Joint Non-Data-Aided Clock Recovery for Space-Division Multiplexed Optical Transmission Systems

In recent years, space-division multiplexing (SDM) has been proposed as a technique to cope with the increasing demand for higher per-fiber capacity in optical networks by modulating multiple independent signals onto multiple spatial paths. This can be accomplished by using specialized fibers that carry multiple signals in a number of fiber cores, fiber modes, or a combination of both types. In such fibers, strong spatial coupling of the signals requires for a joint digital signal processing (DSP) at the receiver. While research has mainly focused on system performance and multiple-input multiple-output (MIMO) equalizers, a reliable joint clock recovery tolerant to spatial-and-polarization-mode dispersion is an active field of research with recent progress. In this paper, we present a novel digital blind joint clock recovery that is tolerant to polarization-and-spatial mode ispersion. The joint clock recovery is implemented in a feedforward architecture, which allows simple implementation. We provide a detailed analysis of the algorithm complexity for hardware implementation. In simulations, we show low clock phase jitter for fiber lengths up to 10,000 km. ... mehrFinally, we demonstrate clock recovery for a 90-GBd 16-QAM signal over a 150-km randomly-coupled 4-core fiber (RC-4CF) resulting in a total data rate of 2.88 Tbit/s per wavelength and analyze equalizer convergence using a dedicated joint clock recovery.