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In this paper, in order to improve fabrication efficiency, a novel multimode open-cavity Mach-Zehnder interferometer (MOC-MZI) is proposed and completed based on joint-assistance of microfiber and multimode fibers (MMFs), through flame brush and arc-discharged core-offset splicing techniques, in which a sub-millimeter-long MMF is used as the expansion fiber. The light field distributions of MOC-MZI with different core diameters of MMF (denoted by dMMF) by beam propagation method were investigated, and the effective beam expansion range was quantified with respect to the length of MMF (denoted by LMMF). Moreover, the optimal offset value of the microfiber (denoted by α) with different waist diameters (denoted by d) was obtained by simulation. According to the simulation results, the maximum fringe visibility can reach 28.3 dB via the optimized LMMF (=600 μm) and microfiber (d=40 μm, α=30 μm). Additionally, the energy attenuation of MOC-MZI is studied with varied cavity length, and the possible intensity-sensitive cavity length is found. Multiple open-cavity structures with different dMMF from 0 to 105 μm were then experimentally prepared and compared. When dMMF=105 μm, a millimeter-length open-cavity MZI is obtained with the visibility of ~8-dB, and its temperature response was characterized in terms of wavelength and intensity.
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