Optical fiber core

The central region of an optical fiber that guides most of its light. Its refractive index is higher than the surrounding cladding, enabling confinement by total internal reflection.

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Total internal reflection: The reflection of light back into a material when it meets a boundary above the critical angle. The core–cladding index contrast allows rays to remain confined by this boundary effect.
Optical fiber: A flexible dielectric waveguide that transmits light along its length. The core is the light-guiding center of this larger structure.
Optical communication: The transmission of information using light as the signal carrier. Telecommunication signals propagate through fiber cores over long distances.
Hollow-core fiber: An optical fiber that guides light primarily through a hollow region rather than a solid glass core. Its hollow guiding region contrasts with the solid, higher-index core described here.
Numerical aperture: A dimensionless measure of an optical system’s ability to accept or emit light over a range of angles. It quantifies the range of input angles that the core can guide.
Optical fiber cladding: The lower-index layer surrounding an optical fiber’s core and helping confine guided light. Its lower refractive index establishes the boundary that guides light in the core.
Fiber-optic sensor: A sensor that uses optical fibers to detect physical, chemical, or biological changes. Changes affecting light in the core can encode a measured quantity.
Photonic crystal fiber: An optical fiber whose microstructured cross-section shapes light guidance through refractive-index contrast or photonic bandgaps. Its engineered hole pattern can guide light by mechanisms beyond a simple core–cladding boundary.
Fiber mode: A self-consistent electromagnetic field pattern that propagates through an optical fiber. Core size and refractive-index profile determine which field patterns can propagate.
Refractive index: A measure of how much light slows in a material compared with its speed in vacuum. The core’s index relative to the cladding controls light confinement.