Mode Field Diameter-MFD, Cut-off wavelength and Zero Dispersion Slope

Mode Field Diameter - MFD

The mode field is the single mode field distribution giving rise to a spatial intensity distribution in the fiber. Mode field diameter is the diameter of energy path in an optical fiber. This parameter is one of the important parameter in a single mode optical fiber. Mode field diameter is measured by using Variable apertures method.

Cut off Wavelength

The cutoff wave length is the wave length greater than which the ratio between the total power including higher order modes and the fundamental mode power has decreased to less than a specified value, the modes being substantially uniformly excited.

1. By definition the specified value is chosen as 0.1 dB for a substantially straight 2 meter length of fiber including one single loop of radius 140 mm.

2. The cut off wave length defined in ITU-T recommendation is generally different from the theoretical cutoff wave length that can be computed from index profile of the fiber.

Zero dispersion slope: - The slope of the chromatic dispersion coefficient versus wave length curve at the zero dispersion wave length.

Zero dispersion wavelength: - The wavelength at which the chromatic dispersion vanishes is called Zero dispersion wavelength. This parameter is measured along with other chromatic dispersion characteristics of an optical fiber.