Sidelnikov O.S.   Redyuk A.   Fedoruk M.P.   Turitsyn S.K.  

Numerical simulation of multi-mode fiber-optic communication lines

Reporter: Sidelnikov O.S.

The annual traffic growth already exceeds the growth of the transmission capacity, and in the nearest years, we may face the problem of the traffic volume exceeding the capabilities of data transmission technologies, if no new technology, providing a significant increase in the transmission capacity of communication lines, will be offered. The development of communication systems based on multi-mode fibers is considered as a promising way for solving the above problem. Multi-mode fibers allow an increase in the transmission capacity of optical networks at the expense of simultaneous transmission of signals through multiple modes of the fibre.
In the present work we consider two important cases of signal propagation through multi-mode fibers (MMF) that are of practical interest, the weak- and strong-coupling regimes. In the present work, we study the process of propagation of electromagnetic radiation in multi-mode fibers. As the basis model, we consider the model based on the Manakov equations and describing the nonlinear propagation of the signal in multi-mode fibers in the case of weak [1] and strong coupling [2]. The aim of the present work is to find the configuration of a digital communication system, optimal with respect to minimising the bit-error rate (BER), depending on the number of propagating modes and the mode coupling regime. To solve propagation equations we used the symmetric version of the split-step Fourier method (SSFM). To transmit the data we used polarisation-division with the quadrature phase-shift keying (QPSK). To shape the pulse we used the filter with the raised cosine characteristic and the smoothing coefficient 0.2. Each signal consisted of 215 symbols with 32 counts per symbol and was transmitted with the symbol rate Rs = 28.5 Gbaud.
In the present work we compared weak- and strong-coupling regimes. It was shown that with the growth of the number of modes the strong coupling regime provides a lower level of BER than the weak coupling one [3]. We also investigated the dependence of BER on differential group delay (DGD) between the modes. It was shown that performance increases with increasing DGD.
One of the main challenges of long-distance propagation in multi-mode fibers in weak-coupling regime is the complexity of MIMO receivers that used to equalize for mode coupling. We compared two types of multi-mode fibers to meet this challenge: MMF with low DGD and with compensated DGD (combining fiber sections with DGD of opposite sign). MMF with low DGD demonstrate better performance than fibers with DGD management for long-distance transmission.
The work is supported by grant of the President of the Russian Federation (MK-9240.2016.9).