Negative chromatic dispersion in selected types of Photonic Crystal Fibres obtained by bending

It is theoretically possible to achieve huge negative chromatic dispersion by fibre bending (-185000 ps/nm/km). On one hand, fibre bending may result in negative chromatic dispersion or coupling modes, which can open possibilities for new applications, such as design of Photonic Crystal Fibres suitable for compensation of Group Velocity Dispersion or for tuning operating wavelengths of dispersion compensating PCFs. Last but not least, it can be a potential tool to design optical filters, optical switches, or directional couplers. On the other hand, fibre bending is responsible for huge bending losses. Minimum dispersion and minimum-dispersion wavelength can be determined by the value of bending radius together with the diameter of a core, normalized hole diameter and the hole pattern. Chromatic dispersion diagrams for bending at different values of bending radius and for different air-filling fraction are demonstrated. The mechanism of negative dispersion occurrence depending on the transformation of geometry is studied. Another approach is to design the fibre that would be single-mode for wide range of bending angles or bending radii, without coupling into the cladding. Full-vectorial FDFD method has been used to obtain results in this work.