Three-dimensional diffractive structure, method for making, and applications thereof
Three-dimensional grating device includes two (crossed) diffraction gratings, exhibits diffraction efficiency substantially independent of the incident polarization inside an optical communication spectral window from 1.5-1.6 μm. The gratings are characterized by different periods in two directions, chosen to support only one dispersive diffraction order in addition to the zero-(specular) order. Gratings may be orthogonal. Exemplary grating profiles include but are not limited to sinusoidal and truncated pyramidal (trapezoidal) profiles. A method for diffracting polarization independent light with 90% or higher efficiency. Applications include various wavelength control devices particularly useful in telecommunications.
1. A three-dimensional diffractive device, comprising:
a substrate having a diffracting structure, wherein the structure further comprises:
a first periodic diffracting structure having a periodicity, d x , in a first direction, and a groove depth, h x , characterized by only a single dispersing diffracting plane that supports a single propagating first-dispersing-order of light and a zero-specular order; and
a second periodic structure having a periodicity, d z , in a second direction that is different than the first direction, and a groove depth, h z , that supports only a zero-specular order for the periodicity d z , wherein the device has a working spectral interval that is related to the periods d x , d z , as follows, where λ is the light wavelength, θ x is the projection of the angle of incidence on a plane parallel to the direction of the first periodicity, and θ z is the projection of the angle of incidence on a plane parallel to the direction of the second periodicity:
for the existence of the first diffractive order created by the first periodicity:
|sin θ x −λ/d x |<1;
for the absence of higher orders created by the first periodicity:
|sin θ x +λ/d x |>1;
|sin θ x −2 λ/d x |>1;and
for the absence of non-specular orders created by the second periodicity:
|sin θ z −λ/d z |>1.
2. The diffractive device of claim 1 , wherein the groove depths are constant for each periodic structure.
3. The diffractive device of claim 1 , wherein the first and second periodic structures are sinusoidal and have a grating profile, f(x, z), expressed as
f ( x,z )=( h x /2)sin( K x x )+( h z /2)sin( K z z ),
where groove numbers K x =2π/d x and K z =2π/d z .
4. The diffractive device of claim 1 , wherein the first and second periodic structures are three-dimensional diffracting structures.
5. The diffractive device of claim 4 , wherein the three-dimensional diffracting structures are vertical cylinders.
6. The diffractive device of claim 4 , wherein the three-dimensional diffracting structures are pyramids.
7. The diffractive device of claim 4 , wherein the three-dimensional diffracting structures are truncated pyramids.
8. The diffractive device of claim 4 , wherein the three-dimensional diffracting structures are conic forms.
9. The diffractive device of claim 1 , wherein the diffracting structure includes a high reflectance metallic layer.
10. The diffractive device of claim 9 , wherein the metallic layer has a thickness from about 50 nanometers to 150 nanometers.
11. The diffractive device of claim 9 , wherein the diffracting structure is covered with a dielectric layer.
12. The diffractive device of claim 11 , wherein the dielectric layer has a thickness of about 50 nanometers.
13. The diffractive device of claim 1 , wherein the first and second periodic structures comprise at least two alternating layers of a high index dielectric material and a low index dielectric material.
14. The diffractive device of claim 1 , wherein the substrate has a curvature.
15. A three-dimensional diffractive device, comprising:
a substrate having a diffracting structure, wherein the structure further comprises:
a first periodic diffracting structure having a periodicity, d x , in a first direction, and a groove depth, h x , characterized by only a single dispersing diffracting plane that supports a single propagating first-dispersing-order of light and a zero-specular order; and
a second periodic structure having a periodicity, d z , in a second direction that is different than the first direction, and a groove depth, h z , that supports only a zero-specular order for the periodicity d z , wherein the first direction is orthogonal to the second direction.
16. The diffractive device of claim 15 , wherein the groove depths are constant for each periodic structure.
17. The diffractive device of claim 15 , wherein the first and second periodic structures are sinusoidal and have a grating profile, f(x, z), expressed as f(x, z)=(h x /2) sin(K x x)+(h z /2)sin(K z z), where groove numbers K x =2π/d x and K z =2π/d 2 .
18. The diffractive device of claim 15 , wherein the first and second periodic structures are three-dimensional diffracting structures.
19. The diffractive device of claim 18 , wherein the three-dimensional diffracting structures are vertical cylinders.
20. The diffractive device of claim 18 , wherein the three-dimensional diffracting structures are pyramids.
21. The diffractive device of claim 18 , wherein the three-dimensional diffracting structures are truncated pyramids.
22. The diffractive device of claim 18 , wherein the three-dimensional diffracting structures are conic forms.
23. The diffractive device of claim 15 , wherein the diffracting structure includes a high reflectance metallic layer.
24. The diffractive device of claim 23 , wherein the metallic layer has a thickness from about 50 nanometers to 150 nanometers.
25. The diffractive device of claim 23 , wherein the diffracting structure is covered with a dielectric layer.
26. The diffractive device of claim 25 , wherein the dielectric layer has a thickness of about 50 nanometers.
27. The diffractive device of claim 15 , wherein the first and second periodic structures comprise at least two alternating layers of a high index dielectric material and a low index dielectric material.
28. A three-dimensional diffractive device, comprising:
a substrate having a diffracting structure, wherein the structure further comprises:
a first periodic diffracting structure having a periodicity, d x , in a first direction, and a groove depth, h x , characterized by only a single dispersing diffracting plane that supports a single propagating first-dispersing-order of light and a zero-specular order; and
a second periodic structure having a periodicity, d z , in a second direction that is different than the first direction, and a groove depth, h z , that supports only a zero-specular order for the periodicity d z , wherein h x =h y .
29. The diffractive device of claim 28 , wherein the groove depths are constant for each periodic structure.
30. The diffractive device of claim 28 , wherein the first and second periodic structures are sinusoidal and have a grating profile, f(x, z), expressed as f(x, z)=(h x /2) sin(K x x)+(h z /2)sin(K z z), where groove numbers K x =2π/d, and K z =2π/d z .
31. The diffractive device of claim 28 , wherein the substrate has a curvature.