Plasmonic Asymmetric Bull's Eye Resonator for angle-resolved color sorting and index sensing
Fan-Cheng Lin1, Kel-Meng See1*, Jer-Shing Huang1
1Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:徐凱明,
We present a novel design of 2D metallic grating, a plasmonic asymmetric bull’s eye resonator (PABER) for angle-resolved color sorting and index sensing. The PABER is composed of a set of non-concentric circular slots on a gold film with continuous azimuthal angle-dependent periodicity. Since the wavelength of surface plasmon of grating is depends on the periodicity, our PABER support a broadband surface plasmon that sorted along the azimuthal angles, whereas the optical range can be modulated by the radius increment and the displacement of circle center. We have performed dark-field scattering analysis on the PABER to study the optical responds. Polarization of white light source has been aligned to specific azimuthal angle in order to selectively excite the grating with chosen periodicity. The collected scattering spectra of each measurement exhibit two peaks corresponding to p-polarization of grating for small and large periodicity. As the azimuthal angle increases from 0 ° to 90 °, the two periods gradually merge, allowing for observation of mode coupling. We have also observed the higher order SPR modes for large periodicity. An analytical model is developed for the resonance in PABER. Our experimental results are in good agreement with FDTD simulations and analytical model. As an example of many possible applications, we demonstrate an environmental index-sensitive color distribution of PABER for index sensing. Our PABER may also find applications in surface plasmon-enhanced spectroscopy and non-linear wave-mixing.

Keywords: Surface plasmon resonance, Nanoslits, Extraordinary transmission, Color sorting