Relative humidity sensor based on FISM-SMS fiber structure coated with PVA film.

A relative humidity (RH) sensor based on femtosecond laser induced spiral micro-structured single mode-multimode-single mode (FISM-SMS) fiber structure was experimentally demonstrated. The spiral micro-groove ablated multimode fiber of the FISM-SMS fiber structure was coated with RH sensitive polyvinyl alcohol (PVA) whose refractive index varies as a function of ambient humidity level. Due to the FISM-SMS fiber structure highly sensitive to ambient refractive index, transmission spectrum of the RH sensor changed greatly at different ambient relative humidity. RH response of the sensor was tested by putting it into a homemade climatic chamber whose humidity level can be adjusted by a series of saturated salt solutions. Experimental results show that a RH sensitivity of ∼650 pm/%RH with linearity of ∼0.99 when humidity level varies from 35 % RH to 70 % RH. Besides, reversibility and stability make the sensor a good candidate for RH sensing. [ABSTRACT FROM AUTHOR]