T.P. Newson

A distributed optical fibre dynamic strain sensor based on phase-OTDR

A distributed optical fibre sensor is introduced which is capable of quantifying multiple dynamic strain perturbations along 1 km of a sensing fibre simultaneously using a standard telecommunication single-mode optical fibre. The technique is based on measuring the phase between the Rayleigh scattered light from two sections of the fibre which define the gauge length. The phase is spatially determined along the entire length of the fibre with a single pulse. This allows multiple moving strain perturbation to be tracked and quantified along the entire length of the fibre. The demonstrated setup has a spatial resolution of 2 m with a frequency range of 500-5000 Hz. The minimum detectable strain perturbation of the sensor was measured to be 80 ne.

Landau Placzek ratio applied to distributed fibre sensing

It 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 the 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.

Simultaneous distributed fibre temperature and strain sensor using microwave coherent detection of spontaneous Brillouin backscatter

Simultaneous 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 μe and temperature resolution of 4 C were achieved.

Self-starting passively mode-locked fibre ring laser exploiting nonlinear polarisation switching

Nonlinear birefringence effects in an all-fibre ring laser cavity have been exploited to produce self-starting passive mode-locking with pulse durations lying in the nanosecond region.

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.

Characterization of a self-starting, passively mode-locked fiber ring laser that exploits nonlinear polarization evolution

A full characterization of a self-starting, passively mode-locked soliton ring fiber laser in terms of its various modes of mode-locked operation, cavity length, and type of fiber used is presented. Direct evidence, based on state-of-polarization measurements, that nonlinear polarization evolution is the responsible mode-locking mechanism is also given.

Simultaneous temperature and strain measurement with combined spontaneous Raman and Brillouin scattering

We report on a novel method for simultaneous distributed measurement of temperature and strain based on spatially resolving both spontaneous Raman and Brillouin backscattered anti-Stokes signals. The magnitude of the intensity of the anti-Stokes Raman signal permits the determination of the temperature. The Brillouin frequency shift is dependent on both the temperature and the strain of the fiber; once the temperature has been determined from the Raman signal, the strain can then be computed from the frequency measurement of the Brillouin signal.

A review of microfiber and nanofiber based optical sensors

Rapid advances in optical microfiber and nanofibers (MNF) based sensors have been driven by powerful industries such as automotive, biomedical and defense, with the increasing demand for highly-sensitive, selective, nonintrusive, fast-response, compact and robust sensors that can perform in-situ measurements at remote and harsh environments. A diverse range of MNF based sensors have been developed for measuring refractive index, bio-chemical, temperature, current, displacement, bend, surface, acceleration, force, rotation, acoustic, electric field and magnetic field. Given the growing interest for this exciting area of scientific research, new designs are emerging continuously at a fast pace. This paper attempts to provide a comprehensive review of all MNF based sensors reported to-date. Sensors are divided according to their morphology and measurand.

Optical fiber microwire current sensor

We demonstrate a compact optical fiber microwire current sensor based on the Faraday effect with gigahertz frequency of current sensing capabilities.

Comparison of the methods for discriminating temperature and strain in spontaneous Brillouin-based distributed sensors

A recently proposed method of measuring the two Brillouin frequencies in a multicompositional fiber core for unambiguously resolving temperature and strain in a distributed sensor is compared with the previously established technique of measuring the intensity and frequency of the single Brillouin peak in a standard single-mode fiber.