Air-clad fibres for astronomical instrumentation: focal-ratio degradation
- 99 Downloads
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.
KeywordsFocal-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.
- 5.Ferwana, S., Eckhardt, H.S., Simon, T., Klein, K.F., Haynes, R., Khalilov, V.K., Nelson, G.W.: All-silica fiber with low or medium OH-content for broadband applications in astronomy. Proc. SPIE 5494, 598 (2004). doi:10.1117/12.568231
- 6.Gloge, D.: Optical power flow in multimode fibers. Bell Syst. Tech. J. 51, 1767–1783 (1972)Google Scholar
- 12.Snyder, A.W., Love, J.D.: Optical Waveguide Theory. Chapman and Hall, London, UK (1983)Google Scholar
- 13.Wadsworth, W.J., Percival, R.M., Bouwmans, G., Knight, J.C., Birks, T.A., Hedley, T.D., Russel, P.St.J: Very high numerical aperture fibers. IEEE Photonics Technol. Lett. 16(3), 843–845 (2004)Google Scholar