Browsing by Author "Habib, Mohsin"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Open Access Connection of collimation, asymmetric beaming, and independent transmission-reflection processes in concentric-groove gratings supporting spoof surface plasmons(Springer, 2019) Habib, Mohsin; Serebryannikov, A. E.; Çağlayan, H.; Vandenbosch, G. A. E.; Özbay, EkmelTransmission through subwavelength apertures enables separation of the incidence half-space and the exit half-space, which leads to that the spatial distribution of the field in the latter is not affected by the distribution in the former. The distribution in the exit half-space is mainly determined by the properties of surface plasmons (SPs) at the exit-side interface. In this paper, for the microwave structures with one-side concentric corrugations around a single annular hole, we demonstrate the possible connections between asymmetric transmission in the beaming regime and collimation of the waves incident at different angles, which can be considered as two sides of the same phenomenon occurring due to the common effect of such a separation and the radiation shaping effect being possible due to the spoof SPs at the corrugated exit interface. Collimation manifests itself in that the waves incident at different angles from a wide range contribute to the single outgoing beam so that a far-zone observer cannot distinguish between the contributions of different angles of arrival. Asymmetry in transmission manifests itself in that the spatial shaping of radiation (beaming) in the exit half-space appears only for one of the two opposite incidence directions. Moreover, even in the structures with the same corrugations on both sides, i.e., without asymmetric transmission, spatial separation of two wave processes, e.g., two symmetric or asymmetric collimation processes, can be obtained for a wide range of nonzero angles of incidence.Item Open Access Electrically controllable plasmon induced reflectance in hybrid metamaterials(American Institute of Physics, 2018) Habib, Mohsin; Gökbayrak, Murat; Özbay, Ekmel; Cağlayan, H.The tunable plasmon induced reflectance (PIR) effect has been numerically investigated and experimentally realized by hybrid metal-graphene metamaterials. The PIR effect is produced by two parallel strips of gold (Au) and controlled electrically by applying the gate voltage to the graphene layer. The PIR response is generated by the weak hybridization of two bright modes of the gold strips and tuned by changing the Fermi level (Ef) of the graphene. The total shift of 211.7 nm was achieved in the reflection peak by applying only 3 V. This concept of real time electrical tuning of PIR, with a modulation depth of ∼49% and a spectral contrast ratio of 66.6%, can be used for designing optical switches, optical modulators, and tunable sensors.Item Open Access Electrically tunable plasmon induced transparency in hybrid metal-graphene structures(Bilkent University, 2018-06) Habib, MohsinHybrid metal-graphene structures offer design flexibility to manipulate and control light efficiently. These structures can be used to generate tunable plasmon induced transparency (PIT) in transmission and reflection mode. PIT is plasmonic analogue of electromagnetically induced transparency (EIT). PIT and reflection type PIT (RPIT) devices have been investigated experimentally but they are not tunable, and the numerical investigations of the tunable designs were limited to simulations. A hybrid metal-graphene design is used to overcome these challenges in this thesis. Tunable PIT and RPIT devices can be used for tunable enhanced biosensing and switchable systems. PIT-effect has been numerically investigated and experimentally realized in two devices with different dimensions. Numerical simulations were performed using Finite Difference Time-Domain (FDTD) method. The design is based on two parallel gold (Au) strips on top of the graphene layer. PIT-effect has been achieved by weak hybridization of two bright modes of these Au strips. The PIT-effect is tuned by changing the Fermi energy (Ef) of graphene. Top gating method is used to achieve high tunability in the experiments. Total shift of 263 nm is obtained in the PIT window by applying the gate voltage up to 3 V. The spectral contrast ratio of the devices is up to 82%. In addition, tunable RPIT effect is achieved using the same metal-graphene structure. I have numerically investigated the four layers design and experimentally realized tunable RPIT. The response of this device is also tuned using top gating method. The tunability of 220.8 nm is observed in RPIT peak for 3 V.Item Open Access Tunable reflection type plasmoninduced transparency with graphene(Institute of Electrical and Electronics Engineers, 2018) Habib, Mohsin; Özbay, Ekmel; Caglayan, H.Plasmon induced transparency (PIT) has always been investigated in transmission mode, which makes the design dependent upon the type of substrate. In this work, we propose a first tunable reflection type PIT (RPIT) device based on simple design of two parallel gold strips on graphene. We have numerically investigated the design by using Finite Difference Time-Domain (FDTD) method. This response is tunable by changing the Fermi level (Ef) of graphene. High tunability of 215 nm shift was observed by changing the Ef of graphene from 0 to 0.8 eV. The spectral contrast ratio of our device is 99.2%.