Efficient mode coupling/(de)multiplexing between a few-mode fiber and a silicon photonic chip

Mode-division multiplexing (MDM) has attracted much attention due to its ability to further increase the transmission capacity of optical interconnects. While further developments of MDM optical interconnects are hindered by the coupling of few-mode fibers (FMFs) and silicon photonic chips, a high-efficiency, broadband, and scalable multimode FMF-chip interface is still eagerly desired. To address this challenge, a novel scheme for efficient multimode coupling is proposed by introducing a silica planar lightwave circuit as an intermediate. The core idea is to couple and demultiplex higher-order modes by leveraging the superiorities of silica optical waveguides for manipulating LP modes, facilitated through tailoring the mode conversion related to different mode symmetric properties. The demultiplexed modes are consequently butt-coupled to the silicon photonic chip in single-mode manner, thus being available for fulfilling further data transmitting/receiving/routing directly. As a proof of concept, a six-channel FMF-chip coupler working with the LP 01- x / y , LP 11a- x / y , and LP 11b- x / y modes is designed with low coupling losses of 0.77–1.39 dB and low intermode crosstalk of <−27.2 dB in a broad bandwidth (>150 nm ). Minimum coupling losses of 1.36–2.48 dB are experimentally demonstrated. It is the first demonstration for the integrated multimode FMF-chip coupler enabling the simultaneous coupling of six mode-channels, to the best of our knowledge. We believe that this work has the great potential for developing energy-efficient and low-cost chip-to-chip MDM interconnections in the future.