Few-layer MOS2-deposited flexible side-polished fiber Bragg grating bending sensor for pulse detection

We demonstrate a flexible side-polished fiber Bragg grating (FBG)-based bending sensor involving the deposition of MoS
₂
onto the FBG fiber core, with a D-shaped zone of ~54 μm depth and ~15 mm length. The MoS
₂
overlay could enable the sensor a higher sensitivity to bending strain because of the overlay-induced additional refractive index changes in the evanescent field interaction with fiber gratings. The bending strain test shows that the developed sensor can achieve one order of wavelength shift higher than that of conventional bare FBG at larger bending deformation. Furthermore, the extracted subtle wrist pulse signal validates the great potential of MoS
₂
-based side-polished fibers as wearable sensors for human activity detection.