The outer layer of an optical fiber cable is called the 'cladding'. The cladding is made of a material that has a lower refractive index than the core of the fiber, which helps to keep the light signals inside the core by reflecting them back towards the center of the fiber. This is known as total internal reflection and is what allows optical fibers to transmit signals over long distances without significant signal loss or degradation. The cladding layer is usually made of a type of glass or plastic material, and it is coated with a protective layer of material to prevent damage or contamination.
