JP2015191230A - resonant element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resonant element that has further improved wavelength selectivity while having a polarization separation function.SOLUTION: A resonant element 10A comprises: a dielectric layer 11; a first metallic diffraction grating 12 on a first principal surface 11a; and a second metallic diffraction grating 13 on a second principal surface 11b. The first and second metallic diffraction gratings include multiple first and second metallic members 12a and 13a arrayed in first and second space periods. When widths in a second direction of the first and second metallic members are respectively represented as w1 and w2, the first and second space periods are respectively represented as Λ1 and Λ2, thickness of the dielectric layer is represented as d, thicknesses of the first and second metallic members are respectively represented as d1 and d2 and a refractive index of the dielectric layer is represented as n, w1/Λ1, d1, d, Λ1, w2/Λ2, d2, Λ2 and nsatisfy the following expressions: 0.5≤w1/Λ1, w2/Λ2≤0.9, 10 nm≤d1, d2≤100 nm, 30 nm≤d≤210 nm, 190 nm≤Λ1, Λ2≤400 nm and 1.55≤n≤2.15.

Description

  The present invention relates to a resonant element.

  Conventionally, as a technique in such a field, the techniques described in Patent Document 1 and Non-Patent Document 1 are known. Patent Document 1 discloses a so-called MIM (metal-insulator-metal) element having a structure in which both sides of a dielectric layer are sandwiched between metal members as a resonant element having polarization separation characteristics and wavelength selection characteristics. . In the technique described in Patent Document 1 or the like, at least one of the metal members disposed on both sides of the dielectric layer is a metal diffraction grating. In the technique described in Patent Document 1 or the like, at least two openings are formed in the resonant element.

US Patent Application Publication No. 2011/0285942

T. Xu, Y-K Wu, X. Luo, and L.J.Guo, "Plasmonic nanoresonators for high-resolution color filtering and spectral imaging", Nature Communications, 2010, pp.1-5, DOI: 10.1038 / ncomms1058.

  However, the conventional technology has a polarization separation function, but the wavelength selectivity is not sufficient.

  Therefore, an object of the present invention is to provide a resonant element having a wavelength separation property while having a polarization separation function.

A resonant element according to one aspect of the present invention includes a dielectric layer having first and second main surfaces, a first metal diffraction grating provided on the first main surface, and a second main surface. A second metal diffraction grating provided. The first metal diffraction grating includes a plurality of first metal members extending in a first direction and arranged in a second direction orthogonal to the first direction at a first spatial period. The second metal diffraction grating includes a plurality of second metal members extending in the first direction and arranged in the second direction at a second spatial period. The width of the first metal member in the second direction is w1, the first spatial period is Λ1, the thickness of the dielectric layer is d, and the thickness of the first metal member in the thickness direction of the dielectric layer is The thickness is d1, the width of the second metal member in the second direction is w2, the second spatial period is Λ2, and the thickness of the second metal member in the thickness direction of the dielectric layer is d2. when the refractive index of the dielectric layer was set to _{n B, w1 / Λ1, d1} , d, Λ1, w2 / Λ2, d2, Λ2及_{n B} satisfies the following formulas.
0.6 ≦ w1 / Λ1 ≦ 0.9
30 nm ≦ d1 ≦ 70 nm
10 nm ≦ d ≦ 60 nm
230 nm ≦ Λ1 ≦ 270 nm
0.6 ≦ w2 / Λ2 ≦ 0.9
30 nm ≦ d2 ≦ 70 nm
230 nm ≦ Λ2 ≦ 270 nm
1.5 ≦ n _B ≦ 2.15

  In the above configuration, since the first and second metal diffraction gratings are provided and the dielectric layer is provided between them, the wavelength selectivity and the polarization separation function are provided. And when each parameter mentioned above satisfy | fills the said range, wavelength selectivity can be improved more.

  In one embodiment, the same material as the material of the dielectric layer is filled between adjacent first metal members among the plurality of first metal members of the first metal diffraction grating, and the second Between the second metal members adjacent to each other among the plurality of second metal members of the metal diffraction grating, the same material as the material of the dielectric layer may be filled.

  In one embodiment, among the plurality of first metal members included in the first metal diffraction grating, a gap is formed between adjacent first metal members, and the plurality of second metals included in the second metal diffraction grating. Between the adjacent second metal members among the members, the same material as the material of the dielectric layer may be filled.

In this case, the n _B may satisfy 1.75 ≦ n _B ≦ 1.95.

  In one embodiment, among the plurality of first metal members included in the first metal diffraction grating, a gap is formed between adjacent first metal members, and the plurality of second metals included in the second metal diffraction grating. There may be a gap between adjacent first metal members among the members.

  In this case, the d may satisfy 40 nm ≦ d ≦ 60 nm.

  In one embodiment, each of the w1 / Λ1 and w2 / Λ2 may satisfy 0.6 ≦ w1 / Λ1 ≦ 0.8 and 0.6 ≦ w2 / Λ2 ≦ 0.8.

  In one embodiment, the d may satisfy 20 nm ≦ d ≦ 60 nm.

In one embodiment, the n _B may satisfy 1.55 ≦ n _B ≦ 1.95.

In one embodiment, each of d1, d2, Λ1, Λ2, and n _B is
30 nm ≦ d1 ≦ 50 nm,
30 nm ≦ d2 ≦ 50 nm,
230 nm ≦ Λ1 ≦ 250 nm,
230 nm ≦ Λ 2 ≦ 250 nm, and 1.5 ≦ n _B ≦ 1.75,
May be satisfied.

  In this configuration, the resonant element can function as a blue filter.

Each of d1, d2, Λ1, Λ2, and n _B is
50 nm ≦ d1 ≦ 60 nm,
50 nm ≦ d2 ≦ 60 nm,
250 nm ≦ Λ1 ≦ 270 nm,
250 nm ≦ Λ 2 ≦ 270 nm, and 1.5 ≦ n _B ≦ 2.15,
May be satisfied.

  The resonant element having this configuration can function as a green filter.

Each of d1, d2, Λ1, Λ2, and n _B is
60 nm ≦ d1 ≦ 70 nm,
60 nm ≦ d2 ≦ 70 nm,
260 nm ≦ Λ1 ≦ 270 nm,
260 nm ≦ Λ 2 ≦ 270 nm, and 1.65 ≦ n _B ≦ 2.15,
May be satisfied.

  The resonant element having this configuration functions as a red filter.

In one embodiment, the d1 and the d2 are different, and the d1 and the d2 are respectively
30 nm ≦ d1 ≦ 70 nm, and
30 nm ≦ d2 ≦ 70 nm,
May be satisfied.

  In this case, the polarization separation function tends to be improved.

  In one embodiment, Λ1 and Λ2 are different, and the absolute value of the difference between Λ1 and Λ2 may be 10 nm or less.

  In this case, the polarization separation function tends to be improved.

In one embodiment, the w1 / Λ1 and the w2 / Λ2 are different, and the w1 / Λ1 and the w2 / Λ2 are respectively
0.7 ≦ w1 / Λ1 ≦ 0.8, and
0.7 ≦ w2 / Λ2 ≦ 0.8,
May be satisfied.

  In one embodiment, the position of the first metal diffraction grating and the position of the second metal diffraction grating are deviated from each other in the second direction, and the positions of the first metal diffraction grating and the second metal diffraction grating are K may satisfy 0 <k ≦ 30 nm, where k is an offset that is an amount of deviation from the position in the second direction.

  ADVANTAGE OF THE INVENTION According to this invention, the resonant element which can improve wavelength selectivity can be provided, having a polarization separation function.

It is a mimetic diagram showing the section composition of the resonant element concerning one embodiment. It is drawing which shows the simulation model in a comparative example. It is drawing which shows the simulation result of an Example. It is drawing which shows the simulation result of a comparative example. In the simulation performed in the Example, it is drawing which shows intensity distribution with respect to the light of TM mode of wavelength 460nm which is a peak wavelength. It is drawing which shows intensity distribution with respect to the light of TM mode with a wavelength of 700 nm in the simulation performed in the Example. It is drawing which shows the other simulation result with respect to the simulation model used by the comparative example. It is drawing which shows the cross-sectional structure of the 1st modification of the resonant element shown in FIG. It is drawing which shows the cross-sectional structure of the 2nd modification of the resonant element shown in FIG. In the simulation model used in the Example, it is a drawing showing the polarization ratio at the peak wavelength of TM mode light and the peak transmittance of TM mode light when the fill factor (ff) is changed. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to a refractive index in the structure of FIG. (B) is a drawing showing the change in wavelength dependence of the TE mode light transmittance with respect to the refractive index in the configuration of FIG. 1. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to a refractive index in the structure of FIG. (B) is a drawing showing the change in wavelength dependence of the transmittance of TE mode light with respect to the refractive index in the configuration of FIG. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to a refractive index in the structure of FIG. (B) is a drawing showing the change in wavelength dependence of the TE mode light transmittance with respect to the refractive index in the configuration of FIG. 9. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to the thickness of a dielectric material layer in the structure of FIG. (B) is a drawing showing the change in the wavelength dependence of the transmittance of light in the TE mode with respect to the thickness of the dielectric layer in the configuration of FIG. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to the thickness of a dielectric material layer in the structure of FIG. (B) is a drawing showing the change in the wavelength dependence of the transmittance of light in the TE mode with respect to the thickness of the dielectric layer in the configuration of FIG. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to the thickness of a dielectric material layer in the structure of FIG. FIG. 9B is a diagram showing a change in wavelength dependence of TE mode light transmittance with respect to the thickness of the dielectric layer in the configuration of FIG. 9. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to the thickness of the 1st and 2nd metal fine wire. (B) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TE mode with respect to the thickness of the 1st and 2nd metal fine wire. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to the period of the 1st and 2nd metal diffraction grating. (B) is a drawing showing the change in wavelength dependence of the transmittance of light in the TE mode with respect to the periods of the first and second metal diffraction gratings. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to offset k. (B) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TE mode with respect to offset k. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode in case the thickness of a 1st and 2nd metal fine wire differs. (B) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TE mode in case the thickness of the 1st and 2nd metal fine wire differs. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode in case the period of a 1st and 2nd metal diffraction grating differs. (B) is a drawing showing the change in wavelength dependence of the transmittance of light in the TE mode when the periods of the first and second metal diffraction gratings are different. (A) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TM mode in case the fill factors of a 1st and 2nd metal diffraction grating differ. (B) is drawing which shows the change of the wavelength dependence of the transmittance | permeability of the light of TE mode in case the fill factors of a 1st and 2nd metal diffraction grating differ. (A) is drawing which shows the wavelength dependence of the transmittance | permeability of the light of TM mode with respect to the resonant element of the structure which can be used as a blue filter, a green filter, and a red filter. (B) is drawing which shows the wavelength dependence of the transmittance | permeability of the light of TE mode with respect to the resonant element of a structure which can be used as a blue filter, a green filter, and a red filter. It is drawing which shows the cross-sectional structure of one Embodiment of the liquid crystal panel to which a resonant element is applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same symbols are assigned to the same elements. A duplicate description is omitted. The dimensional ratios in the drawings do not necessarily match those described. In the description, words indicating directions such as “up” and “down” are convenient words based on the state shown in the drawings.

FIG. 1 is a schematic diagram illustrating a cross-sectional configuration of a resonant element according to an embodiment. The resonant element 10 </ b> A has a dielectric layer 11. The material of the dielectric layer 11 is transparent (that is, hardly absorbs visible light in the wavelength range of 400 nm to 700 nm), and the refractive index is 1.55 or more and 2.15 or less as described later. For example, organic polymer or inorganic metal oxide can be selected as long as the above is satisfied. Examples of organic polymers are polystyrene (PS: Polystyrene, refractive index 1.59 or less), polycarbonate (PC: Polycarbonate, refractive index 1.58 or less), polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). : Polyethylenenaphthalate). Examples of inorganic metal oxides are alumina (Al ₂ O ₃ , refractive index 1.6 or less), indium tin oxide (ITO: Indium Tin Oxide, refractive index 1.7-2.0), zirconia (ZrO ₂ , Refractive index is 1.95 or less), and tantalum pentoxide (Ta ₂ O ₅ , refractive index is 2.1 or less). Organic-inorganic nanocomposites can also be used as the material for the dielectric layer 11.

  A first metal diffraction grating 12 is provided on the first main surface 11a of the dielectric layer 11, and a second main surface 11b opposite to the first main surface 11a is a second main surface 11b. A metal diffraction grating 13 is provided. The resonant element 10A having such a configuration is a so-called MIM element. A substrate 14 is provided on the opposite side of the second metal diffraction grating 13 from the dielectric layer 11. The substrate 14 may be a substrate transparent to visible light having a wavelength range of 400 nm to 700 nm (hereinafter also referred to as a transparent substrate). An example of the material of the substrate 14 is a dielectric material (for example, a polymer material such as PMMA and glass) having a refractive index of 1.45 or more and 1.6 or less.

  The resonant element 10A includes the first and second metal diffraction gratings 12 and 13, thereby having a function of transmitting light having a predetermined wavelength and predetermined polarization. The light transmitted through the resonant element 10A is TM mode (P-polarized) light.

  The first metal diffraction grating 12 has a plurality of first metal thin wires (first metal members) 12a. Each first thin metal wire 12a extends in the first direction. The plurality of first thin metal wires 12a are discretely arranged in a second direction orthogonal to the first direction with a first spatial period (hereinafter simply referred to as “period”) Λ1. The second direction is the left-right direction in FIG. 1, and the cross-sectional configuration of the resonant element 10A shown in FIG. 1 corresponds to the cross-sectional configuration orthogonal to the first direction of the resonant element 10A. The example of the shape of the cross section orthogonal to the 1st direction of the 1st metal fine wire 12a is a rectangle or a square, as shown in FIG.

  Similarly, the second metal diffraction grating 13 has a plurality of second thin metal wires (second metal members) 13a. Each second thin metal wire 13a extends in the first direction. The plurality of second thin metal wires 13a are discretely arranged in a second direction orthogonal to the first direction with a second spatial period (hereinafter simply referred to as “period”) Λ2. The example of the shape of the cross section orthogonal to the 1st direction of the 2nd metal fine wire 13a is a rectangle or a square, as shown in FIG.

  The space between the adjacent first metal fine wires 12a and 12a is filled with the same material as that of the dielectric layer 11, and the space between the adjacent second metal fine wires 13a and 13a is the same as that of the dielectric layer 11. The same material as the material is filled. In this configuration, the portion made of the material filled between the adjacent first thin metal wires 12a and 12a and the dielectric layer 11 are substantially continuous. Similarly, the portion made of the material filled between the adjacent second thin metal wires 13a and 13a and the dielectric layer 11 are substantially continuous. Therefore, in the resonant element 10A having the above configuration, when the thickness of the dielectric layer 11 is d, the thickness of the first metal fine wire 12a is d1, and the thickness of the second metal fine wire 13a is d2, When a plurality of first thin metal wires 12a are embedded in one main surface of a dielectric layer having a length h (= d + d1 + d2), and a plurality of second thin metal wires 13a are embedded in the other main surface. Can also be considered. In FIG. 1, for convenience of explanation, the boundary line between the gap portion of the adjacent first metal thin wires 12a and 12a and the dielectric layer 11 is also shown, but the adjacent first metal thin wires 12a and 12a Since the material filled in the gap portion of 12a and the material of the dielectric layer 11 are the same, no boundary line actually appears. Moreover, the number of the 1st and 2nd metal fine wires 12a and 13a shown in FIG. 1 is an example. FIG. 1 shows a part of the resonant element 10A in the second direction. The same applies to the resonant elements in the other drawings.

  Examples of the material of the first and second fine metal wires 12a and 13a include aluminum (Al), gold (Au), silver (Ag), copper (Cu), platinum (Pt), and the like. A preferred example of the material of the first and second fine metal wires 12a and 13a is aluminum (Al).

When the width of the first metal wire 12a in the second direction is w1, and the thickness of the dielectric layer 11 is d and the thickness of the first metal wire 12a is d1, as described above, w1 / Λ1 , D1, d, and Λ1 satisfy Expressions (1) to (4), respectively.
0.6 ≦ w1 / Λ1 ≦ 0.9 (1)
30 nm ≦ d1 ≦ 70 nm (2)
10 nm ≦ d ≦ 60 nm (3)
230 nm ≦ Λ1 ≦ 270 nm (4)

Further, when the width of the second metal thin wire 13a in the second direction is w2, and the thickness of the second metal thin wire 13a is d2, as described above, w2 / Λ2, d2, and Λ2 are respectively Expressions (5) to (7) are satisfied.
0.6 ≦ w2 / Λ2 ≦ 0.9 (5)
30 nm ≦ d2 ≦ 70 nm (6)
230 nm ≦ Λ 2 ≦ 270 nm (7)

  The w1 / Λ1 and w2 / Λ2 in the equations (1) and (5), that is, the ratio of the width of the thin metal wire to the period of the metal diffraction grating is known as a fill factor (ff). Hereinafter, w1 / Λ1 is referred to as ff1, and w2 / Λ2 is referred to as ff2. Considering the equations (1) and (4), the width between the adjacent first metal wires 12a in the first metal diffraction grating 12, that is, Λ1-w1 is smaller than the wavelength region of visible light, Smaller than 400 nm. Similarly, the width between adjacent second fine metal wires 13a in the second metal diffraction grating 13, that is, Λ2-w2, is smaller than the wavelength region of visible light, that is, smaller than 400 nm.

Further, when the refractive index of the dielectric layer 11 is n _B , n _B satisfies the following condition.
1.5 ≦ n _B ≦ 2.15 (8)

More preferable ranges of the fill factor ff1 and the fill factor ff2 are as follows.
0.6 ≦ ff1 ≦ 0.8
0.6 ≦ ff2 ≦ 0.8
A more preferable range of the thickness d is as follows.
20 nm ≦ d ≦ 60 nm
A more preferable range of the refractive index n _B is as follows.
1.55 ≦ n _B ≦ 1.95

  In one embodiment, in the resonant element 10A, as shown in FIG. 1, the first and second metal diffraction gratings 12 and 13 may be misaligned in the second direction. In the following description, this amount of deviation (deviation amount) is referred to as offset k.

  Here, the offset k is a distance between side surfaces of the first and second metal diffraction gratings 12 and 13 on the same side in the second direction of the corresponding first and second metal fine wires 12a and 13a. . In FIG. 1, the leftmost first and second thin metal wires 12a and 13a are employed as the corresponding first and second thin metal wires 12a and 13a. In FIG. 1, k is defined as the distance between the left side surfaces of the leftmost first and second thin metal wires 12a and 13a in the drawing. k is also a shift of the center position of the first and second metal diffraction gratings 12 and 13 in the second direction. Physically, the offset k corresponds to the phase difference between the two periodic functions for which the structure of the first and second metal wires 12a, 13a can be described.

  The resonance element 10 </ b> A has a resonance structure by providing the dielectric layer 11 between the first and second metal diffraction gratings 12 and 13. Therefore, light having a predetermined wavelength (or a predetermined wavelength region) is selectively output among the light incident on the resonance element 10A. That is, it has a wavelength selection function. The resonance or resonance in the resonance element 10A includes, for example, Fabry-Perot resonance and plasmon resonance according to each element parameter satisfying the expressions (1) to (8). The first and second metal diffraction gratings 12 and 13 are configured by arranging first and second fine metal wires 12a and 13a extending in the first direction in the second direction. By providing the first and second metal diffraction gratings 12 and 13 having such a configuration, the resonant element 10A has a polarization separation function.

The wavelength (predetermined wavelength) of the light transmitted through the resonant element 10A can be selected by adjusting n _B , Λ1, Λ2, d, d1, and d2.

  The resonant element 10A uses thin film formation techniques such as spin coating and chemical vapor deposition (CVD), and lift-off techniques such as extreme ultraviolet lithography and electron beam lithography, and microfabrication techniques such as etching techniques. Can be manufactured. For example, the resonant element 10A first forms a dielectric layer having a thickness h as described above. Thereafter, recesses having depths d1 and d2 are formed at predetermined positions on the principal surfaces of the dielectric layer facing each other by using a fine processing technique. Subsequently, the resonant element 10A having the first and second metal diffraction gratings 12 and 13 can be manufactured by forming a metal that is a material of the first and second fine metal wires 12a and 13a in the recesses. . In the step of forming the recess and the step of forming the first and second thin metal wires 12a and 13a, for example, a mask technique, an etching technique, and a sputtering technique can be appropriately employed.

  In one embodiment, the configuration of the first and second metal diffraction gratings 12 and 13 may be the same. That is, the thickness may be the same (d1 = d2), the period may be the same (Λ1 = Λ2), and the width in the second direction may be the same (w1 = w2).

  The point that the resonant element 10A can selectively transmit light having a predetermined wavelength and light having a predetermined polarization will be described using a simulation result.

As an example, as shown in FIG. 1, a simulation was performed using a configuration in which the resonant element 10 </ b> A was disposed on the substrate 14 as a simulation model. The values of element parameters such as Λ1, Λ2, d, d1, d2, ff1, ff2, k in the embodiment are as follows.
Λ1 = Λ2 = 250 nm
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0
n _B = 1.55
Material of the first and second thin metal wires 12a and 13a: Aluminum (Al)
The substrate 14 was transparent, and the refractive index of the substrate 14 was 1.5.

  FIG. 2 is a drawing showing a simulation model for comparison. The resonant element 20 shown in FIG. 2 is configured by arranging the laminated body 24 at a constant period, and the laminated body 24 is configured by sandwiching the semiconductor layer 23 between a pair of metal layers 21 and 22. Yes. Adjacent laminates 24, 24 are spaced apart and have a gap between them. The plurality of stacked bodies 24 are provided on the substrate 14. The configuration of the resonant element 20 corresponds to the configuration of the resonant element disclosed in Non-Patent Document 1. In the configuration of the resonant element 20, since the plurality of metal layers 21 are arranged at a constant period, the plurality of metal layers 21 function as a metal diffraction grating. Similarly, the plurality of metal layers 22 also function as a metal diffraction grating. The thicknesses of the metal layers 21 and 22 are the same.

When the thickness of the metal layers 21 and 22 is t2, the thickness of the semiconductor layer 23 is t1, and the refractive index of the semiconductor layer 23 is n _S , the width of the stacked body 24 (the width of the metal layers 21 and 22) is w3. Assuming that the period of the laminate 24 is Λ3, the values of the element parameters of the resonant element 20 used in the simulation are as follows.
Λ3 = 250 nm
t1 = 20nm
t2 = 40nm
w3 / Λ3 = 0.7
n _S = 1.55
Material of the metal layers 21 and 22: Aluminum (Al)
The substrate 14 was transparent, and the refractive index of the substrate 14 was 1.5.

The simulations of the example and the comparative example were performed using an FDTD (Finite-Difference time-domain) method incorporating an inductive convolution method. The FDTD method incorporating the inductive convolution method is known as an RC (Recursive convolution) -FDTD method. The RC-FDTD method is described in Reference Document 1 below, for example.
Reference 1: S. Banerjee, T. Hoshino and JB Cole, “Simulation of Subwavelength Metallic Gratings Using a New Implementation of Recursive Convolution FDTD,” JOSA A, 2008, vol. 25, no. 8, pp.1921

As described above, aluminum is assumed as the material of the first and second fine metal wires 12a and 13a and the metal layers 21 and 22. However, the refractive index of aluminum varies depending on the wavelength. In the simulation, the change of the dielectric constant of aluminum at a wavelength in the visible light region was approximated using a first-order approximation equation of Drude. Drude's first-order approximation is expressed as follows.

In the above approximate expression, ω _p is the plasma frequency and ν _c is the collision frequency. The values of ω _p and ν _c that cover the entire visible light were determined by fitting the above approximate expression to the dielectric constant (measured value) of Reference 2. For this fitting, a genetic algorithm and a global optimization algorithm described in Reference 3 were used. In the simulation, ω _p = 2.2637 × 10 ¹⁶ s ⁻¹ and ν _c = 11.99 × 10 ¹³ s ⁻¹ were set.
Reference 2: CLFoiles, “Optical properties of puremetals and binary alloys,” Chapter 4 of Landolt-Bornstein Numerical Data and Functional Relationships in Science and Technology New Series, Vol. 15, Subvolume b, K.-H. Hellwege and JLOlsen, Ed .Springer-Verlag, Berlin 1985, pp.228.
Reference 3: S. Banerjee and LN Hazra, “Experiments with a genetic algorithm for structural design of cemented doublets with prespecified aberration targets,” App. Opt. Vol. 40, No. 34, 2001, pp. 6265.

  Based on the period of the resonant elements 10 and 20 and the symmetry of the configuration, a simulation was performed on the two-dimensional model. In the embodiment, assuming that light of 31 wavelengths selected from a wavelength range of 400 nm to 700 nm at intervals of 10 nm is incident from the side opposite to the substrate 14, that is, from the first metal diffraction grating 12 side, the simulation is performed. The transmittance was calculated. In the comparative example, simulation was performed and transmittance was calculated assuming that light having the same wavelength as that of the example was incident on the resonance element 20 from the side opposite to the substrate 14.

  FIG. 3 is a diagram illustrating a simulation result of the example. In FIG. 3, the horizontal axis indicates the wavelength (nm), and the vertical axis indicates the transmittance (%). FIG. 3 shows the light transmittance of the TM mode and the TE mode. When the legend is shown together with the graph as shown in FIG. 3, the legend shown in the drawings is independent in each figure and is effective in the drawings with the legend attached. The same applies to drawings other than FIG. As shown in FIG. 3, TM mode light is transmitted and light in the blue region in the vicinity of a wavelength of 460 nm is transmitted under the simulation conditions selected in a range satisfying the expressions (1) to (8). It can be understood. The wavelength showing the maximum value (peak) of the transmittance with respect to the TM mode light is 460 nm, and the transmittance at the wavelength of 460 nm is 61%.

  In the following description, the maximum value (peak) of TM mode light transmittance is referred to as peak transmittance, and the wavelength corresponding to the peak transmittance is referred to as peak wavelength.

The FWHM (full width at half maximum) obtained from the result of the TM mode shown in FIG. 3 was 65 nm. On the other hand, the maximum transmittance in TE mode light was 1.2%, and the wavelength corresponding to the maximum transmittance was 400 nm. The transmittance of light in the TM mode and _{T TM,} the transmittance of light in the TE mode and _{T TE,} the polarization ratio _{η = (T TM -T TE)} / if you define _(T TM ₊ T _TE), Wavelength 460nm The polarization ratio η was 0.9772.

  FIG. 4 is a diagram illustrating a simulation result of a comparative example. The horizontal and vertical axes in FIG. 4 are the same as those in FIG. FIG. 4 shows the light transmittance of TM mode and TE mode. As shown in FIG. 4, the peak wavelength of TM mode light is about 435 nm between 430 nm and 440 nm, and the peak transmittance is 37.8%. The FWHM (full width at half maximum) obtained from the TM mode result shown in FIG. 4 was 265 nm. The polarization ratio η based on the peak transmittance is 0.9865.

  Comparing the simulation results of FIGS. 3 and 4, it can be understood that the example can achieve higher peak transmittance than the comparative example. Furthermore, the FWHM of the example is smaller than the FWHM of the comparative example. In addition, the example can realize a polarization ratio η substantially the same as the comparative example. That is, in the embodiment, it can be understood that the wavelength selectivity is improved while maintaining the polarization separation function.

  The resonant element 10A that selectively transmits light of a predetermined wavelength and a predetermined polarization has two functions of a wavelength selection function and a polarization separation. The resonant element 10A having two functions of wavelength selection function and polarization separation can be used as a wavelength selection and polarization separation filter or a color filter.

  As can be understood from the simulation results shown in FIGS. 3 and 4, the resonant element 10 </ b> A can achieve a high transmittance of a predetermined polarization while using the dielectric layer 11 having a smaller refractive index and is narrow. FWHM can be realized. Such a property is a property desired for a color filter. In particular, a narrow FWHM is a property required for performing more realistic color expression in a display device. Therefore, the resonant element 10A is suitably used as a color filter, for example, for a liquid crystal panel.

  5 and 6 are diagrams showing intensity distributions simulated in the simulation performed in the example. FIG. 5 shows an intensity distribution for TM mode light having a wavelength of 460 nm, which is a peak wavelength, and FIG. 6 shows an intensity distribution for TM mode light having a wavelength of 700 nm. 5 and 6, the lighter color (closer to white) indicates that the light intensity is higher, and the light is incident from the upper side in the drawing.

From FIG. 5, it can be seen that the localization and enhancement of the light intensity occur at the interface between the first and second fine metal wires 12a and 13a and the dielectric layer 11, respectively. That is, the results shown in FIG. 5 indicate that localized surface plasmon resonance (LSPR: Localized Surface Plasmon Resonance, see, for example, Reference 4) occurs. On the other hand, in FIG. 6, neither localization nor enhancement of the light intensity occurs at the interface between the first and second fine metal wires 12a and 13a and the dielectric layer 11. Therefore, from FIGS. 5 and 6, it is considered that LSPR and peak wavelength are related, and the color filtering characteristics of the MIM structure are related to plasmons related to resonance.
Reference 4: D. Sarid and W. Challener, “Modern Introduction to Surface Plasmons Theory, Mathematica Modeling, and Applications,” New York, Cambridge University Press, 2010, pp201-255.

  Since the resonant element 10A has two functions of a wavelength selection function and a polarization separation function, it can be suitably applied to a white organic LED (WOLED: White OLED).

  In the second direction, the dielectric layer 11 is continuous, and the first and second metal diffraction gratings 12 and 13 are provided on the continuous dielectric layer 11. Therefore, the resonant element 10A can be easily manufactured.

FIG. 7 is a diagram showing another simulation result for the simulation model used in the comparative example. The simulation was performed under the following conditions.
Λ3 = 250 nm
t1 = 100 nm
t2 = 40nm
ff3 = 0.7
n _S : 1.55 or 2.67
Note that ff3 = w3 / Λ3.

In the simulation obtained from the simulation result of FIG. 7, the thickness t1 is changed and the simulation is performed for the case where the refractive index n _S of the semiconductor layer 23 is 1.55 and 2.67. The simulation was performed as in the case.

FIG. 7 shows the light transmittance of the TM mode and the TE mode when the refractive index n _S is 2.67 and when the refractive index is 1.55. As understood from FIG. 7, if the refractive index n _S of the semiconductor layer 23 is large, the TM mode light transmittance is larger than that when the refractive index n _S is small. In other words, even with the configuration shown in FIG. 2, if the refractive index n _S of the semiconductor layer 23 is increased, a larger transmittance can be obtained in the TM mode, and as a result, a larger polarization ratio η can be obtained. . However, usually, a more expensive material such as an inorganic semiconductor must be selected as the semiconductor material having a large refractive index.

  On the other hand, with the configuration of the resonant element 10A, an MIM element that functions as a polarization separation element can be obtained with a cheaper material (for example, an organic polymer material) having a low refractive index. As a result, since the raw material cost can be reduced, the manufacturing cost of the product to which the resonant element 10A is applied can be reduced.

  A modification of the resonant element 10A will be described with reference to FIGS.

  FIG. 8 is a drawing showing a cross-sectional configuration of a first modification of the resonant element shown in FIG. The resonant element 10B shown in FIG. 8 is different from the resonant element 10A in that a gap is formed between adjacent first metal fine wires 12a among the plurality of first metal fine wires 12a included in the first metal diffraction grating 12. To do. That is, the same material as that of the dielectric layer 11 is not filled between the adjacent first thin metal wires 12a. Except for this difference, the configuration of the resonant element 10B is the same as that of the resonant element 10A. Therefore, the resonant element 10B has at least the same effects as the resonant element 10A. The first metal diffraction grating 12 in the resonant element 10B is formed, for example, by forming a metal layer of the material of the first metal wire 12a on the first main surface 11a, and then between the adjacent first metal wires 12a. The metal layer may be etched so as to form a void.

  FIG. 9 is a drawing showing a cross-sectional configuration of a second modification of the resonant element shown in FIG. 1. The resonant element 10C shown in FIG. 9 includes a second metal diffraction grating in which a gap is formed between adjacent first metal fine wires 12a among the plurality of first metal fine wires 12a included in the first metal diffraction grating 12. 13 is different from the resonant element 10A in that a gap is formed between adjacent second thin metal wires 13a among the plurality of second thin metal wires 13a. That is, the same material as that of the dielectric layer 11 is not filled between the adjacent first metal fine wires 12a and between the adjacent second metal fine wires 13a. Except for this difference, the configuration of the resonant element 10C is the same as that of the resonant element 10A. Therefore, the resonant element 10C has at least the same effects as the resonant element 10A. For example, the second metal diffraction grating 13 can be formed in the same manner as the first metal diffraction grating 12 in the resonant element 10B.

The values of various element parameters (for example, ff1, ff2, d, d1, d2, Λ1, Λ2, and n _B ) of the resonant elements 10A to 10C are set so that the optical characteristics of the resonant elements 10A to 10C are within an allowable range. Is selected. The ranges exemplified for each element parameter (for example, the formulas (1) to (8)) are ranges in which the optical characteristics of the resonant elements 10A to 10C are within the allowable range. The permissible range means that the TE mode light transmittance T _TE is less than 20% at wavelengths longer than 410 nm, the TM mode light transmittance T _TM is greater than 30% at the peak wavelength, and the TM mode light In FIG. 3, the maximum transmittance in the tail band (the portion on the skirt side on the long wavelength side of the transmittance distribution, for example, the portion having a wavelength of 560 nm or more in FIG. 3) is less than 20%. T _TE is less than 20%, _i.e., the maximum value of _{T TE} is less than 20%, tend to be secured a large polarization ratio. The polarization ratio is preferably 0.8 or more at the peak wavelength of the TM mode light.

  Next, the influence of element parameters on the characteristics of the resonant element will be described. In the following description, as in the example, the substrate 14 is transparent, and the refractive index of the substrate 14 is 1.5.

(A) Fill factor (ff) FIG. 10 shows the polarization ratio at the peak wavelength of TM mode light and the peak of TM mode light when the fill factor (ff) is changed in the simulation model used in the example. It is drawing which shows the transmittance | permeability. FIG. 10 shows the fill factor dependence of the absolute value of the polarization ratio η and the peak transmittance of TM mode light. The horizontal axis in FIG. 10 represents the fill factor, the left vertical axis represents the polarization ratio, and the right vertical axis represents the peak transmittance (%). The polarization ratio shown in FIG. 10 is calculated at a wavelength (peak wavelength) corresponding to the peak transmittance of TM mode light.

The simulation conditions were set as follows.
Λ1 = Λ2 = 250 nm
d = 20 nm
d1 = d2 = 40 nm
n _B = 1.55
k = 0
The simulation was performed by changing ff1 and ff2 from 0.3 to 0.8 under the above conditions. Note that ff1 = ff2.

  As understood from FIG. 10, when ff1 (= ff2) becomes smaller than 0.6, the absolute value of the polarization ratio η becomes smaller than 0.8. When ff1 (= ff2) is larger than 0.8, the maximum value of the TM mode light transmittance is smaller than 50%. Therefore, the range of ff1 (= ff2) is preferably 0.6 or more and 0.8 or less. However, when the refractive index of the dielectric layer 11 becomes larger, ff1 (= ff2) may be 0.6 or more and 0.9 or less. This is because the maximum value of TM mode light transmittance increases as the refractive index increases. Here, the influence of the fill factor (ff) has been described by taking the configuration of the resonant element 10A as an example, but the same applies to other configurations (resonant elements 10B and 10C).

(B) Refractive index When the refractive index n _B of the dielectric layer 11 increases, the TM mode light transmittance increases, but the TE mode light transmittance also tends to increase on the short wavelength side. Also, as the refractive index n _B increases, the TM mode light transmittance on the long wavelength side increases, so the FWHM becomes wider. For this reason, FWHM may be in an unfavorable range at a very high refractive index, and this tendency tends to occur particularly on the long wavelength side. The influence of the refractive index on each configuration of the resonant elements 10A, 10B, and 10C will be described.

(B-1) Resonant Element 10A FIG. 11A is a diagram showing a change in wavelength dependency of TM mode light transmittance with respect to the refractive index n _B. FIG. 11B is a diagram showing a change in the wavelength dependence of the TE mode light transmittance with respect to the refractive index n _B.

The results shown in FIGS. 11A and 11B are simulation results for the simulation model used in the example. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

In the simulation, the refractive index n _B was changed to 1.55, 1.75, 1.95 and 2.15.

From the simulation result shown in FIG. 11A, the peak transmittance of TM mode light increases from 61% to 80.48% as the refractive index n _B increases from 1.55 to 2.15. Yes. The peak wavelength is shifted from 460 nm to 580 nm as the refractive index n _B increases from 1.55 to 2.15. As shown in FIG. 11B, as the refractive index n _B increases from 1.55 to 2.15, the light transmittance of the TE mode rapidly increases on the shorter wavelength side than 440 nm. Therefore, in the configuration of the resonant element 10A, the refractive index n _B is appropriately 1.55 or more and 1.95 or less. If the refractive index n _B is within this range, the TM mode light can ensure a transmittance of 60% or more, and the maximum transmittance of the TE mode light is 21.3% at a wavelength of 400 nm. When the refractive index n _B is larger than 1.95, the transmittance of the TE mode light having a wavelength of 400 nm is higher (when the refractive index n _B is 2.15, the transmittance is 48.6%). The desired polarization ratio η cannot be obtained, and the polarization separation function is lowered.

(B-2) Resonant Element 10B FIG. 12A is a diagram showing a change in wavelength dependence of TM mode light transmittance with respect to the refractive index n _B. FIG. 12B is a diagram showing a change in the wavelength dependency of the light transmittance of the TE mode with respect to the refractive index n _B.

The results shown in FIGS. 12A and 12B are the results of simulation performed on the resonant element 10B. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

In the simulation, the refractive index n _B was changed to 1.75, 1.95 and 2.15.

Figure 12 (a) and 12 as shown in FIG. 12 (b), as the refractive index n _B increases, the transmittance of light in the TE mode in a short wavelength side is greater. The peak transmittance of TM mode light increases from 54.1% to 73.4% as the refractive index n _B increases from 1.75 to 2.15. Further, the peak wavelength of the TM mode light is shifted from 460 nm to 510 nm as the refractive index n _B increases from 1.75 to 2.15. Further, as shown in FIG. 12B, as the refractive index n _B increases from 1.75 to 2.15, the transmittance of the TE mode light rapidly increases on the shorter wavelength side than 440 nm. Therefore, in the configuration of the resonant element 10B in which k = 0, the refractive index n _B is appropriately 1.75 or more and 1.95 or less. If the refractive index n _B is within this range, the TM mode light can secure a peak transmittance of 54% or more, and the TE mode light has a maximum transmittance of about 12.4% at 400 nm. If the refractive index n _B is larger than 1.95, the transmittance of the light of the TE mode having a wavelength of 400 nm exceeds 20% (when the refractive index is 2.15, the transmittance is 20.7%). The desired polarization ratio η cannot be obtained, and the polarization separation function is lowered.

(B-3) Resonant Element 10C FIG. 13A is a diagram showing a change in wavelength dependency of TM mode light transmittance with respect to the refractive index n _B. FIG. 13B is a diagram showing a change in the wavelength dependence of the TE mode light transmittance with respect to the refractive index n _B.

The results shown in FIG. 13A and FIG. 13B are the results of a simulation performed on the resonant element 10C. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
d = 40 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

In the simulation, the refractive index n _B was changed to 1.5, 1.75, 1.95 and 2.15.

As shown in FIGS. 13A and 13B, the resonant element 10C has a shorter wavelength than the resonant elements 10A and 10B for all the changed refractive indexes n _B. On the side, the light transmittance of the TE mode is reduced. Therefore, the decrease in the polarization ratio η is smaller than that of the resonant element 10A and the resonant element 10B. The peak transmittance of TM mode light is 33.9% when the refractive index n _B is 1.5, and 70.9% when the refractive index n _B is 2.15. Further, the peak wavelength of TM mode light is shifted from 430 nm to 470 nm as the refractive index n _B increases from 1.5 to 2.15. Further, as shown in FIG. 13B, the maximum transmittance of light in the TE mode occurs at a wavelength of 400 nm when the refractive index n _B is 2.15, and its value is 5.6%. . In the configuration of the resonant element 10C, the refractive index n _B is suitably 1.5 or more and 2.15 or less. When the refractive index n _B is within this range, a peak transmittance exceeding 30% can be obtained in TM mode light, and a polarization ratio η exceeding 0.9052 can be obtained on the longer wavelength side than 440 nm. The peak transmittance of TM mode light is relatively small when the refractive index n _B is 1.5. However, since the peak transmittance can be changed by changing other parameters (for example, the thickness of the fine metal wire), the dielectric having a refractive index of 1.5 or more and 2.15 or less in the resonant element 10C is For example, it can be used to obtain an effective optical filter.

(C) Thickness d of dielectric layer 11 (C-1) Resonant element 10A
FIG. 14A is a drawing showing the change in wavelength dependence of the TM mode light transmittance with respect to the thickness of the dielectric layer 11. FIG. 14B is a diagram showing a change in the wavelength dependency of the transmittance of light in the TE mode with respect to the thickness of the dielectric layer 11.

The results shown in FIG. 14A and FIG. 14B are the results of a simulation performed on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the thickness d of the dielectric layer was changed to 10 nm, 20 nm, 40 nm, 60 nm, and 80 nm.

  As shown in FIG. 14 (a), as the thickness d increases, the peak transmittance for TM mode light decreases from 62.6% to 21.3%, and the peak wavelength starts from 470 nm. Shift to 440 nm. Furthermore, as the thickness d increases, undesirable tailbands in the long wavelength region are suppressed. In the configuration of the resonant element 10A, the thickness d is suitably 10 nm or more and 60 nm or less. Within this range, a peak transmittance exceeding 30% can be obtained in TM mode light, and the polarization ratio η is greater than 0.9 at the peak wavelength of TM mode light. When the thickness d is 80 nm, the maximum transmittance (transmittance at a wavelength of 400 nm) in TE mode light is 25.7%, which exceeds the allowable range.

(C-2) Resonant element 10B
FIG. 15A is a diagram showing a change in wavelength dependency of TM mode light transmittance with respect to the thickness of the dielectric layer 11. FIG. 15B is a diagram showing a change in the wavelength dependence of the TE mode light transmittance with respect to the thickness of the dielectric layer 11.

The results shown in FIG. 15A and FIG. 15B are the results of a simulation performed on the resonant element 10B. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the thickness d was changed to 20 nm, 40 nm, 60 nm, and 80 nm.

  As shown in FIG. 15 (a), as the thickness d increases, the peak transmittance for TM mode light decreases from 42.0% to 20.6%, and the peak wavelength from 440 nm. Shift to 430 nm. Furthermore, as the thickness d increases, undesirable tailbands in the long wavelength region are more suppressed. When the thickness d is smaller than 20 nm, a high transmittance exceeding an allowable range is obtained in an unsuitable tail band on the long wavelength side. In the configuration of the resonant element 10B, the thickness d is appropriately 20 nm or more and 60 nm or less. Within this range, a peak transmittance exceeding 30% can be obtained, and a high polarization ratio η can be obtained. When the thickness d is 60 nm, the polarization ratio η is greater than 0.7 with respect to the transmittance of TM mode light having a wavelength of 430 nm to 600 nm. As the thickness d increases, the TE mode light transmittance rapidly increases on the short wavelength side. However, if the thickness d is 60 nm, the maximum transmittance of the TE mode light (at a wavelength of 400 nm). Transmittance) is about 2.1%.

(C-3) Resonant element 10C
FIG. 16A is a drawing showing a change in wavelength dependency of TM mode light transmittance with respect to the thickness of the dielectric layer 11. FIG. 16B is a diagram showing a change in the wavelength dependency of the transmittance of light in the TE mode with respect to the thickness of the dielectric layer 11.

The results shown in FIG. 16A and FIG. 16B are the results of a simulation performed on the resonant element 10C. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the thickness d was changed to 20 nm, 40 nm, 60 nm, and 80 nm.

  As shown in FIG. 16 (a), as the thickness d increases, the peak transmittance for TM mode light decreases from 42.3% to 22.0%, and the peak wavelength is approximately 430 nm. It is constant at. Further, as the thickness d increases, an undesirable tail band in the long wavelength region is further suppressed. When the thickness d is smaller than 40 nm, a high transmittance exceeding an allowable range is obtained in an undesired tail band on the long wavelength side. In the configuration of the resonant element 10C (where k = 0), the thickness d is suitably 40 nm or more and 60 nm or less. Within this range, a peak transmittance exceeding 30% can be obtained, and the polarization ratio η is greater than 0.9 at the peak wavelength of the TM mode light. As the thickness d increases, the TE mode light transmittance rapidly increases on the short wavelength side. However, if the thickness d is 60 nm, the maximum transmittance of the TE mode light (at a wavelength of 400 nm). Transmittance) is about 0.9%.

(D) Regarding the thicknesses d1 and d2 of the first and second fine metal wires 12a and 13a FIG. 17A shows the TM mode for the thicknesses d1 and d2 of the first and second fine metal wires 12a and 13a. It is drawing which shows the change of the wavelength dependence of the transmittance | permeability of light. FIG. 17B is a diagram showing a change in the wavelength dependency of the light transmittance of the TE mode with respect to the thicknesses d1 and d2 of the first and second fine metal wires 12a and 13a.

The results shown in FIGS. 17A and 17B are results obtained by performing simulation on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d = 20 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the thicknesses d1 and d2 were changed to 20 nm, 30 nm, 40 nm, 60 nm, 70 nm, and 80 nm. However, the thickness d1 and the thickness d2 were the same value.

  As shown in FIG. 17 (a), as the thicknesses d1 and d2 increase from 30 nm to 70 nm, the peak transmittance for TM mode light increases from 35.8% to 89.8%, and the peak wavelength Shift from 440 nm to about 605 nm (between 600 nm and 610 nm). As the thicknesses d1 and d2 increase, the transmittance for light in the TE mode decreases at almost all wavelengths shown in FIG. When the thicknesses d1 and d2 are 20 nm or less, the TM mode light transmittance is less than 10% in almost all the visible light region, and the absolute value of the polarization ratio η is so small that it exceeds the allowable range. When the thicknesses d1 and d2 are larger than 70 nm, the transmittance increases in an undesired tail band on the short wavelength side as the allowable range is exceeded. Therefore, for the resonant element 10A, both the thickness d1 and the thickness d2 are preferably 30 nm or more and 70 nm or less. Within this range, a peak transmittance exceeding 30% can be obtained for TM mode light, and a polarization ratio η exceeding 0.8 can be obtained on the longer wavelength side than the wavelength of 420 nm. When the thicknesses d1 and d2 are 30 nm, the transmittance in TE mode light shows a maximum value (transmittance at a wavelength of 400 nm), and the value is 3.8%. Here, the influence of the thicknesses d1 and d2 has been described by taking the configuration of the resonant element 10A as an example, but the same applies to other configurations (resonant elements 10B and 10C).

(E) Periods Λ1 and Λ2 FIG. 18A is a diagram showing a change in wavelength dependency of TM mode light transmittance with respect to periods Λ1 and Λ2 of the first and second metal diffraction gratings 12 and 13. is there. FIG. 18B is a diagram showing a change in wavelength dependency of the transmittance of light in the TE mode with respect to the periods Λ 1 and Λ 2 of the first and second metal diffraction gratings 12 and 13.

The results shown in FIGS. 18A and 18B are results obtained by performing simulation on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
n _B = 1.55
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the periods Λ1 and Λ2 were changed to 190 nm, 230 nm, 270 nm, and 310 nm. However, the periods Λ1 and Λ2 are the same value.

  18 (a) and 18 (b), it can be seen that in the resonant element 10A, the periods Λ1 and Λ2 are preferably in the range of 230 nm to 270 nm. Within this range, a peak transmittance exceeding 40% can be obtained for TM mode light, and a larger polarization ratio η can be obtained on the longer wavelength side than the wavelength of 400 nm. In the above range, the peak wavelength is red shifted from about 440 nm to about 470 nm. When the periods Λ1 and Λ2 exceed 270 nm, the light transmittance of the TE mode substantially increases at all wavelengths shown in FIG. The absolute value of the polarization ratio η becomes smaller and exceeds the allowable range. When the periods Λ1 and Λ2 exceed 270 nm, the transmittance of light in the TM mode in the undesired tail bands on both the long wavelength side and the short wavelength side increases and exceeds the allowable range. Here, the influence of the periods Λ1, Λ2 has been described by taking the configuration of the resonant element 10A as an example, but the same applies to other configurations (resonant elements 10B, 10C).

(F) Offset k FIG. 19A is a diagram showing a change in wavelength dependency of the transmittance of TM mode light with respect to the offset k. FIG. 19B is a diagram showing a change in wavelength dependence of the transmittance of light in the TE mode with respect to the offset k.

The results shown in FIG. 19A and FIG. 19B are the results of a simulation performed on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7

  In the simulation, the offset k was changed to 10 nm, 20 nm, 30 nm, and 40 nm.

  As shown in FIGS. 19A and 19B, as the offset k increases, the TM mode peak transmittance decreases and the TE mode light peak transmittance also decreases. If it is small but not 0 (for example, k is 30 nm or less), the tail band on the long wavelength side is suppressed, which is preferable as the configuration of the resonant element 10A. On the other hand, if k is 40 nm or more, an undesirable second transmittance peak appears in the vicinity of the wavelength of 520 nm in the transmittance distribution of TM mode light. Therefore, k of 40 nm or more is not preferable for the resonant element 10A. The peak transmittances of TM mode light when k is 10 nm, 20 nm, and 30 nm are 58.5%, 57.6%, and 53.7%, respectively. When k is 30 nm or less, the decrease in peak transmittance is small even when k is large. Therefore, it is preferable that k is greater than 0 and not more than 30 nm because it does not cause significant deterioration of the optical characteristics, but can suppress the tail band on the long wavelength side. Note that when k was 10 nm, the maximum transmittance of light in the TE mode was 1% or less at a wavelength of 400 nm. Here, the influence of the offset k has been described by taking the configuration of the resonant element 10A as an example, but the same applies to other configurations (resonant elements 10B and 10C).

(G) Effect of Asymmetry In the above description, the element parameters representing the first and second metal diffraction gratings 12 and 13 are the same in the first and second metal diffraction gratings 12 and 13. The corresponding element parameters may be different. The difference in the corresponding element parameter values is called asymmetry.

(G-1) Asymmetry of Thicknesses d1 and d2 FIG. 20A is a diagram showing a change in wavelength dependency of TM mode light transmittance when the thicknesses d1 and d2 are different. FIG. 20B is a diagram illustrating a change in wavelength dependency of the light transmittance of the TE mode when the thicknesses d1 and d2 are different.

The results shown in FIG. 20A and FIG. 20B are the results of a simulation performed on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d = 20 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the combination of (d2, d1) was changed to (70 nm, 30 nm), (70 nm, 50 nm), and (50 nm, 70 nm).

  As shown in FIG. 17 (a), when both d1 and d2 were 30 nm, the peak transmittance was low, but as shown in FIG. 20 (a), all the combinations of (d2, d1) above. The peak transmittance of TM mode light exceeded 80%. For example, when d1 is 30 nm and d2 is 70 nm, the peak transmittance was 81%. Therefore, if d1 and d2 are in the range of 30 nm to 70 nm, a configuration in which the thickness d1 and the thickness d2 are different can increase the polarization separation function. Here, the influence of the case where the thickness d1 and the thickness d2 are different has been described by taking the configuration of the resonance element 10A as an example, but the same applies to other configurations (resonance elements 10B and 10C). When the combination of (d2, d1) is inverted, that is, in the cases of (70 nm, 50 nm) and (50 nm, 70 nm), the transmittance of the TE mode light is almost the same. In this case, a peak wavelength shift of about 10 nm occurs, and the peak transmittance also differs by about 4.2%.

(G-2) Asymmetry of Periods Λ1 and Λ2 FIG. 21A is a diagram showing a change in wavelength dependency of the light transmittance of the TM mode when the periods Λ1 and Λ2 are different. The result shown in FIG. 21A is a result of a simulation performed on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
n _B = 1.55
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the combination of (Λ2, Λ1) was changed to (270 nm, 230 nm), (270 nm, 250 nm), (250 nm, 255 nm), and (250 nm, 260 nm).

  As shown in FIG. 21A, when the absolute value of the difference between the periods Λ1 and Λ2 is 20 nm or more, that is, when (Λ2, Λ1) is (270 nm, 230 nm) and (270 nm, 250 nm), The TM mode light transmittance changes irregularly, and the resonant element 10A cannot be used as an optical filter. On the other hand, when the absolute value of the difference between the periods Λ1 and Λ2 is 10 nm or less, that is, when (Λ2, Λ1) is (250 nm, 255 nm) and (250 nm, 260 nm), the transmittance characteristics of TM mode light are This was almost the same as when the periods Λ1 and Λ2 were the same. Specifically, when (Λ2, Λ1) is (250 nm, 250 nm), the peak transmittance of TM mode light is 61% (see FIG. 3), and the peak wavelength is 460 nm. On the other hand, when (Λ2, Λ1) is (250 nm, 255 nm) and (250 nm, 260 nm), the peak transmittance of TM mode light is 60.11% and 54.25%, and the peak wavelengths are 460 nm and 470 nm. Met. From these results, it can be seen that when the absolute value of the difference between the periods Λ1 and Λ2 is 10 nm, the peak wavelength is shifted by about 10 nm compared to the case where the periods Λ1 and Λ2 are the same. Therefore, it can be understood that if the difference between the periods Λ1 and Λ2 is about 10 nm, the TM mode light transmission characteristics are hardly affected.

FIG. 21B is a diagram showing a change in wavelength dependency of the light transmittance of the TE mode when the periods Λ1 and Λ2 are different. The result shown in FIG. 21B is the result of simulation performed on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
n _B = 1.55
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0

  In the simulation, the combination of (Λ2, Λ1) was changed to (250 nm, 255 nm) and (250 nm, 260 nm).

  As shown in FIG. 21 (b), when (Λ2, Λ1) is (250 nm, 255 nm), the maximum transmittance of light in the TE mode is 1.2% at a wavelength of 400 nm. This maximum transmittance is smaller than when the periods Λ1 and Λ2 are the same. Further, it can be seen that when the absolute value of the difference between the periods Λ1 and Λ2 increases to 10 nm, the transmittance decreases at all wavelengths shown in FIG.

  Therefore, from the results of FIGS. 21A and 21B, if the absolute value of the difference between the periods Λ1 and Λ2 is 10 nm or less, the difference between the periods Λ1 and Λ2 contributes to an increase in the polarization ratio η. I understand. Here, the influence of the asymmetry of the periods Λ1 and Λ2 has been described using the configuration of the resonant element 10A as an example, but the same applies to other configurations (resonant elements 10B and 10C).

(G-3) Asymmetry of Fill Factors ff1 and ff2 FIG. 22A is a diagram showing a change in wavelength dependency of TM mode light transmittance when the fill factors ff1 and ff2 are different. FIG. 22B is a diagram illustrating a change in wavelength dependency of the light transmittance of the TE mode when the fill factors ff1 and ff2 are different.

The results shown in FIGS. 22A and 22B are results obtained by performing simulation on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
Λ1 = Λ2 = 250 nm
n _B = 1.55
d = 20 nm
d1 = d2 = 40 nm
k = 0

  In the simulation, the combination of (ff2, ff1) is changed to (0.9, 0.7), (0.7, 0.8), (0.6, 0.7) and (0.6, 0.9) Changed to.

  As shown in FIG. 22A, when the fill factors ff1 and ff2 are different, the peak transmittance of TM mode light tends to be small. This tendency increases as ff1 and ff2 approach the upper limit or lower limit value of their allowable range. Therefore, when ff1 and ff2 are different, the difference between them is preferably smaller than 0.1. This is because if the absolute value of the difference between ff1 and ff2 exceeds 0.1, the transmittance is reduced too much. In addition, when one of ff1 and ff2 is 0.6, the polarization ratio η at a short wavelength becomes too small and exceeds the allowable range. Therefore, when ff1 and ff2 are different, it is preferable to select them from the range of 0.7 to 0.8. Note that the peak transmittance of the TM mode when (ff2, ff1) is (0.6, 0.7), (0.7, 0.8) and (0.9, 0.7) is 57 respectively. 0.03%, 54.9%, and 35.1%, and the peak wavelengths were 460 nm, 480 nm, and 480 nm, respectively. When the absolute value of the difference between ff1 and ff2 is 0.1, a peak wavelength shift of about 20 nm occurs, and the peak transmittance decreases by about 5%. Here, the influence of the asymmetry of the fill factors ff1 and ff2 has been described by taking the configuration of the resonant element 10A as an example, but the same applies to other configurations (resonant elements 10B and 10C).

From the various simulation results so far, it can be seen that n _B , Λ 1, Λ 2, d, d 1 and d 2 are more likely to contribute to the peak transmittance and transmission band of the TM mode light. In particular, d1 and d2 are likely to contribute to the peak transmittance and transmission band. Such _{n B,} .LAMBDA.1, .LAMBDA.2, considering the contribution of d, d1 and d2, _{n B} in the blue region, the green region and the red region, .LAMBDA.1, .LAMBDA.2, preferred ranges of d, d1 and d2 are as follows is there.
(A) Blue region 30 nm ≦ d1, d2 ≦ 50 nm
230 nm ≦ Λ1, Λ2 ≦ 250 nm
1.5 ≦ n _B ≦ 1.75
(B) Green region 50 nm ≦ d1, d2 ≦ 60 nm
250 nm ≦ Λ1, Λ2 ≦ 270 nm
1.5 ≦ n _B ≦ 2.15
(C) Red region 60 nm ≦ d1, d2 ≦ 70 nm
260 nm ≦ Λ1, Λ2 ≦ 270 nm
1.65 ≦ n _B ≦ 2.15

  FIG. 23A is a diagram showing the wavelength dependence of the transmittance of TM mode light with respect to the resonant element 10A that can be used as a blue filter, a green filter, and a red filter. FIG. 23B is a diagram showing the wavelength dependence of the transmittance of light in the TE mode for the resonant element 10A that can be used as a blue filter, a green filter, and a red filter.

The results shown in FIG. 23A and FIG. 23B are the results of a simulation performed on the resonant element 10A. The simulation method is the same as in the embodiment. The simulation conditions are as follows.
(I) Blue filter element parameter Λ1 = Λ2 = 250 nm
n _B = 1.55
d = 20 nm
d1 = d2 = 40 nm
ff1 = ff2 = 0.7
k = 0
(Ii) Green filter element parameter Λ1 = Λ2 = 250 nm
n _B = 1.55
d = 20 nm
d1 = d2 = 60 nm
ff1 = ff2 = 0.7
k = 0
(Iii) Red filter element parameters Λ1 = Λ2 = 270 nm
n _B = 1.65
d = 20 nm
d1 = d2 = 70 nm
ff1 = ff2 = 0.7
k = 0

  The peak transmittances of the blue filter, green filter, and red filter for TM mode light were 61%, 86.7%, and 95.1%, respectively, and the peak wavelengths were 460 nm, 530 nm, and 630 nm. Further, the FWHMs of the blue filter, the green filter, and the red filter for TM mode light were 65 nm, 100 nm, and 100 nm, respectively. The maximum transmittances for TE mode light for the blue, green and red filters were 1.725%, 0.4% and 0.98%. From these simulation results, it is understood that the resonant element 10A can be used as a blue filter, a green filter, and a red filter by appropriately selecting element parameters.

  Next, a liquid crystal panel to which the resonant element 10A is applied will be described with reference to FIG. FIG. 24 is a schematic diagram showing a cross-sectional configuration of an embodiment of a liquid crystal panel to which a resonant element is applied. The liquid crystal panel 30 includes a first substrate 31, a polarizing plate 32, a transparent electrode 33, an alignment film 34, a liquid crystal layer 35, an alignment film 36, a resonant element 10 </ b> A, and a second substrate 37. On the first substrate 31, a polarizing plate 32, a transparent electrode 33, an alignment film 34, a liquid crystal layer 35, an alignment film 36, a resonance element 10A, and a second substrate 37 are stacked in this order. When the liquid crystal panel 30 is incorporated into a transmissive image display device such as a liquid crystal display device, light emitted from the backlight is incident on the first substrate 31.

  The first and second substrates 31 and 37 are the same transparent substrates as the substrate 14. The polarizing plate 32, the transparent electrode 33, the liquid crystal layer 35, and the alignment films 34 and 36 are not particularly limited as long as they are a polarizing plate, a transparent electrode, a liquid crystal layer, and an alignment film used in known liquid crystal panels. The polarizing plate 32 transmits TE mode light.

  In the liquid crystal panel, the resonant element 10A is arranged so that the second main surface 11b is positioned on the alignment film 34 side. In this configuration, the first or second metal diffraction grating 12, 13 can function as an electrode for applying an electric field to the liquid crystal layer 35 together with the transparent electrode 33.

  In manufacturing the liquid crystal panel 30, first, the polarizing plate 32, the transparent electrode 33, the alignment film 34, the liquid crystal layer 35, and the alignment film 36 are formed on the first substrate 31 in the same manner as in the past. Thereafter, after forming the resonant element 10A on the alignment film 36, the second substrate 37 is formed on the resonant element 10A.

  In the liquid crystal panel 30, the resonant element 10A can be formed as follows, for example. First, a metal layer made of the material of the second metal fine wire 13a is formed on the alignment film 36, and the metal layer is patterned to form a plurality of second metal fine wires 13a spaced from each other. Thereafter, the dielectric layer 11 is formed. The dielectric layer 11 is patterned to form a recess in which the first fine metal wire 12a is formed. If the concave portion is filled with the material of the first metal thin wire 12a, the resonant element 10A can be obtained.

  As described above, the resonant element 10A transmits light having a predetermined wavelength and a predetermined polarization. Therefore, FIG. 24 is an enlarged view showing a region through which light in one wavelength region (for example, blue) of the red wavelength region, the blue wavelength region, and the green wavelength region is transmitted in the liquid crystal panel. Correspond.

  A liquid crystal panel that displays a color image usually has regions that respectively transmit a red wavelength region, a blue wavelength region, and a green wavelength region. Accordingly, when configuring a color image liquid crystal panel, the resonant elements 10A that transmit the red wavelength region, the blue wavelength region, and the green wavelength region may be juxtaposed. At this time, the dielectric layer 11 may be common in the plurality of resonant elements 10A.

  Since the resonant element 10A has two functions of a color filter and a polarizer, it is not necessary to dispose a color filter layer and a polarizer in the liquid crystal panel 30. Therefore, the liquid crystal panel 30 can be thinned. Further, the first or second metal diffraction grating 12 or 13 can be used as an electrode for applying an electric field to the liquid crystal layer 35. Also in this respect, the liquid crystal panel 30 can be made thin because it is not necessary to further provide a transparent electrode that forms a pair with the transparent electrode 33.

  The wavelength selectivity of the resonant element 10A is based on a resonant structure, and is not based on light absorption by a dye or the like as in a conventional color filter. As a result, light can be used effectively.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the range which does not deviate from the meaning of this invention. For example, the cross-sectional shapes of the first and second fine metal wires 12a and 13a are not limited to rectangles and squares. Further, the first metal diffraction grating 12 and the second metal diffraction grating 13 have the first metal fine wire 12a and the second metal fine wire 13a, but any metal member that can constitute the metal diffraction grating. It is not limited to thin lines. In the description of the resonant elements 10A, 10B, and 10C using FIGS. 1, 8, and 9, the substrate 14 has been described as a separate component from the resonant elements 10A, 10B, and 10C. However, the resonant elements 10 </ b> A, 10 </ b> B, and 10 </ b> C may include the substrate 14.

  DESCRIPTION OF SYMBOLS 10A-10C ... Resonant element, 11 ... Dielectric layer, 11a ... 1st main surface, 11b ... 2nd main surface, 12 ... 1st metal diffraction grating, 12a ... 1st metal fine wire (1st metal Member), 13 ... second metal diffraction grating, 13a ... second metal fine wire (second metal member).

Claims (16)

A dielectric layer having first and second major surfaces;
A first metal diffraction grating provided on the first main surface;
A second metal diffraction grating provided on the second main surface;
With
The first metal diffraction grating includes a plurality of first metal members extending in a first direction and arranged in a second direction orthogonal to the first direction at a first spatial period,
The second metal diffraction grating includes a plurality of second metal members extending in the first direction and arranged in the second direction at a second spatial period,
The width of the first metal member in the second direction is w1, the first spatial period is Λ1, the thickness of the dielectric layer is d, and the first thickness in the thickness direction of the dielectric layer is The thickness of the first metal member is d1, the width of the second metal member in the second direction is w2, the second spatial period is Λ2, and the first thickness in the thickness direction of the dielectric layer is the thickness of the second metallic member and d2, and the refractive index of the dielectric layer was set to n _B,
w1 / Λ1, d1, d, and Λ1 satisfy Equations (1) to (4), respectively, w2 / Λ2, d2, and Λ2 satisfy Equations (5) to (7), respectively, and n _B Satisfies equation (8),
Resonant element.
0.6 ≦ w1 / Λ1 ≦ 0.9 (1)
30 nm ≦ d1 ≦ 70 nm (2)
10 nm ≦ d ≦ 60 nm (3)
230 nm ≦ Λ1 ≦ 270 nm (4)
0.6 ≦ w2 / Λ2 ≦ 0.9 (5)
30 nm ≦ d2 ≦ 70 nm (6)
230 nm ≦ Λ 2 ≦ 270 nm (7)
1.5 ≦ n _B ≦ 2.15 (8) Between the adjacent first metal members among the plurality of first metal members of the first metal diffraction grating, the same material as the material of the dielectric layer is filled,
Between the second metal members adjacent to each other among the plurality of second metal members of the second metal diffraction grating, the same material as the material of the dielectric layer is filled.
The resonant element according to claim 1. Between the first metal members adjacent to each other among the plurality of first metal members of the first metal diffraction grating, there is a gap.
Between the second metal members adjacent to each other among the plurality of second metal members of the second metal diffraction grating, the same material as the material of the dielectric layer is filled.
The resonant element according to claim 1. Between the first metal members adjacent to each other among the plurality of first metal members of the first metal diffraction grating, there is a gap.
A space is formed between the adjacent first metal members among the plurality of second metal members of the second metal diffraction grating.
The resonant element according to claim 1 or 2. Each of w1 / Λ1 and w2 / Λ2 is
0.6 ≦ w1 / Λ1 ≦ 0.8, and
0.6 ≦ w2 / Λ2 ≦ 0.8,
The resonant element according to any one of claims 1 to 4, which satisfies:   The resonant element according to claim 1, wherein d satisfies 20 nm ≦ d ≦ 60 nm. The resonant element according to claim 1, wherein the n _B satisfies 1.55 ≦ n _B ≦ 1.95. Each of the d1, the d2, the Λ1, the Λ2, and the n _B is
30 nm ≦ d1 ≦ 50 nm,
30 nm ≦ d2 ≦ 50 nm,
230 nm ≦ Λ1 ≦ 250 nm,
230 nm ≦ Λ 2 ≦ 250 nm, and 1.5 ≦ n _B ≦ 1.75,
The resonant element according to any one of claims 1 to 4, which satisfies: Each of the d1, the d2, the Λ1, the Λ2, and the n _B is
50 nm ≦ d1 ≦ 60 nm,
50 nm ≦ d2 ≦ 60 nm,
250 nm ≦ Λ1 ≦ 270 nm,
250 nm ≦ Λ 2 ≦ 270 nm, and 1.5 ≦ n _B ≦ 2.15,
The resonant element according to any one of claims 1 to 4, which satisfies: Each of the d1, the d2, the Λ1, the Λ2, and the n _B is
60 nm ≦ d1 ≦ 70 nm,
60 nm ≦ d2 ≦ 70 nm,
260 nm ≦ Λ1 ≦ 270 nm,
260 nm ≦ Λ 2 ≦ 270 nm, and 1.65 ≦ n _B ≦ 2.15,
The resonant element according to any one of claims 1 to 4, which satisfies: The resonant element according to claim 3, wherein the n _B satisfies 1.75 ≦ n _B ≦ 1.95.   The resonant element according to claim 4, wherein the d satisfies 40 nm ≦ d ≦ 60 nm. The d1 and the d2 are different, and the d1 and the d2 are respectively
30 nm ≦ d1 ≦ 70 nm, and
30 nm ≦ d2 ≦ 70 nm,
The resonant element according to any one of claims 1 to 4, which satisfies:   The resonant element according to any one of claims 1 to 4, wherein the Λ1 and the Λ2 are different, and an absolute value of a difference between the Λ1 and the Λ2 is 10 nm or less. The w1 / Λ1 and the w2 / Λ2 are different from each other.
The w1 / Λ1 and w2 / Λ2 are respectively
0.7 ≦ w1 / Λ1 ≦ 0.8, and
0.7 ≦ w2 / Λ2 ≦ 0.8,
The resonant element according to any one of claims 1 to 4, which satisfies: In the second direction, the position of the first metal diffraction grating is deviated from the position of the second metal diffraction grating;
When k is an offset that is a shift amount in the second direction between the position of the first metal diffraction grating and the position of the second metal diffraction grating, k satisfies 0 <k ≦ 30 nm. The resonant element according to claim 1.