A significant technological achievement was revealed on June 16, with Yangtze Optical Fiber and Cable (YOFC) reporting the success of a pioneering field test. The company, in collaboration with China Telecom and Dekoli, demonstrated a wavelength division multiplexing (WDM) transmission system using hollow core fiber (HCF). This advancement achieved a capacity of 1.2 terabits per second (Tb/s) per wavelength over an ultra-long stretch without the need for repeaters.
The groundbreaking demonstration took place over the longest commercial cross-border hollow core fiber optic cable available. By implementing a scheme optimized for transmission rates and power distribution, the team achieved an impressive 51.3 Tb/s in a single 206.5 kilometer segment, without the use of repeaters and only with erbium-doped fiber amplification (EDFA). This result establishes a new global benchmark for capacity-distance product in WDM transmission systems without repeaters, without resorting to remote pumped amplifiers.
Hollow core fiber operates under a distinctly different light guiding principle, transmitting optical signals through the air as opposed to the conventional glass method. This fundamental feature allows you to overcome the inherent capacity and latency constraints that affect traditional solid-core fibers, positioning HCF as a foundational technology for the next generations of optical communications. It is especially promising for backbone networks and data centers, where the demand for speed and efficiency is increasing.
With the support of the China Telecom Cloud-Network Convergence Pilot Platform, a medium-sized testing framework endorsed by the State-owned Assets Supervision and Administration Commission of China, as well as the National Laboratory of Advanced Optical Fiber and Cable Manufacturing and Application Technologies, the project team overcame a crucial challenge. They successfully performed high-power transmission in an operating HCF network environment, thus validating the high-speed capabilities of the technology.
At the system level, the researchers implemented an adaptive rate control scheme per wavelength, integrated with a flexible power allocation per channel. This strategy allowed for hybrid transmission, supporting multiple data rates, channel spacings and power levels per wavelength. Such an approach was effective in mitigating capacity degradation caused by gas absorption spikes, unlocking even greater transmission potential of the hollow-core fiber.
Regarding the equipment employed, the team opted for a cascaded high-power amplification architecture, which incorporates a dual-gain unit and a multi-element doping design. This resulted in the development of a high-power amplifier that exhibits excellent gain flatness and an output power that reaches 33.5 dBm. To ensure safety, additional safeguards have been introduced, including detection of optical path power anomalies, interlock shutdown functions and alarm switch-on mechanisms, minimizing the risks associated with possible optical link failures.
