Ander Zornoza

Dynamic BOTDA measurements based on Brillouin phase-shift and RF demodulation

We demonstrate a novel dynamic BOTDA sensor based, for the first time to our knowledge, on the use of the Brillouin phase-shift in addition to the conventional Brillouin gain. This provides the advantage of measurements that are largely immune to variations in fiber attenuation or changes in pump pulse power. Furthermore, the optical detection deployed leads to an enhanced precision or measurement time and to the broadening of the measurement range. Proof-of-concept experiments demonstrate 1.66-kHz measurement rate with 1-m resolution over a 160 m sensing fiber length. Moreover, a measurement range of 2560 µε with a precision of 20 µε is successfully proved.

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

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 10.75-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.

Long-range hybrid network with point and distributed Brillouin sensors using Raman amplification.

We propose a novel concept for hybrid networks that combine point and distributed Brillouin sensors in a cost-effective architecture that also deploys remote distributed Raman amplification to extend the sensing range. A 46-km proof-of-concept network is experimentally demonstrated integrating point vibration sensors based on fiber Bragg gratings and tapers with distributed temperature sensing along the network bus. In this network the use of Raman amplification to compensate branching and fiber losses provides a temperature resolution of 0.7 degrees C and 13 m. Moreover, it was possible to obtain good optical signal to noise ratio in the measurements from the four point vibration sensors that were remotely multiplexed in the network. These low-cost intensity sensors are able to measure vibrations in the 0.1 to 50 Hz frequency range, which are important in the monitoring of large infrastructures such as pipelines.

Brillouin distributed sensor using RF shaping of pump pulses

We introduce a novel configuration for long-range Brillouin optical time domain analysis (BOTDA) sensors that is based on shaping the pump pulses in the radio frequency instead of the optical domain. This results in a simplified setup that uses just one standard intensity modulator to generate pulses with an extremely high extinction ratio (60 dB in our experiments). We develop a theoretical model for Brillouin interaction in long-distance BOTDA and use simulations to demonstrate that the availability of such pure pulses completely suppresses measurement errors caused by pulse leakage. Finally, experimental results are shown to confirm theoretical predictions. A 25 km fibre is measured with our system and the results compared to those obtained using pump pulses with lower extinction ratios.

Pulsing the Probe Wave to Reduce Nonlocal Effects in Brillouin Optical Time-Domain Analysis (BOTDA) Sensors

We propose a simple technique that is able to mitigate nonlocal effects in Brillouin optical time domain analysis (BOTDA) sensors. The technique consists in pulsing the probe wave, so that the Brillouin interaction only takes place in a portion of the fiber. A shorter interaction length reduces the nonlocal effects induced by pump depletion. The portion of fiber investigated each time can be easily scanned along the whole fiber length, so that the complete Brillouin frequency shift distribution can be retrieved by successive measurements.

46-km-Long Raman Amplified Hybrid Double-Bus Network With Point and Distributed Brillouin Sensors

We experimentally demonstrate a 46-km hybrid network that combine point and distributed Brillouin sensors. The proposed sensor network multiplexes low-cost intensity point sensors based on fiber-optic tapers, which are able to measure vibrations in the 0.01 to 50 Hz frequency range. The sensor network with a double-bus is a low noise configuration, which offers a higher optical signal to noise ratio and dynamic range than a single-bus. Thus, the number of sensors to be multiplexed could increase or we could reach further distances. The system also deploys remote distributed Raman amplification to extend the sensing range.

Brillouin Spectral Scanning Using the Wavelength Dependence of the Frequency Shift

We present a novel Brillouin spectra characterization method based on the Brillouin frequency shift dependence with pump wavelength. It is applied to a Brillouin optical time-domain analysis sensor, resulting in a cost-effective experimental setup that also avoids pulse leakage distortion in the measured spectra.

Distortion-free Brillouin distributed sensor using RF shaping of pump pulses

We demonstrate a novel configuration for Brillouin optical time domain analysis based on single-sideband modulation and RF shaping that provides pump pulses with 80 dB extinction ratio. This extremely reduced leakage, which to our knowledge is the lowest ever achieved, completely suppresses distortion of the measured spectra, thus sensor precision is enhanced. Furthermore, the proposed setup results in a simplified system with only one modulator and no need for optical filtering in detection.

Self-heterodyne synchronous detection for SNR improvement and distributed Brillouin phase shift measurements in BOTDA sensors

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 RF demodulation to increase the sensibility of the sensor and minimize non-local effects. We also perform for the first time to our knowledge distributed measurements of the Brillouin phase shift in an optical fiber.

Long-range hybrid double-bus network with point and distributed Brillouin sensors using Raman amplification

We propose a hybrid network that combine point and distributed Brillouin sensors in an architecture that also deploys remote distributed Raman amplification to extend the sensing range. A 46-km proof-of-concept network is experimentally demonstrated integrating point vibration sensors based on fiber-optic tapers, with distributed temperature sensing along the network bus. The sensor network with a double-bus topology offers a higher optical signal to noise ratio and dynamic range than a single-bus for intensity point multiplexed sensors. In this network, we include low-cost intensity sensors that are able to measure vibrations in the 0.01 to 50 Hz frequency range, which are important in the monitoring of large infrastructures such as pipelines.