A 1,007 km Hollow-Core Fibre Link Carried 128 Tb/s in Real Time

November 2 — The China Telecom Research Institute announced today that it, together with YOFC and ZTE, has completed the world’s first 1,000-kilometre bidirectional real-time transmission test over hollow-core fibre: on a 1,007.48-kilometre link it achieved single-wavelength 800 Gb/s (PCS-16QAM) transmission in both directions across the extended C+L band, for a total capacity of 128 Tb/s.

The test produced three landmark results:

first, a record for the world’s longest point-to-point, non-loopback real-time transmission over hollow-core fibre, with at least 3 dB of loss margin retained per span and at least 3 dB of OSNR system maintenance margin;

second, the first 1,000-kilometre-class bidirectional real-time transmission over a single hollow-core fibre, confirming that long-distance bidirectional transmission is possible, with reflection-induced OSNR degradation ranging from 0.5 dB to 4 dB;

third, the world’s longest extended C+L band hollow-core fibre link without gas line absorption, achieving 1,000-kilometre extended C+L transmission free of GLA.

The company says that at the fibre end, optimising the manufacturing process eliminated CO2 and CO gas line absorption (GLA) in the extended C+L band, solving the core technical problem of GLA degrading transmission; at the equipment end, taking account of hollow-core fibre’s loss characteristics and amplifier behaviour, the team dropped high-power amplifiers in favour of commercial amplifiers with conventional output power, achieving the best performance for an 800G full-band system; and at the system end, a lightweight transmitter pre-equalisation scheme kept channel performance balanced across the extended C+L band, an end-to-end model assessed reflection and inter-mode interference, and extreme operating scenarios such as dropping a band were validated, confirming no performance degradation.

The company says the test’s success provides a practical technical basis for building high-bandwidth, long-distance, low-latency backbone networks using hollow-core fibre and high-order modulation.