Surface Plasmon Resonance Characteristics of Optical Fiber Incorporated with Au Nano-Particles in Cladding Region.

A novel surface plasmon resonance (SPR) sensor based on specialty optical fiber having its cladding doped with Au nano-particles (NPs) was developed by modified chemical vapor deposition process. To optimize the SPR absorption and sensitivity of the fiber SPR sensor, effect of the fiber length (20 cm-90 cm) on sensing capability of refractive index (n = 1.418-1.448) was investigated. Absorption peaks appearing at 392 and 790 nm were due to SPR from Au NPs in the cladding region of the optical fiber. The SPR was found to occur at particular wavelengths around 390 nm for the corresponding refractive indices regardless of the length of the fiber, increased with the increase of the index. The measured SPR sensitivities (wavelength/RIU) of the fiber were estimated to be 407 nm/RIU, 217 nm/RIU, and 54 nm/RIU with the fiber lengths of 20 cm, 45 cm, and 90 cm, respectively. The SPR absorption intensity and FWHM decreased with the increase of the fiber length because the propagation loss of the signal through the fiber cladding region increased.