Abstract
Undersea systems constitute a distinct application space characterized by intercontinental distances between nodes and the requirement that repeaters deployed on the ocean floor be extremely reliable. Undersea systems with conventional discrete erbium-doped fiber amplifier (EDFA) repeaters support high-capacity dense wavelength division multiplexing (DWDM) transmission over thousands of kilometers with highly reliable underwater equipment. Improved repeater noise performance is important for higher-capacity systems required to meet increasing traffic demand and for increased repeater spacing to reduce system cost. This chapter focuses on advanced hybrid amplifier technologies for undersea systems: hybrids of distributed Raman amplifiers (DRAs) with discrete EDFAs and hybrids of remote optically pumped amplifiers (ROPAs) with discrete EDFAs. They are used in hybrid configurations because discrete EDFAs have superior pump efficiency for producing gain and output power, but DRAs and ROPAs deliver superior noise performance. It examines architectures and performance in ultra-long-haul, high-capacity DWDM systems of such hybrid amplifiers. Because of their superior noise performance, hybrid DRA/EDFAs can be used to increase capacity and repeater spacing. Because of the spectral flexibility of Raman amplification, hybrid DRA/ EDFAs can also be used to increase capacity by increasing the available optical bandwidth. Hybrid ROPA/EDFAs do not have the same spectral flexibility but are found to offer noise performance and transmission performance that is somewhat better than that of hybrid DRA/EDFAs.
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