An Infrared Ultra-Narrowband Intensity-based Plasmonic Sensor/Filter Based on Coupling Through Plasmonic Nano-Cavities

In this paper, an ultra-narrow band integrated refractive index sensor with high sensitivity is proposed that is based on a novel plasmonic nano-cavity made of gold which is located on top of a photonic waveguide. The nano-cavity consists of two metallic slots and two metallic nano-disks. Light is propagating through the photonic waveguide which is silicon nitride (Si
₃
N
₄
). The strong coupling from the photonic waveguide to the plasmonic nano-cavity leads to detection of small refractive index changes which is appropriate for medical applications. The structure presents a full width at half maximum (FWHM) of only 6 nm which is a great improvement in comparison with recent researches. There are a few resent papers that are intensity-based plasmonic sensor. In this article, we use the intensity changes at the output to detect small refractive index changes. This ultra-narrow band structure can be used as an ultra-sharp plasmonic filter as well. The ultra-high selectivity of this infrared plasmonic filter can be used in appropriate applications.