A 50-GHz Bandwidth Traveling-Wave Mach-Zehnder Modulator With Built-In Feedback Equalization

A 50-GHz bandwidth traveling-wave Mach-Zehnder modulator (TWMZM) was designed with a new equalization technique, which takes advantage of the intrinsic delay in a traveling-wave electrode (TWE) and a local negative-feedback circuit. With this idea, given the availability of flip-chip bonding, a long TWE can be equalized as a single stage or be segmented into a few stages, each being equalized separately to optimize the performance of the entire device. The detailed analysis of this equalization technique is presented. As a demonstration, a 1.6-mm long equalized TWMZM was designed using a commercial silicon photonic process and a 0.13 \mu \mathrm{m} SiGe process. A 2-stage cascaded design with equal equalization was adopted and optimized for high bandwidth and high extinction ratio. The circuit was designed using the multi-physics electronic-photonic integrated circuit (EPIC) design flow we developed recently, wherein both electronic and photonic parts were modeled and the EPIC circuit was simulated for system level performance evaluation. Simulation results showed that the equalization technique increased the 3-dB EO bandwidth of the TWMZM from 28 to 50.4 GHz, an 80% increase. Large signal performance with non-return to zero signals upto 100 Gb/s was evaluated and the results showed significant improvements in the eye quality with equalization. The performance evaluation with pulse amplitude modulation (PAM)-4 signal was also carried out and the results showed successful operation at 106 Gbaud PAM-4 for the equalized TWMZM, makes it a promising candidate for future 200 Gbps-per-lambda optical transceivers.