Control of frequency conversion and defragmentation for super-channels [invited]

Super-channel (or multi-carrier) transmission is today one of the most promising techniques for the support of high line rates, which are required to satisfy the massive increase of Internet traffic. Moreover, flex-grid optical networks seem to be the candidates for backbone networks by enabling high spectral efficiency thanks to the adoption of the ITUT flex-grid. Such networks may suffer from spectrum fragmentation, which can prevent the establishment of new connections. For this reason, defragmentation techniques (i.e., reoptimization) have been widely studied, especially considering single-carrier transmission. Inparallel, the software defined networking (SDN) paradigm and the active stateful path computation element (PCE) are emerging as candidates for the control of next-generation optical networks. Such architectures are also particularly suitable in the case of defragmentation since they enable the controller to trigger reoptimization procedures. In this paper, we investigate defragmentation in the presence of super-channels, at both the control and data planes. We propose and experimentally demonstrate a technique based on a periodically poled lithium niobate waveguide to achieve both frequency conversion and defragmentation in elastic (or flex-grid) optical networks. Its peculiarity is that it is suitable for super-channels because it avoids detrimental subcarrier overlapping during a frequency shift. SDN with the OpenFlow protocol is discussed for the control of such operations, as well as the active stateful PCE and generalized multi-protocol label switching (GMPLS). The frequency conversion and defragmentation techniques are demonstrated in a lab trial considering a 200 Gb/s super-channel and extended OpenFlow for the control plane. No loss of data is experienced.