Enhanced Fiber Long-Range Surface Plasmon Sensing Enabled by Resonance Coupling to Surface Plasmon Polaritons

A tunable fiber optic (FO) long-range surface plasmon (LRSP) sensor with strong coupling is developed and demonstrated theoretically in this article. The sensor consists of a square lattice array of Ag nanodisks resting on the FO end face. Utilizing nanodisks with small diameters leads to the pronounced excitation of two distinct and independent resonant modes: surface plasmon polaritons (SPP) and LRSP. A systematic investigation is performed to evaluate the sensing performance and capabilities of the sensor, focusing on its bulk and surface sensitivity. Significantly, the LRSP mode demonstrates high sensitivity and favorable linearity in response to refractive index (RI) changes, with an exceptionally high figure of merit (FOM). On the contrary, the SPP mode is regarded as an ideal self-referencing mode due to its immunity to RI fluctuations. The enlargement of nanodisks diameters results in a swift redshift in the LRSP wavelength, leading to a strong coupling with the SPP mode. This coupling facilitates the transfer of electric fields within the SPP mode, promotes sensing capabilities, and enables the realization of dual-channel sensing functionality. The occurrence of strong coupling phenomena along with the use of FO substrates provides an innovative option for achieving multifunctionality and miniaturization in sensor platforms. A tunable fiber optic long-range surface plasmon sensor strongly coupled with surface plasmon polaritons is proposed which features dual-channel, self-referential sensing with high bulk and surface sensitivity, figure of merit, and noise immunity and provides an innovative option for achieving multifunctionality and miniaturization in sensor platforms.image (c) 2024 WILEY-VCH GmbH