Abstract-Frequency‐Agile Temporal Terahertz Metamaterials

Prakash Pitchappa,   Abhishek Kumar,   Haidong Liang,   Saurav Prakash,   Nan Wang,   Andrew A. Bettiol,   Thirumalai Venkatesan,  Chengkuo Lee,   Ranjan Singh,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202000101

Spatiotemporal manipulation of electromagnetic waves has recently enabled a plethora of exotic optical functionalities, such as non‐reciprocity, dynamic wavefront control, unidirectional transmission, linear frequency conversion, and electromagnetic Doppler cloak. Here, an additional dimension is introduced for advanced manipulation of terahertz waves in the space‐time, and frequency domains through integration of spatially reconfigurable microelectromechanical systems and photoresponsive material into metamaterials. A large and continuous frequency agility is achieved through movable microcantilevers. The ultrafast resonance modulation occurs upon photoexcitation of ion‐irradiated silicon substrate that hosts the microcantilever metamaterial. The fabricated metamaterial switches in 400 ps and provides large spectral tunability of 250 GHz with 100% resonance modulation at each frequency. The integration of perfectly complementing technologies of microelectromechanical systems, femtosecond optical control and ion‐irradiated silicon provides unprecedented concurrent control over space, time, and frequency response of metamaterial for designing frequency‐agile spatiotemporal modulators, active beamforming, and low‐power frequency converters for the next generation terahertz wireless communications

Abstract-Tailoring the slow light behavior in terahertz metasurfaces

Manukumara Manjappa¹, Sher-Yi Chiam², Longqing Cong¹, Andrew A. Bettiol³,Weili Zhang⁴ and Ranjan Singh^1,a)


http://scitation.aip.org/content/aip/journal/apl/106/18/10.1063/1.4919531
1 Center for Disruptive Photonic Technologies, Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
2 NUS High School of Math and Science, 20 Clementi Avenue 1, Singapore, Singapore 129957
3 Department of Physics, National University of Singapore, Science Drive 3, Singapore, Singapore 117542
4 School of Electrical and Computer Engineering, Oklahoma State University, 202 Engineering South, Stillwater, Oklahoma 74078, USA
a) Electronic mail: ranjans@ntu.edu.sg
Appl. Phys. Lett. 106, 181101 (2015); http://dx.doi.org/10.1063/1.4919531

We experimentally study the effect of near field coupling on the transmission of light in terahertz metasurfaces. Our results show that tailoring the coupling between the resonators modulates the amplitude of resulting electromagnetically induced transmission, probed under different types of asymmetries in the coupled system. Observed change in the transmission amplitude is attributed to the change in the amount of destructive interference between the resonators in the vicinity of strong near field coupling. We employ a two-particle model to theoretically study the influence of the coupling between bright and quasi-dark modes on the transmissionproperties of the system and we find an excellent agreement with our observed results. Adding to the enhanced transmission characteristics, our results provide a deeper insight into themetamaterial analogues of atomic electromagnetically induced transparency and offer an approach to engineer slow light devices, broadband filters, and attenuators at terahertz frequencies.

Abstract-Free-standing terahertz chiral meta-foils exhibiting strong optical activity and negative refractive index

Jianfeng Wu¹, Binghao Ng², Shuvan P. Turaga¹, Mark B. H. Breese^1,3, Stefan A. Maier², Minghui Hong⁴, Andrew A. Bettiol¹, and Herbert O. Moser^5
1Department of Physics, Center for Ion Beam Applications (CIBA), National University of Singapore, 2 Science Drive, Singapore 
²Department of Physics, Imperial College, London SW7 2AZ, United Kingdom 
³Singapore Synchrotron Light Source (SSLS), National University of Singapore, 5 Research Link, 117603 Singapore 
⁴Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576 Singapore 
⁵Karlsruhe Institute of Technology (KIT), Network of Excellent Retired Scientists (NES), and Institute of Microstructure Technology (IMT), Postfach 3640, 76021 Karlsruhe, Germany 

http://apl.aip.org/resource/1/applab/v103/i14/p141106_s1?isAuthorized=no

A chiral meta-foil consisting of a self-supported square array of interconnected conjugated rosettes is demonstrated at terahertz frequencies. It exhibits strong optical activity and circular dichroism. Negative refractive index with a figure-of-merit as high as 4.2 is achieved, attributed to its free-standing nature. Experimental results are in good agreement with numerical simulation. Free-standing chiral meta-foils provide a unique approach to create a completely all-metal chiral metamaterial, which can be flexibly integrated into optical setups while eliminating dielectric insertion losses.

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