M–Z Interferometer Constructed by Two S-Bend Fibers for Displacement and Force Measurements

An in-line Mach–Zehnder interferometer (MZI) formed by cascading two S-bend fibers (SBFs) on a single-mode fiber is proposed and fabricated only using a common fusion splicer. The SBFs serve as mode coupling elements for coupling light from the fundamental mode to the cladding modes and vice versa to construct an in-line MZI. The proposed MZI exhibits high sensitivities for displacement and force measurements. Experimental results show that the displacement and force sensitivities of ${-}{\rm 1.533}~{\rm nm}/\mu{\rm m}$ and ${-}{\rm 177.1}~{\rm nm}/{\rm N}$ , respectively, are obtained by the MZI with the length of ${\sim}{\rm 2.3}~{\rm mm}$ .