Is single-mode fiber hollow

No, standard single-mode fiber is not hollow; it has a solid glass core that guides light.Structure of Single-Mode FiberSingle-mode optical fiber consists of a very small solid glass core, typically around 8–10 microns in diameter, surrounded by a cladding layer of slightly lower refractive index glass . This solid core allows only a single mode of light to propagate, minimizing dispersion and enabling high-bandwidth, long-distance transmission . The cladding, usually 125 microns in diameter, confines the light within the core through total internal reflection .Hollow-Core Fiber vs Single-Mode FiberWhile there is a type of fiber called hollow-core fiber, it is a specialized technology and not the standard single-mode fiber . Hollow-core fibers have a structure resembling a honeycomb to guide light, but they are distinct from conventional single-mode fibers, which are entirely solid glass in the core . Hollow-core fibers are designed to reduce signal loss and increase bandwidth, but they are still relatively rare compared to standard single-mode fibers.SummarySingle-mode fiber: Solid glass core, ~9 microns, supports one light mode, used for long-distance, high-bandwidth communication .Hollow-core fiber: Specialized fiber with a hollow or structured core, not typical for standard single-mode applications . In conclusion, standard single-mode fiber is solid, not hollow, and the term "hollow fiber" refers to a separate, advanced fiber technology.