Transmission–Reflection Analysis Using Nanoparticle-Doped Fibers: A Method for Intensity-to-Distance Conversion

The transmission–reflection analysis (TRA) is a highly cost-effective distributed sensing technique that monitors the transmitted and backscattered powers of a waveguide. Originally, the TRA was proposed and analytically formulated for single-mode optical fibers (SMFs). However, nanoparticle-doped optical fibers (NPFs) have been currently explored to increase the spatial resolution at the cost of diminishing the sensing range. Due to nonlinearities in Rayleigh backscattering (RBS), the mathematical assumptions made by the traditional SMF model cannot be applied to NPFs. Artificial intelligence has already been applied to a NPF-based TRA system to convert intensity to distance in a quasi-distributed configuration. To exploit NFPs for distributed sensing, this letter presents a method to convert intensity to distance. When strong disturbances were induced on fiber, the method exhibited an error up to 5 cm for a sensing range up to 3 m. For weak disturbances, relative errors up to 14.3 cm were obtained. Adding the noise of the acquisition system, the method yielded errors up to 29.24 cm for a 5.4 m sensor (5.41%).