Investigation of cladding thicknesses on silver SPR based side-polished optical fiber refractive-index sensor

Abstract

A single mode optical fiber modified using side-polishing method is applied as a sensor based on surface plasmon resonance (SPR) principles. The SPR sensor was designed using side-polished optical fiber of which the cladding was symmetrically removed and coated with different thicknesses of embedded silver film. The amount of cladding removed was based on the insertion power loss during the polishing process, where losses were recorded at 0.65 dB corresponding to 20 μm thickness of remaining cladding and 1.8 dB refers to no cladding respectively. Finite Difference Time Domain (FDTD) simulation was used to investigate the effects of this configuration. The system has been constructed using different refractive indices of liquid. Silver thin layer thickness of 40 nm found to be the most desirable after it display better sensitivity in sensing mechanism. The application of 40 nm-thick Ag has been also coated on the fiber with no cladding, which shows higher sensitivity of ∼2166 nm/refractive index unit (RIU) and 208.333 nm/refractive index unit (RIU) using distilled water (n = 1.333) and alcohol (n = 1.345), respectively. The SPR dip transmission wavelength was recorded as ∼460 nm and ∼530 nm for both fiber conditions at active sensing area as 3 mm length operating at wavelength range of 300–1100 nm. The system has the advantages of being low-cost and applicable in bio-sensors.