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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 theoretically demonstrate a long-period grating (LPG) based single-mode fiber to multi-core fiber coupler. The coupling efficiency achieved was 24% of the input power, evenly distributed by all cores, using LPGs of length 4 cm.

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.

In this paper, we report, to our knowledge, the first extended study of the inscription of Bragg gratings in surface-core fibers and their application in refractive index and directional curvature sensing. The research ranges from fiber fabrication and grating inscription in untapered and tapered fibers to the performance of simulations and sensing measurements. Maximum sensitivities of 40 nm/RIU and 202.7 pm/m−1 were attained in refractive index and curvature measurements respectively. The obtained results compares well to other fiber Bragg grating based devices. Ease of fabrication, robustness and versatility makes surface-core fibers an interesting platform when exploring fiber sensing devices.

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.

In this letter, the light transfer promoted by long-period gratings (LPGs) inscribed in heterogeneous multicore fibers (HeMCFs) is theoretically analyzed. We determined the power evolution along the LPG in two different four-core HeMCFs. This letter demonstrates the selective switch of optical power between the identical cores of the HeMCFs with less than −40 dB of crosstalk to the other cores, regardless the position of the identical cores. The results show that the proposed technique can be used to produce inline selective core switching for multicore space division multiplexing.

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.

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.

Results of the preparation and characterization of graphene oxide–optical fiber coatings will be presented, considering its potential use for sensing applications. The coatings were deposited using the electrostatic self–assembly method, considering different parameters (average sheet size of the graphene oxide colloidal solutions, the number of the deposited layers and the coating methodology) and characterized through SEM and Raman analyses. Aiming to explore this scheme for sensing applications, graphene oxide-coated tilted fiber Bragg gratings were characterized to refractive index variations. An improvement on the sensitivity was obtained and this result suggests that this could be a promising research field for the development of a new line of sensors.

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 characterization of different diamond coatings onto optical fibres is presented. The experimental conditions of each deposition were determined by the Taguchi method, considering five different parameters at four levels. With these experiences it was intended to find the suitable diamond deposition conditions for the optical fibres coating. The application of the Taguchi method demonstrated to be a fundamental tool in the targeting of the appropriate conditions to coating the fibre.

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.

Laser sources with light-emission in the yellow spectral range around 577nm are very favorable for a variety of applications. These include applications in astronomy, in ophthalmology or in quantum optics. The generation and amplification of 1154 nm light is not straight forward when using Yb-doped optical fibers, since lasing occurs preferentially around the gain-maximum of 1030 nm. We generate the radiation within a fiber Bragg grating (FBG) based cavity and focused on reducing the amplified spontaneous emission (ASE). After the cavity, the output is frequency doubled to 577nm by using a second harmonic crystal.

This work presents a technique based on the application of a high birefringent (Hi-Bi) fiber Bragg grating (FBG) to monitor the optical signal to noise ratio (OSNR) of an optical channel.A Hi-Bi FBG produces reflection at two different spectral bands depending on the polarization of the incoming signal. The OSNR can be determined by decomposing, for a data channel, the polarized signal information and the depolarized noise. This work gathers the simulation and experimental results for a single channel system continuous wave signal and modulated at 10 Gb s−1. The results for a multichannel system are also presented. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:6–9, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27228

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.

The impact of five different water/powder (w/p) ratios in the characterization of high strength dental stone was evaluated, since the recommendations of the gypsum' manufacturers are not always correctly followed by the dental prosthesis technicians. Fiber Bragg grating (FBG) sensors were used to measure the setting expansion and temperature variation which occurred during the setting reaction for each w/p ratio, as well as the thermal expansion coefficient. Thick mixtures with low w/p ratios had more crystals impinging upon each other during crystal growth, resulting in more expansion and more heat released. This thermal behavior was only achieved to w/p ratios within the manufacturer-recommended mixing ratio range. The results also revealed the existence of boundary condition; this corresponding to the limit of the mixing ratio recommended by the gypsum' manufacturer. Data provided in this study are particularly important for dental technicians with a view to attaining the best results in accuracy of fit for their prosthetic works.

In this paper, we propose a novel photonic true-time delay beamforming system for phased array antennas. The system relies on tunable delay lines which are based on Mach-Zehnder delay interferometers (MZDIs) with tunable coupling ratio. As the MZDIs are implemented on the polarization domain, a single optical source and a single piece of polarization maintaining fiber are required. The proposed implementation is theoretically assessed and beam squinting is investigated by simulation. A proof-of-concept experiment that validates the operation principle of the proposed delay lines is presented.

This paper presents an experimental methodology to determine plated and intact femur strains using fiber Bragg gratings and strain gauges. A plated and an intact synthetic femur were used and loaded under a simplistic static load of 600 N. A stainless steel (316L) plate was used to fixate a simulated 45° fracture on one femur. Strains were recoded at the same sites on both femurs. Strain shielding is shown to be more pronounced at the distal region of the plated femur. The experimental methodology based on fiber Bragg grating sensors is a novel approach to assess bone plate strains, which could also be used to obtain biologic tissue and implant surface strains in locations where conventional strain gauge use is not technically feasible.

In this work, the simultaneous regeneration of seed fibre Bragg gratings (FBGs) during the diamond-grating coating and the thermal monitoring of that process is presented. The diamond was deposited through the hot filament chemical vapour deposition (HFCVD) process, and due to the high temperatures characteristics of this method (above 800 oC), regenerated FBGs are suitable samples to be coated. The advantages of this study are the possibility to regenerate the seed gratings during the coating process, becoming the fibre more resistant and the procedure less time consuming, and to control the temperature, a critical parameter for the morphology of the deposited layers.

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.

In this work we perform a study about the temperature implications on the optical fibers chromatic dispersion and the implications on the quality of transported information. To solve this constrain we suggest two approaches to dynamically compensate chromatic dispersion, one based on chirped fiber Bragg gratings and other based on dispersion compensation fibers. With the dispersion compensation fibers, we obtain a first and second order tuning coefficients of 3.472 ps nm-1 oC-1 and -2.7 × 10 -3 ps nm-2 oC-1, respectively. With the compensator based on chirped fiber Bragg gratings we obtain dispersion values between -113.2 ps nm-1 and 143.1 ps nm-1, for temperature gradients of 40oC.

Fibre optic Bragg gratings (FBGs) written in normal and reduced diameter high birefringence (HiBi) fibres are studied. Chemical etching is used to reduce the diameter of fibres while the optical properties of the FBG spectrum are measured. The results obtained agree qualitatively with the stress enhanced chemical etching. The birefringence of the fibre is determined as a function of the diameter. Optical characterization of the FBG under transverse strain and temperature is also performed. The results obtained show the feasibility of the simultaneous measurement of those parameters with a HiBi FBG sensor.

A technique for low cost and high precision characterization of fiber Bragg gratings based structures, using transversal pressure, is presented. It is based on the analysis of the amplitude and wavelength changes of the structure reflection spectrum, while being precisely pressed by an electromechanically actuated arm. The theory and the experimental results, which are in good agreement with the expected ones, are also presented.

We used a pair of Bragg gratings written in high birefringence fibre optics to measure, simultaneously, longitudinal and transverse strain and temperature. The Bragg gratings are superimposed in the same position of the fibre optic, so as to behave as a punctual sensor. The sensitivity of the spectral response of the device to longitudinal strain, transverse strain and temperature are all characterized, and the results of its application as a three-parameter sensor are also presented.

In recent years, the coating of fiber Bragg gratings (FBGs) with a specific material has opened up the possibility to broaden the limits of applicability of this technology. Diamond has a set of properties that makes it an attractive candidate to protect the optical fiber against chemically harsh environments, whose sensing is also a great challenge. One of the most used techniques to obtain these coatings is through the hot filament chemical vapor deposition (HFCVD); in this process, the temperature reaches, typically, around 850°C-900°C. In this work, the regeneration of a seed FBG during its coating with a nanocrystalline diamond thin film through the HFCVD process is presented. Simultaneously, the thermal monitoring of the process was also performed using the same grating. The resistance test in a corrosive medium reveals an improvement on the durability of the sensing properties of the diamond-coated FBG compared with an uncoated FBG, foreseeing a vast range of applications.

In this work, the regeneration of saturated fiber Bragg gratings during the diamond coating of the fiber is presented. Due to the high temperatures characteristic of the hot filament chemical vapor deposition (HFCVD) process (around 800 oC), uniform fiber Bragg gratings (FBGs) are not appropriate to be coated. Nevertheless, regenerated Bragg gratings are a suitable solution for this drawback. Its production process involves the inscription of a saturated FBG followed by a time consuming heat treatment. Here it is proposed to take advantage of the high temperatures characteristic of the HFCVD process to simultaneous regenerate the grating and coat the fiber with diamond.

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.

We present a demodulation technique to synthesise the physical parameters of an optical fibre Bragg grating (FBG) resonant cavity. The demodulation is achieved through a genetic algorithm (GA). The estimated parameters allow us to simulate the cavity amplitude response, arriving at an accurate response when compared to the experimental results. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1415–1417, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21644

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.

In this work, Bragg gratings were used to monitor, in real time, the temperature during the diamond deposition process obtained by hot filament chemical vapor deposition (HFCVD). Due to the instability of uniform fiber Bragg gratings (FBGs) to high temperatures, regenerated fiber Bragg gratings (RFBGs) were utilized. The results reveal that the diamond deposition process occurs at about 832 oC (in the experimental conditions used in this case). The work also suggests that RFBGs are suitable devices to monitor processes which, as in the diamond deposition, the temperature is a critical parameter, and where other traditional methods have a little feasibility due to the own experimental setup or samples type under study.

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with experimental data. Recent applications such as the writing of gratings under the acoustic excitation and a novel viscometer sensor based on the acousto-optic mechanism are discussed. © 2013 The Author(s).

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.

In this paper, the coating of optical Bragg gratings with nanocrystalline diamond, obtained by hot filament chemical vapor deposition (HFCVD), is described. Due to the high temperature coating process, uniform fiber Bragg gratings (FBG) were erased during the diamond deposition. However, in the case of regenerated fiber Bragg gratings (RFBG), although attenuated, the optical signal is maintained. The results of the thermal and mechanical characterization of diamond coated RFBG (D-RFBG) suggest that they may be an important tool in the sensing field, including monitoring of high temperatures under harsh environments. Keywords: Optical fiber, uniform fiber Bragg grating (FBG), regenerated fiber Bragg grating (RFBG), nanodiamond, hot filament chemical vapor deposition (HFCVD), sensing. 1. INTRODUCTION Optical fiber sensors have increasingly been applied in distinct areas, including monitoring of civil engineering structures, environmental and biomedical media, due to unique characteristics that distinguish this technology. The growth in the use of optical sensors has led researchers to improve the mechanical resistance, sensitivity and operating range of the sensors, and to develop new devices capable of solving the current requirements. Coating the fiber with a specific material, depending of the desired application, may be an appropriate procedure to attain these goals [1]. Diamond is a material characterized by its high hardness and wear resistance, the lowest coefficient of thermal expansion and the highest thermal conductivity, and high resistant to corrosion. Moreover, it has an excellent response in terms of biocompatibility and non-toxicity. Additionally , the excellent adhesion of diamond to biological material allows its use, for instance, in DNA sensors. From the above characteristics, diamond can be an excellent material for the development of new coated optical fiber sensors. The use of diamond coated fiber as sensor was, firstly, described by Smietana et al. [2, 3]. In the former study diamond like carbon films were used as substitute of the cladding, and the resulting configuration was explored as humidity sensor. In the following work, the same material was deposited in long period grating and it was obtained a resolution in refractive index 15 times higher than that obtained without the coating. The most recent work involving optical fiber and diamond coatings was proposed by Afshar et al. [4]. They presented a theoretical model of the power radiated by a nanodiamond crystal located at the surface of a fiber. From the results, these researchers claim to be facing a new architect ure for high sensitivity refractive index sensing. The research team of this paper developed pioneering work in this field, having described the coating of uniform fiber Bragg gratings (FBG) with nanocrystalline and microcrystalline diamond films obtained by hot filament chemical vapor deposition (HFCVD) [5]. As in [6], it was verified that microc rystalline films are more likely to break, but the same does not happen when nanocrystalline films are gr own. In the same study, they found that as a result of high temperatures of deposition process, the FBG degraded and erased. In this work, a thermal and mechanical characterization of nanodiamond coated regenerated fiber Bragg gratings (D-RFBG) is presented. These optical fiber sensors have a higher thermal resistance to the FBG, not erasing during the deposition process. The results are compared with the values obtained for uniform and regenerated un coated FBGs. Additionally, the surface morphology, grain size and the Raman quality of the diamond coatings are also assessed.

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.