Crosstalk tolerance of spatially multiplexed MIMO systems

We assess the tolerance of an optical MIMO system to crosstalk from other, nominally isolated MIMO systems to trade optical component crosstalk specifications with MIMO digital signal processing complexity in spatially multiplexed transmission. Introduction Space-division multiplexing (SDM) is attracting attention as a cost and energy efficient solution to overcome the looming optical networks capacity crunch [1], [2], [3]. Two regimes of SDM have been predominantly considered, distinguished by whether crosstalk among parallel spatial paths is treated as an uncompensated impairment at the receiver, or whether it is actively managed through multiple-input-multipleoutput (MIMO) coherent digital signal processing (DSP) [4]: Using nominally uncoupled cores of 7core fiber, 2688-km SDM transmission at a perfiber aggregate spectral efficiency of 15 b/s/Hz [5] has been demonstrated, and up to 60 b/s/Hz [6] over 76 km. Using 19-core fiber, 305-Tb/s transmission over 10 km at an aggregate spectral efficiency of 30.5 b/s/Hz has been demonstrated [7], with a residual crosstalk level of as much as -16 dB at the long-wavelength end of the exploited spectrum, revealing the difficulties of building highly scalable low-crosstalk optical components such (such as waveguides, amplifiers, or couplers). On the other hand, managing crosstalk through MIMO processing, coupled-mode SDM transmission of six spatial and polarization modes over 4200-km microstructured [8] and 1200-km few-mode [9] fiber has been reported.