Enhanced THz Transmission by Bull's Eye Structure Integrated with a Concentric Gold Hemisphere

In this work, a hemispheric gold particle is introduced to the conventional bull's eye structure that enhances extraordinary optical transmission in the terahertz region. Transmission enhancement is a result of the coupling of surface plasmon polaritons generated by periodic grooves and localized surface plasmon resonances generated by the hemisphere particle. The maximum normalized-to-area transmission peak reaches 556 for the hemisphere-in-hole bull's eye structure, which is significantly higher than conventional bull's eye structure. Such a transmission property is insensitive to polarization direction. The physical mechanisms are thoroughly analyzed by geometric parameter optimization and electromagnetic simulations. The modified structure can reduce the number of grooves in need, thereby reducing the device area. This novel design can be instructive for future improvement of bull's eye applications.