Traveling wave electrode design for ultra compact carrier-injection HBT-based electroabsorption modulator in a 130nm BiCMOS process

Abstract

Silicon photonic system, integrating photonic and electronic signal processing circuits in low-cost silicon CMOS processes, is a rapidly evolving area of research. The silicon electroabsorption modulator (EAM) is a key photonic device for emerging high capacity telecommunication networks to meet ever growing computing demands. To replace traditional large footprint Mach-Zehnder Interferometer (MZI) type modulators several small footprint modulators are being researched. Carrier-injection modulators can provide large free carrier density change, high modulation efficiency, and compact footprint. The large optical bandwidth and ultra-fast transit times of 130nm HBT devices make the carrierinjection HBT-based EAM (HBT-EAM) a good candidate for ultra-high-speed optical networks. This paper presents the design and 3D full-wave simulation results of a traveling wave electrode (TWE) structure to increase the modulation speed of a carrier-injection HBT-EAM device. A monolithic TWE design for an 180um ultra compact carrier-injection-based HBT-EAM implemented in a commercial 130nm SiGe BiCMOS process is discussed. The modulator is electrically modeled at the desired bias voltage and included in a 3D full-wave simulation using CST software. The simulation shows the TWE has a S11 lower than -15.31dB and a S21 better than -0.96dB covering a bandwidth from DC-60GHz. The electrical wave phase velocity is designed close to the optical wave phase velocity for optimal modulation speed. The 3D TWE design conforms to the design rules of the BiCMOS process. Simulation results show an overall increase in modulator data rate from 10Gbps to 60Gbps using the TWE structure.