Open Access
Latest research on long-range Brillouin distributed sensing
(SPIE, 2019) Loayssa Lara, Alayn; Urricelqui Polvorinos, Javier; Iribas Pardo, Haritz; Mariñelarena Ollacarizqueta, Jon; Mompó Roselló, Juan José; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute for Advanced Materials and Mathematics - INAMAT2; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa; Gobierno de Navarra / Nafarroako Gobernua projecto 0011-1365-2017-000122
We review the latest developments in long-range Brillouin optical time-domain analysis sensors. The factors that impair the performance of these sensors, particularly in terms of their distance range, are discussed together with the latest methods to overcome them. We focus on our recent contributions based on the application of the probe dithering method, which is based on introducing a wavelength modulation to the probe wave. This technique is shown to effectively compensate nonlocal effects originated in the depletion of the pump pulse as well as of its pedestal. In addition, it can provide amplification to the pump wave with a slight modification of the setup. Furthermore, this method can be combined with pump pulse coding and a new technique for coding linearization that we have devised to further extend the sensing length into the hundreds of kilometers range.
Open Access
Fiber-optic brillouin distributed sensors: from dynamic to long-range measurements
(CRC Press, 2018) Loayssa Lara, Alayn; Urricelqui Polvorinos, Javier; Iribas Pardo, Haritz; Mompó Roselló, Juan José; Mariñelarena Ollacarizqueta, Jon; Estadística, Informática y Matemáticas; Ingeniería Eléctrica, Electrónica y de Comunicación; Estatistika, Informatika eta Matematika; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This chapter focuses on Brillouin optical time-domain analysis (BOTDA) sensors because they are the most successful Brillouin distributed sensors (BDS) type in terms of performance and practical applications. Distributed sensor featuring can be done in the time, coherence, or frequency domains, giving rise to the three main analysis BDS types: BOTDA, Brillouin optical correlation-domain analysis (BOCDA), and Brillouin optical frequency-domain analysis (BOFDA). The distance range of measurements performed using a BOTDA sensor is given by the length of sensing fiber that the system is able to measure with a specified performance in terms of measurement precision and time. The chapter reviews the fundamentals and the research directions in BDSs. The applications of the technology are multiple and in diverse fields¿for instance, in the oil and gas industry, where BDSs have been applied to measure temperature and strain along the umbilical cables used for subsea wells.
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
Gain dependence of measured spectra in coherent Brillouin optical time-domain analysis sensors
(SPIE, 2016) Mariñelarena Ollacarizqueta, Jon; Urricelqui Polvorinos, Javier; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We report on the effects of large pump pulse powers on Brillouin optical time-domain analysis (BOTDA) sensors based on phase-modulated probe wave and coherent detection. It is found that the large Brillouin gain that comes from the use of high power pulses induces a narrowing of the RF phase-shift spectrum that is measured in these sensors. This narrowing leads to a Brillouin frequency shift measurement error when the sensor is configured for dynamic measurements. However, the effect has been found to be less significant than that observed in dynamic slope-assisted BOTDA sensors based on amplitude.
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.
Open Access
Structural health monitoring of solar trackers using distributed fiber optic sensors
(SPIE, 2019) Mariñelarena Ollacarizqueta, Jon; Mompó Roselló, Juan José; Zurita Gabasa, Jesús; Urricelqui Polvorinos, Javier; Júdez Colorado, Aitor; López-Amo Sáinz, Manuel; Jiménez Romero, Sergio; Achaerandio, Álvaro; Loayssa Lara, Alayn; Institute of Smart Cities - ISC; Gobierno de Navarra / Nafarroako Gobernua, 0011-1365-2017-000122; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We demonstrate the application of a novel type of distributed fiber optic sensors (DFOSs) to dynamically monitor the effects of wind on solar tracker structures used in photovoltaic power stations. This DFOS is based on the stimulated Brillouin scattering nonlinear optical effect in optical fiber, which can be used to measure the distribution of strain and temperature along a given structure. However, contrary to existing solutions, the sensor provides dynamic real-time measurements with hundreds or even thousands of full simultaneous measurements for all positions in the fiber each second. Moreover, high-precision and high spatial resolution are obtained. This so-called dynamic Brillouin optical time-domain analysis (D-BOTDA) sensor provides real-time monitoring of the bending and torsion of the structure of solar trackers in response to wind load. This helps the solar tracker manufacturer asses and improve the mechanical designs so as to introduce corrective measures and develop cost-effective components that properly withstand the effects of wind at any given location. We experimentally demonstrate the application of a D-BOTDA sensing system to measure distributed bending and, for the first time to our knowledge, also distributed torsion along the stressed beam of the solar tracker. For this purpose, we have developed a procedure to instrument the torsion beam with two optical sensing fibers that are fixed helically wound along the beam in opposite directions, so that any common-mode thermal or bending effects are removed. We initially performed tests in a laboratory facility in which sections of the torsion beam could be subjected to controlled moments. Static and dynamic loads were applied and the measured deformations were compared to those obtained with fiber Bragg gratings, which just provide point measurements of strain. In both cases, full agreement was demonstrated. Finally, the system was installed in an operational solar park.
Open Access
Enhancement of the dynamic range in slope-assisted coherent brillouin optical time-domain analysis sensors
(IEEE, 2017) Mariñelarena Ollacarizqueta, Jon; Urricelqui Polvorinos, Javier; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We present two techniques that provide an extension of the dynamic range of coherent Brillouin optical time-domain analysis (BOTDA) sensors for dynamic measurements. This type of BOTDA sensors rely on self-heterodyne detection of a phase-modulated probe wave and the dynamic range for fast measurements is limited to the linear region of the RF phase-shift spectrum measured. The first method for range extension that we introduce is based on launching pump pulses containing multiple frequency components. This makes the Brillouin spectra generated by each component to overlap, providing a wider linear region of the detected RF phase-shift spectrum and allowing to measure larger Brillouin frequency shift variations. The second method relies on shortening the length of the pump pulses, which leads to the broadening of the detected RF spectra. The theoretical fundamentals of both range enhancing techniques are presented. Moreover, we experimentally demonstrate that they provide a threefold to fourfold enhancement in the dynamic range. Finally, the factors limiting their performance are determined: for the multi-frequency pump pulse technique, it is the worsening of Kerr non-linear effects due to the simultaneous propagation of multiple spectral components in the fiber, and, for the pulse-shortening method, it is the signal-to-noise ratio penalty linked to the reduction of the magnitude of the Brillouin interaction.
Open Access
Phasorial DPP-BOTDA sensor tolerant to non-local effects
(SPIE, 2014) 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 introduce a modification of the differential pulse width pair technique in a BOTDA sensor based on a phase modulated probe wave and RF demodulation. This provides a differential Brillouin phasorial signal with high spatial and spectral resolution in both components (magnitude and phase shift). Moreover, the use of a phase modulated probe wave provides RF phase shift measurements tolerant to the emergence of non local effects. The combination of both techniques can lead to the development of long range BOTDA sensors. Proof of concept experiments demonstrate RF phase shift measurements with 1m spatial resolution over 50km and an uncertainty of 1.3ºC at the worst contrast position.
Open Access
Non-local effects in Brillouin optical time-domain analysis sensors
(MDPI, 2017) Iribas Pardo, Haritz; Urricelqui Polvorinos, Javier; Mompó Roselló, Juan José; Mariñelarena Ollacarizqueta, Jon; Loayssa Lara, Alayn; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Brillouin optical time-domain analysis (BOTDA) sensors have great potential to provide distributed measurements of temperature and strain over large structures with high spatial resolution and measurement precision. However, their performance ultimately depends on the amount of probe and pump pulse power that can be injected into the sensing fiber, which determines the signal-to-noise ratio of the detected measurement signal. The probe wave power is constrained by the generation of noise induced by spontaneous Brillouin scattering and at lower power by the so-called non-local effects. In this work, we focus on the latter. We review the physical origins of non-local effects and analyze the performance impairments that they bring. In addition, we discuss the different methods that have been proposed to counteract these effects comparing their relative merits and ultimate performance. Particularly, we focus on a technique that we have devised to compensate non-local effects which is based on introducing an optical frequency modulation or dithering to the probe wave. This method is shown to provide a comprehensive solution to most of the impairments associated with non-local effects and also to enable some side benefits, such as amplification of the pump pulses to compensate the attenuation of the fiber.
Open Access
Gain dependence of the phase-shift spectra measured in coherent Brillouin optical time-domain analysis sensors
(IEEE, 2016) Mariñelarena Ollacarizqueta, Jon; Urricelqui Polvorinos, Javier; Loayssa Lara, Alayn; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We report on the effects of large pump pulse powers on Brillouin optical time-domain analysis (BOTDA) sensors based on phase-modulated probe wave and coherent self-heterodyne detection. These sensors are particularly suitable to perform dynamic strain and temperature measurements because the radio-frequency (RF) signal that is obtained when the probe wave is detected has a phase-shift spectrum that is independent to first order of the Brillouin gain. Therefore, a fixed optical frequency separation between pump and probe wave can be deployed and uses the stable RF phase-shift spectrum to obtain the Brillouin frequency shift (BFS) from measured changes in the probe RF phase-shift. However, in this paper, it is found that there is a narrowing of the RF phase-shift spectrum that depends on the Brillouin gain. This effect becomes significant when very high power pulses are used and the resultant large gain induces a narrowing of the RF phase-shift spectrum. This narrowing leads to a BFS measurement error when the sensor is configured for dynamic measurements. We analyze, theoretically and experimentally, the origins and the magnitude of the narrowing of RF phase-shift spectra for high pump pulses in a coherent BOTDA sensor. Furthermore, this spectral shape change is compared to the broadening of the gain spectrum that has been recently discovered in conventional direct-detection BOTDA sensors, which is linearly dependent on the pulse peak power injected to the fiber, finding that the spectral shape change is less significant in coherent BOTDA sensors. Finally, we quantify the BFS measurement error that it can induce and find the trade-offs to keep it below a certain threshold. It is found that, from a practical point of view, this effect is significant for short fibers, where nonlinear effects are negligible and large pump pulses can be used.