Abstract
In this paper, a phase-sensitive optical time domain reflectometry ( $\Phi $ -OTDR) based on Rayleigh enhanced optical fiber is proposed to improve the system signal-to-noise ratio (SNR). In the experiment, the vibration performance of the Rayleigh enhanced optical fiber is analyzed and compared with standard single-mode telecom fiber. The results demonstrate that the measured SNRs of peaks in frequency spectra have been improved by 14 dB (at 1 kHz vibration frequency) at the end of the 2 km specialty sensing fiber. A wide range of vibration frequencies from 50 Hz to 15 kHz are demonstrated experimentally. The proposed method overcomes the inherent limitations of the conventional $\Phi $ -OTDR system and significantly enhances the vibration sensing performance.
Highlights
Distributed optical fiber sensors gained lots of attention in recent years, as they are immune to electromagnetic interference, lightweight, easy to install or embed into structures, corrosion resistant, harsh environmental capability, and highly sensitive for ranges over tens of kilometers
A polarization controller (PC) was placed at the laser output to adjust the light polarization before entering the acousto-optic modulator (AOM) which provided a frequency shift of 200 MHz
The measured frequency spectra signal-to-noise ratio (SNR) has been improved by 14 dB compared to standard SMF at the end of the 2 km sensing fiber
Summary
Distributed optical fiber sensors gained lots of attention in recent years, as they are immune to electromagnetic interference, lightweight, easy to install or embed into structures, corrosion resistant, harsh environmental capability, and highly sensitive for ranges over tens of kilometers. The low backscattered intensity or destructive interference of the Rayleigh signal within the pulse width causes the scattered light intensity to be lower than the noise intensity in some areas of the sensing fiber, known as dead zones or fading area In these fading area locations, the signal-to-noise ratio (SNR) is too low to properly demodulate the vibration perturbation [3, 4]. In [8], the authors proposed a direct detection based Φ-OTDR employing a remotely pumped erbium-doped fiber amplifier (EDFA) to enhance the SNR, improve the vibration sensing performance. [17] proposed and demonstrated a pulse width modulation Brillouin amplification to improve the SNR and sensitivity These distributed amplification techniques greatly increase the system cost and complexity further. The experiment was carried out using both the Rayleigh enhanced optical fiber, and the sensing performance is compared with standard SMF
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