High Spatial Resolution Distributed Force Sensor Based on Excessively Tilted Fiber Grating

Distributed and quasi-distributed systems have found extensive applications across various fields. However, their development has been hindered by bulky and expensive demodulation systems and relatively low spatial resolution. We introduced a high spatial resolution distributed force sensor utilizing an excessively tilted fiber grating (ExTFG) encapsulated in PDMS, with the slow axis of the ExTFG oriented perpendicular to the PDMS plane. The transmission spectrum of the ExTFG exhibited differential changes due to variations in contact position and force. In this study, we explained the sensing principle using mode coupling theory and the PM-like characteristics of the ExTFG. A cost-effective optical sensing interrogator collected the transmission spectrum of the sensor, and a CNN-BiLSTM network predicted the contact position and force parameters from the collected spectral data. Experimental results demonstrated a contact position and force prediction resolution of 8.73 μm and 0.02 N, respectively, over a sensing length of 10 mm, significantly smaller than those of traditional distributed or quasi-distributed sensors. Compared to tapered optical fibers (TOF)-based distributed sensors, it offered comparable prediction resolution and a greater sensing length. This sensor exhibited excellent distributed force sensing capabilities and holds promise for applications in electronic skin, human-machine interaction, intelligent robotics, and other fields.