Tunable plasmonic substrates with ultrahigh Q-factor resonances.

Precisely tailored plasmonic substrates can provide a platform for a variety of enhanced plasmonic applications in sensing and imaging. Despite the significant advances made in plasmonics, most plasmonic devices suffer critically from intrinsic absorption losses at optical frequencies, fatally restricting their efficiency. Here, we describe and engineer plasmonic substrates based on metal-insulator-metal (MIM) plasmon resonances with ultra-sharp optical transmission responses. Due to their sharp transmission spectrum, the proposed substrates can be utilized for high quality (Q)-factor multi-functional plasmonic applications. Analytical and numerical methods are exploited to investigate the optical properties of the substrates. The optical response of the substrate can be tuned by adjusting the periodicity of the nanograting patterned on the substrate. Fabricated substrates present Q-factors as high as ∼40 and refractive index sensing of the surrounding medium as high as 1245 nm/RIU. Our results indicate that by engineering the substrate geometry, the dielectric thickness and incident angle, the radiation losses can be greatly diminished, thus enabling the design of plasmonic substrates with large Q factor and strong sensitivity to the environment.