Waveguide mode expander using amorphous silicon
A waveguide mode expander couples a smaller optical mode in a semiconductor waveguide to a larger optical mode in an optical fiber. The waveguide mode expander comprises a shoulder made of crystalline silicon and a ridge made of non-crystalline silicon (e.g., amorphous silicon). In some embodiments, the ridge of the waveguide mode expander has a plurality of stages, the plurality of stages have different widths and/or thicknesses at a given cross section.
1. A waveguide mode expander comprising:
a substrate;
a shoulder, wherein:
the shoulder is disposed on the substrate;
a width of the shoulder tapers; and
the shoulder comprises crystalline silicon; and
a ridge, wherein:
the ridge comprises non-crystalline silicon;
the ridge is disposed on the shoulder such that the shoulder is between the ridge and the substrate; and
the ridge has a narrower width than the shoulder, wherein the ridge and the shoulder are configured to guide and expand an optical beam propagating through the shoulder and the ridge.
2. A waveguide mode expander comprising:
a substrate;
a shoulder, wherein:
the shoulder is disposed on the substrate; and
the shoulder comprises crystalline silicon; and
a ridge, wherein:
the ridge comprises non-crystalline silicon;
the ridge is disposed on the shoulder such that the shoulder is between the ridge and the substrate;
the ridge has a narrower width than the shoulder;
the ridge comprises a plurality of stages;
at a cross section of the waveguide mode expander, each stage of the plurality of stages has a different width;
a first stage of the plurality of stages, which is closer to the shoulder, has a wider width than a second stage of the plurality of stages, which is farther from the shoulder than the first stage; and
the ridge and the shoulder are configured to guide and expand an optical beam propagating through the shoulder and the ridge.
3. The waveguide mode expander of claim 2 , further comprising a waveguide and cladding material disposed on the waveguide, wherein:
a portion of the cladding material has been etched in a pattern to form a recess; and
the ridge is formed by filling the recess with non-crystalline silicon.
4. The waveguide mode expander of claim 2 , wherein the first stage is thinner than the second stage.
5. The waveguide mode expander of claim 2 , wherein:
the plurality of stages has a number of stages; and
the number of stages is three.
6. The waveguide mode expander of claim 2 , wherein:
the plurality of stages has a number of stages; and
the number of stages is at least five.
7. The waveguide mode expander of claim 2 , further comprising a cladding covering the ridge and the shoulder.
8. The waveguide mode expander of claim 7 , wherein the cladding is SiO 2 .
9. The waveguide mode expander of claim 2 , wherein the ridge expands the optical beam by tapering from a narrower width near an input end to a wider width near an output end.
10. The waveguide mode expander of claim 2 , wherein:
the substrate comprises a buried-oxide layer and a handle layer;
the buried-oxide layer is disposed between the shoulder and the handle layer; and
the buried-oxide layer acts as a cladding to the shoulder.