RESUMO
A weakly-coupled few mode fiber (FMF) with a simple double-layer core is designed and fabricated that support five (seven) weakly coupled mode groups with average attenuation of 0.21â dB/km (0.39â dB/km) at the C + L (O) optical wavelength bands. Two data transmission experiments are demonstrated utilizing the fiber. A 2-km orbital angular momentum (OAM) mode-group multiplexing (MGM) experiment in the O band achieves error-free transmission for all five multiplexed mode groups without multiple multiple-input multiple-output (MIMO) processing. A 40-km OAM mode division multiplexing (MDM) experiment supporting 14 mode channels in the C + L bands achieves bit error rates (BER) of below 2.4 × 10-2 (20% soft-decision forward-error-correction threshold) for all channels, based on low-complexity 4 × 4 or 2 × 2 MIMO equalization. These demonstrations prove the capability of the fiber to support weakly coupled MDM/MGM transmission across O + C + L optical wavelength bands.
RESUMO
A successful transmission of 14 multiplexed orbital angular momentum (OAM) channels each carrying 80 wavelengths over a 100-km single-span ring-core fiber (RCF) is experimentally demonstrated. Each transmission channel is modulated by a 20-GBaud quadrature phase-shift keying (QPSK) signal, achieving a record spectral-efficiency-distance product of 1870 (bit/s/Hz)·km for the single-core RCF based mode division multiplexing (MDM) transmissions. In addition, only low-complexity 2×2 or 4×4 multiple-input multiple-output (MIMO) equalization with time-domain equalization tap number no more than 25 is required to deal with the crosstalk among the highly degenerate intra-MG modes at the receiving end of the demonstrated OAM-MDM-WDM system, showing great potential in large-capacity and relatively long-distance MDM transmission with low digital signal processing (DSP) complexity.
RESUMO
Space-division multiplexing (SDM), as a main candidate for future ultra-high capacity fibre-optic communications, needs to address limitations to its scalability imposed by computation-intensive multi-input multi-output (MIMO) digital signal processing (DSP) required to eliminate the crosstalk caused by optical coupling between multiplexed spatial channels. By exploiting the unique propagation characteristics of orbital angular momentum (OAM) modes in ring core fibres (RCFs), a system that combines SDM and C + L band dense wavelength-division multiplexing (DWDM) in a 34 km 7-core RCF is demonstrated to transport a total of 24960 channels with a raw (net) capacity of 1.223 (1.02) Peta-bit s-1 (Pbps) and a spectral efficiency of 156.8 (130.7) bit s-1 Hz-1. Remarkably for such a high channel count, the system only uses fixed-size 4 × 4 MIMO DSP modules with no more than 25 time-domain taps. Such ultra-low MIMO complexity is enabled by the simultaneous weak coupling among fibre cores and amongst non-degenerate OAM mode groups within each core that have a fixed number of 4 modes. These results take the capacity of OAM-based fibre-optic communications links over the 1 Pbps milestone for the first time. They also simultaneously represent the lowest MIMO complexity and the 2nd smallest fibre cladding diameter amongst reported few-mode multicore-fibre (FM-MCF) SDM systems of >1 Pbps capacity. We believe these results represent a major step forward in SDM transmission, as they manifest the significant potentials for further up-scaling the capacity per optical fibre whilst keeping MIMO processing to an ultra-low complexity level and in a modularly expandable fashion.
