2D least-squares mode decomposition for mode division multiplexing

Abstract

We investigate a fast and accurate technique for mode decomposition in multimode optical fibers. Initial decomposition task of near-field beam patterns is reformulated in terms of a system of linear equations, requires neither machine learning nor iterative routines. We apply the method to step and graded-index fibers and compare the decomposition performance. We determine corresponding application boundaries, propose an efficient algorithm for phase retrieval and carry out a specific preselective procedure that increases the number of decomposable modes and makes it possible to handle up to fifteen modes in presence of realistic noise levels.

Speckle backpropagation for compensation of nonlinear effects in few-mode optical fibers

“…However, random receiver noise often plays a crucial role in MD. There is always a trade-off between noise levels and the number of decomposable modes [30,31] . Therefore, investigation of the noise influence on MM-DBP performance is of paramount importance.…”

“…In order to train the MM-DBP network, we need pairs of input and output beam speckles that require numerical simulation of multimode signal propagation. Details on the MD-DNN architecture lie beyond the scope of the current work, as this part is purely technical and can be given by any other method [30,31] . In what follows, under MD-DNN, we understand an appropriately trained vision transformer [33] .…”

“…It is noteworthy that no standards for MDM receiver operation principles have been established yet, and not every spatial demultiplexing scenario would be appropriate for conventional MM-DBP schemes. In particular, demultiplexing may refer to utilization of bulky optics [28] , physical mode separation [29] , or implementation of numerical algorithms [30][31][32][33] . The latter is mostly given by the technique referred to as intensity-only mode decomposition (MD), which implies separation of modes, based on the near-field intensity distributions of multimode signals captured by a digital camera.…”