Fig. 1. Single optical microfiber enabled tactile sensor for simultaneous temperature and pressure sensing. (a) Schematic of the human skin inspired microfiber sensor. Schematic illustration of the (b) temperature and (c) pressure sensing mechanism. (d) SEM image of a bent microfiber. (e) Photograph of a flexible bending sensor. (f) Photograph of a sensor attached to a glass vial.

Fig. 2. Temperature responses of the sensor. (a) The effective refractive indices of supported modes as functions of microfiber diameter at 532 nm wavelength. (b) Transmission spectra at different temperatures. The upper inset and the lower inset show the measured higher-order mode intensity profile and calculated EH21 mode intensity profile, respectively. (c) Peak wavelength of EH21 mode as a function of temperature. The red circles and black triangles represent the heating and cooling process, respectively. T, temperature. (d) Repeatability of the sensor is tested by alternately switching the temperature between 40°C and 80°C.

Fig. 3. Pressure responses of the sensor. (a) Transmission spectra under various pressures. (b) The peak wavelength corresponding to the cutoff of high-order EH21 mode under various pressures. The standard deviation of the wavelength distribution is 0.4 nm. (c) The normalized intensities at 700 nm, 800 nm, and 900 nm, respectively, as functions of pressures. (d) Repeatability of the sensor to static pressure. The sensor response to dynamic pressure at (e) 500 Hz and (f) 1000 Hz, respectively.

Fig. 4. Simultaneous monitoring of temperature and the wrist pulse. (a) Photograph showing a single microfiber sensor for skin temperature and wrist pulse sensing, and the enlarged schematic diagram indicates the effect of temperature on the constriction and dilation of arterial vessels. (b) Wrist pulse waveform before and after exercise. (c) Typical wrist pulse waveform with measured distinguishable P-wave, T-wave, and D-wave peaks. (d) Typical spectral response of a microfiber sensor device directly above the artery of the wrist at room temperature, before and after exercise, and the infrared thermal image showing the temperature distribution of the wrist before and after exercise. (e) Comparison of the artery pulse pressure waveform variation with wrist temperature of 22.5°C and 40.0°C.