An optical fiber basically is a solid glass rod surrounded by concentric glass shell as shown in Fig
The rod is called the core and is made of highly purified glass. Most of the light energy in confined to the core.
The glass shell called cladding. The cladding shields optical fields so as not to get interfered by the outer layers of the fiber. The cladding is an essential part of an optical fiber.
The cladding is surrounded by the buffer layers. These layers have no role in propagation of light. They are essentially there to provide the mechanical support to the glass fiber and to protect the fiber from external damage.
