Abstract-Quasibound states in the continuum in terahertz free-standing metal complementary periodic cross-shaped resonators

Dejun Liu, Feng Wu, Lin Chen, Feng Liu

https://arxiv.org/abs/2007.08104

We numerically and experimentally achieve quasi-bound states in the continuums (BICs) with high-Q factors in the free-standing metal complementary periodic cross-shaped resonators (CPCRs) at terahertz (THz) frequencies. Such induced quasi-BICs arises from the breaking of the mirror symmetry of CPCRs. By properly tuning the asymmetric factor, the measured Q factor of quasi-BIC can reach 102, which is lower than the simulated Q factor of 166 due to the limited system resolutions. We also simulate the electric field magnitude and vector distributions at the quasi-BICs, where the out-phase alignment between the electric dipoles is found. The sharp quasi-BICs realized in this thin free-standing metal structure may immediately boost the performance of filters and sensors in terahertz wave manipulation or biomolecular sensing.

Abstract-Terahertz composite plasmonic slabs based on double-layer metallic gratings

Dejun Liu, Lin Chen, Xiaohu Wu, and Feng Liu

Sketch of the composite plasmonic slab (CPS). The slab consists of double-layer metal gratings and a dielectric film. (a) The side view of the CPS. (b) The 3D model of the CPS. (c) The image of the experimental sample of a single-layer metal (copper) grating.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-12-18212

One composite plasmonic slab with a broad bandgap (40%) is experimentally and numerically demonstrated in the terahertz (THz) region. The composite slab consists of double-layer metallic gratings and a dielectric film, which supports two resonant modes. Electric field vectors and charge distributions proved that the low-frequency resonant mode originates from the symmetric plasmonic mode, while the high-frequency resonant mode is induced by the hybrid mode of plasmonic and dielectric modes. Compared with the double-layer metallic grating, the inserted dielectric film significantly enhances the transmission of the transverse magnetic (TM) waves and induces Fano resonances. The near-field coupling between metal gratings and dielectric film can be manipulated by changing the thickness and the refractive index of dielectric films. We further demonstrated that the plasmonic bandgap can be manipulated by tuning the grating width. These results suggest that this composite plasmonic slab is promising in terahertz integrated components development such as a filter, polarizer, or sensor.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz composite plasmonic slabs based on double-layer metallic gratings

Dejun Liu, Lin Chen, Feng Liu

https://arxiv.org/abs/2003.04113

A composite plasmonic slab based on double-layer metallic gratings and a dielectric film is experimentally and numerically demonstrated in terahertz (THz) regions, which can support two resonance modes and then form a broad bandgap (40%). As compared to the double-layer metal grating, the dielectric film in composite THz slabs significantly enhances the transmission of the transverse magnetic (TM) mode. Electric field vector proved that the low-frequency resonance mode originates from the symmetric plasmonic mode and the high-frequency resonance mode is induced by the hybrid mode of plasmonic and dielectric modes. The inherently near field coupling between metal gratings and dielectric film has been analyzed by changing the structural parameters. We further demonstrate that by tuning the metallic grating width, the plasmonic bandgap can be manipulated. These results suggest that this composite plasmonic slab has great potential for use as a filter, polarizer, and sensor in THz regions.

Abstract-Terahertz Fano-like resonators based on free-standing metallic wire woven meshes

Dejun Liu, Borwen You, Toshiaki Hattori

https://arxiv.org/abs/2001.01965

Most periodic terahertz (THz) structures need a substrate to support; thus, additional absorption occurs, resulting in a low quality (Q) factor. Free-standing structures that do not require any holder or substrate show high levels of flexibility and stretchability and hence are well-suited for THz applications. In this work, a free-standing THz metal structure consisting of metallic wire woven meshes is proposed and demonstrated. Experimental and numerical results exhibit that this metallic mesh achieves a sharp Fano-like resonance dip, which has not been found in previous studies. Investigation results indicate that the high Q Fano-like resonance dip comes from the single-layer metal bent wire because of its bending effect. The resonance field longitudinally covers the input and output end faces due to the large field volume of the woven meshes and benefits from near-field sensing applications.

Abstract-Investigation of spectral properties and lateral confinement of THz waves on a metal-rod-array-based photonic crystal waveguide

Borwen You, Dejun Liu, Toshiaki Hattori, Tze-An Liu, and Ja-Yu Lu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-12-15570

Terahertz (THz) waves laterally confined in a 1 mm-thick microstructured planar waveguide are demonstrated on a free-standing metal rod array (MRA), and one apparent rejection band of a transmission spectrum, resembling the bandgap of a photonic crystal, is found in 0.1–0.6 THz. The visibility of the photonic bandgap in the spectral width and power distinction can be manipulated by changing the MRA geometry parameters, including the rod diameter, the interspace between adjacent rods, and the propagation length based on the interactive MRA-layer number. THz transmission ratio enhanced by a large interactive length is verified in 30 MRA layers due to the longitudinally resonant guidance of transverse-magnetic-polarized waveguide modes along the MRA length, which is critical to the interspace width of adjacent rods and the metal coating of the rod surface. For an MRA with respective rod diameter and interspace dimensions of about 0.16 and 0.26 mm, the highest transmission of the guided resonant THz waves are performed at 0.505–0.512 THz frequency with strong confinement on the metal rod tips and a low scattering loss of 0.003 cm−1.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement