Direction-independent fiber inclinometer based on simplified hollow core photonic crystal fiber

A fiber optical inclinometer based on modal interferometer is demonstrated for bend angle sensing. The device consists of a piece of simplified hollow core photonic crystal fiber sandwiched between single mode fibers with lateral offset. The measurement of bend angles up to 45° is demonstrated, and the spectrum exhibits a blueshift of over 50 nm. The sensitivity is found to increase with the applied bend angles and reaches 2.4 nm/deg at 45°, and the response is independent of the direction of bending. A low temperature sensitivity of 0.5 pm/°C is observed between room temperature and 1000°C. Due to its capacity for withstanding high temperature, the device can work as a direction-independent inclinometer in high-temperature environments.