A sandwich structure of single-mode fiber(SMF)-seven-core fiber(SCF)-SMF based on the Mach-Zehnder interferometer(MZI)principle is designed

especially in the cascade fusion area

the strong coupling between SCF and SMF is used to realize torsional sensing detection

and the torsional sensing characteristics of this structure are compared horizontally under three different SCF lengths of 1.5

2.0 and 2.5cm.A simple model is constructed and simulated by multiphysics coupling software

and when the strongly coupled SCF is twisted the light field intensity in the fiber changes

experimental results show that the structure can achieve directional torsion detection

that is

when the structure is twisted clockwise

the subsidence peaks and troughs of the spectrum move to the long wavelength direction.For counterclockwise twisting

the subsidence peaks and troughs of the spectrum shift to the short wavelengths direction.In addition

the sandwich structure has a significant change response in the light intensity-torsion test

and the maximum sensitivity of the structure can reach 0.0055dB/(°) after parameter quantization.The structure is simple to fabricate and low in cost

and has a good application prospect in the study of mechanical vector mechanics.