Modal cutoff and the V parameter in photonic crystal fibers

We address the long-standing unresolved problem concerning the V parameter in a photonic crystal fiber. In formulating the parameter appropriate for a core defect in a periodic structure, we argue that the multimode cutoff occurs at a wavelength lambda* that satisfies V-PCF(lambda*) = pi. By comparing this approach with numerics and recent cutoff calculations we confirm this result. (C) 2003 Optical Society of America.