Search

We demonstrate the use of a graded-index perfluorinated optical fiber (GI-POF) for distributed static and dynamic strain measurements based on Rayleigh scattering. The system is based on an amplitude-based phase-sensitive Optical Time-Domain Reflectometry (ϕ-OTDR) configuration, operated at the unconventional wavelength of 850 nm. Static strain measurements have been carried out at a spatial resolution of 4 m and for a strain up to 3.5% by exploiting the increase of the backscatter Rayleigh coefficient consequent to the application of a tensile strain, while vibration/acoustic measurements have been demonstrated for a sampling frequency up to 833 Hz by exploiting the vibration-induced changes in the backscatter Rayleigh intensity time-domain traces arising from coherent interference within the pulse. The reported tests demonstrate that polymer optical fibers can be used for cost-effective multiparameter sensing.

In this work, we demonstrate for the first time the capability to inscribe long-period gratings (LPGs) with UV radiation using simple and low cost amplitude masks fabricated with a consumer grade 3D printer. The spectrum obtained for a grating with 690 µm period and 38 mm length presented good quality, showing sharp resonances (i.e., 3 dB bandwidth < 3 nm), low out-of-band loss (~0.2 dB), and dip losses up to 18 dB. Furthermore, the capability to select the resonance wavelength has been demonstrated using different amplitude mask periods. The customization of the masks makes it possible to fabricate gratings with complex structures. Additionally, the simplicity in 3D printing an amplitude mask solves the problem of the lack of amplitude masks on the market and avoids the use of high resolution motorized stages, as is the case of the point-by-point technique. Finally, the 3D printed masks were also used to induce LPGs using the mechanical pressing method. Due to the better resolution of these masks compared to ones described on the state of the art, we were able to induce gratings with higher quality, such as low out-of-band loss (0.6 dB), reduced spectral ripples, and narrow bandwidths (~3 nm).

We report the design, fabrication and characterization of 3D large core (1 mm) multimode fiber splitters using a low-cost stereolithography 3D printer. The results were accomplished for symmetrical 1 × 2 and 1 × 4 splitters, where the angle between the output arms was varied from 10 to 180°, showing good uniformity between the splitting ratios. Asymmetrical 1 × 2 splitters were also studied to achieve different splitting ratios. This was done by fixing one arm at a specific angle, while varying the other. Results were quite satisfactory, paving the way for simple and customizable manufacturing of passive optical elements.

An in-line and real time chromatic sensor for liquids based on plastic optical fiber was developed. It uses an air gap, fiber to fiber, transmission principle. Its dependency to turbidity and refractive index is studied and characterized. This information will provide the necessary knowledge for future implementation of more complex auto-compensations routines. Due to the predictable behavior of the sensor to variations of turbidity and refractive index, it is shown that a posterior compensation could be applied for the discrimination of color. The real-time color sensor can be used in different turbid liquids and contain different refractive indices.

In this work we demonstrate the capability to measure shear-strain and torsion loads by bonding an optical fiber to a 3D printed periodic grooved plate. The device acts as a long period grating where the resonances show loss tunability ranging from ∼0 up to ∼20 dB, achieving sensitivities values for the dip transmission ratio as function of the load of 0.12 /mε and 0.21/deg, for shear-strain and torsion loads ranging from 0–∼8 mε and 1–∼4 deg, respectively. The low wavelength drift allowed us to operate the sensor through intensity demodulation techniques, showing good tracking performance of external stimuli.

In this paper we will discuss a new type of long period grating (LPG) that consists on an optical fibre glued on top of a 3D printed grooved plate. The LPG performance will be tested for the case when pressure is applied transversely to the grooved plate. Results showed the appearance of attenuation bands at specific wavelengths, that grow with increasing load. The evolution of the dip power at those resonances, as function of the curvature will be shown, demonstrating the potentialities of the sensor for low cost intensity detection schemes.

In this paper it will be presented a prototype of a low-cost power interrogator for dynamic sensor applications. The proposed system is based on the edge filter technique, where the slope of an in-house resin based Fabry Perot (FP) filter is used to actively filter the power of a narrowband laser centred at the middle part of the FP slope region. The interrogator is composed of a laser source, circulator, photodetector, Arduino board and laptop. Tests have been performed in order to check the viability of the system. Finally, the measurement of a pulse wave signal has been performed by embedding the FP sensor in a 3D printed elastic membrane and reading the signal through the proposed interrogator.

This work reports the development of a low cost in-line color sensor for turbid liquids based on the transmission and scattering phenomena of light from RGB and IR LED sources, gathering multidimensional data. Three different methodologies to discriminate color from the turbidity influence are presented as a proof of concept approach. They are based in regression models, expectation maximization Gaussian mixtures and artificial neural networks applied to labeled measurements. Each methodology presents advantages and disadvantages which will depend on the intended implementation. Regression models revealed to be best suited for standard or occasional measurements, the EM Gaussian mixture will perform better for well-known controlled range of colors and turbidities and the neural networks have easy implementation and potential suited for real-time IoT platforms.

This study is the first comprehensive testing of a novel plastic optical fibre turbidity sensor with runoff samples collected in the field and, more specifically, with a total of 158 streamflow samples and 925 overland flow samples from a recently burnt forest area in north-central Portugal, collected mainly during the first year after the wildfire, as well as with 56 overland flow samples from a nearby long-unburnt study site. Sediment concentrations differed less between overland flow and streamflow samples than between study sites and, at one study site, between plots with and without effective erosion mitigation treatments. Maximum concentrations ranged from 0.91 to 8.19 g L−1 for the micro-plot overland flow samples from the six burnt sites, from 1.74 to 8.99 g L−1 for the slope-scale overland flow samples from these same sites, and amounted to 4.55 g L−1 for the streamflow samples. Power functions provided (reasonably) good fits to the – expected – relationships of increasing normalized light loss with increasing sediment concentrations for the different sample types from individual study sites. The corresponding adjusted R2 values ranged from 0.64 to 0.81 in the case of the micro-plot samples from the six burnt sites, from 0.72 to 0.89 in the case of the slope-scale samples from these same sites, and was 0.85 in the case of the streamflow samples. While the overall performance of the sensor was thus rather satisfactory, the results pointed to the need for scale of site-specific calibrations to maximize the reliability of the predictions of sediment concentration by the POF (plastic optical fibre) sensor. This especially applied to the cases in which sediment concentrations were comparatively low, for example following mulching with forest residues.

A fine control of the microstructured polymer fiber Bragg grating spectrum properties, such as maximum reflected power and 3-dB bandwidth, through acousto-optic modulation is presented. For simulation purposes, the device is modelled as a single structure, comprising a silica horn and a fiber Bragg grating. For similar sized structures a good correlation between the numerical results and the experimental data is obtained, allowing the strain field to be completely characterized along the whole structure. It is also shown that the microstructured polymer fiber Bragg grating requires less effort from the piezoelectric actuator to produce modification in the grating spectrum when compared with a silica fiber Bragg grating. This technique has potential to be applied on tunable optical filters and tunable cavities for photonic applications.

We report the optimization of the length of a D-shaped plastic optical fiber (POF) sensor for refractive index (RI) sensing from a numerical and experimental point of view. The sensing principle is based on total internal reflection (TIR). POFs with 1 mm in diameter were embedded in grooves, realized in planar supports with different lengths, and polished to remove the cladding and part of the core. All D-shaped POF sensors were tested using aqueous medium with different refractive indices (from 1.332 to 1.471) through intensity-based configuration. Results showed two different responses. Considering the refractive index (RI) range (1.33-1.39), the sensitivity and the resolution of the sensor were strongly dependent on the sensing region length. The highest sensitivity (resolution of 6.48 × 10−3refractive index units, RIU) was obtained with 6 cm sensing length. In the RI range (1.41-1.47), the length of the sensing region was not a critical aspect to obtain the best resolution. These results enable the application of this optical platform for chemical and biochemical evanescent field sensing. The sensor production procedure is very simple, fast, and low-cost.

In this work, we have shown the capability to produce Fabry-Perot (FP) cavities based on photopolymerizable resins sandwiched between two single-mode fibers. The process allows easy control of the length of the cavity and an enhancement on the fringe visibility when compared with standard droplet based FP sensors. The method will be employed for the fabrication of four sensors composed of different photopolymerizable resins. Their performance regarding humidity, temperature, pressure and refractive index will be under analysis, revealing that in some cases it is possible to reach better sensitivities than the ones reported in literature.

The experimental investigations of the performance of a D-shaped Plastic Optical Fiber (POF) sensor are presented. The phenomenon behind this optical fiber sensor based platform is the variation of the transmitted light at the output of the POF with the external refractive index. The resolution of the optical sensing platform is strongly dependent on the length of the sensing region, decreasing from 10 -1 to 10 -3 RIU with length varying from 1cm to 5cm. The sensor production procedure is very easy, fast and low-cost. The obtained resolution allows further development for chemical and biochemical sensing by chemical receptor, e.g. molecularly imprinted polymer. A good resolution was obtained using sensing area length of 5cm.

A novel plastic optical fiber (POF) sensor was investigated to monitor total suspended solids (TSS) concentration continuously, offering insights into wastewater treatment bioreactors without disturbing them. First, off-line experiments with both anaerobic and aerobic sludge (in concentrations ranging between 0.1 and 8.6 g TSS L−1) were used to establish the exponential relationship of the sensor’s transmitted optical power with TSS concentrations. Attenuation coefficients differed clearly with the type of sludge (1.227–1.274 and 0.456–0.679 for anaerobic and aerobic biomass, respectively) and, in the case of the aerobic sludge, with its coloring. The POF sensor was further used for online monitoring of sludge settling profiles inside a sequencing batch reactor (SBR) that was being operated under a “feast-famine” regime. The turbidity profiles agreed very well with the Boltzmann equation. The Boltzmann dx parameter revealed clear differences in the steepness of the settling gradients, which could be explained by the changes in the applied organic loading rates (OLR). OLR in the range of 1.34–1.53 g COD L−1 day−1 resulted in steeper settling gradients than OLR in the range of 2.13–3.12 g COD L−1 day−1 (dx: 0.42–0.50 vs. 0.90–1.36). Thus, the POF sensor not only revealed elevated potential for prediction of biomass concentration but also for becoming an integral part of real-time automation systems in order to diminish repeated sampling and off-line analysis to control the withdrawal phase based on seasonal sludge settling profiles.

The ubiquity and importance of anions in many crucial roles accounts for the current high interest in the design and preparation of effective sensors for these species. Therefore, a tilted fiber Bragg grating sensor was fabricated to investigate individual detection of different anion concentrations in ethyl acetate, namely acetate, fluoride and chloride. The influence of the refractive index on the transmission spectrum of a tilted fiber Bragg grating was determined by developing a new demodulation method. This is based on the calculation of the standard deviation between the cladding modes of the transmission spectrum and its smoothing function. The standard deviation method was used to monitor concentrations of different anions. The sensor resolution obtained for the anion acetate, fluoride and chloride is 79 × 10−5 mol/dm3, 119 × 10−5 mol/dm3 and 78 × 10−5 mol/dm3, respectively, within the concentration range of (39–396) × 10−5 mol/dm3.

We report on the production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in two spectral regions using polymer optical fibers (POFs). Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 850 nm and 1550 nm were fabricated in several types of polymer optical fibers. The 3 dB FBG bandwidth varies from 0.22 nm down to 0.045 nm considering a Bragg grating length of 10 mm and 25 mm, respectively.

Submitted by António Freitas (amsf@uma.pt) on 2021-11-26T10:33:31Z No. of bitstreams: 1 Multiparameter optical monitoring of madeira wine.pdf: 1226708 bytes, checksum: 337b57d54c92660791d596bbe72f6c13 (MD5) Made available in DSpace on 2021-11-26T10:33:31Z (GMT). No. of bitstreams: 1 Multiparameter optical monitoring of madeira wine.pdf: 1226708 bytes, checksum: 337b57d54c92660791d596bbe72f6c13 (MD5) Previous issue date: 2013 info:eu-repo/semantics/publishedVersion

The present work addresses the control of the mPOF Bragg grating spectrum properties through acousto-optic modulation. For the first time, the interaction of a flexural acoustic wave, generated by longitudinal excitation of different frequencies, with the Bragg grating will be presented. Also it will be demonstrated the quasi linear relationship between PZT load and maximum reflected power/ 3dB bandwidth of the reflected spectrum.

Submitted by Patrícia Correia (patriciacorreia@ua.pt) on 2020-05-07T13:37:16Z No. of bitstreams: 1 Bilro et al. - 2010 - Design and performance assessment of a plastic opt.pdf: 194359 bytes, checksum: dc29a9220bf49ed82e20b8b959eff2b3 (MD5) Approved for entry into archive by Patrícia Correia (patriciacorreia@ua.pt) on 2020-05-07T13:37:38Z (GMT) No. of bitstreams: 1 Bilro et al. - 2010 - Design and performance assessment of a plastic opt.pdf: 194359 bytes, checksum: dc29a9220bf49ed82e20b8b959eff2b3 (MD5) Made available in DSpace on 2020-05-07T13:37:38Z (GMT). No. of bitstreams: 1 Bilro et al. - 2010 - Design and performance assessment of a plastic opt.pdf: 194359 bytes, checksum: dc29a9220bf49ed82e20b8b959eff2b3 (MD5) Previous issue date: 2010 published

We report the inscription of a Bragg grating in an undoped polymethylmethacrylate based microstructured fiber in a time record. The fiber has been irradiated with a 248 nm ultraviolet radiation, through the phase mask technique using low fluence and low repetition rate. The experimental conditions were chosen to modify the core refractive index of the fiber at the incubation regime and avoiding polymer ablation. The peak reflection of the Bragg grating was centered in the infrared region with 20 dB reflection and 0.16 nm bandwidth. These spectral properties are well attractive for sensors and communications applications.

We report on the inscription and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in different spectral regions using polymer optical fibers (POFs). Narrow bandwidth FBGs are increasingly essential for optical filtering in POF transmission systems and photonic applications. Long FBGs with resonance wavelengths of around 600, 850 and 1550 nm were inscribed in several types of polymer optical fibers using a scanning technique with a short optical path. The technique allowed the inscription in relatively short periods of time. The achieved 3 dB bandwidth varied from 0.22 down to 0.045 nm considering FBG lengths of 10 and 25 mm, respectively.

This work reports the use of a polymer fiber Bragg grating combined with a resin based Fabry Perot cavity, created by cold splicing between polymer and glass fibers, for the simultaneous detection of strain and temperature.