JP2008026807A - Polarization separation element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization separation element which has a structure different from a wire grid polarizer or a photonic polarizing element and is based on a principle different from the same. <P>SOLUTION: The polarization separation element has a three-dimensional metal structure arrangement formed by stacking fine dot patterns DP1, DP2.. which are prepared by two-dimensionally arranging dot-like metal structures smaller than wavelength of incident light, in multi-layer into a retention medium HMD leaving a prescribed interval on a support base BS, whereby the three-dimensional metal structure arrangement is determined such that transmission light intensities or reflection light intensities with respect to two orthogonal polarization components in the incident light made incident at a desired incident angle is differentiated from each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarization separation element.

  Polarization separation elements are used in various optical devices such as liquid crystal projectors. As a polarization separation element, a polarization beam splitter that performs polarization separation using a dielectric multilayer film has been widely known. However, recently, as another kind of polarization separation element, a wire grid polarizer (Patent Documents 1 and 2), a photonics A crystal polarizer (Patent Document 3) has been proposed.

JP 1998-153706 Special table 2003-502708 JP2003-279746

  This invention makes it a subject to implement | achieve the novel polarization separation element different from the various polarization separation elements mentioned above.

The polarization separation element of the present invention has the following characteristics (claim 1).
That is, a three-dimensional metal structure array is provided on the support substrate.
The metal structure constituting the three-dimensional metal structure array is “a fine dot shape smaller than the wavelength of incident light to be polarized and separated”. These “minute dot-like metal structures” are two-dimensionally arranged to form a “dot pattern”, and this two-dimensional dot pattern is stacked and arranged in a plurality of layers at a predetermined interval. .

  That is, a two-dimensional dot pattern is laminated and arranged in a plurality of layers in a direction perpendicular to the pattern surface to form a “metal structure array that is a three-dimensional arrangement of minute dot-like metal structures”. This three-dimensional arrangement is configured by “the metal structure array is held in the holding medium”, and the holding medium is provided on the support substrate. The “holding medium” is a dielectric, and conductive metal structures are three-dimensionally arranged and held in the dielectric to form a metal structure arrangement.

  The three-dimensional metal structure array is set so that “the transmitted light intensity or the reflected light intensity is different for two polarization components orthogonal to each other in incident light incident at a desired incident angle”.

  That is, when a desired incident angle is selected as the incident angle of incident light incident on the metal structure array, transmitted light intensity or reflection with respect to “two polarization components orthogonal to each other” in incident light incident at this incident angle is selected. The metal structure arrangement is determined so that the light intensities are different.

  Thus, making the transmitted light intensity or the reflected light intensity different from “two polarization components orthogonal to each other” is referred to as “polarizing and separating incident light”.

  Of the “two-dimensional dot patterns arranged in a stack” that constitute a three-dimensional metal structure array, the uppermost layer may have a bare metal structure constituting the dot pattern. From the viewpoint of protecting the dot pattern against mechanical force, it is preferable that the uppermost dot pattern is also embedded in the holding medium, and the surface of the polarization separation element is the “holding medium surface”.

  2. The “dot pattern in which metal structures are two-dimensionally arranged” in the polarization separating element according to claim 1, wherein the minute dot-shaped metal structures are linearly spaced apart by a “distance equal to or smaller than the size”. (Linear arrangement pattern elements) arranged in a pattern can be arranged in a direction orthogonal to the longitudinal direction at a predetermined cycle (Claim 2). Alternatively, “a unit arrangement pattern in which a plurality of metal structures are arranged at a distance equal to or smaller than the size” is a “pattern in which the metal structures are aligned in a two-dimensional arrangement regularly or randomly”. (Claim 3). The “orientation of metal structure” is an arrangement pattern of a plurality of metal structures in a unit arrangement pattern of one unit.

  As described above, the shape of the metal structure is “a minute dot smaller than the wavelength of incident light to be polarized and separated, and all the metal structures constituting the metal structure array are in the same shape”. There are no particular restrictions on the specific shape, but hemispheres, cylinders, square columns, etc. are possible, but spheroid shapes, rod shapes, or shapes that extend long in a specific axial direction, etc. It can be “axisymmetric shape (shape having a rotationally symmetric axis)”. The shape of the metal structure can also be a design factor for the polarization separation characteristics to be realized.

  The material of the “dot-like metal structure” of the polarization separation element according to any one of claims 1 to 4 is gold (Au), silver (Ag), platinum (Pt), aluminum (Al), nickel Any one of (Ni), chromium (Cr), copper (Cu), a combination thereof, or an alloy material / mixed material containing these as a main component can be used.

  The polarization separating element according to any one of claims 1 to 5, wherein the “two-dimensional dot pattern arranged in a plurality of layers in the holding medium” can be congruent to each other (claim 6). In this case, two-dimensional dot patterns that are congruent to each other may be arranged so as to “overlap each other in the stacking direction” (Claim 7), or two-dimensional dots that are arranged in layers. It is also possible to arrange the patterns so as to be “displaced from each other” in a direction parallel to the “pattern surface (arrangement surface of the metal structures constituting the dot pattern)”.

  The polarization separating element according to any one of claims 1 to 8, wherein the incident angle is set to about 45 degrees, and two polarization components orthogonal to each other in the incident light are a P polarization component and an S polarization component. (Claim 9).

  As described above, according to the present invention, a polarization separation element based on a different principle can be realized because the structure is different from that of a wire grid polarizer and a photonic polarization element.

Hereinafter, embodiments will be described.
FIG. 1 is a diagram illustrating the function of the polarization separation element.
The polarization separation element PO transmits, for example, a polarization component LP that vibrates in the vertical direction in a plane parallel to the drawing out of the polarization components of incident light L incident in a random polarization state, and vibrates in a direction orthogonal to the drawing. By reflecting the polarization component LS, the incident light L is separated into two polarization components LP and LS. The angle: θ shown in FIG. 1 is the incident angle.

  The polarization separation element PO shown in FIG. 1 completely separates the polarization components LP and LS of incident light in a random polarization state into transmitted light and reflected light. In the polarization separation element of the present invention, so-called polarization separation is, for example, When attention is paid to the transmitted light, the intensity of “two polarization components orthogonal to each other” in the transmitted light is different.

  As will be described later, the polarization separation element of the present invention has a “three-dimensional metal structure array of a plurality of minute dot-like metal structures” inside the element, and forms a metal structure array. The “incident angle, operating wavelength, operating band” can be designed by selecting the shape, arrangement, and material.

  “Defining a three-dimensional metal structure arrangement” in claim 1 can include selection of the shape and material of the metal structure as described above.

The first embodiment will be described with reference to FIG.
2A and 2B are explanatory diagrams showing the configuration of the polarization beam splitting element 10. FIG. 2A shows a state viewed from a direction parallel to the thickness direction, and FIG. 2B shows a state viewed from the thickness direction.
In FIG. 2A, the symbol BS indicates a “support substrate”, the symbol HMD indicates a “holding medium”, the symbol MS indicates a metal structure, and the symbols DP1, DP2, and DP3 indicate dot patterns.

  FIG. 2B illustrates the dot patterns DP1 and DP2 in an explanatory manner. The dot pattern DP1 will be described as an example. The dot pattern DP1 has an arrangement form in which minute dot-shaped metal structures MS smaller than the wavelength of incident light are “regularly arranged two-dimensionally”. In this embodiment, the dot patterns DP1, DP2, and DP3 are the same as the “two-dimensional arrangement pattern of the metal structures MS”, and the dot patterns DP1, DP2, and DP3 are in the vertical direction of FIG. The layers are arranged so as to overlap each other with a predetermined interval in the (thickness direction).

  In this way, a “metal structure array” that is a three-dimensional array of metal structures MS is configured. The individual metal structures MS that constitute the metal structure array are held in the holding medium HMD. Has been. The holding medium HMD that holds the metal structure array in this way is supported on the support substrate BS. For the metal structure arrangement, the shape, arrangement form, material, and the like of the metal structure MS are selected so that “a desired polarization separation function is realized”.

  In the first embodiment, as shown in FIG. 2B, the dot pattern DP1 and the like have a metal structure MS spaced apart by a distance equal to or smaller than the size of the metal structure in the horizontal direction of the figure. Linearly arranged at equal intervals to form “linear array pattern elements Li (i = 1, 2,...)”, And these linear array pattern elements Li are perpendicular to the longitudinal direction (FIG. 2B ) In a vertical direction) and a two-dimensional pattern arranged in parallel with each other at a predetermined period.

  Hereinafter, in accordance with the polarization separation element 10 of the first embodiment, the “materials of each part” and the manufacturing method of the polarization separation element 10 will be described.

First, the support substrate BS is preferably formed of a material that has low absorption at wavelengths in the visible region and low anisotropy with respect to polarized light in order to increase the efficiency of polarization separation, such as quartz glass, BK7, Pyrex (registered). It is preferable to use an optical crystal material such as borosilicate glass such as trademark), CaF ₂ , Si, ZnSe, Al ₂ O ₃ as a material.

Similarly, the material of the holding medium HMD that holds the three-dimensional metal structure array is preferably a material that has low absorption at a wavelength in the visible region and little anisotropy with respect to polarized light, and is generally used as an “optical element coating material”. Quartz glass, BK7, Pyrex (registered trademark), borosilicate glass such as ZnS—SiO ₂ , CaF ₂ , Si, ZnSe, Al ₂ O ₃ , ZnO, and the like can be suitably used.

It is also possible to cause the polarization separation characteristic to actively change by applying an “external signal such as electricity, light, pressure, etc.” to the polarization separation element. For example, BBO, LiTaO ₃ , KTB, LiNb ₃ , KTB, KTP, KTN and other inorganic crystals that are “ferroelectric materials showing electro-optic crystal effect”, BBO, LBO that are “optical crystal materials showing nonlinear optical effect” A holding medium HMD is formed using inorganic crystals such as BIBO, KTP, and KDP, quartz that is “inorganic material exhibiting electrostrictive effect”, ZnO, LiNbO ₃ , LiTaO ₃ , Li ₂ B ₄ O ₇ , AlN, and the like. By applying external signals such as electricity, light and pressure to the holding medium HMD, it is possible to actively change the polarization separation characteristics by the metal structure arrangement by the electro-optic effect, the nonlinear optical effect, or the electrostrictive effect.

Here, the polarization separation function of the polarization separation element will be explained. The polarization separation element according to the present invention has a polarization separation function based on "the interaction between surface plasmon or localized surface plasmon which is collective motion of electrons in metal and incident light". To realize.
“Surface plasmon” is the collective motion of electrons excited on the metal side of the interface region between metal and dielectric. “Localized surface plasmon” is the entire metal material when the structure of the metal becomes minute. Collective motion of electrons excited over Hereinafter, both surface plasmons and localized surface plasmons are called plasmons.

  Therefore, the material of the metal structure in the polarization separation element is “a material that can excite plasmons”, and any one of the aforementioned Au, Ag, Pt, Al, Ni, Cr, Cu, or an alloy material mainly composed of these, A configuration in which these are combined and spatially arranged, and further, a mixed material composed of these and a nonmetallic material can be preferably used.

  The size of the metal structure and the “interval between the metal structures” are sufficiently larger than the diffraction limit of the incident light so that the light transmitted through or reflected by the polarization separation element 10 has “spatial uniform intensity”. It must be very small. Further, in order to cause polarization anisotropy in transmitted light and reflected light, the dot pattern DP1 and the like are linear array pattern elements in which metal structures MS are arrayed on a straight line at equal intervals. Li is included.

  The specific size of the metal structure is preferably “smaller than the wavelength in the visible region and not more than 100 nm”. The “interval between adjacent metal structures” in the linear array pattern element Li is preferably 50 nm or less, which is half the size. Further, as described above, the shape of the metal structure MS may be “all the metal structures are aligned in the same shape”, and in the embodiment of FIG. 2, the axis orthogonal to the surface constituting the dot pattern DP1 and the like. However, other shapes such as a quadrangular column and a polygonal column are possible.

Below, the manufacturing method of the polarization splitting element shown in FIG. 2 is demonstrated.
For the formation of the metal structure MS having a size equal to or smaller than the wavelength of incident light, a technique having a processing accuracy equal to or lower than the diffraction limit of visible light is used. Specifically, direct writing by 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 BS, and a photoresist layer is formed on a metal film formed by sputtering or vacuum deposition of a metal material such as Au on the flat surface. The “negative pattern corresponding to the dot pattern” is exposed by line drawing.

  When the development is performed, a “photoresist pattern corresponding to the dot pattern to be formed” is obtained on the metal film, and the metal film is exposed at a portion without the photoresist.

  In this state, the exposed metal film portion is removed by etching using RIE, and then the photoresist used as an etching mask is removed to obtain a dot pattern of the metal structure on the support substrate BS. It is done.

A dielectric material such as quartz glass is deposited as a dielectric material film having a predetermined thickness on the dot pattern of the metal structure thus obtained by sputtering or the like.
On the dielectric material film thus formed, the above-mentioned “metal film forming process for forming a metal film such as Au”, “mask for forming a mask pattern (pattern corresponding to a dot pattern) using a photoresist When the “pattern formation process”, “etching process of the metal film portion by RIE”, “dielectric deposition process for depositing a dielectric material to a predetermined thickness” are performed, the first dot pattern formed previously is The second dot pattern can be obtained by stacking at a predetermined interval.

  Further, by repeating the above metal film forming process, mask pattern forming process, etching process, and dielectric deposition process as a “series of processes”, a multi-layered dot pattern having a desired number of layers on the support substrate BS is obtained. A “three-dimensional metal structure arrangement” can be obtained. At this time, the dielectric deposited by the repeated dielectric deposition process constitutes the holding medium HMD. The thickness of the dielectric deposited for each “dielectric deposition process” is a “predetermined spacing” between adjacent dot patterns.

  As another manufacturing method, a dot pattern in which metal structures are two-dimensionally arranged on the surface of a thin film or film is formed to obtain a “single-layer dot pattern”, and such a single-layer dot pattern is desired. The three-dimensional metal structure array is manufactured by stacking and stacking in the thickness direction by the number of layers, and the three-dimensional metal structure array thus obtained is fixed on an appropriate support substrate. As a result, a “polarized light separating element” similar to the above can be obtained. In this case, the thin film or film on which the dot pattern of the metal structure is formed constitutes a “holding medium”, and the thickness of the thin film or film is “predetermined distance between adjacent dot patterns in the three-dimensional metal structure array. "

  In addition, metal fine particles produced by pulverizing metal materials in a solution by laser ablation and metal fine particles produced by a chemical synthesis technique are arranged in a self-organized manner using a microfabricated substrate. It is also possible to produce an array pattern. In this case, the metal fine particles are a metal structure.

  Next, the polarization separation function of the polarization separation element 10 will be described based on “results of numerical simulation”. The numerical simulation was performed based on a self-consistent method using a propagation function.

References: Genichi Otsu Kiyoshi Kobayashi Co-author
"Basics of Near Field Light-New Optics for Nanotechnology-" (2003, published by Ohm)
In this simulation method, a propagation matrix for Maxwell's equation describing an electromagnetic field: T (r, r ′), that is, “response function of an electric field vector when a delta function is used as a light source”, and a polarization vector of a substance: P (r) Is used to calculate an electric field vector at an arbitrary coordinate by the following equation (1).

E (r) = E ₀ (r) + ∫T (r, r ′) P (r ′) dr ′ (1)
Here, E ₀ (r) is “an electric field vector when there is no scattering by a minute dot-shaped metal structure”. Between the polarization vector: P (r) and the electric field vector :: P (r),
P (r) = αE (r) (2)
Therefore, if α is “polarizability of metal structure” and the right side of equation (2) is substituted into equation (1),
E (r) = E ₀ (r) + α∫T (r, r ′) E (r ′) dr ′ (3)
Therefore, the electric field vector: E (r) is successively approximated (E (r ′) on the right side and the starting field amount: E ₀ (r ′) is substituted to obtain E (r) on the left side. E (r) is newly obtained as E (r ') on the right side, and E (r) on the left side is newly obtained.By repeating this process, E (r') on the right side and E (r) on the left side to be calculated are substantially E (r) when they are equal to each other is referred to as “determined solution”).

In the calculation, the polarizability: α was approximated as “an electric dipole with the metal structure positioned at one point”.
FIG. 3 is a diagram for explaining a model of a dot pattern for which simulation has been performed.
As shown in FIG. 3 (a), dot-like metal structures MS are arranged in parallel in the y-direction with a period of 100 nm arranged in a “linear arrangement pattern element arranged in the x-axis direction with a center interval of 50 nm”. Using the dot pattern, the successive approximation was calculated. The xy plane is a “dot pattern pattern plane”.

Assuming that Au is the material of the metal structure MS, the theoretical formula of the polarizability for the Au sphere:
α = 4πa ³ ε ₀ (ε _Au −ε ₀ ) / (ε _Au + 2ε ₀ ) (4)
By substituting “Drude's equation describing the motion (dispersion) of electrons in the metal”, the electric field strength E (r) by the Au metal structure was calculated. In the equation (4), “ε _Au ” is a dielectric constant of Au, and “a” is a radius of a sphere forming the metal structure. In using Drude's formula, the wavelength of electromagnetic waves: the dielectric constant of Au at 500 nm,
ε _Au = 0.0717 + 1.4965i (i is an imaginary unit)
The dielectric constants on the short wavelength side and the long wavelength side were estimated around this value.

  The size of the Au sphere is set to “radius: a = 10 nm”. However, since it is actually necessary to be determined depending on the shape of the metal structure and the like, a precise value cannot be set. Α = 10 nm is set as a value such that the “interaction between light and matter or electrons” at an interval between adjacent metal structures MS in the shape array pattern element: 50 nm is sufficiently affected.

  The incident angle: θ shown in FIG. 3B is arbitrarily determined, and S-polarized light (polarized component in the direction orthogonal to the drawing: θS) and P-polarized light (polarized component having a vibration plane in the drawing: θP) are respectively provided. The electric field intensity at a point (observation point) on the z axis 100 nm away from the dot pattern surface by the metal structure MS when incident was evaluated.

S-polarized light: θ _S is a “polarized component having an electric field vector in the y-direction orthogonal to the x-axis in the diagram in which the metal structures MS are arranged”, and P-polarized light: θ _P has an electric field vector component in the x-axis direction. It is a polarization component.

For simplicity, the background material (retention medium) was vacuum (n = 1.0).
FIG. 4A shows the result of numerical simulation. “Wavelength dependence of transmitted light intensity” when a plane wave having an amplitude of 1.0 is perpendicularly incident (θ = 0) on the dot pattern of FIG. Indicates. FIG. 4B shows a result when a plane wave is incident at an incident angle of θ = 45 ° in the xz plane under the same conditions.

  As shown in FIG. 4B, when a plane wave is made incident at an incident angle of 45 °, “P transmitted light intensity of S-polarized light θS: ≈1.0 with respect to a wavelength of about 500 nm. The transmitted light intensity of the polarized light θP is about 0.8.

  It can be seen from FIG. 4 that the two-dimensional dot pattern of the metal structure causes “anisotropy of the transmitted light intensity with respect to the two polarization components of the incident light”. Such a “two-dimensional dot pattern of a metal structure” is stacked in multiple layers, and the interval between adjacent dot patterns in the stacking direction is “no optical interaction between adjacent metal structures in the stacking direction”. That is, by setting the “interval larger than the size of the metal structure”, the “anisotropy of transmitted light intensity with respect to two orthogonal polarization components of incident light” possessed by each dot pattern is determined for each stacked dot pattern. A desired polarization separation function can be realized by weighting and increasing.

For example (though strictly speaking, it is necessary to calculate the intensity of the far field), it is considered that the obtained transmitted light intensity and the transmittance are equivalent to each other. Therefore, “incident angle: 45 ° shown in FIG. When 10 dots of “dot pattern having characteristics of transmitted light intensity of S-polarized light θS: ≈1.0 and transmitted light intensity of P-polarized light θP: about 0.8 with respect to an incident plane wave of wavelength: 500 nm” The transmittance of the S-polarized component is 1, but the transmittance of the P-polarized component is 0.8 ¹⁰ = 0.107, and about 90% of the P-polarized component is reflected. Accordingly, it is possible to realize a polarization separation element having a “polarization separation function such that S-polarized light: P-polarized light = 10: 1 in terms of transmittance ratio” with respect to light having a wavelength of 500 nm.

  The “interval between the metal structures adjacent to each other in the stacking direction” is “a three-dimensional arrangement in which dot patterns are arranged in a plurality of layers in a holding medium at a predetermined interval”. This is one mode of “predetermined intervals” in “general metal structure arrangement”.

In the configuration of the polarization separation element, the anisotropy (polarization anisotropy) of the incident light with respect to the polarization component can be controlled by utilizing the optical interaction between the metal structures in the stacking direction of the dot pattern.
For example, as shown in FIG. 5, the “array pattern in the dot pattern DP1” and the “array pattern in the dot pattern DP2” of the metal structure MS are “relative displacement: ΔS” in the direction parallel to the pattern surface. When the polarization anisotropy with respect to the S-polarization component and the P-polarization component is “when there is no relative positional deviation (when the dot patterns are arranged so as to overlap each other when viewed from the stacking direction)” Have been confirmed to change.

  Thus, the polarization anisotropy depends on the pattern surface of the dot pattern in the metal structure array and the “relative position between the dot patterns” in the stacking direction, and thus the three-dimensional metal structure array. By “optimally selecting the arrangement of the metal structures” in, it is possible to design suitable for the use conditions such as the operating wavelength and the incident angle characteristics as the polarization separation element.

  In the numerical simulation described above, the result is shown in the case where “linear arrangement pattern elements arranged in the x-axis direction with a center interval of 50 nm” are arranged in parallel in the y direction with a period of 100 nm as the dot pattern. However, the polarization anisotropy with respect to the two polarization components of incident light (S-polarized light and P-polarized light) depends on the size, spacing, and shape of the metal structure MS, and the period of the linear array pattern elements (100 nm in the above example). Varies depending on Therefore, by optimizing the size, interval, shape, and period of the linear array pattern elements of the metal structure MS, it is possible to arbitrarily set the operating wavelength and incident angle dependency of the polarization separation element.

  In the embodiment described above with reference to FIGS. 2 to 5, a polarization separation element capable of designing polarization separation characteristics with a high degree of freedom can be realized by three-dimensionally arranging the metal structures MS. . Further, by arranging the metal structure arrangement as a whole in the holding medium, an optical element resistant to external damage can be realized.

The second embodiment will be described below.
FIG. 6 is a diagram illustrating the polarization separation element 20 according to the second embodiment, and illustrates a cross section in the dot pattern stacking direction. In the first embodiment, the dot-like metal structures MS are arranged in such a manner that “linear arrangement pattern elements Li arranged at equal intervals in the x-axis direction” are arranged in parallel in a predetermined cycle in the y-direction. Although the polarization anisotropy is given as a pattern, in the second embodiment, a unit arrangement pattern UP in which two metal structures MS1 and MS2 are arranged at a distance equal to or smaller than the size is referred to as “metal structure”. The dot pattern is configured as a pattern that is regularly or randomly arranged two-dimensionally by aligning the orientations of the bodies MS1 and MS2.

The arrangement of the unit arrangement pattern UP is “regular or random” as described above. As a typical example, three arrangement examples of “unit arrangement pattern UP by two metal structures MS1 and MS2” are shown in FIG. Show. In order to avoid complications, in FIGS. 7A to 7C, two dot patterns stacked adjacent to each other are indicated by reference numerals DP1 and DP2.
In the example shown in FIG. 7A, the metal structures MS1 and MW2 are oriented in the horizontal direction in the drawing to form unit arrangement patterns UP, and these unit arrangement patterns UP are expressed as “straight lines with the horizontal direction in the drawing as the longitudinal direction. The dot patterns DP1, DP2, etc. are configured by arranging such a linear array periodically in the vertical direction of the figure.

Polarization anisotropy using the design parameters as the spacing between the metal structures MS1 and MS2, the spacing between the unit arrangement patterns UP in the “linear arrangement in the left-right direction” of the unit arrangement pattern UP, and the arrangement period of the periodic arrangement in the vertical direction Can be designed.
In the example shown in FIG. 7B, the metal structures MS1 and MS2 are oriented in the vertical direction of the figure to form a unit arrangement pattern UP, which is arranged along a straight line with the horizontal direction of the figure as the longitudinal direction. The dot structures DP1, DP2, etc. are arranged in such a manner that the metal structures are arranged on two parallel lines that are close to each other, and such two parallel lines are periodically arranged in the vertical direction in the figure. It is composed. With such a configuration, it is possible to design a polarization anisotropy different from that in FIG.

In the example shown in FIG. 7C, the metal structures MS1 and MW2 are aligned in the horizontal direction in the drawing to form a unit arrangement pattern UP. Such unit arrangement pattern UP is “randomly arranged in the same plane”. The dot patterns DP1, DP2, etc.
Unit arrangement patterns in which the metal structures MS1 and MS2 are oriented in the vertical direction as shown in FIG. 7B may be randomly arranged in the same plane to form a dot pattern.
In FIG. 7, the two metal structures MS1 and MS2 constituting the unit array pattern are drawn so as to be in contact with each other, but in reality, they are oriented close to each other with a gap equal to or smaller than the size of the metal structure. Is done.

  Moreover, it can replace with the random arrangement | sequence of a unit arrangement | sequence pattern, and it can also arrange in a "hexagonal close-packed structure", and the density of a unit arrangement | sequence pattern arrangement | sequence can be achieved by such an arrangement | sequence. By laminating these unit array patterns to form a three-dimensional metal structure array, a polarization separation element can be realized.

  Of course, the number of the metal structures constituting the unit array pattern UP does not have to be two as in the embodiment shown in FIGS. 6 and 7, and the number of metal structures is three or more. A unit array pattern can be constructed.

  The gap between the plurality of metal structures forming the unit array pattern is set to “below the size of the metal structure”.

  The polarization separation element according to the second embodiment described above has an incident angle, an operating wavelength, an operating band depending on the orientation of the unit array pattern by the metal structure, the arrangement, the shape of the metal structure, and the metal structure material. Can be designed.

As in the case of the first embodiment, the material used for the support substrate BS has a low absorption at a wavelength in the visible region and a little anisotropy with respect to polarized light, such as quartz glass, BK7, Pyrex (registered trademark), etc. Optical crystal materials such as borosilicate glass, CaF ₂ , Si, ZnSe, and Al ₂ O ₃ can be preferably used.

Similarly to the material of the support substrate BS, the material of the holding medium HMD is also commonly used as a coating material for optical elements that has low absorption at a wavelength in the visible region and little anisotropy with respect to polarized light. BK7 Pyrex (registered trademark), borosilicate glass such as ZnS—SiO _{2, materials} such as CaF ₂ , Si, ZnSe, Al ₂ O ₃ and ZnO can be preferably used.

As in the case of the first embodiment, the polarization separation element of the second embodiment is also modulated by “the action of an external signal such as electricity, light and pressure” to actively change the polarization separation characteristic. In this case as well, as a material of the holding medium HMD, inorganic materials such as BBO, LiTaO ₃ , KTB, LiNb ₃ , KTB, KTP, and KTN, which are ferroelectric materials showing the electro-optic crystal effect, nonlinear optics Inorganic crystals such as BBO, LBO, BIBO, KTP, and KDP, which are optical crystal materials showing the effect, and inorganic crystals showing the electrostrictive effect, such as quartz, ZnO, LiNbO ₃ , LiTaO ₃ , Li ₂ B4O ₇ , AlN, etc. Available.

  The material of the metal structure MS may be any material that can excite plasmons with light in the visible region as in the first embodiment, and is any one of Au, Ag, Pt, Al, Ni, Cr, Cu, Alternatively, an alloy material mainly composed of these materials, a configuration in which these materials are combined and spatially arranged, or a mixed material composed of these and a nonmetallic material can be used.

  The size of the metal structures and the spacing between the metal structures must be sufficiently smaller than the diffraction limit of the incident light so that the light transmitted or reflected by the polarization separation element is spatially uniform. The specific size is preferably smaller than the wavelength in the visible region and not more than 100 nm.

  The interval between the plurality of metal structures constituting the unit array pattern is preferably “less than half the size of the metal structure itself (50 nm or less)”. The shape of the metal structure may be any shape as long as all the metal structures are arranged in the same shape, and any shape such as a hemisphere, a cylinder, or a quadrangular column is possible.

  The polarization separation element as shown in FIGS. 6 and 7 can also be manufactured by the same method as described in the first embodiment. Also, metal fine particles produced by laser ablation and chemical synthesis techniques are “modified by surface modification with specific molecules, chemically bonded to a small number of metal fine particles in a solution, and then oriented by applying an electric field. Can be used. In this case, a three-dimensional metal structure array can be formed in a lump. After the formation of the metal structure array, the solution is solidified to form a holding medium.

  As the polarization separation element of the second embodiment, the result of numerical simulation of the example shown in FIG. 7A will be described.

  As described in the first embodiment, the numerical simulation method represents the polarization vector as a distribution of electric dipoles based on the Maxwell equation, and solves the integral equation with the propagation matrix by successive approximation. The average value of the electric field vector in the surface 100 nm away from the surface where the electric dipole was arranged was calculated. Averaging was performed by calculating the transmitted light intensity at 16 × 16 points in a two-dimensional plane of 128 nm × 128 nm.

FIG. 8 is a model of a dot pattern structure in which a numerical simulation was performed. The center interval between the two metal structures MS1 and MS2 constituting the unit array pattern UP is 30 nm, and “the unit array pattern UP is in the x direction and the y direction. In a square lattice shape with a period of 100 nm.
Au is used as the material of the metal structure, and the dielectric constant is
ε _Au = 0.0717 + 1.4965i (i is an imaginary unit)
Was used. The calculation was performed with the plane wave incident angle set to 0 °, that is, “normal incidence”.

  FIG. 9 is a graph plotting the wavelength dependence of the transmitted light intensity calculated by this numerical simulation. The two curves in FIG. 9 indicate S-polarized light θS (polarized component oscillating in the direction of FIG. 8) and P-polarized light θP (polarized component oscillating in the x direction of FIG. 8).

  From the result of FIG. 9, the S-polarized light θS is not significantly different from the result of FIG. 4A described in the first embodiment, but the transmitted light intensity of the P-polarized light θP is “a metal structure of A large difference appears near the resonance wavelength of 480 nm.

  In FIG. 4A, the wavelength region that is the concave portion of the transmitted light intensity is “increased due to resonant scattering” in FIG. 9, and the transmittance of S-polarized light is around 480 nm. The transmittance of 0.5 and P-polarized light is 1.0 or more. The reason why the transmitted light intensity exceeds 1.0 is that there is a spatial distribution in the transmitted light intensity on the observation surface 100 nm apart, and averaging is not performed in a sufficient area.

Accordingly, when the dot pattern having the polarization separation function shown in FIG. 9 is laminated in four layers and a plane wave in a random polarization state having a wavelength of 480 nm is perpendicularly incident, the transmittance of P-polarized light is 0.5 ⁴ = 0.0625. Thus, “90% or more of P-polarized light” component is reflected, and S-polarized light is transmitted almost 100%.

  Therefore, the “polarization separation function similar to that of the polarization separation element of the first embodiment” can be realized with a simple “layered structure of two dot patterns” as compared with the case of the first embodiment. .

  The numerical simulation described above is for a unit arrangement pattern formed by two metal structures MS1 and MS2. However, a small number of two or more metal structures (with a gap equal to or smaller than the metal structure size) are separated. It has been confirmed that the same effect can be obtained even with unit arrangement patterns arranged at equal intervals in one row. By increasing the number of metal structures constituting the unit array pattern, the optimum design for the operating wavelength and the incident angle becomes possible.

  In addition, as described with reference to FIG. 5, the anisotropy of the incident light with respect to the polarization can be controlled by “adjusting the optical interaction between the metal structures in the stacking direction of the dot pattern”. Therefore, by optimally selecting the arrangement form of the three-dimensional metal structure arrangement, a design suitable for the use conditions such as the operating wavelength and the incident angle characteristic of the polarization separation element can be realized.

  As in the case of the first embodiment, the interval between adjacent metal structures, the size and shape of the metal structures, the two-dimensional arrangement form of the unit arrangement pattern, and the like can also be used as design parameters.

  The third embodiment will be described below.

  10A and 10B are diagrams for explaining the configuration of the polarization beam splitting element according to the third embodiment. FIG. 10A is a cross-sectional view in the dot pattern stacking direction, and FIG. 10B is a state of the pattern surface of the dot pattern. It is a figure explaining. In addition, about the thing which seems not to have the possibility of confusion, the same code | symbol as in FIG.

  In the second embodiment, the polarization anisotropy is controlled by “the orientation of the metal structures MS1 and MS2” of the unit arrangement unit UP of the two metal structures MS1 and MS2. Since it is sufficient that the polarization anisotropy has an “asymmetric structure”, not the arrangement of a plurality of metal structures but “asymmetricity depending on the shape of the metal structures” can be used for the polarization separation function.

  The polarization separation element according to the third embodiment forms a metal structure array by three-dimensionally laminating and arraying dot patterns of axisymmetric metal structures MSA such as a spheroid shape and a rod shape. The size of the metal structure is the size in the direction in which the length of the shape is maximum, which is equal to or smaller than the wavelength of incident light.

  As shown in FIG. 10A, the polarization separation element 30 shown in FIG. 10 includes a holding medium HMD that holds the metal structure MSA and a support substrate BS for supporting these, and the arrangement form of the metal structure MSA, the metal The incident angle, operating wavelength, and operating band can be designed by selecting the shape and material of the structure MSA.

  For the support substrate BS, the holding medium HDM, and the metal structure MSA, the same material as in the first and second embodiments can be used, and the polarization separation element can be controlled by an external signal such as electricity, light, or pressure. Modulating and actively changing the polarization separation characteristic.

  The shape of the metal structure MSA has an asymmetry having a different size in at least one direction with respect to three orthogonal directions such as a spheroid shape and a rod shape, and is transmitted through the polarization separation element. “The size of the metal structure and the distance between the metal structures” are sufficiently smaller than the diffraction limit of the incident light so that the reflected light is spatially uniform.

  The specific size of the metal structure MSA is preferably smaller than the wavelength in the visible region and not more than 100 nm in the longest axial direction. The interval between the metal structures is preferably 50 nm or less, which is half the size.

  Various arrangement forms are possible for the arrangement of the metal structures MSA described above. In FIG. 10B, spheroid-shaped metal structures MSA are “arranged on a straight line at equal intervals so that the longitudinal direction is parallel to the straight line”, and this linear array is parallel to each other at a predetermined interval. In this example, the dot patterns DP1, DP2, etc. are arranged, and the phase of the plasmon excited inside the metal structure MSA is “different in the axial directions having different sizes”, so that the anisotropy with respect to the polarized light Is expressed. Therefore, by laminating the dot patterns of this arrangement in multiple layers, it is possible to realize a polarization separation function that separates S-polarized light and P-polarized light into transmitted light components and reflected light components.

  Similarly to the second embodiment, a unit array pattern is constituted by two or more metal structures MSA, and the unit array pattern is aligned regularly or randomly so that individual unit array patterns are arranged. By imparting anisotropy to the polarization to the polarization, a polarization separation function similar to that of the second embodiment can be realized. Although the metal structure MSA has a spheroid shape in FIG. 10, it may have a shape such as a rod having asymmetry with different sizes in one direction.

  In order to manufacture the polarization separation element as in the third embodiment, an asymmetric metal structure MSA is prepared in a solution by a laser ablation method or a chemical synthesis method, and self-organization is performed using a microfabricated substrate. It may be arranged in order.

  In addition, if the metal structure is “a structure having asymmetry in one direction such as an elliptical cylinder”, the same effect as described above can be expected. The “metal structure” can be produced by the “method using etching” described above.

  Also in the design of the polarization separation element of the third embodiment, as described with reference to FIG. 5, the incident light is adjusted by “adjusting the light interaction between the metal structures” in the stacking direction of the dot pattern. It is possible to control the anisotropy with respect to the polarization. Therefore, by optimally selecting the arrangement form of the three-dimensional metal structure arrangement, a design suitable for the use conditions such as the operating wavelength and the incident angle characteristic of the polarization separation element can be realized. Of course, the interval, size, shape, and two-dimensional arrangement of unit metal arrangement patterns between adjacent metal structures MSA can also be used as design parameters.

It is a conceptual diagram explaining the function of a polarization beam splitting element. It is a figure explaining the structure of the polarization separation element of 1st Embodiment. It is a figure for demonstrating the numerical simulation model of 1st Embodiment. It is a figure which shows the result of a numerical simulation. It is a figure explaining the adjustment method of the polarization characteristic in a polarization separation element. It is a figure explaining the structure of the polarization splitting element of 2nd Embodiment. It is a figure which shows three examples of the arrangement | sequence form of a unit arrangement | sequence unit. It is a figure for demonstrating the numerical simulation model of 2nd Embodiment. It is a figure which shows the result of a numerical simulation. It is a figure for demonstrating 3rd Embodiment.

Explanation of symbols

MS metal structure DP1 dot pattern HMD holding medium BS support substrate

Claims (9)

A three-dimensional metal structure array in which dot patterns in which minute dot-shaped metal structures smaller than the wavelength of incident light are two-dimensionally arranged are stacked in a plurality of layers in a holding medium at predetermined intervals On the support substrate,
Polarization separation characterized in that the three-dimensional metal structure array is defined so that transmitted light intensity or reflected light intensity is different for two polarization components orthogonal to each other in incident light incident at a desired incident angle. element. The polarization separating element according to claim 1,
The dot pattern in which the metal structures are two-dimensionally arranged is a linear array pattern element in which the metal structures are arranged in a straight line with a distance equal to or smaller than the size of the dot structure in a direction orthogonal to the longitudinal direction. A polarized light separating element having a pattern arranged in parallel with each other at a period of The polarization separating element according to claim 1,
A dot pattern in which metal structures are two-dimensionally arranged is a unit arrangement pattern in which a plurality of metal structures are arranged at a distance equal to or smaller than the size of the metal structures. A polarized light separating element having a two-dimensionally arranged pattern. The polarization separation element according to any one of claims 1 to 3,
A polarization separation element, wherein the metal structure has an axisymmetric shape. The polarization separation element according to any one of claims 1 to 4,
The dot-shaped metal structure is any one of gold (Au), silver (Ag), platinum (Pt), aluminum (Al), nickel (Ni), chromium (Cr), copper (Cu), or a combination thereof. Or a polarization separation element comprising an alloy material or a mixed material containing these as a main component. The polarization separation element according to any one of claims 1 to 5,
A polarization separation element, wherein two-dimensional dot patterns stacked in a plurality of layers in a holding medium are congruent with each other. The polarization separation element according to claim 6,
A polarization separation element, wherein two-dimensional dot patterns are arranged so as to overlap each other in the stacking direction. The polarization separation element according to claim 6,
A polarization separation element, wherein two-dimensional dot patterns are arranged so as to be shifted from each other in a direction parallel to a pattern surface. The polarization separation element according to any one of claims 1 to 8,
A polarization separation element, wherein an incident angle is set to about 45 degrees, and two polarization components orthogonal to each other in incident light are a P polarization component and an S polarization component.

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