Self-Heterodyne Detection for SNR Improvement and Distributed Phase-Shift Measurements in BOTDA

Abstract

In this paper we present a Brillouin optical time domain analysis (BOTDA) sensor that takes advantage of the enhanced characteristics obtained employing self-heterodyne optical detection combined with synchronous demodulation. By employing this technique we increase the sensitivity of the sensor and demonstrate experimentally a 12.35-dB enhancement in the SNR compared to conventional direct-detection systems. This detection scheme also enables distributed measurements of the Brillouin phase-shift in an optical fiber, which can lead to enhanced BOTDA schemes.

Brillouin distributed fibre sensing using phase modulated probe

“…A passive microwave detector then realises a phase-insensitive conversion of the RF fundamental into the baseband and the voltage can be classically acquired using an oscilloscope or any data acquisition card. For comparison purpose this set-up can easily be converted into a self-heterodyne detection system [6] by filtering out one of the pump line using a fibre Brag grating. To validate the concept of the proposed PMP scheme, the BGS over a 1.9 km-long fibre has been measured using a spatial resolution of 2 m and 500 time-averaged traces.…”

“…Among other methods, self-heterodyne detection has been proved to be an efficient method to improve the SNR, by shifting the information from the baseband into an arbitrary higher frequency band much more immune to noise. This way a significant SNR improvement of 10.75 dB has been experimentally reported [6]. Additionally, self-heterodyne detection may offer the advantages of low-frequency scanning and of avoiding the optical narrowband filtering of unwanted optical signals.…”

Optimization of Detection Schemes in BOTDA

“…This has been one of the first reasons motivating the use of coherent detection in BOTDA sensing [8], and has led researchers to claim a better SNR with respect to direct detection. This however has never been demonstrated strictly under the same experimental conditions and comparing optimized detection schemes.…”

“…With the aim of enhancing the performance of BOTDA sensors, several advanced techniques have been proposed over the last decade to improve the SNR of the measurements [1][2][3][4][5]. However, in addition to these sophisticated methods, different detection schemes have also been proposed in the literature, such as the use of an optical pre-amplification stage in front of the detector in a direct detection scheme [6], balanced detection [7] and coherent detection [8]. Each of these schemes has demonstrated an improvement in the performance of the sensor; however it still remains unclear which of these methods offers the highest improvement in the SNR.…”

Enhanced performance for differential detection in coherent Brillouin optical time-domain analysis sensors

“…[6][7][8][9] Recently, coherent detection as a new method has been proposed, in which a local light beat and a probe light beam propagate through a photodetector (PD) by generating a GHz carrier to carry the Brillouin gain spectrum (BGS), resulting in significant SNR improvement (>10 dB typically) because of strong baseband noise perturbation reduction. 10 To simultaneously generate local light and probe light in a coherent BOTDA sensor, double-sideband (DSB), phase modulation (PM), and intensity modulation (IM) are normally used. However, DSB modulation is very sensitive to chromatic dispersion (CD) of the sensing fiber, causing PM-IM conversion and power fading, and further introducing crosstalk in the measured BGS.…”