Tunable Nanosensor Based on Fano Resonances Created by Changing the Deviation Angle of the Metal Core in a Plasmonic Cavity

Independently tunable Fano resonances in a metal-insulator-metal coupled cavities system

Herein, multiple Fano resonances with excellent ability to be tuned independently are produced in a sub-wavelength metal-insulator-metal system. The input and output waveguides are separated by a metal gap, and a stub and an end-coupled cavity are placed below and to the right side of the input waveguide, respectively, as discrete states. Owing to the mode interferences, double ultra-sharp and asymmetric Fano resonant peaks are observed in the transmission spectrum. Successfully, the basic structure is extended by two extra rectangular cavities, giving rise to four Fano resonances with high refractive index sensitivity and figure of merit. Due to the discrete modes of Fano resonances from different coupling cavities, their resonant wavelengths can be controlled independently, which can provide greater flexibility for tuning Fano resonances. The performances of the proposed structure are investigated by both the finite-difference time-domain method and the multimode interference coupled-mode theory. It is believed that the research can provide important guidance in designing Fano resonance structures, and the proposed structure has a wide application in sensors, switches, and nano-photonic integrated circuit devices.

Magnetic-field sensor with self-reference characteristic based on a magnetic fluid and independent plasmonic dual resonances

A magnetic-field sensor with self-reference characteristic based on metal-dielectric-metal (MDM) plasmonic waveguides and a magnetic fluid (MF) is proposed and theoretically investigated. Independent dual resonances are supported by the coupled resonator-waveguide system. The physical mechanisms of dual resonances are analyzed by the temporal coupled-mode theory. The transmission response to an external magnetic field is explored by using the remarkable tunability of the refractive index of the MF. Based on the different dependence of two resonances on the external field, a magnetic-field sensor with self-reference characteristic is achieved. The magnetic-field nanosensor shows an excellent performance with a high sensitivity of 27 pm/Oe, i.e., 270 pm/mT. The proposed sensor takes advantage of the refractive-index tunability of the MF and the compactness of the MDM waveguide structure. This research may open new opportunities to design nanoscale magnetic sensors with good performance.