A fast response and highly sensitivity relative humidity sensor with polymer-coated micro-nano fiber Bragg grating

In this paper, we proposed a new approach to measured humidity by polymer-coated micro-nano Bragg grating. The FBG was written in a 21.85-μm –diameter micro-nano fiber by 244-nm UV laser. Humidity changed the force that acting on the micro-nano fiber, thus the bandwidth of the reflection spectra was introduced and humidity measurement was therefore realized. When the humidity increased, the linearity value was 99 % and the bandwidth changed 0.00312 nm/%. The linearity is 97% and 98% in the stages of humidity reduction in 90 to 65 %RH and 65 to 30 %RH, respectively.