We present a polarization-independent metamaterial design for the construction of electrically tunable terahertz (THz) devices. The implemented structure consists of an array of gold crosses fabricated on top of an n-doped gallium arsenide (GaAs) layer. Utilizing THz time-domain spectroscopy, we show that the electric resonance and thus the transmission properties of the cross structure can be tuned by an externally applied bias voltage. We further demonstrate the fast amplitude modulation of a propagating THz wave for modulation frequencies up to 100 kHz.
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"A periodic metallic structure is employed with the purpose of producing a resonance in the optical response, with an electric field intensity efficiently confined in specific regions of space. The width and intensity of this resonance are strongly dependent on the losses of the substrate material in the region where most of the field is localized, and the losses can then be tailored by locally changing the charge carrier density via electrical gating , . Although in this case the operation of the modulator is limited to a relatively narrow bandwidth, roughly defined by the resonance, large modulations of more than 50% can be reached thanks to the field enhancement . "
[Show abstract][Hide abstract] ABSTRACT: Graphene is establishing itself as a new photonic material with huge potential in a variety of applications ranging from transparent electrodes in displays and photovoltaic modules to saturable absorber in mode-locked lasers. Its peculiar bandstructure and electron transport characteristics naturally suggest graphene could also form the basis for a new generation of high-performance devices operating in the terahertz (THz) range of the electromagnetic spectrum. The region between 300 GHz and 10 THz is in fact still characterized by a lack of efficient, compact, solid state photonic components capable of operating well at 300 K. Recent works have already shown very promising results in the development of high-speed modulators as well as of bolometer and plasma-wave detectors. Furthermore, several concepts have been proposed aiming at the realization of lasers and oscillators. This paper will review the latest achievements in graphene-based THz photonics and discuss future perspectives of this rapidly developing research field.
IEEE Journal of Selected Topics in Quantum Electronics 01/2014; 20(1):8500109-8500109. DOI:10.1109/JSTQE.2013.2271692 · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We design and implement a multipixel spatial modulator for terahertz beams using active terahertz metamaterials. Our first-generation device consists of a 4×4 pixel array, where each pixel is an array of subwavelength-sized split-ring resonator elements fabricated on a semiconductor substrate, and is independently controlled by applying an external voltage. Through terahertz transmission experiments, we show that the spatial modulator has a uniform modulation depth of around 40% across all pixels, and negligible crosstalk, at the resonant frequency. This device can operate under small voltage levels, at room temperature, with low power consumption and reasonably high switching speed.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate experimentally and theoretically dielectric metamaterials exhibiting a tunable range of negative effective permeability in the terahertz spectral region 0.2–0.36 THz. Our structures consist of an array of intrinsically nonmagnetic rods made of an incipient ferroelectric SrTiO 3 which shows a high tunable permittivity. The magnetic response and its tuning are achieved by a temperature control of the permittivity of SrTiO 3 , which defines the resonant confinement of the electromagnetic field within the rods.