Cladding in optical fibers is one or more layers of materials of lower refractive index in intimate contact with a core material of higher refractive index). The cladding causes light to be confined to the core of the fiber by total internal reflection at the boundary between the core and cladding. Light propagation within the cladding is typically suppressed for most fibers. However, some fibers can support cladding modes in which light propagates through the cladding as well as the core. Depending upon the quantity of modes that are supported, they are referred to as multi-mode fibers and single-mode fibers). Cladding modes are generally undesired, but double-clad fiber is designed to support a mode in its inner cladding, as well as one in its core). The cladding increases the critical angle between the two materials, which means that only those rays that are close to the axis of the fiber pass through, and the inner fiber is protected from damage. Cladding also reduces dissipation of the optical signal and lessens the travel distance of the signal.