Longitudinal soliton pure tunneling in optical fiber

Optical temporal solitons are waves propagating without changing their shape. In optical fibers, they can only exist in the anomalous group velocity dispersion (GVD) regime. Recent research has demonstrated that a soliton initially propagating in the anomalous GVD region of an axially-varying fiber can annihilate itself into a polychromatic dispersive wave when it passes across the zero-dispersion wavelength (ZDW) [1]. This process is characterized by a strong temporal spreading when the soliton goes from the anomalous to normal GVD section. On the other hand, it has been demonstrated that a dispersive wave can be transformed into a soliton when it propagates from normal to anomalous GVD region in a suitably designed axially-varying fiber [2]. This process has been named solitonization. In the present work, we studied numerically and experimentally an effect that combines both annihilation and solitonization processes that can be interpreted as an overall tunneling of the soliton itself. For that purpose, we designed a fiber constituted by a short normal GVD section (acting as the barrier) between two anomalous GVD fiber sections.