MODE FIELD DIAMETER (MFD)

An expression of distribution of the irradiance , i.e. , the optical power , across the end face of a single- mode fiber. Note: For a Gaussian power distribution in a single-mode optical fiber , the mode field diameter is that at which the electric and magnetic field strengths are reduced to 1/e of their maximum values, i.e., the diameter at which power is reduced to 1/e 2 of the maximum power, because the power is proportional to the square of the field strength .