Diffractive optical element
A diffractive optical element may include sub-wavelength period stack-and-gap structured layers providing transmissive phase delay at a wavelength. The sub-wavelength period stack-and-gap structured layers may include a set of thin anti-reflection layers that are index matched to an environment or a substrate over a range of fill factors of the sub-wavelength period.
1. A diffractive optical element, comprising:
multiple layers on a surface of a substrate,
wherein the multiple layers include a set of holes defining sub-wavelength periods and providing phase delay,
wherein holes, of the set of holes, have different sizes,
wherein the multiple layers include a set of anti-reflection layers that are index matched to an environment, or the substrate, at each different hole size, and
wherein a transmission efficiency of the diffractive optical element is greater than 85% at each different hole size.
2. The diffractive optical element of claim 1 , wherein the set of holes is a set of discrete holes.
3. The diffractive optical element of claim 1 , wherein the different sizes of the holes define different fill factors within a range of fill factors of the diffractive optical element.
4. The diffractive optical element of claim 3 , wherein the range of fill factors includes at least one fill factor less than 30% fill factor and at least one other fill factor greater than 70% fill factor.
5. The diffractive optical element of claim 1 , wherein a hole, of the set of holes, is a particular shape, and wherein the particular shape is at least one of a circle, a square, or a hexagon.
6. The diffractive optical element of claim 1 , wherein the set of holes forms a castellated surface in two dimensions coplanar to a top surface of the substrate.
7. The diffractive optical element of claim 1 , wherein the set of holes forms a castellated surface in a single dimension coplanar to a top surface of the substrate.
8. The diffractive optical element of claim 1 , wherein the set of anti-reflection layers are index matched to the environment and to the substrate over a range of fill factors of the diffractive optical element.
9. The diffractive optical element of claim 1 , wherein the transmission efficiency of the diffractive optical element is greater than 95% at each different hole size.
10. The diffractive optical element of claim 1 , wherein a maximum transmissive phase delay for a first sub-wavelength period is greater than or equal to 2π relative to a second sub-wavelength period.
11. The diffractive optical element of claim 10 , wherein the first sub-wavelength period is defined by a hole, of the set of holes, at a center of the first sub-wavelength period.
12. The diffractive optical element of claim 1 , wherein a maximum transmissive phase delay for a first sub-wavelength period is greater than or equal to 4π relative to a second sub-wavelength period.
13. The diffractive optical element of claim 12 , wherein the first sub-wavelength period is defined by a hole, of the set of holes, at an edge of the first sub-wavelength period.
14. A diffractive optical element, comprising:
multiple layers providing phase delay,
wherein the multiple layers include a set of holes defining sub-wavelength periods,
wherein holes, of the set of holes, have different sizes, and
wherein the multiple layers include a set of anti-reflection layers that are index matched to an environment, or a substrate, over a range of the different hole sizes associated with the set of holes, and
wherein a transmission efficiency of the diffractive optical element is greater than 85% at each different hole size.
15. The diffractive optical element of claim 14 , wherein the set of holes are etched into one or more of the multiple layers.
16. The diffractive optical element of claim 14 , wherein the set of holes is a set of discrete holes.
17. The diffractive optical element of claim 14 , wherein a size of one or more holes, of the set of holes, defines a fill factor, within a range of fill factors, of the diffractive optical element.
18. The diffractive optical element of claim 14 , wherein a hole, of the set of holes, is a particular shape, and wherein the particular shape is at least one of a circle, a square, or a hexagon.
19. A diffractive optical element, comprising:
a set of layers including a set of anti-reflection layers,
wherein the set of layers includes discrete gaps etched into the set of layers,
the discrete gaps extending through the set of layers and through the set of anti-reflection layers, and
the discrete gaps include gaps of different sizes,
wherein the set of anti-reflection layers are index matched to an environment, or a substrate, for each different gap size of the discrete gaps, and
wherein a transmission efficiency of the diffractive optical element is greater than 85% at each different gap size.
20. The diffractive optical element of claim 19 , wherein the diffractive optical element is disposed on a first side of the substrate and another diffractive optical element is disposed on a second side of the substrate.