Mode Field Diameter Mismatch Loss Between Two Single Mode Fibers
The loss associated with mode field diameter (MFD) mismatch between single mode fibers is
Differences in the mode field diameter between single mode fibers (of the same type or different types) lead to a signal loss. The above equation can be used to estimate the loss and can be used with the measured or specified MFD, or the uncertainty of the MFD. The user should realize that MFD is a function of wavelength and changes across the G and L bands, as illustrated below.
There are several companies manufacturing dispersion devices. Each company should supply MFD and Aeff specifications as a function of wavelength to their customers. This will aid the deployment of these components. Using the goniometric radiometer technique, both fast and accurate measurements can be made. Where other methods may take hours, this method takes less than 20 seconds.
As an example, the uncertainty of 10 percent of MFD in a typical single mode fiber results in a loss uncertainty of about 0.039dB or 0.9 percent, while an uncertainty of 0.5 percent leads to a loss uncertainty of merely 0.00011dB or 0.0025 percent.
The MFD is also related to the effective area of the fiber core (Aeff), which in turn is related to the nonlinear index n2, and (n2/Aeff) defines the nonlinear effects in the fiber. Nonlinear effects tend to be less pronounced for larger diameter fibers.