Effects of Fano Resonance on Optical Chirality of Planar Plasmonic Nanodevices

Abstract

The effects of Fano resonance on the optical chirality of planar plasmonic nanodevices in the visible wavelength range are experimentally observed and theoretically explained. The nanodevice consists of a nanodisk at the center with six gold nanorods with an orientation angle to exhibit optical chirality under dark-field illumination. The chiral response induced by the gold nanorods are affected by the presence of the nanodisk with different diameters which causes Fano resonance. An intriguing change to the opposite selection preference of different handedness of the circularly polarized light has been clearly observed experimentally. This change of the preference is understood based on the extended coupled oscillator model. Moreover, electrostatic analysis and the time-dependent simulations provide a further understanding of the phenomenon. The observed and understood effects of Fano resonance on optical chirality enables effective manipulation of chiral characteristics of planar subwavelength nanodevices.

Fano‐Enhanced Circular Dichroism in Deformable Stereo Metasurfaces

“…Consequently, the CD strength can be dramatically enhanced, as plotted in Figure 1g, which is much stronger than that induced by conventional Fano resonances with the same type of lineshapes. [31,53] To validate the proposed new mechanism, a 2D pattern arranged in a hexagonal lattice is first studied, which shows the same transmission upon LCP and RCP incidence, as plotted in Figure 2a. When the 2D patterns are transformed into twisted stereo metamolecules, Fano-like transmissions immediately arise in both cases of LCP and RCP excitations, as shown in Figure 2b.…”

“…[47] In conventional scheme, the LCP and RCP excited Fano resonances have similar lineshapes. [31,53] In the proposed mechanism, the Fano resonances have nearly "opposite" lineshapes, i.e., one with resonant peak and the other with resonant dip. As a result, the CD response based on the proposed mechanism is significantly enhanced in (g).…”

“…When the 2D patterns are transformed into twisted stereo metamolecules, Fano‐like transmissions immediately arise in both cases of LCP and RCP excitations, as shown in Figure b. Importantly, the two Fano resonances exhibit similar profiles but with different amplitudes, which induce clear CD response (Figure d) similar as the conventional Fano‐induced CD in planar chiral oligomers . In comparison, for the broad transmission peak around 2.5 µm (Figure b), the CD is very weak since no Fano resonance occurs.…”

“…In such an assumption, at the resonant wavelength, the LCP light excites a Fano resonance with a resonant dip while the RCP light excites a Fano resonance with a resonant peak. Consequently, the CD strength can be dramatically enhanced, as plotted in Figure g, which is much stronger than that induced by conventional Fano resonances with the same type of lineshapes …”

“…The profiles are plotted based on the general Fano formula method . In conventional scheme, the LCP and RCP excited Fano resonances have similar lineshapes . In the proposed mechanism, the Fano resonances have nearly “opposite” lineshapes, i.e., one with resonant peak and the other with resonant dip.…”