Ambient refractive index-independent bending vector sensor based on seven-core photonic crystal fiber using lateral offset splicing.

A novel, simple, and compact optical fiber directional bending vector sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The device consists of a piece of seven-core photonic crystal fiber (PCF) sandwiched between two single mode fibers (SMFs) with a lateral offset splicing joint that covering two cores of PCF. Bending sensitivity of the seven-core PCF based MZI is changed by an axial rotation angle, which shows its capacity for recognizing positive and negative directions. Within a curvature range of -7.05 m-1 to 7.05 m-1, the calculated bending sensitivities of two resonant central wavelengths with opposite fiber orientations are 1.232 nm/m-1 and 1.174 nm/m-1, respectively. This novel MZI is formed by invoking interference between the LP01-like supermode and other higher order supermodes in the core, which leads to insensitive to ambient refractive index (ARI). We have also investigated the transmission characteristics of the sensor with the temperature change.