High- $Q$ Multiple Fano Resonances Sensor in Single Dark Mode Metamaterial Waveguide Structure

We demonstrate multiple Fano resonances in an integrated single dark mode hybrid metamaterial waveguide structure, which consists of three gold cut wires placed on a dielectric board waveguide. With a symmetrical pattern, the design shows double sharp Fano peaks with high Q-factors of 950 and 216, which are attributed to the interaction between plasmon mode and quasi-guided modes. By breaking the structural symmetry, a quadrupole mode on middle vertical cut wire is excited and further results in multiple Fano resonances through both the diffracted waves and near-field coupling with bright- dark mode. Based on the above-mentioned properties, we show a high Q-factor refractive index sensor with figure of merit values of 330 and 281. Interestingly, these Q-factors of Fano peaks can be increased to 1357 and 361 to improve the sensing performance, by capping a silicon layer on the metal surface. This letter provides a way to obtain multiple high Q-factor Fano resonances, which can widen channels for fabricating device in biochemical sensing.