Sub-Wavelength Dual Capillaries-Assisted Chalcogenide Optical Fibers: Unusual Modal Properties in Mid-IR (2-5 μm) Spectral Range

In this study, we apply the concept of sub-wavelength light confinement to achieve flat effective mode area (A eff ) characteristics over a wide wavelength range of 1400 nm in nano-sized dual capillary assisted chalcogenide core optical fibers. An unusual spectral behavior of A eff is observed where the effective mode area increases, remains constant for a wide bandwidth, decreases and again increases with the increase in wavelength. The spectral region, in which this behavior is observed, can be tuned by varying the structural parameters of the fiber. Additionally, we noticed that the fiber exhibits four zero dispersion wavelengths for a particular polarization which suggests that sub-wavelength light localization can be an alternative solution for the dispersion engineering in order to attain multiple zero dispersion wavelengths. The fabrication tolerance of the dispersion profile has been found to fall within the current fabrication accuracies achievable. We believe that our findings might be useful in different applications such as light-matter interaction and spatial soliton propagation.