In this work, it is presented an analysis of FBG arrays installed in a public road. The arrays were installed in a newly paved urban road and were monitored for more than one year. The study evidences the permanent deformation of the wearing course and the degradation of the reflected spectra of the sensors.
In this work, the potential of using general-purpose paints to fabricate highly reflective, low-cost optical mirrors is evaluated. The study shows that high-reflectivity mirrors can be created in standard single-mode fiber in a reliable, simple and economic manner using the appropriate metallic paint. Preliminary results confirm that the grain size of the metallic particles is a crucial factor in the reflective behavior, together with the substrate in which the particles are suspended. Moreover, interferometric patterns have been observed in some cases, which could lead to the creation of simple and economic fiber optic sensors.
In this work, two new interferometric sensors based on multicore optical fibers for the measurement of strain with the ultimate goal of traffic monitoring are presented. The operating principle of each sensor relied on the monitoring of the phase shift difference accumulated between the supermodes of the structure of the multicore segment in a full round trip. The strain characterization for both sensors resulted in a linear response, with sensitivities of -4.073·10-3 rad/με and - 4.389·10-3 rad/με for the aligned and V-shaped cases respectively, and one-hour instabilities below 4.6·10-3 rad with a 95% confidence level. These results suggest its feasibility in applications requiring high sensitivities over very wide strain ranges, such as heavy-vehicle traffic monitoring. To corroborate the hypothesis, both sensors were integrated into the pavement and their response to the traffic was analyzed.
In this work, we present an experimental measurement of temperature and strain sensitivities of a micro-drilled optical fiber (MDOF). The MDOF consisted of a quasi-randomly distributed reflector along a single mode fiber (SMF). A fiber cavity laser based on MDOF was experimentally studied, attaining a single-wavelength laser emission centered at 1568.6nm. The output power level obtained from this single-laser oscillation when pumped at 140mW was around - 9.6dBm, and an optical signal to noise ratio (OSNR) of around 45dB was measured. Although temperature sensitivities of fiber Bragg gratings used as sensors are similar to our MDOF, strain sensitivity is enhanced around one order of magnitude when the MDOF was used.
In this work we demonstrate the multiplexing capability of new optical fiber Fabry-Perot interferometers based on airmicrocavities using a commercial FBG interrogator. Three optimized air-microcavity interferometer sensors have been multiplexed in a single network and have been monitored using the commercial FBGs interrogator in combination with FFT calculations. Results show a sensitivity of 2.18 π rad/mε and a crosstalk-free operation.
In this work, an all-polarization maintaining fiber loop mirror interferometer is presented and validated as vibration and temperature sensor without crosstalk between measurands. The system is entirely built using polarization-maintaining (PM) fiber and a PM optical coupler. As a consequence, no polarization controllers are needed in the cavity, significantly simplifying the operation of the system and improving the stability and accuracy of the measurements. The loop comprises three PM fiber sections appropriately fused with an angle offset between them. In this manner, the interference is maximized and the sensing contributions of the two PM fibers used as communications channels are suppressed. The third PM fiber is used as the sensor itself, simultaneously monitoring temperature and mechanical vibration up to 1.2 kHz by means of an interrogation technique based on fast Fourier transform.
n this work, a preliminary study of the behavior of two different interferometric fiber optic sensors and two different wavelength selective fiber optic sensors is performed. A photonic crystal fiber Fabry-Pérot interferometer, a Sagnac interferometer, a commercial fiber Bragg grating (FBG) and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser are analyzed. A comparison of their sensitivities and resolutions is carried out to analyze their performance as sensors for cryogenic temperatures, taking into account their advantages and drawbacks. Keywords: cryogenic temperature, interferometric sensor, optical fiber sensor, random distributed feedback fiber lasers
In this work, a new application of random distributed feedback lasers to fiber optic sensing has been presented. The
particular properties of these lasers, such as the lack of longitudinal modes and high stability, have been exploited to
monitor transversal load using a phase-shifted fiber Bragg grating (PS-FBG), obtaining a resolution of 1g and a
sensitivity of 3.95GHz/Kg. Due to the PS-FBG birefringence and the load-interrelated transmission lines generated by
the PS-FBG along the orthogonal polarization directions, the beating of the two emission lines generated in the laser can
be monitored in the electrical domain. As a result, transversal load applied on the sensor can be measured.
In this work, a new multiplexing scheme for ultra-long range measurements (up to 200 km) is presented. Time and wavelength sensor multiplexing is achieved by means of a modulated random distributed feedback laser (DFB). The direct modulation of the laser’s cavity allows the interrogation of sensors by measuring the reflected power for different wavelengths and distances. As a proof of concept, nine fiber Bragg gratings (FBGs) placed at different fiber locations and wavelengths have been interrogated.
Three HiBi PCF sections have been multiplexed and monitored as strain sensors in a single fiber loop mirror (FLM) interferometer. The strain applied to each fiber has been measured without crosstalk by using the fast Fourier transform analysis. This study enhances the multiplexing capability in FLM and improves previous results, where a maximum of two fiber section were multiplexed in a single multi-section FLM. The HiBi fibers are spliced together with an angle offset given by the theoretical analysis of the interference. Consequently, just one polarization controller is needed in the system, which greatly simplifies the operation of the system.
In this study, a new sensing application for random distributed feedback fiber lasers is presented. Temperature measurements of a phase-shifted fiber Bragg grating with a resolution higher than 0.01 ºC have been attained. The resolution limitation of classical fiber lasers has been overcome due to the absence of longitudinal modes and high frequency stability of random fiber lasers. The frequency shift of the grating has been measured as 1.195 ºC/GHz and it is detected in the electrical domain by beating an external laser source with the random emission line generated.
In this work, a new configuration of a multi-wavelength erbium fiber ring laser is proposed and demonstrated experimentally by introducing a feedback fiber loop in a fiber ring cavity. Four-wavelength laser emission lines were obtained simultaneously in single-longitudinal mode operation showing a power instability lower than 0.56 dB, and an optical signal-to-noise ratio higher than 50 dB for all the emitted wavelengths. The sensing capability of the FBGs gives this source the possibility to be also used as sensor-network multiplexing scheme. The system offers a better stability and higher optical signal to noise ratios than similar configurations.
In this work, a wavelength division multiplexed fiber ring laser, based on optical add-drop multiplexers to interconnect intensity sensors has been experimentally demonstrated. Three different laser lines were obtained simultaneously all with an optical signal to noise ratio higher than 30dB. This proposed configuration is based on commercial devices and is adapted to the ITU channels normative. By using this configuration each sensor was associated with a different wavelength directly offered by each OADM and a reference wavelength was also included in order to distinguish between power variations induced by the transducer or to detect a fiber failure. This sensor system has been experimentally verified by using microbending sensors obtaining experimental slope sensitivity as good as -0.327dB/μm.
In this work, we present and demonstrate a novel sensor system for simultaneous measurement of strain and temperature through a unique combination of a long period grating (LPG) and a fibre laser based on a fibre Bragg grating (FBG). In order to achieve this, a new erbium doped fibre laser (EDFL) structure is created, showing an optical signal-to-noise ratio (OSNR) of 55 dB and a peak power measured on the OSA between -5 and 0 dBm. The strain and the temperature variation applied on the FBG and the LPG can be monitored through both the fibre laser wavelength shift and the change of the power level of a unique emission line, both showing a clear linear behaviour.
We experimentally demonstrate a resilient wavelength division multiplexed (WDM) fiber ladder network, based on
optical add-drop multiplexers (OADMs), to interconnect sensors. It recovers operation after failures and it enables "selfdiagnosis",
the identification of the failed element(s) from the patterns of surviving end-to-end connections at all
operating wavelengths. A theory for such topologies, the "binary state connectivity analysis", used a matrix formalism to
predict the surviving channels at the receiver node after damage occurs in one or more sites. We present experimental
measurements for double failures in the network, demonstrating complete agreement with theoretical predictions.
KEYWORDS: Fiber Bragg gratings, Sensors, Fiber lasers, Tunable lasers, Remote sensing, Raman spectroscopy, Signal to noise ratio, Signal detection, Single mode fibers, Sensing systems
We propose and demonstrate the feasibility of a novel Fiber Bragg Grating interrogation technique for remote sensing
based on the use of a hybrid Raman-Brillouin fiber laser configuration. The laser comprises 100 km of standard singlemode
fiber (SMF) in a linear cavity configuration with four Fiber Bragg Gratings (FBGs) arranged in series. The FBGs
are used both for the sensing function and for the selection of the lasing wavelengths. A wavelength-swept laser pumps
Brillouin gain in the fiber cavity, which is previously set just under lasing threshold by the Raman gain. Furthermore, the
sensor signal is detected in the radio frequency domain instead of the optical domain so as to avoid signal to noise ratio
limitations produced by Rayleigh scattering. Experimental results demonstrate that the shift of the Bragg wavelength of
the FBG sensors can be precisely measured with good signal to noise ration when the FBG are used for temperature
sensing.
In this work, a novel single-longitudinal-mode (SLM) four-wavelength laser configuration for sensing applications in
L-band is proposed and experimentally demonstrated. This spectral region presents some advantages for the detection of
dangerous gases. The sensor system presented here is based on ring resonators, and employs fiber Bragg gratings to
select the operation wavelengths. The stable SLM operation is guaranteed when all the lasing channels present similar
output powers. It is also experimentally demonstrated that when a SLM behavior is achieved, lower output power
fluctuations are obtained.
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