Co-Design and Demonstration of a 25-Gb/s Silicon-Photonic Mach–Zehnder Modulator With a CMOS-Based High-Swing Driver

This paper discusses the design considerations of Silicon-based Mach-Zehnder Modulator (MZM) transmitters, consisting of the design of a Si-Photonic MZI modulator and a CMOS-based modulator driver. III-V and silicon-photonic MZMs are compared with respect to electrode design, driving scheme, and velocity matching. A 25-Gb/s hybrid-integrated silicon photonic MZM transmitter is then demonstrated, composed of a 65-nm bulk-CMOS driver directly wire bonded to a 180-nm SOI-CMOS MZM. The driver employs push-pull unit cells to save approximately 40% dc power while delivering 6.4 VPP differential swing to the modulator. Multiple driver cells are distributed along artificial on-chip transmission-lines, extending the bandwidth by 6 times. The lateral PN-interleaved MZM is designed and optimally biased to reach a balance of high-speed with acceptable optical extinction ratio (ER). Experimental results show that the fully assembled Si-Photonic transmitter (including PCB and wire-bonding losses) achieves approximately 11-GHz bandwidth, 6.4 VPP differential output swing, clean 25-Gb/s optical eye diagrams with 4-dB ER, and 520-mW dc power.