GAWBS Noise in Digital Coherent Transmission

Abstract

This paper presents recent progress on guided acoustic wave Brillouin scattering (GAWBS) noise in single-core fiber (SCF), multi-core fiber (MCF), and few-mode fiber (FMF). First, we describe theoretical analyses of GAWBS phase noise generated in these various types of fiber. By using three types of SCF, namely ultra-large area fiber (ULAF), standard single-mode fiber (SSMF), and dispersion-shifted fiber (DSF), we show that the GAWBS phase noise depends strongly on the effective core area A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> . We also describe the GAWBS phase noise in four-core fiber (4CF), where it is shown that GAWBS noise in the off-center core is quite different from that in SCF. Furthermore, we describe the GAWBS phase noise in FMF supporting two LP modes. Then, we compare the GAWBS noise powers induced in SCF, MCF, and FMF. Next, we describe experiments on GAWBS phase noise in various fibers, which agree well with the theory. We also measured and analyzed the GAWBS phase noise correlation between the cores in a 4CF, where it is shown that the correlation between cores strongly depends on the core position. Finally, we describe the influence of GAWBS phase noise on digital coherent transmission. We formulate the GAWBS phase noise based on the Gaussian distribution and evaluate its influence on the BER characteristics in a coherent QAM transmission. We found that it is difficult to realize a transoceanic-class QAM transmission with a QAM multiplicity of higher than 64 even without other impairments. Furthermore, we evaluate the SNR penalty induced by the GAWBS noise in a long-haul transmission by taking account of the amplified spontaneous emission (ASE) and nonlinear interference noise, which are unavoidable in actual systems. The calculated results show that the influence of the GAWBS noise is smaller than the other impairments, but it cannot be neglected in system evaluations.