Abstract-Tutorial: Terahertz beamforming, from concepts to realizations

Daniel Headland, Yasuaki Monnai, Derek Abbott, Christophe Fumeaux, Withawat Withayachumnankul,

https://aip.scitation.org/doi/am-pdf/10.1063/1.5011063?class=chorus+notVisible

The terahertz range possesses significant untapped potential for applications including high-volume wireless communications, noninvasive medical imaging, sensing, and safe security screening. However, due to the unique characteristics and constraints of terahertz waves, the vast majority of these applications are entirely dependent upon the availability of beam control techniques. Thus, the development of advanced terahertzrange beam control techniques yields a range of useful and unparalleled applications. This article provides an overview and tutorial on terahertz beam control. The underlying principles of wavefront engineering include array antenna theory and diffraction optics, which are drawn from the neighboring microwave and optical regimes, respectively. As both principles are applicable across the electromagnetic spectrum, they are reconciled in this overview. This provides a useful foundation for investigations into beam control in the terahertz range, which lies between microwaves and infrared light. Thereafter, noteworthy experimental demonstrations of beam control in the terahertz range are discussed, and these include geometric optics, phased array devices, leaky-wave antennas, reflectarrays, and transmitarrays. These techniques are compared and contrasted for their suitability in applications of terahertz waves. 

Abstract-Dielectric-resonator metasurfaces for broadband terahertz quarter- and half-wave mirrors

Wendy S. L. Lee, Rajour T. Ako, Mei Xian Low, Madhu Bhaskaran, Sharath Sriram, Christophe Fumeaux, and Withawat Withayachumnankul

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-11-14392

Polarization conversion of terahertz waves is important for applications in imaging and communications. Conventional wave plates used for polarization conversion are inherently bulky and operate at discrete wavelengths. As a substitute, we employ reflective metasurfaces composed of subwavelength resonators to obtain similar functionality but with enhanced performance. More specifically, we demonstrate low-order dielectric resonators in place of commonly used planar metallic resonators to achieve high radiation efficiencies. As a demonstration of the concept, we present firstly, a quarter-wave mirror that converts 45° incident linearly polarized waves into circularly polarized waves. Next, we present a half-wave mirror that preserves the handedness of circularly polarized waves upon reflection, and in addition, rotates linearly polarized waves by 90° upon reflection. Both metasurfaces operate with high efficiency over a measurable relative bandwidth of 49% for the quarter-wave mirror and 53% for the half-wave mirror. This broadband and high efficiency capabilities of our metasurfaces will allow to leverage maximum benefits from a vast terahertz bandwidth.

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

Abstract-Broadband Terahertz Circular-Polarization Beam Splitter

Wendy S. L. Lee, Shruti Nirantar, Daniel Headland, Madhu Bhaskaran, Sharath Sriram, Christophe Fumeaux, Withawat Withayachu

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700852/full

Splitting circularly polarized waves is desirable for high-data-rate wireless communications and study of molecular chirality at terahertz frequencies. Typically, this functionality is achieved using bulk optical systems with limitations in material availability, bandwidth, and efficiency. As an alternative, metasurfaces with spatially varying broadband birefringence are employed to attain the same functionality. It is demonstrated that a metasurface designed with gradually rotated birefringent resonators can deflect normally incident left-handed circularly polarized and right-handed circularly polarized waves into different directions. This beam splitting functionality is maintained over an experimentally demonstrated relative deflection bandwidth of 53%, namely, covering the band of 0.58–1.00 THz.

Abstract-Terahertz near-field imaging of dielectric resonators

Wendy S. L. Lee, Korbinian Kaltenecker, Shruti Nirantar, Withawat Withayachumnankul, Markus Walther, Madhu Bhaskaran, Bernd M. Fischer, Sharath Sriram, and Christophe Fumeaux

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-4-3756

As an alternative to metallic resonators, dielectric resonators can increase radiation efficiencies of metasurfaces at terahertz frequencies. Such subwavelength resonators made from low-loss dielectric materials operate on the basis of oscillating displacement currents. For full control of electromagnetic waves, it is essential that dielectric resonators operate around their resonant modes. Thus, understanding the nature of these resonances is crucial towards design implementation. To this end, an array of silicon resonators on a quartz substrate is designed to operate in transmission at terahertz frequencies. The resonator dimensions are tailored to observe their low-order modes of resonance at 0.58 THz and 0.61 THz respectively. We employ a terahertz near-field imaging technique to measure the complex near-fields of this dielectric resonator array. This unique method allows direct experimental observation of the first two fundamental resonances.

© 2017 Optical Society of America

Full Article  |  PDF Article

Abstract-Dielectric Resonator Reflectarray as High-Efficiency Nonuniform Terahertz Metasurface

Daniel Headland*†, Eduardo Carrasco‡¶, Shruti Nirantar§∥, Withawat Withayachumnankul†⊥, Philipp Gutruf§∥,James Schwarz§∥, Derek Abbott†, Madhu Bhaskaran§∥, Sharath Sriram§∥, Julien Perruisseau-Carrier‡, and Christophe Fumeaux†

† School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, SA 5005, Australia

‡ École Polytechnique Fédérale de Lausanne, EPFL, 1015 Lausanne, Switzerland

¶ Foundation for Research on Information Technologies in Society, IT’IS, 8004 Zürich, Switzerland

§Functional Materials and Microsystems Research Group and ∥MicroNano Research Facility, RMIT University, Melbourne, Victoria 3000, Australia

⊥ Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan

ACS Photonics, Article ASAP

DOI: 10.1021/acsphotonics.6b00102

Publication Date (Web): May 13, 2016

Copyright © 2016 American Chemical Society

*E-mail: daniel.headland@adelaide.edu.au.

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00102

Advances in terahertz technology rely on the combination of novel materials and designs. As new devices are demonstrated to address the terahertz gap, the ability to perform high-efficiency beam control will be integral to making terahertz radiation a practical technology. Here, we use a metasurface composed of nonuniform dielectric resonator antennas on a ground plane to achieve efficient beam focusing at 1 THz. The dielectric resonators are made of high-resistivity silicon, which is a low-loss, nondispersive material for terahertz waves. The resonators operate around the resonance of the displacement current in the silicon, which is crucial to attaining high efficiency. The reflectarray’s capacity to focus terahertz radiation is experimentally verified, and hence by the principle of antenna reciprocity, it can also be employed as a terahertz collimator. The demonstrated device can therefore be deployed for high-gain terahertz antennas. Further measurements show that the loss of the reflectarray is negligible, which confirms the high efficiency of the dielectric resonators. This finding will enable the design of efficient flat-profile terahertz reflectarrays and metasurfaces to serve arbitrary beam control requirements in the near and far fields.

Abstract-Dielectric resonator reflectarray as high-efficiency non-uniform terahertz metasurface

Daniel Headland, Eduardo Carrasco, Shruti Nirantar, Withawat Withayachumnankul, Philipp Gutruf, James Schwarz, Derek Abbott, Madhu Bhaskaran, Sharath Sriram, Julien Perruisseau-Carrier, and Christophe Fumeaux

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.6b00102

Publication Date (Web): May 13, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.6b00102

Abstract

Advances in terahertz technology rely on the combination of novel materials and designs. As new devices are demonstrated to address the terahertz gap, the ability to perform high-efficiency beam control will be integral to making terahertz a practical technology. Here, we use a metasurface composed of nonuniform dielectric resonator antennas on a ground plane to achieve efficient beam focusing at 1 THz. The dielectric resonators are made of high-resistivity silicon, which is a low-loss, non-dispersive material for terahertz waves. The resonators operate around the resonance of displacement current in the silicon, which is crucial to attaining high-efficiency. The reflectarray’s capacity to focus terahertz radiation is experimentally verified, and hence by the principle of antenna reciprocity, it can also be employed as a terahertz collimator. The demonstrated device can therefore be deployed for high-gain terahertz antennas. Further measurements show that the loss of the reflectarray is negligible, which confirms the high efficiency of the dielectric resonators. This finding will enable the design of efficient flat-profile terahertz reflectarrays and metasurfaces to serve arbitrary beam control requirements in the near- and far-field.

Abstract-Terahertz Magnetic Mirror Realized with Dielectric Resonator Antennas

1. Daniel Headland¹, 
2. Shruti Nirantar^2,3,
3. Withawat Withayachumnankul^1,2,4, 
4. Philipp Gutruf^2,3, 
5. Derek Abbott¹, 
6. Madhu Bhaskaran^2,3, 
7. Christophe Fumeaux^1,*and
8. Sharath Sriram^2,3,*

Article first published online: 9 OCT 2015

DOI: 10.1002/adma.201503069

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

http://onlinelibrary.wiley.com/doi/10.1002/adma.201503069/abstract;jsessionid=5E1D330CB11C192A553C5E4A3AC815B7.f04t02?userIsAuthenticated=false&deniedAccessCustomisedMessage=

Single-crystal silicon is bonded to a metal-coated substrate and etched in order to form an array of microcylinder passive terahertz dielectric resonator antennas (DRAs). The DRAs exhibit a magnetic response, and hence the array behaves as an efficient artificial magnetic conductor (AMC), with potential for terahertz antenna and sensing applications.

Abstract-Polarization-dependent thin-film wire-grid reflectarray for terahertz waves

Tiaoming Niu^1,2, Aditi Upadhyay³, Withawat Withayachumnankul^1,4, Daniel Headland¹, Derek Abbott¹, Madhu Bhaskaran³, Sharath Sriram³ andChristophe Fumeaux^1,a)
 HIDE AFFILIATIONS
1 School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
2 School of Information Science and Engineering, Lanzhou University, Lanzhou 730000, People's Republic of China
3 Functional Materials and Microsystems Research Group, RMIT University, Melbourne, Victoria 3001, Australia
4 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1-S9-3, Ookayama, Meguro-ku, Tokyo 152-8552, Japan

A thin-film polarization-dependent reflectarray based on patterned metallic wire grids is realized at 1 THz. Unlike conventional reflectarrays with resonant elements and a solid metal ground, parallel narrow metal strips with uniform spacing are employed in this design to construct both the radiation elements and the ground plane. For each radiation element, a certain number of thin strips with an identical length are grouped to effectively form a patch resonator with equivalent performance. The ground plane is made of continuous metallic strips, similar to conventional wire-grid polarizers. The structure can deflect incident waves with the polarizationparallel to the strips into a designed direction and transmit the orthogonal polarizationcomponent. Measured radiation patterns show reasonable deflection efficiency and highpolarization discrimination. Utilizing this flexible device approach, similar reflectarray designs can be realized for conformal mounting onto surfaces of cylindrical or spherical devices for terahertz imaging and communications.

Abstract-Terahertz reflectarray as a polarizing beam splitter

Tiaoming Niu, Withawat Withayachumnankul, Aditi Upadhyay, Philipp Gutruf, Derek Abbott, Madhu Bhaskaran, Sharath Sriram, and Christophe Fumeaux  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-13-16148

Optics Express, Vol. 22, Issue 13, pp. 16148-16160 (2014)
http://dx.doi.org/10.1364/OE.22.016148

A reflectarray is designed and demonstrated experimentally for polarization-dependent beam splitting at 1 THz. This reflective component is composed of two sets of orthogonal strip dipoles arranged into interlaced triangular lattices over a ground plane. By varying the length and width of the dipoles a polarization-dependent localized phase change is achieved on reflection, allowing periodic subarrays with a desired progressive phase distribution. Both the simulated field distributions and the measurement results from a fabricated sample verify the validity of the proposed concept. The designed terahertz reflectarray can efficiently separate the two polarization components of a normally incident wave towards different predesigned directions of ±30°. Furthermore, the measured radiation patterns show excellent polarization purity, with a cross-polarization level below −27 dB. The designed reflectarray could be applied as a polarizing beam splitter for polarization-sensitive terahertz imaging or for emerging terahertz communications.

© 2014 Optical Society of America

Abstract-Plasmonic resonance towards terahertz perfect absorbers

Withawat Withayachumnankul , Charan Manish Shah , Christophe Fumeaux , Benjamin S.-Y. Ung ,Willie Padilla , Madhu Bhaskaran , Derek Abbott , and Sharath Sriram

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/ph500110t

Publication Date (Web): June 3, 2014

Copyright © 2014 American Chemical Society
http://pubs.acs.org/doi/abs/10.1021/ph500110t

Metamaterial perfect absorbers have garnered significant interest with applications in sensing, imaging, and energy harnessing. Of particular interest are terahertz absorbers to overcome the weak terahertz response of natural materials. Here, we propose lossy plasmonic resonance in silicon-based annular microcavities for perfect terahertz absorption. This mechanism is in stark contrast to earlier demonstrations of conventional terahertz perfect absorbers that invoke Lorentzian electric and magnetic resonances. A fundamental cavity mode coupled to coaxial surface plasmon polaritons (SPPs) is responsible for predicted exceptional absorption of -58 dB with a 90% absorption bandwidth of 30%. The performance is in agreement with experimental validation and consistent with critical coupling and resonance conditions. This specific cavity design possesses great thermal isolation and minimal electromagnetic coupling between unit cells. These unique features exclusive to the plasmonic cavity introduce a promising avenue for terahertz imaging with enhanced contrast, resolution, and sensitivity.

Abstract-Terahertz Localized Surface Plasmon Resonances in Coaxial Microcavities

http://onlinelibrary.wiley.com/doi/10.1002/adom.201300021/abstract

1. Withawat Withayachumnankul^1,2,*, 
2. Charan Manish Shah², 
3. Christophe Fumeaux¹,
4. Korbinian Kaltenecker^3,4, 
5. Markus Walther³, 
6. Bernd M. Fischer^1,4, 
7. Derek Abbott¹,
8. Madhu Bhaskaran², 
9. Sharath Sriram^2,*

Coaxial microcavities etched into the surface of a doped silicon substrate are shown to support localized surface plasmon resonances at terahertz frequencies. The underlying mechanism involves coupling freely propagating terahertz waves with surface plasmon polaritons (SPPs), which propagate in a coaxial mode along the cavity walls in the axial direction. A Fabry–Pérot resonance is built up when the SPP wavenumber appropriately relates to the cavity depth. Owing to the Ohmic loss of the silicon at terahertz frequencies, the energy of the resonating SPPs is largely dissipated, leading to a modified reflection spectrum. Strong field enhancement is observed inside the cavities at resonance. The theoretical analysis is supported by numerical and experimental results. This study is a promising pathway for development of terahertz devices with applications in the areas of photonic integrated circuits, molecular sensing, and subwavelength imaging.

Abstract-Experimental demonstration of reflectarray antennas at terahertz frequencies

Tiaoming Niu, Withawat Withayachumnankul, Benjamin S.-Y. Ung, Hakan Menekse, Madhu Bhaskaran, Sharath Sriram, and Christophe Fumeaux »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-3-2875

Reflectarrays composed of resonant microstrip gold patches on a dielectric substrate are demonstrated for operation at terahertz frequencies. Based on the relation between the patch size and the reflection phase, a progressive phase distribution is implemented on the patch array to create a reflector able to deflect an incident beam towards a predefined angle off the specular direction. In order to confirm the validity of the design, a set of reflectarrays each with periodically distributed 360 × 360 patch elements are fabricated and measured. The experimental results obtained through terahertz time-domain spectroscopy (THz-TDS) show that up to nearly 80% of the incident amplitude is deflected into the desired direction at an operation frequency close to 1 THz. The radiation patterns of the reflectarray in TM and TE polarizations are also obtained at different frequencies. This work presents an attractive concept for developing components able to efficiently manipulate terahertz radiation for emerging terahertz communications.

© 2013 OSA