The explosive increase in data traffic over the last few decades has been driving the demand for high-capacity optical transmission systems. State-of-the-art spectrally efficient technologies such as high-order modulation formats, probabilistic constellation shaping (PCS) and high-performance forward error correction (FEC) have realized capacities very close to the theoretical limit of the wavelength bands used. The widely-used erbium-doped fiber amplifier (EDFA) is unable to support another wavelength-division multiplexing (WDM) channel because few amplification bands remain unused. Ultra-wideband (UWB) transmission with extra bandwidths, e.g., S, C and L bands, is a promising candidate for expanding transmission capacity. UWB systems can enlarge capacity without replacing any of the existing fiber infrastructure, which offers dramatic efficiencies in the cost and delay for system deployment. Recently, 100-Tb/s-class UWB transmission has been experimentally demonstrated, and the S-band region is regarded as the next candidate beyond conventional C and/or L band WDM systems. Designing such systems demands an understanding of how interchannel stimulated Raman scattering (ISRS) impacts WDM-system performance; because the S and L bands are separated by around 100 nm, ISRS is a significant issue.
In this paper, we investigate the effects of ISRS on signal quality of UWB transmission systems with experiments on S- (35 channel) and L- (40 channel) band WDM transmission using DP-16QAM signals. The results show that ISRS causes only signal power transfer, whereas the nonlinear cross-talk generated by ISRS has only minimal effect on signal quality. We prove the concept of UWB transmission by a DP-128QAM 150.3-Tb/s transmission experiment over a 40- km single-mode fiber in S, C, and L bands with WDM bandwidth of 13.6 THz; success is due to our proposed signal power optimization scheme which considers ISRS-induced power transfer between S and L bands.