Refractive Index Sensor Based on No-Core Fiber With Optoelectronic Oscillator Interrogation

In this letter, a refractive index sensing system isproposed and experimentally demonstrated. Acting as the sensinghead, the no-core fiber spliced with two sections of single-modefiber (SNS) is fabricated to form a fiber ring laser (FRL). Themeasured salt water changes the self-imaging wavelength ofthe NCF as well as the central wavelength of the FRL. Afterthat, the light is introduced into the dual-loop optoelectronicoscillator (OEO). With the help of the dispersion compensationmodule in the OEO loop, the wavelength change is mapped intothe frequency shift of the generated microwave signal. Hence,the RI of the measured liquid can be recovered by tracking thefrequency change. Both the simulation analysis and the proofof concept experiment are performed. Results show that boththe central wavelength of the FRL and the microwave signalincrease exponentially with the increased RI, agreeing with thesimulated analysis. In the range of 1.33-1.38, the linear fittingresults manifest that the sensitivities of central wavelength changevs. RI and microwave signal shift vs. RI are 87.70 nm/RIU and83.89 MHz/RIU, the corresponding resolutions are 2.28x10(-4)and 1.19x10(-5), respectively. The proposed method showspotential for realizing high sensitivity, fast, and real-time RImeasuring