On the usage of flexible transponder in survivable transparent flex-grid optical network

Transparent optical networks offers several potential advantages such as significant cost reduction, footprints and power saving by eliminating unnecessary optical-electrical-optical (O-E-O) conversion. The current design for such optical network is based on fixed technologies where the same transmission scheme (i.e., modulation format, bit-rate) is enforced for all connections in the network. Indeed, the guarantee of transmission quality for the worst connection (e.g., longest route) put a common operation for the whole network. Such worst-case design inherently faces an inefficient usage of spectrum resources and the situation worsen when protection requirement is taken into account. With the introduction of flexible transponder and flex-grid optical network concept, new opportunities arise to address the inefficiency of worst-case dimensioning. In this paper, we investigate the usage of flexible transponder in different protection architectures and highlight potential benefits compared to previous approaches in literature. In our presented scheme, the flexible transponder could work at most spectrum-efficient modulation format for both working and protection path and enable more opportunities for backup transponder sharing. A case study is performed on realistic network topology to quantify such benefits.