Miniature Fiber-Optic Strain Sensor Based on a Hybrid Interferometric Structure

We present a compact fiber-optic strain sensor with a hybrid interferometric structure, including a micro-cavity Fabry-Pérot interferometer (MC-FPI) and a Mach-Zehnder interferometer (MZI). The sensor is formed by splicing two conventional single-mode fibers (SMFs), one as the lead-in fiber and the other as the lead-out fiber, to both ends of a photonic crystal fiber (PCF). Through controlling the splicing parameters, the lead-in SMF/PCF splice forms a micro-cavity and causes the collapse of the microholes in the PCF, which acts as a mode splitter/combiner. For the lead-out SMF/PCF splice, no micro-cavity is formed and the splicing point only functions as a mode splitter and combiner. The PCF together with the two splicing points form the MZI. Sensor prototypes with different MC-FPI lengths are developed. Combining reflection and transmission spectra together, the sensor achieves a high strain sensitivity, which can find application in real strain measurement.