Browsing by Author "Shu, Jie"

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    Device and method for modulating transmission of terahertz waves
    (2015-08-11) Xu, Quinfan; Shu, Jie; Mittleman, Daniel M.; Qiu, Ciyuan; Rice University; United States Patent and Trademark Office
    A device for modulating terahertz waves includes a metal layer (703) including a continuous metal portion (705) and island metal portions (707). The metal portions (705, 707) are separated by apertures (709). The device further includes a semiconductor layer (715) affixed to a bottom surface of the metal layer (703). The semiconductor layer (715) includes carrier regions (717) located below the apertures (709). The transmission of terahertz waves through the apertures (709) is modulated by changing a voltage applied across the aperture via voltage source (715). By injecting free carriers into carrier regions (717) due to a change of the voltage an extraordinary terahertz transmission effect of the metal layer (703) can be switched off. A small increase in the free-carrier absorption is significantly enhanced by the Fabry-Perot resonance, resulting in a substantial decrease in transmission. The disclosed ring aperture terahertz modulator allows for electrical control of the carrier density only in the area underneath the aperture. This design minimizes the power consumption and maximizes the operation speed.
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    Extraordinary sensitivity enhancement by metasurfaces in terahertz detection of antibiotics
    (Nature Publishing Group, 2015) Xie, Lijuan; Gao, Weilu; Shu, Jie; Ying, Yibin; Kono, Junichiro
    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.
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    Sub-wavelength Metallic Ring Apertures for Communications, Sensing and Nonlinear Optics
    (2013-11-06) Shu, Jie; Xu, Qianfan; Mittleman, Daniel M.; Nordlander, Peter J.
    In this thesis, 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. We also observe enhanced field-matter interaction and the absorption-induced transparency effect caused by the intense E-field in the aperture when a material absorption line is aligned with the dark mode.