Experimental Astronomy

, Volume 24, Issue 1–3, pp 1–7 | Cite as

Air-clad fibres for astronomical instrumentation: focal-ratio degradation

  • Mattias L. ÅslundEmail author
  • John Canning


Focal-ratio degradation (FRD) of light launched into high-numerical aperture (NA) single-annulus all-silica undoped air-clad fibres at an NA of 0.54 is reported. The measured annular light distribution remained Gaussian after 30 m of propagation, but the angular FWHM of the output annulus doubled from 4° after 1 m propagation to 8.5° after 30 m, which is significantly larger than that reported of standard doped-silica fibres (NA < 0.22). No significant diffractive effects were observed. The design of air-clad fibres for broad-band, high-NA astrophotonics applications is discussed.


Focal-ratio degradation High-numerical aperture Air-clad fibres 



We acknowledge funding of this work through Australian Research Council (ARC) Discovery Project grants as well as technical expertise in fibre fabrication and funding from K. Lyytikäinen-Digweed, S. Huntington, J. Digweed and S.D. Jackson.


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Interdisciplinary Photonics Laboratories, School of ChemistryUniversity of SydneySydneyAustralia

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