Largely Tunable Terahertz Circular Polarization Splitters Based on Patterned Graphene Nanoantenna Arrays Largely Tunable Terahertz Circular Polarization Splitters Based on Patterned Graphene Nanoantenna Arrays (original) (raw)

Broadband Tunable Terahertz Polarization Converter based on Graphene-shaped Metasurfaces

arXiv (Cornell University), 2020

In this paper, a broadband tunable polarization converter based on graphene metasurfaces is proposed. This polarization converter works in the terahertz (THz) frequency region, using the advantage of graphene characteristics to have a tunable frequency response. The designed graphene-shaped periodic structure on top of the substrate is utilized to convert the incident wave polarization to the desired target in a flexible operational band in the THz frequencies. The polarization conversion ratio is more than 0.85 in a wide range of frequencies in the THz band from 4.86 to 8.42 THz (the fractional bandwidth is 54%). The proposed polarization converter is insensitive to the angle of the incident wave up to 40°. Using graphene provides a tunable frequency response without changing the geometry of the designed structure.

A Review on the Development of Tunable Graphene Nanoantennas for Terahertz Optoelectronic and Plasmonic Applications

Sensors

Exceptional advancement has been made in the development of graphene optical nanoantennas. They are incorporated with optoelectronic devices for plasmonics application and have been an active research area across the globe. The interest in graphene plasmonic devices is driven by the different applications they have empowered, such as ultrafast nanodevices, photodetection, energy harvesting, biosensing, biomedical imaging and high-speed terahertz communications. In this article, the aim is to provide a detailed review of the essential explanation behind graphene nanoantennas experimental proofs for the developments of graphene-based plasmonics antennas, achieving enhanced light–matter interaction by exploiting graphene material conductivity and optical properties. First, the fundamental graphene nanoantennas and their tunable resonant behavior over THz frequencies are summarized. Furthermore, incorporating graphene–metal hybrid antennas with optoelectronic devices can prompt the ackn...

Switched-Beam Graphene Plasmonic Nanoantenna in the Terahertz Wave Region

Plasmonics, 2021

Large-distance communications beyond a few meters is challenging for Terahertz (THz) signals because of high spreading loss and absorption in the media. The smart antenna concept used for RF antennas to improve the signal-to-interference/noise level can be extended to these THz antennas. Out of the two types of implementations of this concept, viz. (i) adaptive array and (ii) switched-beam antenna, this paper presents the switched-beam nanoantenna for the THz wave region. Based on the Yagi-Uda antenna concept, switched-beam graphene nanoantennas over silicon dioxide (SiO2) substrate is proposed in this paper. In one case (Antenna-I), the antenna is able to switch the beam in ± 90º directions, whereas in the other case (Antenna-II), the switching directions are 0º, ± 90º, 180º. This pattern reconfigurability can also be observed over a frequency range leading to simultaneous pattern and frequency reconfigurable nature of the nanoantenna. The reconfigurability is obtained by changing the graphene conductivity through its chemical potential. Due to plasmonic wave propagation in graphene at THz, the proposed graphene nanoantenna resonates at a sub-wavelength scale. Design aspects and the working principle of switched-beam graphene plasmonic nanoantennas in the THz region are discussed in this paper.

Graphene-based optically tunable structure for terahertz polarization control

Journal of Physics: Conference Series

We present a theoretical model of optically tunable graphene-based structure for polarization characteristics control of transmitted terahertz (THz) wave. The experimental verification was performed using a THz time-domain polarimetry setup. The tunability is achieved by applying an external optical pumping and magnetic field. The structure shows the possibility for dynamical control of ellipticity and azimuth angles of polarization state of THz radiation in a transmission mode. This study indicates a strong potential for using graphene-based structures for polarization sensitive applications such as THz wireless communications and biomedical research.

Optically tunable terahertz chiral metasurface based on multi-layered graphene

Scientific Reports

Active manipulation of the polarization states at terahertz frequencies is crucially helpful for polarization-sensitive spectroscopy, having significant applications such as non-contact Hall measurements, vibrational circular dichroism measurements and anisotropy imaging. the weakness of polarization manipulation provided by natural materials can be overcomed by chiral metamaterials. Chiral metamaterials have a huge potential to achieve the necessary polarization effects, hence they provide the basis for applications such as ultracompact polarization components. terahertz chiral metamaterials that allow dynamic polarization modulation of terahertz waves are of great practical interest and still challenging. Here, we show that terahertz metasurface based on the four conjugated "petal" resonators integrated with multi-layered graphene (MLG) can enable dynamically tunable chiroptical response using optical pumping. In particular, a change of ellipticity angle of 20° is observed around 0.76 THz under optical pumping by a 980 nm continuous wave (CW) laser. Furthermore, using temporal coupled-mode theory, our study also reveals that the chiroptical response of the proposed multi-layered graphene-based metasurface is strongly dependent on the influence of optical pumping on the loss parameters of resonance modes, leading to actively controllable polarization states of the transmitted terahertz waves. the present work paves the way for the realization of fundamental terahertz components capable for active polarization manipulation.

Graphene plasmonics for tunable terahertz metamaterials

Nature Nanotechnology, 2011

Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials 1-3. Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour 4-7 that enables new tunable plasmonic metamaterials 8-10 and, potentially, optoelectronic applications in the terahertz frequency range 8,9,11,12. Here we explore plasmon excitations in engineered graphene microribbon arrays. We demonstrate that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behaviour characteristic of two-dimensional massless Dirac electrons 4-6. The plasmon resonances have remarkably large oscillator strengths, resulting in prominent room-temperature optical absorption peaks. In comparison, plasmon absorption in a conventional two-dimensional electron gas was observed only at 4.2 K (refs 13,14). The results represent a first look at light-plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials. Graphene is an attractive two-dimensional (2D) carbon material. Electrons in graphene behave like massless Dirac fermions and exhibit many exotic physical phenomena, ranging from an anomalous quantum Hall effect 15,16 and Klein tunnelling 17,18 in electrical transport to a universal absorption constant 19,20 and tunable interband transitions 21,22 in optical response. Most of these phenomena are well accounted for by single-particle excitation of electrons. Plasmons in graphene, on the other hand, describe collective excitations of 2D massless electrons. Previous studies established that plasmons have an important role in graphene electron dynamics 23 and lead to new composite excitations in the form of plasmarons 24. Plasmon resonances in graphene have also been probed using inelastic electron scattering spectroscopy 25,26 and inelastic scanning tunnelling microscopy 27. However, the fundamental behaviour of light-plasmon coupling in graphene is little known, and the exciting opportunity to design terahertz metamaterials 1-3 using patterned graphene structures has not been explored. Here we report the first study of tunable plasmon excitations and light-plasmon coupling at terahertz frequencies in graphene micro-ribbon arrays. A micro-ribbon array is the simplest form of sub-wavelength infrared metamaterials. Plasmon excitations in such arrays correspond to collective oscillations of electrons across the width of micro-ribbons. We show that such plasmon excitations can be controlled through micro-ribbon width (w) where plasmon frequency scales as w 21/2. This scaling is characteristic of

Highly Directive Graphene Based Hybrid Plasmonic Nanoantenna for Terahertz Applications

AIUB Journal of Science and Engineering (AJSE)

To satisfy the necessity for elevated data transmission rates in 5G and beyond networks, terahertz band communication (0.1 - 10 THz) is envisaged as a crucial wireless technology. Two-dimensional graphene nanomaterial is being extensively integrated into the plasmonic antennas as it allows them to resonate in the terahertz wave spectrum. In this paper, a graphene-based hybrid terahertz plasmonic nano-scale antenna has been modelled to acquire a maximum gain and directivity of 8.1 dB and 8.23 dBi, respectively, by varying the conductivity of graphene via gate bias voltage. Moreover, a combination of several tailored radiating layers of silver, SiO2 and graphene sheets is arranged in the proposed nanoantenna in such a way that the return loss (S11) of -26.595 dB and a wider bandwidth of 1241.3 GHz are obtained. It is evident that the proposed graphene-based hybrid plasmonic nanoantenna could be considered as an ideal candidate for terahertz communication owing to its excellent radiati...

Dynamic Terahertz Beam Steering Based on Graphene Metasurfaces

arXiv (Cornell University), 2015

A full (2π) phase modulation is critical for efficient wavefront manipulation. In this article, a metasurface based on graphene long/short-strip resonators is used to implement a dynamic 2π phase modulation by applying different voltages to different graphene resonators. The configuration is found to have high reflection efficiency (minimum 56%) and has a full phase modulation in a wide frequency range. Terahertz (THz) beam steering as large as 120 degrees (±60 •) is demonstrated in a broad frequency range (1.2 to 1.9 THz) by changing the Fermi levels of different graphene resonators accordingly. This metasurface can provide a new platform for effectively manipulating THz waves.