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In this paper, we demonstrate both numerically and experimentally the capability to control and enhance the hydrostatic pressure sensitivity of an adhesive based Fabry-Perot (FP) sensor. The fiber sensor consists of a polymerized resin in between two single-mode fiber terminals that act as low-reflectance mirrors. The theoretical evaluation of the proposed sensor showed that the strain in the region between the fiber end faces increases with increasing dimensions of the resin structure surrounding the inner FP cavity. Experimentally, the photopolymerizable resin was added in layers, increasing the structure dimensions, allowing to improve the hydrostatic pressure sensitivity from 102 to 475 pm/MPa for the cavity filled with resin just in between the fiber end faces and for the cavity covered with several layers of resin, respectively. The sensor fabrication is simple and cost effective, allowing an easy and affordable way to control and enhance the hydrostatic pressure sensitivity of resin based FP sensors.

In this work we report the fabrication of a dual fiber sensor composed of an adhesive based Fabry–Perot cavity combined with a polymer fiber Bragg grating (PFBG), for the simultaneous detection of humidity and temperature. The Fabry–Perot structure was fabricated through a modified version of the self-written waveguide technology, by employing a no-core fiber, while the PFBG was inscribed in a flat-sides microstructured polymer fiber (mPOF) using the phase mask technology through the 248 nm UV laser. The combination of these two polymer based technologies allow an easy fabrication and provide an efficient route for the simultaneous detection of humidity and temperature with high resolution.

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).

This study presents the use of a sensing device composed of an all ZEONEX-480R polymer fiber Bragg grating, in series with a silica fiber, for the control/enhancement of the strain sensitivity. The results show that the amount of strain imposed in the total gauge length is unequally distributed in each fiber section. The low Young's modulus and diameter of the polymer fiber employed, compared to the silica one, leads to a higher strain density in the former. Additionally, the control of the length of each fiber section plays also an important role on the distribution of strain in each fiber. Theoretical results show that higher strain sensitivities are easier to achieve for short and long polymer and silica fiber lengths, respectively. Experimental characterization of a sensing head composed by a 2.6 cm polymer optical fiber and different lengths of silica fiber, led us to control and improve the strain sensitivity of the sensing device.

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.

This chapter presents a broad view of some of the published and most used techniques and schemes for sensing with polymer optical fibers (POF), and presents a small part of the sensing devices using POF since the same techniques can be used to measure several different parameters with slight modifications. In quest for low-cost ways of parameter measurement using POF, different approaches can be found in academia. The most common method of detecting is based on intensity variation which requires simple operation principles and instrumentation. One of the extrinsic sensing techniques employed and commonly used is the light transmission configuration. In the intrinsic sensing techniques, light does not physically leave the fiber but tries to promote the interaction of its evanescent field with the external medium. Intrinsic sensors can be produced not only by changing the structure of the fiber but also by altering the refractive index of the fiber waveguide in the sensing area by ultraviolet or infrared-light exposure.

The detection of perfluorobutanesulfonic acid (PFBS) in water is presented for the first time exploiting a low-cost optical chemical sensing strategy, based on plastic optical fibers and molecularly imprinted polymers (MIPs), able to detect pollutants in water. The sensor’s response measured in this work for the detection of PFBS is similar to the one obtained with Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA), already investigated. The detection limit of PFBS is considered of interest when compared to those obtained by using different expensive traditional approaches, e.g. high performance liquid chromatography-mass spectrometry (HPLC-MS). Moreover, the use of this sensing approach is a very attractive perspective for fast, in situ, and remote low-cost detection of pollutants in water for smart cities applications.

Plastic Optical Fibers (POFs) are becoming popular for the development of sensors with multiple applications. In this work, we report a preliminary study related with the coating of modified POFs with proteins. Samples of POF were immersed in buffer and in proteins’ solutions under different experimental conditions: modification of the POF sample, immersion time, temperature, buffer solution and concentration of protein. A simple and easy methodology using protein staining solution was performed to confirm the coating of the POFs with proteins and to evaluate the dependency with the experimental conditions. Further developments will be focused on the coating of POFs with modified proteins for the selective detection of contaminants in water contributing to the development of low-cost POF chemical sensors and biosensors.

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.

During the last years, fiber Bragg gratings (FBGs) written in polymer optical fibers (POFs) have been pointed as an interesting alternative to silica FBGs for applications in sensors and in optical access networks. In order to use such components in real applications, the manipulation of POFs, as well as the increase of quality in the production of FBGs has to be achieved. In this article some of the recent advances regarding these two aspects are reported and include recent developments to produce smooth POFs end face with high quality, benefiting the current splicing process and the inscription of high quality FBGs in a few seconds. Furthermore, additional characterizations to strain, temperature, pressure, and humidity are also shown.

We report for the first time, the fast inscription of high-quality Bragg gratings in highly birefringent microstructured polymer optical fibers by the phase mask method using 248-nm UV radiation. The fibers birefringence is created through a special design of the structure of holes through the fiber. A Bragg grating in these type of fibers allows the creation of two reflection peaks, where the peak separation is related to the phase birefringence.

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.

A theoretical analysis for a new high-sensitivity pressure sensor based on the surface plasmon resonance (SPR) phenomenon is presented. The device consists a thin metal film deposited on the cladding of a U-shaped optical fiber probe embedded in a silicon rubber block. When the block is under pressure, the bending radius will vary and consequently a shift on the SPR wavelength can be noticed and converted to pressure units. Theoretical simulations using the transfer matrix formalism and the N-layer U-shaped fiber model were developed and implemented for three different metals: gold, copper, and silver. A resolution of 5.9 × 10−4, 6.3 × 10 −4, and 1.3 × 10−3 kPa can be expected for gold, copper, and silver, respectively for a working range up to 0.12 MPa. The proposed structure reveals to be suitable to high-sensitivity pressure measurements, including industrial operating machinery and R&D applications.

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.

In the last years, optical fiber based sensors and systems for ehealthcare attracted the attention of the scientific community. Over this chapter, optical fiber technology is presented, referring the different types of optical fibers, its main characteristics, and advantages over other sensing methodologies. In addition, optical fiber based sensors and sensing techniques are discussed and several works reported in the literature are reviewed showing that they are a valuable technique to improve healthcare service to the community and as a potential solution to answer different problems. The final section of the chapter consists of the description of three applications of optical sensors in healthcare, namely monitoring of human joint movement, measuring strain of biological tissues, and characterization of medical materials.

A new approach for the selective detection of the Perfluorinated compounds in water is presented. The low-cost sensor system is based on a Molecular Imprinted Polymer deposited on a D-shaped Plastic Optical Fiber platform.

A wireless refractive index sensor for in-line measurement in liquids was developed. It is based on the Fresnel reflection on a prism–liquid interface, where the critical angle of the totally reflected light in the interface of two media is detected by a charge-coupled device (CCD) array. A LED is used as a light source and a plastic optical fibre, with a well-established numeric aperture, guides the light to the prism interface. Both the LED and the CCD are controlled with a Raspberry Pi 3 Model B board with wireless communication. Resolutions with values lower than 1.0 × 10−4 RIU can be achieved with this potential low-cost configuration.

The production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in different spectral regions using polymer optical fibers (POFs) is reported. Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 600-nm, 850-nm and 1550-nm in several types of polymer optical fibers were inscribed using a scanning technique with a short optical path. The technique allowed the inscription in relative short periods of time. The obtained 3-dB bandwidth varies from 0.22 down to 0.045 nm considering a Bragg grating length between 10 and 25-mm, respectively.

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.

We report the development of a low cost plastic optical fibre (POF) sensor for ammonium detection using molecularly imprinted polymers (MIP’s). The cladding of a 1 mm diameter PMMA fiber is removed, in which is grafted a molecular imprinted polymer (MIP), by radical polymerization with thermal initiation, that act as a selective sensing layer. For the polymerization, 2,2’-Azobis(2-methylpropionamidine)dihydrochloride (AAPH) is used as initiator, methacrylic acid (MAA) as a monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linker, ammonium chloride (NH 4 Cl) as a template and 30% of ethanol in water as a solvent. The sensing method consists of an intensity based scheme. The response to different concentrations of ammonium solutions in water has been evaluated at room temperature. Solutions with (0 - 0.6) M concentration, with the corresponding refractive indexes varying between 1.3325 - 1.3387, at 25°C were used. The response of the fiber with the original cladding, and after cladding removal has been monitored and compared to the response given by the developed sensor. The response is very fast, less than 1 minute and reversible, which allows the continuum use of the sensor. Further developments are focused in optimization of MIP grafting procedure and sensor performance, in order to increase sensitivity.