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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.

The polarization states and orbital angular momentum (OAM) properties of light are of considerable importance for several aspects of high-precision optical measurements. In this work, we have investigated the properties of composited OAM beams propagating in a Bi4Ge3O12 crystal under an applied magnetic field and have demonstrated a magnetic field sensing method based on compositing of OAM beams using a Sagnac configuration. The polarization rotation can be projected into petal-like patterns by the rotation of the OAM beams. However, the accurate measurement of the rotation angles of the petal-like patterns of OAM beams remains challenging. Therefore, an image processing technique based on the Radon transform is explored to enable the accurate calculation of the rotation angle of the petal-like patterns of composite OAM beams under different magnetic fields. The rotation angle of these petal-like patterns is found to have a linear dependence on the magnetic field intensity, which means that the proposed system is appropriate for magnetic field sensing applications. Using this method, a magnetic field sensitivity of 28°/T has been achieved experimentally with a measurement error of 0.0123 T in a high-intensity magnetic field ranging from 191 to 3322 G for OAM beams with topological charge (TC) l=±1.