Design and Optimization of Tapered Optical Fiber Probes for SERS Utilizing FDTD Method

In this work, we report a strategy of Ag nanoparticle (Ag NP)-coated tapered optical fiber probes by finite difference time domain (FDTD) simulations. Investigation shows that the fiber-tip decorated Ag NPs has excellent electric field enhancement and confinement of light capabilities. Moreover, we demonstrate the effect of key parameters such as tip radius, conical angle, Ag NP size, and gaps between them on the field enhanced utilizing typical excitation wavelengths of 532, 633, and 785 nm. To further improve the electrical field effect, a noble metal substrate is introduced below the tip apex, which exhibits a higher field enhancement generated by tip-substrate coupling. The presence of the Au substrate does not lead to a significant change in the plasma characteristic peak of the probes at 490 nm. This study provides a useful reference for the fabrication of tapered optical fiber with plasmonic nanostructures and the design of robust tapered fiber-optic Raman sensors.