Hi
Effective area is another term describing the Mode Field Diameter (MFD), and it has a direct impact on the non-linear effects, those depends directly on the power density of the light injected into the fiber, i.e. the larger the effective area or (MFD), the lower the power density and so the lower impact of non-linear effects, and the smaller the effective area or (MFD), the higher the power density which leads to higher impact of the non-linear effects.
The effective area of a standard singlemode fiber is about 80um, and can be as low as 30um for compensating fiber. the effective area is sometimes included in the description of the fiber name, such as Corning`s LEAF (Large Effective Area Fiber.
regards