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To ensure the safety and durability of structures, the constant monitoring of their structural health has been used by engineers to manage these structures. Optical fiber sensors have the advantage of long transducer-to-processing distances, the capacity to work in harsh environments, immunity to electromagnetic noise, and reliability. Therefore, optical fiber sensors are great candidates to monitor structures in-service. Here, we propose the use of a long-period fiber grating (LPG) array to monitor the loading condition of a structure. The identification method was tested in a simply-supported beam model and the estimated loading conditions were compared to the loading conditions applied to the beam. By analyzing different combinations of force intensity and position along the beam length, the results showed the force position could be estimated with 0.901% accuracy and force intensity with 2.51% accuracy using a four-LPG strain sensor array.

A refractometer based on an etched fiber Bragg gratings (EFBGs) sensor has been developed for monitoring beer fermentation in real time. The sensor was calibrated using synthetic solutions composed of water, maltose, and ethanol with alcohol by volume (ABV) ranging from 4.0% to 12.0% and Brix (sugar content) varying from 5% to 25%. Calibration results showed that the EFBG sensor responds with high sensitivity even to minor density variations less than 0.5 Brix ± 0.03 Brix in a quasi-linear monotonic fashion with respect to sugar and ethanol concentration, which allowed fitting an empirical model with good adherence to experimental data (low model variance) and with well-defined parameters (parameters covariance matrix with elements exhibiting small absolute values). Finally, the developed sensor was tested in a typical fermentation scenario. A rigorous material balance framework was established to relate the fit calibration model to actual density and alcohol content in real time, which is of assistance for process control strategies. As the proposed sensor can be fit in fermentation vessels for real-time (online) fermentation monitoring, it becomes a technological improvement to traditional offline measurements in terms of both biosafety and process control.

This work introduces a new method for long-period fiber grating (LPG) sensors interrogation. This proposal uses a fiber Bragg grating (FBG) array to extract spectral information of the LPG sensor and an Artificial Neural Network to process this information. The information is processed to estimate the LPG resonant wavelength, without prior knowledge on the LPG spectrum. Therefore, the interrogator is LPG-insensitive, can be easily manufactured by optical fiber sensors laboratories at low-cost and is suitable for in-field applications. We demonstrated the filter array and Multilayer Perceptron (MLP) design, which are the proposed interrogator core. Furthermore, we analyzed the interrogation performance by the Mean Squared Error (MSE), the Mean Absolute Error (MAE), and the distribution of the residuals. The results showed our proposal can estimate the LPG resonant wavelength with 2.82 nm uncertainty, considering a 95% confidence interval, over 75 nm dynamic range for several LPGs, with different spectral characteristics. Moreover, our proposal can be easily tailored for different dynamic ranges and resolutions with proper adjustments on the FBG array and MLP.

This article discusses modern techniques of implementation of a wideband digital modulator in an FPGA kit for use in electrical engineering communications laboratory. Previous configurations proposed in literature present limitations, as lack of details about the methods used in the algorithm developed and test procedures. Those key details can help researchers to develop this modulator more effectively. From technical point of view, previous works were also implemented for small bandwidth output signals. The proposed digital modulator has low cost and can generate signals based on several modulation schemes with various output roll-off filters. This proposed kit allows researchers to change digital signal characteristics through dip-switches, customizing the modulated signal. Advanced techniques such as parallelism of processes and fast access to look up tables using an FPGA were used to achieve the desired objective, and are detailed in the article. Besides this implementation, this article also shows test procedures to validate the performance of digital modulators using lab test equipment. Those procedures were used to validate the FPGA modulator developed. The paper shows how researchers can analyze the performance of digitally modulated output signals using an Oscilloscope, a Spectrum Analyzer, and a Vector Signal Analyzer. Features such as symbol rate, modulation constellation, roll-off output filter, and EVM are covered.

This paper presents a mathematical model for the interrogation of long period grating (LPG) fiber optical sensor. The mathematical model is simple and robust, and it is based on an electrical harmonic analysis. The model calculates the harmonic amplitude equations in the electrical domain of a wavelength modulated optical signal as a function of all the spectral parameters of the LPG. In addition, this model takes into account any distortions that might have been introduced by the wavelength modulator and by any other source of distortion. The harmonic amplitude equations are obtained by expanding the demodulated signal in Taylor Series and by taking the Gaussian shape of the LPG absorption spectra into consideration. To validate the model, we implemented a simple interrogation setup to compare the measured electrical harmonic amplitudes with those obtained using the calculated harmonic amplitude equations. A dynamic range of 25 nm was achieved by shifting the resonant wavelength of the LPG with an accuracy better than 1 dB.

Made available in DSpace on 2020-12-11T14:56:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-04-15 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In this paper a new method for the detection of optical phase in passive homodyne interferometers, with high accuracy and wide dynamic range is presented. Unlike the traditional and more recent methods, which use between 3 and 6 harmonic components to calculate the modulation index, the proposed method uses only 2 harmonic components. Because of this, the method has higher accuracy in the presence of noise compared to other methods known in the literature. Further, the method has the advantage of not requiring knowledge of the phase of the excitation signal. The numerical implementation is simple, since it uses a 3rd order polynomial fit for the calculation of the modulation index. For the experimental verification of the method, a configuration based on an unbalanced Mach-Zehnder interferometer (MZI) was used, which resulted in a dynamic range for the modulation index from 8.38 to 16.76 rad. It is important to note that these limits can be easily expanded by means of adaptations of the optical and electronic setup depending on the characteristics of the excitation signal. The proposed method can be used in several applications, such as pressure measurements, vibration, displacement, etc. Fed Fluminense Univ UFF, Telecommun Engn Dept, Postgrad Program Instrumentat & Appl Opt PPGIO, BR-24220900 Niteroi, RJ, Brazil Univ Salgado de Oliveira, Engn Dept, BR-24030060 Niteroi, RJ, Brazil Sao Paulo State Univ, Elect Engn Dept, BR-01001900 Sao Paulo, Brazil Fed Inst Educ Sci & Technol Mato Grosso do Sul, Elect Engn Dept, BR-79641162 Tres Lagoas, Brazil Univ Fed Juiz de Fora, Elect Circuit Dept, BR-36036900 Juiz De Fora, Brazil Sao Paulo State Univ, Elect Engn Dept, BR-01001900 Sao Paulo, Brazil CNPq: 305307/2015-0 CNPq: 420673/2016-4

Information about future streamflow is important for hydropower production planning, especially for damless hydro-power plants. The river flow is a reflection of various hydrological, hydrogeological, and meteorological factors, which increases the direct modeling difficulty, and favors the use of data-driven methods. In this paper, we propose the use of one-dimensional convolutional neural networks (1d-CNN) for multi-day ahead river flow forecasting and we present a multi-input model using correlated-input time-series. The proposed model was applied at the Madeira River, the Amazon's largest and most important tributary, near the Santo Antônio damless hydro-power plant. We compared the proposed correlated-input 1d-CNN to a single-input 1d-CNN model and some baseline models. Furthermore, we conclude that 1d-CNN performed better than all baseline models and that the correlated-input forecasting model is 5 times smaller than the single-input equivalent with accuracy improvements.

Salinity is a key variable in understanding several issues, from public health to food security. Measuring salinity in situ is traditionally done using conductivimetric methods, and can be challenging due to extreme temperatures, corrosive environment, and oxidation. Fiber-based methods and other alternatives proposed to date have brought a number of advantages, but present low sensor strength, complex or expensive setups, cross-influence of temperature, lack of portability, or prohibitively long response times. This work presents a simple, compact salinity sensing system that, associated with a modern interrogation technique, is capable of achieving good accuracy even in remote sensing and low salt concentrations. The sensor is a long-period grating fabricated using the point-by-point electric arc method. The interrogator is based on optical time-domain reflectometry aided by signal processing techniques inspired by audio processing. Experimental data show that the system is capable of estimating salinity in the range from 0 g/L to 80 g/L within 0.49 g/L on average, with the sensor 4 km away from the light source.

The application of signal processing and feature extraction to reflectometry traces aiming at sensor interrogation is not sufficiently explored. In this work, traces produced by an optical time-domain reflectometer in experiments using a long-period grating in different external media are analyzed using signal processing techniques inspired by audio processing. The objective is to demonstrate that, using this type of analysis, it is possible to correctly identify the external medium through the characteristics of the reflectometry trace. Results show that the features extracted from the traces were able to produce good classifiers, one of them achieving 100% correct classification for the data set presently considered. This technology could be applied in scenarios where it is necessary to distinguish among a given set of gases or liquids nondestructively.

We propose a strain sensor based on a long-period fiber grating (LPFG) packaged in a 3D-printed structure made of polymer material. The proposed sensing structure was fabricated using a commercially available 3D printer by embedding a bare LPFG sensor inside the polymer material during the printing process. The raw material used for the fabrication of the polymer structure was Polylactic Acid (PLA). We experimentally investigated the strain-dependent spectral response of the produced sensor by observing the transmitted spectral profile. Finally, the results showed that a linear strain sensitivity of − 4.6 pm/μe with the range of 0–1000 μe was achieved, therefore indicating that the proposed sensing device is suitable for strain deformation measurement.

This article presents the development of an inclinometer device based on a Mach-Zehnder interferometer considering the effects caused by temperature variations. It was demonstrated the operation of a LPG-taper system for angle measurements. The practical results satisfactorily show reliable inclination measures, even with the cross sensibility effect caused by variable temperature.

This research employs displacement fields photogrammetrically captured on the surface of a solid or structure to estimate real-time stress distributions it undergoes during a given loading period. The displacement fields are determined based on a series of images taken from the solid surface while it experiences deformation. Image displacements are used to estimate the deformations in the plane of the beam surface, and Poisson’s Method is subsequently applied to reconstruct these surfaces, at a given time, by extracting triangular meshes from the corresponding points clouds. With the aid of the measured displacement fields, the Boundary Element Method (BEM) is considered to evaluate stress values throughout the solid. Herein, the unknown boundary forces must be additionally calculated. As the photogrammetrically reconstructed deformed surfaces may be defined by several million points, the boundary displacement values of boundary-element models having a convenient number of nodes are determined based on an optimized displacement surface that best fits the real measured data. The results showed the effectiveness and potential application of the proposed methodology in several tasks to determine real-time stress distributions in structures.

The capabilities of signal processing tools to extract high-level features of interest from fiber sensors measurements have not been properly explored for interrogation purposes. In this context, this paper advances an interrogation system for long-period grating sensors by means of a novel low-cost method that combines an optical time-domain reflectometer with suitable descriptors to classify the sample weight under test. The operation principle is based on the attenuation bands induced by cladding modes of a long-period grating, which are affected by the applied mechanical strain. The proposed interrogation system does not require an optical spectrum analyzer, since the measured reflectometry traces directly feed a feature extractor tailored for the intended classification. Experimental results show, for example, that this method is capable of successfully differentiating a load whose mass is 7.2 g from another one whose mass is 14.1 g, with the interrogation equipment located 10 km from the loads. This implies a high sensitivity that is quite unexpected to attain with the commercially available off-the-shelf devices required by the proposed scheme.

Etched fiber Bragg gratings (EFBGs) have been widely employed for refractive index (RI) measurements that can be used to monitor sugar consumption during the fermentation of alcoholic beverages. EFBGs are obtained by removing the cladding of a fiber Bragg grating, which is traditionally performed by a chemical attack with hydrogen fluoride, an extremely hazardous corrosive substance that causes severe wounds and even death. To overcome such drawbacks, this technical note presents a simple, practical, and low cost method for the diameter reduction of single mode optical fibers by mechanical polishing, employing a small scale computer numerical control device and an ad hoc 3D-printed rod. The sensor probe obtained was tested using sucrose aqueous solutions with RIs between 1.333 and 1.394, measured in an Abbe refractometer. The results show a linear shift of the Bragg wavelength with respect to RI with a correlation of 0.928.

Surveillance missions in vast, difficult access environments are responsible for logistic difficulties in comparison to using an in loco monitoring team. For this and many other reasons, solutions with robotic platforms such as unmanned aerial vehicles (UAVs), present economic advantages.

In this paper we demonstrate the development of an adjustable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators that squeezes a defined pieces of an Hi-Bi fiber. Using this device, the first and second order PMD (SOPMD) can be reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators and for the study of several polarizations phenomena that can represent impairments to the high data transmission networks. This emulator was used to perform an analysis of the correlation between the PMD and SOPMD under different climate chamber temperature.

In this paper, we explicitly show a complete analysis and detailed calculation of propagation characteristics of the effective refractive indices of the core and cladding for a long period grating employing both the Two-Layer and Three-Layer Geometries. The results are achieved employing graphical solution methods and presented in terms of the effective refractive indices of the core and cladding. Then, we compare the results with OptiGrating (Optiwave Systems Inc., Ottawa, Canada). Finally, we point the best model to evaluate the effective refractive indices, avoiding incorrect designs of the long period gratings.

This paper presents a historical review of the many behavioral models actually used to model radio frequency power amplifiers and a new classification of these behavioral models. It also discusses the evolution of these models, from a single polynomial to multirate Volterra models, presenting equations and estimation methods. New trends in RF power amplifier behavioral modeling are suggested.

Optical fiber sensors have become a popular alternative to traditional electronic sensors due to their numerous advantages. An important challenge in deploying optical sensors is the interrogation of the sensor, that is, recovering the measured value from the sensor output. This paper aims to present a simple yet effective way of interrogating a fiber Bragg grating (FBG) temperature sensor using optical filters and an artificial neural network (ANN). This interrogation system is capable of giving the precise temperature value without directly measuring the resonance wavelength shift or performing any Fourier calculations. The network was implemented and the training was accomplished using simulated data. Simulated results are presented and compared to traditional methods of interrogation. The system proposed in this paper showed excellent performance in identifying the temperature from the sensor output and showed more precision than the traditional method.

This article discusses the implementation of a wide band vectorial digital modulator and a tool to evaluate the Bit Error Rate. This modulator is capable of generate a wide band (up to 6.3 MHz) 16-QAM modulation in baseband. A second functionality programmed in the tool and reported in this article evaluates the Bit Error rate in order to measure the received signal quality. Results are validated using a Signal Analyzer.

This article presents a new approach to the combined analysis of the first and second-order polarization mode dispersion (SOPMD) and shows their importance in optical communication systems performance. How it affects the relation between second-order polarization mode dispersion (PMD) and the differential group delay (DGD) in a single mode fiber is discussed. The analysis is based on time or wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long term statistical characteristics of second-order PMD over a PMD emulator, and investigate the correlation between SOPMD, depolarization (DEP) and polarization dependent chromatic dispersion (PCD). Some authors calculate these modes from measurements obtained from the first order polarization mode dispersion, assuming a positive correlation between these effects, but this not the real relationship between them. A new interpretation of SOPMD was used to analyze the problem of the spectral stability in terms of the temperature. Actual techniques for determination SOPMD, consequently DEP and PCD, use the variation in time and/or wavelength. In some studies the results obtained for SOPMD are correlated to first-order PMD (FOPMD). This paper shows, based on measurements, that the correlation between first and second order Polarization Mode Dispersion (PMD) in the case where the last one is a function of the temperature can assume positive or negative values.

This article analyzes the polarization mode dispersion (PMD) in optical fibers and presents a new approach for its measurement. This approach permits the combined analysis of the first-order PMD and the second-order polarization mode dispersion (SOPMD) in optical systems for different values of temperature. The relation between SOPMD and the differential group delay (DGD) in a single-mode fiber is discussed. The analysis is based on time/wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long-term statistical characteristics of SOPMD acquired by a PMD emulator constructed with some pieces of high birefringence fiber, and the correlation between the SOPMD, depolarization (Depol) and polarization-dependent chromatic dispersion (PCD) was investigated. A new interpretation of SOPMD is presented to analyze the problem of the temperature spectral stability. The actual techniques for SOPMD determination, consequently Depol and PCD, use the variation with time and/or ...

In this paper, we propose and experimentally investigate an optical sensor based on a novel combination of a long-period fiber grating (LPFG) with a permanent magnet to measure electrical current in unmanned aerial vehicles (UAVs). The proposed device uses a neodymium magnet attached to the grating structure, which suffers from an electromagnetic force produced when the current flows in the wire of the UAV engine. Therefore, it causes deformation on the sensor and thus, different shifts occur in the resonant bands of the transmission spectrum of the LPFG. Finally, the results show that it is possible to monitor electrical current throughout the entire operating range of the UAV engine from 0 A to 10 A in an effective and practical way with good linearity, reliability and response time, which are desirable characteristics in electrical current sensing.

Unmanned Aerial Vehicles (UAVs) have become a prominent research field due to their vast applicability and reduced size. An appealing aspect of the UAVs is the ability to accomplish autonomous flights in several contexts and purposes, and a variety of applications have been developed, from military to civilian fields. The system proposed in this work is a novel and simplified interaction between the user and the UAV for autonomous flight, where the necessary computation is performed in an embedded computer, decreasing response time and eliminating the necessity of long-distance communication links with base stations. Results are presented with both hardware in the loop simulations and a real UAV using Pixhawk, and Odroid and ROS as companion computer and software platform for code development.

We report a production technique of reducing the polarization-dependent loss (PDL) always present in arc-induced long-period fiber gratings (LPFGs). The proposed fabrication method is based upon the rotation of the optical fiber by an axial angle of 180 deg at each electric arc discharge, therefore, inducing opposite point-by-point asymmetric modulations over the entire length of the LPFG. PDL measurements of different arc-induced LPFGs fabricated by both the conventional and proposed method are presented. Finally, the obtained results show a significant decrease of the intrinsic PDL of arc-induced LPFGs with the proposed fabrication technique.

This article presents a generator of digital modulations in FPGA for the teaching and the practice in Telecommunication laboratory. With the increasing demand for technological tools to be used in practical classes, this generator is an alternative to the use of commercial measurement equipments, it presents great flexibility, but at a high cost; and also, to the use of specific laboratory kits, which have a lower cost but have little flexibility. The design, its implementation and tests are showed in this work. Finally, the results are compared to a commercial kit, showing the viability of using this project for laboratory practice.

This article discusses further about the number of coefficients used in the many implementations of Volterra series models, performing a fair comparison between them, using measured data and known figures of merit found in the literature. Among the models implemented, a model that uses sub-sampling techniques allied to Volterra series in a parallel cascade structure aiming accuracy outperforms other variations of Volterra series models, with the drawback of using a higher number of coefficients. Based on the many figures of merit results, this article suggests new trends to be used in RF power amplifier behavioral models.

This article discusses several different implementations of Volterra seriesmodels, and performs a fair comparison between them using measured data and well known figures of merit. Among the implemented models, an approach that uses sub-sampling techniques together with Volterra series in a parallel cascade structure shows an improved performance compared to the other variations of Volterra seriesmodels.Based on the results, new trends in RF power amplifier behavioral modeling are suggested.

As distorções do sinal induzidas pela Dispersão dos Modos de Polarização (PMD) e pelas Perdas Dependentes da Polarização (PDL) em transmissões ópticas são discutidas no ponto de vista do comportamento estatístico das taxas de erro. Os efeitos isolados da PMD de primeira ordem e da PDL, juntamente com seus efeitos combinados em transmissões digitais foram avaliados através das medidas de penalidade de potência. É mostrado que em efeitos combinados, a PDL aumenta substancialmente as flutuações na BER, podendo este aumento ser maior que nos casos isolados de PMD e PDL. Os resultados obtidos indicam que o chirp da fonte tem um papel importante nos efeitos combinados. Signal distortion induced by Polarization Mode Dispersion and Polarization Dependent Losses in long-distance high-capacity optical transmissions is discussed from the viewpoint of the statistical behavior of the bit error rates. Pure first order PMD effects, pure PDL effects and combined PMD/PDL effects in digital transmissions were evaluated through power penalties measurements. It is show that PDL strongly enhances PMD effects and that the BER fluctuations may be much higher than those induced by pure PMD or pure PDL. The results obtained indicate that the chirp of the source plays an important role in the combined PMD-PDL effects. En este trabajo se discute, desde el punto de vista de comportamiento estadístico del error, las distorsiones de señales inducidas por la Dispersión de los Modos de Polarización (PMD) y por las Pérdidas Dependientes de la Polarización (PDL) en transmisiones ópticas. Los efectos alejados de la PMD de primer orden y de la PDL, conjuntamente con sus efectos combinados en transmisiones digitales fueron evaluados a través de las medidas de penalidad de potencia. Se muestra que en efectos combinados, la PDL aumenta substancialmente las flutuaciones en la BER, pudiendo este aumento ser mayor que en los casos isolados de PMD y PDL. Los resultados obtenidos indican que el chirp de la fuente tiene un papel importante en los efectos combinados.

A systematic experimental evaluation of polarization mode dispersion (PMD–) –induced polarization-dependent gain (PDG) in forward pumped Raman amplification in dispersion-shifted and in dispersion-compensating fiber was performed. Good agreement was obtained between the measured statistical parameters and the current analytical model for PDG fluctuation statistics. The probability distribution of the PDG was approximately Maxwellian within the range PMD >0.05 ps/km1/2. The interplay between PMD and gain fluctuations is discussed; random birefringence strongly reduces PDG fluctuations. However, the trade-off between reduction of the power penalties for PDG and increase of the penalties for PMD distortion precludes the use of PMD instead of source depolarization techniques for reduction of PDG.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO Diante do crescimento do interesse pelos amplificadores Raman faz-se necessário um estudo mais detalhado destes. Uma técnica tradicionalmente já utilizada para analise de atenuação em enlaces, a reflectometria óptica no domínio do tempo, é empregada de maneira inovadora neste trabalho para a observação da amplificação Raman distribuída. O objetivo principal deste trabalho não é a analise de amplificadores Raman, mas sim a apresentação desta técnica como nova ferramenta observação do ganho Raman distribuído em fibras ópticas. Due to increased interest in Raman amplifiers, a more detailed study of them is required. A technique traditionally used for analysis of attenuation on optical links, time domain optical reflectometry, is used in an innovative way in this work for observation of distributed Raman amplification. The main objective of this work in not the analysis of Raman amplifiers, but the introduction of this technique as a new tool for the observation of distributed Raman gain in optical fibers.