Flexible Liquid-Filled Fiber Adapter Enabled Wearable Optical Sensors

Wearable optical sensors are attracting intensive research interests owing to their advantage of high sensitivity, fast response, and immunity to electromagnetic interferences. However, tunable optical properties and reconfigurable sensor structures remain great challenges for the wearable optical sensors. Herein, flexible liquid-filled fiber adapters (FLFFAs), which are sensitive to mechanical stimuli, are demonstrated. The novel FLFFA consists of a soft liquid-filled tubing and two silica optical fibers. The liquid core bestows the FLFFA both tunability and reconfigurability in sensing performance. Deformation of the tubing through bending or pressing results in wavelength-insensitive changes in light transmission. By measuring the output intensity, the FLFFA based sensors achieve high angle resolution (0.18°) and low detection limit (0.7 mN) for bending and pressure sensing, respectively. The superior sensing properties together with mechanical flexibility and robustness enable real-time monitoring of finger joint motion, respiration, and wrist pulse. Benefiting from an LED charge-coupled device (CCD) signal recording system, a 4 × 3 keyboard is realized by simultaneously measuring the output signals of 12 FLFFAs. The FLFFA provides a promising method to detect subtle physiological signals and may find applications in healthcare devices, artificial skins, and sensor networks.