Soares, LilianaPérez Herrera, Rosa AnaNovais, SusanaFerreira, AntónioSilva, SusanaFrazão, Orlando2024-09-182024-09-182024Soares, L., Perez-Herrera, R. A., Novais, S., Ferreira, A., Silva, S., Frazão, O. (2024) Linear fiber laser configurations for optical concentration sensing in liquid solutions. Photonics, 11(5), 1-9. https://doi.org/10.3390/photonics11050393.2304-673210.3390/photonics11050393https://academica-e.unavarra.es/handle/2454/51657In this study, different configurations based on linear fiber lasers were proposed and experimentally demonstrated to measure the concentration of liquid solutions. Samples of paracetamol liquid solutions with different concentrations, in the range from 52.61 to 201.33 g/kg, were used as a case-study. The optical gain was provided by a commercial bidirectional Erbium-Doped Fiber Amplifier (EDFA) and the linear cavity was obtained using two commercial Fiber Bragg Gratings (FBGs). The main difference of each configuration was the coupling ratio of the optical coupler used to extract the system signal. The sensing head corresponded to a Single-Mode Fiber (SMF) tip that worked as an intensity sensor. The results reveal that, despite the optical coupler used (50:50, 60:40, 70:30 or 80:20), all the configurations reached the laser condition, however, the concentration sensing was only possible using a laser drive current near to the threshold value. The configurations using a 70:30 and an 80:20 optical coupler allowed paracetamol concentration measurements with a higher sensitivity of (−3.00 ± 0.24) pW/(g/kg) to be performed. In terms of resolution, the highest value obtained was 1.75 g/kg, when it was extracted at 20% of the output power to the linear cavity fiber laser configuration.application/pdfeng© 2024 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.ConcentrationFiber laserFiber tipIntensity sensorLinear cavityLiquid solutionsParacetamolinfo:eu-repo/semantics/article2024-09-18info:eu-repo/semantics/openAccess