Reconfigurable Generation of PAM-4 Signal Based on Fano Effect for Optical Interconnect Systems

Abstract

We present a novel low-power architecture for the generation of multilevel pulse amplitude modulation (PAM-4) signal generation.  A new structure of a micro-ring resonator based on a 4´4 MMI (Multimode interference) coupler is proposed to control the coupling coefficient and Fano shapes. Based on this structure, a high linearity of the transmission is created, compared with the Mach Zehnder Interferometer (MZI) conventional structure. Here, instead of using directional couplers and MZI as shown in the previous reports, in our method only two 4´4 multimode interference structures on silicon on insulator (SOI) waveguides has been used. The new design is compatible and suitable for the current CMOS fabrication technology. In this work, the special design is as follows: one of two MMI couplers is used to be a micro-ring resonator and two segmented phase shifters are used in the micro-ring resonator to generate 4 levels of the PAM-4 signal. The micro-ring resonator is controlled to work at the over-coupled region, so the Fano effect can be generated. This proposed PAM-4 architecture uses the generated Fano effect, therefore an extreme reduction in power consumption can be achieved. A large fabrication tolerance of ±500 nm and a compact footprint of 10´500 µm² can be carried-out. The device is simulated and optimally designed using the FDTD (finite difference time domain) and EME (Eigenmode Expansion). This architecture can be useful for optical interconnects and data center network applications.