High-Sensitivity Strain Sensor Based on Femtosecond Laser-Inscribed Groove- Type Multimode Fiber

In this article, we present a high-sensitivity strain sensor based on a femtosecond (fs) laser-inscribed groove-type multimode fiber (MMF) used as the center section of singlemode–multimode–singlemode (SMS) fiber structure. Unlike conventional SMS structures with homogeneous cylindrical MMFs, our design introduces multiple fs-laser-inscribed grooves into the MMF section, significantly enhancing strain sensitivity and also allowing for a more compact center section length of 10 mm. Simulation results indicate that the average mechanical strain within the groove-type MMF increases with groove depth. Experimental results further show that the strain sensitivity of the groove-type MMF formed SMS fiber structure reaches −21.23 pm/μϵ, representing a 10-fold improvement over a SMS fiber structure employing a non-grooved MMF (−2.04 pm/μϵ). Owing to its superior sensitivity and high fabrication precision, the proposed SMS fiber sensor shows good potential for high-accuracy strain measurement applications.