Tactile sensors with high softness and multisensory functions are highly desirable for applications in humanoid robotics, smart prosthetics, and human-machine interfaces. Here, we report a soft biomimetic fiber-optic tactile (SBFT) sensor that offers skin-like tactile sensing abilities to perceive and discriminate temperature and pressure. The SBFT sensor is fabricated by encapsulating a macrobent fiber Bragg grating (FBG) in an elastomeric droplet-shaped structure that results in two optical resonances associated with the FBG and excited whispering gallery modes (WGMs) propagating along the bent region. Benefiting from the different thermo-optic and stress-optic effects of FBG and WGM resonances, the pressure and temperature can be fully decoupled with a high precision of 0.2 °C and 0.8 mN, respectively. To achieve a compact system for signal demodulation, a single-cavity dual-comb fiber laser is developed to interrogate the SBFT sensor based on dual-comb spectroscopy, which enables fast spectral sampling with a single photodiode. We show that the SBFT sensor is capable of perceiving pressure, temperature, and hardness in touching soft tissues and human skins, demonstrating great promise for soft tissue palpation and human-like robotic perception.
Keywords: dual-comb spectroscopy; fiber Bragg gratings; optical devices; pressure-temperature sensing; tactile sensors; whispering gallery modes.