Photo-generated THz antennas

Georgiou, Giorgos; Tyagi, H. K.; Mulder, P.; Bauhuis, G.J.; Schermer, J.J.; Rivas, Jaime Gómez

doi:10.1038/srep03584

Cited by 53 publications

(44 citation statements)

References 44 publications

(50 reference statements)

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“…For instance, similarly to noble metals, semiconductors exhibit plasmonic properties which can be tuned across a wide spectral range, from the near-infrared down to the terahertz regime, simply by varying their carrier concentration [11,12]. This is also the case for the promising 2D material graphene, where the atomic thickness can produce an unprecedented compression of the field [13][14][15].…”

Section: Introductionmentioning

confidence: 91%

General considerations for the miniaturization of radiative antennae

Francescato¹,

Yang²,

Huang³

et al. 2015

Opt. Express

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The small size of plasmonic nanostructures compared to the wavelength of light is one of their most distinct and defining characteristics. It results in the strong compression of an incident wave to intense hot spots which have been used most remarkably for molecular sensing and nanoscale lasers. But another important direction for research is to use this ability to design miniaturized interconnects and modulators between fast, loss-less photonic components. In this situation one is looking for the smallest optical nanostructure possible while trying to mitigate losses. Here we show that despite their high absorption, conductors are still the best materials to reach the sub-wavelength regime for optical antennae when compared to polar crystals and high-index dielectrics, two classes of material which have shown a lot of potential recently for nanophotonic applications. It is demonstrated through both Mie theory and numerical calculations that the smallest possible, efficient, radiating antenna has a length L > λ res /20 in all cases (this length is typically L = λ res /2 in microwave engineering), including the redshifting mechanism induced by a background or substrate refractive index, the effect of material loss and that of shape. In addition, we show that although the assembly of individual particles can further increase the miniaturization factor, it strongly increases the size-mismatch in detriment of the overall efficiency, thus making this method unfit for radiating antennae. By identifying the relevant dimensionless properties for conductors, polar materials and high index dielectrics, we present an unified understanding of the behaviour of sub-wavelength nanostructures which are at the heart of current nanophotonic research and cast the upper achievable limits for optical antennae crucial to the development of real-life implementation. References and links1. E. Ozbay, "Plasmonics: Merging photonics and electronics at nanoscale dimensions," Science 311, 189-193 (2006). 2. W. L. Barnes, A. Dereux, and T. W. Ebbesen, "Surface plasmon subwavelength optics," Nature 424, 824-830 (2003). 3. A. Alù and N. Engheta, "Wireless at the nanoscale: Optical interconnects using matched nanoantennas," Phys.Rev. Lett. 104, 213902 (2010).

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Section: Introductionmentioning

confidence: 91%

General considerations for the miniaturization of radiative antennae

Francescato¹,

Yang²,

Huang³

et al. 2015

Opt. Express

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“…Each pixel can rotate the polarization vector from 0 • to 90 • in a continuous way. With an analyzer it is thus possible to control the intensity reflected by each pixel [18]. Using this technique we can actively change the free carrier concentration in spatial regions comparable to the pixel-size of the SLM in the GaAs sample.…”

Section: Photo-generation Of Blazed Gratingsmentioning

confidence: 99%

“…In order to measure the beam steering by the photo-generated blazed gratings we used THz pulses generated by a THz time-domain spectrometer (THz-TDS) [18]. These pulses probed the photo-generated grating at a time delay with the optical pulse of 10 ps << τ r .…”

Section: Thz Diffraction Measurementsmentioning

confidence: 99%

“…These devices allows to change the illumination pattern and provides an unprecedented degree of freedom for achieving active steering of the THz beam. Photo-generated antennas [18] and chiral structures [19] have been recently demonstrated using structured illumination of semiconductors. Also photo-generated gratings [20,21] and controlled THz diffraction has been demonstrated [22,23].…”

Section: Introductionmentioning

confidence: 99%

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Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films

Steinbusch¹,

Tyagi²,

Schaafsma³

et al. 2014

Opt. Express

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Abstract:We demonstrate active beam steering of terahertz radiation using a photo-excited thin layer of gallium arsenide. A constant gradient of phase discontinuity along the interface is introduced by an spatially inhomogeneous density of free charge carriers that are photo-generated in the GaAs with an optical pump. The optical pump has been spatially modulated to form the shape of a planar blazed grating. The phase gradient leads to an asymmetry between the +1 and -1 transmission diffracted orders of more than a factor two. Optimization of the grating structure can lead to an asymmetry of more than one order of magnitude. Similar to metasurfaces made of plasmonic antennas, the photo-generated grating is a planar structure that can achieve large beam steering efficiency. Moreover, the photo-generation of such structures provides a platform for active THz beam steering.

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“…Since the resonance frequency can be controlled via carrier concentration, the structure is ready for dynamic operation via carrier injection. 25 The fabrication is relatively inexpensive with silicon as the only bulk raw material and no multilayer processing. The absorber is suitable for emerging terahertz communications to suppress undesirable multipath effects.…”

Section: ■ Conclusionmentioning

confidence: 99%

Plasmonic Resonance toward Terahertz Perfect Absorbers

et al. 2014

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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 is responsible for the 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. KEYWORDS: metamaterial, plasmonics, perfect absorber, cavity mode, THz-TDS, terahertz, multiphysics simulation R esearch on perfect absorption has recently become a very active topic in the rapidly growing field of metamaterials. Providing enhanced performance and flexibility, perfect absorbers have been realized in different applications, including imaging, sensing, and energy harnessing. Soon after the seminal development by Padilla and co-workers, 1,2 metamaterial-based perfect absorbers have been demonstrated across the spectrum, from the microwave, to terahertz, infrared, and optical bands. 3 In general, these traditional perfect absorbers appeared in the form of metallic resonators on a ground plane, designed to eliminate the reflection and enhance the absorption. The perfect absorption mechanism was explained with the coexistence of Lorentzian electric and magnetic responses that match the impedance of the structure to free space and at the same time imposing large energy dissipation on resonance. Another explanation involved wave interference theory where multipath reflections originating from different interfaces lead to completely destructive interference in the direction of reflection. 4 Alternatively, perfect absorption was interpreted as nullified reflection by an out-of-phase wave reradiated from induced electric and magnetic surface currents. 5 Of relevance to this article are perfect absorbers at infrared and visible frequencies, where metals with relatively limited conductivity can support bound surface waves or surface plasmon polaritons (SPPs). Earlier implementations of plasmonic absorbers in the near-infrared 6,7 and visible 8,9 regimes adopted the conventional design of a metallic dipole array on a ground plane separated by a dielectric spacer. This concept was extended to random nanoparticles on a ground plane that exhibit electric and magnetic resonances for visible light absorption. 5,10 Unlike perfec...

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Photo-generated THz antennas

Cited by 53 publications

References 44 publications

General considerations for the miniaturization of radiative antennae

General considerations for the miniaturization of radiative antennae

Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films

Plasmonic Resonance toward Terahertz Perfect Absorbers

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