Mahmoud Farhadiroushan

A fully distributed simultaneous strain and temperature sensor using spontaneous Brillouin backscatter

We report here the first simultaneous measurement of strain and temperature using Brillouin backscatter in an optical fiber. A new sensor arrangement is presented which allows the distributed measurement of Brillouin spectra. Simultaneous measurement of spontaneous Brillouin power and Brillouin shift distributions are made from these spectra, and from this information, we obtain fully distributed measurements of strain and temperature. Our sensor achieves a 100-/spl mu//spl epsiv/ strain and 4/spl deg/C temperature resolution, with 40-m spatial resolution, over a sensing length of 1200 m.

A high spatial resolution distributed optical fiber sensor for high-temperature measurements

One of the advantages of the use of optical fibers for sensing is their ability to perform distributed measurements. Several distributed sensors that measure temperature along optical fibers are already commercially available. All of them are based on Raman thermometry. However, the spatial resolution that they achieve is limited to 1 m, making them unsuitable for applications where higher spatial resolution is needed. Also, their temperature range is very dependent on the behavior of fibers at high temperature, a subject which still needs investigation. In this article, we present a distributed optical fiber sensor that addresses these two issues. On one hand, the combination of Raman thermometry with the time-correlated single-photon counting technique permits the achievement of high spatial resolutions (0.1 m). On the other hand, the use of specially coated fibers allows measurement of high temperatures. We have investigated the system temperature sensitivity and have evaluated the measurement errors i...

Power measurement of noise-initiated Brillouin scattering in optical fibers for sensing applications

We discuss the measurement of noise-initiated Brillouin scattered power in optical fibers and its application to distributed sensing systems. In particular, we consider the use of Brillouin scattering in the nonlinear regime, demonstrating a novel processing technique that compensates for the nonlinear growth of the scattered signals. The signal-to-noise ratio performance of this technique is evaluated, highlighting the importance of the noise contributed by the random statistics of the scattered field and yielding the conditions for optimum system operation.

Zero dead-zone OTDR with high-spatial resolution for short haul applications

The existence of dead-zones is an important drawback for optical time-domain reflectometers (OTDR), specially in short haul applications with a large number of optical components. In this letter, we present an OTDR system with high spatial resolution based on the time-correlated single photon counting (TC-SPC) technique. This system overcomes the deadzone problem by monitoring the spontaneous Stokes Raman emission (SSRE) to avoid the intense Fresnel reflections. The high sensitivity of the TC-SPC technique (-120 dBm) permits a high-loss budget within reasonable measurement integration times.

Advances in distributed optical fibre sensing

The ability to make distributed measurements on extended structures is of increasing importance. For example, the measurement of strain distribution on aircraft operating close to their performance limits, the distribution of temperature in boilers, pressure vessels, high voltage transformers etc.,

Single-shot distributed optical-fiber temperature sensing by the frequency-derived technique

We present, for the first time to our knowledge, a distributed optical-fiber temperature sensor, based on a pulsed laser, that provides distributed temperature measurement by use of a single pulse propagating in an optical fiber. The system uses the frequency-derived technique based on the optical Kerr effect. The performance of the system is investigated for the temperature range 33-150 degrees C. A linear relationship between the temperature and the derived frequency is obtained. The best temperature resolution was determined to be +/-1.2 degrees C. The best measured spatial resolution was 0.56 m.

Advances in high-resolution distributed sensing using a time-resolved photon counting technique

A very high resolution distributed optical-fiber temperature sensor system has been demonstrated using a time-resolved photon counting technique. The spatial resolution of the system is 3.5 cm. A temperature sensitivity of 2 degrees Celsius has been achieved with 1 minute integration time when averaging the data points over 10 cm. The system offers a practical solution for life assessment and monitoring of hot spots along the steam pipes in power plants.

The intelligent distributed acoustic sensing

Distributed Acoustic Sensing (DAS) technology has progressed rapidly from being capable of event detection only to faithfully capturing the full acoustic signal (amplitude, frequency and phase) at all points along the sensing fibre. In this paper we demonstrate the performance of one such sensor and describe how the unique nature of DAS data enables a range of ground-breaking industrial applications.

Analysis of optical Kerr effect induced coupling among polarization modes in high-birefringence optical fibers

Abstract We present a theoretical analysis of the mode coupling induced by the optical Kerr effect in a high birefringence fiber. Several pump-probe architectures which allow mapping of the birefringence along the fiber are studied. The application of nonlinearly induced coupling to distributed sensing is also discussed, showing its performance in terms of signal-to-noise ratio and also its potential for simultaneous measurement of several parameters.

Distributed temperature and distributed acoustic sensing for remote and harsh environments

Advances in opto-electronics and associated signal processing have enabled the development of Distributed Acoustic and Temperature Sensors. Unlike systems relying on discrete optical sensors a distributed system does not rely upon manufactured sensors but utilises passive custom optical fibre cables resistant to harsh environments, including high temperature applications (600°C). The principle of distributed sensing is well known from the distributed temperature sensor (DTS) which uses the interaction of the source light with thermal vibrations (Raman scattering) to determine the temperature at all points along the fibre. Distributed Acoustic Sensing (DAS) uses a novel digital optical detection technique to precisely capture the true full acoustic field (amplitude, frequency and phase) over a wide dynamic range at every point simultaneously. A number of signal processing techniques have been developed to process a large array of acoustic signals to quantify the coherent temporal and spatial characteristics of the acoustic waves. Predominantly these systems have been developed for the oil and gas industry to assist reservoir engineers in optimising the well lifetime. Nowadays these systems find a wide variety of applications as integrity monitoring tools in process vessels, storage tanks and piping systems offering the operator tools to schedule maintenance programs and maximize service life.