Inline amplifier transmission experiments over 4500 km at 2.5 Gb/s

Abstract

Abstruct-An in-line amplifier system is constructed with erbium-doped fiber amplifiers spaced at 100 km and 80-km intervals. The system transmits 2.5-Gb/s signals over 2500 km with continuous-phase frequency-shift-keying heterodyne detection and over 4500 km with intensity-modulation direct-detection. With respect to amplifier output signal power levels, it is experimentally shown that there exists a dynamic range within which long-distance signal transmission can be achieved with only small receiver sensitivity degradation. The range's upper and lower limits are determined by fiber nonlinearities and amplifier noise characteristics, respectively.

Performance limits in optical communications due to fiber nonlinearity

“…Finally, at high power levels, additional phase distortion due to fiber nonlinearity (self-phase modulation) greatly enhances the impact of dispersion with the net result of a quadratic decrease in performance with launched power. Today, such nonlinear threshold curves are a familiar feature of experimental reports of long haul transmission [33][34][35][36][37][38], although they may be plotted in terms of bit error rate rather than signal to noise ratio or Q factor [39][40][41]. Figure 2: Predicted signal to noise ratio for a 10 Gbaud amplitude shift keyed system with direct detection over fifty 65km spans of fiber assuming nonlinear coefficient of 1.4/W/km, loss of 0.2 dB/km, noise figure of 4.8dB and normal chromatic dispersion with magnitudes of 3.2, 1.6, 0.8, 0.4, 0.2, 0.1 and 0.05 ps 2 /km (purple to mauve respectively) based on self-phase modulation and dispersion (solid lines) and for self-phase modulation, dispersion and parametrically amplified noise (dotted lines).…”

“…Unfortunately, even before the practical considerations of fiber power handling and the necessary fiber fabrication precision to control dispersion are taken into account, additional nonlinear effects come into play to restrict the capacity at low dispersion, in particular the parametric interaction between signal and noise [42,43] which was observed in the earliest experiments at 2.5Gbit/s, for straight line [39] systems, recirculating loops [44], and in numerical simulations [45]. The observed effects were attributed to the parametric amplification of the amplified spontaneous emission by the signal, which was sometimes referred to as modulation instability.…”

“…Dots represent reported per wavelength experimental results for low cost short reach systems (red), single channel systems with optical pre-amplifiers (blue) and in-line amplifiers (purple). See [46][47][48][49][50] for selection of references for binary amplitude shift keyed systems (solid symbols) and for more complex formats (open symbols) operating with FEC.…”

IM-DD and DPSK Heterodyne Transmission Experiments at 2.55 μm using Single-mode Fluoride Optical Fibers

“…It was recently pointed out, on the basis of a 1.55 μηι band coherent transmission experiment over 2200 km using 24 erbium doped fiber amplifer repeaters, that a coherent transmission over this distance was difficult due to the nonlinear effect originating from accumulated amplified spontaneous emission (ASE) [36]. As a midinfrared transmission system using a very low loss fluoride fiber does not need an in-line fiber amplifier, the limitation caused by ASE accumulation will be avoided and a coherent transmission over 6000 km is possible in principle.…”