Efficient mode coupling between a few-mode fiber and multi-mode photonic chip with low crosstalk
Xiaoping Cao, Kang Li, Yuanjian Wan, Jian Wang
Abstract
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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msubsup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>LP</mml:mtext> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>01</mml:mn> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>x</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>y</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msubsup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>LP</mml:mtext> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>11</mml:mn> <mml:mi>a</mml:mi> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>x</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>y</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msubsup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>LP</mml:mtext> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>11</mml:mn> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>b</mml:mtext> </mml:mrow> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>x</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>y</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) 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 (TE 0 , TE 1 , TE 2 , TM 0 , TM 1 , TM 2 ) 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.