Optical modulator using a serpentine dielectric layer between silicon layers
View Patent ↗The present invention is a method and an apparatus for optical modulation, for example for use in optical communications links. In one embodiment, an apparatus for optical modulation includes a first silicon layer having one or more trenches formed therein, a dielectric layer lining the first silicon layer, and a second silicon layer disposed on the dielectric layer and filling the trenches.
1. Apparatus comprising:
a first silicon layer, the first silicon layer having a plurality of trenches formed therein, wherein the first silicon layer is n-doped;
a dielectric layer lining the first silicon layer, wherein a cross section of the dielectric layer relative to a direction of propagation of light through the apparatus comprises a substantially serpentine shape;
a second silicon layer disposed on the dielectric layer and filling the one or more trenches, wherein the second silicon layer is undoped; and
a layer of p-doped silicon disposed between the dielectric layer and the second silicon layer, the layer of p-doped silicon lining the dielectric layer, wherein the layer of p-doped silicon is thinner than the second silicon layer.
2. The apparatus of claim 1 , wherein the first silicon layer comprises crystalline silicon.
3. The apparatus of claim 1 , wherein the dielectric layer comprises a gate oxide.
4. The apparatus of claim 3 , wherein the gate oxide comprises silicon dioxide.
5. The apparatus of claim 3 , wherein the gate oxide comprises silicon nitride.
6. The apparatus of claim 3 , wherein the gate oxide comprises a high-k dielectric.
7. The apparatus of claim 1 , wherein a refractive index of the dielectric layer is less than a refractive index of the second silicon layer.
8. The apparatus of claim 1 , wherein the second silicon layer comprises crystalline silicon.
9. The apparatus of claim 1 , further comprising:
a first oxide layer disposed laterally relative to a first side of the dielectric layer, such that the first oxide layer is positioned between the first silicon layer and the second silicon layer; and
a second oxide layer disposed laterally relative to a second side of the dielectric layer, such that the second oxide layer is positioned between the first silicon layer and the second silicon layer,
wherein the first oxide layer and the second oxide layer are spaced apart relative to each other by a section of the dielectric layer residing between the first side of the dielectric layer and the second side of the dielectric layer.
10. The apparatus of claim 1 , wherein a refractive index of the dielectric layer is approximately equal to a refractive index of the second silicon layer.
11. The apparatus of claim 1 , wherein the second silicon layer comprises polysilicon.
12. The apparatus of claim 1 , wherein the cross section of the dielectric layer comprises a surface charge region.
13. The apparatus of claim 12 , wherein the surface charge region comprises a plurality of horizontal portions and a plurality of vertical portions.
14. The apparatus of claim 12 , wherein the surface charge region overlaps with a region through which an optical mode propagates through the apparatus.
15. The apparatus of claim 1 , wherein the first silicon layer is disposed directly on a buried oxide layer.
16. The apparatus of claim 15 , wherein the second silicon layer is separated from the buried oxide layer by the first silicon layer, the dielectric layer, and the layer of p-doped silicon.