Method of fabricating diffractive backlight
Fabricating a diffractive backlight employs a universal grating and selects a portion of the universal grating using a reflective island to define a grating element, a reflective diffraction grating element of the diffractive backlight including the grating element and the reflective island. A method of fabricating a diffractive backlight includes forming the universal grating, forming the reflective island, and selecting a portion of the universal grating using the reflective island to define the grating element. The method of fabricating a diffractive backlight may include forming the reflective island on a light guide surface and forming the universal grating over the reflective island. Alternatively, the method of fabricating a diffractive backlight may include forming the universal grating on the light guide surface and forming the reflective island over the universal grating.
1. A method of fabricating a diffractive backlight, the method comprising:
forming a reflective island on a surface of a light guide substrate;
forming a universal grating over the reflective island on the surface of the light guide substrate; and
selecting a portion of the universal grating using the reflective island to define a grating element by:
applying a photoresist to cover the universal grating;
exposing the photoresist using a collimated light source to illuminate the photoresist from a side of the light guide substrate that is opposite to a side on which the reflective island is located, the photoresist being a positive photoresist and the reflective island serving as a photomask to define a portion of the photoresist that remains after the photoresist is developed; and
removing an exposed portion of the universal grating not covered by the photoresist that remains,
wherein a reflective diffraction grating element of the diffractive backlight comprises a combination of the grating element and the reflective island.
2. The method of fabricating a diffractive backlight of claim 1 , wherein forming the universal grating on the light guide substrate comprises nanoimprinting the universal grating in a nanoimprint receiving layer of the light guide substrate using a nanoimprint mold.
3. The method of fabricating a diffractive backlight of claim 1 , wherein forming the reflective island comprises patterning a layer of reflective material to define the reflective island, the layer of reflective material comprising one or more of a metal, a metal polymer, and a high-index dielectric.
4. The method of fabricating a diffractive backlight of claim 1 , further comprising providing an optical material layer between the reflective island and the universal grating, wherein the optical material layer is index-matched to a material of the light guide substrate, the universal grating being formed on the optical material layer.
5. The method of fabricating a diffractive backlight of claim 1 , wherein removing the exposed portion of the universal grating comprises etching the exposed portion to remove material of the universal grating not covered by the photoresist.
6. The method of fabricating a diffractive backlight of claim 1 , further comprising:
applying a negative photoresist to cover reflective island and the grating element;
exposing the negative photoresist using the collimated light source to illuminate the negative photoresist and define an opening in the photoresist above the grating element; and
depositing a reflective material on the grating element through the opening in the photoresist,
wherein the reflective material exclusively covers the grating element.
7. The method of fabricating a diffractive backlight of claim 6 , further comprising depositing a layer of optical material on the light guide substrate, the optical material layer embedding the grating element, the reflective island, and the reflective material covering the grating element, wherein removing the exposed portion of the universal grating comprises the exposed portion being covered by the optical material layer.
8. A method of fabricating a diffractive backlight, the method comprising:
forming a reflective island on a surface of a light guide, the reflective island comprising one or more of a metal, a metal polymer, and a high-index dielectric;
depositing a layer of optical material on the light guide to cover the reflective island, the optical material being index-matched to a material of the light guide;
forming a universal grating on the optical material layer using nanoimprint lithography; and
selecting a portion of the universal grating using the reflective island to define a grating element by:
applying a photoresist to cover the universal grating; and
exposing the photoresist using a collimated light source to illuminate the photoresist from a side of the light guide that is opposite to a side on which the reflective island is located, the reflective island serving as a photomask to define a portion of the photoresist that remains after the photoresist is developed,
wherein selecting a portion of the universal grating to define the grating element comprises one of etching an exposed portion of the universal grating not covered by the photoresist that remains and covering the exposed portion of the universal grating with a layer of the optical material,
wherein a reflective diffraction grating element of the diffractive backlight comprises a combination of the grating element and the reflective island.
9. The method of fabricating a diffractive backlight of claim 8 , further comprising depositing a reflective material layer on the grating element and further covering the deposited reflective material layer with a layer of the optical material.