Simultaneous measurement of temperature and relative humidity using a dual-wavelength erbium doped fiber ring laser sensor

A fiber ring laser sensor setup utilizing fiber Bragg gratings (FBGs) for simultaneous measurement of ambient temperature and relative humidity (RH) is presented. Two FBGs are incorporated as tunable filters for a dual-wavelength laser emission, where one FBG was coated with polyimide (PI) in order to achieve sensitivity to RH changes, while the other bare FBG was used for temperature sensing. An increase in RH would induce a strain on the grating, which results in a variation in the resonance wavelength of the PI-coated FBG. This causes a shift in the laser emission wavelength. Being insensitive to RH changes, the bare FBG was employed to measure temperature. The dual-wavelength fiber ring laser sensor created, and thus allows to determine simultaneous measurement of RH and temperature. The RH sensitivities observed by the PI-coated FBG to RH and temperature are 3.6 pm/%RH and 12.15 pm/°C. The temperature sensitivity of the bare FBG was observed to be 9.6 pm/°C. The main advantage of the proposed setup is an optical signal to noise ratio (OSNR) higher than 55 db 3 dB bandwidth less than 0.02 nm, which points out efficient capabilities for both precise sensing and remote detection applications.