Size effect of gold nanoparticles on optical microfiber refractive index sensors

Here we demonstrate an optical microfiber refractive index sensor based on the localized surface plasmon resonance of gold nanoparticles. The size effect of gold nanoparticles, meaning larger gold nanoparticles have a longer resonance wavelength, is observed through such a platform. The microfiber is fabricated by fixed flame-drawing method and then coated with gold nanoparticles by chemical method taking advantage of silane coupling agent. Broadband white-light is launched into the microfiber and the transmission spectrum is measured. A transmission dip is observed in the spectrum around the resonance wavelength. The dip red-shifts when the surrounding index increases, indicating its sensing potential for refractive indices. An average sensitivity of 218.67 nm/RIU is achieved and a redshift of more than 40 nm of the transmission dip is observed when the diameter of the gold nanoparticles goes from 20 nm to 100 nm.