Cone-of-acceptance meaning

The maximum angle, represented in three-dimensional view as a cone, at which an optical fiber will accept incident light. Within that cone, as defined by those angles, a light source can inject an optical signal into the fiber core and the signal will remain in the core, reflecting off of the interface between the core and cladding, as illustrated in Figure C-5. At a more severe angle, i.e., outside the cone, the signal will penetrate the interface and enter, and perhaps be lost in, the cladding. The angle of acceptance and, therefore, the cone of acceptance are determined by the difference in index of refraction (IOR) between the core and cladding. See also angle of acceptance, cladding, core, and IOR.