Cascaded wavelength multiplexed refractive index sensors in optical fibers based on surface plasmon resonances

Surface plasmon resonance (SPR) based cascaded wavelength multiplexed fiber-optic sensors provide immense scope for multi-channel and multi-analyte detection benefiting from all the advantages prerogative to single-channel fiber-optic sensors. This work describes the numerical simulations carried out for performance analysis of SPR based refractive index (RI) sensor implemented in cascaded dual- and triple-channel fiber-optic configurations using thin films of Ag, Cu, and Au as plasmonic metals and ZnO and Si as high RI overlayers. A dual-channel sensor is simulated using Ag and Cu/ZnO layers in two well-separated sensing channels on a multimode optical fiber, while a triple-channel sensor is studied using Ag, Cu/ZnO, and Au/Si in the three sensing channels. Due to different SPR resonance wavelengths of Ag, Cu, and Au, distinct sets of SPR spectra are obtained when the sensor response is analyzed by varying analyte RIs circumscribing different sensing regions of the cascaded fiber-optic probe. This feature furnishes an efficient option for easy tailoring of operating range of the sensor desired for different applications. The reported results provide promising perspectives for in-line sensing applications to analyze different constituents of the mixtures of biomolecules, clinical samples, petroleum products, and others.