Multimode interferometer based on no-core fiber with GQDs-PVA composite coating for relative humidity sensing

Abstract

Abstract A simple fabrication multimode interferometer (MMI) with graphene quantum dots (GQDs) and polyvinyl alcohol (GQDs-PVA) composite for relative humidity (RH) measurement is proposed and verified in this letter. The MMI includes two sections of single-mode fiber (SMF) and a length of 1.5 cm no-core fiber (NCF) is spliced between two sections of SMF, one of the splicing point is normal fused and the other splicing point is offset fusion splicing. The GQDs-PVA composite is prepared using a magnetic stirrer, and then is transferred to the surface of NCF by dip-coating machine. Refractive index of GQDs-PVA composite decreases with the increase of RH values caused by porous surface and water absorption characteristics of GQDs-PVA nanoparticle, which will lead to changes in the peak intensity of the interference spectrum. Experiment is executed at room temperature and the results indicate that the resonance intensity would decrease and the total intensity reduction of the interference spectrum was −20.473 dB with the measurement range changing from 38.8%RH to 88.65%RH. In addition, the proposed sensor presents good reversibility and repeatability. In a whole, the proposed sensor has simple structure, small size, low cost, high sensitivity and great repeatability.