Highly Sensitive Humidity Sensor Based on a GO/Co-MOF-74 Coated Long Period Fiber Grating

A humidity sensor based on graphene oxide (GO)/Co-MOF-74 coated long period fiber grating is experimentally demonstrated. The long period fiber grating is prepared by CO
₂
laser direct writing method, with GO/Co-MOF-74 composite humidity sensitive material coated around the grating region. Combination of GO and Co-MOF-74 with porous structure can absorb water molecules effectively and improve the sensitivity. A high humidity sensitivity of 0.204 nm/%RH can be realized in the RH range of 30-50% as well as a value of 0.16 dB/%RH in the range of 50-90%, both with a linearity of more than 0.98. The proposed highly sensitive humidity sensor also shows a good performance in the stability and repeatability.