There are two types of fiber relative to the paths that the light rays, or modes, travel within the fiber core:



Multimode and single mode. Multimode fiber cores are classified as either step or graded index, depending on the refractive index. Step index multimode fiber has a uniform core and an abrupt change in refractive index at the core/cladding interface. In graded index multimode fiber the core contains many layers of glass, each with a lower index of ht pulses do not overlap, distortion is eliminated.

Graded index fibers are commercially available with core diameter/ cladding diameters of 50/125, 62.5/125, and 100/140 microns. Single mode fibers have a smaller core, typically 8.5µm, but also have 125µm cladding diameter. Coatings are available from 250 microns to 900 microns.