Plasmon-induced transparency in twisted Fano terahertz metamaterials

Abstract

We investigate the effect of tweaking the quality (Q) factor of split ring resonators in a coupled state, giving rise to plasmonic induced transparency (PIT) which has two distinct, individually engineered resonance modes. The Q factor and the amplitude of each resonance are tuned by twisting them mutually in the unit cell consisting of a subradiant and a superradiant resonator. We experimentally observe that introducing a gradual twist in the three U-shape resonators has a dramatic impact on the PIT spectral response, leading to the disappearance of the transparency peak beyond a certain critical degree of twist. This mainly happens due to the change in the in-plane coupling between the resonators as well the variation in coupling of the twisted resonators with the incident electric field. Further investigation based on the Fano model provides good agreement with the experimental results. The scheme presented here for controlling the Q factor of each resonator in the coupled regime is a unique way to tune the PIT response in terahertz metamaterials and can be easily scaled across the entire electromagnetic spectrum.

Active control of electromagnetically induced transparency analogue in terahertz metamaterials

“…In particular, optical tuning of metamaterials has attracted growing interest in the terahertz regime due to its ultrafast modulation speed and on-to-off switching capability [26][27][28][29][30] . However, so far the EIT effect in most metamaterials can only be tuned passively by varying the geometrical parameters of the resonator structures [32][33][34][35][36][37][38] . Only cryogenic-temperature-dependent EIT metamaterials have been reported recently 39 .…”

PIT-like effect in asymmetric and symmetric C-shaped metamaterials

“…And it is likewise expected that when two particles (be they similar resonant frequency and different Q-factor) are coupled into a plasmonic molecule, the resonant modes will hybridize and form super-modes and sub-modes. Similarly, a crucial rule in design of the electromagnetically induced transparency (EIT)-like effect structures is that the chosen unit cell can excite two resonance modes with exactly identical resonance frequency but significantly different quality factors (Q-factor) [22,23], namely a narrow high-Q mode and a broad low-Q mode. The PIT spectral response is therefore a result of coupling between a low-Q (superradiant) resonator and a high-Q (subradiant) resonator [8] in a manner of destructive interference.…”

“…To satisfy the requirements for the PIT design rule described above, the RCR is designed with long length and serves as the high-Q mode with a narrow spectral linewidth, while the LCR has short length, generating a broad spectral linewidth (as the low-Q mode) because of a larger dipolar moment and hence a stronger coupling with the free space radiation [13,23]. And notice that the length of LCR is slightly shorter than the RCR, leading the RCR to a higher resonant frequency.…”

“…For example, a series of micro-and nano-structures such as cut wires [9], split-ringresonators (SRRs) [8,[9][10][11][12][13], SRR combines with nano-rods [14], optical dipole antenna [15], coupled waveguide micro-resonators and other multi-layer structures [16,17] have been theoretically and experimentally demonstrated that the EIT-like effect can be realized in metamaterials via destructive interference between different excitation pathways that are closely related to the symmetry breaking of the structures [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. And it was considered that the asymmetry is a prerequisite for the plasmonic EIT from the mostly reported works; in its absence, only a single absorption peak is visible, without any sign of an EIT-like effect, because of no evident coupling between bright and dark modes.…”

Polarization-independent and angle-insensitive electromagnetically induced transparent (EIT) metamaterial based on bi-air-hole dielectric resonators

“…To be more specic, a broad (low Q-factor) superradiant mode and a narrow (high Q-factor) subradiant mode with similar resonant frequencies need to be excited simultaneously. 7,17,18 Thus, the coupling between these two modes can induce the EIT effect. This approach is much easier for the realization of the EIT effect than that of the bright-dark model.…”