1,720,967 research outputs found
Reduction of coherent noise in the Landau Placzek ratio method for distributed fibre optic temperature sensing
No full textThe Landau Placzek ratio method for distributed fibre optic temperature sensing is based on the ratio of the Rayleigh and Brillouin backscattered light. However, because of the coherent nature of Rayleigh scattering. use of the same narrow bandwidth source as required for the Brillouin signal results in significant coherent noise in the Rayleigh signal. A novel technique is demonstrated whereby the amplified spontaneous emission noise and amplifying properties of an erbium doped fibre amplifier may be exploited to reduce the coherent noise on the Rayleigh backscatter signal. This results in a significant improvement in both temperature and spatial resolution over previously reported results
Landau Placzek ratio applied to distributed fibre sensing
No full textIt is shown experimentally that the ratio of the intensities of Rayleigh and Brillouin backscattered light (Landau Placzek ratio) in an optical fibre has a temperature dependence which may be used for the basis of a distributed temperature sensor. This result, combined with the known frequency dependence of be Brillouin backscattering on temperature and strain, indicates that spontaneous Brillouin backscatter may be used for the unique determination of either temperature or strain in a distributed optical fibre sensing system
Distributed temperature sensing using the Landau-Placzek ratio
No full textWe report a commercially viable high spatial resolution, long range optical fibre distributed temperature sensor based on Brillouin scattering exploiting a low cost detection system. A spatial resolution of 3.5 metres with a Brillouin temperature resolution of 0.9°C at a range of 16km has been achieved
A theoretical comparison of spontaneous Raman and Brillouin based fibre optic distributed temperature sensors
Full text linkPresent day commercially available fibre optic distributed temperature sensors exploit the temperature dependence of spontaneous Raman scattering. Spontaneous Brillouin scattering is also temperature dependent and provides a signal which is an order of magnitude greater. Advances in narrow bandwidth pulsed laser technology and low loss all fibre filters allow the Brillouin signal to be separated from the Rayleigh signal. Theoretical analysis now demonstrates that distributed temperature sensing based on Brillouin scattering offers considerably increased range beyond the theoretical limit of the spontaneous Raman based sensor
Characterisation of strain dependence of the Landau-Placzek ratio for distributed sensing
Full text linkThe authors report on the strain dependence of the Landau-Placzek ratio (LPR). This, together with the known temperature dependence of the LPR and the Brillouin frequency dependence on strain and temperature, may be used to form the basis of a combined distributed strain and temperature sensor
Double-pass configured fibre Mach-Zehnder interferometric optical filter for distributed fibre sensing
Full text linkA double-pass configured all-fibre Mach-Zehnder interferometric optical filter has been developed and used in a distributed fibre-optic sensor for separation of Rayleigh and Brillouin signals. Its superior performance over a single-pass all-fibre Mach-Zehnder interferometer is highlighted by its 15dB improved rejection of the Rayleigh signal and comparable throughput
Measurement of Brillouin scattering coherence length as a function of pump power to determine Brillouin linewidth
No full textMeasurements of Brillouin scattering coherence length using a fibre Mach-Zehnder interferometer are presented. It is shown experimentally that the SBS lineshape narrows as the Brillouin pump power is increased from below to above threshold and that the coherence length approaches a limiting value
Diode-pumped Landau-Placzek based distributed temperature sensor utilising an all-fibre Mach-Zehnder interferometer
No full textFor the first time, a Mach-Zehnder interferometer has been used in the detection system of a distributed temperature sensor, based on the Landau-Placzek ratio method. The interferometer separates the back-scattered Rayleigh and Brillouin signals with very low losses. Used together with a novel diode-pumped Q-switched fibre laser source, performance has been improved at a substantial cost saving over previously reported work
Experimental measurement of multiple Brillouin Stokes orders in a fibre amplifier under pulsed excitation
No full textThe influence of optical gain on SBS is explored experimentally in an Er-doped fibre, and the observation of multiple Stokes orders for pulsed excitation reported
A Raman backscatter distributed temperature sensor based on a self starting passively mode locked fibre ring laser
No full textThis paper reports on intracavity Raman backscatter measurements in it passively mode locked 1300m long fibre ring laser for distributed temperature sensing. The high intracavity power leads to a relatively large and easily detected Raman backscatter signal, whereas the short pulse duration (0.7ns) promises high spatial resolution
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