A Mach-Zehnder interferometric relative humidity( RH) sensor based on optical fiber tapers cascading with core diameter mismatched is proposed. The waist-enlarged fiber tapers are fabricated by two section of the dispersion compensation fiber
and a 6 mm graded-index multimode fiber( GI MMF) is cascaded by fusion splicing method
which form Mach-Zehnder interferometer. Fiber core diameter mismatched point and graded-index multimode fiber serve as optical couplers. When the external RH changes
the transmission spectrum energy of the sensor will be changed. The experimental results show that the peak power changes with respect to surrounding RH with good linearity. When the RH change in range of 35 %~ 95 % RH
sensitivity of the sensor is-0. 074 9 d B/% RH with linearity R2 of 0. 995. The proposed RH sensor has compact structure
high sensitivity
which makes it possible to be widely applied in RH measurement.