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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.

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.

In this work, we report the comparison of regression methods in a long-period grating (LPG) for transverse strain measurement. We analyze the transverse strain sensing characteristics, such as load intensity and azimuthal angle, based on the birefringence effect induced in LPG sensor. Therefore, we employ the different orthogonal responses of the grating to develop regression methods, which allow the estimation of the strain behavior of the LPG sensor. The predictive performances of these interrogation models are compared in terms of square correlation coefficient (R2) and root mean square error (RMSE). Finally, the results indicate that the best method to predict load intensity is the Fourth-Degree Polynomial Fit, whereas the artificial neural network (ANN) model could be successfully employed to predict the azimuthal angle.

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.

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.

This paper presents a modification for the already consolidated analytical model that calculates the gain and ripple in multi-pump Raman amplifiers by considering energy conservation. The original analytical model precisely computes the pump-pump interaction to the C- and L-band for a WDM input signal. However, when this method is used to amplify a large bandwidth, as the entire C and a part of the L band, the increase in the number of pump lasers impacts the obtained results. The error, if compared with results obtained by a numerical method, becomes significant. An analysis in terms of energy is proposed to minimize the discrepancy between analytical and numerical results. An improvement is observed to the gain results.

In this work, we propose and experimentally validate a novel optical fiber-based sensor for monitoring and assessing electric current in unmanned aerial vehicles electric motors. The proposed sensing technology combines a Long-Period Fiber Grating sensor and a permanent Neodymium magnet, providing a small and flexible sensing scheme deployed inside the arm of the drone. The experimental results show that good accuracy and linear electric current sensitivity of 0.21 A and 2.08 A/nm, respectively, were achieved with electric current measurements at a 100 Hz sampling rate. The values of hysteresis and repeatability achieved were 0.08 A and 0.22 A, respectively. Finally, a Robot Operating System package for interfacing with the sensing system was developed and tested, which greatly simplifies the deployment of the sensor in robotics applications.

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 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.

The differential group delay (DGD) behavior of single-mode optical fibers was analyzed with regards to temperature variation. It was observed that the DGD curve shape along the wavelength axis could change if the fiber was submitted to high-temperature values. The study was carried out under laboratory conditions. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2070–2074, 2012; View this article online at wileyonlinelibrary.com.). DOI 10.1002/mop.27038

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.

Optical fiber sensors based on long period grating (LPG) are effective devices in sensing simultaneously temperature and mechanical strain. It was shown that different shifts in the resonant bands for the transmitted spectrum of an LPG sensor can be correlated with variation in temperature or mechanical strain. This paper presents the effects of non-linearity and cross-sensibility in the LPG resonance condition arising from combined effects of temperature and mechanical strain, proposing an adjustment coefficient in order to compensate these effects in a simple and effective way, reducing uncertainties in simultaneous measurements of temperature and mechanical strain.

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.

Polarisation-mode dispersion (PMD) in optical fibres causes a time-varying power penalty for the receiver. This variation has the same time-scale as low bit error rate (BER) measurements. Hereby, power penalty statistics can be difficult to determine with traditional BER measurements. A method where the statistics can be measured both quickly and accurately is proposed.