Photonic crystal fiber based M-Z interferometer for refractive index measurement

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 a MZI with interference length of 3.2 cm as the refractive index ranges from 1.34 to 1.384.To enhance the coupling coefficient between the interference field and the refractive index,the interference beam of the MZI was etched.The refractive index sensitivity has been increased up to 198.77 nm/RIU after being etched,which is 2.8 times of the aforementioned MZI.In addition,such a sensor is insensitive to temperature with a sensitivity of 0.001 9 nm/℃ as the temperature ranges from 30 ℃ to 100 ℃.Therefore,such a MZI can overcome the temperature cross-sensitivity when it is used for the refractive index measurement,which offers an alternative device in chemical and biology fields.