High-density MDM silicon photonic transmitter assisted with MRMs and a two-dimensional grating coupler for single-fiber 4 × 80-Gbps signaling

In this paper, a four-channel silicon photonic mode division multiplexing (MDM) transmitter chiplet is proposed over a 1.85-mm² footprint, utilizing micro-ring modulators and a two-dimensional grating coupler (2D GC) with side-distributed Bragg reflectors. Through genetic optimization approach, the optimized 2D GC can simultaneously couple the two orthogonal polarizations of the on-chip TE₀ and TE₁ modes to the four LP modes in the FMF, all exhibiting high coupling efficiency beyond -3.8 dB, so as to support the MDM optical fiber interface. High data rate up to 4 × 80-Gbps signaling is experimentally demonstrated with a bit error rate below the 7% hard-decision forward-error-correction threshold. The proposed transmitter chiplet features single fiber and single-wavelength applications of quad small form-factor pluggable (QSFP) transceivers, pave the way toward future high-density and large-capacity optical interconnects scenarios.