Polarization conversion in plasmonic nanoantennas for metasurfaces using structural asymmetry and mode hybridization

Peter R. Wiecha,Christian Girard,Vincent Paillard,Otto L. Muskens,Arnaud Arbouet,Leo-Jay Black,Yudong Wang

doi:10.1038/srep40906

Abstract

Polarization control using single plasmonic nanoantennas is of interest for subwavelength optical components in nano-optical circuits and metasurfaces. Here, we investigate the role of two mechanisms for polarization conversion by plasmonic antennas: Structural asymmetry and plasmon hybridization through strong coupling. As a model system we investigate L-shaped antennas consisting of two orthogonal nanorods which lengths and coupling strength can be independently controlled. An analytical model based on field susceptibilities is developed to extract key parameters and to address the influence of antenna morphology and excitation wavelength on polarization conversion efficiency and scattering intensities. Optical spectroscopy experiments performed on individual antennas, further supported by electrodynamical simulations based on the Green Dyadic Method, confirm the trends extracted from the analytical model. Mode hybridization and structural asymmetry allow address-ing different input polarizations and wavelengths, providing additional degrees of freedom for agile polarization conversion in nanophotonic devices.

Highlights

To cite this version: Peter Wiecha, Leo-Jay Black, Yudong Wang, Vincent Paillard, Christian Girard, et al
Optical spectroscopy experiments performed on individual antennas, further supported by electrodynamical simulations based on the Green Dyadic Method, confirm the trends extracted from the analytical model
When coupling is introduced to the antennas, the B →A conversion becomes weaker while the Y →X conversion increases. This behaviour is in perfect agreement with the theoretical considerations in the context of our analytical model, reflecting the fact of antenna-mode driven polarization conversion for asymmetric antennas (B →A) and PC induced by mode hybridization due to coupling in the symmetric case (Y →X)

Summary

Gap 29 nm

The maximum cross-polarized intensity I⊥ in Fig. 3(e) and the PC efficiency e →⊥ in Fig. 3(f) follow this trend. The parallel polarized scattering cross sections are labelled as σXX, σYY, σAA, and σBB, where the first subscript represents the incident polarization and the second the detection polarization To interpret these results and go beyond the analytical model, we perform numerical simulations using the Green Dyadic Method (GDM)[27,28] for which the dielectric response of gold was taken from Johnson and Christy[29]. This behaviour is in perfect agreement with the theoretical considerations in the context of our analytical model, reflecting the fact of antenna-mode driven polarization conversion for asymmetric antennas (B →A) and PC induced by mode hybridization due to coupling in the symmetric case (Y →X)

Conclusion

Methods