8 December 2005 Co-directionally pumped Raman amplification and its application to long-span transmission
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Proceedings Volume 6021, Optical Transmission, Switching, and Subsystems III; 60211K (2005) https://doi.org/10.1117/12.635166
Event: Asia-Pacific Optical Communications, 2005, Shanghai, China
Distributed Raman amplification in the transmission fiber is an important technology for advancing the system performance. Co-directionally pumped Raman amplifiers can enhance the performance and allow more flexibility in the system design. However, several sources of non-amplified spontaneous emission noise need to be carefully considered in the amplifier design. The intrinsic cross gain modulation associated with the transient nature of Raman effect can impair the system performance, if the amplifier is not properly designed. We have isolated and measured the impairment due to cross gain modulation in 200-km bi-directionally pumped fiber spans. The penalty depends on the fiber dispersion characteristics and can be small for up to 20 dB on-off co-gain. The benefit of co-directionally pumped Raman amplifiers can be used in multiple long-span transmission to compensate the high loss while maintaining a low nonlinear impairment. It can also be used to extend the length of a single span and achieve a simple system configuration for unrepeatered applications. As opposed to using a span containing multiple fiber types and remotely pumped erbium-doped fiber amplification to achieve transmission over spans with > 60 dB loss, we have demonstrated an unrepeatered link over a single type of fiber with bi-directional Raman pumping. Using the simple conventional non-return-to-zero data format, we achieved transmission of 20 × 10Gb/s channels over a 300-km span of non-zero dispersion-shifted fiber. This simple system configuration provides an important option for terrestrial transmission in remote areas where service access is difficult.
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Mei Du, Mei Du, Lynn E. Nelson, Lynn E. Nelson, Peter Borg Gaarde, Peter Borg Gaarde, David DiGiovanni, David DiGiovanni, } "Co-directionally pumped Raman amplification and its application to long-span transmission", Proc. SPIE 6021, Optical Transmission, Switching, and Subsystems III, 60211K (8 December 2005); doi: 10.1117/12.635166; https://doi.org/10.1117/12.635166

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