by performing measurement while moving the optical fiber 31, spatial mapping of the measurement result can be performed.
  • 21a) to f) show a method of manufacturing the metamaterial structure 11 on the tip surface 31a of the optical fiber 31.
  • FIG. In the manufacturing method first, the distal end surface 31a of the cut optical fiber 31 is cleaned by ultrasonic cleaning or ultraviolet / ozone treatment using pure water or an organic solvent, and then the distal end surface 31a of the cut optical fiber 31 is , UV curing resin (UV curing resin) 33 is applied.
  • UV curing resin UV curing resin
  • the tip surface 31a of the optical fiber 31 coated with the ultraviolet curable resin 33 is vertically pressed against the flat glass surface 34, and the ultraviolet curable resin 33 is cured by irradiating the ultraviolet (see FIG. 21a)). Then, it is separated from the flat glass plane 34, and the ultraviolet curing resin 33 is planarized.
  • the process of FIG. 21a is not necessary. In addition, even when the end face 31a of the optical fiber 31 is sufficiently smooth, the process of FIG. 21a) is not necessary.
  • Ti, Au, and Cr are deposited in this order with a thickness of 1 nm, 40 nm, and 5 nm on the surface of the planarized UV curable resin 33 (the surface of the glass substrate when formed on a glass substrate).
  • Film formation (see FIG. 21 b)).
  • a sputtering apparatus or a vapor deposition apparatus is used for deposition.
  • an ultraviolet curable resin 35 is applied on the film formation surface (see FIG. 21c).
  • a separately manufactured silicon or quartz mold (mold) is prepared, and the mold is pressed against the UV curable resin 35, and the UV curable resin 35 is cured by irradiating the UV for about 120 seconds (see FIG. 21d)) .
  • Ti is used for the purpose of enhancing the adhesion between Au and the ultraviolet curable resin 33 (or the glass substrate), and Ti is not necessary when the adhesion is good.
  • FIGS. 22 (a) to 22 (c) Electron micrographs of the metamaterial structure 11 produced on the front end face 31a of the optical fiber 31 are shown in FIGS. 22 (a) to 22 (c).
  • the reflection spectrum of the manufactured optical fiber type refractive index sensor 10 is shown in FIG.
  • FIG. 23 when the metamaterial structure 11 formed on the tip surface 31a of the optical fiber 31 is exposed to the environment of air (Air) and ethanol (Ethanol), the resonance wavelength is changed by the change of the refractive index. It was confirmed that it changed and functioned as the refractive index sensor 10.
  • w width of cut wire
  • g width between cut wires arranged in parallel
  • d vertical arranged
  • the gap between the cut wires and l should be greater than 0 nm.
  • t may be 13 nm or more.
  • the lower limit of dimensional parameters other than t is determined by the limit of the manufacturing technology at that time.
  • the transparent substrate 12 is made of SiO 2
  • the fine structure 11 a of the metamaterial structure 11 is made of silver (Ag).
  • the transmission spectrum and reflection spectrum of the metamaterial structure 11 when the refractive index n around the metamaterial structure 11 shown in FIG. 24 is changed from 1.0 to 1.2 are calculated.
  • Shown in FIG. The Rigorous Coupled-Wave Analysis method was used for the calculation.
  • the harmonics at the time of calculation was set to 6.
  • the refractive index sensitivity of this metamaterial structure 11 is obtained from FIG. 25 and is 750 nm / RIU. This result greatly exceeds the sensitivity of the conventional refractive index sensor using surface plasmons.
  • each dimension parameter is not limited in manufacturing, and can be arbitrarily set according to which wavelength (frequency) the application range of the refractive index sensor 10 is extended.
  • wavelength frequency
  • terahertz wave specifically, 0.3 THz (wavelength) from heat wavelength (about 10 ⁇ m) 999 ⁇ m)
  • Terahertz (THz) waves are safe for living beings, and there are many chemical / biomaterials that have absorption peaks at THz (the absorption frequency is unique to substances, so they can be used to identify substances), while paper and clothes etc. From the characteristic of THz to be transmitted, it is considered to use THz for security check at an airport or for narcotics check of international mail (such as drug has a unique fingerprint spectrum at a specific frequency of THz).
  • THz Terahertz
  • the refractive index sensor 10 may have a glass plate, and the metamaterial structure 11 may be provided on the surface of the glass plate.
  • a ligand such as detection DNA 21 shown in FIG. 7A may be attached to the surface of the fine structure 11 a of the metamaterial structure 11.
  • the blood can be detected by dropping blood on the metamaterial structure 11 on the surface of the glass plate and determining the refractive index from the change in refractive index.
  • a substance such as another liquid on the metamaterial structure 11 as well as blood, components in the substance can also be detected.
  • the metamaterial structure 11 can be manufactured on the surface of a glass plate.

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Abstract

[Problem] To provide a metamaterial structure and a refractive index sensor with which it is possible to perform precise measurement inexpensively. [Solution] A metamaterial structure 11 includes a microstructure 11a on the same level as the wavelength of incident light or less than or equal to the wavelength of incident light, and exhibits a wavelength selective optical response as a result of a strengthening, under resonance conditions, of optical coupling between the incident light and a surface plasmon mode which depends on the microstructure 11a. The microstructure 11a comprises a unit structure arranged with two-dimensional periodicity and rotational symmetry, and is polarization independent. A refractive index sensor 10 includes the metamaterial structure 11.

Description

メタマテリアル構造体および屈折率センサMetamaterial structure and refractive index sensor

　本発明は、メタマテリアル構造体および屈折率センサに関する。 The present invention relates to a metamaterial structure and a refractive index sensor.

　近年、様々なバイオ・ケミカル検知技術が開発されている中で、表面プラズモン共鳴を利用した屈折率センサが注目を集めている。従来の表面プラズモン共鳴を用いた屈折率センサには、大きく分けて二種類ある。一つは金（Ａｕ）薄膜を成膜したガラスプリズム上での伝搬表面プラズモンを利用したものであり（例えば、非特許文献１または２参照）、もう一つはＡｕコロイドの局在表面プラズモンを利用したものである（例えば、非特許文献３参照）。 In recent years, as various biochemical detection techniques have been developed, refractive index sensors utilizing surface plasmon resonance have attracted attention. The conventional refractive index sensors using surface plasmon resonance are roughly divided into two types. One uses propagation surface plasmons on a glass prism on which a gold (Au) thin film is formed (see, for example, Non-Patent Document 1 or 2), and the other uses localized surface plasmons of Au colloid. It is utilized (for example, refer nonpatent literature 3).

石田昭人、「バイオセンシングとプラズモニクス」、表面技術、2011年、Vol.62、No.6、p.285-290Akito Ishida, "Biosensing and Plasmonics", Surface Technology, 2011, Vol. 62, No. 6, p. 285-290 K. Willets and R. V. Duyne, “Localized surface plasmon resonance spectroscopy and sensing”, Annual Review of Physical Chemistry, 2007, Vol. 54, No. 1, p.267-297K. Willets and R. V. Duyne, “Localized surface plasma resonance spectroscopy and sensing”, Annual Review of Physical Chemistry, 2007, Vol. 54, No. 1, p.267-297 J. Homola, “Surface plasmon resonance sensors for detection of chemical and biological species”, Chemical Reviews, 2008, Vol. 108, No. 2, p.462-493J. Homola, “Surface plasma resonance sensors for detection of chemical and biological species”, Chemical Reviews, 2008, Vol. 108, No. 2, p. 462-493

　しかしながら、非特許文献１および２に記載のような、金（Ａｕ）薄膜を成膜したガラスプリズム上での伝搬表面プラズモンを利用した屈折率センサは、精密な測定が可能であるが、装置が複雑で高額であるという課題があった。また、非特許文献３に記載のような、Ａｕコロイドの局在表面プラズモンを利用した屈折率センサは、安価で簡易的な測定が可能であるが、伝搬表面プラズモンを利用した屈折率センサに比べて、検出精度が劣るという課題があった。 However, although a refractive index sensor using propagating surface plasmons on a glass prism on which a gold (Au) thin film is formed as described in Non-Patent Documents 1 and 2 can perform precise measurement, the device There was a problem that it was complicated and expensive. In addition, although a refractive index sensor using localized surface plasmons of Au colloid, as described in Non-Patent Document 3, is inexpensive and simple measurement is possible, compared to a refractive index sensor using propagating surface plasmons There is a problem that the detection accuracy is inferior.

　本発明は、このような課題に着目してなされたもので、安価で且つ精密な測定を行うことができるメタマテリアル構造体および屈折率センサを提供することを目的とする。 The present invention has been made in view of such problems, and an object of the present invention is to provide a metamaterial structure and a refractive index sensor capable of performing inexpensive measurement with high precision.

　本発明者らは、上記目的を達成するために鋭意研究した結果、メタマテリアルが周囲の屈折率変化に敏感な反応を示すこと、および、自由度の高い形状設計ができることに着目し、メタマテリアルを用いて表面プラズモンのモード分布を最適化することにより、高性能な屈折率センサを実現できることに想到した。これにより、安価で且つ精密な測定を可能とする屈折率センサを提供することが可能となる。 As a result of intensive studies to achieve the above object, the present inventors have noted that the metamaterial is sensitive to changes in the refractive index of its surroundings, and that it is possible to design the shape with a high degree of freedom. By optimizing the mode distribution of surface plasmons using the above, we have realized that a high performance refractive index sensor can be realized. This makes it possible to provide a refractive index sensor that enables inexpensive and accurate measurement.

　すなわち、本発明に係るメタマテリアル構造体は、入射光の波長と同程度又は前記波長以下の微細構造を有し、前記入射光と前記微細構造に依存した表面プラズモンモードとの光結合が共振条件で強くなることにより、波長選択的な光応答を示すメタマテリアル構造体であって、前記微細構造は、回転対称に二次元周期配列された単位構造から成ることを特徴とする。 That is, the metamaterial structure according to the present invention has a fine structure equal to or less than the wavelength of incident light, and the optical coupling between the incident light and the surface plasmon mode depending on the fine structure has a resonance condition In the metamaterial structure exhibiting a wavelength selective light response, the fine structure is characterized by comprising a unit structure in which a two-dimensional periodic arrangement is rotationally symmetrical.

　本発明に係る屈折率センサは、本発明に係るメタマテリアル構造体を有することを特徴とする。 The refractive index sensor according to the present invention is characterized by having the metamaterial structure according to the present invention.

　本発明に係るメタマテリアル構造体は、微細構造の寸法により、光応答の選択波長を調整することができる。また、本発明に係るメタマテリアル構造体は、周囲の媒質により選択波長が敏感に変化する。このため、本発明に係るメタマテリアル構造体および屈折率センサは、メタマテリアル構造体の周囲の媒質による選択波長の変化または特定波長における反射率の変化から、周囲の媒質の屈折率を検出することができる。本発明に係るメタマテリアル構造体および屈折率センサは、従来の伝搬表面プラズモンを利用した屈折率センサと比べて、簡単な構造を有しており、安価に製造することができる。 The metamaterial structure according to the present invention can adjust the selected wavelength of the light response by the size of the microstructure. In the metamaterial structure according to the present invention, the selected wavelength is sensitively changed by the surrounding medium. Therefore, the metamaterial structure and the refractive index sensor according to the present invention detect the refractive index of the surrounding medium from the change of the selected wavelength or the change of the reflectance at a specific wavelength by the medium around the metamaterial structure. Can. The metamaterial structure and the refractive index sensor according to the present invention have a simple structure and can be manufactured at low cost, as compared with a conventional refractive index sensor using propagating surface plasmons.

　従来の表面プラズモンを利用した屈折率センサは、金の薄膜あるいは金の微粒子をランダムに配置して構成されているため、表面プラズモンの増強度が最適化されていなかった。また、ボトムアップ的に作られているため、最適化も困難であった。これに対し、本発明に係るメタマテリアル構造体および屈折率センサは、メタマテリアルの考え方により、メタマテリアル構造体の形状を任意に設計することができるため、プラズモン増強の最適化が可能である。このため、従来よりも高感度にすることができ、精密な測定を行うことができる。本発明に係る屈折率センサは、屈折率感度が300乃至1000 nm/RIUであることが好ましい。 Since the conventional refractive index sensor using surface plasmons is configured by randomly arranging a thin film of gold or fine particles of gold, the degree of enhancement of surface plasmons has not been optimized. In addition, optimization is difficult because it is made bottom up. On the other hand, in the metamaterial structure and the refractive index sensor according to the present invention, the shape of the metamaterial structure can be arbitrarily designed according to the concept of the metamaterial, so that the plasmon enhancement can be optimized. Therefore, the sensitivity can be made higher than that of the conventional case, and accurate measurement can be performed. The refractive index sensor according to the present invention preferably has a refractive index sensitivity of 300 to 1000 nm / RIU.

　本発明に係るメタマテリアル構造体は、微細構造が、回転対称に二次元周期配列された単位構造から成るため、偏光無依存にすることができる。本発明に係るメタマテリアル構造体は、微細構造の形状加工にはいかなる技術を用いてもよく、例えば、半導体微細加工技術や、ナノ構造を安価かつ大量に生産することができるナノインプリントを用いることができる。 The metamaterial structure according to the present invention can be made polarization independent because the fine structure is composed of a unit structure in which the two-dimensional periodic arrangement is rotationally symmetric. The metamaterial structure according to the present invention may use any technique for shape processing of a fine structure, for example, using a semiconductor fine processing technique or nanoimprint capable of mass-producing nanostructures inexpensively. it can.

　本発明に係るメタマテリアル構造体で、入射光は、検出対象に応じていかなる波長であってもよい。本発明に係るメタマテリアル構造体は、微細構造の寸法を小さくすることにより、小型化が可能であり、その場合、例えば、入射光の波長は２５００ｎｍ以下であってもよい。 In the metamaterial structure according to the present invention, the incident light may have any wavelength depending on the object to be detected. The metamaterial structure according to the present invention can be miniaturized by reducing the size of the fine structure, in which case, for example, the wavelength of incident light may be 2500 nm or less.

　本発明に係るメタマテリアル構造体で、前記微細構造は、前記単位構造の二次元の配列面に沿って、前記単位構造を、縦方向および／または横方向に規則的に複数並べて配置して成っていてもよい。 In the metamaterial structure according to the present invention, the fine structure is formed by arranging a plurality of the unit structures regularly in the longitudinal direction and / or the lateral direction along the two-dimensional array plane of the unit structures. It may be

　本発明に係るメタマテリアル構造体で、前記微細構造は、入射光の波長に応じていかなる材料から成っていてもよく、例えば、金、銀、銅、アルミニウムまたは遷移金属系窒化物から成っていてもよい。遷移金属系窒化物としては、例えば、ＴｉＮ、ＺｒＮ、ＨｆＮ、ＴａＮが挙げられる。 In the metamaterial structure according to the present invention, the microstructure may be made of any material depending on the wavelength of incident light, for example, made of gold, silver, copper, aluminum or transition metal nitride. It is also good. Examples of transition metal nitrides include TiN, ZrN, HfN, and TaN.

　本発明に係る屈折率センサは、屈折率に応じてメタマテリアル構造体の周囲の媒質を検出可能であれば、いかなる構成を有していてもよい。例えば、本発明に係る屈折率センサは、光ファイバを有し、前記メタマテリアル構造体は、前記光ファイバの先端に設けられていてもよい。この場合、試料を切り取る侵襲的な測定ではなく、本来ある場所（in situ）での測定が可能となる。このため、生体などのように、環境依存性がある測定対象であっても、精密な測定が可能である。また、注射針より細い光ファイバを使用することにより、生体等へのダメージが少ない測定が可能となる。また、測定範囲が光ファイバの直径で決まるため、細い光ファイバを使用することにより、微細領域の物理量を測ることができる。また、光ファイバを移動させることにより、測定結果の空間マッピングを行うことができる。 The refractive index sensor according to the present invention may have any configuration as long as the medium around the metamaterial structure can be detected according to the refractive index. For example, the refractive index sensor according to the present invention may include an optical fiber, and the metamaterial structure may be provided at the tip of the optical fiber. In this case, in-situ measurement can be performed rather than invasive measurement in which the sample is cut out. For this reason, precise measurement is possible even for a measurement target that is environment-dependent, such as a living body. Further, by using an optical fiber thinner than the injection needle, measurement with less damage to a living body or the like becomes possible. In addition, since the measurement range is determined by the diameter of the optical fiber, the physical quantity of the minute area can be measured by using a thin optical fiber. Also, by moving the optical fiber, spatial mapping of measurement results can be performed.

　また、本発明に係る屈折率センサは、ガラスプレートを有し、前記メタマテリアル構造体は、前記ガラスプレートの表面に設けられていてもよい。この場合、ガラスプレート表面のメタマテリアル構造体の上に、液体などの物質を載せることにより、その物質中の成分を検出することができる。このため、例えば、メタマテリアル構造体の上に、血液を滴下して、血液検査を行うことができる。 The refractive index sensor according to the present invention may have a glass plate, and the metamaterial structure may be provided on the surface of the glass plate. In this case, by placing a substance such as a liquid on the metamaterial structure on the surface of the glass plate, the components in the substance can be detected. Therefore, for example, blood can be dropped on the metamaterial structure to perform a blood test.

　また、本発明に係る屈折率センサは、前記微細構造の表面に付着された検出用作用体を有し、前記検出用作用体は、検出対象と相互作用可能であってもよい。この場合、検出用作用体および検出対象は、検出用作用体が検出対象と相互作用可能であり、その相互作用の前後で、測定可能な屈折率の変化が認められるものであれば、いかなるものであってもよい。検出用作用体と検出対象との相互作用は、例えば検出用作用体への検出対象の結合など、いかなる相互作用であってもよい。検出用作用体と検出対象の組合せとしては、例えば、検出用ＤＮＡと相補ＤＮＡ、検出用ＲＮＡと相補ＲＮＡ、ビオチンとアビジンまたはストレプトアビジン、抗原と抗体、各種のたんぱく質とそのたんぱく質に作用する物質、各種のアミノ酸とそのアミノ酸に作用する物質、リガンドとレセプターなどである。検出用作用体が、検出用ＤＮＡまたは検出用ＲＮＡから成る場合、検出対象であるＤＮＡまたはＲＮＡと相補鎖を形成可能であり、相補鎖の形成による屈折率の変化を測定することにより、所望の検出対象のＤＮＡやＲＮＡを検出することができる。なお、この場合、微細構造は、検出用ＤＮＡまたは検出用ＲＮＡを結合可能な材料から成ることが好ましい。 The refractive index sensor according to the present invention may have a detecting agent attached to the surface of the fine structure, and the detecting agent may be capable of interacting with the object to be detected. In this case, as long as the agent for detection and the object to be detected are such that the agent for detection can interact with the object to be detected and the change in refractive index that can be measured is recognized before and after the interaction, It may be The interaction between the agent for detection and the object to be detected may be any interaction such as binding of the object to be detected to the agent for detection. The combination of a detection agent and a detection target includes, for example, a detection DNA and a complementary DNA, a detection RNA and a complementary RNA, biotin and avidin or streptavidin, an antigen and an antibody, various proteins and substances acting on the protein, These include various amino acids and substances acting on the amino acids, ligands and receptors. When the agent for detection comprises DNA for detection or RNA for detection, it can form a complementary strand with the DNA or RNA to be detected, and by measuring the change in refractive index due to the formation of the complementary strand, the desired DNA or RNA to be detected can be detected. In this case, the fine structure is preferably made of a material capable of binding the detection DNA or the detection RNA.

　本発明に係るメタマテリアル構造体は、屈折率センサのみならず、例えば、ケミカルセンサ、バイオセンサ、in situ 分析装置、カテーテルや内視鏡と集積した医療装置、屈折率やケミカル・バイオ物質の高分解能空間マッピング装置に適用されてもよい。ここで、ケミカルセンサは、ガス・有機化学物質などを対象とするセンサで、例えば、味覚、食品、化学薬品、アルコールチェックなどに適用されるものである。また、バイオセンサは、生体・生物などを対象とするセンサで、例えば、毒性センサ、血糖センサ、DNAセンサ、医療用センサなどに適用されるものである。これらの場合、測定結果を空間マッピング可能な構成にすることにより、例えば、バイオセンサであれば、細胞・DNAの形や寸法、種類の特定などを行うことができ、ケミカルセンサであれば、薬品の濃度分布分析などを行うことができる。なお、空間マッピングができない従来のスポット計測では、例えば、測定対象が混合物質のとき、一点しか測れないため、混合しているのかどうかが分からず、それらがどのような空間分布や形状を有しているのかも分からない。 The metamaterial structure according to the present invention is not limited to a refractive index sensor, for example, a chemical sensor, a biosensor, an in situ analysis device, a medical device integrated with a catheter or an endoscope, high refractive index and chemical / biomaterial It may be applied to a resolution spatial mapping device. Here, the chemical sensor is a sensor intended for gas and organic chemical substances, and is applied to, for example, taste, food, chemicals, alcohol check and the like. Further, the biosensor is a sensor intended for a living body or the like, and is applied to, for example, a toxicity sensor, a blood glucose sensor, a DNA sensor, a medical sensor or the like. In these cases, by making the measurement results spatially mappable, for example, in the case of a biosensor, it is possible to identify the shape, size, and type of cells and DNA, and in the case of a chemical sensor, Concentration distribution analysis etc. can be performed. In the conventional spot measurement where spatial mapping can not be performed, for example, when the object to be measured is a mixed substance, only one point can be measured, so it is not known whether they are mixed or not, and they have spatial distribution and shape. I do not know it.

　本発明によれば、安価で且つ精密な測定を行うことができるメタマテリアル構造体および屈折率センサを提供することができる。 According to the present invention, it is possible to provide a metamaterial structure and a refractive index sensor capable of performing inexpensive measurement with high precision.

（ａ）本発明の実施の形態の屈折率センサを示す側面図、（ｂ）本発明の実施の形態のメタマテリアル構造体を示す平面図である。(A) It is a side view which shows the refractive index sensor of embodiment of this invention, (b) It is a top view which shows the metamaterial structure of embodiment of this invention. 本発明の実施の形態の屈折率センサの、メタマテリアル構造体の周囲の屈折率ｎが１．０～１．５のときの（ａ）反射スペクトル、（ｂ）反射ピーク波長（Peak wavelength）の周囲屈折率（Refractive index）依存性を示すグラフである。The refractive index sensor according to the embodiment of the present invention has (a) reflection spectrum when the refractive index n around the metamaterial structure is 1.0 to 1.5, (b) reflection peak wavelength (Peak wavelength) It is a graph which shows ambient refractive index (Refractive index) dependence. 本発明の実施の形態のメタマテリアル構造体の、共振波長1250 nmで（ａ）X方向の偏光、（ｂ）X方向から45°傾いた偏光を設計したものに、光が垂直入射したときの、メタマテリアル構造体の上部の電場強度分布図である。When light is vertically incident on a light with a resonant wavelength of 1250 nm designed for (a) polarized light in the X direction, and (b) polarized light tilted 45 ° from the X direction in the metamaterial structure of the embodiment of the present invention Fig. 10 is an electric field intensity distribution map of the upper part of the metamaterial structure. 本発明の実施の形態のメタマテリアル構造体の走査型電子顕微鏡（SEM）画像である。It is a scanning electron microscope (SEM) image of the metamaterial structure of embodiment of this invention. 本発明の実施の形態の屈折率センサの、空気（Air）、純水（DIW）、イソプロパノール（IPA）、グリセリン（Glycerin）の４種類の媒質中で測定された（ａ）反射スペクトル、（ｂ）反射ピーク波長（Peak wavelength）の周囲屈折率（Refractive index）依存性を示すグラフである。(A) Reflection Spectrum Measured in Four Types of Media of Air (Air), Pure Water (DIW), Isopropanol (IPA), and Glycerin (G) of the Refractive Index Sensor of the Embodiment of the Present Invention Fig. 7 is a graph showing the refractive index (Refractive index) dependency of the reflection peak wavelength (Peak wavelength). 本発明の実施の形態の屈折率センサの、IPA水溶液中で測定された、IPA水溶液の濃度（Concentration）と反射スペクトルのピーク波長（Peak wavelength）との関係を示すグラフである。It is a graph which shows the relationship of the concentration (Concentration) of IPA aqueous solution and the peak wavelength (Peak wavelength) of a reflective spectrum measured in IPA aqueous solution of the refractive index sensor of embodiment of this invention. 本発明の実施の形態の屈折率センサの、DNAの検出実験の（ａ）実験手順を示す側面図、（ｂ）乾燥状態での相補DNA結合前後の反射スペクトル、（ｃ）湿潤状態での相補DNA結合前後の反射スペクトルである。(A) Side view showing experimental procedure of DNA detection experiment of the refractive index sensor according to the embodiment of the present invention, (b) reflection spectrum before and after binding of complementary DNA in dry state, (c) complementation in wet state It is a reflection spectrum before and after DNA binding. 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例、（ｅ）他の変形例、（ｆ）　（ｅ）に示す配置を反転させた変形例を示す平面図である。(A) Modification of fine structure of the metamaterial structure of the embodiment of the present invention, (b) Modification in which the arrangement shown in (a) is reversed, (c) Other modification, (d) ( It is a top view which shows the modification which reversed the arrangement | positioning shown to c), (e) other modification, and the modification which reversed the arrangement | positioning shown to (f) and (e). 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）他の変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例、（ｅ）他の変形例、（ｆ）　（ｅ）に示す配置を反転させた変形例を示す平面図である。(A) Other Modifications of the Microstructure, (b) Modifications in which the Arrangement Shown in (a) is Inverted, (c) Other Modifications, (d) The metamaterial structure of the embodiment of the present invention FIG. 14 is a plan view showing a modification in which the arrangement shown in (c) is reversed, (e) another modification, and a modification in which the arrangement shown in (f) and (e) is reversed. 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）他の変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例、（ｅ）他の変形例、（ｆ）　（ｅ）に示す配置を反転させた変形例を示す平面図である。(A) Other Modifications of the Microstructure, (b) Modifications in which the Arrangement Shown in (a) is Inverted, (c) Other Modifications, (d) The metamaterial structure of the embodiment of the present invention FIG. 14 is a plan view showing a modification in which the arrangement shown in (c) is reversed, (e) another modification, and a modification in which the arrangement shown in (f) and (e) is reversed. 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）他の変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例、（ｅ）他の変形例、（ｆ）　（ｅ）に示す配置を反転させた変形例、（ｇ）他の変形例、（ｈ）　（ｇ）に示す配置を反転させた変形例を示す平面図である。(A) Other Modifications of the Microstructure, (b) Modifications in which the Arrangement Shown in (a) is Inverted, (c) Other Modifications, (d) The metamaterial structure of the embodiment of the present invention ) (C) a modification in which the arrangement is reversed, (e) another modification, (f) a modification in which the arrangement shown in (e) is reversed, (g) another modification, (h) It is a top view which shows the modification which reversed the arrangement | positioning shown to g). 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）他の変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例、（ｅ）他の変形例、（ｆ）　（ｅ）に示す配置を反転させた変形例を示す平面図である。(A) Other Modifications of the Microstructure, (b) Modifications in which the Arrangement Shown in (a) is Inverted, (c) Other Modifications, (d) The metamaterial structure of the embodiment of the present invention FIG. 14 is a plan view showing a modification in which the arrangement shown in (c) is reversed, (e) another modification, and a modification in which the arrangement shown in (f) and (e) is reversed. 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）他の変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例、（ｅ）他の変形例、（ｆ）　（ｅ）に示す配置を反転させた変形例、（ｇ）他の変形例、（ｈ）　（ｇ）に示す配置を反転させた変形例を示す平面図である。(A) Other Modifications of the Microstructure, (b) Modifications in which the Arrangement Shown in (a) is Inverted, (c) Other Modifications, (d) The metamaterial structure of the embodiment of the present invention ) (C) a modification in which the arrangement is reversed, (e) another modification, (f) a modification in which the arrangement shown in (e) is reversed, (g) another modification, (h) It is a top view which shows the modification which reversed the arrangement | positioning shown to g). 本発明の実施の形態のメタマテリアル構造体の、微細構造の（ａ）他の変形例、（ｂ）　（ａ）に示す配置を反転させた変形例、（ｃ）他の変形例、（ｄ）　（ｃ）に示す配置を反転させた変形例を示す平面図である。(A) Other Modifications of the Microstructure, (b) Modifications in which the Arrangement Shown in (a) is Inverted, (c) Other Modifications, (d) The metamaterial structure of the embodiment of the present invention It is a top view which shows the modification which reversed the arrangement | positioning shown to (c). 本発明の実施の形態のメタマテリアル構造体の、（ａ）シミュレーションに使用した微細構造、（ｂ）メタマテリアル構造体の周囲の屈折率ｎが１．０～１．５のときの反射スペクトル、（ｃ）反射ピーク波長の周囲屈折率依存性を示すグラフである。(A) The fine structure used in the simulation of the metamaterial structure of the embodiment of the present invention, (b) the reflection spectrum when the refractive index n around the metamaterial structure is 1.0 to 1.5, (C) It is a graph which shows the surrounding refractive index dependence of a reflective peak wavelength. 本発明の実施の形態のメタマテリアル構造体の、（ａ）シミュレーションに使用した微細構造、（ｂ）メタマテリアル構造体の周囲の屈折率ｎが１．０～１．５のときの反射スペクトル、（ｃ）反射ピーク波長の周囲屈折率依存性を示すグラフである。(A) The fine structure used in the simulation of the metamaterial structure of the embodiment of the present invention, (b) the reflection spectrum when the refractive index n around the metamaterial structure is 1.0 to 1.5, (C) It is a graph which shows the surrounding refractive index dependence of a reflective peak wavelength. 本発明の実施の形態のメタマテリアル構造体の、（ａ）シミュレーションに使用した微細構造、（ｂ）メタマテリアル構造体の周囲の屈折率ｎが１．０～１．５のときの反射スペクトル、（ｃ）反射ピーク波長の周囲屈折率依存性を示すグラフである。(A) The fine structure used in the simulation of the metamaterial structure of the embodiment of the present invention, (b) the reflection spectrum when the refractive index n around the metamaterial structure is 1.0 to 1.5, (C) It is a graph which shows the surrounding refractive index dependence of a reflective peak wavelength. 本発明の実施の形態の屈折率センサの、光ファイバの先端面にメタマテリアル構造体を有する変形例を示す斜視図である。It is a perspective view which shows the modification which has a metamaterial structure in the front end surface of the optical fiber of the refractive index sensor of embodiment of this invention. 本発明の実施の形態の屈折率センサの、（ａ）メタマテリアル構造体と光源および光検知器（Optical detector）との接続状態、（ｂ）その接続状態の変形例、（ｃ）その接続状態の他の変形例、（ｄ）その接続状態の他の変形例を示す斜視図である。In the refractive index sensor according to the embodiment of the present invention, (a) connection state between the metamaterial structure and the light source and the optical detector (optical detector), (b) a variation of the connection state, (c) the connection state FIG. 16 is a perspective view showing another modified example of (d) and another modified example of the connected state. 図１８に示す屈折率センサの光学応答を示すグラフである。It is a graph which shows the optical response of the refractive index sensor shown in FIG. ａ）～ｆ）図１８に示す屈折率センサの製造方法を示す断面図である。a) to f) are cross-sectional views showing a method of manufacturing the refractive index sensor shown in FIG. 図２１に示す屈折率センサの製造方法で製造された、（ａ）光ファイバの先端面のメタマテリアル構造体を示す電子顕微鏡写真、（ｂ）　（ａ）に示す光ファイバの先端面の中心部を拡大した電子顕微鏡写真（上面図）、（ｃ）　（ａ）に示す光ファイバの先端面の中心部を拡大した電子顕微鏡写真（斜視図）である。(A) an electron micrograph showing a metamaterial structure of the tip end face of the optical fiber manufactured by the method for producing a refractive index sensor shown in FIG. 21, (b) center part of the tip end face of the optical fiber shown in (a) 6 (c) is an electron micrograph (a perspective view) obtained by enlarging the central portion of the tip surface of the optical fiber shown in (c) (a). 図２２に示す屈折率センサの、空気（Air）中およびエタノール（Ethanol）中での反射スペクトルである。It is a reflection spectrum in the air (Air) and in ethanol (Ethanol) of the refractive index sensor shown in FIG. 本発明の実施の形態のメタマテリアル構造体の、寸法パラメータを小さくしたときの変形例を示す平面図である。It is a top view which shows the modification at the time of reducing the dimensional parameter of the metamaterial structure of embodiment of this invention. 図２４に示すメタマテリアル構造体の、周囲の屈折率ｎが１．０～１．２のときの透過（Transmittance）スペクトルおよび反射（Reflectance）スペクトルである。24 is a transmission spectrum and a reflection spectrum of the metamaterial structure shown in FIG. 24 when the surrounding refractive index n is 1.0 to 1.2.

　以下、図面に基づいて、本発明の実施の形態について説明する。
　図１乃至図２５は、本発明の実施の形態のメタマテリアル構造体および屈折率センサを示している。 Hereinafter, embodiments of the present invention will be described based on the drawings.
1 to 25 show a metamaterial structure and a refractive index sensor according to an embodiment of the present invention.

（センサの構成と原理）
　図１に示すように、屈折率センサ１０は、メタマテリアル構造体１１と透明基板１２と光源１３とハーフミラー１４と分光器１５とを有している。図１に示すように、メタマテリアル構造体１１は、複数のカットワイヤで構成される微細構造１１ａを有し、透明基板１２の上に設けられている。図１（ｂ）に示すように、微細構造１１ａは、入射光の波長と同程度または入射光の波長以下の構造であり、回転対称に二次元周期配列された単位構造から成っている。なお、メタマテリアル構造体１１は、入射光と微細構造１１ａに依存した表面プラズモンモードとの光結合が共振条件で強くなることにより、波長選択的な光応答を示すよう構成されている。メタマテリアル構造体１１は、単位構造が回転対称であり、偏光無依存である。 (Structure and principle of sensor)
As shown in FIG. 1, the refractive index sensor 10 includes a metamaterial structure 11, a transparent substrate 12, a light source 13, a half mirror 14, and a spectroscope 15. As shown in FIG. 1, the metamaterial structure 11 has a microstructure 11 a composed of a plurality of cut wires, and is provided on a transparent substrate 12. As shown in FIG. 1B, the fine structure 11a has a structure similar to or less than the wavelength of incident light, and is composed of a unit structure in which a two-dimensional periodic arrangement is made in rotational symmetry. The metamaterial structure 11 is configured to exhibit a wavelength-selective light response by the optical coupling between incident light and the surface plasmon mode depending on the microstructure 11a becoming stronger under resonance conditions. The metamaterial structure 11 is rotationally symmetric in unit structure and polarization independent.

　微細構造１１ａは、近赤外域で反射率が高い金（Au）から成っている。なお、微細構造１１ａは、金の他にも、銀、銅、アルミニウム、または高いキャリア濃度を有しプラズモン特性を示すＴｉＮ、ＺｒＮ、ＨｆＮ、ＴａＮの遷移金属系窒化物などから成っていてもよい。図１（ｂ）に示す具体的な一例では、微細構造１１ａは、カットワイヤで形成され、平行に配置された２つの長方形を、４回対称に配置した構造を成している。 The fine structure 11 a is made of gold (Au) having a high reflectance in the near infrared region. In addition to gold, the microstructure 11a may be made of silver, copper, aluminum, or TiN, ZrN, HfN, or TaN transition metal nitride having high carrier concentration and exhibiting plasmon characteristics. . In a specific example shown in FIG. 1 (b), the microstructure 11a is formed of a cut wire, and has a structure in which two rectangles arranged in parallel are arranged in four-fold symmetry.

　図１（ａ）に示すように、光源１３は、ハーフミラー１４を介して、入射光を透明基板１２の側からメタマテリアル構造体１１に入射するよう設けられている。ハーフミラー１４は、光源１３からの入射光を透過させると共に、メタマテリアル構造体１１からの反射光を反射して、９０度曲げるよう設けられている。なお、ハーフミラー１４の代わりに、２分岐の光ファイバを用いてもよい。分光器１５は、ハーフミラー１４で反射された、メタマテリアル構造体１１からの反射光を受光し、そのスペクトルを検出可能に設けられている。なお、分光器１５の代わりに、波長可変光源と光検出器との組合せを用いてもよい。 As shown in FIG. 1A, the light source 13 is provided to cause incident light to be incident on the metamaterial structure 11 from the side of the transparent substrate 12 through the half mirror 14. The half mirror 14 transmits incident light from the light source 13 and reflects reflected light from the metamaterial structure 11 so as to bend it 90 degrees. Note that, instead of the half mirror 14, a two-branch optical fiber may be used. The spectroscope 15 receives the reflected light from the metamaterial structure 11 reflected by the half mirror 14 and is provided so as to detect its spectrum. Instead of the spectroscope 15, a combination of a wavelength variable light source and a photodetector may be used.

　次に、作用について説明する。
　屈折率センサ１０は、以下のようにして使用される。すなわち、図１（ａ）に示すように、屈折率を測定したい試料１を、透明基板１２の上のメタマテリアル構造体１１の上に滴下し、メタマテリアル構造体１１の反射スペクトルを分光器１５で検出する。これにより、空気（屈折率n = 1.0）を基準として、試料１の滴下による屈折率変化に応じた反射スペクトルシフトから、試料１の屈折率を算出することができる。 Next, the operation will be described.
The refractive index sensor 10 is used as follows. That is, as shown in FIG. 1A, the sample 1 whose refractive index is to be measured is dropped on the metamaterial structure 11 on the transparent substrate 12, and the reflection spectrum of the metamaterial structure 11 is measured by the spectrometer 15. To detect. Thereby, the refractive index of the sample 1 can be calculated from the reflection spectrum shift according to the change of the refractive index due to the dropping of the sample 1 based on air (refractive index n = 1.0).

　メタマテリアル構造体１１は、微細構造１１ａの寸法により、光応答の選択波長を調整することができる。また、メタマテリアル構造体１１は、周囲の媒質により選択波長が敏感に変化する。このため、屈折率センサ１０は、メタマテリアル構造体１１の周囲の媒質による選択波長の変化または特定波長における反射率の変化から、周囲の媒質の屈折率を検出することができる。また、屈折率センサ１０は、従来の伝搬表面プラズモンを利用した屈折率センサと比べて、簡単な構造を有しており、安価に製造することができる。 The metamaterial structure 11 can adjust the selected wavelength of the light response by the size of the microstructure 11a. Also, in the metamaterial structure 11, the selection wavelength is sensitively changed by the surrounding medium. For this reason, the refractive index sensor 10 can detect the refractive index of the surrounding medium from the change in the selected wavelength by the medium around the metamaterial structure 11 or the change in the reflectance at a specific wavelength. In addition, the refractive index sensor 10 has a simple structure as compared to a conventional refractive index sensor using propagating surface plasmons, and can be manufactured at low cost.

　メタマテリアル構造体１１および屈折率センサ１０は、メタマテリアルの考え方により、メタマテリアル構造体１１の形状を任意に設計することができるため、プラズモン増強の最適化が可能である。このため、従来よりも高感度にすることができ、精密な測定を行うことができる。なお、メタマテリアル構造体１１は、微細構造１１ａの形状加工にはいかなる技術を用いてもよく、例えば、半導体微細加工技術や、ナノ構造を安価かつ大量に生産することができるナノインプリントを用いることができる。 In the metamaterial structure 11 and the refractive index sensor 10, the shape of the metamaterial structure 11 can be arbitrarily designed according to the concept of the metamaterial, so that the plasmon enhancement can be optimized. Therefore, the sensitivity can be made higher than that of the conventional case, and accurate measurement can be performed. As the metamaterial structure 11, any technique may be used for shape processing of the microstructure 11a. For example, semiconductor microfabrication technology or nanoimprint capable of mass-producing nanostructures inexpensively can be used. it can.

（光学設計）
　メタマテリアル構造体１１を製造し、屈折率の感度測定を行った。
　まず、メタマテリアル構造体１１の光学設計を行った。光学設計には、Rigorous Coupled-Wave Analysis法を用いた。設計に用いたメタマテリアル構造体１１は、図１（ｂ）に示す微細構造１１ａの単位構造が、縦方向および横方向に規則的に複数並べて配置されたものとした。また、メタマテリアル構造体１１は、図中のｗ（カットワイヤの幅）を９０ｎｍ、ｇ（平行配置されたカットワイヤ間のギャップ）を１５０ｎｍ、ｄ（垂直配置されたカットワイヤ間のギャップ）を１５０ｎｍ、ｌ（カットワイヤの長さ）を３３０ｎｍ、Λ（周期）を１０００ｎｍ、t（厚さ）を４０ｎｍとした。なお、図１（ｂ）のような、微細構造１１ａが長方形のカットワイヤから成る構成では、屈折率感度を高めるために、アスペクト比（ｌ／ｗ）が３～４、単位構造を有する面でのカットワイヤが占める割合（フィルファクタ）が０．０８～０．１２であることが好ましい。 (Optical design)
The metamaterial structure 11 was manufactured, and sensitivity measurement of refractive index was performed.
First, optical design of the metamaterial structure 11 was performed. The Rigorous Coupled-Wave Analysis method was used for optical design. In the metamaterial structure 11 used for the design, a plurality of unit structures of the fine structure 11a shown in FIG. 1B are regularly arranged in the longitudinal direction and the lateral direction. In addition, the metamaterial structure 11 has a w (width of cut wire) of 90 nm, a g (gap between cut wires disposed in parallel) of 150 nm, and a d (gap between cut wires disposed in vertical) in the figure. 150 nm, 1 (cut wire length) was 330 nm, Λ (cycle) was 1000 nm, and t (thickness) was 40 nm. In the configuration in which the microstructure 11a is formed of a rectangular cut wire as shown in FIG. 1 (b), the aspect ratio (l / w) is 3 to 4 and the surface has a unit structure in order to enhance the refractive index sensitivity. The ratio (fill factor) occupied by the cut wire is preferably 0.08 to 0.12.

　メタマテリアル構造体１１の周囲の屈折率ｎを１．０～１．５まで変化させたときの、各屈折率での反射スペクトルを設計計算により求め、その計算結果を図２（ａ）に示す。なお、計算時のハーモニクスは６とした。また、図２（ａ）から、反射スペクトルのピーク波長（Peak wavelength）と屈折率（Refractive index）との関係を求め、図２（ｂ）に示す。図２（ｂ）に示すように、メタマテリアル構造体１１の周囲の屈折率変化に応じて、反射スペクトルのピーク波長が線形的に変化することが確認された。図２（ｂ）から求めた屈折率センサ１０の屈折率感度は、593 nm/refractive index unit (RIU) である。 The reflection spectrum at each refractive index when the refractive index n around the metamaterial structure 11 is changed from 1.0 to 1.5 is obtained by design calculation, and the calculation result is shown in FIG. . The harmonics at the time of calculation was set to 6. Further, the relationship between the peak wavelength (Peak wavelength) of the reflection spectrum and the refractive index (Refractive index) is obtained from FIG. 2 (a), and is shown in FIG. As shown in FIG. 2 (b), it was confirmed that the peak wavelength of the reflection spectrum changes linearly in accordance with the change of the refractive index around the metamaterial structure 11. The refractive index sensitivity of the refractive index sensor 10 determined from FIG. 2B is 593 nm / refractive index unit (RIU).

　共振波長1250 nmで、Ｘ方向の偏光およびＸ方向から45°傾いた偏光を設計したメタマテリアル構造体１１に、光が垂直入射したときの、メタマテリアル構造体１１の上部の電場強度分布を、図３（ａ）および（ｂ）にそれぞれ示す。なお、偏光の方向は、図３（ａ）および（ｂ）中に、それぞれ矢印で示している。また、メタマテリアル構造体１１の周囲の屈折率は、1.0としている。なお、共振波長の1250 nm付近は、「第二の生体の光学窓」と呼ばれ、生体による吸収・散乱が少ないことが知られている。 The electric field intensity distribution on the upper portion of the metamaterial structure 11 when light is perpendicularly incident on the metamaterial structure 11 designed to design polarized light in the X direction and 45 ° inclined from the X direction at a resonance wavelength of 1250 nm It shows in FIG. 3 (a) and (b), respectively. The direction of polarization is indicated by arrows in FIGS. 3 (a) and 3 (b). The refractive index around the metamaterial structure 11 is 1.0. Incidentally, the vicinity of 1250 nm of the resonance wavelength is called "the optical window of the second living body", and it is known that absorption and scattering by the living body are small.

　図３（ａ）では、長手方向がＸ方向のカットワイヤの両端で電場が増幅されており、Ｘ方向に対して共振特性を示すことが確認された。また、図３（ｂ）では、全てのカットワイヤの両端で電場が増幅されており、どの偏光方向に対しても共振特性を示すことが確認された。 In FIG. 3A, it has been confirmed that the electric field is amplified at both ends of the cut wire in the longitudinal direction which is the X direction, and exhibits resonance characteristics in the X direction. Further, in FIG. 3 (b), the electric field was amplified at both ends of all the cut wires, and it was confirmed that the resonance characteristics were exhibited in any polarization direction.

（製造結果）
　光学設計に基づいて、リフトオフプロセスにより、石英基板上にメタマテリアル構造体１１を製造した。すなわち、まず、基板上にEB（Electron beam）レジストをスピンコートした後、EBリソグラフィでレジストパターンを作製した。その上に、EB蒸着によりTi（膜厚：1 nm）およびAu（膜厚：40 nm）を成膜した後、EBレジストを剥離することにより、メタマテリアル構造体１１を製造した。なお、メタマテリアル構造体１１の製造には、他の半導体微細加工技術やナノインプリントを用いても良い。 (Production result)
Based on the optical design, the metamaterial structure 11 was manufactured on a quartz substrate by a lift-off process. That is, first, an EB (Electron Beam) resist was spin-coated on a substrate, and then a resist pattern was produced by EB lithography. On top of that, Ti (film thickness: 1 nm) and Au (film thickness: 40 nm) were formed into a film by EB evaporation, and then the EB resist was peeled off to produce metamaterial structure 11. Note that other semiconductor microfabrication techniques or nanoimprinting may be used to manufacture the metamaterial structure 11.

　製造したメタマテリアル構造体１１の走査型電子顕微鏡（SEM）画像を、図４に示す。製造したメタマテリアル構造体１１の寸法は、ｗ（カットワイヤの幅）が８４ｎｍ、ｇ（平行配置されたカットワイヤ間のギャップ）が１５６ｎｍ、ｄ（垂直配置されたカットワイヤ間のギャップ）が１６２ｎｍ、ｌ（カットワイヤの長さ）が３１２ｎｍ、Λ（周期）が１０００ｎｍ、t（厚さ）が４０ｎｍであった。設計時より、幅（ｗ）および長さ（ｌ）が若干小さくなり、ギャップ（ｇ，ｄ）が若干増加しているが、ほぼ精度良く製造できた。なお、各カットワイヤのエッジの丸まりは、共振のＱ値に影響することから、可能な限りシャープなエッジにすることが望ましい。また、カットワイヤの側面は、テーパー状にならず、基板の表面に対してほぼ垂直な面であることが好ましい。 The scanning electron microscope (SEM) image of the manufactured metamaterial structure 11 is shown in FIG. The dimensions of the manufactured metamaterial structure 11 are 84 nm for w (cut wire width), 156 nm for g (gap between cut wires arranged in parallel), and 162 nm for d (gap between cut wires arranged in perpendicular) , L (cut wire length) was 312 nm, Λ (cycle) was 1000 nm, and t (thickness) was 40 nm. Although the width (w) and the length (l) were slightly smaller than in the design and the gaps (g, d) were slightly increased, it could be manufactured almost accurately. In addition, since rounding of the edge of each cut wire affects the Q value of resonance, it is desirable to make the edge as sharp as possible. In addition, the side surfaces of the cut wire are preferably non-tapered and substantially perpendicular to the surface of the substrate.

（光学測定結果）
　製造したメタマテリアル構造体１１を用いて、空気（Air）、純水（DIW）、イソプロパノール（IPA）、グリセリン（Glycerin）の４種類の媒質中で、分光器１５による反射スペクトル測定を行った。測定された反射スペクトルを図５（ａ）に、反射スペクトルのピーク波長（Peak wavelength）と周囲の媒質の屈折率（Refractive index）との関係を、図５（ｂ）に示す。なお、図５（ｂ）において、各媒質の屈折率を、空気が 1.000、DIWが 1.321、IPAが 1.368、グリセリンが 1.461 とした。図５（ｂ）から屈折率の感度を求めると、599 nm/RIUとなり、非常に高感度であることが確認された。なお、製造されたメタマテリアル構造体１１の寸法で再計算を行った結果、屈折率の感度は 605 nm/RIUとなり、実測値に近い値が得られた。この結果は、従来の表面プラズモンを利用した屈折率センサの屈折率感度が６０～１９０ nm/RIU（吉田隆、「プラズモニクス」、株式会社エヌ・ティー・エス、２０１１年８月２４日発行、p.129）であったことと比較すると、最大で３倍以上感度が上回っている。計算値と実測値との差異は、リフトオフ時に剥離したAu素片の一部が、メタマテリアル構造体１１の近傍に再付着して表面プラズモンモードを乱すことに起因する信号ノイズ成分に伴う計測誤差が一因と考えられる。 (Optical measurement result)
The reflection spectrum measurement by the spectrometer 15 was performed in four types of media of air (Air), pure water (DIW), isopropanol (IPA), and glycerin (Glycerin) using the manufactured metamaterial structure 11. The measured reflection spectrum is shown in FIG. 5A, and the relationship between the peak wavelength of the reflection spectrum (Peak wavelength) and the refractive index of the surrounding medium (Refractive index) is shown in FIG. 5B. In FIG. 5B, the refractive index of each medium is 1.000 for air, 1.321 for DIW, 1.368 for IPA, and 1.461 for glycerin. When the sensitivity of the refractive index is determined from FIG. 5 (b), it is 599 nm / RIU, and it was confirmed that the sensitivity is very high. As a result of recalculation using the dimensions of the manufactured metamaterial structure 11, the sensitivity of the refractive index was 605 nm / RIU, and a value close to the measured value was obtained. The result is that the refractive index sensitivity of a conventional refractive index sensor using surface plasmons is 60 to 190 nm / RIU (Takashi Yoshida, "Plasmonics", NTS Inc., August 24, 2011, p. The sensitivity is more than three times higher than that at the maximum. The difference between the calculated value and the measured value is the measurement error due to the signal noise component due to the reattachment of a part of the Au piece peeled off at the time of lift-off in the vicinity of the metamaterial structure 11 and disturbing the surface plasmon mode. Is considered to be a cause.

（IPAの濃度測定）
　製造したメタマテリアル構造体１１を用い、IPA水溶液の濃度を変化させたときの、それぞれの濃度における反射スペクトルの変化を測定した。室温は24℃で、IPAと水とを混合してから30秒以内に測定を行った。IPA水溶液の濃度（Concentration）と反射スペクトルのピーク波長（Peak wavelength）との関係を、図６および表１に示す。なお、使用した分光器１５の最小波長分解能は、1.7 nmである。図６および表１に示すように、IPA濃度を薄くしていくと、それに伴って反射ピーク波長が短波長側へシフトしていくことが確認された。また、IPA濃度が4.6%～1.2%の範囲において、反射ピーク波長が1357.4 nmから変化しておらず、濃度が0.6%になったときに1355.7 nmに変化したことが確認された。この結果から、最小で4%のIPA濃度変化を観測できたといえる。 (Measurement of IPA concentration)
Using the manufactured metamaterial structure 11, the change of the reflection spectrum at each concentration when the concentration of the IPA aqueous solution was changed was measured. The measurement was carried out within 30 seconds after mixing IPA and water at a room temperature of 24 ° C. The relationship between the concentration of IPA aqueous solution (Concentration) and the peak wavelength (Peak wavelength) of the reflection spectrum is shown in FIG. 6 and Table 1. The minimum wavelength resolution of the spectroscope 15 used is 1.7 nm. As shown in FIG. 6 and Table 1, it was confirmed that as the IPA concentration is reduced, the reflection peak wavelength shifts to the short wavelength side accordingly. It was also confirmed that the reflection peak wavelength did not change from 1357.4 nm in the IPA concentration range of 4.6% to 1.2%, and changed to 1355.7 nm when the concentration reached 0.6%. From this result, it can be said that the IPA concentration change of 4% at the minimum was observed.

Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001

（DNAの検出）
　製造したメタマテリアル構造体１１を用い、DNAの存在を検出する実験を行った。図７（ａ）に示すように、実験では、まず、メタマテリアル構造体１１の微細構造１１ａの表面を、検出用ＤＮＡ２１で修飾し、その検出用ＤＮＡ２１に検出対象の相補ＤＮＡ２２を結合させて相補鎖２３を形成した。相補ＤＮＡ２２を結合する前後の、乾燥状態および湿潤状態での反射スペクトルを測定し、相補ＤＮＡ２２を結合する前後でのピーク波長（屈折率）の変化を検出した。なお、実験では、検出用ＤＮＡ２１および相補ＤＮＡ２２として、特に意味を持たない塩基配列を有する遺伝子を作製して使用している。また、塩基配列の設計次第で、特定の蛋白質のみと結合するようなDNAも製作可能である。 (Detection of DNA)
An experiment was conducted to detect the presence of DNA using the manufactured metamaterial structure 11. As shown in FIG. 7 (a), in the experiment, first, the surface of the fine structure 11a of the metamaterial structure 11 is modified with the detection DNA 21, and the complementary DNA 22 to be detected is bound to the detection DNA 21 for complementation. The chain 23 was formed. The reflection spectra in the dry state and in the wet state before and after binding the complementary DNA 22 were measured, and changes in peak wavelength (refractive index) before and after binding the complementary DNA 22 were detected. In the experiment, genes having base sequences having no particular meaning are prepared and used as the detection DNA 21 and the complementary DNA 22. Also, depending on the design of the base sequence, it is possible to produce a DNA which binds only to a specific protein.

　乾燥状態および湿潤状態での、相補ＤＮＡ２２結合前後の反射スペクトルの測定結果を、それぞれ図７（ｂ）および（ｃ）に示す。図７（ｂ）に示すように、乾燥状態では、相補ＤＮＡ２２の結合によって反射ピーク波長が長波長側へ8.5 nmシフトしていることが確認された。また、図７（ｃ）に示すように、湿潤状態では、短波長側に1.7 nmシフトしていることが確認された。このように、相補鎖の形成前後で反射ピーク波長のシフトが認められ、屈折率が変化していることが確認できることから、製造したメタマテリアル構造体１１により、ＤＮＡを検出できたといえる。なお、測定結果から、相補ＤＮＡ２２の屈折率を計算すると、乾燥状態における屈折率は 1.13、湿潤状態における屈折率は 1.30となる。 The measurement results of the reflection spectra before and after the binding of the complementary DNA 22 in the dry state and the wet state are shown in FIGS. 7 (b) and (c), respectively. As shown in FIG. 7 (b), it was confirmed that the reflection peak wavelength is shifted 8.5 nm to the long wavelength side in the dry state due to the binding of the complementary DNA 22. Further, as shown in FIG. 7 (c), it was confirmed that in the wet state, the wavelength was shifted by 1.7 nm to the short wavelength side. As described above, since the shift of the reflection peak wavelength is recognized before and after the formation of the complementary strand, and it can be confirmed that the refractive index is changed, it can be said that the manufactured metamaterial structure 11 can detect DNA. When the refractive index of the complementary DNA 22 is calculated from the measurement results, the refractive index in the dry state is 1.13 and the refractive index in the wet state is 1.30.

　なお、検出用作用体および検出対象は、それぞれ検出用ＤＮＡ２１および相補ＤＮＡ２２に限らず、検出用作用体が検出対象と相互作用可能であり、その相互作用の前後で、測定可能な屈折率の変化が認められるものであれば、いかなるものであってもよい。検出用作用体と検出対象との相互作用は、例えば検出用作用体への検出対象の結合など、いかなる相互作用であってもよい。検出用作用体と検出対象の組合せとしては、例えば、ビオチンとアビジンまたはストレプトアビジン、抗原と抗体、各種のたんぱく質とそのたんぱく質に作用する物質、各種のアミノ酸とそのアミノ酸に作用する物質、リガンドとレセプターなどである。 The agent for detection and the object to be detected are not limited to the detection DNA 21 and the complementary DNA 22, respectively, and the agent for detection can interact with the object to be detected, and the change in measurable refractive index before and after the interaction. As long as it is recognized, it may be anything. The interaction between the agent for detection and the object to be detected may be any interaction such as binding of the object to be detected to the agent for detection. The combination of a detection agent and a detection target includes, for example, biotin and avidin or streptavidin, an antigen and an antibody, various proteins and substances acting on the proteins, various amino acids and substances acting on the amino acids, ligands and receptors Etc.

［変形例：メタマテリアル構造体の配置バリエーション］
　メタマテリアル構造体１１の二次元配置については、複数のカットワイヤで構成される微細構造１１ａが回転対称に二次元周期配列されたものであれば、特に限定されない。図８～図１４にメタマテリアル構造体１１の配置バリエーションの例を示す。 [Modification: Placement variation of metamaterial structure]
The two-dimensional arrangement of the metamaterial structures 11 is not particularly limited as long as the fine structures 11 a composed of a plurality of cut wires are rotationally symmetric and two-dimensionally arranged. 8 to 14 show examples of arrangement variations of the metamaterial structure 11. FIG.

　メタマテリアル構造体１１は、例えば、１または平行に配置された複数の長方形に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図８参照）や、格子、円形、十字型に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図９参照）、卍型、Ｉ型をクロスさせた形状に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図１０参照）、円環状、四角形の枠状、それらを二重にした形状に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図１１参照）、十字型、卍型の中心部を除いた形状に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図１２参照）、円環状、四角形の枠状の一部を除いた形状に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図１３参照）、三角形の枠状に形成したカットワイヤを、６回対称に配置した微細構造１１ａ、および、三角形に形成したカットワイヤを、４回対称に配置した微細構造１１ａ（図１４参照）を有している。 The metamaterial structure 11 is formed into, for example, a microstructure 11a (see FIG. 8) in which four or more rectangular cut wires arranged in parallel are arranged in four-fold symmetry, a lattice, a circle, or a cross A microstructure 11a (see FIG. 9) in which the cut wires are arranged in four-fold symmetry, and a microstructure 11a in which a cut wire formed in a shape in which a bowl shape and an I shape are crossed are arranged four-fold ), An annular ring, a square frame shape, and a cut wire formed into a doubled shape thereof, a microstructure 11a (see FIG. 11) disposed in four-fold symmetry, a cruciform, and a central portion of a bowl shape are removed. The cut wire formed in the shape is arranged in four-fold symmetry, the microstructure 11a (see FIG. 12) arranged in four-fold symmetry, and the cut wire formed in the shape excluding a ring-shaped, square frame-like part Microstructure 11a (FIG. 1) (Refer to Fig. 14), there is a microstructure 11a in which cut wires formed in a triangular frame are arranged in six-fold symmetry, and a microstructure 11a in which cut wires formed in a triangle are arranged four-fold (see FIG. 14) doing.

　また、メタマテリアル構造体１１は、図８～図１４に示すように、各バリエーションのカットワイヤで構成される部分と、カットワイヤのない部分とを反転（相補）させたものであってもよい。また、メタマテリアル構造体１１は、図８～図１４に示す４回対称または６回対称の配置に限らず、ｎ回対称（ｎは２以上の整数）の配置であってもよい。 In addition, as shown in FIGS. 8 to 14, the metamaterial structure 11 may be one in which a portion constituted by cut wires of each variation and a portion without cut wires are inverted (complementary) . In addition, the metamaterial structures 11 are not limited to the arrangement of four-fold symmetry or six-fold symmetry shown in FIGS. 8 to 14, and may be of n-fold symmetry (n is an integer of 2 or more).

（様々なバリエーションのメタマテリアル構造体のシミュレーション）
　３種類のメタマテリアル構造体１１について、Rigorous Coupled-Wave Analysis法を用いたシミュレーションを行った。なお、計算時のハーモニクスは６とした。シミュレーションに使用したメタマテリアル構造体１１は、それぞれ図１５（ａ）、図１６（ａ）、図１７（ａ）に示す配置およびサイズの微細構造１１ａのものである。透明基板１２は、ＳｉＯ２から成り、微細構造１１ａはＡｕから成っている。微細構造１１ａの厚みは、40 nmである。 (Simulation of metamaterial structure of various variations)
A simulation using the Rigorous Coupled-Wave Analysis method was performed on three types of metamaterial structures 11. The harmonics at the time of calculation was set to 6. The metamaterial structures 11 used in the simulation are those of the fine structures 11a of the arrangement and size shown in FIGS. 15 (a), 16 (a) and 17 (a), respectively. The transparent substrate 12 is made of SiO 2 , and the microstructure 11 a is made of Au. The thickness of the microstructure 11a is 40 nm.

　各メタマテリアル構造体１１の周囲の屈折率ｎを１．０～１．５まで変化させたときの、各屈折率での反射スペクトルを求め、その計算結果をそれぞれ図１５（ｂ）、図１６（ｂ）、図１７（ｂ）に示す。また、図１５（ｂ）、図１６（ｂ）、図１７（ｂ）から、反射スペクトルのピーク波長と屈折率との関係を求め、それぞれ図１５（ｃ）、図１６（ｃ）、図１７（ｃ）に示す。図１５（ｃ）、図１６（ｃ）、図１７（ｃ）に示すように、メタマテリアル構造体１１の周囲の屈折率変化に応じて、反射スペクトルのピーク波長がほぼ線形的に変化することが確認された。図１５（ｃ）、図１６（ｃ）、図１７（ｃ）から求めた屈折率センサ１０の屈折率感度は、それぞれ 368 nm/RIU、458 nm/RIU、824 nm/RIU であった。 When the refractive index n around each metamaterial structure 11 is changed from 1.0 to 1.5, the reflection spectrum at each refractive index is determined, and the calculation results are shown in FIG. (B), it shows in FIG.17 (b). Further, the relationship between the peak wavelength of the reflection spectrum and the refractive index is determined from FIGS. 15 (b), 16 (b) and 17 (b), and FIGS. 15 (c), 16 (c) and 17 (b), respectively. It shows in (c). As shown in FIGS. 15 (c), 16 (c) and 17 (c), the peak wavelength of the reflection spectrum changes almost linearly according to the change of the refractive index around the metamaterial structure 11. Was confirmed. The refractive index sensitivities of the refractive index sensor 10 determined from FIGS. 15 (c), 16 (c), and 17 (c) were 368 nm / RIU, 458 nm / RIU, and 824 nm / RIU, respectively.

［変形例：光ファイバ型屈折率センサ］
　図１８に示すように、屈折率センサ１０は、光ファイバ（Optical fiber）３１を有し、メタマテリアル構造体１１が、光ファイバ３１の先端面３１ａに設けられていてもよい。この場合、図１９（ａ）に示すように、屈折率センサ１０は、光ファイバ３１を介して、メタマテリアル構造体１１と光源１３および光検知器（Optical detector）３２とが接続されている。なお、光検知器３２は、分光器１５やパワーメータを含むものである。図１９（ａ）に示すように、屈折率センサ１０は、光源１３からの入射光を、光ファイバ３１の後端面から導入し、メタマテリアル構造体１１で反射して戻ってきた光を、光検知器３２で読み取るようになっている。 [Modification: Optical fiber type refractive index sensor]
As shown in FIG. 18, the refractive index sensor 10 may include an optical fiber 31, and the metamaterial structure 11 may be provided on the tip surface 31 a of the optical fiber 31. In this case, as shown in FIG. 19A, in the refractive index sensor 10, the metamaterial structure 11, the light source 13, and the optical detector 32 are connected via the optical fiber 31. The photodetector 32 includes the spectroscope 15 and a power meter. As shown in FIG. 19A, the refractive index sensor 10 introduces the incident light from the light source 13 from the rear end face of the optical fiber 31, reflects the light by the metamaterial structure 11, and returns the light It is read by the detector 32.

　なお、屈折率センサ１０は、図１９（ａ）に示す構成に代えて、図１９（ｂ）～（ｄ）に示す構成であってもよい。図１９（ｂ）に示す構成では、入射光を光ファイバ３１の後端面から導入し、メタマテリアル構造体１１の透過光を光検知器３２で読み取るようになっている。また、図１９（ｃ）に示す構成では、試料側から光を照射し、メタマテリアル構造体１１および光ファイバ３１を通過した光を、光検知器３２で読み取るようになっている。図１９（ｄ）に示す構成では、試料側から光を照射し、メタマテリアル構造体１１に当った光の反射光を、光検知器３２で読み取るようになっている。 The refractive index sensor 10 may be configured as shown in FIGS. 19 (b) to 19 (d) instead of the configuration shown in FIG. 19 (a). In the configuration shown in FIG. 19 (b), incident light is introduced from the rear end face of the optical fiber 31, and light transmitted through the metamaterial structure 11 is read by the light detector 32. Further, in the configuration shown in FIG. 19C, light is irradiated from the sample side, and the light passing through the metamaterial structure 11 and the optical fiber 31 is read by the light detector 32. In the configuration shown in FIG. 19D, light is emitted from the sample side, and the reflected light of the light that has hit the metamaterial structure 11 is read by the light detector 32.

　以上のような構成を用いて、共振波長の変化や反射率の変化を読み取ることにより、周囲の屈折率の値をセンシングすることができる。すなわち、メタマテリアル構造体１１の周囲の屈折率のわずかな変化により、共振波長がシフトするため、メタマテリアル構造体１１からの反射光をモニターすることにより、図２０に示すように、周辺の屈折率Ｎのわずかな変化ΔＮに応じた、反射率の変化ΔＲあるいは中心（共振）波長の変化Δλを読み取ることができる。 By reading the change of the resonant wavelength and the change of the reflectance using the configuration as described above, it is possible to sense the value of the surrounding refractive index. That is, since the resonant wavelength shifts due to a slight change in the refractive index around the metamaterial structure 11, by monitoring the reflected light from the metamaterial structure 11, as shown in FIG. A change in reflectance ΔR or a change in central (resonance) wavelength Δλ in response to a slight change ΔN in the factor N can be read.

　光ファイバ３１の先端面３１ａにメタマテリアル構造体１１を設けた屈折率センサ１０は、光ファイバ３１の先端が届く範囲であれば、試料を切り取る侵襲的な測定ではなく、本来ある場所（in situ）での測定が可能となる。このため、生体などのように、環境依存性がある測定対象であっても、精密な測定が可能である。また、注射針より細い光ファイバ３１を使用することにより、生体等へのダメージが少ない測定が可能となる。また、測定範囲が光ファイバ３１の直径で決まるため、細い光ファイバ３１を使用することにより、微細領域の物理量を測ることができる。また、光ファイバ３１を移動させながら測定することにより、測定結果の空間マッピングを行うことができる。 The refractive index sensor 10 in which the metamaterial structure 11 is provided on the front end surface 31a of the optical fiber 31 is not an invasive measurement for cutting out the sample, as long as the front end of the optical fiber 31 can reach. It becomes possible to measure in). For this reason, precise measurement is possible even for a measurement target that is environment-dependent, such as a living body. Further, by using the optical fiber 31 thinner than the injection needle, measurement with less damage to a living body or the like becomes possible. Further, since the measurement range is determined by the diameter of the optical fiber 31, the physical quantity of the fine region can be measured by using the thin optical fiber 31. Also, by performing measurement while moving the optical fiber 31, spatial mapping of the measurement result can be performed.

（光ファイバ型屈折率センサの製造方法）
　光ファイバ３１の先端面３１ａにメタマテリアル構造体１１を設けた屈折率センサ１０を製造した。図２１ａ）～ｆ）に、光ファイバ３１の先端面３１ａに、メタマテリアル構造体１１を製造する方法を示す。その製造方法では、まず、カットした光ファイバ３１の先端面３１ａを、純水もしくは有機溶剤を用いた超音波洗浄または紫外線・オゾン処理により洗浄し、その後、カットした光ファイバ３１の先端面３１ａに、紫外線硬化樹脂（UV curing resin）３３を塗布する。次に、平坦なガラス平面３４に、紫外線硬化樹脂３３が塗布された光ファイバ３１の先端面３１ａを垂直に押し当て、紫外線を照射して紫外線硬化樹脂３３を硬化し（図２１ａ）参照）、その後、平坦なガラス平面３４から離し、紫外線硬化樹脂３３を平坦化する。なお、光ファイバ３１の先端面３１ａに形成するのではなく、ガラス基板上にメタマテリアル構造体１１を形成する場合、図２１ａ）の工程は不要となる。また、光ファイバ３１の先端面３１ａが十分に平滑な場合も、図２１ａ）の工程は不要である。 (Method of manufacturing optical fiber type refractive index sensor)
The refractive index sensor 10 in which the metamaterial structure 11 was provided on the front end surface 31 a of the optical fiber 31 was manufactured. 21a) to f) show a method of manufacturing the metamaterial structure 11 on the tip surface 31a of the optical fiber 31. FIG. In the manufacturing method, first, the distal end surface 31a of the cut optical fiber 31 is cleaned by ultrasonic cleaning or ultraviolet / ozone treatment using pure water or an organic solvent, and then the distal end surface 31a of the cut optical fiber 31 is , UV curing resin (UV curing resin) 33 is applied. Next, the tip surface 31a of the optical fiber 31 coated with the ultraviolet curable resin 33 is vertically pressed against the flat glass surface 34, and the ultraviolet curable resin 33 is cured by irradiating the ultraviolet (see FIG. 21a)). Then, it is separated from the flat glass plane 34, and the ultraviolet curing resin 33 is planarized. In the case where the metamaterial structure 11 is formed on the glass substrate instead of forming on the distal end surface 31a of the optical fiber 31, the process of FIG. 21a is not necessary. In addition, even when the end face 31a of the optical fiber 31 is sufficiently smooth, the process of FIG. 21a) is not necessary.

　次に、平坦化した紫外線硬化樹脂３３の表面（ガラス基板上に形成する場合はガラス基板表面）に、Ti、Au、Crを、この順に 1 nm、40 nm、5 nmの厚さで堆積して成膜する（図２１ｂ）参照）。堆積には、スパッタ装置または蒸着装置を用いる。続いて、その成膜面上に、紫外線硬化樹脂３５を塗布する（図２１ｃ）参照）。その後、別途製造したシリコン製または石英製のモールド（鋳型）を用意し、モールドを紫外線硬化樹脂３５に押し当て、紫外線を120秒程度照射して紫外線硬化樹脂３５を硬化させる（図２１ｄ）参照）。なお、Tiは、Auと紫外線硬化樹脂３３（またはガラス基板）との密着性を高める目的で使われており、密着性が良好な場合、Tiは不要である。 Next, Ti, Au, and Cr are deposited in this order with a thickness of 1 nm, 40 nm, and 5 nm on the surface of the planarized UV curable resin 33 (the surface of the glass substrate when formed on a glass substrate). Film formation (see FIG. 21 b)). For deposition, a sputtering apparatus or a vapor deposition apparatus is used. Subsequently, an ultraviolet curable resin 35 is applied on the film formation surface (see FIG. 21c). Thereafter, a separately manufactured silicon or quartz mold (mold) is prepared, and the mold is pressed against the UV curable resin 35, and the UV curable resin 35 is cured by irradiating the UV for about 120 seconds (see FIG. 21d)) . Ti is used for the purpose of enhancing the adhesion between Au and the ultraviolet curable resin 33 (or the glass substrate), and Ti is not necessary when the adhesion is good.

　次に、光ファイバ３１の側面などに付着している未硬化の余分な紫外線硬化樹脂３５を、エタノールで30秒程度リンスして除去した後、100℃のホットプレートで光ファイバ３１を30秒程度乾燥させる。その後、45秒程度のイオンミリング（8kV、200 μA）により、Cr、Au、Tiを順次エッチングする（図２１ｅ）参照）。続いて、Crを10秒程度ウェットエッチングし、CrおよびCr上に残った紫外線硬化樹脂３５を除去する（図２１ｆ）参照）。ここで、Crがウェットエッチングにより除去されることにより、Cr上に残っていた紫外線硬化樹脂３５も剥離される。こうして、光ファイバ３１の先端面３１ａに、メタマテリアル構造体１１が製造される。 Next, after removing the uncured excess UV curable resin 35 adhering to the side surfaces of the optical fiber 31 by rinsing with ethanol for about 30 seconds, remove the optical fiber 31 for about 30 seconds with a 100 ° C. hot plate. dry. Thereafter, Cr, Au and Ti are sequentially etched by ion milling (8 kV, 200 μA) for about 45 seconds (see FIG. 21 e)). Subsequently, Cr is wet-etched for about 10 seconds to remove the UV curable resin 35 remaining on the Cr and the Cr (see FIG. 21 f)). Here, since the Cr is removed by wet etching, the ultraviolet curable resin 35 remaining on the Cr is also peeled off. Thus, the metamaterial structure 11 is manufactured on the distal end surface 31 a of the optical fiber 31.

（光ファイバ型屈折率センサの製造結果）
　光ファイバ３１の先端面３１ａに製造したメタマテリアル構造体１１の電子顕微鏡写真を、図２２（ａ）～（ｃ）に示す。また、製造された光ファイバ型の屈折率センサ１０の反射スペクトルを、図２３に示す。図２３に示すように、光ファイバ３１の先端面３１ａに形成したメタマテリアル構造体１１を、空気（Air）およびエタノール（Ethanol）のそれぞれの環境下にさらすと、その屈折率変化によって共振波長が変化し、屈折率センサ１０として機能することが確認された。 (Result of manufacturing optical fiber type refractive index sensor)
Electron micrographs of the metamaterial structure 11 produced on the front end face 31a of the optical fiber 31 are shown in FIGS. 22 (a) to 22 (c). The reflection spectrum of the manufactured optical fiber type refractive index sensor 10 is shown in FIG. As shown in FIG. 23, when the metamaterial structure 11 formed on the tip surface 31a of the optical fiber 31 is exposed to the environment of air (Air) and ethanol (Ethanol), the resonance wavelength is changed by the change of the refractive index. It was confirmed that it changed and functioned as the refractive index sensor 10.

［変形例：メタマテリアル構造体の配置寸法］
　メタマテリアル構造体１１はスケーリング則に従うため、その寸法について基本的に物理的制限はない。すなわち、寸法を小さくすれば、共振波長が短波長側にシフトし、寸法を大きくすれば、共振波長が長波長側にシフトするため、その波長に合った光源１３と光検出器３２とがあれば、図１に示すようなシステム構成が可能である。但し、メタマテリアル構造体１１の単位構造を構成するカットワイヤ同士が接触することを避けるため、ｗ（カットワイヤの幅）、ｇ（平行配置されたカットワイヤ間のギャップ）、ｄ（垂直配置されたカットワイヤ間のギャップ）、ｌ（カットワイヤの長さ）は０ｎｍよりも大きくした方がよい。 [Modification: Layout dimension of metamaterial structure]
Since the metamaterial structure 11 obeys the scaling law, there is basically no physical limitation on its dimensions. That is, if the size is reduced, the resonant wavelength is shifted to the short wavelength side, and if the size is increased, the resonant wavelength is shifted to the long wavelength side, the light source 13 and the photodetector 32 are matched to the wavelength. For example, a system configuration as shown in FIG. 1 is possible. However, w (width of cut wire), g (gap between cut wires arranged in parallel), d (vertically arranged) in order to avoid contact between the cut wires constituting the unit structure of the metamaterial structure 11 The gap between the cut wires) and l (the length of the cut wires) should be greater than 0 nm.

　また、カットワイヤの厚さtについては、表皮深さ（skin depth)という物理量を目安とすると、例えば、アルミニウムの可視光での表皮深さが１３ｎｍであるので、ｔを１３ｎｍ以上にすればよい。また、ｔ以外の寸法パラメータの下限は、その時点での製造技術の限界で決まる。 Further, regarding the thickness t of the cut wire, taking the physical quantity of skin depth as a standard, for example, since the skin depth of aluminum in visible light is 13 nm, t may be 13 nm or more. . Also, the lower limit of dimensional parameters other than t is determined by the limit of the manufacturing technology at that time.

　各寸法パラメータを小さくしたときのメタマテリアル構造体１１の配置の一例を、図２４に示す。ここで、透明基板１２はSiO2、メタマテリアル構造体１１の微細構造１１ａは銀（Ag）から構成されている。寸法は、ｗ＝４０ｎｍ、ｇ＝６０ｎｍ、ｄ＝２０ｎｍ、ｌ＝１４０ｎｍ、Λ＝５００ｎｍ、ｔ＝４０ｎｍである。 An example of arrangement | positioning of the metamaterial structure 11 when each dimension parameter is made small is shown in FIG. Here, the transparent substrate 12 is made of SiO 2 , and the fine structure 11 a of the metamaterial structure 11 is made of silver (Ag). The dimensions are w = 40 nm, g = 60 nm, d = 20 nm, l = 140 nm, Λ = 500 nm, t = 40 nm.

　図２４に示すメタマテリアル構造体１１の周囲の屈折率ｎを１．０～１．２まで変化させたときの、メタマテリアル構造体１１の透過（Transmittance）スペクトルおよび反射（Reflectance）スペクトルを計算し、図２５に示す。なお、計算には、Rigorous Coupled-Wave Analysis法を用いた。計算時のハーモニクスは６とした。図２５に示すように、屈折率変化およびピーク波長シフトはおおよそ線形関係となることが確認された。図２５から、このメタマテリアル構造体１１の屈折率感度を求めると、750 nm/RIUとなる。この結果は、従来の表面プラズモンを利用した屈折率センサの感度を大きく上回っている。 The transmission spectrum and reflection spectrum of the metamaterial structure 11 when the refractive index n around the metamaterial structure 11 shown in FIG. 24 is changed from 1.0 to 1.2 are calculated. , Shown in FIG. The Rigorous Coupled-Wave Analysis method was used for the calculation. The harmonics at the time of calculation was set to 6. As shown in FIG. 25, it was confirmed that the refractive index change and the peak wavelength shift have a roughly linear relationship. The refractive index sensitivity of this metamaterial structure 11 is obtained from FIG. 25 and is 750 nm / RIU. This result greatly exceeds the sensitivity of the conventional refractive index sensor using surface plasmons.

　一方、各寸法パラメータの上限については、製造上の制約がないため、どの波長（周波数）まで屈折率センサ１０の応用範囲を広げるかにより任意に設定可能である。以上では、可視～近赤外（波長2000 nm程度以下）を想定してきたが、屈折率センサ１０の応用範囲として、熱波長（１０μｍ程度）からテラヘルツ波（具体的には、０．３ＴＨｚ（波長９９９μｍ））まで想定することもできる。この場合、単純にスケーリング則により寸法を見積もると、例えば、設計波長１．２４μｍを０．３ＴＨｚ（波長９９９μｍ）に相似的に拡大して、ｗ＝７２．５μｍ、ｇ＝１２０．８μｍ、ｄ＝１２０．８μｍ、ｌ＝２６５．９μｍ、Λ＝８０５．６μｍ、ｔ＝３２．２μｍとなる。 On the other hand, the upper limit of each dimension parameter is not limited in manufacturing, and can be arbitrarily set according to which wavelength (frequency) the application range of the refractive index sensor 10 is extended. In the above, visible to near infrared (wavelength of about 2000 nm or less) is assumed, but as an application range of the refractive index sensor 10, terahertz wave (specifically, 0.3 THz (wavelength) from heat wavelength (about 10 μm) 999 μm)) can also be assumed. In this case, when the dimensions are simply estimated by the scaling law, for example, the design wavelength 1.24 μm is similarly expanded to 0.3 THz (wavelength 999 μm), w = 72.5 μm, g = 120.8 μm, d = 120.8 μm, l = 265.9 μm, Λ = 805.6 μm, and t = 32.2 μm.

　テラヘルツ（ＴＨｚ）波は生体に安全で、ＴＨｚで吸収ピークを持つケミカル・バイオ物質（吸収周波数は物質固有であるため、物質の特定に用いることができる）が多数ある一方、紙や服などを透過するというＴＨｚの特性から、空港でのセキュリティチェックや国際郵便物の麻薬チェック（ドラッグなどは、ＴＨｚの特定周波数で固有指紋スペクトルを持つ）にＴＨｚを使うことが検討されている。本発明の実施の形態のメタマテリアル構造体１１および屈折率センサ１０によれば、テラヘルツ領域における屈折率センサ１０に基づくバイオ・ケミカルセンサの開発も可能となる。 Terahertz (THz) waves are safe for living beings, and there are many chemical / biomaterials that have absorption peaks at THz (the absorption frequency is unique to substances, so they can be used to identify substances), while paper and clothes etc. From the characteristic of THz to be transmitted, it is considered to use THz for security check at an airport or for narcotics check of international mail (such as drug has a unique fingerprint spectrum at a specific frequency of THz). According to the metamaterial structure 11 and the refractive index sensor 10 of the embodiment of the present invention, development of a bio-chemical sensor based on the refractive index sensor 10 in the terahertz region also becomes possible.

［変形例：血液検査への応用］
　屈折率センサ１０は、ガラスプレートを有し、メタマテリアル構造体１１がガラスプレートの表面に設けられていてもよい。また、メタマテリアル構造体１１の微細構造１１ａの表面に、図７（ａ）に示す検出用ＤＮＡ２１などのリガンドが付着していてもよい。この場合、ガラスプレート表面のメタマテリアル構造体１１の上に血液を滴下して、屈折率変化から屈折率を求めることにより、血液中の成分を検出することができる。なお、血液に限らず、他の液体などの物質をメタマテリアル構造体１１の上に載せることにより、その物質中の成分を検出することもできる。また、図２１の製造方法に従って、ガラスプレートの表面にメタマテリアル構造体１１を製造することができる。 [Modification: Application to blood test]
The refractive index sensor 10 may have a glass plate, and the metamaterial structure 11 may be provided on the surface of the glass plate. In addition, a ligand such as detection DNA 21 shown in FIG. 7A may be attached to the surface of the fine structure 11 a of the metamaterial structure 11. In this case, the blood can be detected by dropping blood on the metamaterial structure 11 on the surface of the glass plate and determining the refractive index from the change in refractive index. By placing a substance such as another liquid on the metamaterial structure 11 as well as blood, components in the substance can also be detected. Moreover, according to the manufacturing method of FIG. 21, the metamaterial structure 11 can be manufactured on the surface of a glass plate.

　　１　試料
　１０　屈折率センサ
　１１　メタマテリアル構造体
　　１１ａ　微細構造
　１２　透明基板
　１３　光源
　１４　ハーフミラー
　１５　分光器
 
　２１　検出用ＤＮＡ
　２２　相補ＤＮＡ
　２３　相補鎖
 
　３１　光ファイバ
　　３１ａ　先端面
　３２　光検知器
　３３、３５　紫外線硬化樹脂
　３４　ガラス平面
  1 Sample 10 Refractive Index Sensor 11 Metamaterial Structure 11a Fine Structure 12 Transparent Substrate 13 Light Source 14 Half Mirror 15 Spectroscope
21 Detection DNA
22 Complementary DNA
23 Complementary strand
31 Optical Fiber 31a Tip Surface 32 Optical Detector 33, 35 UV Curing Resin 34 Glass Plane

Claims (10)

　入射光の波長と同程度又は前記波長以下の微細構造を有し、前記入射光と前記微細構造に依存した表面プラズモンモードとの光結合が共振条件で強くなることにより、波長選択的な光応答を示すメタマテリアル構造体であって、
　前記微細構造は、回転対称に二次元周期配列された単位構造から成ることを
　特徴とするメタマテリアル構造体。 A wavelength selective light response by having a fine structure equal to or less than the wavelength of incident light, and intensifying optical coupling between the incident light and the surface plasmon mode depending on the fine structure under resonance conditions. Is a metamaterial structure that
A metamaterial structure characterized in that the fine structure is composed of unit structures which are two-dimensionally periodically arranged in rotational symmetry. 　前記入射光の波長が２５００ｎｍ以下であることを特徴とする請求項１記載のメタマテリアル構造体。 The metamaterial structure according to claim 1, wherein a wavelength of the incident light is 2500 nm or less. 　偏光無依存であることを特徴とする請求項１または２記載のメタマテリアル構造体。 3. The metamaterial structure according to claim 1, which is polarization independent. 　前記微細構造は、前記単位構造の二次元の配列面に沿って、前記単位構造を、縦方向および／または横方向に規則的に複数並べて配置して成ることを特徴とする請求項１乃至３のいずれか１項に記載のメタマテリアル構造体。 The fine structure is characterized in that a plurality of the unit structures are regularly arranged in a longitudinal direction and / or a lateral direction along a two-dimensional array surface of the unit structures. The metamaterial structure according to any one of the above. 　前記微細構造は、金、銀、銅、アルミニウムまたは遷移金属系窒化物から成ることを特徴とする請求項１乃至４のいずれか１項に記載のメタマテリアル構造体。 The metamaterial structure according to any one of claims 1 to 4, wherein the microstructure is made of gold, silver, copper, aluminum or a transition metal nitride. 　請求項１乃至５のいずれか１項に記載のメタマテリアル構造体を有することを特徴とする屈折率センサ。 A refractive index sensor comprising the metamaterial structure according to any one of claims 1 to 5. 　光ファイバを有し、
　前記メタマテリアル構造体は、前記光ファイバの先端に設けられていることを
　特徴とする請求項６記載の屈折率センサ。 With optical fiber,
The refractive index sensor according to claim 6, wherein the metamaterial structure is provided at the tip of the optical fiber. 　ガラスプレートを有し、
　前記メタマテリアル構造体は、前記ガラスプレートの表面に設けられていることを
　特徴とする請求項６記載の屈折率センサ。 Has a glass plate,
The said metamaterial structure is provided in the surface of the said glass plate. The refractive index sensor of Claim 6 characterized by the above-mentioned. 　前記微細構造の表面に付着された検出用作用体を有し、
　前記検出用作用体は、検出対象と相互作用可能であることを
　特徴とする請求項６乃至８のいずれか１項に記載の屈折率センサ。 Having a detection agent attached to the surface of the microstructure,
The refractive index sensor according to any one of claims 6 to 8, wherein the detection acting body is capable of interacting with a detection target. 　前記検出用作用体は、検出用ＤＮＡまたは検出用ＲＮＡから成り、前記検出対象であるＤＮＡまたはＲＮＡと相補鎖を形成可能であり、
　前記微細構造は、前記検出用ＤＮＡまたは前記検出用ＲＮＡを結合可能な材料から成ることを
　特徴とする請求項９記載の屈折率センサ。
  The agent for detection comprises DNA for detection or RNA for detection, and can form a complementary strand with the DNA or RNA to be detected,
The refractive index sensor according to claim 9, wherein the fine structure is made of a material capable of binding the detection DNA or the detection RNA.
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