Optical fibers fall into two major categories, namely: step
index optical fiber, which include single mode optical fiber
and multimode optical fiber, and graded index optical fiber.
Single mode step index optical fiber has a core diameter less
than 10 micrometers and only allows one light path.
Multimode step index optical fiber has a core diameter greater
than or equal to 50 micrometers and allows several light paths,
this leads to modal dispersion. Graded index optical fibers
have their core refractive index gradually decrease farther
from the centre of the core, this increased refraction at the core
centre slows the speed of some light rays, thereby allowing all
the light rays to reach the receiver at almost the same time,
thereby reducing dispersion. Figure 2 gives a description of
the various optical fiber modes.