Efficient mode coupling between a few-mode fiber and multi-mode photonic chip with low crosstalk

The mode-division multiplexing technology has been developing slowly in the field of fiber-chip-fiber optical interconnects, mainly limited by the inefficient mode coupling between few-mode fiber and multi-mode photonic chip. Here we propose and design a multi-mode coupler composed of tapered few-mode fiber and silicon integrated multistage waveguide tapers, which allows the direct coupling between high-order fiber modes and high-order waveguide modes with high coupling efficiency and low crosstalk. Based on the edge coupling scheme, the six linear polarization modes (LP01x/y, LP11a x/y, LP11bx/y) in few-mode fiber are firstly coupled into the integrated waveguide with low insertion loss, then the input modes are converted to the desired waveguide modes (TE₀, TE₁, TE₂, TM₀, TM₁, TM₂) with low mode crosstalk relying on the mode evolution principle. The obtained results show that the coupling efficiency is higher than 87%, while for the mode conversion process, the efficiency is higher than 99% and the mode crosstalk is lower than -25 dB. The favorable performance achieved may open new perspectives for diverse mode-division multiplexing applications, enabling efficient capacity scaling in fiber-chip-fiber optical interconnects and optical communication systems.