What is a mode in few mode fibers?: Proposal of MIMO-free mode division multiplexing using true eigenmodes

Abstract

The evolution of electromagnetic field profile of LP modes along with the propagation owing to the difference of propagation constants between constituent true eigenmodes is accurately analyzed. It is shown that the mode demultiplexer can’t accurately discriminate the LP mode at the output end and so the MIMO-DSP is inevitable for the mode division multiplexed transmission using LP modes. From the accurate analysis, a transform matrix between LP modes and constituent true eigenmodes is derived and a novel method to configure true eigenmode multi/demultiplexer is proposed to realize MIMO-free transmission.