Mode control and loss compensation of propagating surface plasmons

Plasmonic devices can be used to construct nanophotonic circuits and are very promising candidates for next-generation information technology. The functions of plasmonic circuits rely on the rigorous control of plasmon modes. Two different methods were proposed to control the propagation of surface plasmons (SPs) supported by Ag nanowires (NWs). The first one is modulating the beat period of the near-field distribution pattern, which can be realized by depositing Al₂O₃ layer or changing the refractive index of surrounding medium. The beat period increasing by 90 nm per nanometer of Al₂O₃ coating or by 16 Î1/4m per refractive index unit was obtained in experiments. The second one is introducing local structural symmetry breaking to realize mode conversion of SPs. Three typical structures including NW-nanoparticle (NP) structure, branched NW and bent NW were used to investigate the mode conversion. It’s revealed that the mode conversion is a scattering induced process. The lossy characteristic of SPs at optical frequencies typically limits the propagation length and hinders the further development of integrated plasmonic circuits. CdSe nanobelt/Al₂O₃/Ag film hybrid plasmonic waveguide was proposed to compensate the loss of SPs by using an optical pump-probe technique. Compared to the measured internal gain, the propagation loss was almost fully compensated for the TM mode. These results for mode control and loss compensation of propagating SPs are important for constructing functional nanophotonic circuits.