Open Access
Enhanced tolerance to pulse extinction ratio in Brillouin optical time domain analysis sensors by dithering of the optical source
(SPIE, 2015) Iribas Pardo, Haritz; Urricelqui Polvorinos, Javier; Sagüés García, Mikel; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We demonstrate the relaxation of the stringent requirements placed on the pulse extinction ratio in long-range Brillouin optical time-domain analysis sensors (BOTDA) by modulating the wavelength of the laser source that is used to generate both pump and probe waves. This modulation makes the counter-propagating pulse pedestal and probe waves to become correlated only at certain locations in the fiber, thus reducing the gain experienced by the probe wave, which is precisely the process that limits the performance in long-range BOTDAs. Proof-of-concept experimental results in a 20-km sensing link demonstrate a 6-dB reduction of the required modulator extinction ratio.
Open Access
Second-order non-local effects mitigation in BOTDA sensors by tracking the BFS profile
(SPIE, 2017) Mompó Roselló, Juan José; Iribas Pardo, Haritz; Urricelqui Polvorinos, Javier; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
We demonstrate a technique to mitigate the residual second-order non-local effects in Brillouin optical time-domain analysis (BOTDA) sensors in which the Brillouin frequency shift (BFS) profile is not uniform along the fiber. It is based on adding a wavelength modulation to the probe wave that makes it track the average BFS found along its way. Using this method we are able to inject a total probe wave power of 15 dBm in a 120-km sensing fiber link, which, to the best of our knowledge, is the highest probe power ever demonstrated in a long-range BOTDA sensing fiber link. The enhancement in the detected signal-to-noise ratio brought by the use of such power provides 2-MHz BFS measurement precision at the end of the 120-km sensing link with 3-m spatial resolution, all without the need to resort to additional means such as the use of coding or Raman gain.
Open Access
Cost-effective Brillouin optical time-domain analysis sensor using a single optical source and passive optical filtering
(Hindawi Publishing Corporation, 2016) Iribas Pardo, Haritz; Urricelqui Polvorinos, Javier; Mariñelarena Ollacarizqueta, Jon; Sagüés García, Mikel; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We present a simplified configuration for distributed Brillouin optical time-domain analysis sensors that aims to reduce the cost of the sensor by reducing the number of components required for the generation of the two optical waves involved in the sensing process. Te technique is based on obtaining the pump and probe waves by passive optical filtering of the spectral components generated in a single optical source that is driven by a pulsed RF signal. Te optical source is a compact laser with integrated electroabsorption modulator and the optical filters are based on fiber Bragg gratings. Proof-of-concept experiments demonstrate 1m spatial resolution over a 20km sensing fiber with a 0.9MHz precision in the measurement of the Brillouin frequency shiſt, a performance similar to that of much more complex setups. Furthermore, we discuss the factors limiting the sensor performance, which are basically related to residual spectral components in the filtering process.
Open Access
Effects of pump pulse extinction ratio in Brillouin optical time-domain analysis sensors
(Optical Society of America, 2017) Iribas Pardo, Haritz; Mariñelarena Ollacarizqueta, Jon; Feng, Cheng; Urricelqui Polvorinos, Javier; Schneider, Thomas; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We report on two previously unknown non-local effects that have been found to impair Brillouin optical time-domain analysis (BOTDA) sensors that deploy limited extinction ratio (ER) pump pulses. The first one originates in the increased depletion of the pedestal of the pump pulses by the amplified probe wave, which in turn entails a reduced amplification of the probe and a measurement distortion. The second effect is due to the interplay between the transient response of the erbium-doped fiber amplifiers (EDFA) that are normally deployed to amplify the pump and the pedestal of the pump pulses. The EDFA amplification modifies the pedestal that follows the pulses in such a way that it also leads to a distortion of the measured gain spectra after normalization. Both effects are shown to lead to non-local effects in the measurements that have similar characteristics to those induced by pump pulse depletion. In fact, the total depletion factor for calculations of the Brillouin frequency shift (BFS) error in BOTDA sensors is shown to be the addition of the depletion factors linked to the pump pulse as well as the pedestal. A theoretical model is developed to analyze both effects by numerical simulation. Furthermore, the effects are investigated experimentally in long-range BOTDA sensors. The pedestal depletion effect is shown to severely constrain the probe power as well as the minimum ER of the pulses that can be deployed in BOTDA sensors. For instance, it is shown that, in a long-range dual-probe BOTDA, an ER higher that 32-dB, which is above that provided by standard electro-optic modulators (EOM), is necessary to be able to deploy a probe power of -3 dBm, which is the theoretical limit for that type of sensors. Even more severe can be the limitation due to the depletion effect induced by the EDFA transient response. It is found that the impairments brought by this effect are independent of the probe power, hence setting an ultimate limit for the BOTDA sensor performance. Experimentally, a long-range BOTDA deploying a 26-dB ER EOM and a conventional EDFA is shown to exhibit a BFS error higher than 1 MHz even for very small probe power.

Urricelqui Polvorinos, Javier

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