All-optical signal processing technologies in flexible optical networks

All-optical signal processing has always been critical assistance for the flexible optical networks (FONs) development which realizes various signal processing functions in all-optical domain avoiding electronic bottlenecks. The sustained demands for the transmission capacity and network functions drive the optical networks to enlarge the bandwidth, extend formats and increase network structures. The optical vectors are multiplexed in four domains at least in practical which are amplitude, phase, polarization and wavelength, and more multiplexing technologies are under researching. Moreover, various kinds of optical networks are employed to fulfill the constantly emerging applications such as core, metro and access networks. Facing the higher-order modulation formats, multiple multiplexing technologies and more and more complicated network structure, the future FON needs to have the feature of modulation format transparency, bandwidth transparency, wavelength transparency (3T), multi-function, multi-channel, multi-network (3M), self-perceiving, self-learning, self-adapting (3S). The transmission capacity, network flexibility and efficiency will always be the critical index for the whole network performance. The all-optical signal processing technologies have great potential in realizing the FON with the feature of 3T, 3M and 3S to process the multiple multiplexing optical signals and the problems among various optical networks. In this paper, the future FON features including 3T, 3M and 3S are introduced in detail, and the key issues in the ultra-large-capacity FON (e.g., 400G FON) are analyzed including transmission distance, flexible connecting and performance monitoring. Then, the crucial all-optical signal processing technologies and the principle and important applications of the phase-sensitive amplifier are introduced. Finally, the current existing problems and future developing trend for the all-optical signal processing technologies are discussed.