Refractometer based on extinction ratio demodulation using no-core and dispersion-compensating fiber structure

A simple and cost-efficient fiber sensor based on multi-mode interference and core diameter mismatch tech-nologies is proposed to detect the refractive index (RI) in this paper. The refractometer is fabricated by embedding a section of no-core fiber between a section of multimode fiber and dispersion-compensating fiber. Since the power distribution in the fiber will change with the effective refractive index of the cladding, the extinction ratio can be used to characterize the RI sensitivity. The experimental results show that a linear response is obtained with a RI sensitivity of 392.585 dB/RIU in the range of 1.333-1.374. Featured with high sensitivity, simple construction, easy fabrication, low cost and good repeatability, the novel refractometer has potential applications in practical chemical detecting and portable biological sensing.