Diffractive backlight fabrication method
Diffractive backlight fabrication employs a diffraction grating to scatter light from a light guide and define a reflective island that is aligned with the diffraction grating. A method of fabricating a diffractive backlight includes providing the light guide having the diffraction grating, diffractively scattering guided light out of the light guide using the diffraction grating to selectively expose photoresist and provide an opening in the photoresist, and depositing a reflective material into the opening to form a reflective island that is aligned with the diffraction grating. A reflective diffraction grating element of the diffractive backlight includes the diffraction grating and reflective island.
1. A method of fabricating a diffractive backlight, the method comprising:
providing a light guide having a diffraction grating;
diffractively scattering guided light out of the light guide using the diffraction grating to selectively expose photoresist adjacent to a surface of the light guide, selective exposure providing an opening in the photoresist that is aligned with the diffraction grating; and
depositing a reflective material into the opening to form a reflective island aligned with the diffraction grating,
wherein a reflective diffraction grating element of the diffractive backlight comprises a combination of the diffraction grating and the reflective island.
2. The method of fabricating a diffractive backlight of claim 1 , wherein providing a light guide having a diffraction grating comprises nanoimprinting a surface of the light guide using a nanoimprint mold to form the diffraction grating in the light guide surface.
3. The method of fabricating a diffractive backlight of claim 2 , wherein nanoimprinting a surface of the light guide using a nanoimprint mold comprises:
applying a nanoimprint receiving layer to a surface of the light guide; and
pressing the nanoimprint mold into the nanoimprint receiving layer to form the diffraction grating.
4. The method of fabricating a diffractive backlight of claim 1 , wherein diffractively scattering guided light out of the light guide using the diffraction grating comprises:
guiding light along a length of the light guide according to total internal reflection as guided light; and
diffractively scattering a portion of the guided light out of the light guide using the diffraction grating.
5. The method of fabricating a diffractive backlight of claim 4 , wherein the guided light comprises one or both of blue light and ultraviolet light provided by a light source that is optically connected to an edge of the light guide.
6. The method of fabricating a diffractive backlight of claim 1 , further comprises applying the photoresist to the light guide surface; and
developing the photoresist after selective exposure by the diffractively scattered portion of the guided light to provide the opening.
7. The method of fabricating a diffractive backlight of claim 1 , wherein depositing a reflective material into the opening to form a reflective island comprises:
depositing a layer of the reflective material on a surface of the photoresist and into the opening in the photoresist; and
lifting off the photoresist to leave only the reflective material that was within the opening.
8. The method of fabricating a diffractive backlight of claim 1 , wherein the light guide comprises:
a light guide substrate;
a layer of high-index material on a surface of the light guide substrate, the high-index material having a refractive index that is greater than a refractive index of the light guide substrate; and
a layer of low-index material having a refractive index that is less than the refractive index of the high-index material, the high-index material being sandwiched between the low-index material layer and the light guide substrate,
wherein light is guided within the light guide by total internal reflection at an interface between the high-index material layer and the low-index material layer.
9. The method of fabricating a diffractive backlight of claim 8 , wherein the high-index material extends into diffractive features of the diffraction grating in the surface of the light guide substrate.
10. The method of fabricating a diffractive backlight of claim 8 , further comprising etching an opening in the low-index material layer through the opening in the photoresist to expose the high-index material layer.
11. The method of fabricating a diffractive backlight of claim 10 , wherein depositing a reflective material into the opening to form a reflective island comprises:
depositing a layer of the reflective material on a surface of the photoresist and into the opening in the photoresist and the opening in the low-index material layer; and
lifting off the photoresist to leave only the reflective material that was within the opening and on a surface of the of the high-index material layer.
12. The method of fabricating a diffractive backlight of claim 11 , further comprising removing the low-index material layer from the light guide.
13. The method of fabricating a diffractive backlight of claim 1 , wherein the reflective material comprises one or more of a metal, a metal polymer, and a high-index dielectric.