A type of optical fiber that guides light primarily through an air-filled core rather than solid glass, enabling lower latency and reduced nonlinear effects compared to conventional singlemode fiber.

In hollow-core fiber, light propagates through a hollow central region surrounded by a microstructured cladding that confines the optical signal. Because most of the light travels through air, HCF can deliver significantly lower propagation delay and reduced sensitivity to certain impairments common in glass fiber. These characteristics make HCF attractive for latency-critical and high-performance applications such as data center interconnects, financial trading networks, and emerging 5G and future network architectures.

From a testing perspective, HCF introduces new considerations. Lower Rayleigh backscatter (RBS) impacts OTDR visibility and splice characterization, while chromatic dispersion, polarization mode dispersion, and latency still need to be measured—especially in hybrid networks combining singlemode fiber and hollow-core fiber. As HCF moves from research into early field trials, validating real-world performance requires test solutions adapted to its unique propagation and backscatter behavior.

Learn more

• Blog post: Hollow-core fiber: power and precision for critical networks
• Q+A blog post: Hollow-core fiber (HCF) testing  explained: questions and misconceptions
• Application note: Why hollow-core fiber is the next big leap in optical connectivity
• Discover EXFO’s test solution for hollow-core fiber: NS-348x - Hollow-Core Fiber OTDR Test Kit