Multiple Tb/s Coherent Optical Transceivers for Short Reach Interconnect

This paper investigates coherent optical transceivers for short-reach interconnect, where a local oscillator laser is used to boost received optical signals for high receiver sensitivity. We review the state-of-the-art technologies and propose a miniature Mach-Zehnder modulator (mMZM) array with 3D silicon photonic-electronic integration to enable high-density, low-power multiple Tb/s coherent transceivers. For design optimization at transceiver level performances, we develop methodology and models to simulate PN junction and mMZM for high-efficiency high-speed modulation, which can be linked to system performances, including high-speed performances, receiver sensitivity, optical link budget, and coherent optical transceiver power consumption. With the optimized design and state-of-the-art technologies, we achieve highly integrated multiple Tb/s coherent transceivers with high density, high speed, and low power. Our simulation results show 3 pJ/bit for integrated driver/mMZM, 5 pJ/bit for integrated PIC/IC and 6.5 pJ/bit with transceiver optics for 6.4 Tb/s with 60 Gbaud 16QAM. Compared with conventional long phase shifter (PS) MZM (4 mm), mMZM with short PS (2.4 mm) only have an extra loss of ∼2 dB under 60 Gbaud 16QAM modulation with optimized designs. We study the scalability from 6.4 Tb/s to 12.8 Tb/s using 120 Gbaud 16QAM for intra-DC interconnect. The results show that further improvement for modulation efficiency, frequency response and laser output power are needed to enable the 12.8 Tb/s.