Multi-doped slab silicon optical modulator
A silicon optical modulator with improved bandwidth includes a silicon waveguide with a rib structure in cross section connected to a first slab region and a second slab region respectively on two opposite sides of the rib structure. The silicon optical modulator further includes a PN junction formed in the rib structure with a P-type part joined with the first slab region and a N-type part joined with the second slab region. Additionally, the silicon optical modulator includes multiple P-type doped sections formed one next to another in the first slab region ended with a first end region and multiple N-type doped sections one next to another formed in the second slab region ended with a second end region. The multiple P-type or N-type doped sections are configured with increasing doping levels for sections further away from the rib structure.
1. An optical modulator comprising:
a substrate;
a PN junction disposed on the substrate, the PN junction formed by a first L-shaped region doped with a p-type doping abutting a second L-shaped region doped with an n-type doping;
a first plurality of regions doped with the p type doping arranged adjacent to the first L-shaped region on the substrate, the first plurality of regions having respective increasing doping levels and decreasing lengths as distances of the first plurality of regions increase from the first L-shaped region;
a second plurality of regions doped with the n type doping arranged adjacent to the second L-shaped region on the substrate, the second plurality of regions having respective increasing doping levels and decreasing lengths as distances of the second plurality of regions increase from the second L-shaped region.
2. The optical modulator of claim 1 wherein:
the first L-shaped region includes (i) a first portion having a first height and (ii) a second portion extending perpendicularly from the first portion and having a second height that is greater than the first height;
the second L-shaped region includes (i) a third portion having a third height and (ii) a fourth portion extending perpendicularly from the third portion and having a fourth height, the fourth portion abutting the second portion to form the PN junction;
the first plurality of regions have the first height and are arranged adjacent to the first portion of the first L-shaped region;
the second plurality of regions have the third height and are arranged adjacent to the third portion of the second L-shaped region; and
the first portion of the first L-shaped region, the third portion of the second L-shaped region, the first plurality of regions, and the second plurality of regions lie in a plane parallel to the substrate.
3. The optical modulator of claim 2 wherein the third height is equal to the first height and the fourth height is equal to the second height.
4. The optical modulator of claim 1 wherein:
respective electrical resistances among regions of the first plurality of regions decrease monotonically as the distances of the first plurality of regions increase from the first L-shaped region; and
respective electrical resistances among regions of the second plurality of regions decrease monotonically as the distances of the second plurality of regions increase from the second L-shaped region.
5. The optical modulator of claim 1 wherein each region among the first plurality of regions is of the same length as a corresponding region among the second plurality of regions that is located at the same distance from the PN junction.
6. The optical modulator of claim 1 wherein the PN junction is centered between the first and second plurality of regions.