Abstract-Characterization of an active metasurface using terahertz ellipsometry

Nicholas Karl, Martin S. Heimbeck,   Henry O. Everitt,   Hou-Tong Chen, Antoinette J. Taylor, Igal Brener, Alexander Benz, John L. Reno, Rajind Mendis,  Daniel M. Mittleman,

http://aip.scitation.org/doi/abs/10.1063/1.5004194

Switchable metasurfaces fabricated on a doped epi-layer have become an important platform for developing techniques to control terahertz (THz) radiation, as a DC bias can modulate the transmission characteristics of the metasurface. To model and understand this performance in new device configurations accurately, a quantitative understanding of the bias-dependent surface characteristics is required. We perform THz variable angle spectroscopic ellipsometry on a switchable metasurface as a function of DC bias. By comparing these data with numerical simulations, we extract a model for the response of the metasurface at any bias value. Using this model, we predict a giant bias-induced phase modulation in a guided wave configuration. These predictions are in qualitative agreement with our measurements, offering a route to efficient modulation of THz signals.

Abstract-Bilayer Metasurfaces for Dual- and Broadband Optical Antireflection

Li Huang, Chun-Chieh Chang , Beibei Zeng, John Nogan, Sheng-Nian Luo,  Antoinette J. Taylor,  Abul K. Azad, Hou-Tong Chen,

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b00471?journalCode=apchd5

Optical antireflection has long been pursued for a wide range of applications, but existing approaches encounter issues in the performance, bandwidth, and structure complexity, particularly in the long-wavelength infrared regime. Here we present the demonstration of bilayer metasurfaces that accomplish dual- and broadband optical antireflection in the terahertz and mid-infrared spectral ranges. By simply tailoring the structural geometry and dimensions, we show that subwavelength metal/dielectric structures enable dramatic reduction of Fresnel reflection and significant enhancement of transmission at a substrate surface, operating either at two discrete narrow bands or over a broad bandwidth up to 28%. We also use a semianalytical interference model to interpret the obtained results, in which we find that the dispersion of the constituent structures plays a critical role in achieving the observed broadband optical antireflection.

Abstract-Experimental demonstration of terahertz metamaterial absorbers with a broad and flat high absorption band

Li Huang, Dibakar Roy Chowdhury, Suchitra Ramani, Matthew T. Reiten, Sheng-Nian Luo, Antoinette J. Taylor, and Hou-Tong Chen
https://www.osapublishing.org/ol/abstract.cfm?URI=ol-37-2-154

We present the design, numerical simulations and experimental measurements of terahertz metamaterial absorbers with a broad and flat absorption top over a wide incidence angle range for either transverse electric or transverse magnetic polarization depending on the incident direction. The metamaterial absorber unit cell consists of two sets of structures resonating at different but close frequencies. The overall absorption spectrum is the superposition of individual components and becomes flat at the top over a significant bandwidth. The experimental results are in excellent agreement with numerical simulations.

© 2012 Optical Society of America

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Abstract-Terahertz Surface Wave Modulation in a Dielectric Slab Metasurface

Nicholas Karl, Hou-Tong Chen, Antoinette J. Taylor, Igal Brener, Alexander Benz, John Reno, Rajind Mendis, and Daniel Mittleman
https://www.osapublishing.org/abstract.cfm?uri=CLEO_SI-2015-STu1H.6

We experimentally and numerically investigate a switchable dielectric-slab-waveguide metasurface device. We use an active metasurface to manipulate the interaction with a propagating THz surface wave, giving us dynamic control of the wave at 0.3 THz.

© 2015 OSA

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Abstract-Terahertz metamaterials for linear polarization conversion and anomalous refraction

Nathaniel K. Grady, Jane E. Heyes, Dibakar Roy Chowdhury, Yong Zeng, Matthew T. Reiten, Abul K. Azad, Antoinette J. Taylor, Diego A. R. Dalvit, Hou-Tong Chen
Polarization is one of the basic properties of electromagnetic waves conveying valuable information in signal transmission and sensitive measurements. Conventional methods for advanced polarization control impose demanding requirements on material properties and attain only limited performance. Here, we demonstrate ultrathin, broadband, and highly efficient metamaterial-based terahertz polarization converters that are capable of rotating a linear polarization state into its orthogonal one. Based on these results we create metamaterial structures capable of realizing near-perfect anomalous refraction. Our work opens new opportunities for creating high performance photonic devices and enables emergent metamaterial functionalities for applications in the technologically difficult terahertz frequency regime.