Absorptive wire-grid polarizer and optical apparatus
The absorptive wire-grid polarizer includes a periodic structure formed on a substrate surface of a dielectric substrate and constituted by a metal and one or more dielectric materials. The periodic structure has a one-dimensional grating structure in which, in a sectional plane orthogonal to a normal to the substrate surface, grating portions of a metal grating formed of the metal and grating portions of dielectric gratings formed of the one or more dielectric materials are one-dimensionally arranged with a grating period P. The Conditions of n m ≧1.0, k m ≧2.0, 0.01≦FF≦0.25, N b ≧1.40, and h≧250 [nm] are satisfied where h represents an entire height of the metal and dielectric gratings, n m represents a refractive index of a real part of a complex refractive index of the metal, k m represents an extinction coefficient of an imaginary part of the complex refractive index, and n b represents an average refractive index of the dielectric grating.
1. An absorptive wire-grid polarizer comprising:
a dielectric substrate; and
a periodic structure formed on a substrate surface of the dielectric substrate and constituted by a metal and one or more dielectric materials whose number is represented by i,
wherein the periodic structure has a one-dimensional grating structure in which, in a sectional plane orthogonal to a normal to the substrate surface, grating portions of a metal grating formed of the metal and grating portions of dielectric gratings formed of the one or more dielectric materials are one-dimensionally arranged with a grating period P smaller than that of an entering light entering the polarizer, and
wherein the following conditions are satisfied:
n m ≧2.0;
k m ≧3.0;
0.01≦ FF≦ 0.25;
n b ≧1.40; and
h ≧250 nm,
where h represents an entire height of the metal and dielectric gratings, n m represents a refractive index of a real part of a complex refractive index of the metal for a wavelength of the entering light, k m represents an extinction coefficient of an imaginary part of the complex refractive index, n b represents an average refractive index of the dielectric gratings, and FF represents an average filling factor of the metal grating to the grating period P, FF and n b being expressed by the following expressions:
F
F
=
1
h
∫
0
h
W
(
z
)
p
ⅆ
z
n
b
=
1
h
∫
0
h
(
∑
1
ni
2
·
Wi
W
(
z
)
)
)
0.5
ⅆ
z
,
W
(
z
)
=
∑
i
W
i
(
z
)
where W(z) represents a grating width of the grating portion of the metal grating occupying in the grating period p at a grating height z, and n i and Wi respectively represent a refractive index and a grating width of an i-th dielectric material.
2. An absorptive wire-grid polarizer according to claim 1 , wherein the periodic structure has, in a sectional plane parallel to the normal to the substrate surface, a structure in which each grating portion of the metal grating is formed between rectangular grating portions of the dielectric gratings.
3. An absorptive wire-grid polarizer according to claim 1 , wherein the periodic structure has, in a sectional plane parallel to the normal to the substrate surface, a structure in which each grating portion of the metal grating is formed on an oblique surface of each triangular grating portion of the dielectric gratings and each triangular grating portion of the dielectric gratings is formed between the grating portions of the metal grating.
4. An absorptive wire-grid polarizer according to claim 1 , wherein the periodic structure has, in a direction in which the normal to the substrate surface extends, a structure in which multiple one-dimensional grating structure layers each having the one-dimensional grating structure are laminated.
5. An absorptive wire-grid polarizer according to claim 4 , further comprising:
an intermediate layer formed of a dielectric material disposed between the laminated one-dimensional grating structure layers, and
wherein a product of a refractive index and a thickness of the intermediate layer is 20 nm or more and 300 nm or less.
6. An absorptive wire-grid polarizer according to claim 1 , wherein the periodic structure is formed on the substrate surface of each of both sides of the substrate.
7. An absorptive wire-grid polarizer according to claim 1 , wherein the metal is any of Cr, V, W, Mo, Ta, Fe, Te, Co, Ni, Ge, Ti, or an alloy or a compound including any thereof, but not including Au, Ag and Al.
8. An optical apparatus comprising:
a body; and
an absorptive wire-grid polarizer housed in the body,
wherein the absorptive wire-grid polarizer comprises:
a dielectric substrate; and
a periodic structure formed on a substrate surface of the dielectric substrate and constituted by a metal and one or more dielectric materials whose number is represented by i,
wherein the periodic structure has a one-dimensional grating structure in which, in a sectional plane orthogonal to a normal to the substrate surface, grating portions of a metal grating formed of the metal and grating portions of dielectric gratings formed of the one or more dielectric materials are one-dimensionally arranged with a grating period P smaller than that of an entering light entering the polarizer, and
wherein the following conditions are satisfied:
n m ≧2.0;
k m ≧3.0;
0.01≦ FF≦ 0.25;
n b ≧1.40; and
h ≧250 nm,
where h represents an entire height of the metal and dielectric gratings, n m represents a refractive index of a real part of a complex refractive index of the metal for a wavelength of the entering light, k m represents an extinction coefficient of an imaginary part of the complex refractive index, n b represents an average refractive index of the dielectric gratings, and FF represents an average filling factor of the metal grating to the grating period P, FF and n b being expressed by the following expressions:
F
F
=
1
h
∫
0
h
W
(
z
)
p
ⅆ
z
n
b
=
1
h
∫
0
h
(
∑
1
ni
2
·
Wi
W
(
z
)
)
)
0.5
ⅆ
z
,
W
(
z
)
=
∑
i
W
i
(
z
)
where W(z) represents a grating width of the grating portion of the metal grating occupying in the grating period p at a grating height z, and n i and Wi respectively represent a refractive index and a grating width of an i-th dielectric material.