Ultra-sensitive refractive index sensor based on extremely simple femtosecond-laser-induced structure

Abstract

We demonstrate here an extremely simple, compact and robust RI probe sensor based on a femtosecond-laser induced refractive-index-modified-dot (RIMD) fabricated near the end face of a single mode fiber. The RIMD and the fiber end face form a Fabry-Perot interferometer, which is highly sensitive to surrounding RI. The fabrication process of the RIMD involves only one step and takes ~0.1s, which is extremely short compared with other techniques. The proposed sensor exhibits an ultra-high sensitivity of ~2523.2 dB/RIU at an RI of 1.435, which is 1-2 orders of magnitude higher than that of the existing intensity-modulated RI sensors. Moreover, the proposed sensor has the distinct advantages of compact size (~50 µm), easy fabrication and no temperature cross-sensitivity. The advantages of the device make it a promising candidate for applications in designing highly sensitive sensors in biochemical and environmental measurement field.