Gelatin-coated long period fiber grating humidity sensor with temperature compensation

We propose a gelatin-coated long period fiber grating humidity sensor which has temperature compensation for low-error humidity detection. The output spectrum shows three resonance dips. The dip caused by gelatin-coated grating has humidity sensitivity of 0.09 nm/%RH and temperature sensitivity of 0.15 nm/°C. Another two dips caused by PDMS-coated grating have almost no response to humidity, which can be used for temperature compensation under low temperature and high temperature range, respectively. We come up with a coefficient matrix and experimentally obtain the humidity and temperature sensitivity of both resonance dips, thus temperature and humidity can be demodulated.