Guided‐Mode Resonances in All‐Dielectric Terahertz Metasurfaces

Abstract

The important parameters that describe a resonance feature are its intensity and spectral linewidth. For most practical applications, resonances with strong intensity and narrow linewidth are desirable. Higher resonance intensity provides better signal to noise ratio, while narrower linewidth signifies larger field confinement. However, most of the resonances are constrained by the trade-off between resonance intensity and linewidth. [20] This limits the possibility of independent tailoring of resonance features at will. On the contrary, guided mode resonance (GMR) can provide arbitrary resonance intensity and linewidth through geometrical design and selection of materials. [8] Due to this versatile nature of GMRs, they have found wide range of applications, including extremely high-Q filters, ultrabroadband reflectors, wavelength selective polarizers, and beam splitters. [8,[21][22][23][24][25][26][27][28][29][30][31] The GMR filter primarily comprises of a diffractive grating and an in-plane waveguide. The grating diffracts the incident light and couples it into the waveguide, which propagates as a guided mode. However, this guided mode is designed to be leaky, which then interferes with the free-space propagating electromagnetic wave to give rise to the GMRs. Through the selection of material, grating design, dielectric layer thickness, and angle of incidence, GMRs can provide a wide range of spectral features. Currently, the exploration of GMRs is limited to optical and radio frequency regions of the electromagnetic spectrum. However, terahertz (THz) technologies are attracting a lot of attention to cater to the challenges of meeting ever-increasing demand for highspeed wireless communications. [32] THz GMR devices could play a crucial role in communication applications due to its capability for constructing high-Q filters, polarization selective beam splitters, differentiators, integrators, and wavelength division (de)multiplexers. [8] Earlier reports on THz GMRs were realized through 1D grating elements on quartz substrate [33] and periodic metallic patterns on cyclo-olefin substrates. [34] Here, we experimentally demonstrate silicon-based all-dielectric metasurfaces that support GMRs at THz frequencies.The 2D metasurface, building block with periodic array of subwavelength silicon microstructures, simultaneously acts as the diffraction grating as well as the slab waveguide and hence enables the observation of GMRs. At oblique incidence, two frequency detuned GMRs are observed, which arises from two Coupling of diffracted waves in gratings with the waveguide modes gives rise to the guided mode resonances (GMRs). The GMRs provide designer linewidth and resonance intensity amidst a broad background, and thus have been widely used for numerous applications in visible and infrared spectral regions. Here, terahertz GMRs are demonstrated in low-loss, all-dielectric metasurfaces, which are periodic square lattices of silicon cuboids on quartz substrates. The silicon cuboid lattice simultaneously acts as a diffract...

Resonant Excitation Analysis on Asymmetrical Lateral Leakage of Light in Finite Zero-Contrast Grating Mirror

“…In Fig. 3(b), it can be seen that the resonant modes of the ZCG mirror split at oblique incidence, and every order-mode resonance pair splits into two branches of resonances due to the mode nondegeneracy [26], [27]. The mode degeneracy is broken as the incident light is deviated from the normal incidence, which permits interaction of the resulting differentiated modes with interesting consequences.…”

“…As the incident angle is varied in the range of ±5°, the locations of the two quasi-BICs in the shorter and longer wavelengths are almost kept the same at 0.74 μm and 0.88 μm, respectively. Unlike the HCG which supports only one symmetry-protected BIC mode [13], [27], [32], the ZCG mirror can support two symmetry-protected BIC modes due to the sublayer. In Figs.…”

Materials for Terahertz Optical Science and Technology

“…In the works discussed in Z. Ren et al, [12] and Y.-G. Jeong et al, [13] various devices based on microelectromechanical structures (MEMS) and vanadium dioxide (VO 2 ) interfaced tunable metamaterials are shown to actively modulate the THz waves through electrical/thermal controls. [16] A different class of low-loss metasurfaces fabricated with dielectric materials (see the review by R. T. Ako et al [17] ) with appropriate geometry can assist in sharp guided mode resonances with extremely high quality (Q)-factors (see the work by S. Han et al [18] ). Interfacing the graphene layer with metamaterials also enables an efficient modulation of resonant THz waves through voltage control (see the work on graphene metasurfaces from X. Chen et al [14] ).…”

“…The strong THz resonances with the combination of dielectric engineering in metamaterials enable sensitive molecule-specific detection capabilities by enhancing the resonant vibrational/ absorption peaks of the target bio/chemical molecules or any material systems, as reported in M. Seo and H.-R. Park. [16] A different class of low-loss metasurfaces fabricated with dielectric materials (see the review by R. T. Ako et al [17] ) with appropriate geometry can assist in sharp guided mode resonances with extremely high quality (Q)-factors (see the work by S. Han et al [18] ). Whispering gallery mode (WGM) resonators offer another exotic platform to realize high Q-factor resonances at THz frequencies that enable capabilities for single molecule sensing with high specificity for medical, chemical and security applications, as discussed in the works reviewed by S. S. Prabhu and V. G. Achantha.…”

Achromatic Dielectric Metasurface with Linear Phase Gradient in the Terahertz Domain

“…utilizing subwavelength structures. In terahertz frequency band, up to now, metasurface has resulted in the design of numerous terahertz devices such as terahertz metasurface holography, [3][4][5][6][7] terahertz metalens, [8][9][10][11][12] terahertz absorber, [13][14][15] terahertz beam rotator, [16] coding terahertz metasurface, [17] terahertz topological waveguide, [18] terahertz guided-mode resonances, [19] boundstate in the continuum, [20] terahertz beam steering metasurface, [21] etc. Even though some of metasurface based devices have similar functions near the design frequency, the intrinsic chromatic aberration [22] impedes the utility of these devices in splitter, which holds the output angle the same for frequencies from 0.6 to 1.1 THz.…”