Abstract-Extraordinary sensitivity enhancement by metasurfaces in terahertz detection of antibiotics

Lijuan Xie,

Weilu Gao,

Jie Shu,

Yibin Ying

& Junichiro Kono

http://www.nature.com/srep/2015/150302/srep08671/full/srep08671.html?WT.ec_id=SREP-639-20150303

We have detected trace amounts of molecules of antibiotics (kanamycin sulfate) dispersed on metasurfaces with terahertz (THz) spectroscopy. Utilizing the extraordinary optical transmission resonance of an array of square-shaped slits on a silicon substrate at ~0.3 THz, we were able to monitor varying concentrations of kanamycin sulfate as low as ~100 picogram/L. In contrast, the lowest detectable concentration of kanamycin sulfate on silicon without any metallic structure was ~1 gram/L. This dramatic ~10¹⁰ times enhancement of sensitivity is due to the near-field enhancement of THz electric fields by the metamaterial structure. This result thus demonstrates the power and usefulness of metamaterial-assisted THz spectroscopy in trace molecular detection for biological and chemical sensing as well as for food product quality and safety inspection and control.

Abstract-High-Q terahertz Fano resonance with extraordinary transmission in concentric ring apertures

Jie Shu, Weilu Gao, Kimberly Reichel, Daniel Nickel, Jason Dominguez, Igal Brener, Daniel M. Mittleman, and Qianfan Xu  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-4-3747

Optics Express, Vol. 22, Issue 4, pp. 3747-3753 (2014)

We experimentally demonstrate a polarization-independent terahertz Fano resonance with extraordinary transmission when light passes through two concentric subwavelength ring apertures in the metal film. The Fano resonance is enabled by the coupling between a high-Q dark mode and a low-Q bright mode. We find the Q factor of the dark mode ranges from 23 to 40, which is 3~6 times higher than Q of bright mode. We show the Fano resonance can be tuned by varying the geometry and dimension of the structures. We also demonstrate a polarization dependent Fano resonance in a modified structure of concentric ring apertures.

© 2014 Optical Society of America

Abstract-High-Contrast Terahertz Wave Modulation by Gated Graphene Enhanced by Extraordinary Transmission through Ring Apertures

Weilu Gao , Jie Shu , Kimberly Reichel , Daniel V. Nickel , Xiaowei He , Gang Shi , Robert Vajtai ,Pulickel M Ajayan , Junichiro Kono , Daniel M. Mittleman , and Qianfan Xu

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/nl4041274

Publication Date (Web): February 3, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl4041274

Gate-controllable transmission of terahertz (THz) radiation makes graphene a promising material for making high-speed THz wave modulators. However, to date, graphene-based THz modulators have exhibited only small on/off ratios due to small THz absorption in single-layer graphene. Here we demonstrate a ~50% amplitude modulation of THz waves with gated single-layer graphene by the use of extraordinary transmission through metallic ring apertures placed right above the graphene layer. The extraordinary transmission induced ~7 times near-filed enhancement of THz absorption in graphene. These results promise CMOS-compatible THz modulators with tailored operation frequencies, large on/off ratios, and high speeds, ideal for applications in THz communications, imaging, and sensing.

Thesis Defense-Sub-wavelength Metallic Ring Apertures for Communications, Sensing and Nonlinear Optics

Thesis Defense Graduate and Postdoctoral Studies Electrical and Computer Engineering Speaker: Jie Shu Doctoral Candidate   Sub-wavelength Metallic Ring Apertures for Communications, Sensing and Nonlinear Optics Monday, October 28, 2013 9:30 AM  to 10:30 AM 300  Brockman Hall for Physics In this defense, we demonstrate sub-wavelength ring aperture arrays in a metal film which can be used for communications, material sensing, and nonlinear optics. We show in simulation and experiment extraordinary optical transmission through ring apertures on a metal film both in terahertz (THz) and mid-infrared (MIR) regions. For THz metallic ring aperture arrays, transmission of 60% is obtained with an aperture-to-area ratio of only 1.4%. We show that the high transmission can be suppressed by over 18 dB with a thin layer of free carriers in the silicon substrate underneath the metal film. We also experimentally demonstrate graphene-based active electro-optic modulation of THz waves. The metallic nanostructure provides ~4 times absorption enhancement and ~50% modulation depth is obtained with monolayer graphene. These results suggest that CMOS-compatible terahertz modulators can be built by controlling the carrier density near the aperture. We also demonstrate extraordinary optical transmission in MIR metallic ring aperture arrays. We observe enhanced field-matter interaction with the MIR ring apertures due to enhanced near field, and we present its applications in sensing and nonlinear optical effects. We demonstrate using the devices for enhancing the absorption of PMMA by ~8 times. We also show in simulation the enhanced sensing of monolayer graphene with different Fermi level. We obtain a 60 cm-1 shift of resonance frequency per 0.1 eV change of Fermi level in graphene, and a 6% change in transmission peak intensity. Next we experimentally demonstrate enhanced 2D IR spectrum by using the MIR concentric apertures. At last, we experimentally show polarization-independent Fano resonance in concentric metallic ring apertures both in THz and MIR regions. A high-Q and intensive dark mode is indirectly excited by coupling with a low-Q bright mode. The coupling is enabled by the intrinsic asymmetry between the two concentric rings. A coupled optical resonator model is used to analyze the coupling process between the bright and dark modes. We find the Q of the dark mode is 3~6 times higher than that of the bright mode. We show that the dark mode can be selectively disabled without affecting the bright mode due to its unique current flow pattern.

Abstract-Fano resonance in concentric ring apertures

Jie Shu, Weilu Gao, and Qianfan Xu  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-9-11101

We demonstrate a polarization-independent mid-infrared Fano resonance with extraordinary transmission when light passes through two concentric metallic ring apertures. A high-Q dark mode is indirectly excitated by coupling with a low-Q bright mode. A coupled optical resonator model is used to analyze the coupling process between the bright and dark modes. We find the Q of the dark mode is 3~6 times higher than that of the bright mode. We show that the dark mode can be selectively disabled without affecting the bright mode.

© 2013 OSA