Surface Plasmon Resonance Studies In Two-dimensional Cavities

Because traditional optical devices are affected by the optical diffraction limit,they are greatly limited in terms of achieving compactness,integration,and adjustment of optical devices.Surface plasmons can overcome the optical diffraction limit,and surface plasmons are particularly important at this time.On the one hand,Surface Plasmon Polaritons(SPPs)are transverse magnetic waves formed by the collective oscillation of free electrons at the interface between metal and dielectric.The energy of SPPs has the largest electromagnetic energy at the metal interface,and it decays exponentially.On the other hand,SPPs also have strong local electromagnetic field enhancement characteristics,which provide the possibility for optical devices to manipulate and control light.The current research on metal surface plasmons can generate Fano resonance phenomenon,EIT effect,bright and dark mode,slow light effect and so on.Three similar cavities connected with waveguides are investigated through the finite difference time domain(FDTD)method and the coupled mode theory.Two fundamental surface resonance modes are demonstrated in the two simple cavities separately.Then two simple cavities are combined to form the third cavity.The fundamental resonant modes couple positively or oppositely to form coupled-mode resonances in the combined cavity.When the combined cavity structures are symmetric,the coupled-mode resonances lead to two transmission peaks.While the symmetry is broken with tens of nanometers displacements,the transmission peaks convert to dips.It is believed the Q value variation of coupled-mode resonances plays a key role in the conversion.When the structure is symmetric,the coupled-mode resonances in the upper and lower parts of the cavity have the same Q value and are degenerate.The superposition of them leads transmission peaks.While the symmetry is broken,the Q values of resonances in the upper and lower part of the cavity are different,leading to the degenerate coupled mode division.The superposition of the different Q-factor modes leads to the dips.The sensitive variation to the symmetry of structures can be used to control light-material interactions,optical switch,and improve the sensitivity of sensor devices.