Long-term stability of fibre-optic transmission for multi-object spectroscopy

We present an analysis of the long-term stability of fibre-optic transmission properties for fibre optics in astronomy. Data from 6 years of operation of the AAOmega multi-object spectrograph at the Anglo-Australian Telescope are presented. We find no evidence for significant degradation in the bulk transmission properties of the 38-m optical fibre train. Significant losses (≤20 per cent relative, 4 per cent absolute) are identified and associated with the end termination of the optical fibres in the focal plane. Improved monitoring and maintenance can rectify the majority of this performance degradation.