Selective laser etched side-polished single mode fiber with phase-OFDR readout: a novel platform for high resolution distributed refractive index sensing

This study introduces a novel refractive index sensor incorporating selective laser etched (SLE) side-polished fibers and a phase-sensitive Optical Frequency Domain Reflectometry (φ-OFDR) system. The φ-OFDR system enables distributed refractive index sensing along the sensing region with sub-millimeter spatial resolution. Microliter liquid sample containers are fabricated by laser engraving the flat surface of the side-polished single mode fiber exploiting the precise three-dimensional structuring capabilities of selective laser etching. These optical grade microgrooves stably hold the microliter-scale samples for the localized light-matter interaction. By combining the laser structured sensor head with the φ-OFDR system that provides distributed readout along the sensing region, precise detection of refractive index changes across the laser structured fiber surface can be realized. Here we present initial experimental results and discuss how this concept can support new applications in diagnostics and lab-on-fiber technologies.