Side polished graded index multimode fiber based refractive index sensor for biology measurement

A side polished graded index multimode fiber based refractive index sensor is proposed for use in biology measurements. The side polished graded index multimode fiber is fabricated using the wheel polishing method; that is, a part of the cladding and core of a graded index multimode fiber are removed to develop a leaking “window” called a side polished region. The optical power loss through this structure is sensitive to the refractive index of the analyte liquid that covers the leaking “window.” A highly linear correlation between the optical power loss and refractive index has been achieved. Additionally, we also investigated the influence of each structure parameter on the sensitivity and linearity. From simulation and experiment results, a fiber core of 50 μm and R of 10 μm are considered as the best choices of fiber structure with a sensitivity is 40.92 dB/RIU in the refractive index range of 1.300–1.450. A bio-culture solution of fetal bovine serum can be easily detected with this structure whose concentration gradient is two percent. It provides a simple and quick method to detect refractive indices in biology measurements from 1.300 to 1.450.