Plasmonic circular resonators for refractive index sensors and filters

A plasmonic refractive index sensor based on a circular resonator is proposed. With all three dimensions below 1 μm, the sensor has a compact and simple structure granting it ease-of-fabrication and ease-of-use. It is capable of sensing trace amounts of liquid or gas samples. The sensing properties are investigated using finite elements method. The results demonstrate that the plasmonic sensor has a relatively high sensitivity of 1,010 nm/RIU, and the corresponding sensing resolution is 9.9 × 10−5 RIU. The sensor has a relatively high quality factor of 35, which is beneficial for identifying each transmission spectrum. More importantly, the sensitivity is not sensitive to changes of structure parameters, which means that the sensitivity of the sensor is immune to the fabrication deviation. In addition, with a transmittance of 5% at the resonant wavelength, this plasmonic structure can also be employed as a filter. In addition, by filling material like LiNbO3 or liquid crystal in the circular resonator, this filter can realize an adjustable wavelength-selective characteristic in a wide band.