Resolution-improved refractive index sensing system based on microwave photonics filter and microfiber gratting

A novel refractive index (RI) sensing system with improved resolution based on a microwave photonics filter (MPF) is proposed and experimentally demonstrated. The sensing probe used for RI measurement is a microfiber Bragg grating. We use the frequency interrogation scheme (different from the traditional wavelength demodulation method) for resolution improvement of RI detection. The frequency shift of MPF notch point shows a linear relationship with the surrounding RI change over the range of 1.33 to 1.38 and a RI sensing resolution of 2.63×10^-5 RIU has been achieved experimentally. The proposed MPF based RI sensing system provides a new interrogation method over the frequency domain with improved RI sensing resolution, as a good candidate for rapid and highly sensitive detection in chemical and environmental monitoring.