JP4949876B2 - Polarization control element - Google Patents

Description

  The present invention relates to a polarization control element.

  The “polarization control element” is an optical element having a function of changing the polarization state of incident light, that is, the polarization direction (polarization angle) and ellipticity to a desired output polarization state, as indicated by reference numeral 1 in FIG. And widely used in display devices such as liquid crystal projector devices and various optical devices.

  Specific embodiments of the polarization control element include a polarizing plate that extracts a specific polarization component of incident light and outgoing light to a spatial modulation element such as a liquid crystal panel, and two orthogonal crosses of natural light to improve light use efficiency. Examples thereof include a polarization conversion element that aligns polarization components in one direction, a phase shifter such as a half-wave plate and a quarter-wave plate.

  Conventionally, as a polarization control element, “a substrate that is made of polyvinyl alcohol or the like is dyed / adsorbed with a dichroic material such as iodine, and is highly stretched / oriented to exhibit absorption dichroism, thereby providing a polarization selection function. "Achieved polarizing plate" and "various wave plates that give a phase difference between two orthogonal polarization components using the difference in refractive index between ordinary and extraordinary rays in birefringent optical crystals such as calcite and quartz. Recently, as a polarization control element based on a new optical principle, a metal structure whose size is smaller than the wavelength of incident light is brought close to the support at a distance smaller than the size of the metal structure itself. That have been arranged to express the polarization control function have been proposed (Patent Documents 1 to 4, etc.).

  These polarization control elements described in Patent Documents 1 to 4 perform polarization control with high efficiency by using a plasmon resonance phenomenon that is an electronic vibration in a fine metal structure.

JP 2006-330105 A JP 2006-330106 A JP 2006-330107 A JP 2006-330108 A

  This invention is the above-mentioned “polarization control element capable of performing polarization control with high efficiency using the plasmon resonance phenomenon, which is an electronic vibration in a fine metal structure”, and has a high degree of design freedom for polarization control. The challenge is to achieve this.

The polarization control element of the present invention has the following characteristics (claim 1).
That is, at least three “metal structures whose size is smaller than the wavelength of incident light” are arranged close to each other at a distance smaller than the size of the metal structure itself on the planar surface of the support, and at least three metals The arrangement of the structures is “1 unit”, and the units are two-dimensionally arranged on the surface.

The number of "metal structure constituting one unit" is 3 or more as described above, two of at least three metal structures Ri der "same shape and the same size", otherwise 1 The size of each metal structure is made different from the size of each of the two metal structures. That is, the at least three metal structures constituting one unit include at least one metal structure having a “shape and / or size” different from that of the two metal structures.

The polarization control element according to claim 1 is described as follows: “N (≧≧ 3 metal structures) are brought close to each other at a distance smaller than the size of the metal structure with another metal structure having a size smaller than the wavelength of the incident light. 1) A configuration in which the 3 + N metal structures are arranged as one unit and the units are arranged two-dimensionally ”can be obtained. That is, in the polarization control element according to claim 2 include "4 or more metal structure" to 1 unit of the array of metallic structures.

The units of the metal structure according to claim 1 or 2 can be "three-dimensionally arranged on the planar surface of the support" (claim 3).
That is, a unit for arranging metal structures by stacking the “two-dimensional arrangement of one unit by arranging three or more metal structures” according to claim 1 or 2 on a support in a plurality of layers. Can be arranged three-dimensionally.

  The polarization control element according to any one of claims 1 to 3, wherein "the metal material constituting the metal structure" is gold (Au), silver (Ag), platinum (Pt), aluminum (Al), nickel ( Any of Ni), chromium (Cr), copper (Cu), a combination thereof, or an alloy material / mixed material containing these as a main component can be used.

5. The “two-dimensional array of metal structure units” in the polarization control element according to claim 1 is any of a line array, a square lattice array, a rectangular lattice array, a hexagonal lattice array, and a random array. (Claim 5). If the units of the metal structure are arranged three-dimensionally as in the third aspect, the two-dimensional arrangement in each layer to be laminated can be the above-described various arrangements.
Further, in the polarization control element according to claim 1, “the one metal structure can be arranged at a symmetrical position with respect to the center line of the orientation of the two metal structures. (Claim 6).

As described above, according to the present invention, a novel polarization control element can be realized.
In the polarization control element of the present invention, “the arrangement of the metal structures constituting one unit includes“ at least three metal structures, and the two metal structures have the same size and shape, at least one of which Since the “shape and / or size” is different from the two metal structures, the degree of freedom in design with respect to polarization control is large, and a structure having desired polarization control characteristics can be easily realized.

FIG. 2 is a diagram for explaining one embodiment of the polarization control element of the present invention.
In FIG. 2, the polarization control element denoted by reference numeral 10 is a metal structure unit 10 </ b> B (hereinafter referred to as a metal structure unit 10 </ b> B) on a planar surface of a parallel plate-like support substrate 10 </ b> A that is a “support”. ).

The support substrate 10A is preferably made of “a material that has low absorption at a wavelength in the visible region and has little anisotropy with respect to polarized light in order to obtain high light utilization efficiency”. Specifically, quartz glass or BK7 An optical crystal material such as borosilicate glass such as Pyrex (registered trademark), CaF ₂ , Si, ZnSe, or Al ₂ O ₃ can be suitably used.

  In the embodiment of FIG. 2, the metal structure unit 10 </ b> B is configured by “arrangement of three metal structures”. The metal structure unit 10B is shown in FIG. In FIG. 3, the arrangement of three metal structures MS1, M2S, MS3 constitutes a metal structure unit. Of these three metal structures MS1, MS2, and MS3, the metal structures MS1 and MS2 have the same shape and size, and the metal structures MS1 and MS2 are collectively referred to as a “metal structure pair”. Called with the symbol MSP12.

  The metal structure MS3 is different in size from the metal structures MS1 and MS2 constituting the metal structure pair MSP12. These metal structures MS1, MS2, and MS3 need to be disposed at a “distance that allows interaction between adjacent metal structures via near-field light” when irradiated with incident light.

“Near-field light” means a “locally distributed electromagnetic field” generated when electrons in a metal are excited by incident light. “Distance interacting via near-field light” is because the origin of near-field light depends on the motion of electrons in the metal, so if the metal structure is sufficiently smaller than the wavelength of the light, It is roughly “about the size of the metal structure itself”. Accordingly, the metal structures MS1, MS2, and MS3 are arranged close to each other at a “distance smaller than the size of the metal structure”.
In the embodiment shown in FIG. 2 and FIG. 3, the metal structures MS1 to MS3 are all “cylindrical shapes”, but not limited to this, spherical shapes, hemispherical shapes, triangular / square prism shapes, conical shapes, Various shapes such as an elliptic cylinder shape are allowed as shapes.

In this case, depending on the shape of the metal structure, the size may not be uniquely determined. In this specification, the size of the metal structure is determined as follows.
FIG. 4 shows (a) a circular shape, (b) an elliptical shape, (c) an equilateral triangular shape, (d) as a two-dimensional shape of the metal structure (a shape viewed from a direction orthogonal to the surface of the support). ) A rectangular shape, and (e) a general indefinite shape.

Among these, the shape viewed from the direction orthogonal to the support surface, such as the circular shape of (a), the regular triangle shape of (c), and a regular polygonal shape such as a square (not shown) is “ In the case of “isotropic”, “the diameter of a circle having the same area as those shapes: d” is defined as “the size of the metal structure”. In the case of other anisotropic shapes (the elliptical shape in FIG. 4B, the rectangular shape in (d), and the indefinite shape in (e)), the same area as the shape of the metal structure viewed from the above direction An ellipse having a major axis: d1 and a minor axis: d2 is defined as “size of metal structure”.
The size of the metal structure must be “smaller than the wavelength of light”. In other words, the above “d”, “d1”, and “d2” are equal to or shorter than the use wavelength of light.

  When the shape of the metal structure is the above-mentioned “anisotropic shape” and the size is considered to be an ellipse having the same area as this, when arranging the metal structures in the “ellipse major axis direction”, The distance between the metal structures is smaller than d1, and when the metal structures are arranged in the “ellipse minor axis direction”, the distance between the metal structures is set smaller than d2.

  The “size in the direction perpendicular to the support surface” of the metal structure is determined so that the polarization direction of the incident light is in a plane parallel to the support surface (the incident direction of the incident light is orthogonal to the support surface). The size of the metal structure in the “direction perpendicular to the support surface” does not affect the distance of interaction between the metal structures via the near-field light. The “size of the metal structure” is not particularly limited.

Here, specific materials and sizes of the metal structures MS1 to MS3 will be described.
When the metal structure is irradiated with light, electrons in the metal are excited, and this excitation becomes resonantly strong with respect to the “specific wavelength”. This is due to “collective oscillation of electrons in metal”, and such “collective motion of electrons” is called plasmon.

  “Plasmon” is generally surface plasmon excited at the interface between metal and dielectric, but in a minute metal structure, “vibration mode depending on the size of metal structure” is excited. Such vibration mode plasmons are called “localized surface plasmons”. In this specification, surface plasmons and localized surface plasmons are not distinguished and are simply called plasmons.

  When the plasmon is excited, an oscillating electric field in the vicinity of the metal structure is strengthened and affects another adjacent metal structure. When the two metal structures influence each other, anisotropy of the strength of interaction with respect to the orientation direction of the metal structure appears. This anisotropy modulates both the amplitude and phase of plasmons, so that the light scattered by two or more metal structures has a polarization state that is different from that of incident light.

The metal material constituting the metal structure must be “a material capable of resonantly exciting plasmons with respect to the wavelength of incident light”, and Au, Ag, Pt, Al, Any of Ni, Cr, Cu, or “alloy material mainly composed of these”, and a mixed material composed of these and a non-metallic material can be suitably used.
The operating wavelength of the polarization control element of the present invention varies depending on the material of the metal structure.

  “The size of the metal structure” prevents the occurrence of a spatial intensity distribution due to diffraction, and makes it easy to design “the complex vibration mode of electrons in the metal is not excited”. It is preferable that the size is approximately 100 nm or less so that “the polarization control function is realized with respect to light in the visible light region”.

  The “interval between metal structures” is a region where interaction via near-field light works, and is a “distance smaller than the size of the metal structure” as described above. If the thickness is 100 nm or less, the distance between the metal structures is also 100 nm or less. Since the metal structures are more prone to change in polarization state when they are closer to each other, in this case, the preferable interval is 50 nm or less.

Here, the numerical value was implemented to quantitatively evaluate the change in the polarization state when two metal structures having a size equal to or smaller than the wavelength of the incident light are arranged closer to the size of the metal structure itself. “Simulation” will be described.
This numerical simulation uses a finite-difference time-domain method (FDTD method), in which Maxwell's equations representing the time-space response of an electromagnetic field are differentiated and solved in the time domain and space domain, and a calculation model is shown in FIG. .
FIG. 5A shows the state of the zx plane of the calculation model, and FIG. 5B shows the state of the xy plane.
As the metal structure, two Au spheres Au1 and Au2 (refractive index: n = 0.0717, extinction coefficient: k = 1.4965) are arranged in the x-axis direction.

The incident light is “a plane wave propagating in the z-axis direction” and is linearly polarized light (see FIG. 5B) having a polarization plane inclined by 45 degrees with respect to the x-axis in a plane parallel to the xy plane. The wavelength of incident light used was 544 nm, which is in the vicinity of “the refractive wavelength of Au spheres Au1 and Au2: n and the extinction coefficient: the plasmon resonance wavelength for k”.
The diameter of the Au spheres Au1 and Au2 is 40 nm, and the interval between the Au spheres: ds (as shown in the figure, the distance between the closest ends of the two Au spheres) is varied in the range of 0 to 80 nm. Changes in amplitude and phase were investigated.

  FIG. 6 shows “results of numerical simulation”. FIG. 6 shows the amplitude ratio (left diagram in FIG. 6) and phase difference (right diagram in FIG. 6) of the electric field component in the x direction and the electric field component in the y direction on the coordinates shown in FIG. The “distance between metal particles on the horizontal axis” is the distance between the above Au spheres: ds. The closer the two Au spheres are (the smaller the ds is), the larger the amplitude ratio between the x component and the y component of the electric field: Ay / Ax, and the “phase difference between the x component and the y component” is the distance between the Au spheres. : It was about 45 ° when ds was 0 nm. Accordingly, it can be seen that when the spacing between the Au spheres: ds becomes smaller, the incident linearly polarized light is converted to “elliptical polarized light” and the ellipticity also changes.

As described above, by controlling the distance ds between the two Au spheres as the metal structure pair, it is possible to obtain outgoing light in which the polarization characteristics (amplitude ratio, phase difference) are arbitrarily changed.
In addition, it is confirmed from numerical simulation that when the diameter (size) of the Au sphere changes, the amplitude ratio and the phase difference also change “the distance between the Au spheres: ds”, and the diameter of the Au sphere is also polarized. It has been confirmed that this is a control parameter.

In the embodiment shown in FIGS. 2 and 3, the metal structure unit 10B is composed of three metal structures MS1, MS2, and MS3. In this case, the metal structures MS1 and MS2 have the same shape and size to form the metal structure pair MSP12, and polarization control is possible as in the numerical simulation described above.
By adding a third metal structure MS3 to this metal structure pair MSP12, "control of polarization state using spatial symmetry of arrangement of metal structures constituting the metal structure unit" is possible. become.

  Referring to FIGS. 7 and 8, FIG. 7 is an explanatory view of the metal structure unit 10 </ b> B “as viewed from the direction orthogonal to the support surface”, and the metal structure unit 10 </ b> B has the same shape and the same size. On the center line (vertical broken line in the figure) perpendicular to the metal structure pair MSP12 composed of the metal structures MS1 and MS2 and the orientation (the left and right arrangement in the figure) of the metal structure pair MSP12 The metal structure MS3 is arranged. That is, the arrangement of the three metal structures MS1 to MS3 is symmetrical with respect to the center line of the orientation of the metal structures MS1 and MS2.

FIG. 7 shows a case where the metal structure MS3 is larger than the metal structures MS1 and MS2 in the metal structure unit 10B. The size of the metal structure MS3 is the metal structure pair MSP12 and the metal structure. It depends on the design condition of “strength of interaction via near-field light” acting between MS3 and does not necessarily need to be larger than metal structures MS1 and MS2.

  The distance between the metal structures MS1 and MS2: g1 and the distance between the metal structure pair MSP12 and the metal structure MS3: g2 are of course smaller than the “size of the metal structure itself”, but should be used as design parameters. Can be set according to design conditions.

  The interaction through the near field in the case of “metal structures MS1 to MS3 symmetrically arranged” as shown in FIG. 7 will be described using “conceptual diagram of electric dipole interaction” in FIG. When the incident light having polarized light in the parallel direction (FIGS. 8A and 8B) and the vertical direction (FIGS. 8C and 8D) is irradiated to the metal structure pair MSP12 in FIG. Electrons in MS1 to MS3 are excited, and as shown by arrows in the metal structures MS1 and MS2 of the metal structure pair MSP12 in the figure, “four electric dipole moments depending on the polarization direction of incident light”. An “alignment state” is formed.

  The electric dipole moments are “aligned in one direction” (FIGS. 8A and 8C) and those having “different directions” (FIGS. 8B and 8D) are the polarizations of incident light. Exists for direction.

  The light energies that excite these states are shown as E1, E2, E3, and E4 in FIG. These light energies: “E1 <E4 <E3 <E2” are different from each other and are different from each other. Accordingly, when the metal structure MS3 is brought close to the metal structure pair MSP12, the resonance energy of the metal structure MS3 depends on the size of the metal structure MS3. Can act.

  Since the metal structure MS3 is “arranged at positions symmetrical to the center line of the orientation of the metal structure pair MSP12”, two states with different electric dipole moments (FIG. 8 (b) In (d)), “excitation of the metal structure 3 is forbidden” and no interaction occurs. Therefore, by arranging the metal structure MS3 symmetrically with respect to the center line of the orientation of the metal structure pair MSP12 and adjusting the “size and distance: g2” of the metal structure MS3, Polarization anisotropy can be exhibited with respect to incident polarized light parallel to the orientation (FIG. 8A) and perpendicular polarized light (FIG. 8C), and the polarization state can be controlled. .

  FIG. 7 shows the metal structure MS3 having a circular shape when viewed from the direction orthogonal to the support surface. However, in order to control the polarization state, the metal structure MSP12 is aligned. On the other hand, a metal structure having a “shape that is not circularly symmetric”, for example, an elliptical metal structure MS3 as shown in FIG. 9 may be used.

  In the case shown in FIG. 9, the “plasmon resonance wavelength” differs between the major axis direction and the uniaxial direction of the elliptical metal structure MS3, and the electric dipole is parallel to the orientation of the metal structure pair MSP12 (the horizontal direction in the figure). The strength of the interaction via near-field light differs between the state having and the state having a vertical electric dipole. Thus, the polarization state can also be controlled by the shape of the metal structure MS3.

  As described above, the polarization anisotropy can be expressed by the metal structure unit 10B in which the “size and arrangement” of the three metal structures MS1 to MS3 are set, but the polarization state is controlled in a large area. In order to function as a control element, the metal structure units 10B need to be two-dimensionally arranged.

  Various arrangements of the metal structure units 10B are possible, but in particular, when the arrangement is periodically arranged at intervals of about the wavelength of the incident light, it is possible to have “specific angle dependency” in the transmittance or reflectance. Further, when the electrodes are arranged at a high density with an interval larger than the size of the metal structure and shorter than the wavelength, the polarization control efficiency can be increased.

A typical pattern of the arrangement of the metal structure units is shown in FIG.
FIG. 10A shows a “line arrangement pattern”, which plays the same role as the diffraction grating in the direction orthogonal to the line arrangement (the horizontal direction in the figure). FIG. 10B shows a “square lattice arrangement pattern”. By adjusting the period of the lattice, “angle dependency of transmittance or reflectance or optimization of spatial intensity distribution at a distance” can be achieved. FIG. 10C shows a “rectangular array pattern”, which is an array having the characteristics of FIGS. 10A and 10B.

  FIG. 10D shows a “hexagonal lattice arrangement pattern”, in which the metal structure units 10B can be integrated at a higher density, and the polarization control efficiency can be improved. FIG. 10E shows a “random arrangement pattern”. Since the polarization control function is generated only by the structure of the unit arrangement pattern, the function can be expressed without the “perfect periodic arrangement pattern”.

Here, a method for manufacturing the polarization control element described above in the embodiment will be described.
As shown in FIG. 3, a method having a processing accuracy below the diffraction limit of visible light is applied to the fabrication of the metal structures MS1 to MS3 having a size equal to or smaller than the wavelength of incident light. Further, a method using electron beam lithography, DUV / EUV lithography, nanoimprinting, etching utilizing alteration of material properties, and the like can be used.

  For example, a parallel plate optical glass is used as the support substrate 10A as a support, and a metal material such as Au is deposited on the flat surface by sputtering or vacuum evaporation, and a photoresist film is formed on the metal film. Then, a negative pattern is formed so as to leave a “metal structure unit arrangement pattern” by electron beam drawing. Thereafter, unnecessary metal portions are etched by RIE or the like, whereby a metal structure unit and its two-dimensional array pattern can be formed.

  In the embodiment described above, the metal structures MS1 to MS3 constituting the metal structure unit and the two-dimensional array thereof are directly formed on the planar surface of the support substrate 10A as the support. This is a case where the two-dimensional arrangement of the metal structure units is exposed in the air, but as shown in FIG. 11A, the two-dimensional arrangement of the metal structure units 10B by the metal structure is covered. A protective film 10C may be formed on the substrate, and as shown in FIG. 11B, a support film 10D is formed on the support substrate 10A, and two metal structure units 10B are formed on the support film 10D. It may be arranged in a dimensional manner and further covered with a protective film 10C. In the case of FIG. 11B, the support substrate 10 </ b> A and the support film 10 </ b> D constitute a “support”.

  Polarization control characteristics differ depending on the presence or absence of such a support film or protective film. The material of the protective film 10C and the support film 10D is also preferably a “material with low light absorption and low anisotropy with respect to polarized light”, similar to the support substrate 10A, and is generally used as a coating material for optical elements. Materials such as BK7, Pyrex (registered trademark), borosilicate glass such as ZnS-SiO2, CaF2, Si, ZnSe, Al2O3, and ZnO can be preferably used.

When providing a support film or a protective film as in the embodiment shown in FIGS. 11A and 11B, these materials include BBO, LiTaO ₃ , and KTB, which are ferroelectric materials showing the electro-optic crystal effect. Inorganic crystals such as LiNb ₃ , KTB, KTP, and KTN, inorganic crystals such as BBO, LBO, BIBO, KTP, and KDP that are optical crystal materials that exhibit nonlinear optical effects, quartz that exhibits electrostrictive effects, ZnO, LiNbO ₃ , Using an inorganic crystal such as LiTaO ₃ , Li ₂ B ₄ O ₇ , AlN, etc., and causing an “external signal such as electricity, light and pressure” to act on the polarization control element, the electro-optic crystal effect, nonlinear optical effect, electrostrictive effect, etc. The polarization control function may be modulated by actively changing the polarization control characteristic. It is also possible to adjust the “operating wavelength of the polarization control element” according to the optical characteristics of the material of the protective film / support film and the support substrate.

  Further, by depositing a dielectric material such as quartz glass, an electro-optical material, a non-linear optical material or the like as the support film 10D or the protection film 10C by a sputtering method or the like, the interface between the support substrate 10A and the protection film 10C, or the support A polarization control element having a two-dimensional arrangement of metal structure units inside the film 10D and the protective film 10C can be realized.

  In order to form a two-dimensional array of metal structure units, a self-organized array of metal fine particles may be used. For example, metal fine particles produced by pulverizing metal materials in a solution by laser ablation or metal fine particles produced by a chemical synthesis technique are selected by arranging them in a self-organized manner using a microfabricated substrate. It is also possible to form a metal structure unit.

  As described above, in the polarization control element described in the above embodiment, the metal structure unit 10B composed of the metal structure pair MSP12 and the metal structure MS3 is two-dimensionally arranged on the support substrate 10A. The polarization control function is realized by utilizing “the spatial symmetry of the three metal structures MS1 to MS3” in the structure unit 10B. In addition, by using plasmon resonance in a metal that is an inorganic material, a polarization control element that can realize polarization control characteristics with extremely high efficiency and that has high heat resistance and light resistance can be realized.

Another embodiment will be described with reference to FIG. In addition, in order to avoid complication, the thing which does not seem to have a possibility of confusion is attached | subjected with the same code | symbol as FIG. 2, FIG.
Also in the embodiment shown in FIG. 12, a metal structure unit 10B composed of three metal structures MS1 to MS3 is two-dimensionally arranged on a support substrate 10A that is a support. In the embodiment, the metal structure MS3 is “shifted from the center line of the orientation of the metal structure pair MSP12 to the left in the drawing by a distance: s” to constitute the metal structure unit 10B.

  The support substrate 10, the shapes and sizes of the metal structures MS1 to MS3, and the two-dimensional arrangement of the metal structure units 10B are the same as those of the above-described embodiment, and the manufacturing method is also the same.

  As described with reference to FIG. 8, the polarization control element of the present invention indicates the state of the electric dipole moment generated on the metal structure pair 12 depending on the polarization state of the incident light, and the magnitude of the metal structure MS3. By adjusting the position, the polarization anisotropy is expressed by causing a “selective interaction” with the metal structure MS3.

  As shown in FIG. 8, “the state in which the electric dipole moments generated in the metal structures MS1 and MS2 are in different directions” indicates that the metal structure MS3 is “with respect to the center line of the orientation of the metal structure pair MSP12”. In the symmetrical arrangement, the interaction between the metal structure pair MSP12 and the metal structure MS3 via the near field is forbidden. However, as shown in FIG. When the arrangement of the metal structures MS1 to MS3 in the metal structure unit 10B is asymmetric with respect to the center line, the distance: s is shifted to the left in the figure with respect to the center line of the orientation of the metal structure pair MSP12. The above interaction becomes an “acceptable state”, and a polarization anisotropy different from the “symmetric arrangement” shown in FIG. 8 occurs. The polarization anisotropy at this time varies depending on the change of the “allowable state” depending on the distance: s.

  In particular, the “states in which the directions of the electric dipoles of the metal structures MS1 and MS2 are different” are “states in which light cannot be emitted far away” because the sum of the electric dipole moments of these metal structures is zero. It is possible to greatly delay the phase with respect to the polarization component.

  As described above, in the embodiment shown in FIG. 12, the metal structure unit composed of the metal structure pair MSP12 and the metal structure MS3 is two-dimensionally arranged on the support substrate. By arranging the metal structure MS3 in a “spatial asymmetric position” with respect to the metal structure pair MSP12 of the metal structures MS1 and MS2 having the same shape and the same size, “polarization obtained by the polarization control element” The degree of freedom of state ”is increased.

Another embodiment will be described with reference to FIGS.
In these embodiments, the polarization control element is formed as a “metal structure unit” by arranging four or more metal structures having a size smaller than the wavelength of incident light on the planar surface of the support. “Control of the polarization state of incident light” is performed by a structure in which structure units are two-dimensionally arranged.
The shape and size of the support and the metal structure, and the two-dimensional arrangement method of the metal structure units are the same as those in each of the embodiments described above, and the production method is also a method such as the electron beam lithography. Is used.

  In the example illustrated in FIG. 13, the metal structure unit includes four metal structures MS1, MS2, MS3, and MS4. This arrangement example is shown in FIG. 6 as “a metal structure pair MSP12 formed of metal structures MS1 and MS2 having the same size and shape, and symmetrical with respect to the center line of the metal structure pair MSP12. In this example, the fourth metal structure MS4 is added to the arrangement of the arranged metal structure MS3 ”.

The metal structures MS3 and MS4 have the same shape and size.
The “metal structure pair by the metal structure MS3 and the metal structure MS4” has “different orientation (direction of arrangement of the metal structures)” from the “metal structure pair by the metal structures MS1 and MS2”. . In such a structure of the metal structure unit, optical rotation occurs due to the “interaction via near-field light” of the two types of metal structure pairs having different orientation directions.

  The arrangement pattern of the “four metal structures MS1 to MS4” constituting the metal structure unit is not limited to that shown in FIG. 13, and various patterns are possible. In some examples of arrangement patterns, in the example shown in FIG. 14A, the metal structures MS3 and MS4 are “on the whole as compared to the centerline” on the centerline of the orientation of the metal structures MS1 and MS2. In the arrangement pattern shown in FIG. 13B, the orientation of the metal structure pair MS3 and MS4 in the arrangement pattern of FIG. 13 is the same as that of the metal structures MS1 and MS2. The arrangement is shifted to the right in the figure by a distance: s with respect to the center line of the orientation.

  In the arrangement pattern shown in FIG. 14 (c), the metal structure MS3 is arranged by shifting the metal structure MS3 to the right of the figure by a distance: s from the center line of the orientation of the metal structure pair MS1, MS2, and the metal structure This is a pattern in which MS4 is arranged on the center line on the opposite side (downward in the figure) from metal structure MS3 through the orientation of metal structures MS1 and MS2.

  FIGS. 14D and 14E are patterns obtained by adding metal structures MS5 and MS6 to the arrangement pattern of the metal structures MS1 to MS4 shown in FIG. The metal structures MS5 and MS6 have the same shape and size as the metal structures MS3 and MS4.

  The arrangement pattern in FIG. 14D is an arrangement pattern in which the metal structures MS3 to MS6 are rotated by 180 degrees with respect to the orientation centers of the metal structures MS1 and MS2.

  In the arrangement pattern of FIG. 14E, the metal structures MS3 and MS4 are located on one side (upper side in the figure) with respect to the straight line connecting the centers of the metal structures MS1 and MS2, and the metal structures MS5 and MS6 are on the opposite side. It is a pattern arranged as shown in (the lower side of the figure).

  With such various arrangement patterns of four or more metal structures, it is possible to control the polarization state at a higher level by adjusting the forbidden / allowable state of the electric dipole and the orientation of the metal structures. Become.

  Of course, in the case of the two-dimensional arrangement of the “metal structure units” in the arrangement pattern shown in FIGS. 13 and 14, as shown in the example shown in FIG. Needless to say, it can be formed on the support film 10D and covered with the protective film 10C.

Another embodiment will be described with reference to FIG.
The embodiment shown in FIG. 15 is an example of a form in which the units of the metal structure are three-dimensionally arranged on the planar surface of the support. For the sake of concreteness of description, as the unit of the metal structure, a case where the unit is an arrangement of the three metal structures MS1 to MS3 described with reference to FIG. 3 is shown.

Figure 15 (a), (c) is a support in which the support substrate 10 A plane on the surface of an example of stacked in three layers of two-dimensional array of the metal structure unit. That is, the surface of the support base plate 10A, forming the first layer is formed two-dimensional array of units of the metal structure. A protective film 10C1 for protecting the first layer is formed, and a two-dimensional array of units of metal structures is formed on the protective film 10C1 to form a second layer. A protective film 10C2 that protects the second layer is formed, and a two-dimensional array of metal structure units is formed on the protective film 10C2 to form a third layer. The protective film 10C3 that protects the third layer Is formed.
The

  In the example shown in FIG. 15A, the “two-dimensional arrangement of the units of the metal structure” in the first to third layers is exactly the same, and when viewed from the third layer side, FIG. As shown in b), the “two-dimensional arrangement of the units of the metal structure” of each layer completely overlap each other.

  In the example shown in FIG. 15C, the “two-dimensional arrangement of the units of the metal structure” in the first to third layers is exactly the same, but when viewed from the third layer side, FIG. ), The first layer and the third layer “two-dimensional array of metal structure units” completely overlap each other, and the second layer “two-dimensional array of metal structure units”. Is deviated from the arrangement of the first and third layers.

  The basic principle of polarization control is the same as that described in each embodiment described above.

  As shown in FIG. 15, in order to produce a three-dimensional array of metal structure units, the above-described technique such as electron beam lithography is used to create a “two-dimensional metal structure unit in a two-dimensional plane. And the process of forming the protective layer may be repeated.

  The number of two-dimensional arrangements of the metal structure units is not limited to three, but can be adjusted according to a desired polarization control function. Further, the interval between adjacent layers needs to be separated to such an extent that interaction via near-field light does not work between the units of the metal structure. The height of the layer of the two-dimensional arrangement of the metal structure units need not be specified, but is preferably 30 nm or more because of manufacturing restrictions. Therefore, the height of one layer is 60 nm or more. I just need it.

  As shown in FIGS. 15B and 15D, the layer including the metal structure unit may be arranged so that the positions of the metal structure units overlap (FIG. 15B), or the layers of the metal structure units between the layers. The arrangement (FIG. 15 (d)) where the position is shifted may be used. However, since the diffraction effect due to the displacement of the position of the metal structure unit for each layer cannot be ignored, it is a stack where the positions of the metal structure units are completely coincided as shown in FIG. 15B, or as shown in FIG. It is preferable that the “lamination is shifted by a half cycle”.

Thus, by arranging the units of the metal structure three-dimensionally, the frequency of interaction between the incident light and the metal structure can be increased, and the polarization control efficiency can be increased.
Further, by forming “an arrangement of metal structure units having different polarization control characteristics” in each layer, the polarization control function can be combined. For example, by combining the arrangement of metal structure units having a half-wave plate function and the arrangement of metal structure units having a polarization selection function of separating and transmitting one of two orthogonal polarization components, A polarization conversion function can be realized.

It is a figure for demonstrating the optical effect | action of a polarization control element. It is a figure for demonstrating one Embodiment of a polarization control element. It is a figure for demonstrating an example of a metal structure unit. It is a figure which shows the example of the two-dimensional shape of a metal structure. It is a figure for demonstrating the model of numerical simulation. It is a figure which shows the result of a numerical simulation. It is a figure for demonstrating control of a polarization state. It is a figure for demonstrating control of a polarization state. It is a figure which shows another example of a metal structure unit. It is a figure which shows the typical pattern of the arrangement | sequence of a metal structure unit. It is a figure for demonstrating another form of implementation of a polarization control element. It is a figure for demonstrating another form of implementation of a polarization control element. It is a figure explaining another example of a metal structure unit. It is a figure explaining the other example of a metal structure unit. It is a figure for demonstrating the other form of implementation of a polarization control element.

Explanation of symbols

10 Polarization Control Element 10A Support Substrate (Support)
10B Metal structure unit

Claims (6)

At least three metal structures having a size smaller than the wavelength of incident light are arranged close to each other at a distance smaller than the size of the metal structure on the planar surface of the support, and two of these metal structures are arranged. The body has the same shape and the same size, and the size of one other metal structure is different from the size of each of the two metal structures, and the arrangement of these at least three metal structures is one unit. A polarization control element characterized in that the units are two-dimensionally arranged on the surface. The polarization control element according to claim 1,
Wherein the three metal structure, a wavelength smaller than another of the metallic structure of the size incident light, in close proximity at a small distance than the size of the metal structure N (≧ 1) pieces placed, these 3 + N pieces A polarization control element characterized in that the metal structure is a unit and the units are two-dimensionally arranged. A polarization control element, wherein the units of the metal structure according to claim 1 or 2 are three-dimensionally arranged on a planar surface of the support. The polarization control element according to any one of claims 1 to 3,
The metal material constituting the metal structure is any one of gold (Au), silver (Ag), platinum (Pt), aluminum (Al), nickel (Ni), chromium (Cr), copper (Cu), or A polarization control element characterized by being a combination thereof, or an alloy material / mixed material containing these as a main component. The polarization control element according to any one of claims 1 to 4,
The polarization control element, wherein the two-dimensional arrangement of the metal structure units is any one of a line arrangement, a square lattice arrangement, a rectangular lattice arrangement, a hexagonal lattice arrangement, and a random arrangement.   2. The polarization control element according to claim 1, wherein the one structure is disposed at a position symmetrical to a center line of the orientation of the two metal structures.

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