Exploiting Propagation and Polarization Effects of Multimode Fibers for In-Network Physical Layer Key Distribution

Optical multicore and multimode fibers (MCF/MMF) are promised to pace with the capacity crunch of back-bone networks by their spatial domain using space division multiplexing (SDM) [1]. Although multiple channels propagate within the same media in parallel, material inhomogenities and bendings induce inter- and intra-core crosstalk (XT), the compensation of which is crucial for long-haul SDM-fiber deployment [2]. In addition, the inherent XT provides random scattering to be exploited for physical layer security (PLS), either as physical un-clonable function (PUF) [3] or secret key generation (SKG) for end-to-end security [4], [5]. For both, SDM and PLS, the main challenge is to recover the spatial amplitude and phase contributions of each channel at the receiver-side in real-time, e.g. by digital signal processing (DSP). With increased number of SDM channels the computational effort in DSP-based channel diagonalization arises.