This paper presents a fiber-optic refractive index sensor based on the Mach-Zehnder interferometer(MZI) formed by splicing a section of endless singlemode photonic crystal fiber between two sections of conventional single-mode fibers.The relationship between the resonance wavelength shift and the refractive index is investigated.Experimental results show that the resonance wavelength shifts to the longer wavelength with the increase of the refractive index,and the sensitivity is 70.45 nm/RIU for...