High-sensitivity plasmonic refractive index sensor based on embedded gratings with triple self-reference characteristics

To enhance the sensitivity and precision in detecting the refractive index of substances in complex environments, we propose a surface plasmon resonance (SPR) sensor. This sensor features an embedded grating composite structure with triple self-reference characteristics. The design incorporates a gold nanograting encased within a magnesium fluoride (MgF 2 ) film, coupled with a gold thin film. This configuration enables the excitation of two localized surface plasmon (LSP) modes within the MgF 2 film, providing self-referential properties. The surface plasmon polariton (SPP) mode, excited by the grating coupling structure, penetrates the MgF 2 film and exhibits high sensitivity to analytes. Another SPP mode, which serves as a reference, interacts effectively with the substrate material, enhancing the sensor’s self-referential capabilities. This embedded grating structure facilitates high-sensitivity detection of both gas and liquid analytes, achieving sensitivities of up to 1222nmRIU −1 and 1269nmRIU −1 , respectively. The sensor’s three self-reference channels have sensitivities of 0, 0, and 16nmRIU −1 for gases and 0, 9, and 37nmRIU −1 for liquids, making it a valuable tool for precise and sensitive measurement of refractive indices under challenging conditions.