Distributed stress and temperature sensing based on Rayleigh scattering of low-coherence light

Abstract

A novel arrangement for fiber optic distributed stress and temperature sensing based on the Rayleigh scattering spectra correlation method is proposed. The principal feature of the arrangement is usage of low-coherence light in probe pulses, which ensures a wide dynamic range for measurements at moderate sensitivity. Such a characteristic corresponds to performance specifications for infrastructure monitoring systems. A theory of optical time domain reflectometry for arbitrary coherence light is developed describing the contrast in reflectograms and Rayleigh scattering spectra properties. The experimental setup uses a wideband source of light pulses and an electronically controlled micro-electro-mechanical system optical filter for wavelength tuning. Temperature change experiments show root mean square (RMS) noise levels of 0.13 °C, 0.24 °C and 0.3 °C for fiber lengths of 2 km, 8 km and 25 km, respectively, at a spatial resolution of about 1 m (for 10 min data collection). As much as 2000 µstrain dynamic range is demonstrated in the stress measurement experiment while the noise level (RMS error) is estimated to be 2 µstrain. Our experimental results are compared with the theory and a satisfactory match is demonstrated.

Nonlinear spectrum broadening and its impact on performance of Rayleigh-scattering-based distributed strain/temperature fiber optic sensors

“…The experiments performed at a low peak power level of probe pulses (up to 66 mW) repeated the results given in [5]. Increasing the peak power above this level, we observed nonlinear effects.…”

“…The basic experimental setup is shown in figure 1(a). It is similar in general detail to the one described in [5], figure 1, and represents a tunable wavelength optical time-domain reflectometer (TW-OTDR) arrangement, with an operating wavelength tuned in the range 1555-1561 nm in steps of 0.05 nm (121 steps in total) by a tunable MEMS filter TF (DiCon Fiberoptics MTF500B) with an optical bandwidth of around 0.17 nm (full width at half maximum, FWHM). A superluminescent diode SLD based on a Superlum SLD-761 integrated module followed by an erbium-doped fiber amplifier (EDFA) AMP1 is used as a probe source.…”

“…The highest sensitivity can be provided by a Rayleigh-scatteringbased DFOS [3,4], but a sufficient measurement range has not been achieved using coherent light sources. The nearly optimum trade-off between dynamic range and sensitivity is demonstrated in a Rayleigh-scattering-based distributed strain/ temperature fiber optic sensor using low-coherent light, with a 50-100 GHz bandwidth whose operating wavelength is tuned over a range of 1555-1561 nm [5]. In the cited work every performance of such a sensor is presented for cases in which no nonlinear effects are observed.…”

“…So the present work is devoted to the investigation of a Rayleigh-scattering-based distributed strain/temperature lowcoherence fiber optic sensor arrangement [5], functioning in conditions when nonlinear effects are observed, to identify the nature of such nonlinear effects, and finally to develop solutions to overcome the limitations associated with said nonlinear effects.…”

Fidelity of the dual-pulse phase-OTDR response to spatially distributed external perturbation

“…Special attention is drawn to the possibility of simultaneous measurement of strain and temperature by the OTDR. However, this issue is complicated by the fact that both these disturbances are detected by the same principle of measurement of the induced change in the optical phase of the backscattered field, and serious efforts are being made to distinguish them, see [5][6][7][8][9] and the references therein.…”