The velocity factor (VF) of a is the ratio of the at which a (of an electromagnetic signal, a signal, a light pulse in an or a change of the electrical voltage on a ) passes through the medium, to the. For optical signals, the velocity factor is the reciprocal of the. The speed of in, for example, is the, and so the velocity factor of a ra. An optical fiber is a cylindrical ( waveguide) that transmits light along its axis through the process of total internal reflection. The fiber consists of a core surrounded by a layer, both of which are made of materials. To confine the optical signal in the core, the of the core must be greater than that of the cladding. The boundary between the core and cladding m.