Analysis of a photonic integrated circuit for passive optical network for 5G NR.

This work presents the performance analysis of a passive optical network (PON) proposal with photonic integrated circuits (PIC). The PON architecture was simulated on MATLAB, focusing on the main functionalities of the optical line terminal, distribution network, and network unity regarded its effects on the physical layer. We show a simulated PIC, implemented on MATLAB through its analytic transfer function equation, used to implement orthogonal frequency division multiplexing in the optical domain to enhance the current optical networks for the 5G New-Radio (NR) scenario. We analyzed the OOK and optical PAM4 compared with phase modulation formats such as the DPSK and DQPSK. All modulation formats can be directly detected for the case in the study, simplifying the reception. Consequently, this work achieved a maximum symmetric transmission capacity of 1.2 Tbps over 90 km of standard single-mode fiber with 128 carriers, 64 carriers for downstream and 64 for upstream, obtained from an optical frequency comb with 0.3 dB flatness. We concluded that phase modulation formats associated with PIC could increase PON capability and push further our current scenario to the 5G new era.

Static and Dynamic Multiparameter Assessment of Structural Elements Using Chirped Fiber Bragg Gratings.

This paper presents the development, analysis, and application of chirped fiber Bragg gratings (CFBGs) for dynamic and static measurements of beams of different materials in the single-cantilever configuration. In this case, the beams were numerically analyzed using the finite-element method (FEM) for the assessment of the natural frequencies and vibration modes of the beam for the dynamic analysis of the structural element. Furthermore, the static numerical analysis was performed using a load at the free end of the beam, where the maximum strain and its distribution along the beam were analyzed, especially in the region at which the FBG was positioned. The experimental evaluation of the proposed CFBG sensor was performed in static conditions for forces from 0 to 50 N (in 10 N steps) applied at the free end of the beam, whereas the dynamic evaluation was performed by means of positioning an unbalanced motor at the end of the beam, which was excited at 16 Hz, 65 Hz, 100 Hz, and 131 Hz. The results showed the feasibility of the proposed device for the simultaneous assessment of the force and strain distribution along the CFBG region using the wavelength shift and the full-width at half-maximum (FWHM), respectively. In these cases, the determination coefficients of the spectral features as a function of the force and strain distribution were higher than 0.99 in all analyzed cases, where a potential resolution of 0.25 N was obtained on the force assessment. In the dynamic tests, the frequency spectrum of the sensor responses indicated a frequency peak at the excited frequency in all analyzed cases. Therefore, the proposed sensor device is a suitable option to extend the performance of sensors for structural health assessment, since it is possible to simultaneously measure different parameters in dynamic and static conditions using only one sensor device, which, due to its multiplexing capabilities, can be integrated with additional optical fiber sensors for the complete shape reconstruction with millimeter-range spatial resolution.

Soft-Sensor System for Grasp Type Recognition in Underactuated Hand Prostheses.

This paper presents the development of an intelligent soft-sensor system to add haptic perception to the underactuated hand prosthesis PrHand. Two sensors based on optical fiber were constructed, one for finger joint angles and the other for fingertips' contact force. Three sensor fabrications were tested for the angle sensor by axially rotating the sensors in four positions. The configuration with the most similar response in the four rotations was chosen. The chosen sensors presented a polynomial response with R2 higher than 92%. The tactile force sensors tracked the force made over the objects. Almost all sensors presented a polynomial response with R2 higher than 94%. The system monitored the prosthesis activity by recognizing grasp types. Six machine learning algorithms were tested: linear regression, k-nearest neighbor, support vector machine, decision tree, k-means clustering, and hierarchical clustering. To validate the algorithms, a k-fold test was used with a k = 10, and the accuracy result for k-nearest neighbor was 98.5%, while that for decision tree was 93.3%, enabling the classification of the eight grip types.

Liquid Level Sensor with Two FBGs Embedded in a PDMS Diaphragm: Analysis of the Linearity and Sensitivity.

This paper presents a fiber optic, liquid level sensor system based on a pair of fiber Bragg gratings (FBGs), embedded in a circular silicone (PDMS-polydimethylsiloxane) rubber diaphragm. The measurement principles of this sensor, whose diaphragm structure is about 2.2 mm thick with 45 mm in diameter, are introduced. To analyze the linearity and sensitivity of the sensor, the diaphragm was subjected to compression tests as well as to liquid level loading and unloading. The force and liquid level increase tests showed that inserting two FBGs (0.99453 for force and 0.99163 for liquid level) in the diaphragm resulted in a system with greater linearity than that with individual FBGs. This occurred where FBG1 showed 0.97684 for force and 0.98848 for liquid level and FBG2 presented 0.89461 for force and 0.93408 for liquid level. However, the compression and water level decrease tests showed that the system (R2 = 0.97142) had greater linearity with FBG2 (0.94123) and lower linearity with FBG1 (0.98271). Temperature characterization was also performed, and we found that sensitivity to FBG1 temperature variation was 11.73 pm/°C and for FGB2 it was 10.29 pm/°C. Temperature sensitivity was improved for both FBGs when compared with uncoated FBGs with typical values of 9.75 pm/°C. Therefore, the proposed FBG-based sensor system is capable of simultaneous measurement of force and temperature in a compact diaphragm-embedded system.

Polymer Optical Fiber-Based Integrated Instrumentation in a Robot-Assisted Rehabilitation Smart Environment: A Proof of Concept.

Advances in robotic systems for rehabilitation purposes have led to the development of specialized robot-assisted rehabilitation clinics. In addition, advantageous features of polymer optical fiber (POF) sensors such as light weight, multiplexing capabilities, electromagnetic field immunity and flexibility have resulted in the widespread use of POF sensors in many areas. Considering this background, this paper presents an integrated POF intensity variation-based sensor system for the instrumentation of different devices. We consider different scenarios for physical rehabilitation, resembling a clinic for robot-assisted rehabilitation. Thus, a multiplexing technique for POF intensity variation-based sensors was applied in which an orthosis for flexion/extension movement, a modular exoskeleton for gait assistance and a treadmill were instrumented with POF angle and force sensors, where all the sensors were integrated in the same POF system. In addition, wearable sensors for gait analysis and physiological parameter monitoring were also proposed and applied in gait exercises. The results show the feasibility of the sensors and methods proposed, where, after the characterization of each sensor, the system was implemented with three volunteers: one for the orthosis on the flexion/extension movements, one for the exoskeleton for gait assistance and the other for the free gait analysis using the proposed wearable POF sensors. To the authors' best knowledge, this is the first time that optical fiber sensors have been used as a multiplexed and integrated solution for the simultaneous assessment of different robotic devices and rehabilitation protocols, where such an approach results in a compact, fully integrated and low-cost system, which can be readily employed in any clinical environment.

Long period grating in a multimode cyclic transparent optical polymer fiber inscribed using a femtosecond laser.

In this Letter, we report, to the best of our knowledge, the first inscription of long period gratings (LPGs) in a multimode cyclic transparent optical polymer (CYTOP) fiber using a femtosecond laser inscription method. The LPG was inscribed directly in the center of the fiber core, tailored for operation at 1560 nm. The CYTOP-LPG was characterized in transmission, and its response for relative humidity and temperature was measured. The humidity measurements, to the best our knowledge, are the first for a POF-LPG, whereas the temperature sensitivity is significantly higher than reported in other works. In addition, dynamic mechanical measurements were performed comparing the mechanical characteristics of the laser exposed sections of the polymer fiber, where the LPG was inscribed, with the unexposed regions.

3D-Printing Techniques on the Development of Multiparameter Sensors Using One FBG.

We report the development of a fiber Bragg grating (FBG) sensor for multiparameter sensing using only one FBG. The FBG was half-embedded in a 3D-printed structure, which resulted in a division of the grating spectrum creating two peaks with different sensitivities with respect to different physical parameters. A numerical analysis of the proposed technique was performed using the coupled-mode theory with modified transfer matrix formulation. Then, experimental analyses were performed as function of temperature, strain and force, where the peaks showed different sensitivities in all analyzed cases. Such results enable the application of a technique for simultaneous measurement of multiple physical parameters using both peaks and the full width half maximum of the FBG embedded in a 3D structure. In the simultaneous multiparameter assessment, the proposed sensor system was able to estimate the three tested parameters (strain, temperature and force) with relative errors as low as 4%.

Polymer Optical Fiber Sensors in Healthcare Applications: A Comprehensive Review.

Advances in medicine and improvements in life quality has led to an increase in the life expectancy of the general population. An ageing world population have placed demands on the use of assistive technology and, in particular, towards novel healthcare devices and sensors. Besides the electromagnetic field immunity, polymer optical fiber (POF) sensors have additional advantages due to their material features such as high flexibility, lower Young's modulus (enabling high sensitivity for mechanical parameters), higher elastic limits, and impact resistance. Such advantages are well-aligned with the instrumentation requirements of many healthcare devices and in movement analysis. Aiming at these advantages, this review paper presents the state-of-the-art developments of POF sensors for healthcare applications. A plethora of healthcare applications are discussed, which include movement analysis, physiological parameters monitoring, instrumented insoles, as well as instrumentation of healthcare robotic devices such as exoskeletons, smart walkers, actuators, prostheses, and orthosis. This review paper shows the feasibility of using POF sensors in healthcare applications and, due to the aforementioned advantages, it is possible to envisage a further widespread use of such sensors in this research field in the next few years.

Material features based compensation technique for the temperature effects in a polymer diaphragm-based FBG pressure sensor.

Fiber Bragg grating (FBG) based sensors have been applied to measure several parameters, such as pressure, vibration, liquid level, humidity, the concentration of chemical compounds, among others. An approach to measure parameters like liquid level, pressure and vibration are to embed the FBG on a diaphragm, which is generally made of a polymeric material. Nevertheless, the mechanical properties of polymers depend on temperature variation. For this reason, a polymer diaphragm can enhance the cross-sensitivity between the strain and temperature on an FBG sensor. In order to overcome this limitation, this paper presents a compensation technique for the temperature effects on an oblong polymer diaphragm-based FBG pressure sensor. The presented technique is based on the analytical model of the sensor, which takes into account the variation of the diaphragm properties with temperature obtained through a dynamic mechanical analysis of the diaphragm material. Results show that the developed technique reduces the sensor cross-sensitivity to about 1.74 Pa/°C. Furthermore, the presented technique is compared with the direct difference between the FBG strain and temperature responses presented in reference works. The comparison shows a better performance of the technique presented in this paper with respect to the cross-sensitivity and the root mean squared error.

Strain, temperature, moisture, and transverse force sensing using fused polymer optical fibers.

This paper presents the characterization of polymer optical fibers (POFs) submitted to the catastrophic fuse effect towards intensity-variation-based sensing of strain, transverse force, temperature, and moisture. In the experiments, POFs with and without the fuse effect are tested and the results are compared with respect to the sensitivity, linearity, and root mean squared error (RMSE). The fused POFs have higher linearity and lower RMSE than non-fused POFs in strain and transverse force sensing. Also, the sensitivity of the fused POFs is higher in transverse force and temperature sensing, which can be related to the higher sensitivity to the curvature that the transverse force creates on the POF and to the more significant variations of the refractive index with temperature increase. Additionally, the fused POFs present lower moisture absorption than the non-fused POFs. The presented results indicate a great potential of the fused POFs intensity-variation-based sensing applications of various physical parameters.

Characterization of a new polymer optical fiber with enhanced sensing capabilities using a Bragg grating.

We present results for the mechanical characterization of a bisphenol-A acrylate-based polymer optical fiber (POF) manufactured using a novel light polymerization spinning (LPS) process. The particular manufacturing process allows the development of POFs having unique mechanical characteristics, which result from an exceptionally low Young's modulus. The lower Young's modulus enables optical sensors for measuring stress or pressure with improved sensitivity and potentially a higher tunable mechanical range than conventional POFs. Moreover, properties such as the storage modulus variations with respect to the temperature and humidity were studied. Fiber Bragg gratings (FBGs), were inscribed in the POF using the plane-by-plane femtosecond laser, direct-write method for selective FBG mode excitation, and were characterized for changes to temperature, pressure, and relative humidity. The response of FBGs in this LPS-POF for all the three aforementioned measurands was several times higher than that measured for conventional POFs.

Dynamic mechanical analysis on fused polymer optical fibers: towards sensor applications.

This Letter presents, for the first time, to the best of our knowledge, the dynamic mechanical analysis of a polymer optical fiber (POF) that was previously damaged by the catastrophic fuse effect. The variation of the fiber Young's modulus was evaluated with respect to the increase of temperature, humidity, and frequency of strain cycles. The obtained data for the fused POF are compared with the ones for the same POF without the fuse effect. The results show the feasibility of the fused POF for sensor applications, such as strain and acceleration measurement, since it presents temperature sensitivity almost two times lower in temperatures between 26°C and 90°C and Young's modulus 2.3 times lower than those obtained with the bare fiber. The Young's modulus variation with the humidity is 1.5 MPa/%RH in a humidity range of 66-96%. In addition, the fused POF presented a variation of its dynamic modulus with the frequency increase four times lower than non-fused POFs on the range of 0.01-100.00 Hz. These results pave the way for future applications of fused POFs as sensing elements.

Design considerations, analysis, and application of a low-cost, fully portable, wearable polymer optical fiber curvature sensor.

This paper presents the development of a low-cost, fully portable, wearable sensor for joint angle assessment based on a polymer optical fiber (POF) curvature sensor. The mechanical support configurations as well as the fiber length are analyzed to obtain a sensor with lower hysteresis and higher sensitivity and linearity. In addition, the annealing is made in the fiber to further reduce the sensor errors, and an analysis to obtain the sensor cross-sensitivity with respect to temperature and relative humidity is performed. Finally, a viscoelastic-based compensation technique is applied on the proposed wearable sensor not only to reduce its hysteresis and errors, but also to increase the sensor linearity. The sensor is validated on flexion and extension cycles with different angular velocities. Results show that the proposed sensor presents root mean squared errors of about 1.5° and mean hysteresis of about 1%. The wearable POF curvature sensor was applied on the angle measurement of an elbow joint during flexion and extension cycles and on the knee during the gait cycle, where high repeatability and low errors also were found.

Measurement of Temperature and Relative Humidity with Polymer Optical Fiber Sensors Based on the Induced Stress-Optic Effect.

This paper presents a system capable of measuring temperature and relative humidity with polymer optical fiber (POF) sensors. The sensors are based on variations of the Young's and shear moduli of the POF with variations in temperature and relative humidity. The system comprises two POFs, each with a predefined torsion stress that resulted in a variation in the fiber refractive index due to the stress-optic effect. Because there is a correlation between stress and material properties, the variation in temperature and humidity causes a variation in the fiber's stress, which leads to variations in the fiber refractive index. Only two photodiodes comprise the sensor interrogation, resulting in a simple and low-cost system capable of measuring humidity in the range of 5-97% and temperature in the range of 21-46 °C. The root mean squared errors (RMSEs) between the proposed sensors and the reference were 1.12 °C and 1.36% for the measurements of temperature and relative humidity, respectively. In addition, fiber etching resulted in a sensor with a 2 s response time for a relative humidity variation of 10%, which is one of the lowest recorded response times for intrinsic POF humidity sensors.

A Polymer Optical Fiber Temperature Sensor Based on Material Features.

This paper presents a polymer optical fiber (POF)-based temperature sensor. The operation principle of the sensor is the variation in the POF mechanical properties with the temperature variation. Such mechanical property variation leads to a variation in the POF output power when a constant stress is applied to the fiber due to the stress-optical effect. The fiber mechanical properties are characterized through a dynamic mechanical analysis, and the output power variation with different temperatures is measured. The stress is applied to the fiber by means of a 180° curvature, and supports are positioned on the fiber to inhibit the variation in its curvature with the temperature variation. Results show that the sensor proposed has a sensitivity of 1.04 × 10-3 °C-1, a linearity of 0.994, and a root mean squared error of 1.48 °C, which indicates a relative error of below 2%, which is lower than the ones obtained for intensity-variation-based temperature sensors. Furthermore, the sensor is able to operate at temperatures up to 110 °C, which is higher than the ones obtained for similar POF sensors in the literature.

Application of Additive Layer Manufacturing Technique on the Development of High Sensitive Fiber Bragg Grating Temperature Sensors.

This paper presents the development of temperature sensors based on fiber Bragg gratings (FBGs) embedded in 3D-printed structures made of different materials, namely polylatic acid (PLA) and thermoplastic polyurethane (TPU). A numerical analysis of the material behavior and its interaction with the FBG sensor was performed through the finite element method. A simple, fast and prone to automation process is presented for the FBG embedment in both PLA and TPU structures. The temperature tests were made using both PLA- and TPU-embedded FBGs as well as an unembedded FBG as reference. Results show an outstanding temperature sensitivity of 139 pm/°C for the FBG-embedded PLA structure, which is one of the highest temperature sensitivities reported for FBG-based temperature sensors in silica fibers. The sensor also shows almost negligible hysteresis (highest hysteresis below 0.5%). In addition, both PLA- and TPU-embedded structures present high linearity and response time below 2 s. The results presented in this work not only demonstrate the feasibility of developing fully embedded temperature sensors with high resolution and in compliance with soft robot application requirements, but also show that the FBG embedment in such structures is capable of enhancing the sensor performance.

Polymethyl methacrylate (PMMA) recycling for the production of optical fiber sensor systems.

This paper proposes the recycling of poly (methyl methacrylate) plates, formerly used in LCD monitors to produce polymer optical fibers without cladding for sensor systems and a discussion about the fabrication process of the fiber cladding is briefly presented. After disassembling LCD monitors the acrylic plate is cleaned and submitted to an extrusion process. Extrusion temperatures of 220°C, 230°C and 240°C were applied, and the produced polymer fibers were characterized by infrared and visible spectrometry, as well as evaluated for thermal analysis through differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Furthermore, a refractive index sensor was developed with the recycled fibers. Results show that the recycled fiber refractive index sensor is linear (R2 = 0.99) and presents a sensitivity of more than 4 times higher when compared to a sensor using a commercial POF.

Low-Cost Interrogation Technique for Dynamic Measurements with FBG-Based Devices.

Fiber Bragg gratings are widely used optical fiber sensors for measuring temperature and/or mechanical strain. Nevertheless, the high cost of the interrogation systems is the most important drawback for their large commercial application. In this work, an in-line Fabry-Perot interferometer based edge filter is explored in the interrogation of fiber Bragg grating dynamic measurements up to 5 kHz. Two devices an accelerometer and an arterial pulse wave probe were interrogated with the developed approach and the results were compared with a commercial interrogation monitor. The data obtained with the edge filter are in agreement with the commercial device, with a maximum RMSE of 0.05 being able to meet the requirements of the measurements. Resolutions of 3.6 pm and 2.4 pm were obtained, using the optical accelerometer and the arterial pulse wave probe, respectively.

Envelope-based technique for liquid level sensors using an in-line fiber Mach-Zehnder interferometer.

This paper proposes a sensor interrogation technique based on the analysis of the overall spectrum envelope of an in-line Mach-Zehnder interferometer structure with three different fibers. The interference pattern created by a level sensor of 120 mm was evaluated with both the traditional and the proposed interrogation techniques. The result shows that the technique here proposed improves the sensitivity of the sensor by more than an order of magnitude. Moreover, our new interrogation technique allows the length of an in-line Mach-Zehnder interferometer to be extended up to 470 mm while maintaining high linearity and sensitivity.

Corrosion Resistant FBG-Based Quasi-Distributed Sensor for Crude Oil Tank Dynamic Temperature Profile Monitoring.

This article presents a corrosion resistant, maneuverable, and intrinsically safe fiber Bragg grating (FBG)-based temperature optical sensor. Temperature monitoring is a critical activity for the oil and gas industry. It typically involves acquiring the desired parameters in a hazardous and corrosive environment. The use of polytetrafluoroethylene (PTFE) was proposed as a means of simultaneously isolating the optical fiber from the corrosive environment and avoiding undesirable mechanical tensions on the FBGs. The presented sensor head is based on multiple FBGs inscribed in a lengthy single mode fiber. The sensor presents an average thermal sensitivity of 8.82 ± 0.09 pm/°C, resulting in a typical temperature resolution of ~0.1 °C and an average time constant value of 6.25 ± 0.08 s. Corrosion and degradation resistance were verified by infrared spectroscopy and scanning electron microscopy during 90 days exposure to high salinity crude oil samples. The developed sensor was tested in a field pilot test, mimicking the operation of an inland crude tank, demonstrating its abilities to dynamically monitor temperature profile.