Mode field diameter
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In fiber optics, the mode field diameter (MFD) is an expression of distribution of the irradiance, i.e., the optical power per unit area, across the end face of a single-mode fiber.
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/e2 of the maximum power, because the power is proportional to the square of the field strength.
This article contains material from the Federal Standard 1037C, which, as a work of the United States Government, is in the public domain.
