In this study, we present a direct detection distributed acoustic sensor based on phase-sensitive optical time domain reflectometer (φ-OTDR) with long sensing range and high signal-to-noise ratio (SNR), which is field-tested over a 50 kmlong fiber. Due to the random nature of Rayleigh backscattered light and fading phenomena, it is hard to characterize the performance of the system. For this reason, the performance of our sensor is specified in a statistical manner in which the mean SNR is determined using the histograms of the SNR. The SNR values are measured for identical acoustic signals in five different days, total of 48 hours and the SNR histograms are obtained for fiber distances of 100 m, 12 km, 21 km, 30 km, 40 km and 50 km. The system is field-tested using external disturbances that are generated from a 50-Hz vibrator. The SNR values are extracted from the power spectral density (psd) of the collected data over the monitored fiber span. Our results show that the φ-OTDR system exhibits a mean SNR of 22.5 dB at 50 km distance.
In this work, we present the experimental results of a direct detection ϕ-OTDR based distributed acoustic sensor system. The system uses two cascaded acousto-optic modulators in order to generate optical pulses with very high extinction ratio and dual photodetector scheme for high dynamic range. The proposed schemes are investigated in detail and their performance enhancement is experimentally verified. Four piezoelectric based fiber stretchers are placed on a ∼104 km single-mode test fiber at the distances of 1 km, 10 km, 87 km and 102.7 km and used for perturbation tests. The stretchers generated vibration signals which are analyzed to quantify the system performance. The signal-to-noise ratio (SNR) of vibration signals at the monitored distances is measured over the 12-hour recorded data within 34-second time windows considering the multi-point random interference of scattered light and fading phenomena. Using the 12-hour data, SNR histograms at four different locations are generated and mean SNR values are obtained. The signals received from 102.7 km has a maximum SNR of 24.7 dB and a mean SNR of 7.3 dB with a spatial resolution of 15 m. To the best of our knowledge, this is the highest-range reported direct detection ϕ-OTDR based distributed acoustic sensor system.
In this manuscript, we experimentally demonstrate a parity-time-symmetric optoelectronic oscillator with polarization multiplexed channels. We obtained a microwave single-mode oscillation at 9.5 GHz with phase noise values of -116.2 dBc/Hz and -122.3 dBc/Hz at 10 kHz offset frequencies, and side mode suppression values below -68 dBc/Hz and -75 dBc/Hz, by utilizing a 1 km long and 5 km long single mode fiber delay lines, respectively. Our experimental results suggest that parity-time-symmetric optoelectronic oscillators with polarization multiplexed channels are simple and cost-efficient alternatives to their more complex counterparts.
This work demonstrates an ultra-long range direct detection fiber optic distributed acoustic sensor which can detect vibrations at a distance of 94.8 km with 10 m resolution along the sensing fiber. OCIS codes: (060.2370) Fiber optics sensors; (280.4788) Optical sensing and sensors; (120.4825) Optical time domain reflectometry.
Brillouin spectrum of dispersion compensating fiber (DCF38) is investigated and strain and temperature measurement based on Brillouin frequency shift is performed.
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