Optical elements based on polymeric structures incorporating inorganic materials
The present disclosure relates to display systems and, more particularly, to augmented reality display systems. In one aspect, a method of fabricating an optical element includes providing a substrate having a first refractive index and transparent in the visible spectrum. The method additionally includes forming on the substrate periodically repeating polymer structures. The method further includes exposing the substrate to a metal precursor followed by an oxidizing precursor. Exposing the substrate is performed under a pressure and at a temperature such that an inorganic material comprising the metal of the metal precursor is incorporated into the periodically repeating polymer structures, thereby forming a pattern of periodically repeating optical structures configured to diffract visible light. The optical structures have a second refractive index greater than the first refractive index.
1. An optical element comprising:
a substrate having a first refractive index; and
a pattern of periodically repeating structures formed on the substrate and configured to diffract light, the structures having a second refractive index greater than the first refractive index, the structures comprising a polymer-based material that includes a polymer and inorganic material comprising one or more of a metal oxide, a metal nitride, and a metal oxynitride, wherein the inorganic material is incorporated within the polymer, wherein adjacent structures of the pattern of periodically repeating structures are separated by respective spaces such that the polymer-based material extends discontinuously over the substrate and a surface of the substrate is exposed in the spaces.
2. The optical element of claim 1 , wherein the inorganic material comprises one or more of the metal oxide, the metal nitride, and the metal oxynitride of at least one transition metal.
3. The optical element of claim 2 , wherein the at least one transition metal includes one or more of aluminum, zinc, zirconium, hafnium, titanium, and tantalum.
4. The optical element of claim 1 , wherein the inorganic material includes one or more of a stoichiometric compound and a sub stoichiometric compound.
5. The optical element of claim 1 , wherein the inorganic material comprises two or more of the metal oxide, the metal nitride, and the metal oxynitride.
6. The optical element of claim 1 , wherein each of the structures includes a first region that includes the polymer and a second region that includes the polymer infiltrated with the inorganic material.
7. The optical element of claim 6 , wherein the second region is a surface region of a structure.
8. The optical element of claim 6 , wherein the first region does not include the inorganic material.
9. The optical element of claim 6 , wherein the first region includes a concentration of the inorganic material that is less than 40%, 30%, 20%, 10%, 5%, 1%, 0.5%, or 0.1%.
10. The optical element of claim 6 , wherein the second region includes a concentration of the inorganic material that is greater than 40%, 50%, 60%, 70%, 80%, or 90%.
11. The optical element of claim 1 , wherein the second refractive index is greater than 1.7, 1.8, 1.9, 2.0, or 2.1.
12. The optical element of claim 1 , wherein the second refractive index is greater than the first refractive index by at least 0.2, 0.4, 0.6, 0.8, or 1.0.
13. The optical element of claim 1 , wherein the polymer is a photoresist.
14. The optical element of claim 1 , wherein the pattern of periodically repeating structures is configured as one or more of an incoupling grating, an eye pupil expander, and an orthogonal pupil expander.
15. The optical element of claim 1 , wherein the substrate has a refractive index greater than 1.5.
16. The optical element of claim 1 , wherein the periodically repeating structures comprise nanobeams arranged as a metasurface, the metasurface comprising a plurality of repeating unit cells, wherein each unit cell comprises:
a first set of nanobeams formed by one or more first nanobeams; and
a second set of nanobeams formed by one or more second nanobeams disposed adjacent to the one or more first nanobeams and separated from each other by a sub-wavelength spacing, and wherein the one or more first nanobeams and the one or more second nanobeams are elongated in different orientation directions.
17. The optical element of claim 16 , wherein the one or more first nanobeams and the one or more second nanobeams are oriented at an angle relative to each other to cause a phase difference between the light diffracted by the one or more first nanobeams and the light diffracted by the one or more second nanobeams.
18. The optical element of claim 16 , wherein the one or more first nanobeams and the one or more second nanobeams are oriented in orientation directions that are rotated by about 90 degrees relative to each other.
19. The optical element of claim 16 , wherein the unit cells repeat at a period less than or equal to a wavelength of the light.
20. The optical element of claim 16 , wherein the one or more first nanobeams and the one or more second nanobeams have a height smaller than a wavelength of the light.
21. The optical element of claim 1 , wherein the polymer-based material is completely removed in the spaces between adjacent structures of the pattern of periodically repeating structures.
22. The optical element of claim 1 , wherein each of the structures includes an internal base region that includes the polymer and a second external surface region that includes the polymer infiltrated with the inorganic material.