Refractive boundary elements, devices, and materials
View Patent ↗An optical device includes an interface between two or more media. The refractive indices, orientations of media, and alignment relative to a propagating wave define a refractive boundary at which reflections may be reduced or eliminated, and at which, for certain incident angles, rays may be refracted on the same side of the normal as the incident ray.
1. An optical element comprising:
a first layer of a first anisotropic material having a first surface, the first layer having a first optical index of refraction corresponding to a first internal axis and a second optical index of refraction corresponding to a second internal axis, the first and second indices being different;
a second layer of a material different from the first anisotropic material and having a second surface in intimate contact with the first surface, the second layer having a third optical index of refraction in a region adjacent to the second surface that is a geometric mean of the first and second optical indices of refraction, the second layer having a non-zero index gradient from the region adjacent to the second surface,
the second layer including a third surface separated from the second surface; and
a third layer of a third material having a fourth surface in intimate contact with the third surface,
wherein the third material is oriented relative to the second material an angle at which the second material principal axis and third material principal axis are related according to the equation:
β
2
cos
2
ϕ
2
+
1
β
2
sin
2
ϕ
2
=
β
3
cos
2
ϕ
3
+
1
β
3
sin
2
ϕ
3
where:
β 2 is a ratio of dielectric constants of the second material relative to its principal material axis and another material axis; β 3 is a ratio of dielectric constants of the third material relative to its principal material axis and another material axis; and φ 2 is an orientation angle of the principal material axis of the second material and φ 3 is an orientation angle of the principal material axis of the third material in a region adjoining the second surface.
2. The optical element of claim 1 wherein the first anisotropic material is biaxial.
3. The optical element of claim 1 wherein the second layer is operable to produce a polarization rotation in a wave traveling from the region adjacent to the second surface to a location separated from the second surface.
4. The optical element of claim 1 wherein the first internal axis and the second internal axis define a plane.
5. The optical element of claim 1 wherein the material different from the anisotropic material is an isotropic material.
6. The optical element of claim 1 wherein second material has a fourth index of refraction in a region adjacent to the third surface, the fourth index of refraction differing from the third index of refraction, and wherein the third layer has an index of refraction that has a geometric mean substantially equal to the fourth index of refraction.
7. The optical element of claim 1 wherein the third material is oriented relative to the second material an angle at which reflected energy at a boundary between the second and third materials is substantially zero.
8. The optical element of claim 1 wherein the material different from the first anisotropic material is rotated relative to the anisotropic material.
9. The optical device of claim 1 wherein the third layer includes a second anisotropic material, and wherein the first and second anisotropic materials are the same type of material.
10. The optical device of claim 1 wherein the third layer includes a second anisotropic material, and wherein the first and second anisotropic materials are different types of material.
11. The optical element of claim 1 wherein the third layer includes a second anisotropic material, and wherein the second anisotropic material in the third layer is oriented substantially identically with the first anisotropic material in the first layer.
12. An optical element comprising:
a first layer of a first anisotropic material having a first surface, the first layer having a first optical index of refraction corresponding to a first internal axis and a second optical index of refraction corresponding to a second internal axis, the first and second indices being different; and
a second layer of a material different from the first anisotropic material and having a second surface in intimate contact with the first surface, the second layer having a third optical index of refraction in a region adjacent to the second surface that is a geometric mean of the first and second optical indices of refraction, the second layer having a non-zero index gradient from the region adjacent to the second surface,
wherein the first and second materials are materials having principal material axes, and wherein the angle of rotation of the material different from the first anisotropic material relative to the first anisotropic material substantially satisfies the relationship:
β 1 ∈ 1 2 =β 2 ∈ 2 2
β
1
cos
2
ϕ
1
+
1
β
1
sin
2
ϕ
1
=
β
2
cos
2
ϕ
2
+
1
β
2
sin
2
ϕ
2
where:
∈ 1 is a dielectric constant of the first material relative to its principal material axis; ∈ 2 is a dielectric constant of the second material relative to its principal material axis;
β 1 ∈ 1 is a dielectric constant of the first anisotropic material relative to a second material axis; β 2 ∈ 2 is a dielectric constant of the second material relative to a second material axis; and
φ 1 is an orientation angle of the principal material axis of the first anisotropic material and φ 2 is an orientation angle of the principal material axis of the second material in a region adjoining the second surface.
13. The optical element of claim 12 wherein the anisotropic material is a crystalline material having crystal planes.
14. The optical element of claim 12 wherein the geometric mean is the square root of the first optical index of refraction times the second optical index of refraction.
15. The optical element of claim 12 wherein the first layer of anisotropic material is a planar slab having parallel faces.
16. The optical element of claim 12 wherein the first layer of anisotropic material includes an input face configured to receive an optical beam.
17. The optical element of claim 12 wherein the input face is non-parallel relative to the first surface.
18. The optical element of claim 12 wherein the first surface includes a non-infinite radius of curvature.