High-Efficiency Fluorescent-Coupled Optical Fiber Passive Tactile Sensor with Integrated Microlens for Surface Texture and Roughness Detection

Integrating ZnS:Cu@Al₂O₃/polydimethylsiloxane (PDMS) flexible matrices with optical fibers is crucial for the development of practical passive sensors. However, the fluorescence coupling efficiency is constrained by the small numerical aperture of the fiber, leading to a reduction in sensor sensitivity. To mitigate this limitation, a microsphere lens was fabricated at the end of the multimode fiber, which resulted in a 21.585% enhancement in the fluorescence coupling efficiency. A passive, flexible mechanoluminescent (ML) tactile sensor (MLTS) was developed by embedding a fiber microsphere probe within a ZnS:Cu@Al₂O₃/PDMS film featuring a pyramid surface structure. The MLTS demonstrated exceptional pressure sensing capabilities, exhibiting rapid response times of 250 ms for loading and 200 ms for unloading, along with strong durability, surviving over 2000 cycles. It effectively distinguished Braille patterns and sandpapers of varying roughness by detecting the ML signals generated by the sensor's surface microstructures. Notably, this sensor operates without the need for external light stimulation, making it a promising candidate for application in photonic skin and robotic tactile perception.