Question:What is an optical fiber?
An Optical fiber is a long thin rod of glass.
The glass is so thin that it can be bent and curved and even tied in knots (loosely) without breaking.
The diagram below shows the cross section of an optical fiber.
The core of the fiber is made of glass.
The cladding layer is there to protect the surface of the glass, mainly by keeping it clean.
The cladding and the outer coating are not necessary for the fiber to work.
The cladding keeps the surface of the fibre clean so that TIR can happen and the outercoating provides extra strength and protection against actual damage because at the end of the day an optical fiber is a long glass rod and not exactly indestructible.
Optical fibers are also known as fiberoptics or fiberoptic cables.