Low-Cost FBG Interrogator Using Random Nanoparticle-Doped Fiber Laser and Fiber Optic Interferometer
The use of fiber Bragg gratings (FBGs) is widespread in a broad range of applications. However, one of the main drawbacks is the cost and practicality of FBG interrogation systems, which are generally bulky and more expensive than electronic sensors or alternative optical fiber sensing approaches. This article presents a novel, low-cost FBG interrogator that employs a random laser based on a nanoparticle-doped fiber (RNPFL) and an unbalanced Mach–Zehnder fiber interferometer (MZI). The system uses the RNPFL connected to an unbalanced interferometer to convert Bragg wavelength shifts into phase changes, enabling precise interferometric detection with higher resolution than conventional spectral methods. Experimental results obtained with four FBGs of varying reflectivity, spectral width, and sidelobe suppression ratio (SLSR) demonstrate that, when operated with the RNPFL, the interrogator achieves up to 30 dB higher optical power (OP) and interference visibility of 60%–90%, substantially outperforming a standard superluminescent light-emitting diode (SLED) source. The relative error (RE) in phase demodulation remains below 0.2% for optimal configurations, characterizing the precision and phase-noise performance of the demodulation rather than the absolute accuracy of the system. The method is effective for FBGs with a wide range of parameters, provided that the SLSR is at least 15 dB. The main advantages of this approach are its compatibility with standard FBGs, high measurement resolution, and reduced cost, while the primary limitations are the requirement for a star topology in multichannel setups and the sensitivity of the resonator to external disturbances.
Polymer optical fiber Bragg gratings for multiparameter analysis in UAV wings: an AI-integrated approach
This paper presents the development of a polymer optical fiber Bragg grating (POFBG)-based sensor system for measurement of vibration, force amplitude and position for fixed-wing unmanned aerial vehicle (UAV). The POFBG is positioned along the wing structure, where forces amplitude and locations resulted in spectral changes in the POFBG. Then, predefined spectral features are used as input of a Generative Adversarial Network (GAN) for data augmentation, which increased the dataset to 1000 different force amplitude and locations. The accuracy of 1.9 Hz was obtained for vibration analysis. In the force amplitude and location analysis, the feed forward neural network (FFNN) resulted in relative errors of 3.30% and 3.51% for force amplitude and position, such errors are related to root mean squared errors (RMSE) and standard deviations of 0.33 N±0.05 N and 35.18 mm±2.3 mm for force amplitude and location, respectively. If the number of input features is reduced to only 3 predefined spectral features the RMSE without GAN increases to 1.23 N ± 0.15 N and 75.34 mm ± 9.20 mm for force amplitude and position, respectively. The FFNN with data augmentation resulted in relative errors of 7.8% for force amplitude and 2.4% for force location (RMSE of 0.78 N±0.10 N and 24.90 mm±2.1 mm, respectively), using 3 input features. The data augmentation resulted in accuracy increase with almost twofold reduction in the RMSE for the force amplitude and more than 3 times reduction of the RMSE for position estimation. Therefore, the POFBG sensor is a feasible option for shape reconstruction in UAV structures.
Distributed sensing with nanoparticle-doped fibers in standard OTDR systems: Validation and performance analysis
This paper presents the implementation of enhanced backscattering optical fibers in optical time-domain reflectometry (OTDR). The increase in the backscattering is achieved by doping the fiber core with nanoparticles, resulting in the so-called nanoparticle-doped optical fibers (NPFs). The so-called NPF-OTDR sensor system takes advantage of the higher scattering of the NPFs to increase the spatial resolution and strain sensitivity of the distributed sensor system. The wavelength-dependent optical attenuation is measured over a wide range of wavelengths using the cutback method to evaluate the operational wavelength for the OTDR. In this case, the results indicated smaller attenuation in 1310 nm than at the other operational wavelengths of the OTDR system (i.e., 1550 nm and 1625 nm). For this reason, the OTDR is applied at the 1310 nm wavelength for different strains applied along the optical fiber (with 1 m separation between them). The results for strain estimation showed relative errors of around 3%, whereas the strain position estimation is around 0.24 m. These results indicate the feasibility of the proposed system with a potential spatial resolution of around 0.5 m (which can be even lower depending on the OTDR setup). Thus, the advantages of the OTDR using the NPF result in a better sensor system performance when compared with the standard optical fibers, significantly enhancing the conventional OTDR capabilities in terms of resolution with even comparable performance to specialty OTDR systems at a lower cost and with a simpler design.
A Comparison Between Nanoparticle-Doped Fibers and Standard Single-Mode Fibers for Distributed Temperature Sensing
This article presents a comprehensive analysis of the thermal properties and distributed temperature-sensing responses of nanoparticles (NPs)-doped optical fiber using optical frequency-domain reflectometry (OFDR). The thermomechanical analysis (TMA) for the NP-doped fiber is performed to evaluate the thermal expansion coefficient of such fibers and their differences compared with standard telecom optical fibers (SMFs). In addition, the thermo-optical coefficient of such fibers is analyzed as a function of their steady-state temperature responses, whereas the thermal conductivity is assessed from the transient thermal analysis of the NP-doped fiber. The results in distributed temperature measurement indicate better sensing performance of NP-doped fiber, which has 2.6 times higher temperature sensitivity, a smaller response time, and high accuracy estimated from a determination coefficient (R2) of 0.993 and root mean squared error (RMSE) of 1.28 ∘ C. Therefore, the main findings of this work indicate the influence of the NPs composition on the thermal properties of the optical fibers, where the addition of oxide particles (in conjunction with the changes in the glass matrix) presented a positive effect on the distributed temperature sensing capabilities with a thermal expansion coefficient increase of 30% and thermal conductivity increase of 25% when compared with SMF. Thus, this article provides not only the comparison of the temperature sensing performance of an NP-doped fiber but also a straightforward method for the assessment of distributed physical parameters of the fiber that can be used for any specialty optical fiber, which can also be used as a nondestructive method for the assessment of the optical fiber composition.