China Telecom Sends 128 Tb/s Through 1,007 km of Hollow-Core Fiber

How it works

Instead of a solid glass core, the fiber has a gas-filled channel. A precisely shaped glass structure around it keeps the light inside, and because the light travels mostly through air, its speed is much closer to that in a vacuum. Nonlinear effects, which limit high-power signals in standard fiber, are also reduced.

The team used commercial optical amplifiers at standard power. Engineers had to limit absorption by carbon dioxide and carbon monoxide in the fiber and control reflections and interference between light modes. A single wavelength carried 800 Gb/s, and the system ran in the extended C and L bands.

Is it a record?

Hollow-core fiber is not new. Microsoft has used it in parts of Azure since 2023, and in 2025 it presented a transmission over 11,154 km. That test used a recirculating loop of about 360 km, though, so the signal passed through it repeatedly. The Chinese team built a physical path of more than 1,000 km with simultaneous two-way transmission in one fiber and no recirculation, so the two experiments test different things.

The companies also claim twice the capacity and a 60 percent longer reach than comparable glass-core fiber, but they gave no precise baseline, so those numbers deserve caution.

Replacing standard fiber across the internet is unlikely soon. Conventional fiber is cheap, durable and easy to splice, while hollow-core must justify its production, installation and maintenance costs. The case is strongest between data centers, where AI clusters depend on fast links. Microsoft is already scaling up production, and the Chinese side reports more than ten pilot and commercial projects.