Breaking efficiency-bandwidth limits of integrated silicon modulator using rib waveguide slab region doping design

Doping optimization in the slab waveguide region of a silicon photonic (SiP) modulator has always been considered to balance the optical loss and electrical resistance–capacitance constant. We found that the AC PN junction capacitance could be significantly decreased by specific doping concentrations in the slab areas. Benefiting from this effect, microwave losses are reduced and the electro-optic (EO) bandwidth is increased. As a proof-of-concept, we propose a silicon modulator based on a conventional lateral PN junction with optimized doping in the waveguide slab region. The simulation results show that a 3 dB-EO bandwidth exceeds 100 GHz can be achieved with a modulation length of 2 mm. In addition, the modulation efficiencies are 1.26 V·cm and 1.45 V·cm under −4 V bias and −6 V bias, respectively. This design shows the potential of high-speed signal transmission in SiPs.