The development of artificially structured electromagnetic materials, termed metamaterials, has led to the realization of phenomena that cannot be obtained with natural materials 1 . This is especially important for the technologically relevant terahertz (1 THz 5 10 12 Hz) frequency regime; many materials inherently do not respond to THz radiation, and the tools that are necessary to construct devices operating within this range-sources, lenses, switches, modulators and detectors-largely do not exist. Considerable efforts are underway to fill this 'THz gap' in view of the useful potential applications of THz radiation 2-7 . Moderate progress has been made in THz generation and detection 8 ; THz quantum cascade lasers are a recent example 9 . However, techniques to control and manipulate THz waves are lagging behind.Here we demonstrate an active metamaterial device capable of efficient real-time control and manipulation of THz radiation. The device consists of an array of gold electric resonator elements (the metamaterial) fabricated on a semiconductor substrate. The metamaterial array and substrate together effectively form a Schottky diode, which enables modulation of THz transmission by 50 per cent, an order of magnitude improvement over existing devices 10 .A great deal of research into metamaterials has used microwave radiation; this is in part due to the ease of fabrication of sub-wavelength structures at these frequencies. Indeed, negative refractive index media 11,12 composed of negative permittivity 13 (e 1 , 0) and negative permeability 14 (m 1 , 0) metamaterial elements was first demonstrated at microwave frequencies. This has led to intense theoretical, computational and experimental studies of exotic phenomena, such as perfect lensing 15 and cloaking 16,17 . Recently, researchers have ventured to create functional metamaterials at near-infrared and visible frequencies [18][19][20] . Considerably less work has concentrated on THz frequencies 21,22 . However, the design flexibility associated with metamaterials provides a promising approach, from a device perspective, towards filling the THz gap.Metamaterials are geometrically scalable, which translates to operability over many decades of frequency. This engineering tunability is in fact a distinguishing and advantageous property of these materials. However, for many applications it is desirable to have real-time tunability. For instance, short-range wireless THz communication or ultrafast THz interconnects 23,24 require switches and modulators. Current state-of-the-art THz modulators based on semiconducting structures have the desirable property of being broadband, which is of relevance to THz interconnects, but are only able to modulate a few per cent 10 and usually require cryogenic temperatures 25 . Therefore, further improvement of the performance characteristics are required for practical applications. Here we present an efficient active metamaterial switch/modulator operating at THz frequencies. Although the modulation is based on a narrowband me...
Planar electric split ring resonator (eSRR) metamaterials and their corresponding inverse structures are designed and characterized computationally and experimentally utilizing finite element modeling and THz time domain spectroscopy. A complementary response is observed in transmission. Specifically, for the eSRRs a decrease in transmission is observed at resonance whereas the inverse structures display an increase in transmission. The frequency dependent effective complex dielectric functions are extracted from the experimental data and, in combination with simulations to determine the surface current density and local electric field, provide considerable insight into the electromagnetic response of our planar metamaterials. These structures may find applications in the construction of various THz filters, transparent THz windows, or THz grid structures ideal for constructing THz switching/modulation devices.
Fabrication and characterization of the first large area metamaterial structures patterned on free‐standing biocompatible silk substrates is reported. Strong resonance responses at terahertz frequencies are shown, providing a promising path towards the development a new class of metamaterial‐inspired bioelectric and biophotonic devices.
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