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Appl. Sci. 2017, 7(5), 473;

Single Mode Air-Clad Single Crystal Sapphire Optical Fiber

Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061, USA
Center for Photonics Technology, Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24061, USA
Author to whom correspondence should be addressed.
Academic Editor: Christophe Finot
Received: 16 March 2017 / Revised: 14 April 2017 / Accepted: 30 April 2017 / Published: 3 May 2017
(This article belongs to the Special Issue Distributed Optical Fiber Sensors)
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The observation of single mode propagation in an air-clad single crystal sapphire optical fiber at wavelengths at and above 783 nm is presented for the first time. A high-temperature wet acid etching method was used to reduce the diameter of a 10 cm length of commercially-sourced sapphire fiber from 125 micrometers to 6.5 micrometers, and far-field imaging provided modal information at intervals as the fiber diameter decreased. Modal volume was shown to decrease with decreasing diameter, and single mode behavior was observed at the minimum diameter achieved. While weakly-guiding approximations are generally inaccurate for low modal volume optical fiber with high core-cladding refractive index disparity, consistency between these approximations and experimental results was observed when the effective numerical aperture was measured and substituted for the theoretical numerical aperture in weakly-guiding approximation calculations. With the demonstration of very low modal volume in sapphire at fiber diameters much larger than anticipated by legacy calculations, the resolution of sapphire fiber distributed sensors may be increased and other sensing schemes requiring very low modal volume, such as fiber Bragg gratings, may be realized in extreme environment applications. View Full-Text
Keywords: sapphire optical fiber; single mode optical fiber; distributed sensing sapphire optical fiber; single mode optical fiber; distributed sensing

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Hill, C.; Homa, D.; Yu, Z.; Cheng, Y.; Liu, B.; Wang, A.; Pickrell, G. Single Mode Air-Clad Single Crystal Sapphire Optical Fiber. Appl. Sci. 2017, 7, 473.

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