Simultaneous excitation of extremely high-Q-factor trapped and octupolar modes in terahertz metamaterials

Abstract

Achieving high-Q-factor resonances allows dramatic enhancement of performance of many plasmonic devices. However, the excitation of high-Q-factor resonance, especially multiple high-Q-factor resonances, has been a big challenge in traditional metamaterials due to the ohmic and radiation losses. Here, we experimentally demonstrate simultaneous excitation of double extremely sharp resonances in a terahertz metamaterial composed of mirror-symmetric-broken double split ring resonators (MBDSRRs). In a regular mirror-arranged SRR array, only the low-Q-factor dipole resonance can be excited with the external electric field perpendicular to the SRR gap. Breaking the mirror-symmetry of the metamaterial leads to the occurrence of two distinct otherwise inaccessible ultrahigh-Q-factor modes, which consists of one trapped mode in addition to an octupolar mode. By tuning the asymmetry parameter, the Q factor of the trapped mode can be linearly modulated, while the Q factor of the octupolar mode can be tailored exponentially. For specific degree of asymmetry, our simulations revealed a significantly high Q factor (Q>100) for the octupolar mode, which is more than one order of magnitude larger than that of conventional metamaterials. The mirror-symmetry-broken metamaterial offers the advantage of enabling access to two distinct high-Q-factor resonances which could be exploited for ultrasensitive sensors, multiband filters, and slow light devices.

Ultra-high Q terahertz whispering-gallery modes in a silicon resonator

“…Considering the large uncertainty for the material absorption of HRFZ-Si reported in the literature using THZ time-domain spectroscopy, in particular below 0.5 THz, the observed frequency dependent material absorption is well within the expectations [33]. Furthermore, the decrease in the Q factor by a factor of 3.5 from MDAK theory compared to the expected factor of 1.5 can be explained with higher radiation losses of the TE 22,9,0 WGM at about 420 GHz compared to the TE 36,12,0 WGM at about 620 GHz. The higher radiation losses, similar to bend losses for a waveguide, observed in the 0.4 THz frequency range compared to the 0.6 THz frequency range can qualitatively be explained with the larger ratio of the wavelength to the radius of the resonator.…”

“…Assuming a material absorption of 0.015cm −1 of the HRFZ-Si in the MDAK calculations reproduces the Q factor of the TE 36,12,0 WGM of 1.5 × 10 4 . At the same time, the MDAK calculations show an about 3.5 times lower Q factor of the TE 22,9,0 WGM. The discrepancy in the drop of the Q factor between the measurements (by a factor of about 4.3) and the numerical analysis (by a factor of about 3.5) can only be accounted for by a frequency dependent material absorption.…”

“…In this work, we report on the first experimental observation of ultra high Q THz WGMs with a Q factor of 1.5 × 10 4 for critical coupling at 0.62 THz in a 4 mm diameter spherical HRFZ-Si resonator. To the best of our knowledge, the achieved Q factor of 1.5 × 10 4 exceeds by far any other reported resonant structure in the THz frequency range [13][14][15][16][17][18][19][20][21][22][23]. Amongst the resonant structures with the highest Q factors reported in literature are, e.g., a bragg grating in a parallel plate waveguide (Q= 436) [13], a silicon photonic crystals slab (Q= 1020) [15], a plasmonic Fano metamaterial (Q= 227) [14], a 3D-printed hollow core bragg waveguide with defect layer (Q= 55) [16], and a HDPE disc WGM resonator (Q= 3000) [7].…”

Lattice‐Enhanced Fano Resonances from Bound States in the Continuum Metasurfaces

“…Controlling losses in metamaterials to obtain narrow resonances is important for photonic applications such as sensors, low‐power switches/modulators, and narrowband filters across the electromagnetic spectrum. These losses can be nonradiative or radiative and can be minimized by choosing favorable materials and an optimal metamaterial design.…”

Intrinsic Chirality and Multispectral Spin‐Selective Transmission in Folded Eta‐Shaped Metamaterials

“…The slight discrepancies in resonant frequencies and shallower depth of the resonances are possibly attributed to the fabrication tolerances. As shown in Figure c, two pronounced plasmonic resonances are clearly observed for both LCP and RCP incidence light at 44 and 72 THz, respectively, which is associated with the excitation of the fundamental modes in the eta‐shaped metasurface . The unfolded metasurface provides the expected nearly identical transmission of LCP and RCP light, which implies that there is no intrinsic chirality in the eta‐shaped metasurface.…”