Thin and soft optical tactile sensor for highly sensitive object perception.

Tactile sensing is essential for enabling safe and reliable interaction in robotics and wearable systems. Among various approaches, optical tactile sensors are particularly attractive due to their immunity to electromagnetic interference and inherently high spatial resolution. However, existing optical solutions, especially vision-based tactile sensors, typically depend on complex optical assemblies involving lenses and cameras, leading to bulky, rigid, and alignment-sensitive systems. Here, we present a thin, compact, and compliant optical tactile sensor with an alignment-free architecture. The proposed sensor captures deformation-induced variations in speckle patterns generated within a soft silicone medium, from which tactile information is inferred using a data-driven model. Experiments demonstrate a spatial resolution better than 20 µm and a force measurement precision below 40 mN. Notably, contact position, applied force, and ambient temperature are simultaneously estimated from a single speckle observation, demonstrating inherent multimodal sensing capabilities and robustness to thermal drift. To validate its practical utility, we integrate the sensor into a robotic gripper, achieving classification of nine engraved surface patterns with an accuracy of 93.33%. This speckle-based sensing paradigm offers a compact, easily manufacturable, and mechanically compliant platform, providing a promising solution for next-generation soft robotic and wearable haptic systems.