Abstract
Both the localized resonance and excitation of spoof surface plasmon polaritons are observed in the terahertz transmission spectra of periodic subwavelength hole arrays. Analyzing with the coupled oscillator model, we find that the terahertz transmission is actually facilitated by three successive processes: the incident terahertz field first initiates the localized oscillation around each hole, and then the spoof surface plasmon polaritons are excited by the localized resonance, and finally the two resonances couple and contribute to the transmission. Tailoring the localized resonance by hole size, the coupling strength between spoof surface plasmon polaritons and localized resonances is quantitatively extracted. The hole size dependent transmittance and the coupling mechanism are further confirmed by fitting the measured spectra to a modified multi-order Fano model.
Highlights
To THz transmission through subwavelength hole arrays, their mode nature and quantitative analysis to their relation still remain unexplored
The coupled oscillator model provides an intuitive and quantitative method to investigate the original nature of Fano coupling between the localized resonance and Surface Plasmon Polaritons (SPPs) resonance[17,18], and their interactions with the external electromagnetic waves, which opens a door for the in-depth exploration on the THz transmission through subwavelength hole arrays
The quantitative analysis manifests that the strong coupling between SPP and localized resonances can be realized by tailoring the hole size to align the two resonances, which is essentially caused by the variation of the localized resonance for different hole sizes
Summary
Comparing to the results using fitted finite values of α1 and α2, we find that the change of fitted transmission spectra described by Eq (4) is almost indistinguishable (see Supplementary Fig. S1 online), which verifies that the SPP modes are not excited by the external E-field directly. The experimental transmittance spectra of the periodic hole arrays in the vicinity of SPP resonance frequencies of the [0, 1] and [1, 1] modes are fitted by Eq (5). The analytical methods can be extended to study the transmission enhancement in other wavelength regions
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