ABSTRACT
Another important term in the world of fiber-optic
cabling is “graded index.” Most multimode fiber is
“graded-index” fiber, meaning that the refractive index
decreases progressively from the center of the core out
toward the cladding. This causes light in the core to con-
tinuously bend toward the center of the core as it progresses
down the fiber. The diagram is oversimplified, in that it
shows three modes of light traveling in straight lines, one
traveling directly down the center of the core and two
bouncing off the cladding, as they progress down the core
of the fiber. With a graded-index fiber, this light beam
travels in a more helical fashion down the fiber, always
tending toward the center of the core as it progresses down
the fiber. Further, because light traveling through a med-
ium with a higher refractive index travels slower, the
effects of “modal distortion” are significantly diminished
in a graded index fiber.
