Engineering of evanescent field in plasmonic nanostructure integrated tapered optical fibers

Tapered optical fibers (TOFs) have mitigated the issue of exponential decrement of the evanescent field across the diameter of the cladding in conventional optical fiber; thereby finding its promising application in optical fiber-based sensors. TOFs have shown to be highly sensitive to the refractive index of its environment. Integrating Au nanostructures (AuNS) on tapered fiber can result in coupling of the evanescent field (EF); thereby enhancing the localized surface plasmon resonance effect.

The enhanced coupling of the EF with AuNS, depends on the uniformity of self assembly monolayer (SAM) on the surface of the fiber. The -SH group of 3-mercaptopropyltrimethoxysilane (MPTMS) helps to achieve this uniformity. The comparison between physical and chemical treatment of MPTMS to support optimized distribution of SAM of AuNS confirms that chemical treatment provides better control of gold distribution on the surface than physical adsorption. The results are confirmed by SEM images and UV/vis spectroscopy. The study will also show the correlation between SAM of AuNS fractals and EF coupling for the aforementioned treatments, which will enable efficient optical biosensors using this platform.