Fiber interferometer based on standard fiber spliced between two thin-core insertions

•A new fiber interferometer based on two short thin-core fiber insertions is presented.•Separate control of thin-core fibers adds flexibility in obtaining desirable spectra.•Optimum length of thin-core fiber section for creating interferometer is 0.3–0.8 mm. A new type of fiber interferometer based on two short thin-core fiber insertions with a section of standard fiber in between is proposed. The thin-core fiber insertions excite cladding modes and provide energy exchange between different fiber modes. We have simulated and measured transmission through a single thin-core fiber section. The standard fiber section is used to accumulate phase differences between core and cladding modes propagating through the structure. Transmission spectra are measured for various lengths of the interferometer. Separate control of thin-core and standard fiber insertions adds flexibility in obtaining spectra desirable for sensing applications.