31 research outputs found

    The sensitivity characteristics of tilted fibre Bragg grating sensors with different cladding thicknesses

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    In this paper, we present the sensitivity characteristics of core and cladding modes in weakly tilted fibre Bragg grating sensors with different cladding thicknesses. Both experimental and analysis results are presented. The results show that the strain sensitivity of cladding mode resonances in tilted fibre Bragg gratings does not depend on the cladding diameter but on the wavelength separation from the core resonance over the range of the cladding diameters studied

    Quasi-distributed refractometer using tilted Bragg gratings and time domain reflectometry

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    Tilted fiber Bragg gratings (TFBGs) have been demonstrated to be accurate refractometers as they couple light from the fiber core to the cladding. Because they require spectral measurements on several tens of nanometers, demodulation techniques reported so far are not suited for quasi-distributed refractive index sensing using TFBGs cascaded along a single optical fiber. We demonstrate here that a commercial Optical Time Domain Reflectometer (OTDR) can be used to multiplex identical TFBGs refractometers written in the same optical fiber. Our solution is simple, relatively fast, cost-effective and is particularly interesting for the monitoring of long structures

    Tilted fiber Bragg grating refractometer using polarization-dependent loss measurement

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    In this letter, a novel demodulation technique based on the monitoring of the polarization-dependent loss in a 1-nm wavelength range is proposed to measure the surrounding refractive index by means of weakly tilted fiber Bragg gratings. A 110-3 refractive index resolution as well as a temperature-insensitive behaviour are reported

    Sensitivity of photonic crystal fiber modes to temperature, strain and external refractive index

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    Several strong narrowband resonances are observed in the transmission spectra of fiber Bragg gratings photo-written in photonic crystal fiber that has a refractive index-neutral germanium/fluorine co-doped core. Experimental results for the strain, temperature and refractive index sensitivities of these mode resonances are reported and compared to those of conventional single mode fiber. In particular, we identify three kinds of resonances whose relative sensitivities to strain, temperature and refractive index are markedly different and present numerical simulations to explain these properties. Potential multiparameter optical sensor applications of these mode resonances are briefly discussed

    Optical fiber refractometer using narrowband cladding-mode resonance shifts

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    Short-period fiber Bragg gratings with weakly tilted grating planes generate multiple strong resonances in transmission. Our experimental results show that the wavelength separation between selected resonances allows the measurement of the refractive index of the medium surrounding the fiber for values between 1.25 and 1.44 with an accuracy approaching 1 × 10 -4. The sensor element is 10 mm long and made from standard single-mode telecommunication grade optical fiber by ultraviolet light irradiation through a phase mask

    Temperature insensitive refractometer using core and cladding modes in open-top ridge waveguide

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    In order to overcome the well-known limitation of temperature instability in Bragg grating waveguide sensors, a temperature insensitive open-top ridge waveguide refractometer is developed by using a cladding mode resonance as a temperature reference. The relative shift of the core mode resonance to cladding mode resonance is used to measure the refractive index of substances under test. Specifically, the device fabricated here produces a relative resonance shift of 1 pm for every 5 × 10-4 of measured index change, with a temperature sensitivity ∼ 0.5 pm/°C

    Sensitivity of tilted fiber Bragg grating sensors with different cladding thicknesses

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    Experimental measurements of the strain sensitivity of cladding mode resonances in tilted fiber Bragg gratings show that the sensitivity does not depend on the cladding diameter but on the wavelength separation from the core resonance
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