Silicon optical phase shifter with a series of P—N junctions

An apparatus, comprising:

• a Mach-Zehnder optical modulator having a parallel pair of optical waveguide arms;
• wherein an optical phase shifter is along one of the optical waveguide arms, the optical phase shifter comprising:
• a planar optical waveguide having a silicon optical core and a geometry of a rib waveguide, wherein dimensions of the silicon optical core as the rib waveguide include a rib width and a core thickness;
• and
• a pair of biasing electrodes located along opposite sides of a segment of the silicon optical core;
• wherein the segment of the silicon optical core comprises a series of p-n junctions, the series extending in a direction transverse to an optical propagation direction of an optical signal and across the rib width of the silicon optical core in a segment of the planar optical waveguide including the segment of the silicon optical core;
• wherein the series comprises at least three of the p-n junctions configured to be reverse biased by applying a voltage across the biasing electrodes;
• wherein the optical phase shifter is configured to control a phase of the optical signal propagating through the planar optical waveguide by changing carrier densities at the at least three of the p-n junctions, due to varying the voltage, to alter a refractive index of the planar optical waveguide.

An apparatus, comprising:

• a traveling-wave Mach-Zehnder optical modulator having a parallel pair of optical waveguide arms;
• wherein an optical phase shifter is along one of the optical waveguide arms, the optical phase shifter comprising:
• an optical waveguide having a silicon optical core and a geometry of a rib waveguide, wherein dimensions of the silicon optical core as the rib waveguide include a rib width and a core thickness;
• and
• a pair of biasing electrodes located along opposite sides of a segment of the silicon optical core;
• wherein a transverse cross-section of the silicon optical core includes a plurality of p-n junctions in series extending in a direction transverse to an optical propagation direction of an optical signal and across the rib width of the silicon optical core in a segment of the optical waveguide including the segment of the silicon optical core;
• wherein at least two of the p-n junctions are configured to be reverse biased by applying a voltage across the biasing electrodes;
• wherein the optical phase shifter is configured to control a phase of the optical signal propagating through the optical waveguide by changing carrier densities at the at least two of the p-n junctions, due to varying the voltage, to alter a refractive index of the optical waveguide;
• wherein the at least two of the p-n junctions comprise two reverse-biased p-n junctions offset from a lateral center of the silicon optical core in the segment thereof, and a single reverse-biased p-n junction aligned with the lateral center.