Bending losses in large mode area holey fibres
The aims of the study presented here are to develop methods of accurately predicting bend loss in arbitrary index fibres, to use these techniques to explore the potential offered by holey fibres in the large-mode-area, single-mode regime, and to place their performance in context against conventional step-index fibres. In the study presented here, numerical and experimental techniques have been developed that are capable of accurately evaluating the bending losses, the fundamental mode area and the modedness of holey fibres. Note that these techniques are also applicable to conventional solid fibres, which is essential in order to form accurate comparisons. These techniques are applied here to the problem of understanding the bending losses of large-mode-area holey fibres and are successfully used to assess the practical limits that bend loss imposes on large-mode-area holey fibres designed for single-mode operation. These properties are also evaluated for a range of equivalent conventional fibres, the results of which are used to benchmark the potential of holey fibre technology in this regime. The results of this study reveal that the performance of large-mode-area holey and conventional fibres at any given wavelength are similar, and that holey fibres offer advantages for broadband applications. Methods of improving bend loss in holey fibres are also investigated, and it is shown that more complex hole arrangements can be used to improve bend loss in a holey fibre.