Symmetry breaking induced mode splitting based on a plasmonic waveguide system

Mode splitting is numerically predicted in a symmetry breaking plasmonic waveguide system, which consists of a metal–insulator–metal structure with a square cavity. By introducing a baffle in the square cavity, the anti-symmetric waveguide mode is excited and the transmission properties analyzed in detail. Simulation results show that we can obtain a longer resonant wavelength by only increasing the length of the baffle. Using the relationship between the length h and resonant wavelength λ, we can get a resonant cavity with a quality factor (Q-factor) as high as Q ≈ 150. Furthermore, a compact 1 × 2 plasmonic wavelength demultiplexer is successfully achieved without increasing the total size of the structure, which is very conducive to integration. In addition, a refractive index sensor with a high sensitivity about 1320 nm/RIU is also realized. When the lateral symmetry of the structure is broken, the anti-symmetric waveguide mode splits into two high-order modes, and a typical Fano profile is also achieved. Our compact plasmonic structure may have potential applications in nanoscale optical switching, nanosensors, nanolasers, wavelength demultiplexers and slow-light devices in highly integrated optical circuits.