Optical filter, solid state imaging device, and electronic apparatus
An optical filter that suppresses the occurrence of color mixing due to wavelength components on the short wavelength side relative to the desired transmission component. The optical filter includes a metal thin-film filter in which a plurality of openings are periodically arranged, and a first dielectric layer that coats a surface of the metal thin-film filter and coats or fills an interior of the opening of the metal thin-film filter. The optical filter also includes a second dielectric layer having a refractive index lower than a refractive index of the first dielectric layer and formed at least on an incidence surface side of the metal thin-film filter. The present technology can be applied to a hole array filter.
1. An optical filter, comprising:
a metal thin-film filter that comprises a plurality of openings, wherein
the plurality of openings is periodically arranged in a triangular array in the metal thin-film filter,
in the triangular array a horizontal distance is different from a vertical distance,
the horizontal distance is a distance between a first opening of the plurality of openings and a second adjacent opening of the plurality of openings in a horizontal direction, and
the vertical distance is a distance between the first opening of the plurality of openings and a third adjacent opening of the plurality of openings in a vertical direction;
a first dielectric layer on a surface of the metal thin-film filter,
wherein the first dielectric layer coats an entire portion of an inner wall of each opening of the plurality of openings of the metal thin-film filter; and
a second dielectric layer having a first refractive index lower than a second refractive index of the first dielectric layer, wherein
the second dielectric layer is above an incidence surface side of the metal thin-film filter and below an emitting surface side of the metal thin-film filter,
an electromagnetic wave is incident on the incidence surface side and transmitted to the emitting surface side, and
a thickness of the first dielectric layer is equal to or thinner than an effective wavelength of the transmitted electromagnetic wave in the second dielectric layer.
2. The optical filter according to claim 1 , wherein
a first real part of a first complex refractive index of a first material of the first dielectric layer is larger than a second real part of a second complex refractive index of a second material of the second dielectric layer,
the first complex refractive index is associated with the second refractive index of the first dielectric layer, and
the second complex refractive index is associated with the first refractive index of the second dielectric layer.
3. The optical filter according to claim 1 , wherein
a spacing between two openings of the plurality of openings of the metal thin-film filter is set to a distance equal to a wavelength of the electromagnetic wave to be transmitted, and
the spacing corresponds to a period.
4. The optical filter according to claim 3 , wherein
the wavelength of the electromagnetic wave is denoted by λ,
a first real part of a first complex refractive index of a first material of the first dielectric layer is denoted by N,
the first complex refractive index is associated with the second refractive index of the first dielectric layer, and
the spacing between the two openings of the metal thin-film filter is set to a distance of 0.5λ/N to 2.0λ/N.
5. The optical filter according to claim 1 , wherein
the metal thin-film filter comprises one of Aluminum (Al), Silver (Ag), Gold (Au), Copper (Cu), or Tungsten (W), or an alloy of at least one of Al, Ag, Au, Cu, or W.
6. The optical filter according to claim 1 , wherein
a thickness of the metal thin-film filter is set between 50 nm to 300 nm.
7. The optical filter according to claim 1 , wherein
the first dielectric layer comprises at least one of silicon nitride, hafnium oxide, aluminum oxide, titanium oxide, zirconium oxide, or tantalum oxide.
8. The optical filter according to claim 1 , wherein
the second dielectric layer comprises a material of at least one of silicon oxide or magnesium fluoride.
9. The optical filter according to claim 1 , wherein
a shape of each opening of the plurality of openings of the metal thin-film filter is a rectangular shape in which a horizontal to vertical ratio is different from 1:1.
10. The optical filter according to claim 1 , wherein
each opening of the plurality of openings of the metal thin-film filter is a slit,
a first side of the slit is longer than a second side of the slit,
the first side of the slit is longer than a wavelength of the incident electromagnetic wave,
the second side of the slit is shorter than the wavelength of the incident electromagnetic wave, and
the plurality of openings is aligned in a short side direction of the slit.
11. A solid state imaging device, comprising:
an optical filter including:
a metal thin-film filter that comprises a plurality of openings, wherein
the plurality of openings is periodically arranged in a triangular array in the metal thin-film filter,
in the triangular array a horizontal distance is different from a vertical distance,
the horizontal distance is a distance between a first opening of the plurality of openings and a second adjacent opening of the plurality of openings in a horizontal direction, and
the vertical distance is a distance between the first opening of the plurality of openings and a third adjacent opening of the plurality of openings in a vertical direction;
a first dielectric layer on a surface of the metal thin-film filter,
wherein the first dielectric layer coats an entire portion of an inner wall of each opening of the plurality of openings of the metal thin-film filter; and
a second dielectric layer having a first refractive index lower than a second refractive index of the first dielectric layer, wherein
the second dielectric layer is above an incidence surface side of the metal thin-film filter and below an emitting surface side of the metal thin-film filter,
an electromagnetic wave is incident on the incidence surface side and transmitted to the emitting surface side, and
a thickness of the first dielectric layer is equal to or thinner than an effective wavelength of the transmitted electromagnetic wave in the second dielectric layer.
12. An electronic apparatus, comprising:
a solid state imaging device including:
an optical filter including:
a metal thin-film filter that comprises a plurality of openings, wherein
the plurality of openings is periodically arranged in a triangular array in the metal thin-film filter,
in the triangular array a horizontal distance is different from a vertical distance,
the horizontal distance is a distance between a first opening of the plurality of openings and a second adjacent opening of the plurality of openings in a horizontal direction, and
the vertical distance is a distance between the first opening of the plurality of openings and a third adjacent opening of the plurality of openings in a vertical direction;
a first dielectric layer on a surface of the metal thin-film filter,
wherein the first dielectric layer coats an entire portion of an inner wall of each opening of the plurality of openings of the metal thin-film filter; and
a second dielectric layer having a first refractive index lower than a second refractive index of the first dielectric layer, wherein
the second dielectric layer is above an incidence surface side of the metal thin-film filter and below an emitting surface side of the metal thin-film filter,
an electromagnetic wave is incident on the incidence surface side and transmitted to the emitting surface side, and
a thickness of the first dielectric layer is equal to or thinner than a second wavelength of the transmitted electromagnetic wave in the second dielectric layer.