Anti-reflective coatings on optical waveguides
An anti-reflective waveguide assembly comprising a waveguide substrate having a first index of refraction, a plurality of diffractive optical elements disposed upon a first surface of the waveguide and an anti-reflective coating disposed upon a second surface of the waveguide. The anti-reflective coating preferably increases absorption of light through a surface to which it is applied into the waveguide so that at least 97 percent of the light is transmitted. The anti-reflective coating is composed of four layers of material having different indices of refraction that the first index of refraction and an imaginary refractive index less than 1×10 −3 but preferably less than 5×10 −4 .
1. An anti-reflective waveguide, comprising:
a planar waveguide substrate having a first index of refraction, the planar waveguide substrate being transparent and having first and second opposing surfaces;
a plurality of diffractive optical elements disposed upon the first surface of the waveguide, the second surface opposing the first surface being flat; and
an anti-reflective coating disposed upon the second surface of the waveguide, wherein the waveguide is planar and configured to propagate light by total internal reflection between the plurality of diffractive optical elements and the anti-reflective coating in a substantially first direction, and outcouple light in a second direction substantially orthogonal to the first direction, wherein the light propagating by total internal reflection comprises an s polarization component and a p polarization component, wherein the anti-reflective coating is configured to reduce phase retardation between the two components such that an angle of incidence of the s component is substantially similar to that of the p component through the waveguide for a select color of the light, the anti-reflective coating being transparent and improving transmission of light therethrough.
2. The anti-reflective waveguide of claim 1 , wherein anti-reflective coating has no phase retardation, it only imparts a phase shift to the output, with no change of polarization state or magnitude.
3. The anti-reflective waveguide of claim 2 , wherein:
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4. The anti-reflective waveguide of claim 2 , wherein select color has a first wavelength light the reduce phase retardation is similar for the first wavelength and for a second wavelength that is different from the first wavelength.
5. The anti-reflective waveguide of claim 1 , wherein the anti-reflective coating reduces reflection from and increases transmission of light through the second surface into the waveguide.
6. The anti-reflective waveguide of claim 5 , wherein at least 97 percent of the light is transmitted through the second surface.
7. The anti-reflective waveguide of claim 1 , wherein the waveguide substrate is glass and the anti-reflective coating comprises a layer of MgF 2 .
8. The anti-reflective waveguide of claim 7 , wherein the layer of MgF 2 has a thickness between 75 and 125 nm.
9. The anti-reflective waveguide of claim 7 , wherein the anti-reflective coating comprises a layer of SiO 2 .
10. The anti-reflective waveguide of claim 8 , wherein the layer of MgF 2 is disposed immediately adjacent to the second surface.
11. The anti-reflective waveguide of claim 10 , wherein a layer of SiO 2 is disposed upon the layer of MgF 2 .
12. The anti-reflective waveguide of claim 11 , wherein a cumulative index of refraction of the anti-reflective coating has an imaginary refractive index component value less than 5×10 −4 .
13. The anti-reflective waveguide of claim 11 , wherein a cumulative index of refraction of the anti-reflective coating has an imaginary refractive index component value between 5×10 −4 and 1×10 −3 .
14. The anti-reflective waveguide of claim 1 , wherein the anti-reflective coating is comprised less than eight layers alternating between a first material and a second material.
15. The anti-reflective waveguide of claim 14 , wherein the anti-reflective coating consists of four layers.
16. The anti-reflective waveguide of claim 14 , wherein the first material has comparatively higher index of refraction than the second material.
17. The anti-reflective waveguide of claim 14 , wherein the first material is TiO 2 .
18. The anti-reflective waveguide of claim 14 , wherein each layer of TiO 2 has an index of refraction greater than 2.
19. The anti-reflective waveguide of claim 14 , wherein the second material is SiO 2 .
20. The anti-reflective waveguide of claim 19 , wherein each layer of SiO 2 has an index of refraction between 1.45 and 1.58.
21. The anti-reflective waveguide of claim 20 , wherein a cumulative index of refraction of the anti-reflective coating has an imaginary refractive index component value less than 5×10 −4 .
22. The anti-reflective waveguide of claim 20 , wherein a cumulative index of refraction of the anti-reflective coating has an imaginary refractive index component value between 5×10 −4 and 1×10 −3 .
23. The anti-reflective waveguide of claim 1 , wherein a cumulative index of refraction of the anti-reflective coating has an imaginary refractive index component value less than 5×10 −4 .
24. An anti-reflective waveguide, comprising:
a planar waveguide substrate having a first index of refraction;
a plurality of diffractive optical elements disposed upon a first surface of the waveguide; and
an anti-reflective coating disposed upon a second surface of the waveguide, wherein the waveguide is planar and configured to propagate light by total internal reflection between the plurality of diffractive optical elements and the anti-reflective coating in a substantially first direction, and outcouple light in a second direction substantially orthogonal to the first direction, wherein the light propagating by total internal reflection comprises an s polarization component and a p polarization component, wherein the anti-reflective coating is configured to reduce phase retardation between the two components such that an angle of incidence of the s component is substantially similar to that of the p component through the waveguide for a select color of the light, wherein anti-reflective coating has no phase retardation, it only imparts a phase shift to the output, with no change of polarization state or magnitude and
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25. An anti-reflective waveguide, comprising:
a planar waveguide substrate comprising a layer of glass having a first index of refraction;
a plurality of diffractive optical elements disposed upon a first surface of the waveguide; and
an anti-reflective coating comprising a layer of MgF 2 disposed upon a second surface of the waveguide, wherein the waveguide is planar and configured to propagate light by total internal reflection between the plurality of diffractive optical elements and the anti-reflective coating in a substantially first direction, and outcouple light in a second direction substantially orthogonal to the first direction, wherein the light propagating by total internal reflection comprises an s polarization component and a p polarization component, wherein the anti-reflective coating is configured to reduce phase retardation between the two components such that an angle of incidence of the s component is substantially similar to that of the p component through the waveguide for a select color of the light.