Self-referenced fiber microbend displacement sensor based on dual-wavelength fiber-Bragg gratings interposed with a multimode fiber micro bender

A self-referenced multimode fiber (MMF) micro bend displacement sensor is presented in this paper. In this sensor, two single mode fiber Bragg gratings (FBGs) with different wavelengths are employed for the self-reference of the micro bend displacement measurement. A short piece of MMF with a mechanical micro bender, inserted between the two FBGs, acts as the sensing part. The sensor output is very stable (variation in the intensity difference was ~ 0.07dB) within the 8dB dynamic range of the transmission loss. And the maximum variation of the intensity difference with temperature is about 0.55dB from 20°C to 75°C. The sensor system offers many advantages, including higher stability, single end access, and high sensitivity.