Hexabundles - imaging fibre bundles for astronomy

New multi-core imaging fibre bundles hexabundles will provide simultaneous spatially-resolved spec troscopy for hundreds of celestial sources across a wide angular field. These are a natural progression from the use of single fibres in existing galaxy surveys. Hexabundles will allow us to address fundamental questions in astronomy without the biases introduced by a fixed entrance aperture. In preparation for several new instrument concepts that will exploit hundreds of hexabundles over the widest possible field of view, we have characterised the performance of 5 hexabundles each with 7 cores of 100μm diameter per core. The cladding is etched off the fibres to thickness of 1,2,4, 6 and 8 μm for the 5 bundles respectively. The fibres are then fused over a short length (~2cm) in order to minimise the cross-talk. The advantage of thinner cladding is to increase the fill-fraction (ratio of core area to bundle area) in order to minimise light loss in the interstitial holes between cores.