Abstract: A method of planarizing an overcoat layer on a surface-relief grating includes dispensing a layer of a resin material that is curable by heat or electromagnetic radiation on a surface-relief grating that includes a plurality of grating grooves, pressing the layer of the resin material using a planar imprint stamp, curing the resin material in the layer of the resin material, and detaching the planar imprint stamp from the layer of the resin material. In one example, a thickness of the overcoat layer on top of grating ridges of the surface-relief grating is equal to or less than 20 nm, and a surface peak-to-valley height of a top surface of the overcoat layer is equal to or less than 5 nm.

Abstract: Disclosed herein are techniques for fabricating a straight or slanted surface-relief grating with a uniform or non-uniform grating depth. According to certain embodiments, a gray-tone photoresist includes a novolac resin, a diazonaphthoquinone (DNQ) dissolution inhibitor, and one or more crosslinking agents for crosslinking the novolac resin at an elevated temperature to increase a glass transition temperature of the gray-tone photoresist and/or lower an etch rate of the gray-tone photoresist. After gray-tone photo exposure and development, the gray-tone photoresist is baked at the elevated temperature to crosslink. The crosslinked gray-tone photoresist has a higher density and a higher glass transition temperature, and thus would not become flowable to cause ripples or other surface roughness during the etching.

Abstract: An optical device includes a substrate, a first surface-relief grating including grooves and ridges formed on or in the substrate, a first overcoat layer in the grooves of the first surface-relief grating, and a first antireflective layer on the first overcoat layer. The ridges of the first surface-relief grating include high-refractive index, photoactive metal oxide nanoparticles and a material of the first overcoat layer in regions between the metal oxide nanoparticles, or the first overcoat layer includes the metal oxide nanoparticles and a material of the first antireflective layer in regions between the metal oxide nanoparticles. Methods of fabricating the optical device are also described.

Abstract: An optical device includes a substrate, a surface-relief grating including grooves and ridges formed on or in the substrate, and an overcoat layer in the grooves of the surface-relief grating. The ridges of the surface-relief grating or the overcoat layer includes a plurality of clusters of metal oxide (e.g., TiO2 or NbOx) nanoparticles. Each cluster of the plurality of clusters of metal oxide nanoparticles includes metal oxide nanoparticles dispersed in an inorganic barrier that isolates the metal oxide nanoparticles from other materials of the optical device. The ridges of the surface-relief grating or the overcoat layer is made of a resin material that includes a resin with inorganic content, and/or TiOx or NbOx nanoparticles including inorganic-containing ligands. A high-energy treatment process can remove organics surrounding the metal oxide nanoparticles and form the barrier layers that surround clusters of metal oxide nanoparticles.