We have investigated the validity of the V parameter to identify the single-mode operation regime for photonic quasi-crystal fibers. Our results show that the V parameter can be considered only for smoothly changing fibers. On the other hand, for fibers showing isolated high refractive regions around the core, only a mode area analysis can allow the estimation of the threshold for the single-mode operation regime. Finally, these findings can be generalized to any kind of optical fiber.
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