H.H. Kee

Optical fibre sensors for earth sciences: From basic concepts to optimising glass composition for high temperature applications

This paper reviews the technical evolution of optical fibre sensors relevant to earth sciences with particular reference to high temperature measurements. Optimisation of fibre composition and system design to fully realise the potential of these sensors has led to the substantial advances in both distributed and point sensor systems. Applications of these sensors in the field of earth sciences are discussed to provide a deeper understanding of the potential for monitoring geodynamical and chemical processes in areas of high seismic and volcanic risk.

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.

Low-loss, low-cost spontaneous Brillouin-based system for simultaneous distributed strain and temperature sensing

Summary form only given. The ability to perform long-range distributed sensing fibre strain and temperature measurements with a high spatial resolution has many applications including power utilities, oil industries and structural monitoring. We present results using a novel signal detection technique for resolving independent strain and temperature measurements by obtaining both the spontaneous Brillouin backscattered intensity and frequency shift at every point along the sensing fiber.

High temperature point sensor using tin-doped silica fiber gratings

Summary form only given. We show the enhanced thermal stability and excellent reliability of grating sensors written in tin-doped silica fibers (SS) up to a temperature of approximately 800/spl deg/C. At this temperature all the other gratings have been completely erased. Due to the improved stability above 500/spl deg/C and excellent repeatability, SS fiber is the best choice for high temperature thermometers or fiber Bragg sensors.

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.

1.65-/spl mu/m long-range distributed testing of optical fibers using a compact Q-switched fiber laser

Summary form only given. High-power pulsed sources operating at 1.65-/spl mu/m allow active monitoring of existing telecommunication links operating at around 1.5 /spl mu/m. They are also becoming increasingly important for characterizing losses at the higher wavelengths of extended bandwidth systems designed around the L-band erbium-doped fiber amplifiers. A compact design based on Raman shifting the output of a Q-switched fiber laser operating at 1.5 /spl mu/m is described. It is first demonstrated as a source for a 1.65-/spl mu/m OTDR measurement and then as a source for a 1.65-/spl mu/m Raman-based distributed temperature sensor, in contrast to distributed temperature sensors normally operating at 1.5 /spl mu/m.

1.5µm Brillouin-based fibre optic distributed temperature sensor with high spatial resolution of 20cm

We 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.