Fiber Optic Wiki

Multimode Fiber

September 6, 2011

Fibers that carry more than one mode are called multimode fibers. There are two types of multimode fibers. One type is step-index multimode fiber and the other type is graded-index multimode fiber.

Advantages of Single Mode Fiber. Single mode fiber doesn’t have modal dispersion, modal noise, and other effects that come with multimode transmission; single mode fiber can carry signals at much higher speeds than multimode fibers. They are standard choice for high data rates or long distance span (longer than a couple of kilometers) telecommunications which use laser diode based fiber optic transmission equipment.

Mode Field Diameter (MFD)

September 6, 2011

The typical core diameter of communication single mode fibers is from 8~10um for operating wavelength 1.31um to 1.5um. Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics as we did in the explanation of step-index multimode fiber. Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell's equations as reduced to the electromagnetic wave equation.

Mode Field Diameter

September 6, 2011

Single Mode Fiber (Single Mode Fiber Optic Cable)

September 6, 2011

When the fiber core is so small that only light ray at 0° incident angle can stably pass through the length of fiber without much loss, this kind of fiber is called single mode fiber. The basic requirement for single mode fiber is that the core be small enough to restrict transmission to a singe mode. This lowest-order mode can propagate in all fibers with smaller cores (as long as light can physically enter the fiber).