Cylindrical vector modes based Mach-Zehnder interferometer with vortex fiber for sensing applications

We have proposed and demonstrated a cylindrical vector mode (CVMs) based Mach–Zehnder interferometer (MZI) in a vortex fiber (VF) for strain sensing. The VF has a coaxial structure supporting the fundamental mode of the HE11 mode in the center core and the first-order CVMs of TE01, HE21, and TM01 modes in the ring core, respectively. By applying a pair of separated microbend long period gratings (MLPGs), the HE11 mode is partially coupled to the CVMs and then combined for constructing an in-fiber MZI. Three separated interference spectra are observed distinctly corresponding to TE01, HE21, and TM01 modes, which exhibit a good linear response to the strain change. Among these three CVMs, the TE01 mode demonstrates the highest sensitivity of −2.41 nm/mε and temperature insensitivity feature. The low cross-sensitivity from temperature benefits the CVMs based MZI to be an ideal strain sensor without compensation, having potential applications of next-generation sensors in smart engineering structures.