Sensitivity-enhanced fiber strain sensing system based on microwave frequency scanning with the Vernier effect

A sensitivity enhanced fiber-optic strain sensing system based on microwave frequency scanning is proposed and experimentally demonstrated. The strain sensor consists of two cascaded fiber rings which are composed of just standard single-mode fibers. Since the two fiber rings are set to have almost same free spectra ranges, Vernier effect is generated in the transmission spectrum. The experimental results show that the strain sensitivity has been improved over 20 times higher than that of a single fiber ring. Moreover, owing to the high speed and small frequency resolution of the microwave frequency scanning in our system, micro-strain can be fast detected within several milliseconds with nano-strain resolution, which is hard for using a traditional grating-based optical spectrum analyzer.