# mode field diameter (MFD)

The term ModeField Diameter (MFD) is used for the distribution of radiant intensity present at the end of a single mode fiber

. Given a Gaussian power distribution within a single mode fiber, the mode field diameter is calculated by reducing the electric and magnetic field strength to the magnitude of 1/e, where e = 2.718, of the maximum value. The diameter can also be determined via the power, since this is quadratic to the field strength, the quotient of the square of "e" is to be applied.