Plug‐and‐Play Polarization‐Controller‐Free All‐Fiber Optical Vortex Interferometer

ABSTRACT Optical vortex interferometers (OVIs) linearly map phase variations to the rotation of interferograms, demonstrating immense potential in high‐precision metrology. However, free‐space OVIs are hindered by cumbersome coaxial alignment, while existing all‐fiber architectures rely heavily on polarization controllers to maintain high‐purity vortex states, severely limiting their plug‐and‐play capability and engineering reliability. Here, we propose a polarization‐controller‐free, plug‐and‐play all‐fiber OVI. At the hardware level, a mode‐selective coupler is utilized to excite higher‐order modes within the fiber and accomplish interference, thereby eliminating free‐space coaxial alignment. At the physical mechanism and software demodulation levels, this paper reveals the “intensity redistribution” phenomenon and the trajectory degradation mechanism of the corresponding azimuthal complex spectrum in the complex plane during interference involving impurity modes, and accordingly proposes a generalized azimuthal complex spectrum demodulation algorithm. Crucially, our results demonstrate that even under a marginal 2% impurity, the proposed algorithm enhances phase measurement accuracy by nearly two orders of magnitude compared to standard methods. As a proof‐of‐concept, the system achieves a normalized temperature sensitivity of 36.53 rad/() in temperature sensing without requiring manual polarization tuning. This work innovatively shifts the hardware calibration burden to the underlying analytical algorithm, significantly enhancing OVI feasibility for on‐site and industrial deployment.