Browsing by Subject "Nanoantennas"

Now showing 1 - 5 of 5

Open Access
Nanoantenna couplers for metal-insulator-metal waveguide interconnects
(SPIE, 2010) Onbasli, M.C.; Okyay, Ali Kemal
State-of-the-art copper interconnects suffer from increasing spatial power dissipation due to chip downscaling and RC delays reducing operation bandwidth. Wide bandwidth, minimized Ohmic loss, deep sub-wavelength confinement and high integration density are key features that make metal-insulator-metal waveguides (MIM) utilizing plasmonic modes attractive for applications in on-chip optical signal processing. Size-mismatch between two fundamental components (micron-size fibers and a few hundred nanometers wide waveguides) demands compact coupling methods for implementation of large scale on-chip optoelectronic device integration. Existing solutions use waveguide tapering, which requires more than 4λ-long taper distances. We demonstrate that nanoantennas can be integrated with MIM for enhancing coupling into MIM plasmonic modes. Two-dimensional finite-difference time domain simulations of antennawaveguide structures for TE and TM incident plane waves ranging from λ = 1300 to 1600 nm were done. The same MIM (100-nm-wide Ag/100-nm-wide SiO2/100-nm-wide Ag) was used for each case, while antenna dimensions were systematically varied. For nanoantennas disconnected from the MIM; field is strongly confined inside MIM-antenna gap region due to Fabry-Perot resonances. Major fraction of incident energy was not transferred into plasmonic modes. When the nanoantennas are connected to the MIM, stronger coupling is observed and E-field intensity at outer end of core is enhanced more than 70 times. © 2010 SPIE.
Open Access
Performance enhancement of graphene based optoelectronic devices
(2016-08) Özdemir, Onur
Graphene is a strong candidate for active optoelectronic devices because of its electrostatically tunable optical response. Current substrate back-gating methods are unable to sustain high fields through graphene unless a high gate voltage is applied. In order to solve this problem, ionic liquid gating is used which allows substrate front side gating, thus eliminating major loss factors such as a dielectric layer and a thick substrate layer. On the other hand, due to its two dimensional nature, graphene interacts weakly with light and this interaction limits its efficiency in optoelectronic devices. However, V-shaped plasmonic antennas can be used to enhance the incident electric field intensity and confine the electric field near graphene thus allowing further interaction with graphene. Combining V-shaped nanoantennas with the tunable response of graphene, the operation wavelength of the devices that employ V-shaped antennas can be tuned in situ. We demonstrate a reflection enhancement by utilising different V-shaped nanoantenna geometries on a Si-SiO2 substrate. After studying the response of these nanoantennas, we demonstrate a graphene-based device with ionic liquid gating and V-shaped plasmonic antennas to both enhance and more effectively tune the total optical response. We are able to tune the transmission response of the device for up to 389 nm by changing the gate voltage by 3.8 Volts in the mid-infrared regime.
Open Access
Plasmonic nanoantennas for enhanced light-matter interactions and graphene based tunable nanophotonic devices
(2015) Çakmakyapan, Semih
Focusing, manipulating and beaming of electromagnetic waves are important for many applications such as antennas, optical isolators, biological sensor, chemical sensors, and solar cells. There is an extensive research about the manipulation of light, and its interaction with di erent types of materials including subwavelength structures. However, manipulating light at the nanoscale has many di culties due to the di raction limit. In this thesis, we mainly focus on the characterization and experiments of subwavelength plasmonic structures. We investigated the spatial distribution of the electric eld through subwavelength slits by using symmetric and non-symmetric periodic metallic grating structures in order to obtain one-way transmission, o -axis beaming, collimation and diode-like beaming. We also studied various plasmonic structures such as circular rings and fractal bowtie antennas. After combining them with Raman active molecules, we showed that these plasmonic structures can be used as e cient surface enhanced Raman spectroscopy substrates. Finally, we designed, fabricated and measured nanoantennas and split ring resonators on graphene in order to tune their optical response using the electrically controllable doping property of the graphene.
Open Access
Resonance tuning and broadening of bowtie nanoantennas on graphene
(Elsevier BV, 2014-04) Cakmakyapan, S.; Sahin, L.; Pierini, F.; Özbay, Ekmel
Metallic bowtie antennas are used in nanophotonics applications in order to confine the electromagnetic field into volumes much smaller than that of the incident wavelength. Electrically controllable carrier concentration of graphene opens the door to the use of plasmonic nanoantenna structures with graphene so that the resonant nature of nanoantennas can be tuned. In this study, we demonstrated with the Fourier transform infrared (FTIR) spectroscopy and the Finite Difference Time Domain (FDTD) method that the intensity and resonance peak of bowtie nanoantennas on monolayer graphene can be tuned at mid-infrared (MIR) wavelength regime by applying a gate voltage, since the optical properties of graphene change by changing the carrier concentration. (C) 2014 Elsevier B.V. All rights reserved.
Open Access
Three-dimensional study of planar optical antennas made of split-ring architecture outperforming dipole antennas for increased field localization
(Optical Society of America, 2012-01-09) Kilic, V. T.; Erturk, V. B.; Demir, Hilmi Volkan
Optical antennas are of fundamental importance for the strongly localizing field beyond the diffraction limit. We report that planar optical antennas made of split-ring architecture are numerically found in three-dimensional simulations to outperform dipole antennas for the enhancement of localized field intensity inside their gap regions. The computational results (finite-difference time-domain) indicate that the resulting field localization, which is of the order of many thousandfold, in the case of the split-ring resonators is at least 2 times stronger than the one in the dipole antennas resonant at the same operating wavelength, while the two antenna types feature the same gap size and tip sharpness.