Accurate SPICE Model of Forward-Biased Silicon PIN Mach-Zehnder Modulator for an Energy-Efficient Multilevel Transmitter

A precise device model of a silicon forward-biased PIN phase shifter was developed to realize a codesign of an integrated multilevel optical transmitter combining a compact silicon-based Mach-Zehnder modulator (MZM) and a low-power CMOS driver circuit by utilizing SPICE simulation. Both electric and optical responses of the PIN phase shifter were carefully investigated at various bias conditions and temperatures in order to build a SPICE device model that precisely emulates a highly nonlinear electric-to-optical (EO) response of the PIN phase shifter. The validity of the developed model was assessed for a dc response, small-signal RF electric, and optical responses, and also for large-signal EO responses. The simulation outputs exhibited very good agreement with the responses measured at each operation condition. Using this PIN phase shifter model, we designed a multilevel optical transmitter integrating a 750-mu m long silicon PIN-based MZM with a 28-nm CMOS driver circuit via passive RC circuit equalizers. The SPICE simulation demonstrated the feasibility of the integrated transmitter for 56 Gbps PAM4 operation with a very high energy efficiency: 1.2 mW/Gbps.