The effect of metal layer microstructure on optical fiber SPR sensor: a simulation study

The performance of an optic fiber SPR sensor is affected by the optical property of the metal layer. The optical property of the metal layer is affected by the surface morphology and the grain structure of itself. In this paper, the optical property of metal film based on the Drude-Lorentz model is improved by employing the Fuchs-Sondheimer theory and the Mayadas-Shatzkes theory. In the new law, the surface roughness and the grain structure are taken into account to describe the permittivity of metal layer theoretically. Then the improved model is used to analyze the performance of the optical fiber SPR sensor. The results shows that the surface roughness and the grain structure of metal layer significantly affect the resonance properties of the sensor. Specifically, the surface roughness of metal film can change the resonance wavelength of the SPR sensor. When the surface becomes smooth, resonance wavelength of SPR will decrease. In addition, with the increasing of grain size, the depth of the SPR curve increases obviously, while the full width at half maximum of the sensor decreases a lot. It means that, for a certain metal layer, the effects of the surface roughness and the grain structure should be considered in SPR technique.