You know that fiber cable is made of a transparent glass. But Did You Know that without the mirror-like cladding, the light within the fiber core would escape, making the the fiber cable useless.
Light passes through the cable, bouncing off the cladding until it reaches the other end of the fiber channel – this is called total internal reflection. Without the cladding, the light within the fiber would disperse and never make it to the destination.
Fiber specifications list the core and cladding diameters as a ratio. Multimode fiber is commonly 62.5/125 or 50/125 micron, single mode fiber is commonly 9/125 micron.