Optical Tactile Sensor Based on Monolithically Integrated GaN Devices with PDMS/CaCO₃ Reflective Domes

With the rapid advancements in modern technology, the demand for advanced tactile sensors capable of precisely detecting the magnitude and position of the applied force has grown exponentially urgent. Optical methodologies in force sensing, despite offering exceptional sensitivity and swift responsiveness, often necessitate the alignment of external optics, hindering the pursuit of high-density integration and downscaling. In this work, a compact optical tactile sensor incorporating a GaN device with a deformable reflective dome is introduced. The device adopts a monolithic integration approach comprising a light emitter and four photodetectors. The PDMS dome, embedded with calcium carbonate powder, functions as a light modulator, effectively converting tactile signals into optical signals. The developed sensor exhibits a compact footprint of 4 × 4 mm2 and a measurement range from 0 to 1.1 N with a high resolution of 1.5 mN. Additionally, an encoding system is implemented to recognize the orientation of the applied force and wirelessly transmit the results to a user interface, revealing the potential use of the proposed optical tactile sensor in practical applications.