Enhancing Sensor Strain Sensitivity via Simulated Reference Arm for Optical Harmonic Vernier Effect

This article presents a novel approach for enhancing the sensitivity of fiber optic sensors through the utilization of the simulated reference arm (SRA) technique and the optical harmonic Vernier effect. Unlike traditional methods that rely on physical reference arms, this approach achieves the Vernier effect by using a single interferometric fiber sensor, offering the advantage of adjustable sensitivity. Specifically, a multimode interferometer (MMI) is constructed using a few-mode fiber (FMF) as a sensing arm. Real-time implementation of the SRA is demonstrated, resulting in a strain sensitivity of up to −5.18 pm/
$\mu \varepsilon$
at the harmonic order of 0, which is 10.36 times higher than that of a standalone FMF-based MMI. Furthermore, as the harmonic order increases to 1, 2, and 3, the sensitivity improves to −10.45, −15.62, and −20.38 pm/
$\mu \varepsilon$
, respectively. The proposed sensor offers tunable sensitivity and cost-effectiveness, making it convenient for high-sensitivity measurements and monitoring applications.