Light detector
The light detector includes a light detection substrate having at least one light receiving region and a light incident surface on which a detection target light is incident, and a meta-lens including a plurality of unit structures arranged in a grid pattern and disposed on the light incident surface to focus the detection target light. When viewed in a thickness direction of the light detection substrate, an opening region in which no unit structure is formed is provided in a region including a center of the meta-lens.
1. A light detector comprising:
a light detection substrate having at least one light receiving region and a light incident surface on which a detection target light is incident; and
a meta-lens configured by a plurality of unit structures arranged in a grid pattern and disposed on the light incident surface to focus the detection target light,
wherein when viewed in a thickness direction of the light detection substrate, an opening region in which the unit structure is not formed is provided in a region including a center of the meta-lens,
the plurality of unit structures are configured such that a phase distribution of the meta-lens follows a quadratic phase pattern,
a width of each unit structure constituting the meta-lens is set such that phase Φ (x, y) at each coordinate (x, y) satisfies the following Equation (1), and
in the Equation (1), the coordinate (x, y) is two dimensional coordinate in a case where the center of the meta-lens is set as an origin (0, 0) when viewed in the thickness direction, λ eff is an effective wavelength of the detection target light passing through the meta-lens, and f is a focal length in accordance with a maximum angle between the detection target light passing through the meta-lens and an optical axis of the meta-lens
φ
(
x
,
y
)
=
-
2
π
λ
eff
2
f
(
x
2
+
y
2
)
2
.
(
1
)
2. The light detector according to claim 1 , further comprising:
a dielectric layer disposed between the light detection substrate and the meta-lens, and having a refractive index lower than that of the light detection substrate.
3. The light detector according to claim 1 , wherein a numerical aperture NA of the meta-lens is set so as to satisfy the following Equation (2), and in the Equation (2), λ eff is the effective wavelength of the detection target light passing through the meta-lens, and P is a period in which the plurality of unit structures are arranged
λ
eff
4
*
P
<
N
A
<
λ
eff
2
*
P
.
(
2
)
4. The light detector according to claim 1 , wherein when viewed in the thickness direction, the opening region has a rectangular shape.
5. The light detector according to claim 1 , wherein the light detection substrate includes an avalanche photodiode.
6. The light detector according to claim 1 , wherein when viewed in the thickness direction, the meta-lens is formed to overlap both an adjacent region adjacent to the light receiving region and a peripheral region inside of the light receiving region along a boundary between the light receiving region and the adjacent region.
7. The light detector according to claim 1 , wherein
the meta-lens is formed such that a first distance is shorter than a second distance, and
the second distance is a distance in the thickness direction from the meta-lens to a focus point set by the meta-lens, and
the first distance is a distance in the thickness direction from the meta-lens to a light-condensing point formed at a position closer to the light incident surface than the focus point due to the opening region being provided.
8. The light detector according to claim 7 , wherein the meta-lens is formed such that the first distance is 40% or more and 90% or less of the second distance.
9. The light detector according to claim 8 , wherein the meta-lens is formed such that the first distance is not less than 50% and not more than 80% of the second distance.
10. The light detector according to claim 1 , wherein when viewed in the thickness direction, a width of the opening region is equal to or greater than a half of a width of the meta-lens.