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.

Demonstration of true-eigenmode propagation in few-mode fibers by selective LP mode excitation and near-field observation

“…The relationship between LP modes and true eigenmodes in a cylindrical core optical fiber can be expressed in terms of a matrix formalism. We analyzed the electromagnetic field distribution along with the propagation when an LP mode is selectively launched into a fiber, and showed that the profile of the electromagnetic field of guided light launched as an LP mode at the input end evolves along with its propagation [10] owing to the difference in the propagation constants between the true eigenmodes [11]. As a result, mode discrimination and demultiplexing are difficult at the output end of an FMF and MIMO-DSP is essential.…”

“…As a result, mode discrimination and demultiplexing are difficult at the output end of an FMF and MIMO-DSP is essential. To overcome this problem, we previously proposed a method of realizing MDM transmission using true eigenmodes as transmission channels by constructing a multi/demultiplexer of true eigenmodes utilizing that of LP modes [10]. As long as the transmission distance is less than several kilometers so that the mode conversion or mode coupling is negligibly small [12], the MDM transmission using true eigenmode will be effective for a MIMO-free transmission.…”

Full-set high-speed mode analysis in few-mode fibers by polarization-split segmented coherent detection method: Proposal and simulation of calculation error

“…In general, LP 11 modes are represented by a linear combination of TE 01 , TM 01 , and HE 21 modes [15]. The matrix relating true eigenmodes and LP modes is given by Eq.…”

“…The matrix relating true eigenmodes and LP modes is given by Eq. (27) in Ref [15], and the inverse matrix is derived as Eq. (30) in Ref [15].…”

“…(27) in Ref [15], and the inverse matrix is derived as Eq. (30) in Ref [15]. Therefore, using the complex amplitudes of the LP modes obtained by the proposed method, we can also derive the complex amplitudes of the true eigenmodes using these matrix formulas.…”