Experimental comparison of the effect of the structure on MZI fiber gas sensor performance A compact refractive index (RI) sensor, based on Mach Zehnder Interferometer (MZI), was developed for high sensitive detection and measurement of gases using Single Mode Fiber (SMF), Photonic Crystal Fiber (PCF), and HollowCore Photonic Crystal Fibers (HCPCF). The device was constructed by placing a short stub of sensing element fiber between a leadin and a leadout single mode fiber (SMF) with an airgap at each interface. Three MZIs were fabricated using 4 mm stub of PCF, 10 xc2xb5m HCPCF and 20 xc2xb5m HCPCF as the sensing element, and performance of these sensors were compared. The gas sample was able to effectively fill the air gaps between fibers. Using PCF and HCPCF as the sensing element provides a great opportunity for gas sensing because of the possibility of a stronger interaction between the light and gas molecules. Additionally, gas molecules penetrate the cavities within the air holes of photonic crystal fibers. The resulting fiber sensors were able to measure the RI of the gas filled cavity and showed excellent sensitivity to helium, methane, and carbon dioxide. The highest RI sensitivity of 3210 nmRIU was demonstrated in the RI range of 1.0000347 xe2x80x93 1.000449 for a sensor with 4 mm length of 10 xc2xb5m HCPCF. The cyclic tests show great measurement repeatability of different gases. Response and recovery times were found for these MZIs. It was concluded that 20 xc2xb5m HCPCF sensor has the lowest and the PCF sensor has the highest responserecovery time. This study shows that sensors fabricated by the proposed method have good potential for detecting and quantifying pure gases. Additionally, they are highly sensitive to low percentages of methane and CO2 which is suitable for greenhouse gas measurement.

A Refractive Index Sensor Based on HShaped Photonic Crystal Fibers Coated with AgGraphene Layers An Aggraphene layerscoated Hshaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor with a Ushaped grooves open structure for refractive index (RI) sensing is proposed and numerically simulated by the finite element method (FEM). The designed sensor could solve the problems of airholes material coating and analyte filling in PCF. Two big airholes in the xaxis produce a birefringence phenomenon leading to the confinement loss and sensitivity of xpolarized light being much stronger than ypolarized. Graphene is deposited on the layer of silver in the grooves; its high surface to volume ratio and rich xcfx80 conjugation make it a suitable dielectric layer for sensing. The effect of structure parameters such as airholes size, Ushaped grooves depth, thickness of the silver layer and number of graphene layers on the sensing performance of the proposed sensor are numerical simulated. A large analyte RI range from 1.33 to 1.41 is calculated and the highest wavelength sensitivity is 12,600 nmRIU. In the linear RI sensing region of 1.33 to 1.36; the average wavelength sensitivity we obtained can reach 2770 nmRIU with a resolution of 3.61 xc3x97 10xe2x88x925 RIU. This work provides a reference for developing a highsensitivity; multiparameter measurement sensor potentially useful for water pollution monitoring and biosensing in the future