Visible-light fiber Bragg grating-based wearable optical sensor

In this work, we proposed, for what we believe to be the first time, a wearable optical sensor based on the higher-order harmonic fiber Bragg grating (FBG), which has the advantages of easy fabrication, visible window operation and cross-talk removal. The fifth-order harmonic Bragg grating was inscribed by use of the conventional C-band phase masks and excimer laser but resonated in the visible spectrum. The visible window FBG can not only significantly improve the bandwidth of utilization, but also endow the sensor with visual perception. As was encapsulated by the PDMS pad, the wearable FBG held the temperature and bending sensitivity of 7.16 pm/°C and 4 pm/deg, respectively. Furthermore, taking advantage of the abundant resonances in harmonic FBG, a sensitivity matrix was established based on the orchestration of fifth and second-order harmonic resonances to discriminate the cross-sensitivity between temperature and bending. Our research provides new sight for the future development of wearable optical sensors.