1,720,975 research outputs found
1.5µm Brillouin-based fibre optic distributed temperature sensor with high spatial resolution of 20cm
No full textWe demonstrate a high spatial resolution single-ended spontaneous Brillouin-based distributed temperature sensor for a 500m length of single-mode silica fibre. Using a short pulsewidth laser source at 1.5µm, measurements down to a spatial resolution of 20cm and temperature resolution of 4.4°C were achieved
The design and application of optical sources for distributed fibre sensing systems
No full textThis thesis investigates pulsed optical sources for distributed fibre sensing applications. Such sensors operate on the optical time domain reflectometry (OTDR) principle, and the source requirements depend on the desired sensing range, spatial resolution and nonlinear thresholds. A number of Q-switched Erbium-doped fibre lasers at 1.5µm optimised for high peak powers and short pulse widths were designed and constructed. Experimental results were compared and contrasted with theoretical predictions. The successful development of high peak power Q-switched fibre lasers at 1.5µm enabled the generation of broadband Stokes-shifted Raman pulses at the wavelength region of 1.65µm, with approximately 1.4W peak power and 45ns pulse width. Using both the 1.5µm and 1.65µm pulses, a novel technique referred to as delayed Raman amplification was demonstrated to increase the range of an OTDR sensor operating at 1.65µm. An increase in sensing dynamic range of 17.5dB was achieved. A Raman-based distributed temperature sensor was also developed using the 1.65µm source, and had a spatial and temperature resolution of 10m and 4ºC respectively, over a 10km sensing range. Both the OTDR and distributed temperature measurements potentially allow losses and temperature to be monitored in active communication links operating at 1.5µm. A narrow linewidth amplified and gated semiconductor DFB source was constructed and its suitability for two spontaneous Brillouin-based distributed sensors investigated. The first sensor was a high spatial resolution distributed temperature sensor with a 35cm spatial resolution. The second sensor was a combined distributed strain and temperature sensor which used two Mach-Zehnder interferometers in series as filters to measure the Brillouin intensity and frequency shift. Temperature and strain resolutions of 4°C and strain resolution of 290µε were accomplished over a 15km sensing range. Finally, investigations into using pulsed fibre sources compared to a semiconductor DFB source were performed. Both unidirectional Q-switched fibre ring lasers and short fibres Bragg grating lasers with stable and narrow linewidths were demonstrated. A stable, robust and high output power DFB Erbium/Ytterbium fibre laser was eventually selected to perform simultaneous strain and temperature measurements
57km single-ended spontaneous Brillouin-based distributed fiber temperature sensor using microwave coherent detection
No full textWe present a novel technique for performing single-ended distributed fiber temperature measurements by use of microwave heterodyne detection of spontaneous Brillouin scattering. Brillouin frequency-shift measurements were obtained for a sensing length of 57km, with a spatial resolution of 20m. The rms error in frequency measurements at the far end of the sensing fiber was less than 3MHz, and the overall frequency dependence on temperature was 1.07±0.06 MHz/K
Simultaneous independent distributed strain and temperature measurements over 15km using spontaneous Brillouin scattering
No full textLong range simultaneous distributed strain and temperature sensors have many applications for measurements in the power and oil industries and also for structural monitoring. We present an efficient technique to measure both the intensity and frequency shift at every point along the sensing fibre with a low loss filtering device utilising two in-fibre Mach-Zehnder interferometers. From these two measurements, it is possible to compute accurately the strain and temperature profile. The first interferometer was used in a double-pass configuration and served to separate the Brillouin from the Rayleigh signal, the second allowed the frequency shift to be determined. It is possible to tune the Mach-Zehnder such that the launched source signal (and hence the Rayleigh) lies at the maximum or minimum of the transfer function. The Brillouin backscattered signals for the condition of maximum and minimum throughput at the signal wavelength are summed thus obtaining a Brillouin backscattered intensity measurement independent of frequency shift. The measurement obtained when the Rayleigh lies at a minimum of the transfer function provides information of both Brillouin intensity and frequency shift variations which then allows the frequency shift to be determined. The temperature and strain resolutions were estimated to be 4°C and 290µε with a 10m spatial resolution over a sensing range of 15km
1.65µm long range distributed testing of optical fibres using a compact Q-switched fibre laser
No full textA simple Q-switched Erbium-doped fibre laser operating at 1.5µm forms the basis of a high peak power pulsed source at 1.65µm. Applications include monitoring of active telecommunication links, loss measurement at 1.65µm and distributed temperature sensing
Distributed optical fibre sensing at 1.65µm using a Q-switched fibre laser
No full textIt is becoming increasingly vital to monitor telecommunication links during operation and installation process. By using a high peak power source and the optical time domain reflectometry (OTDR) technique operating at the wavelength region of 1.6µm, it is possible to monitor conventional C-band Erbium-doped fibre amplifier (EDFA) systems whilst transmitting data, and to characterise losses at the higher wavelengths of extended bandwidth systems designed around the L-band EDFA systems. We describe a compact design based on Raman shifting the output of an Erbium-doped Q-switched fibre laser operating at 1.5µm for obtaining a pulsed source at 1.6µm. This source was used for an OTDR measurement and also as a source for a 1.65µm Raman-based distributed temperature sensor, in contrast to distributed temperature sensors normally operating at 1.5µm. OTDR measurements at 1.65µm provide more accurate determination of macro and micro-bend losses than at 1.5µm as such losses increase with wavelength. The temperature measurement extracted from the anti-Stokes Raman signal at 1.5µm was made over a sensing range of 10.1km, with a spatial resolution of 10m and temperature resolution of 4°C
Novel distributed fibre sensor using microwave heterodyne detection of spontaneous Brillouin backscatter
No full textA new distributed sensing technique using spontaneous Brillouin backscatter has been demonstrated. For the first time ever, direct 11GHz heterodyne detection allows measurements of both Stokes and anti-Stokes signals. Results have been obtained for a sensing fibre length of over 10km with a spatial resolution of 20m.<br/
OTDR system using Raman amplification of a 1.65µm probe pulse
No full textA technique for increasing the dynamic of a 1.65µm OTDR system has been demonstrated. This is achieved by Raman amplification of the 1.65µm pulse within the sensing fibre using a co-propagating 1.53µm pulse generated from a Q-switched erbium doped fibre laser. An increase in dynamic range of 17.5dB has been demonstrated, providing an OTDR trace over 100km on the test fibre
Simultaneous distributed fibre temperature and strain sensor using microwave coherent detection of spontaneous Brillouin backscatter
No full textSimultaneous optical fibre distributed strain and temperature measurements have been obtained, by measuring the spontaneous Brillouin intensity and frequency shift, using the technique of microwave heterodyne detection. The enhanced stability from using a single coherent source combined with optical preamplification results in a highly accurate sensor. Using this sensor, distributed temperature sensing at 57 km and simultaneous distributed strain and temperature sensing at 30 km were achieved, the longest reported sensing lengths to date for these measurements. As a simultaneous strain and temperature sensor, a strain resolution of 100 µε and temperature resolution of 4 °C were achieved
1.65µm Raman based distributed temperature sensor
No full textThis paper demonstrates a novel Raman-based distributed temperature sensing (DTS) system using a laser source at a wavelength of 1.65µm, which permits monitoring of temperature in active transmission lines. This Raman based DTS system has been demonstrated utilising conventional telecommunications single-mode silica fibres over a range exceeding 10km, spatial resolution of 10m and temperature resolution of 4°C was achieved
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