Fiber optic index sensor enhanced by gold nanoparticle assembly on long period grating

The sensing performance of long period grating (LPG) in integration with colloidal gold nanoparticles (LPG-AuNPs) is investigated. An LPG coupled with a higher cladding mode of LP0,10 is fabricated on single mode fiber (SMF) with higher sensitivity to refractive index compared with lower cladding modes such as LP0,2, LP0,3 and LP0,4 via symmetric CO2 laser irradiation. A bilayer of poly (allylamine hydrochloride) (PAH) and gold nanoparticles is deposited on the grating portion via layer-by-layer self-assembly technique. It is found that the sensitivity is increased from 460 nm/refractive index unit (RIU) to 759 nm/RIU using the LPG-AuNPs.