▎ 摘　　要

A novel photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) was proposed for detecting hydrogen sulfide (H2S) gas. Two single-mode fibers (SMFs), two multi-mode fibers (MMFs), and a PCF are sequentially fused to form a MZI with SMF-MMF-PCF-MMF-SMF structure. Titanium dioxide/amino-functionalized graphene quantum dots (TiO2/af-GQDs) composite is coated on the surface of the PCF as a sensing membrane. The fabricated sensing membrane is characterized by x-ray photoelectron spectroscopy, x-ray diffraction and scanning electron microscopy. Furthermore, the properties of the sensor are examined. The results show that a uniform TiO2/af-GQDs film with a thickness of 1 mu m is successfully coated on the surface of the PCF. The sensor has a sensitivity of 26.62 pm ppm(-1), showing good linearity and selectivity for H2S in the range of 0 similar to 55 ppm. The response time and recovery time are about 68 s and 77 s, respectively. The sensor has the advantages of low cost, small volume and simple structure, which is suitable for on-line monitoring of H2S.