Optical fiber relative-humidity sensor with evaporated dielectric coatings on fiber end-face

• Multilayers construction was used to optimize the reflected spectrum.
• The porous sensor was fabricated in batch volume by EB-PVD process.
• The sensor shows promising prospect in the lower humidity measurement.
• The sensor has a faster response time than some of optical fiber RH sensors.

An optical fiber relative-humidity sensor (OFRHS) with evaporated dielectric coatings is proposed and demonstrated. The sensitive coatings, composed of multilayers of Ti3O5 and SiO2, form an extrinsic Fabry–Perot cavity on the distal end of the multimode fiber. As the effective refractive index of the porous coatings were correlated with the change of ambient Relative-humidity (RH), which will at last result in the shift of interference fringe. By monitoring the drift of reflected interference fringe under different RH levels, the information about RH of the environment under test can be extracted. Experimental results show that the average sensitivity is 0.43 nm/% RH when environmental RH changes from 1.8% RH to 74.7% RH. The proposed sensor was proved to be high repeatability, little hysteresis and especially highly sensitive to lower moisture measure.