Electronic skin, a class of wearable electronic sensors that mimic the functionalities of human skin, has made remarkable success in applications including health monitoring, human-machine interaction and electronic-biological interfaces. While electronic skin continues to achieve higher sensitivity and faster response, its ultimate performance is fundamentally limited by the nature of low-frequency AC currents. Herein, highly sensitive skin-like wearable optical sensors are demonstrated by embedding glass micro/nanofibers (MNFs) in thin layers of polydimethylsiloxane (PDMS). Enabled by the transition from guided modes into radiation modes of the waveguiding MNFs upon external stimuli, the skin-like optical sensors show ultrahigh sensitivity (1870 kPa-1), low detection limit (7 mPa) and fast response (10 μs) for pressure sensing, significantly exceeding the performance metrics of state-of-the-art electronic skins. Electromagnetic interference (EMI)-free detection of high-frequency vibrations, wrist pulse and human voice are realized. Moreover, a five-sensor optical data glove and a 2×2-MNF tactile sensor are demonstrated. These initial results pave the way toward a new category of optical devices ranging from ultrasensitive wearable sensors to optical skins.

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A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from As 2 S 3 glass fibers and assembled into MKRs in liquid without surface damage. The measured Q factor of a typical 824 μm diameter ChG MKR is about 2.84 × 10 4 at the wavelength of 4469.14 nm. The free spectral range (FSR) of the MKR can be tuned from 2.0 nm (28.4 GHz) to 9.6 nm (135.9 GHz) by tightening the knot structure in liquid. Benefitting from the high thermal expansion coefficient of As 2 S 3 glass, the MKR exhibits a thermal tuning rate of 110    pm · ° C − 1 at the resonance peak. When embedded in polymethyl methacrylate (PMMA) film, a 551 μm diameter MKR retains a Q factor of 1.1 × 10 4 . The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.

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