Opportunities and Challenges for Long-Distance Transmission in Hollow-Core Fibres

Anti-resonant hollow-core fiber of the Nested Antiresonant Nodeless type (NANF) has been showing a steady decrease in loss over the last few years, gradually approaching that of standard Single-Mode Fiber (SMF). It already by far outperforms SMF as to non-linear effects, which are three to four orders of magnitude lower in NANF than in SMF. Theoretical predictions and experimental evidence also hint at a much wider usable bandwidth than SMF, potentially amounting to several tens of THz. Propagation speed is 50% faster, a key feature in certain contexts. In this paper we investigate the potential impact of possible future high-performance NANF on long-haul optical communication systems, assuming NANF continues on its current steady path towards better performance. We look at the system throughput in different long-haul scenarios, addressing links of various length, from 100~km to 4,000~km, and different NANF optical bandwidths, loss and total launch power. We compare such throughput with a benchmark state-of-the-art SMF Raman-amplified C+L system. We found that NANF might enable relative throughput gains vs.~the benchmark on the order of 1.5x to 5x, at reasonable NANF and system parameter values. We also study the problem of the impact of NANF Inter-Modal-Interference (IMI) on system performance and show that a value of -60~dB/km, close to the currently best reported values, is low enough to have no substantial harmful effect. We finally look at a more long-term scenario in which NANF loss gets below that of SMF and we show that in this context repeterless or even completely amplifierless systems might be possible, delivering 300-400 Tb/s per NANF, over 200 to 300~km distances. The system simplification and ease of wideband exploitation implied by these systems might prove quite attractive especially in densely populated regions where inter-node distances are modest. While several technological hurdles remain towards NANF systems becoming practical contenders, in our opinion NANF appears to have the potential to become an attractive and possibly disruptive alternative to conventional solid-core silica fibers.