Chiral hybrid waveguide-plasmon resonances.

We investigate the chiroptical responses of the hybrid systems consisting of metal-insulator-metal (MIM) gammadion arrays on top of a dielectric slab waveguide. We demonstrate that both the transverse magnetic (TM) and transverse electric (TE) waveguide modes could be coupled to the antisymmetric localized surface plasmon resonances (LSPRs) of the individual MIM-gammadions, leading to the formation of narrow hybrid waveguide-plasmon resonances (WPRs), of which the TM-WPR is less dependent while the TE-WPR is highly dependent on the handedness of the incident light. Associated with the excitation of the TE-WPRs, strong negative and positive circular dichroism (CD) peaks with high quality factors could be obtained on the short-wavelength and long-wavelength side of the LSPRs of the MIM-gammadion, respectively. Moreover, we show that the variation on either the lattice period or slab waveguide thickness allows for easily tuning the TE-WPRs based CD peaks over a relative wide spectral range. Our proposed hybrid system provides tunable and strong CD responses with narrow linewidth, which may have applications in chiral selective imaging, chiral plasmonic bio-sensing and spectroscopy.