Mode

A single wave traveling in an optical fiber or in a light path through a fiber. Light has modes in optical-fiber cable. A high-order mode is a path that results in numerous reflections off the core/cladding interface. A loworder mode results in fewer reflections. A zero-order mode is a path that goes through the fiber without reflecting off the interface at all. In a single-mode fiber, only one mode (the fundamental mode) can propagate through the fiber. Multimode fiber has several hundred modes that differ in field pattern and propagation velocity. The number of modes in an optical fiber is determined by the diameter of the core, the wavelength of the light passing through it, and the refractive indexes of the core and cladding. The number of modes increases as the core diameter increases, the wavelength decreases, or the difference between refractive indexes increases.