BOTDA Sensing Employing a Modified Brillouin Fiber Laser Probe Source

Abstract

A theoretical and experimental study has been carried out on a tunable dual pump-probe optical source for distributed Brillouin optical time-domain analysis (BOTDA). The developed source exploits a modified Brillouin ring laser technology and is capable of a tuning range of ∼200 MHz without using phaselocked loop or optical sideband generation techniques, and exhibits a linewidth smaller than 2.5 MHz and ∼0.5 mW power. In BOTDA experiments, the proposed source has demonstrated to be an efficient solution enabling distributed sensing over 10 km single mode fiber with a spatial resolution of ∼4 m, and a strain and temperature resolutions of ∼10 με and ∼0.5°C respectively.

Enhanced performance low-noise Brillouin ring laser for Brillouin sensing

“…For schemes employing sources affected by intensity noise, as in the case of fiber lasers, RIN represents the biggest contribution to SNR degradation and ultimately limits the strain and temperature resolution [7]. In [3] we reported the results of BOTDA measurements using a long-cavity BRL for the generation of both pump and probe signals. The LC BRL showed relatively high intensity fluctuation due to mode hopping with RIN values up to -85dB/Hz in sub-MHz range in line with those reported in figure for LC-BRL.…”

“…(0) and ( ) represent the Brillouin frequency shifts of unstrained sensing fiber and of sensing fiber at reference temperature. The SNR values of the DR-SC BRL and LC BRL have been obtained integrating the RIN values that we have measured over the receiver bandwidth used in [3] (125 MHz), and Eqs. (2-3) are used for the evaluation of the strain-temperature resolution.…”

“…In BOTDA pump-probe schemes, a pulsed signal (pump) and a CW radiation (probe) downshifted in frequency, are launched from both ends of the sensing fiber: the probe signal is amplified through SBS with a maximum gain occurring at a pump-probe frequency difference is equal to the Brillouin frequency shift (BFS) of the sensing fiber [2]. Since the BFS is temperature and strain dependent, the measurement of the Brillouin gain spectra and in particular of the BFS values allows to reconstruct the spatial distribution of temperature and strain along the sensing fiber [3]. The techniques that are commonly employed for the generation of the pump and probe signals are based on phase-locked-loop (PLL) systems [4] and optical sideband generation (OSB) technique [5].…”

“…The techniques that are commonly employed for the generation of the pump and probe signals are based on phase-locked-loop (PLL) systems [4] and optical sideband generation (OSB) technique [5]. In [3] we have demonstrated a BOTDA systems employing a long-cavity (~ 2 km) Brillouin ring laser as source for pump and probe signals achieving an accuracy in the BFS evaluation of ~ 1 MHz over a more than 10 km sensing distance. Using the BRL as BOTDA source the shift between the pump and the Stokes signal is already in the range of the Brillouin frequency shift and it is possible to tune their frequency shift using an electro-optic modulator (EOM) with a much narrower bandwidth than modulators used in the OSB method.…”

Recent Advances in Brillouin Optical Correlation-Domain Reflectometry

“…The basic limitation of the pulse width is known to be approximately 10 ns (corresponding to the spatial resolution of~1 m) because of the spectral broadening of the Brillouin gain spectrum (BGS) and reduced accuracy of BFS detection [7]. It is noteworthy that the performance including the spatial resolution has been drastically enhanced with various schemes both in BOTDR [8][9][10][11] and in BOTDA [12][13][14][15][16][17][18][19][20]; refer to each reference for the details. Researchers have also developed Brillouin optical frequency-domain analysis (BOFDA) [21][22][23] and Brillouin optical frequency-domain reflectometry (BOFDR) [24], which seem to suffer from their relatively slow operation speed because of the large amount of calculation; their details are also out of the scope of this paper.…”