Gray scale fabrication method using a spin-on glass material and integrated optical designs produced therefrom
The subject invention relates to the fabrication of micro-optical structures in a glass-like transparent material using conventional photolithography processing steps. The glass-like material is a spin-on glass (SOG) material, which behaves like a negative-tone photoresist, and has high quality optical properties similar to those of glass. The present invention can take advantage of gray scale photomasks to illuminate the uncured spin-on material with various illumination intensities, thus resulting in variations in resultant film thickness of the SOG material after the chemical development step. This results in micro-optical structures that can be fabricated with the desired shapes, depending on the transmission characteristics of each region of the gray scale photomask.
1. A process for fabricating a micro-optical element which method comprises: (1) depositing on the surface of a suitable transparent substrate a coating consisting essentially of a spin-on glass material, at a process temperature of less than 225° C., wherein the spin-on glass material is directly patternable as a negative photoresist; (2) providing a gray scale mask, having a desired gray scale pattern, between an illumination source and the coated substrate of step (1); (3) exposing the coated substrate of step (1) to illumination through the gray scale mask of step (2) and thereby forming a negative image of the desired pattern on the coated substrate; and (4) developing the desired image on the coated substrate by dissolving away the unexposed portions of spin-on glass coating.
2. The process of claim 1 , wherein the spin-on glass material of step (1) contains a photoinitiator.
3. The process of claim 1 , wherein the illumination source is ultraviolet light, a laser beam or an electron beam.
4. The process of claim 1 , wherein the substrate comprises a glass, silicate glass, or Germanium substrate.
5. The process of claim 1 further comprising one or more thermal curing steps after step (4).
6. The process of claim 5 further comprising an etching step, after the one or more thermal curing steps, and thereby forming the desired pattern on the transparent substrate.
7. The process of claim 1 wherein the resulting micro-optical element has a thickness between 0.1 micrometer and 100 micrometers.
8. The process of claim 1 , wherein the resulting micro-optical element is an optical refractive lens.
9. The process of claim 1 , wherein the resulting micro-optical element is an optical diffractive lens.
10. The process of claim 1 , wherein the resulting micro-optical element is a tapered waveguide.
11. The process of claim 10 , wherein the waveguide is suitable for use in a planar lightwave circuit.
12. The process of claim 10 , wherein the waveguide is suitable for use in a mode converter for efficiently coupling light from an optical fiber into a smaller planar lightwave circuit.
13. The process of claim 8 , wherein the waveguide is suitable for use in a mode converter for efficiently coupling light from a smaller planar lightwave circuit into an optical fiber.
14. The process of claim 1 , wherein the micro-optical element is a mechanical standoff for providing a specific controlled separation between two substrates.
15. The process of claim 10 , wherein the micro-optical element is an optical beam splitter, mirror, or other micro-optical component.