A 3D-Integrated 56 Gb/s NRZ/PAM4 Reconfigurable Segmented Mach-Zehnder Modulator-Based Si-Photonics Transmitter

Silicon photonic interconnects have the potential to break bandwidth-distance limitations intrinsically associated with electrical links This paper presents a dual-mode NRZ/PAM4 silicon photonic transmitter based on a segmented-electrode Mach-Zehnder Modulator (SE-MZM). The electrical portion of the transmitter, fabricated in a 16nm FinFET process, utilizes stacked-CMOS push-pull driver stages that include a parallel asymmetric fast discharging path to compensate for the slow transition edge caused by the nonlinear capacitance of the reversed-biased MZM diode segments. High-speed PAM4 modulation is achieved with phase interpolators for coarse delay control between the MSB and LSB segments and by employing independent digital-controlled delay lines on a per-segment basis to match the optical propagation delay. The 56 Gb/s optical transmitter achieves 9.5 dB extinction ratio and 12.6 pJ/bit power efficiency, excluding laser power, when driving the flip-chip bonded MZM designed in a 130 nm SOI process.