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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.

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.

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.

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.

This manuscript presents low-cost sensing systems for the monitoring of liquids, namely water and beverages quality assessment, with remote and in-site monitoring capabilities. The collaboration with several research groups allowed the development of smart optical platforms and low-cost sensors based on plastic optical fibers for the measurement of turbidity, color, refractive index and water contaminants.

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.

In this study the influence of the surface roughness on the transmission capacities of D-shaped plastic optical fibers (POFs) and sensors performance was investigated. Five D-shaped POF sensors were produced and characterized for refractive index sensing between 1.33 and 1.41. The sensors were characterized using a low-cost optical sensing system based on the variation of the transmitted light though the POF with refractive index changes (RI). Higher surface roughness increases the scattering losses through the POF and influences the sensors&rsquo, performance, therefore, a balance must be attained. Generally, the best performance was achieved when the sensing region was polished with P600 sandpaper as a final polishing step. Polishing with sandpapers of lower grit size resulted in lower scattering, higher linearity of the sensor response and generally lower performance for RI sensing. A sensor resolution of 10&minus, 3&ndash, 10&minus, 4 RIU, dependent on the value of the external refractive index, was obtained through simple and low-cost manufacturing procedures. The obtained results show the importance of surface roughness in the development of POF sensors which can be used in several applications, such as for water quality assessment.

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 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.

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.

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.

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.

The modeling of a side-polished plastic optical fiber as a sensor of two distinct physical parameters is presented. A comprehensive analytical study is performed using a geometric optic approach. Different details are taken into account, such as the geometric description of the sensor, the intensity profile of the emitter, and the possibility of a multireflection for a light ray at the sensitive area. The good agreement between the experimental and theoretical results validates the developed analytical model.

In this work, the inscription in few seconds of a Bragg grating array in undoped PMMA mPOF using the phase mask technique is reported. The fast growth was possible through the use of a 248 nm UV laser, with suited laser parameters, allowing the creation of a core refractive index modulation without damaging the fiber surface. The Bragg gratings were written in the IR region presenting good spectral properties, achieving for the best case 30 dB reflectivity and 0.2 nm bandwidth. The Bragg grating array was characterized to strain and results are in agreement with the values reported in literature.

A new technique, based on a partially automated process, for smooth end face termination of three types of plastic optical fibers (microstructured, graded-index, and step-index) is presented. The cross-sectional shape of the fibers is preserved, and the structure in microstructured plastic optical fibers (POFs) is of good quality, showing no plastic deformations. The termination is achieved in a fast and easy way, independent of material properties or structures inside the fiber. The process is reproducible and it shows that thin-diameter POFs can be used. The POFs' near-field pattern and the insertion loss are also analyzed, showing good coupling capabilities.

In the last years, polymer optical fibers (POFs) were pointed out as a viable alternative to silica fibers in many fields such as in sensing and optical communications. In this work we will show our recent developments regarding the production of high quality fiber Bragg gratings in polymer optical fibers and their potential applications.

Currently, the surface plasmon resonance (SPR) based sensors are mainly focused in visible frequencies, being a barrier for a better integration with the typical fiber optical communication transmission bands. Here, it is presented a theoretical analysis of a SPR based fiber optic sensor with a uniform gold coating on a U-shaped probe. The sensor does not require any fiber etching treatment which eases and improves the control of the overall process. The response of the device to refractive index variations was investigated and a resolution of 10-8 is foreseen for refractive indices around 1.413, becoming the proposed sensor a useful tool for biological and chemical applications.

A refractive index and viscosity sensor based on FBGs in mPOF is reported for the first time. The refractive index was measured with a sensitivity of -10:98nm=RIU and a resolution of 1 – 10-4RIU. Viscosity measurements were performed with acousto-optic modulation, obtaining a sensitivity of -94:42%=mPa • s and a resolution of 0:06mPa • s.

The inscription of Bragg gratings in different POFs, including GI-POF is presented. Additionally the cross-sensitivity characterization to temperature and strain for an mPOF FBG is reported for the first time. Results show better sensitivity performances after the annealing process which will help to develop new sensitive optical devices.

In this work, the study of a particular step of Madeira’s winemaking process called estufagem with a plastic optical fibre sensor is presented. Madeira wine is a type of fortified wine produced in the Madeira island of Portugal. The characteristic aroma and exceptional stability of these wines result from the singular used winemaking method that consists in the estufagem where the wine is heated up to 55 °C for at least 3 months, among other steps. This heating based process can produce significant changes in wine colour, aroma and taste. By measuring the transmitted optical power through the wine in three different cells at three different wavelengths it is possible to monitor wine colour evolution during the estufagem. The plastic optical fibres offer easy non-skilled handling, ruggedness and low cost, overcoming the difficulties of the electronic and conventional systems and improving the time of the laboratory offline methods. Results show that it is possible to distinguish the different Madeira wines (from sweet to dry wines) obtained based on different wine grapes as well as the colour evolution during the diverse months of the estufagem.

Madeira fortified wines are typically aged under controlled conditions. The present demo describes the existing pilot plant facility in Madeira University, with the installed controlled systems and safety devices. An optical fiber based platform for real time monitoring and interactive visualization tools for data analysis will be described and its potential use demonstrated.

The present work addresses the need for new devices felt in the context of quality control, especially in the food industry. Due to the spectral dependence of the attenuation coefficient, a novel dual-parameter sensor for colour and refractive index was developed and tested. The sensor employs plastic optical fibres to measure the transmitted optical power in three measurement cells each with a different incident wavelength. The performance of the sensor was tested using several dyes at different concentrations and aqueous solutions of glycerine and ethanol. Results show that this technique allows the monitoring of refractive index and colour without cross-sensitivity.

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.

A fine control of the mPOF Bragg grating spectrum properties, such as maximum reflected power and 3dB bandwidth, through acousto-optic modulation (AOM) using flexural regime is presented. A numerical comparison of the strain field along mPOFBG - AOM and the similar structure with SMFBG-AOM was presented, showing that the strain field amplitude is higher along the mPOFBG due to its smaller mechanical stiffness. The obtained results can be used in the development of fine-tuned optical filters using low voltage sources and low frequency regimes, to obtain tunable optical filters and to control the shape of the spectrum. Studies of the behavior in different gratings (such as phase shifted and long period gratings) for photonic applications, such as tunable notch filters or tunable cavities, are in progress. It can potentially be applied on tunable optical filters for POF transmission.

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.

Cardiovascular diseases are the leading cause of death in the world, arising their early prediction as a key aspect. The analysis of pulse wave propagation characteristics, such as velocity and morphology, can give important data about arterial stiffness, a parameter with growing significance in cardiovascular events prediction. In this paper it is presented a new optical fibre sensor to assess the pressure waveform in the carotid artery. The optical sensor is based on fibre Bragg grating technology, increasingly applied in several fields, including biomedical sensing due to its advantageous features. The Bragg sensor was characterized and tested in human carotids. It is presented a case study showing the great potential of Bragg technology in the assessment of the pressure waveform.

Sensors based on side-polished plastic optical fibre are presented. To enhance the sensitivity to a certain physical parameter, the guiding properties of an optical fibre have to be weakened. Side-polishing technique offers a simple implementation, since the mechanical resistance of the POF allows an easy removal of a portion of the jacket, cladding and core. Three sensors are characterized under a wide range of external refractive indexes. Both, theoretical and experimental results show that the range of operation of the refractive index sensor can be shifted by using different geometries or different macrobending conditions of the sensitive area. The phenomenon behind the principle of operation of the sensor is the reflection and transmission of light at an interface of two dielectric media expressed by Fresnel's equations. The use of this intrinsic scheme to monitor the cure process of a material or the viscosity of a liquid is also presented. The changes in refractive index are used to monitor, in real time, the cure of different materials such as resins and varnishes because the optical properties of the material can be related to the density of the material. The viscosity of a liquid is related to the droplet formation in a convexly bended sensor.

In this work we review the structural health monitoring techniques based on fiber Bragg gratings. The working principle of the fiber Bragg gratings sensors and the most common techniques to inscribe and interrogate these sensors are described. Several implemented examples are also presented, like the deformation monitoring of one historical building with reduced visual impact, the unidirectional acceleration measurements in a metallic bridge structure and the bidirectional acceleration monitoring in a 50 m mobile telecom tower. Finally, the implementation of an automated remote structural health monitoring system design to operate with optical sensors in a highway bridge is described.

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The characterization of fiber Bragg grating (FBG) sensors integrated on 2D and 3D mesh structures is presented. Several materials and configurations were tested, namely cork, foams, PVC, hexagonal 3D. Sensors were embedded between two substrates using textile lamination technique. Every sample was subjected to temperature variations and mechanical deformations. Through Bragg wavelength monitoring, thermal, deformation and pressure performance were evaluated. These results provide significant information to the conception of smart textiles.

A wearable low-cost system designed to evaluate quantitatively the human gait is presented in this report. The system is based on transmittance changes when a plastic optical fiber is bent. To enhance sensibility, a portion of the fiber was side-polished improving attenuation due to macro bending. By calibration, the intensity of light received by a photo detector was related to the flexion angle. The fiber was bonded to the location of a commercial knee-support where it is desired to measure the joint angles. The prototype was calibrated with a video-based system and a gait cycle was obtained. The preliminary results show that the technique can be an important tool to aid physicians in diagnosis and rehabilitation of knee injuries or to monitor the performance of high competition athletes.

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.

A wearable and wireless system designed to evaluate quantitatively the human gait is presented. It allows knee sagittal motion monitoring over long distances and periods with a portable and low-cost package. It is based on the measurement of transmittance changes when a side-polished plastic optical fibre is bent. Four voluntary healthy subjects, on five different days, were tested in order to assess inter-day and inter-subject reliability. Results have shown that this technique is reliable, allows a one-time calibration and is suitable in the diagnosis and rehabilitation of knee injuries or for monitoring the performance of competitive athletes. Environmental testing was accomplished in order to study the influence of different temperatures and humidity conditions.

A novel cure monitoring system based on a side-polished interface on a plastic optical fibre is presented. Due to the mismatch of the refractive index of the fibre core and the external medium, part of the light beam is transmitted along the optical fibre by internal reflection and part is refracted in the sensitive zone. The phenomenon behind the principle of operation of the sensor is the reflection and transmission of light at an interface of two dielectric media traduced by Fresnel's equations. A good agreement between numerical and experimental results was achieved and real-time monitoring of the cure process was accomplished for a polyurethane resin and two different varnishes.