  Soliton-soliton collisions have a crucial role in enhancing the spectrum of
dispersive waves in optical fibers and collisions among in-phase solitons lead
to a dramatic enhancement of the dispersive wave power, as well as to its
significant spectral reshaping. We obtained a simple analytical model to
estimate the spectral position, width and amplitude of the dispersive waves
induced by a collision of two in-phase solitons. We tested our theory in the
case of a dual concentric core microstructured fiber.
