A protective layer, made of glass or plastic, which surrounds the core. The cladding has a lower index of refraction than the core, which helps keep light in the core.

• 环绕著光纤核心[纤核]之保护层称为光纤外壳,材质为石英玻璃或塑胶,光纤外壳具备低反射指数,可以将传输光束局限于光纤核心。