Abstract-Tunable plasmonic toroidal terahertz metamodulator

Burak Gerislioglu, Arash Ahmadivand, and Nezih Pala

https://journals.aps.org/prb/accepted/a007fO69A30E071822288ce861d87db2c9e4e9c5c

Optical modulators are essential and strategic parts of micro and nanophotonic circuits to encode electro-optical signals to the optical domain. Here, by using arrays of multipixel toroidal plasmonic terahertz (THz) metamolecules, we developed a functional plasmonic metamodulator with high efficiency and tunability. Technically, the dynamic toroidal dipole induces nonradiating charge-current arrangements leading to have exquisite role in defining the inherent spectral features of various materials. By categorizing in a different family of multipoles far from traditional electromagnetic multipoles, the toroidal dipole corresponds to poloidal currents flowing on the surface of a closed-loop torus. Utilizing the sensitivity of the optically driven toroidal momentum to the incident THz beam power, and by employing both numerical tools and experimental analysis, we systematically studied the spectral response of the proposed THz plasmonic metadevice. In this study, we uncover a correlation between the existence and excitation of toroidal response and the incident beam power. This mechanism is employed to develop THz toroidal metamodulators with strong potential to be employed for practical advanced and next-generation communication, filtering, and routing applications

Abstract-Extreme sensitive metasensor for targeted biomarkers identification using colloidal nanoparticles-integrated plasmonic unit cells

Arash Ahmadivand, Burak Gerislioglu, Asahi Tomitaka, Pandiaraj Manickam, Ajeet Kaushik, Shekhar Bhansali, Madhavan Nair, and Nezih Pala

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-2-373&origin=search

Engineered terahertz (THz) plasmonic metamaterials have emerged as promising platforms for quick infection diagnosis, cost-effective and real-time pharmacology applications owing to their non-destructive and harmless interaction with biological tissues in both in vivo and in vitroassays. As a recent member of THz metamaterials family, toroidal metamaterials have been demonstrated to be supporting high-quality sharp resonance modes. Here we introduce a THz metasensor based on a plasmonic surface consisting of metamolecules that support ultra-narrow toroidal resonances excited by the incident radiation and demonstrate detection of an ultralow concertation targeted biomarker. The toroidal plasmonic metasurface was designed and optimized through extensive numerical studies and fabricated by standard microfabrication techniques. The surface then functionalized by immobilizing the antibody for virus-envelope proteins (ZIKV-EPs) for selective sensing. We sensed and quantified the ZIKV-EP in the assays by measuring the spectral shifts of the toroidal resonances while varying the concentration. In an improved protocol, we introduced gold nanoparticles (GNPs) decorated with the same antibodies onto the metamolecules and monitored the resonance shifts for the same concentrations. Our studies verified that the presence of GNPs enhances capturing of biomarker molecules in the surrounding medium of the metamaterial. By measuring the shift of the toroidal dipolar momentum (up to Δω~0.35 cm−1) for different concentrations of the biomarker proteins, we analyzed the sensitivity, repeatability, and limit of detection (LoD) of the proposed toroidal THz metasensor. The results show that up to 100-fold sensitivity enhancement can be obtained by utilizing plasmonic nanoparticles-integrated toroidal metamolecules in comparison to analogous devices. This approach allows for detection of low molecular-weight biomolecules (≈13 kDa) in diluted solutions using toroidal THz plasmonic unit cells.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Tunable Plasmonic Toroidal Terahertz Metamodulator

Burak Gerislioglu, Arash Ahmadivand,  Nezih Pala,

https://arxiv.org/ftp/arxiv/papers/1712/1712.04908.pdf

Optical modulators are essential parts of photonic circuits to encode electro-optical signals to the optical domain. Here, using arrays of multipixel toroidal plasmonic terahertz (THz) metamolecules, we developed a plasmonic metamodulator with high efficiency and tunability. Using the ultrasensitivity of the excited toroidal momentum to the incident THz beam power, we numerically and experimentally studied the plasmonic response of the proposed device. We showed that the proposed THz toroidal metamodulator have strong potential to be employed for practical advanced communication applications

Abstract-Tunable THz wave absorption by graphene-assisted plasmonic metasurfaces based on metallic split ring resonators

Arash Ahmadivand, Raju Sinha, Mustafa Karabiyik, Phani Kiran Vabbina, Burak Gerislioglu, Serkan Kaya, Nezih Pala

https://www.springerprofessional.de/en/tunable-thz-wave-absorption-by-graphene-assisted-plasmonic-metas/11953806

Graphene plasmonics has been introduced as a novel platform to design various nano- and microstructures to function in a wide range of spectrum from optical to THz frequencies. Herein, we propose a tunable plasmonic metamaterial in the THz regime by using metallic (silver) concentric microscale split ring resonator arrays on a multilayer metasurface composed of silica and silicon layers. We obtained an absorption percentage of 47.9% including two strong Fano resonant dips in THz regime for the purely plasmonic metamaterial without graphene layer. Considering the data of an atomic graphene sheet (with the thickness of ~0.35 nm) in both analytical and experimental regimes obtained by prior works, we employed a graphene layer under concentric split ring resonator arrays and above the multilayer metasurface to enhance the absorption ratio in THz bandwidth. Our numerical and analytical results proved that the presence of a thin graphene layer enhances the absorption coefficient of MM to 64.35%, at the highest peak in absorption profile that corresponds to the Fano dip position. We also have shown that changing the intrinsic characteristics of graphene sheet leads to shifts in the position of Fano dips and variations in the absorption efficiency. The maximum percentage of absorption (~67%) was obtained for graphene-based MM with graphene layer with dissipative loss factor of 1477 Ω. Employing the antisymmetric feature of the split ring resonators, the proposed graphene-based metamaterial with strong polarization dependency is highly sensitive to the polarization angle of the incident THz beam.

Abstract-Graphene-based field-effect transistor structures for terahertz applications

[SPIE Proceedings]

Ahmad Abbas ; Mustafa Karabiyik ; Nezih Pala
http://proceedings.spiedigitallibrary.org/article.aspx?articleid=1353728
We propose Terahertz (THz) plasmonic devices based on linearly integrated FETs (LFETs) on Graphene. LFET structures are advantageous for (THz) detection since the coupling between the THz radiation and the plasma wave is strongly enhanced over the single gate devices and accordingly higher-order plasma resonances become possible. AlGaN/GaN heterostructure LFETs with their high sheet carrier concentration and high electron mobility are promising for plasmonic THz detection. Nevertheless, our numerical studies show that room temperature resonant absorption of THz radiation by the plasmons in AlGaN/GaN LFETs is very weak even if the integration density is sufficiently large. Our simulations also demonstrate that similar LFETs on Graphene, which has very large electron mobility, can resonantly absorb THz radiation up to 5th harmonic at room temperature. Additionally, we investigated LFETs with integrated cavities on Graphene. Such Periodic Cavity LFETs substantially enhance the quality factor of the resonant modes.