Facebook Patent | Curable Formulation With High Refractive Index And Its Application In Surface Relief Grating Using Nanoimprinting Lithography

Patent: Curable Formulation With High Refractive Index And Its Application In Surface Relief Grating Using Nanoimprinting Lithography

Publication Number: 20200249568

Publication Date: 20200806

Applicants: Facebook

Abstract

Disclosed herein is a nanoimprint lithography (ML) precursor material comprising a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component. According to certain embodiments, further disclosed herein are a cured NIL material made by curing the NIL precursor material, a NIL grating comprising the cured NIL material, an optical component comprising the NIL grating, and methods for forming the NIL grating and the optical component using a NIL process.

RELATED APPLICATIONS

[0001] This application claims the benefit of, and priority to, U.S. Provisional Patent Application Ser. No. 62/801,554, filed on Feb. 5, 2019 and U.S. Provisional Patent Application Ser. No. 62/968,057, filed on Jan. 30, 2020, both of which are incorporated by reference herein in their entireties.

[0002] This application is related to U.S. patent application Ser. No. 16/778,492, filed Jan. 31, 2020, which is incorporated by reference herein in its entirety.

BACKGROUND

[0003] An artificial reality system, such as a head-mounted display (HMD) or heads-up display (HUD) system, generally includes a near-eye display (e.g., a headset or a pair of glasses) configured to present content to a user via an electronic or optic display within, for example, about 10-20 mm in front of the user’s eyes. The near-eye display may display virtual objects or combine images of real objects with virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user may view both images of virtual objects (e.g., computer-generated images (CGIs)) and the surrounding environment by, for example, seeing through transparent display glasses or lenses (often referred to as optical see-through).

[0004] One example optical see-through AR system may use a waveguide-based optical display, where light of projected images may be coupled into a waveguide (e.g., a substrate), propagate within the waveguide, and be coupled out of the waveguide at different locations. In some implementations, the light of the projected images may be coupled into or out of the waveguide using a diffractive optical element, such as a slanted surface-relief grating. To achieve desired performance, such as high efficiency, low artifact, and angular selectivity, deep surface-relief gratings with large slanted angles and wide ranges of grating duty cycles may be used. However, fabricating the slanted surface-relief grating with the desired profile at a high fabrication speed and high yield remains a challenging task.

SUMMARY

[0005] This disclosure relates generally to waveguide-based near-eye display system. More specifically, this disclosure relates to curable formulation with high refractive index and its application in nanoimprint lithographic (NIL) techniques, including but not limited to UV-NIL techniques, for manufacturing surface-relief structures, such as slanted or non-slanted surface-relief gratings used in a near-eye display system.

[0006] The disclosure provides a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component. In some embodiments, the base resin component is UV curable. In some embodiments, the base resin component is light-sensitive. In some embodiments, the first refractive index ranges from 1.52 to 1.73. In some embodiments, the first refractive index ranges from 1.52 to 1.71. In some embodiments, the first refractive index ranges from 1.52 to 1.70. In some embodiments, the first refractive index ranges from 1.55 to 1.77. In some embodiments, the first refractive index ranges from 1.58 to 1.77. In some embodiments, the first refractive index ranges from 1.55 to 1.73. In some embodiments, the first refractive index ranges from 1.50 to 1.73. In some embodiments, the first refractive index ranges from 1.58 to 1.73. In some embodiments, the first refractive index ranges from 1.60 to 1.77. In some embodiments, the first refractive index ranges from 1.60 to 1.73. In some embodiments, the first refractive index ranges from 1.50 to 1.80, from 1.55 to 1.80, from 1.57 to 1.80, from 1.58 to 1.77, from 1.58 to 1.70, or from 1.60 to 1.70. In some embodiments, the first refractive index is selected from about 1.50, about 1.51, about 1.52, about 1.53, about 1.54, about 1.55, about 1.56, about 1.57, about 1.58, about 1.59, about 1.60, about 1.61, about 1.62, about 1.63, about 1.64, about 1.65, about 1.66, about 1.67, about 1.68, about 1.69, about 1.70, about 1.71, about 1.72, about 1.73, about 1.74, about 1.75, about 1.76, and about 1.77. In some embodiments, the first refractive index is measured at 589 nm.

[0007] In some embodiments, the base resin component has a viscosity ranging from 0.5 cps to 400 cps. In some embodiments, the base resin component has a viscosity ranging from 2 cps to 100 cps. In some embodiments, the base resin component has a viscosity ranging from 10 cps to 100 cps. In some embodiments, the base resin component has a viscosity ranging from 10 cps to 60 cps. In some embodiments, the base resin component has a viscosity selected from about 1 cps, about 2 cps, about 3 cps, about 4 cps, about 5 cps, about 6 cps, about 7 cps, about 8 cps, about 9 cps, about 10 cps, about 11 cps, about 12 cps, about 13 cps, about 14 cps, about 15 cps, about 16 cps, about 17 cps, about 18 cps, about 19 cps, about 20 cps, about 21 cps, about 22 cps, about 23 cps, about 24 cps, about 25 cps, about 26 cps, about 27 cps, about 28 cps, about 29 cps, about 30 cps, about 31 cps, about 32 cps, about 33 cps, about 34 cps, about 35 cps, about 36 cps, about 37 cps, about 38 cps, about 39 cps, about 40 cps, about 41 cps, about 42 cps, about 43 cps, about 44 cps, about 45 cps, about 46 cps, about 47 cps, about 48 cps, about 49 cps, about 50 cps, about 51 cps, about 52 cps, about 53 cps, about 54 cps, about 55 cps, about 56 cps, about 57 cps, about 58 cps, about 59 cps, and about 60 cps. In some embodiments, the viscosity is measured in the absence of the nanoparticles component. In some embodiments, the viscosity is measured in the absence of a solvent. In some embodiments, the base resin component is a liquid at room temperature. In some embodiments, room temperature is considered between 15 and 25.degree. C. In some embodiments, the base resin component is a liquid at a temperature between 20 and 25.degree. C.

[0008] In some embodiments, the base resin component comprises one or more crosslinkable monomers, one or more polymerizable monomers, or both. In some embodiments, the crosslinkable monomers or the polymerizable monomers include one or more crosslinkable or polymerizable moieties. In some embodiments, the crosslinkable or polymerizable moieties are selected from an ethylenically unsaturated group, an oxirane ring, and a heterocyclic group. In some embodiments, the crosslinkable or polymerizable moieties are selected from vinyl, allyl, epoxide, acrylate, and methacrylate. In some embodiments, the crosslinkable or polymerizable moieties are selected from optionally substituted alkenyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted acrylate, optionally substituted methacrylate, optionally substituted styrene, optionally substituted epoxide, optionally substituted thiirane, optionally substituted lactone, and optionally substituted carbonate. In some embodiments, the crosslinkable or polymerizable moieties are selected from:

STR00001

[0009] In some embodiments, the crosslinkable monomers or the polymerizable monomers include one or more moieties selected from optionally substituted alkyl, optionally substituted heteroalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, and optionally substituted heteroarylalkyl. In some embodiments, the crosslinkable monomers or the polymerizable monomers include one or more moieties selected from fluorene, cardo fluorene, spiro fluorene, thianthrene, thiophosphate, anthraquinone, and lactam. In some embodiments, the crosslinkable monomers or the polymerizable monomers include one or more linking groups selected from –C.sub.1-10 alkyl-, –O–C.sub.1-10 alkyl-, –C.sub.1-10 alkenyl-, –O–C.sub.1-10 alkenyl-, –C.sub.1-10 cycloalkenyl-, –O–C.sub.1-10 cycloalkenyl-, –C.sub.1-10 alkynyl-, –O–C.sub.1-10 alkynyl-, –C.sub.1-10 aryl-, –O–C.sub.1-10–, -aryl-, –O–, –S–, –C(O)–, –C(O)O–, –OC(O)–, –OC(O)O–, –N(R.sup.b)–, –C(O)N(R.sup.b)–, –N(R.sup.b)C(O)–, –OC(O)N(R.sup.b)–, –N(R.sup.b)C(O)O–, –SC(O)N(R.sup.b)–, –N(R.sup.b)C(O)S–, –N(R.sup.b)C(O)N(R.sup.b)–, –N(R.sup.b)C(NR.sup.b)N(R.sup.b)–, –N(R.sup.b)S(O).sub.w–, –S(O).sub.wN(R.sup.b)–, –OS(O).sub.w–, –OS(O).sub.wO–, –O(O)P(OR.sup.b)O–, (O)P(O–).sub.3, –O(S)P(OR.sup.b)O–, and (S)P(O–).sub.3, where w is 1 or 2, and R.sup.b is independently hydrogen, optionally substituted alkyl, or optionally substituted aryl.

[0010] In some embodiments, the crosslinkable monomers or the polymerizable monomers include one or more terminal groups selected from optionally substituted thiophenyl, optionally substituted thiopyranyl, optionally substituted thienothiophenyl, and optionally substituted benzothiophenyl. In some embodiments, the base resin component includes one or more derivatives of bisfluorene, dithiolane, thianthrene, biphenol, o-phenylphenol, phenoxy benzyl, bisphenol A, bisphenol F, benzyl, or phenol. In some embodiments, the base resin component includes one or more of (2,7-bis[(2-acryloyloxyethl)-sulfanyl]thianthrene), benzyl methacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, acryloxypropylsilsesquioxane, or methylsilsesquioxane.

[0011] In some embodiments, the base resin component includes one or more of trimethylolpropane (EO)n triacrylate, caprolactone acrylate, polypropylene glycol monomethacrylate, cyclic trimethylolpropane formal acrylate, phenoxy benzyl acrylate, 3,3,5-trimethyl cyclohexyl acrylate, isobornyl acrylate, o-phenylphenol EO acrylate, 4-tert-butylcyclohexyl acrylate, benzyl acrylate, benzyl methacrylate, biphenylmethyl acrylate, lauryl acrylate, lauryl methacrylate, tridecyl acrylate, lauryl tetradecyl methacrylate, isodecyl acrylate, isodecyl methacrylate, phenol (EO) acrylate, phenoxyethyl methacrylate, phenol (EO)2 acrylate, phenol (EO)4 acrylate, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, nonyl phenol (PO)2 acrylate, nonyl phenol (EO)4 acrylate, nonyl phenol (EO)8 acrylate, ethoxy ethoxy ethyl acrylate, stearyl acrylate, stearyl methacrylate, methoxy PEG600 methacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,6-hexanediol (EO)n diacrylate, polypropylene glycol 400 diacrylate, 1,4-butanediol dimethacrylate, polypropylene glycol 700 (EO)6 dimethacrylate, 1,6-Hexanediol (EO)n diacrylate, hydroxy pivalic acid neopentyl glycol diacrylate, bisphenol A (EO)10 diacrylate, bisphenol A (EO)10 dimethacrylate, neopentyl glycol dimethacrylate, neopentyl glycol (PO)2 diacrylate, tripropylene glycol diacrylate, ethylene glycol dimethacrylate, dipropylene glycol diacrylate, bisphenol A (EO)30 diacrylate, bisphenol A (EO)30 dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, bisphenol A (EO)4 diacrylate, bisphenol A (EO)4 dimethacrylate, bisphenol A (EO)3 diacrylate, bisphenol A (EO)3 dimethacrylate, 1,3-butylene glycol dimethacrylate, tricyclodecane dimethanol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol 400 diacrylate, polyethylene glycol 400 dimethacrylate, polyethylene glycol 200 diacrylate, polyethylene glycol 200 dimethacrylate, polyethylene glycol 300 diacrylate, polyethylene glycol 600 diacrylate, polyethylene glycol 600 dimethacrylate, bisphenol F (EO)4 diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, trimethylolpropane (EO)3 triacrylate, trimethylolpropane (EO)15 triacrylate, trimethylolpropane (EO)6 triacrylate, trimethylolpropane (EO)9 triacrylate, glycerine (PO)3 triacrylate, pentaerythritol triacrylate, trimethylolpropane (PO)3 triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol (EO)n tetraacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate.

[0012] In some embodiments, the base resin component includes one or more of a phosphate methacrylate, an amine acrylate, an acrylated amine synergist, a carboxylethyl acrylate, a modified epoxy acrylate, a bisfluorene diacrylate, a modified bisphenol fluorene diacrylate, a modified bisphenol fluorene type, a butadiene acrylate, an aromatic difunctional acrylate, an aliphatic multifunctional acrylate, a polyester acrylate, a trifunctional polyester acrylate, a tetrafunctional polyester acrylate, a phenyl epoxy acrylate, a bisphenol A epoxy acrylate, a water soluble acrylate, an aliphatic alkyl epoxy acrylate, a bisphenol A epoxy methacrylate, a soybean oil epoxy acrylate, a difunctional polyester acrylate, a trifunctional polyester acrylate, a tetrafunctional polyester acrylate, a chlorinated polyester acrylate, a hexafunctional polyester acrylate, an aliphatic difunctional acrylate, an aliphatic difunctional methacrylate, an aliphatic trifunctional acrylate, an aliphatic trifunctional methacrylate, an aromatic difunctional acrylate, an aromatic tetrafunctional acrylate, an aliphatic tetrafunctional acrylate, an aliphatic hexafunctional acrylate, an aromatic hexafunctional acrylate, an acrylic acrylate, a polyester acrylate, a sucrose benzoate, a caprolactone methacrylate, a caprolactone acrylate, a phosphate methacrylate, an aliphatic multifunctional acrylate, a phenol novolac epoxy acrylate, a cresol novolac epoxy acrylate, an alkali strippable polyester acrylate, a melamine acrylate, a silicone polyester acrylate, a silicone urethane acrylate, a dendritic acrylate, an aliphatic tetrafunctional methacrylate, a water dispersion urethane acrylate, a water soluble acrylate, an aminated polyester acrylate, a modified epoxy acrylate, or a trifunctional polyester acrylate.

[0013] In some embodiments, the base resin component includes one or more of:

STR00002

In some embodiments, the base resin component includes one or more of:

STR00003

[0014] In some embodiments, the base resin component includes one or more fluorinated compounds. In some embodiments, the one or more fluorinated compounds are selected from: 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heneicosafluor- ododecyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 1H,1H,2H,2H-perfluorodecyl acrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate, 2,2,2-trifluoroethyl methacrylate, and 2-[(1’,1’,1’-trifluoro-2’-(trifluoromethyl)-2’-hydroxy)propyl]-3-norborny- l methacrylate.

[0015] In some embodiments, the base resin component further includes one or more solvents. In some embodiments, the one or more solvents are selected from 2-(1-methoxy)propyl acetate, propylene glycol monomethyl ether acetate, propylene glycol methyl ether, ethyl acetate, xylene, and toluene.

[0016] In some embodiments, the base resin component further includes one or more of a photo radical generator, a photo acid generator, or both.

[0017] In some embodiments, the base resin component further includes one or more inhibitors. In some embodiments, the one or more inhibitors are selected from monomethyl ether hydroquinone and 4-tert-butylcatechol.

[0018] In some embodiments, the base resin component further includes one or more surfactants. In some embodiments, the one or more surfactants are selected from a fluorinated surfactant, a crosslinkable surfactant, and a non-crosslinkable surfactant.

[0019] In some embodiments, the base resin component further includes one or more siloxane derivative compounds. In some embodiments, the base resin component does not include silicon.

[0020] In some embodiments, the nanoparticles component comprises one or more of titanium oxide, zirconium oxide, hafnium oxide, tungsten oxide, zinc tellurium, gallium phosphide, or any combination or derivative thereof. In some embodiments, the nanoparticles component includes titanium oxide nanoparticles. In some embodiments, the nanoparticles component includes zirconium oxide nanoparticles. In some embodiments, the nanoparticles component includes a mixture of titanium oxide nanoparticles and zirconium oxide nanoparticles.

[0021] In some embodiments, the nanoparticles component includes a plurality of surface-modified nanoparticles, a plurality of capped nanoparticles, or both. In some embodiments, the surface-modified nanoparticles, the capped nanoparticles, or both, include a substantially inorganic core, and a substantially organic shell. In some embodiments, the substantially organic shell includes one or more crosslinkable or polymerizable moieties. In some embodiments, the one or more crosslinkable or polymerizable moieties are linked to the substantially inorganic core.

[0022] In some embodiments, the crosslinkable or polymerizable moieties include one or more of an ethylenically unsaturated group, an oxirane ring, or a heterocyclic group. In some embodiments, the crosslinkable or polymerizable moieties include one or more of vinyl, allyl, epoxide, acrylate, and methacrylate. In some embodiments, the crosslinkable or polymerizable moieties include one or more of optionally substituted alkenyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted acrylate, optionally substituted methacrylate, optionally substituted styrene, optionally substituted epoxide, optionally substituted thiirane, optionally substituted lactone, and optionally substituted carbonate. In some embodiments, the crosslinkable or polymerizable moieties include one or more linking groups selected from –Si(–O–).sub.3, –C.sub.1-10 alkyl-, –O–C.sub.1-10 alkyl-, –C.sub.1-10 alkenyl-, –O–C.sub.1-10 alkenyl-, –C.sub.1-10 cycloalkenyl-, –O–C.sub.1-10 cycloalkenyl-, –C.sub.1-10 alkynyl-, –O–C.sub.1-10 alkynyl-, –C.sub.1-10 aryl-, –O–C.sub.1-10–, -aryl-, –O–, –S–, –C(O)–, –C(O)O–, –OC(O)–, –OC(O)O–, –N(R.sup.b)–, –C(O)N(R.sup.b)–, –N(R.sup.b)C(O)–, –OC(O)N(R.sup.b)–, –N(R.sup.b)C(O)O–, –SC(O)N(R.sup.b)–, –N(R.sup.b)C(O)S–, –N(R.sup.b)C(O)N(R.sup.b)–, –N(R.sup.b)C(NR.sup.b)N(R.sup.b)–, –N(R.sup.b)S(O).sub.w–, –S(O).sub.wN(R.sup.b)–, –S(O).sub.wO–, –OS(O).sub.w–, –OS(O).sub.wO–, –O(O)P(OR.sup.b)O–, (O)P(O–).sub.3, –O(S)P(OR.sup.b)O–, and (S)P(O–).sub.3, where w is 1 or 2, and R.sup.b is independently hydrogen, optionally substituted alkyl, or optionally substituted aryl.

[0023] In some embodiments, the substantially organic shell includes one or more of an organosilane or a corresponding organosilanyl substituent, an organoalcohol or a corresponding organoalkoxy substituent, or an organocarboxylic acid or a corresponding organocarboxylate substituent. In some embodiments, the organosilane is selected from n-propyltrimethoxysilane, n-propyltriethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, phenylrimethoxysilane, 2-methoxy(polyethyleneoxy)propyl-trimethoxysilane, methoxy(triethyleneoxy)propyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-(methacryloyloxy)propyl trimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-isocyanatopropyltrimethoxysilane, and glycidoxypropyltrimethoxysilane. In some embodiments, the organoalcohol is selected from heptanol, hexanol, octanol, benzyl alcohol, phenol, ethanol, propanol, butanol, oleylalcohol, dodecylalcohol, octadecanol and triethylene glycol monomethyl ether. In some embodiments, the organocarboxylic acid is selected from octanoic acid, acetic acid, propionic acid, 2-2-(2-methoxyethoxy)ethoxyacetic acid, oleic acid, and benzoic acid. In some embodiments, the substantially organic shell includes one or more of 3-(methacryloyloxy)propyl trimethoxysilane, 3-(methacryloyloxy)propyl dimethoxysilyl, or 3-(methacryloyloxy)propyl methoxysiloxyl.

[0024] In some embodiments, the diameter of a substantially inorganic core ranges from about 1 nm to about 25 nm. In some embodiments, the diameter of a substantially inorganic core is selected from about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm, and about 25 nm. In some embodiments, the diameter of a substantially inorganic core is measured by transmission electron microscopy (TEM).

[0025] In some embodiments, the diameter of a surface-modified nanoparticle, a capped nanoparticle, or both, including a substantially organic shell, ranges from about 5 nm to about 100 nm. In some embodiments, the diameter of a surface-modified nanoparticle, a capped nanoparticle, or both, including a substantially organic shell, ranges from about 10 nm to about 50 nm. In some embodiments, the diameter of a surface-modified nanoparticle, a capped nanoparticle, or both, including a substantially organic shell, is selected from about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm, and about 25 nm, about 26 nm, about 27 nm, about 28 nm, about 29 nm, about 30 nm, about 31 nm, about 32 nm, about 33 nm, about 34 nm, about 35 nm, about 36 nm, about 37 nm, about 38 nm, about 39 nm, about 40 nm, about 41 nm, about 42 nm, about 43 nm, about 44 nm, about 45 nm, about 46 nm, about 47 nm, about 48 nm, about 49 nm, about 50 nm, about 51 nm, about 52 nm, about 53 nm, about 54 nm, about 55 nm, about 56 nm, about 57 nm, about 58 nm, about 59 nm, about 60 nm, about 61 nm, about 62 nm, about 63 nm, about 64 nm, about 65 nm, about 66 nm, about 67 nm, about 68 nm, about 69 nm, about 70 nm, about 71 nm, about 72 nm, about 73 nm, about 74 nm, about 75 nm, about 76 nm, about 77 nm, about 78 nm, about 79 nm, about 80 nm, about 81 nm, about 82 nm, about 83 nm, about 84 nm, about 85 nm, about 86 nm, about 87 nm, about 88 nm, about 89 nm, about 90 nm, about 91 nm, about 92 nm, about 93 nm, about 94 nm, about 95 nm, about 96 nm, about 97 nm, about 98 nm, about 99 nm, and about 100 nm. In some embodiments, the diameter of a surface-modified nanoparticle, a capped nanoparticle, or both, including a substantially organic shell, is measured by dynamic light scattering (DLS).

[0026] In some embodiments, the volume fraction of the substantially inorganic core in the surface-modified nanoparticles, the capped nanoparticles, or both, ranges from about 60% to about 90%. In some embodiments, the volume fraction of the substantially inorganic core in the surface-modified nanoparticles, the capped nanoparticles, or both, is selected from about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, and about 90%. In some embodiments, the volume fraction of the substantially organic shell in the surface-modified nanoparticles, the capped nanoparticles, or both, ranges from about 10% to about 40%. In some embodiments, the volume fraction of the substantially organic shell in the surface-modified nanoparticles, the capped nanoparticles, or both, is selected from about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, and about 40%.

[0027] In some embodiments, the second refractive index ranges from 2.00 to 2.61. In some embodiments, the second refractive index is selected from about 2.00, about 2.01, about 2.02, about 2.03, about 2.04, about 2.05, about 2.06, about 2.07, about 2.08, about 2.09, about 2.10, about 2.11, about 2.12, about 2.13, about 2.14, about 2.15, about 2.16, about 2.17, about 2.18, 2.19, about 2.20, about 2.21, about 2.22, about 2.23, about 2.24, about 2.25, about 2.26, about 2.27, about 2.28, about 2.29, about 2.30, about 2.31, about 2.32, about 2.33, about 2.34, about 2.35, about 2.36, about 2.37, about 2.38, about 2.39, about 2.40, about 2.41, about 2.42, about 2.43, about 2.44, about 2.45, about 2.46, about 2.47, about 2.48, about 2.49, about 2.50, about 2.51, about 2.52, about 2.53, about 2.54, about 2.55, about 2.56, about 2.57, about 2.58, about 2.59, about 2.60, and about 2.61.

[0028] The disclosure also provides a cured NIL material including a substantially cured resin component and a nanoparticles component ranging from 45 wt. % 90 wt. % of the cured NIL material, where the cured NIL material has a third refractive index, and where the cured material is made by exposing to a light source a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component.

[0029] In some embodiments, the nanoparticles component ranges from 45 wt. % to 85 wt. %, from 45 wt. % to 80 wt. %, or from 45 wt. % to 75 wt. % of the cured NIL material. In some embodiments, the nanoparticles component is about 45 wt. %, about 46 wt. %, about 47 wt. %, about 48 wt. %, about 49 wt. %, about 50 wt. %, about 51 wt. %, about 52 wt. %, about 53 wt. %, about 54 wt. %, about 55 wt. %, about 56 wt. %, about 57 wt. %, about 58 wt. %, about 59 wt. %, about 60 wt. %, about 61 wt. %, about 62 wt. %, about 63 wt. %, about 64 wt. %, about 65 wt. %, about 66 wt. %, about 67 wt. %, about 68 wt. %, about 69 wt. %, about 70 wt. %, about 71 wt. %, about 72 wt. %, about 73 wt. %, about 74 wt. %, or about 75 wt. % of the cured NIL material. In some embodiments, the third refractive index ranges from 1.75 to 2.00. In some embodiments, the third refractive index is selected from about 1.75, about 1.76, about 1.77, about 1.78, about 1.79, about 1.80, 1.81, about 1.82, about 1.83, about 1.84, about 1.85, about 1.86, about 1.87, about 1.88, about 1.89, about 1.90, about 1.91, about 1.92, about 1.93, about 1.94, about 1.95, about 1.96, about 1.97, about 1.98, about 1.99, and about 2.00.

[0030] The disclosure also provides a NIL grating comprising a cured NIL material including a substantially cured resin component and a nanoparticles component ranging from 45 wt. to % 90 wt. % of the cured NIL material, where the cured NIL material has a third refractive index, and where the cured material is made by exposing to a light source a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component.

[0031] In some embodiments, the third refractive index ranges from 1.75 to 2.00. In some embodiments, the grating is a slanted grating or a non-slanted grating. In some embodiments, the grating has a duty cycle ranging from 10% to 90%. In some embodiments, the grating has a duty cycle ranging from 30% to 90%. In some embodiments, the grating has a duty cycle ranging from 35% to 90%. In some embodiments, a slanted grating includes at least one slant angle ranging from more than 0.degree. to 70.degree.. In some embodiments, a slanted grating includes at least one slant angle greater than 30.degree.. In some embodiments, a slanted grating includes at least one slant angle greater than 35.degree.. In some embodiments, the grating has a depth greater than 100 nm. In some embodiments, the grating has an aspect ratio greater than 3:1.

[0032] The disclosure also provides an optical component comprising a NIL grating including a cured NIL material including a substantially cured resin component and a nanoparticles component ranging from 45 wt. to % 90 wt. % of the cured NIL material, where the cured NIL material has a third refractive index, and where the cured material is made by exposing to a light source a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component.

[0033] The disclosure also provides a method of modulating the third refractive index of a cured NIL material including a substantially cured resin component and a nanoparticles component ranging from 45 wt. % 90 wt. % of the cured NIL material, where the cured NIL material has a third refractive index, and where the cured material is made by exposing to a light source a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component, the method comprising modulating the first refractive index of the base resin component of the NIL precursor material. In some embodiments, decreasing the first refractive index of the base resin component of the NIL precursor material results in an increase of the third refractive index of the cured NIL material.

[0034] The disclosure also provides a method of forming a NIL grating including a cured NIL material including a substantially cured resin component and a nanoparticles component ranging from 45 wt. to % 90 wt. % of the cured NIL material, where the cured NIL material has a third refractive index, and where the cured material is made by exposing to a light source a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component, the method comprising imprinting the NIL precursor material using a NIL process.

[0035] The disclosure also provides a method of forming an optical component comprising a NIL grating including a cured NIL material including a substantially cured resin component and a nanoparticles component ranging from 45 wt. to % 90 wt. % of the cured NIL material, where the cured NIL material has a third refractive index, and where the cured material is made by exposing to a light source a nanoimprint lithography (NIL) precursor material including a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component, the method including imprinting the NIL precursor material using a NIL process.

[0036] This summary is neither intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings, and each claim. The foregoing, together with other features and examples, will be described in more detail below in the following specification, claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Illustrative embodiments are described in detail below with reference to the following figures.

[0038] FIG. 1 is a simplified block diagram of an example artificial reality system environment including a near-eye display according to certain embodiments.

[0039] FIG. 2 is a perspective view of an example near-eye display in the form of a head-mounted display (HMD) device for implementing some of the examples disclosed herein.

[0040] FIG. 3 is a perspective view of an example near-eye display in the form of a pair of glasses for implementing some of the examples disclosed herein.

[0041] FIG. 4 illustrates an example optical see-through augmented reality system using a waveguide display according to certain embodiments.

[0042] FIG. 5. illustrates an example slanted grating coupler in an example waveguide display according to certain embodiments.

[0043] FIGS. 6A and 6B illustrate an example process for fabricating a slanted surface-relief grating by molding according to certain embodiments. FIG. 6A shows a molding process. FIG. 6B shows a demolding process.

[0044] FIGS. 7A-7D illustrate an example process for fabricating a soft stamp used to make a slanted surface-relief grating according to certain embodiments. FIG. 7A shows a master mold.

[0045] FIG. 7B illustrates the master mold coated with a soft stamp material layer. FIG. 7C illustrates a lamination process for laminating a soft stamp foil onto the soft stamp material layer. FIG. 7D illustrates a delamination process, where the soft stamp including the soft stamp foil and the attached soft stamp material layer is detached from the master mold.

[0046] FIGS. 8A-8D illustrate an example process for fabricating a slanted surface-relief grating using a soft stamp according to certain embodiments. FIG. 8A shows a waveguide coated with an imprint resin layer. FIG. 8B shows the lamination of the soft stamp onto the imprint resin layer. FIG. 8C shows the delamination of the soft stamp from the imprint resin layer. FIG. 8D shows an example of an imprinted slanted grating formed on the waveguide.

[0047] FIG. 9 is a simplified flow chart illustrating an example method of fabricating a slanted surface-relief grating using nanoimprint lithography according to certain embodiments.

[0048] FIGS. 10A-10D are plots showing the nanoimprint lithography (NIL) material refractive index versus light wavelength for various NIL materials having different base resin materials and varying nanoparticle loadings.

[0049] FIG. 11 is a plot showing the NIL material refractive index for visible light at 589 nm versus nanoparticle loading for the various NIL materials of FIGS. 10A-10D.

[0050] FIG. 12A is a plot showing the NIL material refractive index for visible light at 589 nm versus nanoparticle loading.

[0051] FIG. 12B is a plot showing the NIL material refractive index for visible light at 589 nm versus weight percentage of the component nanoparticles.

[0052] FIG. 13 is a plot showing the NIL material refractive index versus light wavelength for various NIL materials having different base resin materials and the same nanoparticle loading.

[0053] FIG. 14 is a simplified block diagram of an example electronic system of an example near-eye display according to certain embodiments.

[0054] FIG. 15 illustrates a cross-sectional view of an example nanoparticle, showing the structure of the nanoparticle in accordance with some embodiments.

[0055] FIGS. 16A and 16B illustrate a non-slanted grating 16A and a slanted grating 16B in accordance with some embodiments.

[0056] FIG. 17 is a plot showing that the refractive index of various imprinting formulations comprising 75% TiO.sub.2 nanoparticles increases as the viscosity of the base resin component decreases, in accordance with some embodiments.

[0057] FIG. 18 is a plot showing that the refractive index of various imprinting formulations comprising 75% TiO.sub.2 nanoparticles increases as the viscosity of the base resin component decreases, in accordance with some embodiments.

[0058] FIG. 19 illustrates the results of slanted imprinting processes for the various imprinting formulations of FIG. 18 in accordance with some embodiments.

[0059] FIGS. 20A and 20B illustrate the impact of various post-exposure bake processes on the refractive index and optics of a surface-relief grating using an example imprinting formulation of FIG. 18 in accordance with some embodiments.

[0060] FIG. 21 illustrates the impact of various post-exposure bake processes on the refractive index of a surface-relief grating using an example imprinting formulation of FIG. 18 in accordance with some embodiments.

[0061] The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated may be employed without departing from the principles, or benefits touted, of this disclosure.

[0062] In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

Introduction

[0063] This disclosure relates generally to waveguide-based near-eye display system. More specifically, and without limitation, this disclosure relates to curable nanoimprint materials with high refractive index for nanoimprinting surface-relief structures, such as slanted or non-slanted surface-relief gratings used in a near-eye display system.

[0064] The slanted surface-relief structures may be fabricated using many different nanofabrication techniques, including nanoimprint lithography (NIL) molding techniques. NIL molding may significantly reduce the cost of the slanted surface-relief structures. In NIL molding, a substrate may be coated with a layer of a NIL material, which may include a mixture of a base resin, high refractive index nanoparticles, solvent, and other additives. A NIL stamp with slanted structures may be pressed against the NIL material layer for molding a slanted grating in the NIL material layer. The NIL material layer may be cured subsequently using, for example, ultraviolet (UV) light and/or heat. The NIL mold may then be detached from the NIL material layer, and slanted structures may be formed in the NIL material layer.

[0065] Generally, it is desirable to use a NIL material with a high refractive index (e.g., greater than 1.78 or higher) for imprinting the slanted surface-relief structure in order to achieve, for example, high efficiency, low artifact, and angular selectivity. However, it may be very difficult and/or more expensive to obtain base resins with a high refractive index (e.g., 1.7 or higher). Using high refractive index nanoparticles (e.g., comprising zirconium oxide (ZrO.sub.x), hafnium oxide (interchangeably, HfO.sub.x), titanium oxide (interchangeably, TiO.sub.x or TiO.sub.2), etc.) and/or increasing the loading of the high refractive index nanoparticles in a NIL material mixture can increase the refractive index of the NIL material mixture. However, a NIL-molded grating with a high refractive index may not be obtained by merely increasing the weight percentage of the nanoparticles in the NIL material mixture. A certain amount of base resin needs to be maintained for the NIL material mixture to be hardened to maintain the molded shape or structure, which is achieved by curing the base resin that acts as a binder in the NIL material. Further, when the molded structure includes a high aspect ratio and/or inclined surfaces, the NIL material mixture needs to have certain viscosity and/or elasticity at the imprinting temperature (e.g., room temperature) so that the NIL material mixture can flow inside the mold and conform to the shape of the mold for carrying out the NIL molding process. Additionally, photocatalytical effect may occur when certain nanoparticles, such as titanium oxide nanoparticles, are included in the NIL material and the NIL material is exposed to low wavelength UV light. Such photocatalytical effect may cause degradation of the base resin over time, which can further affect the refractive index of the cured NIL-molded grating. Therefore, it can be challenging to obtain curable formulations that are stable, yield a high refractive index in the NIL-molded grating, and are also suitable for NIL molding.

[0066] The present disclosure provides a nanoimprint lithography (NIL) precursor material comprising a base resin component having a first refractive index ranging from 1.45 to 1.80, and a nanoparticles component having a second refractive index greater than the first refractive index of the base resin component. Some embodiments of the present disclosure further provide a cured NIL material made by curing the NIL precursor material, a NIL grating comprising the cured NIL material, an optical component comprising the NIL grating, and methods for forming the NIL grating and the optical component using a NIL process.

[0067] According to some embodiments, a NIL precursor material may be provided for NIL molding of a slanted grating having a refractive index greater than 1.75, greater than 1.78, greater than 1.8, greater than 1.85, greater than 1.9, greater than 1.93, greater than 1.95, or greater than 2. The NIL precursor material may include an electromagnetic radiation sensitive material or, more specifically, a light sensitive or light-curable optical material. For example, the NIL precursor material may include a light-sensitive base resin that includes a base material having a functional group for polymerization during photo-curing (e.g., UV-curing). The NIL precursor material may also include nanoparticles having relatively high refractive indices for increasing the refractive index of the NIL precursor material as well as the refractive index of the cured NIL material. The NIL precursor material may also include some optional additives, one or more radical and/or acid generators, one or more crosslinking agents, and one or more solvents. In general, the base resin material, the functional group, the nanoparticle material, and/or the loading of the nanoparticles can be selected to tune the refractive index of the moldable NIL precursor material.

[0068] According to some embodiments, a NIL material may be provided for molding a slanted grating having a refractive index greater than 1.78, greater than 1.8, greater than 1.85, greater than 1.9, greater than 1.93, greater than 1.95, or greater than 2. In some embodiments, the NIL material includes nanoparticles and a base resin characterized by a refractive index greater than 1.55, such as from about 1.58 to about 1.77. The weight percentage of the nanoparticles may range from 45% to 90%, 45% to 85%, 45% to 80%, or 45% to 75%, depending on the types of the nanoparticles utilized to maintain sufficient imprintability for carrying out NIL molding and the cured NIL material to be achieved. In some embodiments, the NIL material includes nanoparticles and an organic base resin. The organic base resin may be characterized by a refractive index ranging from 1.45 to 1.8. The nanoparticle loading percentage may range from 45% to 90%, 45% to 85%, 45% to 80%, or 45% to 75%.

[0069] According to certain embodiments, the NIL material may include a light-curable optical material for molding a slanted grating having a refractive index greater than 1.78, greater than 1.8, greater than 1.85, greater than 1.9, greater than 1.93, greater than 1.95, or greater than 2. The base resin refractive index may range between 1.58 and 1.77. The nanoparticles may include titanium oxide nanoparticles. The nanoparticle weight percentage may range from 45% to 90%, 45% to 85%, 45% to 80%, or 45% to 75%. In some embodiments, the NIL material may be formulated with a combination of (A) base resin refractive index and (B) nanoparticle loading percentage, such that a decrease in the base resin refractive index corresponds to an increase in the refractive index of the cured NIL material.

[0070] The various NIL materials disclosed herein can be used to imprint or NIL mold surface-relief structures, such as slanted surface-relief gratings with large slanted angles, small critical dimensions, wide ranges of grating duty cycles, varying periods, and/or high depths at a high fabrication speed and yield. In some embodiments, the NIL-molded surface-relief structures may include slanted surface-relief gratings having a wide range of grating duty cycles (e.g., from about 0.1 to about 0.9), large slant angles (e.g., greater than 10.degree., 20.degree., 30.degree., 40.degree., 50.degree., 60.degree., 70.degree. or larger), varying periods (e.g., 300 nm to 600 nm), and/or high depths (e.g., greater than 100 nm). The NIL materials provided herein are non-limiting and do not preclude any alternative embodiments or substitutions as will be apparent to one skilled in the art.

[0071] Near-Eye Displays for Artificial Reality Systems:

[0072] In the following description, for the purposes of explanation, specific details are set forth in order to provide a thorough understanding of examples of the disclosure. However, it will be apparent that various examples may be practiced without these specific details. For example, devices, systems, structures, assemblies, methods, and other components may be shown as components in block diagram form in order not to obscure the examples in unnecessary detail. In other instances, well-known devices, processes, systems, structures, and techniques may be shown without necessary detail in order to avoid obscuring the examples. The figures and description are not intended to be restrictive. The terms and expressions that have been employed in this disclosure are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. The word “example” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

[0073] FIG. 1 is a simplified block diagram of an example of an artificial reality system environment 100 including a near-eye display 120 in accordance with certain embodiments. Artificial reality system environment 100 shown in FIG. 1 may include near-eye display 120, an optional external imaging device 150, and an optional input/output interface 140 that may each be coupled to an optional console 110. While FIG. 1 shows example artificial reality system environment 100 including one near-eye display 120, one external imaging device 150, and one input/output interface 140, any number of these components may be included in artificial reality system environment 100, or any of the components may be omitted. For example, there may be multiple near-eye displays 120 monitored by one or more external imaging devices 150 in communication with console 110. In some configurations, artificial reality system environment 100 may not include external imaging device 150, optional input/output interface 140, and optional console 110. In alternative configurations, different or additional components may be included in artificial reality system environment 100.

[0074] Near-eye display 120 may be a head-mounted display that presents content to a user. Examples of content presented by near-eye display 120 include one or more of images, videos, audios, or some combination thereof. In some embodiments, audios may be presented via an external device (e.g., speakers and/or headphones) that receives audio information from near-eye display 120, console 110, or both, and presents audio data based on the audio information. Near-eye display 120 may include one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other. A rigid coupling between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity. A non-rigid coupling between rigid bodies may allow the rigid bodies to move relative to each other. In various embodiments, near-eye display 120 may be implemented in any suitable form factor, including a pair of glasses. Some embodiments of near-eye display 120 are further described below with respect to FIGS. 2-4. Additionally, in various embodiments, the functionality described herein may be used in a headset that combines images of an environment external to near-eye display 120 and artificial reality content (e.g., computer-generated images). Therefore, near-eye display 120 may augment images of a physical, real-world environment external to near-eye display 120 with generated content (e.g., images, video, sound, etc.) to present an augmented reality to a user.

[0075] In various embodiments, near-eye display 120 may include one or more of display electronics 122, display optics 124, and an eye-tracking unit 130. In some embodiments, near-eye display 120 may also include one or more locators 126, one or more position sensors 128, and an inertial measurement unit (IMU) 132. Near-eye display 120 may omit any of these elements or include additional elements in various embodiments. Additionally, in some embodiments, near-eye display 120 may include elements combining the function of various elements described in conjunction with FIG. 1.

[0076] Display electronics 122 may display or facilitate the display of images to the user according to data received from, for example, console 110. In various embodiments, display electronics 122 may include one or more display panels, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (mLED) display, an active-matrix OLED display (AMOLED), a transparent OLED display (TOLED), or some other display. For example, in one implementation of near-eye display 120, display electronics 122 may include a front TOLED panel, a rear display panel, and an optical component (e.g., an attenuator, polarizer, or diffractive or spectral film) between the front and rear display panels. Display electronics 122 may include pixels to emit light of a predominant color such as red, green, blue, white, or yellow. In some implementations, display electronics 122 may display a three-dimensional (3D) image through stereoscopic effects produced by two-dimensional panels to create a subjective perception of image depth. For example, display electronics 122 may include a left display and a right display positioned in front of a user’s left eye and right eye, respectively. The left and right displays may present copies of an image shifted horizontally relative to each other to create a stereoscopic effect (i.e., a perception of image depth by a user viewing the image).

[0077] In certain embodiments, display optics 124 may display image content optically (e.g., using optical waveguides and couplers) or magnify image light received from display electronics 122, correct optical errors associated with the image light, and present the corrected image light to a user of near-eye display 120. In various embodiments, display optics 124 may include one or more optical elements, such as, for example, a substrate, optical waveguides, an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, input/output couplers, or any other suitable optical elements that may affect image light emitted from display electronics 122. Display optics 124 may include a combination of different optical elements as well as mechanical couplings to maintain relative spacing and orientation of the optical elements in the combination. One or more optical elements in display optics 124 may have an optical coating, such as an anti-reflective coating, a reflective coating, a filtering coating, or a combination of different optical coatings.

[0078] Magnification of the image light by display optics 124 may allow display electronics 122 to be physically smaller, weigh less, and consume less power than larger displays. Additionally, magnification may increase a field of view of the displayed content. The amount of magnification of image light by display optics 124 may be changed by adjusting, adding, or removing optical elements from display optics 124. In some embodiments, display optics 124 may project displayed images to one or more image planes that may be further away from the user’s eyes than near-eye display 120.

[0079] Display optics 124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or a combination thereof. Two-dimensional errors may include optical aberrations that occur in two dimensions. Example types of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and transverse chromatic aberration. Three-dimensional errors may include optical errors that occur in three dimensions. Example types of three-dimensional errors may include spherical aberration, chromatic aberration, field curvature, and astigmatism.

[0080] Locators 126 may be objects located in specific positions on near-eye display 120 relative to one another and relative to a reference point on near-eye display 120. In some implementations, console 110 may identify locators 126 in images captured by external imaging device 150 to determine the artificial reality headset’s position, orientation, or both. A locator 126 may be a light emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which near-eye display 120 operates, or some combinations thereof. In embodiments where locators 126 are active components (e.g., LEDs or other types of light emitting devices), locators 126 may emit light in the visible band (e.g., about 380 nm to 750 nm), in the infrared (IR) band (e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about 10 nm to about 380 nm), in another portion of the electromagnetic spectrum, or in any combination of portions of the electromagnetic spectrum.

[0081] External imaging device 150 may generate slow calibration data based on calibration parameters received from console 110. Slow calibration data may include one or more images showing observed positions of locators 126 that are detectable by external imaging device 150. External imaging device 150 may include one or more cameras, one or more video cameras, any other device capable of capturing images including one or more of locators 126, or some combinations thereof. Additionally, external imaging device 150 may include one or more filters (e.g., to increase signal to noise ratio). External imaging device 150 may be configured to detect light emitted or reflected from locators 126 in a field of view of external imaging device 150. In embodiments where locators 126 include passive elements (e.g., retroreflectors), external imaging device 150 may include a light source that illuminates some or all of locators 126, which may retro-reflect the light to the light source in external imaging device 150. Slow calibration data may be communicated from external imaging device 150 to console 110, and external imaging device 150 may receive one or more calibration parameters from console 110 to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, sensor temperature, shutter speed, aperture, etc.).

[0082] Position sensors 128 may generate one or more measurement signals in response to motion of near-eye display 120. Examples of position sensors 128 may include accelerometers, gyroscopes, magnetometers, other motion-detecting or error-correcting sensors, or some combinations thereof. For example, in some embodiments, position sensors 128 may include multiple accelerometers to measure translational motion (e.g., forward/back, up/down, or left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, or roll). In some embodiments, various position sensors may be oriented orthogonally to each other.

[0083] IMU 132 may be an electronic device that generates fast calibration data based on measurement signals received from one or more of position sensors 128. Position sensors 128 may be located external to IMU 132, internal to IMU 132, or some combination thereof. Based on the one or more measurement signals from one or more position sensors 128, IMU 132 may generate fast calibration data indicating an estimated position of near-eye display 120 relative to an initial position of near-eye display 120. For example, IMU 132 may integrate measurement signals received from accelerometers over time to estimate a velocity vector and integrate the velocity vector over time to determine an estimated position of a reference point on near-eye display 120. Alternatively, IMU 132 may provide the sampled measurement signals to console 110, which may determine the fast calibration data. While the reference point may generally be defined as a point in space, in various embodiments, the reference point may also be defined as a point within near-eye display 120 (e.g., a center of IMU 132).

[0084] Eye-tracking unit 130 may include one or more eye-tracking systems. Eye tracking may refer to determining an eye’s position, including orientation and location of the eye, relative to near-eye display 120. An eye-tracking system may include an imaging system to image one or more eyes and may optionally include a light emitter, which may generate light that is directed to an eye such that light reflected by the eye may be captured by the imaging system. For example, eye-tracking unit 130 may include a non-coherent or coherent light source (e.g., a laser diode) emitting light in the visible spectrum or infrared spectrum, and a camera capturing the light reflected by the user’s eye. As another example, eye-tracking unit 130 may capture reflected radio waves emitted by a miniature radar unit. Eye-tracking unit 130 may use low-power light emitters that emit light at frequencies and intensities that would not injure the eye or cause physical discomfort. Eye-tracking unit 130 may be arranged to increase contrast in images of an eye captured by eye-tracking unit 130 while reducing the overall power consumed by eye-tracking unit 130 (e.g., reducing power consumed by a light emitter and an imaging system included in eye-tracking unit 130). For example, in some implementations, eye-tracking unit 130 may consume less than 100 milliwatts of power.

[0085] Near-eye display 120 may use the orientation of the eye to, e.g., determine an inter-pupillary distance (IPD) of the user, determine gaze direction, introduce depth cues (e.g., blur image outside of the user’s main line of sight), collect heuristics on the user interaction in the VR media (e.g., time spent on any particular subject, object, or frame as a function of exposed stimuli), some other functions that are based in part on the orientation of at least one of the user’s eyes, or some combination thereof. Because the orientation may be determined for both eyes of the user, eye-tracking unit 130 may be able to determine where the user is looking. For example, determining a direction of a user’s gaze may include determining a point of convergence based on the determined orientations of the user’s left and right eyes. A point of convergence may be the point where the two foveal axes of the user’s eyes intersect. The direction of the user’s gaze may be the direction of a line passing through the point of convergence and the mid-point between the pupils of the user’s eyes.

[0086] Input/output interface 140 may be a device that allows a user to send action requests to console 110. An action request may be a request to perform a particular action. For example, an action request may be to start or to end an application or to perform a particular action within the application. Input/output interface 140 may include one or more input devices. Example input devices may include a keyboard, a mouse, a game controller, a glove, a button, a touch screen, or any other suitable device for receiving action requests and communicating the received action requests to console 110. An action request received by the input/output interface 140 may be communicated to console 110, which may perform an action corresponding to the requested action. In some embodiments, input/output interface 140 may provide haptic feedback to the user in accordance with instructions received from console 110. For example, input/output interface 140 may provide haptic feedback when an action request is received, or when console 110 has performed a requested action and communicates instructions to input/output interface 140.

[0087] Console 110 may provide content to near-eye display 120 for presentation to the user in accordance with information received from one or more of external imaging device 150, near-eye display 120, and input/output interface 140. In the example shown in FIG. 1, console 110 may include an application store 112, a headset tracking module 114, an artificial reality engine 116, and eye-tracking module 118. Some embodiments of console 110 may include different or additional modules than those described in conjunction with FIG. 1. Functions further described below may be distributed among components of console 110 in a different manner than is described here.

[0088] In some embodiments, console 110 may include a processor and a non-transitory computer-readable storage medium storing instructions executable by the processor. The processor may include multiple processing units executing instructions in parallel. The non-transitory computer-readable storage medium may be any memory, such as a hard disk drive, a removable memory, or a solid-state drive (e.g., flash memory or dynamic random access memory (DRAM)). In various embodiments, the modules of console 110 described in conjunction with FIG. 1 may be encoded as instructions in the non-transitory computer-readable storage medium that, when executed by the processor, cause the processor to perform the functions further described below.

[0089] Application store 112 may store one or more applications for execution by console 110. An application may include a group of instructions that, when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the user’s eyes or inputs received from the input/output interface 140. Examples of the applications may include gaming applications, conferencing applications, video playback application, or other suitable applications.

[0090] Headset tracking module 114 may track movements of near-eye display 120 using slow calibration information from external imaging device 150. For example, headset tracking module 114 may determine positions of a reference point of near-eye display 120 using observed locators from the slow calibration information and a model of near-eye display 120. Headset tracking module 114 may also determine positions of a reference point of near-eye display 120 using position information from the fast calibration information. Additionally, in some embodiments, headset tracking module 114 may use portions of the fast calibration information, the slow calibration information, or some combination thereof, to predict a future location of near-eye display 120. Headset tracking module 114 may provide the estimated or predicted future position of near-eye display 120 to artificial reality engine 116.

[0091] Headset tracking module 114 may calibrate the artificial reality system environment 100 using one or more calibration parameters, and may adjust one or more calibration parameters to reduce errors in determining the position of near-eye display 120. For example, headset tracking module 114 may adjust the focus of external imaging device 150 to obtain a more accurate position for observed locators on near-eye display 120. Moreover, calibration performed by headset tracking module 114 may also account for information received from IMU 132. Additionally, if tracking of near-eye display 120 is lost (e.g., external imaging device 150 loses line of sight of at least a threshold number of locators 126), headset tracking module 114 may re-calibrate some or all of the calibration parameters.

[0092] Artificial reality engine 116 may execute applications within artificial reality system environment 100 and receive position information of near-eye display 120, acceleration information of near-eye display 120, velocity information of near-eye display 120, predicted future positions of near-eye display 120, or some combination thereof from headset tracking module 114. Artificial reality engine 116 may also receive estimated eye position and orientation information from eye-tracking module 118. Based on the received information, artificial reality engine 116 may determine content to provide to near-eye display 120 for presentation to the user. For example, if the received information indicates that the user has looked to the left, artificial reality engine 116 may generate content for near-eye display 120 that mirrors the user’s eye movement in a virtual environment. Additionally, artificial reality engine 116 may perform an action within an application executing on console 110 in response to an action request received from input/output interface 140, and provide feedback to the user indicating that the action has been performed. The feedback may be visual or audible feedback via near-eye display 120 or haptic feedback via input/output interface 140.

[0093] Eye-tracking module 118 may receive eye-tracking data from eye-tracking unit 130 and determine the position of the user’s eye based on the eye tracking data. The position of the eye may include an eye’s orientation, location, or both relative to near-eye display 120 or any element thereof. Because the eye’s axes of rotation change as a function of the eye’s location in its socket, determining the eye’s location in its socket may allow eye-tracking module 118 to more accurately determine the eye’s orientation.

[0094] In some embodiments, eye-tracking module 118 may store a mapping between images captured by eye-tracking unit 130 and eye positions to determine a reference eye position from an image captured by eye-tracking unit 130. Alternatively or additionally, eye-tracking module 118 may determine an updated eye position relative to a reference eye position by comparing an image from which the reference eye position is determined to an image from which the updated eye position is to be determined. Eye-tracking module 118 may determine eye position using measurements from different imaging devices or other sensors. For example, eye-tracking module 118 may use measurements from a slow eye-tracking system to determine a reference eye position, and then determine updated positions relative to the reference eye position from a fast eye-tracking system until a next reference eye position is determined based on measurements from the slow eye-tracking system.

[0095] Eye-tracking module 118 may also determine eye calibration parameters to improve precision and accuracy of eye tracking. Eye calibration parameters may include parameters that may change whenever a user dons or adjusts near-eye display 120. Example eye calibration parameters may include an estimated distance between a component of eye-tracking unit 130 and one or more parts of the eye, such as the eye’s center, pupil, cornea boundary, or a point on the surface of the eye. Other example eye calibration parameters may be specific to a particular user and may include an estimated average eye radius, an average corneal radius, an average sclera radius, a map of features on the eye surface, and an estimated eye surface contour. In embodiments where light from the outside of near-eye display 120 may reach the eye (as in some augmented reality applications), the calibration parameters may include correction factors for intensity and color balance due to variations in light from the outside of near-eye display 120.

[0096] Eye-tracking module 118 may use eye calibration parameters to determine whether the measurements captured by eye-tracking unit 130 would allow eye-tracking module 118 to determine an accurate eye position (also referred to herein as “valid measurements”). Invalid measurements, from which eye-tracking module 118 may not be able to determine an accurate eye position, may be caused by the user blinking, adjusting the headset, or removing the headset, and/or may be caused by near-eye display 120 experiencing greater than a threshold change in illumination due to external light. In some embodiments, at least some of the functions of eye-tracking module 118 may be performed by eye-tracking unit 130.

[0097] FIG. 2 is a perspective view of an example of a near-eye display in the form of a head-mounted display (HMD) device 200 for implementing some of the examples disclosed herein. HMD device 200 may be a part of, e.g., a virtual reality (VR) system, an augmented reality (AR) system, a mixed reality (MR) system, or some combinations thereof. HMD device 200 may include a body 220 and a head strap 230. FIG. 2 shows a top side 223, a front side 225, and a right side 227 of body 220 in the perspective view. Head strap 230 may have an adjustable or extendible length. There may be a sufficient space between body 220 and head strap 230 of HMD device 200 for allowing a user to mount HMD device 200 onto the user’s head. In various embodiments, HMD device 200 may include additional, fewer, or different components. For example, in some embodiments, HMD device 200 may include eyeglass temples and temples tips as shown in, for example, FIG. 2, rather than head strap 230.

[0098] HMD device 200 may present to a user media including virtual and/or augmented views of a physical, real-world environment with computer-generated elements. Examples of the media presented by HMD device 200 may include images (e.g., two-dimensional (2D) or three-dimensional (3D) images), videos (e.g., 2D or 3D videos), audios, or some combinations thereof. The images and videos may be presented to each eye of the user by one or more display assemblies (not shown in FIG. 2) enclosed in body 220 of HMD device 200. In various embodiments, the one or more display assemblies may include a single electronic display panel or multiple electronic display panels (e.g., one display panel for each eye of the user). Examples of the electronic display panel(s) may include, for example, a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (mLED) display, an active-matrix organic light emitting diode (AMOLED) display, a transparent organic light emitting diode (TOLED) display, some other display, or some combinations thereof. HMD device 200 may include two eye box regions.

[0099] In some implementations, HMD device 200 may include various sensors (not shown), such as depth sensors, motion sensors, position sensors, and eye tracking sensors. Some of these sensors may use a structured light pattern for sensing. In some implementations, HMD device 200 may include an input/output interface for communicating with a console. In some implementations, HMD device 200 may include a virtual reality engine (not shown) that can execute applications within HMD device 200 and receive depth information, position information, acceleration information, velocity information, predicted future positions, or some combination thereof of HMD device 200 from the various sensors. In some implementations, the information received by the virtual reality engine may be used for producing a signal (e.g., display instructions) to the one or more display assemblies. In some implementations, HMD device 200 may include locators (not shown, such as locators 126) located in fixed positions on body 220 relative to one another and relative to a reference point. Each of the locators may emit light that is detectable by an external imaging device.

[0100] FIG. 3 is a perspective view of an example of a near-eye display 300 in the form of a pair of glasses for implementing some of the examples disclosed herein. Near-eye display 300 may be a specific implementation of near-eye display 120 of FIG. 1, and may be configured to operate as a virtual reality display, an augmented reality display, and/or a mixed reality display. Near-eye display 300 may include a frame 305 and a display 310. Display 310 may be configured to present content to a user. In some embodiments, display 310 may include display electronics and/or display optics. For example, as described above with respect to near-eye display 120 of FIG. 1, display 310 may include an LCD display panel, an LED display panel, or an optical display panel (e.g., a waveguide display assembly).

[0101] Near-eye display 300 may further include various sensors 350a, 350b, 350c, 350d, and 350e on or within frame 305. In some embodiments, sensors 350a-350e may include one or more depth sensors, motion sensors, position sensors, inertial sensors, or ambient light sensors. In some embodiments, sensors 350a-350e may include one or more image sensors configured to generate image data representing different fields of views in different directions. In some embodiments, sensors 350a-350e may be used as input devices to control or influence the displayed content of near-eye display 300, and/or to provide an interactive VR/AR/MR experience to a user of near-eye display 300. In some embodiments, sensors 350a-350e may also be used for stereoscopic imaging.

[0102] In some embodiments, near-eye display 300 may further include one or more illuminators 330 to project light into the physical environment. The projected light may be associated with different frequency bands (e.g., visible light, infra-red light, ultra-violet light, etc.), and may serve various purposes. For example, illuminator(s) 330 may project light in a dark environment (or in an environment with low intensity of infra-red light, ultra-violet light, etc.) to assist sensors 350a-350e in capturing images of different objects within the dark environment. In some embodiments, illuminator(s) 330 may be used to project certain light pattern onto the objects within the environment. In some embodiments, illuminator(s) 330 may be used as locators, such as locators 126 described above with respect to FIG. 1.

[0103] In some embodiments, near-eye display 300 may also include a high-resolution camera 340. Camera 340 may capture images of the physical environment in the field of view. The captured images may be processed, for example, by a virtual reality engine (e.g., artificial reality engine 116 of FIG. 1) to add virtual objects to the captured images or modify physical objects in the captured images, and the processed images may be displayed to the user by display 310 for AR or MR applications.

[0104] FIG. 4 illustrates an example of an optical see-through augmented reality system 400 using a waveguide display according to certain embodiments. Augmented reality system 400 may include a projector 410 and a combiner 415. Projector 410 may include a light source or image source 412 and projector optics 414. In some embodiments, image source 412 may include a plurality of pixels that displays virtual objects, such as an LCD display panel or an LED display panel. In some embodiments, image source 412 may include a light source that generates coherent or partially coherent light. For example, image source 412 may include a laser diode, a vertical cavity surface emitting laser, and/or a light emitting diode. In some embodiments, image source 412 may include a plurality of light sources each emitting a monochromatic image light corresponding to a primary color (e.g., red, green, or blue). In some embodiments, image source 412 may include an optical pattern generator, such as a spatial light modulator. Projector optics 414 may include one or more optical components that can condition the light from image source 412, such as expanding, collimating, scanning, or projecting light from image source 412 to combiner 415. The one or more optical components may include, for example, one or more lenses, liquid lenses, mirrors, apertures, and/or gratings. In some embodiments, projector optics 414 may include a liquid lens (e.g., a liquid crystal lens) with a plurality of electrodes that allows scanning of the light from image source 412.

[0105] Combiner 415 may include an input coupler 430 for coupling light from projector 410 into a substrate 420 of combiner 415. Input coupler 430 may include a volume holographic grating, a diffractive optical element (DOE) (e.g., a surface-relief grating), or a refractive coupler (e.g., a wedge or a prism). Input coupler 430 may have a coupling efficiency of greater than 30%, 50%, 75%, 90%, or higher for visible light. As used herein, visible light may refer to light with a wavelength between about 380 nm to about 750 nm. Light coupled into substrate 420 may propagate within substrate 420 through, for example, total internal reflection (TIR). Substrate 420 may be in the form of a lens of a pair of eyeglasses. Substrate 420 may have a flat or a curved surface, and may include one or more types of dielectric materials, such as glass, quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, or ceramic. A thickness of substrate 420 may range from, for example, less than about 1 mm to about 10 mm or more. Substrate 420 may be transparent to visible light. A material may be “transparent” to a light beam if the light beam can pass through the material with a high transmission rate, such as larger than 50%, 40%, 75%, 80%, 90%, 95%, or higher, where a small portion of the light beam (e.g., less than 50%, 40%, 25%, 20%, 10%, 5%, or less) may be scattered, reflected, or absorbed by the material. The transmission rate (i.e., transmissivity) may be represented by either a photopically weighted or an unweighted average transmission rate over a range of wavelengths, or the lowest transmission rate over a range of wavelengths, such as the visible wavelength range.

[0106] Substrate 420 may include or may be coupled to a plurality of output couplers 440 configured to extract at least a portion of the light guided by and propagating within substrate 420 from substrate 420, and direct extracted light 460 to an eye 490 of the user of augmented reality system 400. As input coupler 430, output couplers 440 may include grating couplers (e.g., volume holographic gratings or surface-relief gratings), other DOEs, prisms, etc. Output couplers 440 may have different coupling (e.g., diffraction) efficiencies at different locations. Substrate 420 may also allow light 450 from environment in front of combiner 415 to pass through with little or no loss. Output couplers 440 may also allow light 450 to pass through with little loss. For example, in some implementations, output couplers 440 may have a low diffraction efficiency for light 450 such that light 450 may be refracted or otherwise pass through output couplers 440 with little loss, and thus may have a higher intensity than extracted light 460. In some implementations, output couplers 440 may have a high diffraction efficiency for light 450 and may diffract light 450 to certain desired directions (i.e., diffraction angles) with little loss. As a result, the user may be able to view combined images of the environment in front of combiner 415 and virtual objects projected by projector 410.

[0107] Surface-Relief Structures:

[0108] FIG. 5 illustrates an example slanted grating 520 in an example waveguide display 500 according to certain embodiments. Waveguide display 500 may include slanted grating 520 on a waveguide 510, such as substrate 420. Slanted grating 520 may act as a grating coupler for coupling light into or out of waveguide 510. In some embodiments, slanted grating 520 may include a structure with a period p. For example, slanted grating 520 may include a plurality of ridges 522 and grooves 524 between ridges 522. Ridges 522 may be made of a material with a refractive index of n.sub.g1, such as silicon containing materials (e.g., SiO.sub.2, Si.sub.3N.sub.4, SiC, SiO.sub.xN.sub.y, or amorphous silicon), organic materials (e.g., polymers, spin on carbon (SOC) or amorphous carbon layer (ACL) or diamond like carbon (DLC)), inorganic metal oxide layers (e.g., TiO.sub.x, AlO.sub.x, TaO.sub.x, HfO.sub.x, etc.), or a combination thereof.

[0109] Each period of slanted grating 520 may include a ridge 522 and a groove 524, which may be an air gap or a region filled with a material with a refractive index n.sub.g2. In some embodiments, the period p of the slanted grating may vary from one area to another on slanted grating 520, or may vary from one period to another (i.e., chirped) on slanted grating 520. The ratio between the width W of a ridge 522 and the grating period p may be referred to as the duty cycle. Slanted grating 520 may have a duty cycle ranging, for example, from about 10% to about 90% or greater. In some embodiments, the duty cycle may vary from period to period. In some embodiments, the depth d or height of ridges 522 may be greater than 50 nm, 100 nm, 200 nm, 300 nm, or higher.

[0110] Each ridge 522 may include a leading edge 530 with a slant angle .alpha. and a trailing edge 540 with a slant angle .beta.. Slant angle .alpha. and slant angle .beta. may be greater than 10.degree., 20.degree., 30.degree., 40.degree., 50.degree., 60.degree., 70.degree., or higher. In some embodiments, leading edge 530 and training edge 540 of each ridge 522 may be parallel to each other. In other words, slant angle .alpha. is approximately equal to slant angle .beta.. In some embodiments, slant angle .alpha. may be different from slant angle .beta.. In some embodiments, slant angle .alpha. may be approximately equal to slant angle .beta.. For example, the difference between slant angle .alpha. and slant angle .beta. may be less than 20%, 10%, 5%, 1%, or less.

[0111] In some implementations, grooves 524 between ridges 522 may be over-coated or filled with a material having a refractive index n.sub.g2 higher or lower than the refractive index of the material of ridges 522. For example, in some embodiments, a high refractive index material, such as Hafnia, Titania, Tantalum oxide, Tungsten oxide, Zirconium oxide, Gallium sulfide, Gallium nitride, Gallium phosphide, silicon, or a high refractive index polymer, may be used to fill grooves 524. In some embodiments, a low refractive index material, such as silicon oxide, alumina, porous silica, or fluorinated low index monomer (or polymer), may be used to fill grooves 524. As a result, the difference between the refractive index of ridges 522 and the refractive index of grooves 524 may be greater than 0.1, 0.2, 0.3, 0.5, 1.0, or higher.

[0112] The slanted grating, such as slanted grating 520 shown in FIG. 5, may be fabricated using many different nanofabrication techniques. The nanofabrication techniques generally include a patterning process and a post-patterning (e.g., over-coating) process. The patterning process may be used to form slanted ridges of the slanted grating. There may be many different nanofabrication techniques for forming the slanted ridges. For example, in some implementations, the slanted grating may be fabricated using lithographic techniques including slanted etching. In some implementations, the slanted grating may be fabricated using nanoimprint lithography (NIL) molding techniques. The post-patterning process may be used to over-coat the slanted ridges and/or to fill the gaps between the slanted ridges with a material having a different refractive index than the slanted ridges. The post-patterning process may be independent from the patterning process. Thus, a same post-patterning process may be used on slanted gratings fabricated using any pattering technique.

[0113] Techniques and processes for fabricating the slanted grating described below are for illustration purposes only and are not intended to be limiting. A person skilled in the art would understand that various modifications may be made to the techniques described below. For example, in some implementations, some operations described below may be omitted. In some implementations, additional operations may be performed to fabricate the slanted grating. Techniques disclosed herein may also be used to fabricate other slanted structures on various materials.

[0114] As described above, in some implementations, the slanted grating may be fabricated using NIL molding techniques. In NIL molding, a substrate may be coated with a NIL material layer. The NIL material may include an electromagnetic radiation sensitive material or, more specifically, a light-curable optical material. For example, the NIL material may include a light-sensitive base resin that includes a base polymer and a functional group for polymerization during photo-curing (e.g., UV-curing). The NIL material mixture may also include metal oxide nanoparticles (e.g., titanium oxide, zirconium oxide, etc.) for increasing the refractive index of the mixture. The mixture may also include some optional additives and solvent. In general, the base resin material, e.g., the base polymer and the functional group of the base resin material, the nanoparticle material, and/or the loading of the nanoparticles (i.e., weight percentage of the nanoparticles in the cured NIL material) can be selected to tune the refractive index of the moldable NIL material.

[0115] A NIL mold (e.g., a hard stamp, a soft stamp including a polymeric material, a hard-soft stamp, or any other working stamp) with a slanted structure may be pressed against the NIL material layer for molding a slanted surface-relief structure in the NIL material layer. A soft stamp (e.g., made of polymers) may offer more flexibility than a hard stamp during the molding and demolding processes. The NIL material layer may be cured subsequently using, for example, heat and/or ultraviolet (UV) light. The NIL mold may then be detached from the NIL material layer, and a slanted structure that is complementary to the slanted structure in the NIL mold may be formed in the NIL material layer.

[0116] In various embodiments, different generations of NIL stamps may be made and used as the working stamp to mold the slanted gratings. For example, in some embodiments, a master mold (which may be referred to as a generation 0 mold) may be fabricated (e.g., etched) in, for example, a semiconductor substrate, a quartz, or a metal plate. The master mold may be a hard stamp and may be used as the working stamp to mold the slanted grating directly, which may be referred to as hard stamp NIL or hard NIL. In such case, the slanted structure on the mold may be complimentary to the desired slanted structure of the slanted grating used as the grating coupler on a waveguide display.

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