A novel setup for a Double-Taper Mach-Zehnder Interferometer (DTMZI) is presented to measure axial strain and torsion. An epoxy section is added between the two tapers as a fixture to ensure torsion sensing. The modal filtering effect of the epoxy upon the interferometry response is experimentally verified. The transmission spectrum of DTMZI under strain and torsion is modelled and further analyzed through the differential accumulated phase between the beating modes.The experimental spectral observation confirms our estimate. The relationships between the spectral shifts in wavelength and applied displacements are obtained. The sensor shows a very high sensitivity against the applied strain and twists.

In-line fiber interferometers based on abrupt tapers have been shown as a promising low-cost platform for various sensing applications. Many variations have been demonstrated experimentally using combinations and permutations of novel photonic devices such as photonic crystal fibers or multimode fibers. In this manuscript, an analytical model for light propagation in an abrupt taper Mach-Zehnder Interferometer in commercial single-mode fiber based on coupled-mode theory is detailed. The model calculates the mode propagation process, and the result is compared with previous numerical simulations. For experimental verification, an in-line Mach-Zehnder interferometer based on an abruptly tapered fiber is fabricated and tested. The spectrum calculated by the model matches well with the measured spectrum. To reduce the computational complexity, a method for step size estimation and the corresponding error accumulation is discussed and verified. This can serve as a basis to estimate the optical responses of this class of abrupt taper based fiber sensors. With the right packaging, these sensors can play a vital role in rugged and hostile environments.

This work presents an analytical coupling model for perturbed abrupt fiber tapers in single-mode fibers. In addition to LP0m modes, the modeling predicts the presence of LP11 and LP12 modes for a bent taper. Our model also introduces a perturbation function that can match most cases of bending variations on a taper. We have shown that the tapering and bending effect can be treated separately within one abstract formulation. Agreement amongst the model predictions and experimental results support the viability of our method.

A novel interrogation method is presented in the application of strain sensing with a double taper Mach-Zehnder interferometer (DTMZI). The proposed sensing setup comprises a laser source and an optical power meter, which significantly lowers future integration cost and complexity. An analytical coupling model is established to study the sensor's strain-related modal behaviour. The design parameters of the DTMZI device are conditioned to satisfy a single-wavelength measurement. The spectral responses of several fabricated sensors are examined. Our experiments confirm the direct mapping between different strain values and particular transmission measures for the single wavelength case.

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