Interferometric Interrogation of the Inclination and Displacement of Tapered Fiber Mach-Zehnder Interferometers.

All-fiber inclinometers and displacement sensors using tunable Mach–Zehnder interferometers with an extinction ratio of >30.4~dB are produced by introducing two abrupt tapers in a short length (<1.4~cm) of highly Er/Yb co-doped fiber. The abrupt tapers partially convert the core mode into cladding modes and interference occurs when the phase difference between the core and cladding modes accumulate to \pi after a certain propagation length. The maximal wavelength shift for the resonant transmission dips can reach 40.8 nm (from 1648 to 1607.2 nm) when the inclination angle, \theta, varies from 0^\circ to 32^\circ. The wavelength shift can reach 26 nm (from 1404.4 to 1430.4 nm) when the compressive strain \varepsilon is 0.004. [ABSTRACT FROM PUBLISHER]