Enhanced O-Band Si Mach--Zehnder Modulator With Dual/Triple Low-Impedance Termination

By designing the traveling-wave electrode of the O-band Si-waveguide Mach-Zehnder modulator (MZM) with dual-end-port signal-to-ground p-n junction resistors, and encoding the pre-emphasized non-return-to-zero on-off keying (NRZ-OOK) data stream with dual- or triple-port low-impedance (low-Z) termination, the superposition between transmitted and reflected modulations can be fine-tuned to achieve beyond 67-Gbps operation per channel. Such a low-impedance-mismatched termination by using either a dual-port (with 45 Ω or 20 Ω) built-in resistors or a triple-port (with 30 Ω) terminators is compared with each other, indicating that the overly reflected modulation (with 20-Ω impedance) lengthens the rising/falling edges by 3-5 ps and scales down the electrical-to-optical bandwidth to 34.4 GHz. The high voltage standing wave ratio provides a degraded bandwidth of 5.5 GHz and a bit-error ratio of 2 orders of magnitude higher than the other two designs. In contrast, the dual-parallel-resistor-based low-Z (45-Ω) MZM respectively improves the NRZ-OOK to beyond 60-Gbps and nearly 50-Gbps after back-to-back, 2-km, and 10-km SMF transmissions defined by the IEEE 802.3bs standard. By using the tri-port terminated scheme with leveraged impedance of nearly 30 Ω, the managed reflection further enhances the standing-wave effect with periodical carrier depletion to improve the modulation efficiency, hence achieving the highest NRZ-OOK data rate of 67 Gbps and passing the telecom BER criterion after 2-km and 10-km SMF transmissions.