Fiber optic connectors are produced by polishing their endfaces to create a smooth domed shape.
If the shape or endface geometry is precisely controlled, the result will be physical contact between
fiber cores when two connectors are mated together. The polishing process creates a very small
damaged layer at the tip of the fiber that has a higher index of refraction (index layer) than the
glass before the damaged layer. Since reflections in optical fiber are caused by changes in index of
refraction, it is the index layer that causes the return loss associated with a mated pair of