Comparison between one layer and bilayer surface Plasmon resonance optical fiber chemical sensor

Surface Plasmon Resonance (SPR) - based plastic optical fiber has been provided as a sensor to estimating the refractive index and then the concentration of specific chemical samples. Two configurations were suggested for a design. The first was through using a single layer of gold with a thickness of about 40nm deposited on a 10mm portion in the middle of plastic optical fiber. In the second configuration, a bilayer deposited on the fiber. This bilayer consisted of a gold layer with a thickness of about 30 nm and an aluminum layer with a thickness of about 30 nm. Both of these configurations utilized as a chemical sensor. The resonance wavelength for the bilayer-based sensor was higher than that of the single-layer sensor for all studied chemical samples. The highest resonance wavelength was for the salt-water solution with a concentration of 30%. For the salt-water solution with a concentration of 30%, the resonance wavelength with the bilayer-based sensor was 568nm while it was 540nm with the single-layer sensor.