Optically active nanoparticles-embedded optical fiber for random fiber laser distributed sensor
This paper presents the development of a multifunctional photonic device using nanoparticle (NP)-doped fiber as an optical amplification medium and distributed sensing element simultaneously. The proposed system comprises a linear cavity Random Fiber Laser (RFL) in which the NP-doped fiber is used as an amplification medium due to the erbium ions in the NP composition and a distributed cavity due to the enhanced Rayleigh scattering of the fiber. In this case, the RFL is employed as a distributed sensor by means of localized changes on the optical transmission and reflection signals when temperature and strain are applied along the NP-doped fiber. The proposed RFL is analyzed in terms of stability and configurations. In this case, the RFL demonstrated a maximum output power of around 17 mW with a power stability demonstrated by 0.07 nm variations in wavelength stability tests. The RFL distributed sensor validation, and the sensor system was submitted to simultaneous variation of temperature, strain, and location of the mechanical disturbance, where the Random Forest machine learning method was employed for the simultaneous assessment of all three parameters. The results show high accuracy of the sensor system, where relative errors of 0.02%, 2.0%, and 5.3% were found for temperature, strain, and location of strain application along the laser cavity, respectively. Therefore, the proposed RFL distributed sensor is a feasible solution for dynamic monitoring of different physical parameters, which can close the gap between the distributed optical fiber sensors and applications that require lower cost and high portability.
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.