Vector Brillouin optical time-domain analyzer for high-order acoustic modes

Abstract

Thanks to a double-frequency phase modulation scheme, we report a vector Brillouin optical time-domain analyzer (BOTDA). This BOTDA has a high immunity level to noise, and it features a phase spectrogram capability. It is well suited for complex situations involving several acoustic resonances, such as high-order longitudinal modes. It has notably been used to characterize a dispersion-shifted fiber, allowing us to report spectrograms with multiple acoustic resonances. A very high 57 dB dynamic range is also reported for 100-ns-long pulses simultaneously with a 16 cm numerical resolution.

Evaluation of the accuracy of BOTDA systems based on the phase spectral response

“…2). The local phase response of the SBS interaction can be obtained from homodyne or heterodyne BOTDA measurements [5][6][7][8][9][10][11][12]. In any case, in a typical small gain case, the recovered phase profile is also affected by white Gaussian noise, and a fitting is convenient to recover the true zero-phase position.…”

“…Several techniques have been recently proposed to retrieve the longitudinal BFS profile by measuring the BPS along the fiber. For instance, techniques based on phase modulation make use of a complex coherent detection system employing high-bandwidth photo-detection [5][6][7] or IQ demodulation [8]. In contrast to these coherent methods, the use of a Sagnac interferometer within the sensing fiber of a standard BOTDA system (SI-BOTDA) has been recently proposed [9][10][11] to determine the distributed BPS feature using a conventional direct-detection scheme.…”

“…Independently of the different features that all these implementations have, the BFS of the fiber is always retrieved by fitting a linear curve to the central spectral region of the BPS. This has allowed the implementation of reliable sensing systems based on the phase response of the SBS induced in the sensing fiber [5][6][7][8][9][10][11][12], instead of using the classical SBS gain response typically measured by conventional BOTDA sensors.…”

Novel Concepts and Recent Progress in Distributed Optical Fiber Sensing

“…The most promising techniques are those based on stimulated Brillouin scattering and on coherent Rayleigh scattering, which can today commonly reach a distance range of 50 km with a spatial resolution of 1 m and an acquisition time below 1 minute, for a typical temperature accuracy of 1 K. In addition, Brillouin-based distributed sensors can be implemented in sophisticated configurations to obtain a very sharp spatial resolution down to the centimeter range [1][2][3][4] or to realize efficient signal enhancement by combining gain and loss Brillouin processes [5][6][7].…”

Brillouin distributed fibre sensing using phase modulated probe

“…This method can be applied to both static and dynamic measurements. It offers the advantage of creating only spectral lines that enter into the interaction, maximising response and minimising coherent noise, in contrast with the vector BOTDA [7] also based on probe phase modulation. The different approach in the hereafter proposed configuration suppresses this issue, simplifies the processing and brings a crucial advantage for real implementations.…”