Abstract-THz characterization and demonstration of visible-transparent/terahertz-functional electromagnetic structures in ultra-conductive La-doped BaSnO3 Films

Sara Arezoomandan, Abhinav Prakash, Ashish Chanana, Jin Yue, Jieying Mao, Steve Blair, Ajay Nahata, Bharat Jalan,  Berardi Sensale-Rodriguez

https://www.nature.com/articles/s41598-018-22038-w

We report on terahertz characterization of La-doped BaSnO3 (BSO) thin-films. BSO is a transparent complex oxide material, which has attracted substantial interest due to its large electrical conductivity and wide bandgap. The complex refractive index of these films is extracted in the 0.3 to 1.5 THz frequency range, which shows a metal-like response across this broad frequency window. The large optical conductivity found in these films at terahertz wavelengths makes this material an interesting platform for developing electromagnetic structures having a strong response at terahertz wavelengths, i.e. terahertz-functional, while being transparent at visible and near-IR wavelengths. As an example of such application, we demonstrate a visible-transparent terahertz polarizer.

Abstract-THz metamaterials and plasmonics using 2D materials & highly conductive transparent oxides

Sara Arezoomandan

https://128.84.21.199/abs/1801.00851

Driven by a myriad of potential applications such as communications, medical imaging, security, spectroscopy, and so on, terahertz (THz) technology has emerged as a rapidly growing technological field during the last three decades. However, since conventional materials typically used in microwave and optical frequencies are lossy or do not effectively respond at these frequencies, it is essential to find or develop novel materials that are suitable for device applications in the THz range. Therefore, there is wide interest in the community in employing novel naturally-occurring materials, such as 2D materials, as well as in designing artificial metamaterial structures for THz applications. Here, we combined both of these approaches so to develop reconfigurable THz devices capable of providing amplitude modulation, phase modulation, and resonance frequency tuning

Abstract-Graphene-based reconfigurable terahertz plasmonics and metamaterials

Sara Arezoomandan^a, 

Hugo O. Condori Quispe^a, 

Nicholas Ramey^b, 

Cesar A. Nieves^c, 

Berardi Sensale-Rodriguez

http://www.sciencedirect.com/science/article/pii/S000862231630985X

This work discusses and compares two proposed practical approaches for realizing graphene-based reconfigurable terahertz metamaterials, namely: graphene-only plasmonic structures, and graphene/metal hybrid structures. From rigorous theoretical analysis, full-wave electromagnetic numerical simulations, as well as supporting experiments, several reconfigurable structures are analyzed and compared in terms of their: (i) Quality-factor, (ii) Extinction-ratio, (iii) Unit-cell dimensions, and (iv) Resonance-frequency tunability-range. From this analysis it is observed that at terahertz frequencies, although typically possessing larger unit-cell dimensions and being limited by a restricted resonance-frequency tunability-range, reconfigurable metamaterials based on graphene/metal hybrid structures can provide much larger quality-factors, extinction levels, and, when reconfigured, smaller extinction-level degradation than graphene-only plasmonic structures. As a result, when analyzed in the context of reconfigurable terahertz metamaterials, graphene might result attractive as a reconfigurable media providing tunability to otherwise passive metallic structures rather than as a reconfigurable plasmonic material per-se.

Abstract-Near-field Enhancement and Optimal Performance in Metamaterial Terahertz Modulators Based on 2D-materials

Sara Arezoomandan, Rusen Yan, Prashanth Gopalan, Kun Tian, Ashish Chanana, Ashutosh Tiwari, Huili Grace Xing, Ajay Nahata, and Berardi Sensale-Rodriguez

https://www.osapublishing.org/abstract.cfm?uri=LAOP-2016-LW2B.4

In this work we analyze metamaterial terahertz modulators consisting of 2D-material/metal hybrid-structures. Influence of the near-field enhancement in the modulator performance is discussed. Devices are fabricated and tested using graphene and MoS2 as active materials.

© 2016 OSA

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Abstract-Exceptional Terahertz Wave Modulation in Graphene Enhanced by Frequency Selective Surfaces

Rusen Yan, Sara Arezoomandan, Berardi Sensale-Rodriguez, and Huili Grace Xing

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.5b00639

Publication Date (Web): February 11, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.5b00639

In this paper we theoretically and experimentally analyze the design tradeoffs in terahertz metamaterial modulators consisting of hybrid graphene/metal stacked structures. In these devices graphene is used as the active medium whereas a passive metallic frequency selective surface is employed to enhance the light-matter interaction in graphene. When altering the structure key geometrical parameters, we observe a close match between our experiments and theory, showing that it is possible to achieve an optimal tradeoff between modulation depth, insertion loss, and speed in these devices. Moreover, a transmission line based compact mathematical model is introduced in order to explain our experimental observations and predict the performance limits in these structures.

Abstract-Graphene-based tunable metamaterial terahertz filters

Kai Yang¹, Shuchang Liu¹, Sara Arezoomandan¹, Ajay Nahata¹ and Berardi Sensale-Rodriguez^1,a)
http://scitation.aip.org/content/aip/journal/apl/105/9/10.1063/1.4894807
1 Department of Electrical and Computer Engineering, The University of Utah, 50 S. Central Campus Dr., Salt Lake City, Utah 84112, USA
a) Electronic mail: berardi.sensale@utah.edu
Appl. Phys. Lett. 105, 093105 (2014); http://dx.doi.org/10.1063/1.4894807

We propose and describe a micro-machined tunable metamaterial terahertz filter based ongraphene. The device structure consists of periodic metallic rings with several gaps where tunablegraphene stripes are located. We demonstrate that the filter resonance frequency can be adjusted easily by varying the conductivity of graphene and implement this by changing the number of stacked graphene layers. Moreover, the proposed design is scalable, in the sense that the resonance frequency tuning can be controlled by scaling the inner and outer radius of the metal rings. Using numerical simulations and terahertz time-domain spectroscopy measurements of the fabricated samples, we show that the resonance frequency of the structure can be altered by 40% (i.e., from ∼0.2 THz to ∼0.12 THz) by simply tuning the conductivity of graphene. Importantly, the active area of the device is ≪0.1% of the total unit cell area, which can boost the device speed upon electrostatic actuation.

Abstract-Graphene-based electrically reconfigurable deep-subwavelength metamaterials for active control of THz light propagation

• Sara Arezoomandan, 
• Kai Yang, 
• Berardi Sensale-Rodriguez

http://link.springer.com/article/10.1007%2Fs00339-014-8693-8

This work studies the terahertz light propagation through

graphene-based reconfigurable metasurfaces where the unit cell dimensions are much smaller than the terahertz wavelength. The proposed devices, which poses deep-subwavelength unit cell and active region dimensions can operate as amplitude and/or phase modulators in certain specific frequency bands determined by the device geometry. Reconfigurability is attained via electrostatically tuning the optical conductivity of patterned graphene layers, which are strategically located in each unit cell. The ultra-small unit cell dimensions can be advantageous for beam shaping applications.