LAYERED WAVEGUIDE FABRICATION BY ADDITIVE MANUFACTURING
A multi-layer waveguide display includes a base waveguide layer, one or more grating couplers on one or two surfaces of the base waveguide layer, an overcoat layer on each grating coupler of the one or more grating couplers and filling grating grooves of the grating coupler, and a first waveguide layer stack on a first side of the base waveguide layer. The first waveguide layer stack includes one or more polymer layers. Each of the one or more polymer layers is characterized by a respective refractive index lower than the refractive index of the base waveguide layer. Each polymer layer is formed in a plurality of process cycles, where each process cycle includes dispensing a two-dimensional array of droplets of a resin material to form a thin layer and cross-linking the thin layer to form a sublayer of the polymer layer.
1 . A method of fabricating a multi-layer waveguide display, the method comprising:
obtaining a first waveguide layer including one or more grating couplers formed thereon, each grating coupler of the one or more grating couplers including an overcoat layer that fills grating grooves of the grating coupler and is characterized by a refractive index different from a refractive index of the first waveguide layer; and
forming a second waveguide layer on a first side of the first waveguide layer in a plurality of process cycles, each process cycle of the plurality of process cycles comprising:
depositing a thin layer of a first resin material on the first waveguide layer, the first resin material characterized by a refractive index lower than the refractive index of the first waveguide layer; and
cross-linking the thin layer of the first resin material to form a sublayer of the second waveguide layer.
2 . The method of claim 1 , wherein depositing the thin layer of the first resin material on the first waveguide layer includes dispensing a two-dimensional array of droplets of the first resin material on the first waveguide layer.
3 . The method of claim 1 , wherein depositing the thin layer of the first resin material on the first waveguide layer includes depositing the thin layer of the first resin material on selected but not all regions of the first waveguide layer.
4 . The method of claim 1 , wherein cross-linking the thin layer of the first resin material comprises curing the thin layer of the first resin material by electromagnetic radiation or thermal treatment.
5 . The method of claim 1 , wherein the thin layer of the first resin material is characterized by a thickness equal to or less than 10 μm.
6 . The method of claim 1 , wherein the first resin material comprises:
an actinic light curable moiety that includes acrylate, epoxide, vinyl, thiols, allyls, vinylether, allylethers, epoxy acrylates, urethane acrylates, polyester acrylates, or a combination thereof; and
a photoinitiator.
7 . The method of claim 1 , wherein the first resin material comprises nanoparticles of titanium oxide, zirconium oxide, hafnium oxide, tungsten oxide, zinc tellurium, gallium phosphide, or a combination thereof.
8 . The method of claim 1 , further comprising, before forming the second waveguide layer on the first side of the first waveguide layer, forming an adhesion promoting layer on the first waveguide layer.
9 . The method of claim 8 , wherein forming the adhesion promoting layer on the first waveguide layer comprises:
inkjetting or spin coating, on the first waveguide layer, a layer of epoxy acrylate, silane acrylate, silane epoxy, diacrylate, diepoxy, or a combination thereof; or
depositing, on the first waveguide layer, a thin SiO 2 layer or another inorganic material layer.
10 . The method of claim 1 , further comprising forming a third waveguide layer on the second waveguide layer in a second plurality of process cycles, each process cycle of the second plurality of process cycles comprising:
depositing a thin layer of a second resin material on the second waveguide layer, the second resin material characterized by a refractive index lower than the refractive index of the first resin material; and
cross-linking the thin layer of the second resin material.
11 . The method of claim 1 , further comprising forming a third waveguide layer on a second side of the first waveguide layer opposing the first side in a second plurality of process cycles, each process cycle of the second plurality of process cycles comprising:
depositing a thin layer of a second resin material on the second side of the first waveguide layer, the second resin material characterized by a refractive index same as or lower than the refractive index of the first waveguide layer; and
cross-linking the thin layer of the second resin material.
12 . A multi-layer waveguide display comprising:
a base waveguide layer;
one or more grating couplers on one or two surfaces of the base waveguide layer;
an overcoat layer on each grating coupler of the one or more grating couplers, wherein the overcoat layer fills grating grooves of the grating coupler and is characterized by a refractive index different from a refractive index of the base waveguide layer; and
a first waveguide layer stack on a first side of the base waveguide layer, the first waveguide layer stack including one or more polymer layers, wherein each of the one or more polymer layers is characterized by a respective refractive index lower than the refractive index of the base waveguide layer.
13 . The multi-layer waveguide display of claim 12 , wherein the first waveguide layer stack is characterized by a refractive index profile that decreases with an increase in a distance of the first waveguide layer stack from the base waveguide layer.
14 . The multi-layer waveguide display of claim 12 , further comprising a second waveguide layer stack on a second side of the base waveguide layer opposing the first side, the second waveguide layer stack including a second set of one or more polymer layers, wherein each polymer layer of the second set of one or more polymer layers is characterized by a respective refractive index lower than the refractive index of the base waveguide layer.
15 . The multi-layer waveguide display of claim 12 , wherein the first waveguide layer stack is characterized by:
a thickness of each of the one or more polymer layers greater than 100 μm;
a total thickness variation of the first waveguide layer stack less than 1 μm;
a root mean squared areal roughness of a surface of the first waveguide layer stack less than 1 nm;
a refractive index of the first waveguide layer stack between 1.45 and 2.0;
a density less than about 2 g/cm 3 ; or
a combination thereof.
16 . The multi-layer waveguide display of claim 12 , wherein the first waveguide layer stack includes acrylate, epoxide, vinyl, thiols, allyls, vinylether, allylethers, epoxy acrylates, urethane acrylates, polyester acrylates, or a combination thereof.
17 . The multi-layer waveguide display of claim 12 , wherein the first waveguide layer stack includes nanoparticles dispersed in the one or more polymer layers, the nanoparticles comprising nanoparticles of titanium oxide, zirconium oxide, hafnium oxide, tungsten oxide, zinc tellurium, gallium phosphide, or a combination thereof.
18 . The multi-layer waveguide display of claim 12 , wherein the one or more grating couplers are on two surfaces of the base waveguide layer and include slanted surface-relief gratings.
19 . The multi-layer waveguide display of claim 12 , further comprising an antireflection layer on the first waveguide layer stack.
20 . The multi-layer waveguide display of claim 12 , further comprising an adhesion promoting layer between the base waveguide layer and the first waveguide layer stack, wherein the adhesion promoting layer includes:
a layer of epoxy acrylate, silane acrylate, silane epoxy, diacrylate, diepoxy, or a combination thereof; or
a thin layer of SiO 2 or another inorganic material.
21 . The multi-layer waveguide display of claim 12 , wherein the first waveguide layer stack is on selected but not all regions of the base waveguide layer.