Refractive index sensing based on Mach-Zehnder interferometer formed by three cascaded single-mode fiber tapers

We report the fabrication of a highly sensitive refractive-index sensor based on three cascaded single-mode fiber tapers, in which a weak taper is sandwiched between the two tapers to improve the sensitivity of the sensor. Experimental results show that the sensitivity of the device is 0.286 nm for a 0.01 RI change, which is about eleven times higher than that of the normal two cascaded tapers MZ interferometer. Such kind of low-cost and highly sensitive fiber-optic refractive index sensors will find applications in chemical or bio-chemical sensing fields.