Highly sensitive micro-hygrometer based on microfiber knot resonator

In this work, we experimentally demonstrated a microfiber knot resonator (MKR) for ambient relative humidity (RH) measurement. The microfiber device was manufactured by forming a ring from a low-loss microfiber, fabricated from a single-mode fiber (SMF) by using flame-heating technique. The resonator was successfully formed when a periodic output resonance spectrum was achieved. Without employing any coating hygroscopic material, the MKR was observed to highly sensitive to the variation of ambient RH ranging from of 30% RH to 94% RH. The proposed device is an extremely compact and fast response sensor, useful for a wide spectrum of industrial applications.