BUSCADOR RECOLECTA

In this work, an erbium-doped fiber ring cavity based on a 3dB optical coupler for refractive index measurements is presented and experimentally verified. This interrogation system, based on a 1 x 2 optical coupler, uses one of these output ports to increase the reflected optical power by means of a fiber Bragg Grating (FBG), used as a reflector. Moreover, the other output port is used as a refractive index sensing head. A spectral analysis of this interrogator system as well as a fiber cavity ring refractive index sensor characterization are carried out. Finally, an experimental comparison of the refractive index sensor range when the 3dB coupler is replace by a 1x3 one is also presented., This work is financed by the program “José Castillejo para estancias de movilidad en el extranjero de jóvenes doctores”,
funded by the Ministerio de Universidades of Spain (reference CAS21/00351); project PID2019-107270RB-C22, funded
by MCIN/AEI/10.13039/501100011033 and FEDER “A way to make Europe”; projects PDC2021-121172-C21 and
TED2021-130378B-C22 funded by MCIN/AEI/10.13039/501100011033 and European Union “Next generation
EU”/PTR; and National Funds through the Portuguese funding agency, FCT—Fundação para a Ciência e a Tecnologia,
within project UIDB/50014/2020 and FCT, Portugal through the Grant 2020.05297.BD

We introduce a method to compensate for the deleterious effects of the phase noise of the laser source on long-range distributed acoustic sensors (DAS) that implement optical pulse compression (OPC). Pulse compression can be used in coherent optical
time-domain reflectometry (COTDR) sensors to extend the measurement range without compromising spatial resolution. In fact,
OPC-COTDR sensors have demonstrated the longest measurement
range to date in passive sensing links that do not require distributed
amplification to compensate fiber attenuation. However, it has been
found that the limited coherence of the laser source has a degrading
effect on the actual performance enhancement that pulse compression can bring because it constrains the maximum duration of the
compression waveforms that can be used and makes the use of lasers
with extremely low phase noise necessary.We introduce a technique
to compensate for the effects of phase noise on OPC-COTDR sensors so that they can demonstrate their full potential for long-range
measurements using lasers with less stringent phase noise requirements. The method is based on sampling the phase noise of the
laser with an auxiliary interferometer and using this information
in a simple signal processing technique to mitigate its deleterious
effect on the signal measured. We test our method in an OPCCOTDR sensor that uses 500-μs linear frequency modulated pulses
to demonstrate 100-km range measurements with 200 p/√Hz
of strain sensitivity at 2-m initial spatial resolution that becomes
10-m after applying the gauge length. To our knowledge, this is the
longest compression waveform demonstrated to date in an OPCCOTDR sensor. Its use provides an extra 20-km range compared
to previous demonstrations using laser sources of comparable
linewidth. Furthermore, comparable performance is also demonstrated when using a laser source with an order of magnitude larger
linewidth., This work was supported in part by European Union “Next
generationEU”/PRTR and MCIN/AEI/10.13039/501100011033 under grant
PDC2021-121172-C21, in part by FEDER “A way to make Europe” and
MCIN/AEI/10.13039/501100011033 under Grant PID2019-107270RB-C22,
and in part by the Gobierno de Navarra under Grant PC210-211 FIBRATRAFIC.

This letter presents an experimental comparison between two linear-cavity erbiumdoped fiber lasers (EDFL) assisted by two different artificial backscatter fiber-based reflectors.
Both reflectors were inscribed by femtosecond laser direct writing, one of them within a
single-mode fiber (SMF) and the other one within a multi-mode fiber (MMF). Although the
erbium-doped fiber amplifier (EDFA) used in both structures was the same and both reflectors
were manufactured under the same parameters, the reflection spectrum of each was clearly
different due to their different physical properties. The first linear-cavity EDFL, consisting of
an SMF-based reflector with 9µm core and 125µm cladding, resulted in a single laser emission
line located in the C-band and centered at 1564.4 nm, exhibiting an optical signal-to-noise ratio
(OSNR) of 52dB when pumped at 100mW. On the other hand, a single laser emission line with a
similar OSNR but in L-band (centered at 1574.5nm) was obtained when using an MMF-based
reflector with 50µm core and 125µm cladding., Ministerio de Educacion, Cultura y Deporte (PhD grant FPU2018/02797); European Commission (Next generation EU/PTR); FEDER (A way to make Europe); MCIN/AEI/10.13039/501100011033 (PDC2021-121172-C21, PID2019-107270RB).

A linear fiber laser system for measurements of paracetamol concentration is experimentally demonstrated. The cavity is based on a fiber loop mirror and an FBG centered at 1567.8 nm. The sensing head corresponds to a refractometric sensor, whose which principle of operation is based on Fresnel reflection in the fiber tip (FBG side). The system works at detected variations of paracetamol concentrations with a sensitivity of [8.74± 0.34)× 10-5] µW/(g/kg) and a resolution of 2.77 g/kg. The results prove that the fiber laser system could be an asset for processing industries, specifically for non-invasive and real-time measurements of concentration., This work was financially supported by the Wellcome Trust, UK, through the Innovator Award “Light-activated cap for catheter sterilization” (WT223940/Z/21/Z); National Funds through FCT/MCTES (PIDDAC), within projects LA/P/0045/2020 (ALiCE), UIDB/00511/2020 and UIDP/00511/2020 (LEPABE); Program “José Castillejo para estancias de movilidad en el extranjero de jóvenes doctores”, funded by the Ministerio de Univesidades of Spain (reference CAS21/00351); project PID2019-107270RB-C22, funded by MCIN/AEI/10.13039/501100011033 and FEDER “A way to make Europe”; projects PDC2021-121172-C21 and TED2021- 130378B-C22 funded by MCIN/ AEI/10.13039/501100011033 and European Union “Next generation EU”/PTR. Liliana Soares acknowledges the support of FCT, Portugal, through the Grant 2020.05297.BD.

We demonstrate traffic monitoring over tens of kilometres of road using an enhanced distributed acoustic sensing system based on optical pulse compression and a novel transformed-domain-based processing scheme with enhanced vehicle detection and tracking capabilities., This work was supported in part by European Union “Next generationEU”/PRTR and MCIN/AEI/10.13039/501100011033 under grant PDC2021-121172-C21, in part by FEDER ”A way to make Europe” and MCIN/AEI/10.13039/501100011033 under grant PID2019-107270RB, and in part by Gobierno de Navarra under grant PC210-211 FIBRATRAFIC. The authors would like to thank Gobierno de Navarra and NASERTIC S.A.U for their support by giving access to the dark fiber deployed in this work.

In this study, an interrogation system based on an erbium-doped fiber ring cavity for refractive index measurements is presented and experimentally demonstrated. This cavity ring includes a 1 × 3 coupler wherein one of the fiber output ports is used to increase the optical power of the system by means of an FBG used as a reflector. The other two output ports are used as a refractive index sensing head and reference port, respectively. An experimental demonstration of this proposed sensor system for the measurement of a distinct refractive index is presented., This work is financed by the program “José Castillejo para estancias de movilidad en el extranjero de jóvenes doctores”, funded by the Ministerio de Universidades of Spain (reference CAS21/00351); project PID2019-107270RB-C22, funded by MCIN/AEI/10.13039/501100011033 and FEDER “A way to make Europe”; projects PDC2021-121172-C21 and TED2021-130378B-C22 funded by MCIN/AEI/10.13039/501100011033 and European Union “Next generation EU”/PTR; and National Funds through the Portuguese funding agency, FCT—Fundação para a Ciência e a Tecnologia, within project UIDB/50014/2020. Liliana Soares acknowledges the support of FCT, Portugal through the Grant 2020.05297.BD.

This research explores the impact of cyclic uniaxial transverse deformation on an in-line hollow-core fiber etalon. The structure consists of a 6 mm long section of capillary fiber spliced between two standard single-mode fibers. The optical response of the structure is theoretically analyzed in spectral and transformed domains, evidencing Fabry-Perot and antiresonant interferometric mechanisms. A validation of the theoretical behavior is carried out both through simulation and experimentation. The performance of the structure for uniaxial transverse deformation is subsequently evaluated by tracking the phase of the main component in the transformed domain. The relevance of measuring in the time domain is discussed, demonstrating improved accuracy over wavelength shift and inverse spatial domain methods. Several sensors with different internal diameters underwent cycles of transverse deformation, revealing robust linear trends in every case. On average, the structure demonstrated elastic behavior under deformations up to 42 μm, with a mean sensitivity of 0.174 rad/μm, and mechanical breakage taking place at 58 μm. The results confirmed the suitability of the sensor to withstand uniaxial micro-displacements or pressures, with smaller inner diameter capillary fibers showing the best performance., This work was supported in part by
MCIN/AEI/10.13039/501100011033 and FEDER "A way to make Europe"
under Project PID2019-107270RB-C22 and Project PID2022-137269OB-C21,
in part by MCIN/AEI/10.13039/501100011033 and European Union "Next generation
EU"/PRTR under Project PDC2021-121172-C21 and Project TED2021-
130378B-C22, and in part by the Public University of Navarre under Project
PJUPNA06-2022. Open access funding provided by Public University of
Navarre.

We introduce a novel long-range traffic monitoring system for vehicle detection, tracking, and classification based on fiber-optic distributed acoustic sensing (DAS). High resolution and long range are provided by the use of an optimized setup incorporating pulse compression, which, to our knowledge, is the first time that is applied to a traffic-monitoring DAS system. The raw data acquired with this sensor feeds an automatic vehicle detection and tracking algorithm based on a novel transformed domain that can be regarded as an evolution of the Hough Transform operating with non-binary valued signals. The detection of vehicles is performed by calculating the local maxima in the transformed domain for a given time-distance processing block of the detected signal. Then, an automatic tracking algorithm, which relies on a moving window paradigm, identifies the trajectory of the vehicle. Hence, the output of the tracking stage is a set of trajectories, each of which can be regarded as a vehicle passing event from which a vehicle signature can be extracted. This signature is unique for each vehicle, allowing us to implement a machine-learning algorithm for vehicle classification purposes. The system has been experimentally tested by performing measurements using dark fiber in a telecommunication fiber cable running in a buried conduit along 40 km of a road open to traffic. Excellent results were obtained, with a general classification rate of 97.7% for detecting vehicle passing events and 99.6% and 85.7% for specific car and truck passing events, respectively., This work was supported in part by European Union “Next generationEU”/PRTR and MCIN/AEI/10.13039/501100011033 under grant PDC2021-121172-C21, in part by FEDER “A way to make Europe” and MCIN/AEI/10.13039/501100011033 under grant PID2019-107270RB, and in part by Gobierno de Navarra under grant PC210-211 FIBRATRAFIC.

A paracetamol concentration-sensing scheme based on a linear cavity fiber laser configuration is demonstrated experimentally. The laser cavity has a fiber sensor at one end, that allows refractive index measurements. The refractometer consists of a cleaved fiber tip combined with an FBG functioning as a reflecting mirror. The combination of a fiber loop mirror at the other end allows to reflect all the light from the FBG and refractometer, forming a linear cavity. By measuring the intensity variation of the Fresnel reflection at the fiber-to-liquid interface, the measured concentration is linear and have a concentration sensitivity of -8.74±0.34×10-5 µW/(g/kg), over a range of 52.61 to 219.25 g/kg, and with a resolution of 2.77 g/kg. The results obtained present high stability and prove the potential of the fiber laser system to performed real-time measurements of concentration, in a non-invasive way., This research was funded by: National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia, within project UIDB/50014/2020; National Funds through FCT/MCTES (PIDDAC), within projects LA/P/0045/2020 (ALiCE), UIDB/00511/2020 and UIDP/00511/2020 (LEPABE); Program “José Castillejo para estancias de movilidad en el extranjero de jóvenes doctores”, funded by the Ministerio de Univesidades of Spain (reference CAS21/00351); project PID2019-107270RB-C22, funded by MCIN/AEI/https://doi.org/10.13039/501100011033 and FEDER “A way to make Europe”; projects PDC2021-121172-C21 and TED2021-130378B-C22 funded by MCIN/ AEI/https://doi.org/10.13039/501100011033 and European Union “Next generation EU”/PTR. Liliana Soares acknowledges the support of FCT, Portugal, through the Grant 2020.05297.BD.

We introduce a technique to compensate the performance impairments due to the laser phase noise in long-range pulse-compression DAS sensors. Experiments demonstrate the use of the longest duration pulse compression waveform to date., This work was supported in part by European Union "Next generationEU"/PRTR and MCIN/AEI/10.13039/501100011033 under grant PDC2021-121172-C21, in part by FEDER "A way to make Europe"and MCIN/AEI/10.13039/501100011033 under grant PID2019-107270RB, in part by Gobierno de Navarra under grant PC210-211 FIBRATRAFIC, and in part by the Israeli Science Foundation (ISF) under grant number 2675/20.

Process Analytical Technology (PAT) has been increasingly used in the pharmaceutical industry to monitor essential parameters in real-time during pharmaceutical processes. The concentration of Active Pharmaceutical Ingredients (APIs), such as paracetamol, is one of these parameters, and controlling its variations allows for optimization of the production process. In this study, a refractometric sensor, implemented by an interrogation system based on an Erbium-Doped Fiber Ring Cavity (EDFRC), was presented and experimentally demonstrated. The Cavity Ring proposed included a 1 × 3 coupler. One port of the coupler was used to increase the optical power of the system through a Fiber Bragg Grating (FBG), and the other two ports were used as sensing head and reference. The sensor detected variations of paracetamol concentration with a sensitivity of [(−1.00 ± 0.05) × 10−3] nW/(g/kg) and a resolution of 5.53 g/kg. The results demonstrate the potential of this technology as a possible non-invasive PAT tool., and European Union “Next generation EU”/PTR. Liliana Soares acknowledges the support of FCT, Portugal, through the Grant 2020.05297.BD.This research was funded by: National Funds through the Portuguese funding agency, FCT—Fundação para a Ciência e a Tecnologia, within project UIDB/50014/2020; National Funds through FCT/MCTES (PIDDAC), within projects LA/P/0045/2020 (ALiCE), UIDB/00511/2020, and UIDP/00511/2020 (LEPABE); Program “José Castillejo para estancias de movilidad en el extranjero de jóvenes doctores”, funded by the Ministerio de Univesidades of Spain (reference CAS21/00351); project PID2019-107270RB-C22, funded by MCIN/AEI/10.13039/501100011033 and FEDER “A way to make Europe”; projects PDC2021-121172-C21 and TED2021-130378B-C22, funded by MCIN/AEI/10.13039/501100011033