Fabrication of optical waveguide devices
Disclosed is a method of fabricating an optical waveguide device including the steps of forming a mask over a waveguide core material layer so as to leave a portion of the layer exposed, and exposing the structure to an oxidizing environment to form an oxide layer on the waveguide core material layer at least in the exposed portion thereby defining the lateral dimension of the waveguide core. The resulting waveguide core has extremely smooth surfaces for low optical losses.
1. A method of fabricating an optical waveguide device which includes a core having a lateral dimension comprising the steps of:
forming a mask which is permeable to an oxidizing species over a waveguide core material layer so as to leave a portion of the layer exposed; and
exposing the structure to an oxidizing environment including the oxidizing species to form an oxide layer on the waveguide core material layer in the exposed portion and an oxide layer on the waveguide core layer in a portion of the layer under the mask with a thickness less than the oxide formed in the exposed portion thereby defining the lateral dimension of the waveguide core.
2. The method according to claim 1 wherein the permeable mask comprises SiO 2 with a thickness in the range 100-1000 nm.
3. The method according to claim 1 wherein the permeable mask is annealed in dry nitrogen.
4. The method according to claim 1 wherein the oxidizing environment includes a liquid bath, and the structure is exposed to the bath for a time and temperature sufficient to form the oxide layer.
5. The method according to claim 4 wherein the oxidizing environment includes a nitric acid solution.
6. The method according to claim 1 wherein the waveguide core has surfaces adjacent to the oxide with a root mean square roughness, σ, at or below 0.3 nm.
7. The method according to claim 1 wherein the device further includes a cladding layer, and the difference between the index of refraction of the core and cladding, Δn, is approximately 2.
8. The method according to claim 1 wherein the device further includes a cladding layer, and the difference between the index of refraction of the core and cladding, Δn, is within the range 0.2 to 3.
9. The method according to claim 1 wherein the waveguide core material layer comprises silicon with a thickness in the range 100-500 nm.
10. The method according to claim 1 wherein the mask is formed by oxidizing the surface of the waveguide core material layer, and patterning the resulting oxide layer.