Analysis of graphene coated optical fiber for visible range refractive index sensing

In this work, graphene coated optical fiber structure has been exploited theoretically for refractive index sensing within visible operating region. A high refractive index polymer layer is also considered as a matching layer between graphene and the fiber core to generate lossy mode resonances in the desired spectrum. It is observed that multilayer graphene coating supports much sharper and narrower resonances than the graphene monolayer. Sensing characteristics with variation in number of graphene layers and polymer layer thickness are investigated with different polarizations of light. Calibration curves indicating change in resonant wavelength corresponding to the refractive index variation of sensing medium are also presented. It is observed that polymer layer act as the catalyst in enabling the structure to support resonances and shifting the operating region in visible spectrum. A maximum sensitivity of 300 nm/RIU for RI range of 1.33-1.40 is reported for p-polarization of light. It is believed that visible range operation of the proposed structure will make it cost effective and highly suitable for the development of bio-chemical sensors.