G.P. Lees

All-fiber system for simultaneous interrogation of distributed strain and temperature sensing by spontaneous Brillouin scattering.

We demonstrate a low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously. By using the Landau¿Placzek ratio and cascaded Mach¿Zehnder interferometric filters, we measure both the intensity and the frequency changes in the Brillouin backscattered signal. Strain and temperature measurements can then be independently resolved. A temperature resolution of 4 degrees C, a strain resolution of 290 muepsilon, and a spatial resolution of 10 m have been achieved for a sensing length of 15 km.

Advances in optical fiber distributed temperature sensing using the Landau-Placzek ratio

This letter demonstrates the recent achievements in the field of optical fiber distributed temperature sensing utilising the Landau-Placzek ratio. We report a novel method of producing both the Rayleigh and Brillouin backscattered signals using a single laser source that may be scanned over 5 nm to reduce coherent Rayleigh noise. A spatial resolution of 10 m and temperature resolution of 1.4/spl deg/C has now been achieved using this technique.

Extended-range optical time domain–reflectometry system at 1.65??µm based on delayed Raman amplification

We describe both theoretical and experimental results obtained in an investigation of a new technique for increasing the dynamic range of 1.65-microm optical time domain-reflectometry (OTDR) systems. The technique utilizes delayed Raman amplification of a 1.65-microm signal pulse by a 1.53-microm pump pulse. Amplification occurs when the two pulses overlap, and this position is determined by the initial delay between the pulses and the fiber dispersion. An increase in dynamic range of 17.5 dB has been observed, and the OTDR backscattered Rayleigh signal was detected up to 100 km. No significant noise penalty is introduced as a result of the directionality of the Raman gain.

Technique for measuring distributed temperature with 35-cm spatial resolution utilizing the Landau-Placzek ratio

The authors report a spontaneous Brillouin-based distributed temperature sensing (DTS) system using a short-pulsewidth laser source at 1.5 /spl mu/m, which permits measurements down to an accuracy of 35-cm spatial resolution. This DTS system has been demonstrated utilizing conventional single-mode silica fibers for a range of 1 km from a single-ended source, and a temperature resolution of 4.3/spl deg/C was achieved.

Recent advances in distributed optical fiber temperature sensing using the Landau-Placzek ratio

Distributed optical fiber temperature sensing (DTS) provides an elegant way of monitoring the temperature at many points without necessitating the accurate positioning of individual discrete sensors. This paper demonstrates recent advances in distributed temperature sensing based on spontaneous Brillouin scattering. A high spatial and temperature resolution is achieved by exploiting a novel low cost detection system. The experimental configuration consists of two key components; a Q-switched laser source to generate the backscattered signal and the low cost detection system which comprises an in-fiber double pass Mach-Zehnder interferometer and a sensitive InGaAs APD connected to a computer based averaging system. It is the relative low cost of these components which has made the Brillouin based temperature sensor so attractive for commercial exploitation. A spatial resolution of 3.0 meters with a Brillouin temperature resolution of 0.9 degrees C at a range of 16km has been achieved.

An Integrated System for Pipeline Condition Monitoring

Pipelines are at risk from external threats including third-party intrusion, societal development and ground movement in addition to the ongoing potential for leaks due to corrosion or other causes. Although the appropriate use of internal inspection practices and regular survey of coating and cathodic protection systems will give timely information on any deterioration in pipeline condition, external threats can be unpredictable.

Simultaneous independent distributed strain and temperature measurements over 15 km using spontaneous Brillouin scattering

Long 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 sensitive fiber with a low loss filtering device utilizing two in-fiber Mach-Zehnder interferometers. From these two measurements, it is possible to compute accurately the strain and temperature profile.

Spontaneous Brillouin-based distributed temperature fiber sensor with 35-cm spatial resolution

Certain distributed sensing applications require sub-meter spatial resolution accuracy, and there is interest as to whether the Brillouin linewidth ultimately limits the spatial resolution that can be achieved. We present a single-ended, spontaneous Brillouin-based distributed temperature fiber sensor with measurements operating with a spatial accuracy of 35 cm. The sensor consists of two main components, a laser source to generate the Brillouin backscattered signal and a low cost filtering system which comprises an all-fiber Mach-Zehnder interferometer connected to a InGaAs detector and computer based averaging system. The sensing fiber was 1 km in total, consisting of three sections of conventional single-mode fiber spliced together with lengths of 600 m, 200 m and 200 m respectively. The second drum was at 67 degree(s)C, an increase of 44 degree(s)C from the two other drums at room temperature of 23 degree(s)C. The results show a rise in the Brillouin signal in the heated section. To take absolute measurements independent of fiber attenuation and localized splice/bend losses, the Brillouin signal has to be referenced to the Rayleigh backscattered signal that is independent of temperature fluctuations. The ratio of the Brillouin and Rayleigh signals (Landau-Placzek ratio) provides a temperature dependent signal which is corrected for splice/bend losses and fiber attenuation.

A stable narrow linewidth Q-switched Er-doped fibre laser

Summary form only given. Compact sources with high peak powers and short pulsewidths are required for applications such as distributed sensing and laser range finding. Previously reported Q-switched erbium-doped fibre lasers consisting of Fabry-Perot or ring cavities are suitable for many applications in the operation wavelength around 1550 nm, but for distributed strain sensing based on spontaneous Brillouin scattering, a stable ultra-narrow linewidth pulsed source with sufficient peak powers is required to resolve the spectral information of the Brillouin signals.

Distributed temperature sensing using the Landau-Placzek ratio

This letter demonstrates the recent achievements in the field of optical fiber distributed temperature sensing utilising the Landau-Placzek ratio. We report a novel method of producing both the Rayleigh and Brillouin backscattered signals using a single laser source that may be scanned over 5 nm to reduce coherent Rayleigh noise. A spatial resolution of 10 m and temperature resolution of 1.4/spl deg/C has now been achieved using this technique.