Abstract
We report on the impact of topological defects on the formation of discrete spatial solitons in waveguide arrays. The influence of defects, i.e. waveguides with a detuned effective refractive index, is well understood within such systems. They have been shown to support linear bound states and thus influence the formation of spatial solitons in the surrounding sites. We show numerically and demonstrate experimentally how the presence of topological defects caused by junctions within the otherwise periodical system also has a strong influence on the surrounding sites.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Discrete solitons in arrays of evanescently coupled waveguides offer a variety of potential applications for integrated optics. Among the most intriguing possibilities is the ability of tightly localized solitons to block off certain paths at junctions, thus providing essential components for all-optical signal processing. In this context, knowledge about the impact of junctions on soliton formation is vital.
Main results. We demonstrate numerically and experimentally that the topological defect constituted by the increased number of neighbors around the pivotal guide influences the formation of solitons in close resemblance to detuned waveguides. Topological defects of sufficient strength support strongly localized linear modes. Interestingly, the influence of topological defects on solitons centered on the pivotal guide vanishes for high powers. Solitons centered on neighboring waveguides exhibit a significant power threshold. Nevertheless, tightly localized solitons emerge as the influence of topological perturbations diminishes for sufficiently high powers. In order to minimize the impact of topological defects, and hence the power requirements for soliton formation in the adjacent sites, the number of branches per junction should be as low as possible.
Wider implications. Y junctions constitute the building block of choice for array-based photonic networks. We believe our findings will pave the way for future developments in utilizing solitons as blockers in array junctions for two- and even three-dimensional all-optical routing and switching schemes.
Figure. (a) Micrographs and observed nonlinear diffraction patterns of the X junction at 800 nm for excitation at the pivotal guide and neighboring sites. White circles mark the excited waveguides. (b) Characteristic functions for solitons in the vicinity of an X junction.