Fiber-tip dual-cavity Fabry-Perot sensor for weak magnetic-field measurement enabled by Vernier-like envelope modulation.

In this work, a fiber-tip weak magnetic-field sensor based on a dual-cavity Fabry-Perot interferometer is experimentally demonstrated. A miniature magnetic disk loaded on a polydimethylsiloxane (PDMS) diaphragm converts magnetic force into air-cavity modulation, while the finite PDMS thickness introduces an additional optical path to generate a Vernier-like envelope. By tracking the envelope valley, sensitivities of -3.963 and 2.937 nm/mT are achieved over 0-5 mT under repulsive and attractive loading, respectively. Hysteresis, baseline drift, FFT-derived optical path difference, and parallel-FBG-assisted temperature compensation are further evaluated.