Ultra-Low Power PAM-4 Generation Based on a Cascaded 2x2 MMI Coupler for Optical Interconnect and Computing Systems.

We propose a new structure for multilevel pulse amplitude modulation (PAM-4) signal generation for on-chip optical interconnects and data center networks. The proposed architecture use cascaded 3x3 multimode interference (MMI) and 2x1 MMI couplers to form only one two-port device. The feedback waveguide is used to create a ring resonator and two segmented phase shifters are used for implementing four PAM-4 levels. Two segmented phase shifters applied the plasma dispersion effect in silicon waveguide are used in the feedback ring resonator waveguide. The structure provides a very steep slope compared with the conventional structure based on Mach Zehnder Interferometer (MZM) and ring resonators. As a result, an extreme reduction of power consumption of 27 times is achieved. Based on this structure, an extreme high bandwidth and compact footprint are also achieved. In addition, the proposed structure can improve the linearity for PAM-4 operation due to the high slope of the Fano effect shape. The device is designed and analyzed using the 3D-Beam Propagation Method (BPM) integrated with the Finite Difference-Time Difference (FDTD) simulations. [ABSTRACT FROM AUTHOR]