Optical Fiber Head Sensors with Controlled Polarization for Flow Measurement in Pipelines

Abstract This experimental study discusses developing methodologies linked to optical fiber sensing (OFS), focused on structural health monitoring with sensors based on multimodal interference and the core diameter mismatch approach to monitor the flow of single and two-phase pipeline systems. Singlemode-multimode-singlemode (SMS), singlemode-nocore-singlemode (SNCS), singlemode-multimode-singlemode-multimode-singlemode (SMSMS), singlemode-multimode-erbium doped-multimode-singlemode (SMErDMS), and singlemode-multimode-dispersion compensation-multimode-singlemode (SMDCMS) were the five different heads sensors used in the sensor structure. Results showed that the polarization effect causes a spike in the sensitivity levels and alters the sensor's behavior with a polarizer among the optical source path. Sensitivity values of SMS sensor changed from 0.027 dBm/(h/m³) to 0.041 dBm/(h/m³) for the single-phase flow measurement tests; the SNCS structure's sensitivity changed from 0.093 dBm/(h/m³) to 0.221 dBm/(h/m³); and the SMSMS sensor's sensitivity changed from 0.862 dBm/(h/m³) to 1.122 dBm/(h/m³). The sensitivity values for the two-phase flow increased for the SMS from -0.126 dBm/(h/m³) to -0.288 dBm/(h/m³) and for the SMErDFMS from -0.028 dBm/(h/m³) to -0.929 dBm/(h/m³), respectively. All structures had a good acceptable coefficient of determination and the polarization mode maintained by a polarizer also to prevent random power coupling between the polarization modes and assisted in controlling the optical power.