Matching long-period grating modes and localized plasmon resonances: effect on the sensitivity of the grating to the surrounding refractive index.

The sensitivity and dynamical range of an optical-fiber transducer consisting of a long-period grating coated with gold nanoparticles is investigated. For a grating with an 80 μm spatial periodicity, the resonances close to the turning point lie within the 450-900 nm spectral range. Employing a bottom-up production route, the localized surface plasmon resonance of gold nanoparticles is matched to the grating resonances; it is shown that this results in an increase in the refractive index sensitivity of the device. The device also shows increased dynamic range and enhanced refractive index sensitivity in water.