▎ 摘　　要

A new U-shape panda polarization-maintaining fiber (PPMF) based microfiber interferometer coated with graphene oxide (GO) film was proposed and experimentally demonstrated for relative humidity (RH) sensing. Experimental results show that the U-shape sensor has refractive index (RI) sensitivity of 1692.5 nm/RIU in the RI range of 1.33 when the diameter of the taper waist is 10.08 mu m. The surface of the U-shape sensor was then modified chemically and coated with a thin layer of GO film (59.64 nm) for RH detection and the sensitivity is proportional to RH: as RH increases from 30% to 98%, the sensitivity increases from 0.111 to 0.361 nm/%RH and the response time is 0.28 s. In addition, the cross sensitivity to temperature, stability, reproducibility, and response/recovery time of the RH sensor were studied in detail. The proposed U-shape fiber RH sensor has advantage of high sensitivity, good reproducibility and fast response (0.28 s), which has potential application in areas requiring dynamic measurement of RH variations such as industrial product fabrication process control and breath state monitoring.