Nonlinear depolarization of light in optical communication fiber

Lothar Moeller

doi:10.1063/1.5097270

Abstract

We report the experimental observation of a novel transmission phenomenon in optical long-haul communication systems. Unpolarized ASE depolarizes via nonlinear fiber interactions a cw laser light during their copropagation which leads to small but measurable ultrafast polarization state fluctuations at the fiber output. We provide a phenomenological approach and a theory that qualitatively corroborates our experimental results. One of our major findings suggests that the applicability of the often used Manakov equation needs to be scrutinized for highly accurate studies of nonlinear polarization state evolutions in noisy environments. The described phenomenon leads to a qualitatively different microscopic understanding of nonlinear light propagation in fiber and can contribute toward an explanation for today’s commonly perceived gap between simulated and experimentally obtained system performance in optical data transmission.

Highlights

INTRODUCTIONThe basis of all backbone networks, enable global long-reach and high-capacity data exchange like the WWW
Modern optical fiber communications, the basis of all backbone networks, enable global long-reach and high-capacity data exchange like the WWW
The observed repeater power dependence of the state of polarization (SOP) speed allows us to rule out guided acoustic-wave Brillouin scattering (GAWBS) as the origin for NL depolarization of light (NLDP)

Summary

INTRODUCTION

The basis of all backbone networks, enable global long-reach and high-capacity data exchange like the WWW. Unpolarized optical noise rapidly changes via the fiber’s Kerr nonlinearity the state of polarization (SOP) from a fully polarized cw light by inducing antisymmetric phase noise in both of its orthogonal polarization states These fluctuations become resolvable with a new generation of high-speed polarimeters and do not average out over wide noise bandwidths, but grow with the propagation distance. We contrast the receive SOP speed distributions from the transmitted probe with the one from a reference signal that possesses equal power, equal ASE, and equal OSNR but bypasses the MONET cable (back-to-back signaling, btb). This reference is obtained by superimposing the transmitter signal with the noise output of the transmission link and launched via a short fiber jumper directly into the receiver [dashed path, Fig. 1(a)]. This mitigates linear polarization effects along the cable with negligible bias on the histograms

Nonlinear depolarization vs transmission distance

Nonlinear depolarization vs repeater output power

MATHEMATICAL APPROACH TO NLDP

NLDP IMPACT ON THE SYSTEM CHANNEL CAPACITY

CONCLUSION