Spatially and Spectrally Flexible Elastic Optical Networking

While the rapid deployment of wavelength-division multiplexing (WDM) technologies sustained the explosive and exponential network traffic growths in the past decade, the continuing trend of exponential traffic growth driven by data centers and emerging new services is demanding deployment of more scalable and flexible networking technologies. The legacy WDM technologies can support traffic up to multiple terabits per seconds on a single fiber, but this is not sufficient to support future traffic demands with peak link capacity beyond 10 Tb/s. It is expected that commercial systems will need to support link capacity as high as 100 Tb/s by 2018 [1]. The recent renaissance of coherent optical communications with polarization-division multiplexing has enabled capacity of single fiber links up to 20 Tb/s. Further increases in capacity and spectral efficiency are very challenging because of the nonlinear Shannon limit [2]. The high optical power required for a high signal-to-noise ratio (SNR) starts to degrade the transmitted signal quality due to nonlinear optical effects in the transmission link [2] even for moderate (~500 km) transmission distances. Hence, transmission capacities beyond 100 Tb/s must explore a new and final frontier in optical communications — the space domain — by using spacedivision multiplexing (SDM). SDM allows the nonlinear Shannon capacity limit over a singlemode fiber to be overcome, providing a pathway toward petabit per second link capacities and spectrum efficiencies beyond 10 b/s/Hz for practical transmission distances. Several papers in the literature have already discussed the advances and technological challenges in actual deployments of SDM. In addition to the straightforward bundled fiber approach, where the SDM system is composed of N independent single-mode fiber (SMF) systems, an SDM system can exploit few-mode fibers (FMFs) [3], multi-(many)-mode fibers (MMFs), multi-core fibers (MCFs) supporting orbital angular momentum (OAM) [4, 5], or other eigenstates. Each approach has benefits and drawbacks related to some particular technological challenges. FMF systems strongly rely on multiple-input multiple-output (MIMO) digital signal processing (DSP) due to strong mode coupling, but can benefit from the availability of FMF amplifiers [3]. MCF systems require complex fiber fabrication and the use of N separated amplification stages, but compared to FMF, the crosstalk and coupling between cores can be carefully controlled to levels that do not require or strongly limit the use of MIMO DSP. OAM states have relatively well defined azimuthal orthogonality, leading to possibly simpler MIMO DSP for propagation through ring-core FMFs or MMFs compared to other multimode propagation methods. Figure 1 shows some representations of the three physical domains used to increase the capacity in fiber optic communication systems. In addition to the capacity increase, future networks must achieve flexible and agile utilization of network resources with scalable network control and management (NC&M). Recently, researchers proposed a new optical networking ABSTRACT