Diffractive optical elements with mitigation of rebounce-induced light loss and related systems and methods
Display devices include waveguides with in-coupling optical elements that mitigate re-bounce of in-coupled light to improve overall in-coupling efficiency and/or uniformity. A waveguide receives light from a light source and/or projection optics and includes an in-coupling optical element that in-couples the received light to propagate by total internal reflection in a propagation direction within the waveguide. Once in-coupled into the waveguide the light may undergo re-bounce, in which the light reflects off a waveguide surface and, after the reflection, strikes the in-coupling optical element. Upon striking the in-coupling optical element, the light may be partially absorbed and/or out-coupled by the optical element, thereby effectively reducing the amount of in-coupled light propagating through the waveguide. The in-coupling optical element can be truncated or have reduced diffraction efficiency along the propagation direction to reduce the occurrence of light loss due to re-bounce of in-coupled light, resulting in less in-coupled light being prematurely out-coupled and/or absorbed during subsequent interactions with the in-coupling optical element.
1. A method of making an optical waveguide structure comprising a reflective layer, the method comprising:
providing an optical waveguide comprising a surface, the surface comprising a region comprising a pattern of protrusions;
depositing a liquid mixture on at least part of the region, the liquid mixture comprising a metal salt;
forming the reflective layer by coating the region with the metal of the metal salt, wherein coating the region comprises precipitating the metal onto the region by dissociating metal from the metal salt; and
removing residual liquid mixture material following the precipitating of the metal.
2. The method of claim 1 , wherein dissociating metal from the metal salt comprises reducing the metal salt by exposure to a reducing agent.
3. The method of claim 2 , wherein the reducing agent comprises at least one of a carbohydrate comprising an alpha-hydroxy aldehyde or a carbohydrate comprising an alpha-hydroxy ketone.
4. The method of claim 2 , wherein the liquid mixture comprises the reducing agent.
5. The method of claim 2 , further comprising adding the reducing agent to the liquid mixture after depositing the liquid mixture.
6. The method of claim 1 , wherein forming the reflective layer comprises selectively forming the reflective layer on the region while leaving one or more areas around the region free of the metal.
7. The method of claim 6 , wherein the surface of the waveguide comprises a vertically-extending wall that defines a volume in the region, wherein depositing the liquid mixture comprises depositing the depositing mixture into the volume.
8. The method of claim 1 , wherein the protrusions define a diffractive optical element, wherein the protrusions and reflective layer form a reflective diffractive optical element.
9. The method of claim 8 , wherein the diffractive optical element is an incoupling optical element configured to redirect incident light at angles such that the light propagates through the waveguide by total internal reflection.
10. The method of claim 1 , wherein the protrusions comprise photoresist.
11. The method of claim 1 , further comprising:
forming an additional reflective layer on an additional optical waveguide by depositing the liquid mixture on an additional region of a surface of the additional optical waveguide, wherein the additional reflective optical element is configured to reflect incident light; and
attaching at least the additional waveguide to a surface of the waveguide, thereby producing a stack of waveguides.
12. The method of claim 1 , wherein a hydrophilicity of the region is increased by selectively pretreating, prior to depositing the liquid mixture, the region with one or more agents selected from the group consisting of: a plasma, a surfactant, a coating, a wet chemical etchant, and a catalyst.
13. The method of claim 12 , wherein at least one of:
pretreating the region with plasma comprises performing an atmospheric plasma treatment;
the wet chemical etch agent comprises chromic acid;
the coating comprises silica; and/or
the catalyst comprises tin or palladium.
14. The method of claim 1 , further comprising, prior to depositing the liquid mixture, selectively applying a catalyst to the region, the catalyst configured to expedite reduction of the metal salt.
15. The method of claim 1 , wherein the liquid mixture consists essentially of the metal salt, a reducing agent, and a base.
16. The method of claim 1 , wherein the reflective layer is pure or substantially pure metal.
17. The method of claim 1 , wherein the liquid mixture is deposited on the region by at least one of: nano-dispensing, micro-dispensing, micropipetting, inkjet printing, and spraying.
18. The method of claim 1 , wherein removing the residual liquid mixture material comprises rinsing the optical waveguide.
19. The method of claim 1 , further comprising depositing a capping layer on the reflective layer.
20. The method of claim 1 , wherein the reflective layer is free or substantially free of pinholes.
21. The method of claim 1 , wherein the metal is silver.