Physical Differences In terms of physical properties, the difference between these two fiber types is the diameter of the core: The light-carrying region of the fiber. In 62.5/125 fiber, the core has a diameter of 62.5 microns and the cladding diameter is 125 microns. For 50/125 the core has a diameter of 50 microns and the cladding diameter is 125 microns.
