Mode analysis of in-line Mach-Zehnder interferometer with offset splicing

Abstract

Mode excitation of in-line Mach-Zehnder interferometer (MZI) with offset splicing between standard single-mode fiber (SMF) and thin-core fiber (TCF) is investigated. Based on the mode field profiles of high order modes in TCF, dependence of mode excitation on core offset is researched firstly. It is revealed that which modes can be significantly excited is strongly dependent on the mode fields matching between LP01 mode in SMF and LP1n mode in TCF, by which the dominant excited modes can be predicted and this method can be expanded to any two fibers with offset splicing. Based on the energy distributions of excited modes with/without considering interference among cladding modes, transmission spectra can be calculated by interference equations theoretically. By comparing with experimental results, it can be concluded that for kind of MZIs based on offset splicing, it is difficult to make the calculated results to be identical with experimental results due to the large number of modes excited, so an equivalent mode approach is proposed to solve this problem and verified by the temperature sensing experiment. In addition, dependence of mode excitation on probing wavelength or refractive index (RI) of surroundings, and effect of fiber parameters on signal shape are also studied. The MZI proposed here shows advantages of low cost, easy fabrication, no special splicing equipment required, and relative high sensitivity. Results shown here will provide valuable information for kind of MZIs based on core-offset splicing between TCF and SMF, and afford useful references for other kinds of in-line MZIs based on the interference between core and cladding modes.