Broadband and efficient multi-mode fiber-chip edge coupler on a silicon platform assisted with a nano-slot waveguide

Abstract

Mode-division multiplexing (MDM) has been extensively utilized to expand the capacity of chip-scale or fiber-based optical communication, whereas it is still challenging to implement the MDM for fiber-chip optical interconnects due to the huge mode mismatch between few-mode fiber (FMF) and multi-mode waveguide. In this work, we propose and design a silicon integrated six-mode edge coupler assisted with a slot waveguide, which achieves the efficient direct conversion of multiple modes between the waveguide and fiber in a broad bandwidth. Based on the principle of mode conversion, this edge coupler enables the mode conversion between six linear polarization (LP) modes (i.e. LP x/y 01 , LP x/y 11a , LP x/y 11 b ) in FMF and six on-chip waveguide modes (i.e. TE 0 , TE 1 , TE 2 , TM 0 , TM 1 , TM 2 ) with low insertion loss, low mode crosstalk and broad bandwidth. The obtained results show that over the whole C-band the efficiency of mode conversion is higher than 98% and the mode crosstalk is low than -19 dB, while the total coupling loss is higher than 85%. The favorable results offer an important reference for designing related broadband photonic devices, and the presented scheme could be potentially exploited to further increase the transmission capability for prospective fiber-chip optical interconnections and communications.