Browsing by Author "Cheng, Yujie"

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    Mode Volume Reduction in Single Crystal Sapphire Optical Fibers
    Cheng, Yujie (Virginia Tech, 2017-04-07)
    This research provides the original work on the geometry factors selection for single crystal sapphire optical fiber (SCSF) to improve the optical property in sensing applications. Single crystal sapphire fibers were fabricated with a Laser Heated Pedestal Growth (LHPG) system, which was constructed in-house at Virginia Tech. The cost effective, high efficiency and fully operational Laser-heated Pedestal Growth (LHPG) system as well as the fiber fabrication process were also demonstrated in this research. The results indicated the windmill single crystal sapphire optical fiber (SCSF) will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that are limited by the optical property of unclad single crystal sapphire optical fiber (SCSF).
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    Single Mode Air-Clad Single Crystal Sapphire Optical Fiber
    Hill, Cary; Homa, Daniel S.; Yu, Zhihao; Cheng, Yujie; Liu, Bo; Wang, Anbo; Pickrell, Gary R. (MDPI, 2017-05-03)
    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.