Browsing by Author "Ye, Chen-Chun"

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    AFM observation of surface topography of fibre Bragg gratings fabricated in germanium-boron codoped fibres and hydrogen-loaded fibres.
    (Elsevier Science B.V., Amsterdam., 2002-11-01T00:00:00Z) Wei, C. Y.; Ye, Chen-Chun; James, Stephen W.; Irving, Phil E.; Tatam, Ralph P.
    This paper reports the measurement of the surface topology of optical fibres containing a fibre Bragg grating (FBG) using an atomic force microscope (AFM). The AFM observation was made on FBGs fabricated via the phase mask technique in germanium–boron codoped optical fibres, in hydrogen-loaded germanium–boron codoped fibres and in standard telecommunications optical fibres. The surface images reveal that a spatial corrugation pattern was induced by the UV- irradiation, with a period that is half of the period of the phase mask. This UV-induced surface structure was found only on the side of the fibre facing towards the incident UV-irradiation and did not appear on the rear surface. The AFM probe scanned a 10×10 μm2 surface area at seven sites along the 6.0 mm length of fibre that was exposed to the UV-irradiation. The amplitude of the spatial corrugation pattern observed on the AFM image was quantified for each site. It was found that the amplitude in a range of 0.7–3.2 nm was a function of UV-laser intensity distribution and the type of fibre. Hydrogen loaded optical fibres exhibited a corrugation with an amplitude twice as large as that observed in the Ge–B doped fibres that were not hydrogen-loaded. This correlates with the increase in photosensitivity produced by the hydrogen loading. A similar UV- induced spatial corrugation was also observed on standard telecom fibres, but without inducing the refractive index change in the fibre core. The observation of surface topology provides an insight into the structural changes induced during FBG fabrication. UV-induced densification and laser ablation could account for the formation of the surfac
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    Characterization of the response of fibre Bragg gratings fabricated in stress and geometrically induced high birefringence fibres to temperature and transverse load.
    (Institute of Physics, 2004-08-01T00:00:00Z) Chehura, Edmon; Ye, Chen-Chun; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.
    The transverse load and temperature sensitivities of fibre Bragg gratings (FBGs) fabricated in a range of commercially available stress and geometrically induced high birefringent (HiBi) fibres have been experimentally investigated. The wavelength reflected by the FBG in each polarization eigenmode was measured independently and simultaneously using a custom designed interrogation system. The highest transverse load sensitivity, of 0.23 ± 0.02 nm/(N/mm), was obtained with HiBi FBGs fabricated in elliptically clad fibre. This was higher than for any other HiBi fibre, which, coupled with the small diameter of the fibre, makes it a good candidate for an embedded or surface mounted strain sensor. The highest temperature sensitivity of 16.5 ± 0.1 pm °C-1, approximately 27% greater than any other fibre type, was obtained with the HiBi FBG fabricated in Panda fibre. HiBi FBG sensors fabricated in D-clad fibre were the only ones to exhibit identical temperature sensitivities for the slow and fast axes (11.5 ± 0.1 pm °
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    An experimental approach to quantify strain transfer efficiency of fibre bragg grating sensors to host structures
    (2001-06-25T00:00:00Z) Wei, C. Y.; Ye, Chen-Chun; James, Stephen W.; Tatam, Ralph P.; Irving, Phil E.
    This paper developed a method to evaluate the strain transfer efficiency of fibre Bragg grating sensors to host structures. Various coatings were applied to fibre Bragg grating sensors after being fabricated. They were epoxy, silane agent and polypropylene, representing different surface properties. A neat epoxy resin plate was used as the host in which the coated fibre sensors were embedded in the central layer. The tensile strain output from the FBGs was compared with that obtained from electrical strain gauges which were attached on the surface of the specimen. A calculating method based on the measured strains was developed to quantify the strain transfer function of different surface coatings. The strain transfer coefficient obtained from the proposed method provided a direct indicator to evaluate the strain transfer efficiency of different coatings used on the FBG sensors, under either short or long-term loading. The results demonstrated that the fibre sensor without any coating possessed the best strain transfer, whereas, the worst strain transfer was created by polypropylene coating. Coatings play a most influential role in strain measurements using FBG sensors.
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    The influence of hydrogen loading and the fabrication process on the mechanical strength of optical fibre Bragg gratings.
    (Elsevier Science B.V., Amsterdam., 2002-11-01T00:00:00Z) Wei, C. Y.; Ye, Chen-Chun; James, Stephen W.; Tatam, Ralph P.; Irving, Phil E.
    This paper investigates the influence of hydrogen loading and other stages of the fabrication process on the mechanical strength of fibre Bragg gratings. Following UV irradiation, tensile tests were carried out on Ge–B codoped photosensitive fibres with and without hydrogen loading. Fibre Bragg gratings (FBGs) were written using a range of UV wavelengths, namely 246, 255 and 266 nm. The tensile strength of the optical fibres was determined in their as-received status and following the various stages of FBG fabrication. The mechanical strength was assessed using Weibull statistics. The results indicate that the strength of FBGs is influenced by the UV irradiation parameters and by the hydrogen-loading process. FBGs fabricated using shorter UV wavelengths and low pulse power intensity exhibit a high mechanical strength. The FBGs written in hydrogen loaded fibres have less than 50% of the strength of FBGs that have not been hydrogen loaded. Fibre fracture morphology observed by scanning electron microscope reveals fracture mechanisms of FBGs, which are correlated with the structural change of the silica fibres induced during the FBG inscription process. Combined with surface information gathered by atomic force microscopy, fracture mechanics is applied to understand the mechanisms of strength degradation caused by the FBG inscription proces
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    A polarisation maintaining fibre Bragg grating interrogation system for multi- axis strain sensing
    (International Society for Optical Engineering; 1999, 2002-12-31T00:00:00Z) Ye, Chen-Chun; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.; Daniele, Inaudi; Eric, Udd
    Fibre Bragg gratings (FBGs) written into polarisation maintaining (PM) fibres have been employed for multi-axis strain and temperature sensing. In this paper we report the development of a FBG interrogation system that is capable of detecting independently the two orthogonally polarised signals reflected from a PM FBG. The interrogation system imposes no limitation on the measurable strain range. This relaxes the requirements on the bandwidth of the grating spectrum, allowing the use of a shorter PM FBG (larger bandwidth) for sensing applications where a higher spatial resolution is required. In particular, this system is useful in the cases where the spectra of the reflected polarised signals are broadened or split, resulting from strain-induced structural changes of the PM fibre, or caused by the application of a non-uniform strain on the FBG.
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    Thermal dependence of the strain response of optical fibre Bragg gratings.
    (Iop Publishing Ltd, 2004-08-01T00:00:00Z) O'Dwyer, Martin; Ye, Chen-Chun; James, Stephen W.; Tatam, Ralph P.
    The temperature dependence of the strain sensitivity of fibre Bragg gratings written into a number of different fibre types has been investigated. It was found that the strain response changed on average by 0.21 ± 0.03 fm µε-1 °C-1 over a range of temperatures between 100–400 °C. These results were in agreement with predictions based on material parameters.
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    Ultrasonic sensing using Yb3+/Er3+-codoped distributed feedback fibre grating lasers.
    (Institute of Physics, 2005-02-01T00:00:00Z) Ye, Chen-Chun; Tatam, Ralph P.
    Yb3+/Er3+-codoped distributed feedback (YbEr-DFB) fibre grating lasers have been investigated for the detection of ultrasonic Lamb waves generated in an aluminum plate. Two sensor configurations have been investigated. A path length imbalanced readout Mach- Zehnder interferometer was used to measure the laser frequency shift induced by ultrasonic vibration. The resolution to out-of-plane displacement was 3 x10-15 m/Ã Â Hz for a continuous ultrasonic wave at a frequency of 470 kHz. Ultrasonic waves were also detected by directly monitoring the laser output power. This simplified configuration is useful for tone burst AE signals generated by a low energy impact