Experimental Evaluation of Impairments in Unrepeatered DP-16QAM Link with Distributed Raman Amplification

Abstract

Abstract:The transmission impairments of a Raman amplified link using dual-polarization 16-quadrature amplitude modulation (DP-16QAM) are experimentally characterized. The impact of amplitude and phase noise on the signal due to relative intensity noise (RIN) transfer from the pump are compared for two pumping configurations: first-order backward pumping and bi-directional pumping. Experimental results indicate that with increased Raman backward pump power, though the optical signal-to-noise ratio (OSNR) is increased, so is the pump-induced amplitude and phase noise. The transmission performance is firstly improved by the enhanced OSNR at a low pump power until an optimum point is reached, and then the impairments due to pump-induced noise start to dominate. However, the introduction of a low pump power in the forward direction can further improve the system's performance.

Modeling of Ultra-Long Span Bidirectional Raman Transmission Link Using Three-Segment Hybrid Fiber Core Structure

“…In order to restore signal power at the receiver end after propagating several hundred kilometers, unrepeatered ultra-long single-span systems require high Raman gains in both forward and backward directions to compensate for very large accumulated fiber attenuation [4,5]. There are two major limiting factors in such systems: the first factor is nonlinear Kerr effect-induced nonlinearity, such as self-phase modulation in a single-channel systems, cross-phase modulation, and four-wave mixing for a multi-channel systems; the second factor is optical signal-to-noise ratio (OSNR) degradation due to spontaneous Raman noise accumulation caused by high Raman pump power from both the forward and backward directions [6,7]. Figure 1 illustrates the typical profile of signal power transmission along an ultra-long span based on [8] with modifications and recalculations for various pump power ratios over a very-long span length (in this case 390 km); additional details will be provided in the following sections.…”

“…Therefore, to improve transmission performance, a solution that can modify the gain profile of bidirectional distributed Raman amplification and simultaneously reduce the Kerr nonlinear limit and the Raman noise limit is required. mixing for a multi-channel systems; the second factor is optical signal-to-noise ratio (OSNR) degradation due to spontaneous Raman noise accumulation caused by high Raman pump power from both the forward and backward directions [6,7]. Figure 1 illustrates the typical profile of signal power transmission along an ultra-long span based on [8] with modifications and recalculations for various pump power ratios over a very-long span length (in this case 390 km); additional details will be provided in the following sections.…”