Investigation of focal ratio degradation in optical fibres for astronomical instrumentation

Type Conference Paper
Names Lisa Crause, Matthew Bershady, David Buckley, Ian S. McLean, Mark M. Casali
Proceedings Title Proceedings of the SPIE
Conference Name Ground-based and Airborne Instrumentation for Astronomy II
Volume 7014
Pages 210
Series Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series
Date August 1, 2008
Library Catalog NASA ADS
Abstract A differential method was used to investigate the focal ratio degradation (FRD) exhibited by, and throughput of, a selection of current-generation optical fibres. These fibres were tested to establish which would be best suited to feed the High Resolution Spectrograph being built for the Southern African Large Telescope (SALT), as well as for future instruments on WIYN and SALT. The double re-imaging system of Bershady et al. (2004) was substantially modified to improve image quality and measurement efficiency, and to permit a direct FRD-measurement in the far-field. The re-imaging method compares the beam profile produced by light which passes through a fibre to that which does not. Broad and intermediate band-pass filters were used between 400-800 nm to test for wavelength dependence in the observed FRD over a wide range in beam-speeds. Our results continue to be at odds with a mico-bend model for FRD. We conclude that the new Polymicro FBP fibre is the most suitable product for broadband applications.
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