A fiber inclinometer using a fiber microtaper with an air-gap microcavity fiber interferometer

•A fiber microtaper with an air-gap microcavity fiber interferometer is designed and demonstrated to measure tilt angles.•A section of HCF is employed to initiate the interference and the taper functions as a bridge for the coupling and recoupling of core-to-cladding modes.•A interference is obtained and sensitive to fiber bending.

A micro-inclinometer is proposed and demonstrated experimentally; the device consists of a micro-fiber taper followed by an air-gap microcavity. A part of the core mode can couple to cladding modes via the taper. These cladding modes and residual core modes transmitted to downstream of the Fabry–Perot (FP) interferometer. A fraction of these modes are reflected back to the SMF by two surfaces of the FP cavity and eventually recoupled to the leading-in SMF, resulting in a well-defined interference spectrum. The fringe contrast of the interferometer is highly sensitive to fiber bending with direction-independence and thus is capable of measuring tilt angles in high resolution. In addition, the interference wavelength always remains unchanged during the fiber bending.