Glass fiber optics are made up of a bundle of very small (usually about 0.002 inch or 50 micron diameter) glass fiber strands. A typical glass fiber optic assembly consists of a bundle of several hundred glass fibers protected by a sheathing material, usually a flexible armored cable. The cable terminates in an end tip that is partially filled with rigid clear epoxy. The sensing face is optically polished so that the end of each fiber is perfectly flat.
The outer sheath of a glass fiber optic assembly is usually made from stainless steel, sometimes referred to as “square lock” flexible conduit, but may be PVC or some other type of flexible plastic tubing. Even when a non-armored outer covering is used, a protective steel coil is usually included beneath the sheath to protect the fiber bundle.