In this paper, a compact nanostructure is proposed that includes a metal insulator metal (MIM) waveguide with a metal wall and a side-coupled half-ring resonator. The transmission characteristics of the system are studied numerically by using the finite element method (FEM). The simulation results show that double Fano resonances can be produced in the structure, and the two Fano resonances can be controlled independently by two different half rings. The position and intensity of the Fano resonance peaks can be adjusted flexibly and easily by changing the refractive index of the filling medium. The waveguide is sensitive to the refractive index of the filling medium inside the resonator and the maximum sensitivity and figure of merit (FOM) are 1260 nm/RIU and 26,000 respectively. By adding two more half-rings below, four independently adjustable Fano resonances are obtained. The structure of this paper can be used as a sensor which can detect the glucose concentration, so it has a broad application prospect in biomedical and chemical sensing fields.

A plasmon structure based on a metal-insulator-metal (MIM) waveguide composed of three stubs (TSs) is proposed, and its transmission characteristics are studied numerically by the finite element method (FEM). The simulation results show that multiple plasmon-induced transparencies (PITs) with high transmission can be produced in the structure and can be tuned effectively. By adjusting the structure parameters, more high-order PITs with narrower window are generated. Furthermore, the proposed MIM waveguide is sensitive to the environment and the maximum values of refractive index sensitivity and figure of merit (FOM) are 1340 nm R−1IU−1 and 251/RIU, respectively. Multiple, adjustable and narrow PITs with high FOM can be induced in the proposed structure, which can be used in the fields of multi-channel filters, optical switches, storages, sensors, and so on.

Metal-dielectric-metal (MIM) waveguide coupling systems based on surface plasmon polaritons (SPPs) are designed and studied. The finite element method is used to simulate the transmission spectra of structures in the whole simulation process. One waveguide coupling system consists of an inverted T-shaped cavity with defect (ITD) and a waveguide with a metal wall. The filter band appears in the transmission spectrum due to the opposite direction of two Fano resonances. The filter band width and the filtering range can be tuned effectively by changing the structure parameters. In this system, the center frequency and bandwidth of the filter band are 1330 nm and 114 nm, respectively. The insertion loss and reflection loss are −1.41 dB and −16.89 dB, respectively. The optimization is carried out on the basis of the first system in order to improve the filtering performance. Optimized waveguide coupling system contains an ITD and a waveguide with a slot cavity. Electromagnetically induced transparency (EIT) and Fano resonance exist simultaneously, and the filter band is induced in the transmission spectrum. In this system, the center frequency and bandwidth of the filter band are 1412 nm and 120 nm, respectively. The insertion loss and reflection loss are −0.50 dB and −37.32 dB, respectively. EIT and Fano resonance can not only be regulated independently, but also be regulated simultaneously by changing the structural parameters. And the intensity of EIT and the width of the filter band can be manipulated with changes of the structural parameters. The transmission response of SPPs propagating in the structure can be adjusted dynamically. Moreover, these novel SPPs optical waveguide structures have good filtering efficiency and can meet different filtering needs. These results show that the proposed systems are promising for filter, slow light device and photonic device integration applications.

A plasmonic structure composed of a metal-insulator-metal waveguide, a stub cavity, a T-shaped cavity (T-SC), and a split-rectangular cavity (S-RC) is proposed and investigated using the finite element method. The results demonstrate triple Fano resonances in the transmission spectrum due to the interaction between cavities. The maximum sensitivity and figure of merit were 1600 nm RIU −1 and 14 455, respectively. The Fano resonance can be independently modulated by changing the structural parameters of the T-SC or S-RC, and a new Fano resonance can be generated by breaking the symmetry of the structure. Through the addition of three semi-ring cavities and a semi-disk cavity to the original structure, we obtained eight ultra-sharp and asymmetric Fano resonances, which improved the integration and performance of the structure. Therefore, the proposed device has potential applications in refractive index sensors, optical communication areas, and multi-control Fano switches.

A kind of dimer nanostructure similar to panda’s eye (P-E), consisting two center biased elliptical rings, is proposed in this paper. The finite element method is used to study the nanostructure with the vertical incident light. The structure exhibits high order magnetic modes and the magnetic modes intensity can be manipulated independently by changing the structure parameters. The intensities of the magnetic dipole and magnetic quadrupole modes can be controlled by changing the angle between two rings and the distance of two cavity centers, respectively. Moreover, when two circular cavities increase simultaneously, the intensity of the magnetic octupole mode increases accordingly. Fano resonance can be induced when the electric mode couples with the magnetic mode. When the radius of the left circular cavity decreases, triple Fano resonance is formed. And when the whole structure is rotated, quintuple Fano resonance can be formed. More interesting, when the radii of the circular cavities of the two elliptical rings increase to 50 and 55 nm, the nanostructure becomes crescent dimer, and the enhancements of magnetic field and electric field reach 38 and 390, respectively. The P-E structure has potential application value in multiwavelength surface enhanced spectroscopy and biochemical sensing.