Laser transmission in solid-core fibers struggles to simultaneously maintain high beam quality and high power, severely limiting its industrial applications. Recently, a research team from the Nanhu Light Laboratory at the National University of Defense Technology, in collaboration with relevant institutions, achieved the first-ever efficient and stable all-fiber transmission of a 2kW high-power laser over an ultra-long distance of 2.45 kilometers using hollow-core fiber. This breakthrough marks the transition of high-power, long-distance energy transmission via hollow-core fiber from theoretical exploration to practical engineering application.
In recent years, the demand for flexible, long-distance transmission of high-power lasers has grown significantly. However, traditional solid-core fibers can only transmit 5kW power over 20 meters, and transmission distance plummets to just 3 meters at 8kW-far short of industrial requirements. Compared to solid-core fibers, hollow-core fibers offer advantages such as low latency, low loss, and low nonlinear coefficients. However, existing high-power laser transmission systems using hollow-core fibers primarily rely on optical components like lenses, making them susceptible to environmental influences and resulting in poor stability. Therefore, developing fully fiber-coupled technology is the key pathway to constructing stable, compact, and practical hollow-core fiber laser systems.
Dr. Shi Jing, the paper's first author, explained that to achieve a truly stable and efficient "all-fiber" system, the team designed a five-tube double-nested anti-resonant hollow-core fiber with mode-field matching to solid-core fiber. Through simulation optimization, they determined the optimal structural parameters and successfully pulled ultra-low-loss hollow-core fiber. The team overcame challenges in low-loss fusion splicing between quartz and hollow-core fibers, mode field matching, and high-power fiber end-capping technology. They achieved the world's first long-distance high-power laser transmission through an all-fiber hollow-core structure, maintaining near-diffraction-limited beam quality. Both the transmitted power and distance represent the highest levels internationally.
"Although the 2.45-kilometer transmission distance is constrained by currently available fiber lengths, the developed technology paves the way for future efficient laser transmission over even greater distances," stated Shi Jing.
Corresponding author Chen Zilun noted that compared to traditional solid-core fibers, the ultra-low-loss hollow-core fiber extends effective flexible transmission distance by two orders of magnitude. This breakthrough provides technical support for engineering applications of long-distance flexible laser transmission in industrial settings, with broad potential across multiple fields. For instance, in industrial processing, remote flexible laser transmission can increase the distance between operators and hazardous work zones, significantly enhancing operational safety. In scientific research, hollow-core fibers can capture and accelerate particles via radiation pressure, enabling the development of novel "flying particle sensors" operating at kilometer-scale dimensions.
"Although hollow-core fiber costs currently exceed those of conventional fibers, this primarily stems from its nascent industrialization phase, characterized by complex manufacturing processes and room for yield improvement. As the technology matures, production scales up, and upstream-downstream industrial chains develop synergistically, hollow-core fiber costs are expected to enter a sustained downward trajectory, paving the way for large-scale deployment in specific high-value applications." Chen Zilun stated that the research team will further optimize fiber structures, enhance coupling efficiency, increase transmission power and distance, and explore broader application scenarios.
