Multi-layer thin film stack for diffractive optical elements

1. An optical element, comprising:

a substrate;

a first anti-reflectance structure for a particular wavelength range formed on the substrate;

at least one layer disposed on a fractional portion of the first anti-reflectance structure; and

a second anti-reflectance structure for the particular wavelength range formed on the at least one layer,

wherein a depth between a first surface of the first anti-reflectance structure and a second surface of the second anti-reflectance structure, a first effective index of refraction of the first anti-reflectance structure, a second effective index of refraction of the second anti-reflectance structure, and a third index of refraction of the at least one layer are selected to form a diffractive optical element associated with a particular phase delay for a particular wavelength included in the particular wavelength range,

wherein the second effective index of refraction is different from the third index of refraction,

wherein the first anti-reflectance structure includes two or more layers with a corresponding index of refraction that is different from each other,

wherein the first anti-reflectance structure has a top layer that is an etch stop layer for the second anti-reflectance structure, and

wherein the first anti-reflectance structure, including the etch stop layer, and the second anti-reflectance structure, are formed of alternating layers of two materials.

2. The optical element of claim 1 , wherein the first anti-reflectance structure is formed onto a first side of the substrate; and

further comprising:

an anti-reflectance coating formed on a second side of the substrate.

3. The optical element of claim 1 , wherein at least one of the first anti-reflectance structure, the second anti-reflectance structure, or the at least one layer is formed using thin film deposition.

4. The optical element of claim 1 , wherein the first anti-reflectance structure includes a first silicon layer and a first silicon dioxide layer;

wherein the at least one layer includes a second silicon layer;

wherein the second anti-reflectance structure includes a second silicon dioxide layer; and

wherein the particular wavelength range is between approximately 840 nanometers and 860 nanometers.

5. The optical element of claim 1 , wherein the two materials comprise silicon and silicon dioxide.

6. The optical element of claim 1 , wherein the two materials comprise hydrogenated silicon and silicon dioxide.

7. The optical element of claim 1 , wherein the first anti-reflectance structure is formed from a first layer of a first material and a second layer of a second material;

wherein the at least one layer is formed from a third layer of the first material; and

wherein the second anti-reflectance structure is formed from the first layer, the second layer, the third layer, a fourth layer of the second material, and a fifth layer of the first material.

8. The optical element of claim 1 , wherein the first anti-reflectance structure is formed on a first side of the substrate; and

further comprising:

a third anti-reflectance structure for another particular wavelength range formed on a second side of the substrate;

another at least one layer disposed on a fractional portion of the third anti-reflectance structure; and

a fourth anti-reflectance structure for the other particular wavelength range formed on the other at least one layer.

9. The optical element of claim 1 , wherein the first anti-reflectance structure and the second anti-reflectance structure form a two-level relief profile.

10. The optical element of claim 1 , wherein the first anti-reflectance structure includes a first silicon layer and a first silicon dioxide layer;

wherein the at least one layer includes a second silicon layer;

wherein the second anti-reflectance structure includes a second silicon dioxide layer; and

wherein the particular wavelength range is between approximately 930 nanometers and 950 nanometers.

11. The optical element of claim 1 , wherein the first anti-reflectance structure includes a first silicon layer and a first silicon dioxide layer;

wherein the at least one layer includes a second silicon layer and a second silicon dioxide layer;

wherein the second anti-reflectance structure includes a third silicon layer; and

wherein the particular wavelength is between approximately 1540 nanometers and 1560 nanometers.

12. The optical element of claim 1 , wherein the particular wavelength is between approximately 840 nanometers and 940 nanometers.

13. The optical element of claim 1 , wherein the depth is between λ/4 and 3λ/4,

wherein λ represents the particular wavelength.

14. The optical element of claim 1 , wherein an effective refractive index of the optical element is between 2.0 and 3.0.

15. The optical element of claim 1 , wherein the particular phase delay is a π phase delay.

16. The optical element of claim 1 , wherein the particular phase delay is a non-π phase delay.

17. An optical element, comprising:

a substrate;

a first set of layers, with a first effective refractive index and formed from a first two or more layers with a first two or more different refractive indices, disposed on the substrate;

at least one spacer layer, with a particular refractive index, disposed on a fractional portion of the first set of layers; and

a second set of layers, with a second effective refractive index and formed from a second two or more layers with a second two or more different refractive indices, disposed on the at least one spacer layer,

wherein the first set of layers form a first anti-reflectance structure at a particular wavelength on the substrate,

wherein the first set of layers, the at least one spacer layer, and the second set of layers collectively form a second anti-reflectance structure at the particular wavelength on the substrate and form a diffractive optical element on the substrate with a particular phase delay for the particular wavelength,

wherein a depth between a first surface of the second set of layers and a second surface of the first set of layers forms the particular phase delay,

wherein the first anti-reflectance structure has a top layer that is an etch stop layer for the second anti-reflectance structure, and

wherein the first anti-reflectance structure, including the etch stop layer, and the second anti-reflectance structure, are formed of alternating layers of two materials.

18. The optical element of claim 17 , wherein the first anti-reflectance structure and the second anti-reflectance structure are formed onto a first side of the substrate; and

further comprising:

an anti-reflectance coating formed on a second side of the substrate.

19. A method, comprising:

depositing a plurality of layers onto a wafer,

wherein the depositing forms a first anti-reflectance structure for a particular wavelength beneath at least one layer formed on a fractional portion of the first anti-reflectance structure and a second anti-reflectance structure for the particular wavelength,

wherein an effective index of refraction of the second anti-reflectance structure is different from an index of refraction of the at least one layer,

wherein the first anti-reflectance structure includes two or more layers with a corresponding index of refraction that is different from each other,

wherein the second anti-reflectance structure is formed on top of the at least one layer,

wherein the first anti-reflectance structure has a top layer that is an etch stop layer for the second anti-reflectance structure, and

wherein the first anti-reflectance structure, including the etch stop layer, and the second anti-reflectance structure, are formed of alternating layers of two materials; and

etching a subset of layers of the plurality of layers to form a two-level relief profile, wherein the etching forms a diffractive optical element associated with a particular phase delay for the particular wavelength between the first anti-reflectance structure and the second anti-reflectance structure.

20. The optical element of claim 17 , wherein the two materials comprise:

silicon and silicon dioxide, or

hydrogenated silicon and silicon dioxide.