Browsing by Subject "Electrically tunable"

Now showing 1 - 7 of 7

Open Access
Broadband THz modulators based on multilayer graphene on PVC
(IEEE, 2016) Kaya, E.; Kakenov, Nurbek; Kocabaş, Coşkun; Altan, H.; Esentürk, O.
In this study we present the direct terahertz time-domain spectroscopic measurement of CVD-grown multilayer graphene (MLG) on PVC substrate with an electrically tunable Fermi level. In a configuration consisting MLG and injected organic dopant, the transmitted intensity loss of terahertz radiation was observed with an applied voltage between 0 and 3.5 V. We showed that MLG on PVC devices provided approximately 100 % modulation between 0.2 and 1.5 THz at preferentially low operation voltage of ca. 3V. The observed modulation bandwidth in terahertz frequencies appears to be instrument limited.
Open Access
Electrically controlled resistive switching assisted active ultra-broadband optical tunability in the infrared
(IEEE, 2013) Battal, Enes; Özcan, Ayşe; Okyay, Ali Kemal
We present an electrically tunable optical device with ultra-broadband tunability operating in 2-10 μm spectrum. We also, for the first time, optically observe resistive switching behavior in reflection measurements under electrical bias. © 2013 IEEE.
Open Access
Graphene-based optical modulators
(World Scientific Publishing Co. Pte. Ltd., 2017) Balci S.; Kocabas, C.
In this chapter, we summarize the recent progress on graphene based optical modulators. Ability to control density of high mobility electrons on large area graphene surface enables realization of new type of electrooptical modulators in optoelectronics. Due to the low electronic density of states, accumulation of charges on graphene significantly shifts the Fermi energy up to 1 eV giving rise to profound optical effects in the infrared and visible spectra. On the other hand, graphene operates as a tunable Drude metal in long wavelengths such as THz and microwave. This unique broadband activity of graphene has stimulated a great deal of interest in graphene community due to its potential use in new optoelectronic devices. After discussing the electrically tunable optical properties of graphene, we highlight the key achievements in the field.
Open Access
Metamaterials as broadband absorbers, tunable color filters, and multi-functional metasurfaces
(2019-06) Aalizadeh, Majid
Metamaterials have enabled us to come up with artificial structures and designs that can perform optical functionalities which are not achievable with natural materials. Here we design and implement three important applications of metamaterials as: 1. Ultra-broadband absorbers, 2. Real-time tunable color filters, and 3. Wideband and wide-angle efficient beam deflector and Multi-functional angular filter. By lithogra-phy being a major hinder on the way to mass production and cost-effectiveness, most of our works are lithography-free. We have introduced Manganese (Mn) for the first time as a very promising metal for broadband absorption and have used it in all our works. Four different Mn-based broadband absorbers are designed and fabricated in different chapters. Mn is used in the Metal-Insulator-Metal (MIM) cavity, annealed MIM configuration, top-layer-patterned MIM configuration, and random nanopyra-mids. It is shown in all works that Mn has a much better performance compared to other metals. For instance, in the work based on random nanopyramids, we obtain ultraviolet (UV) to far-infrared (FIR) perfect absorption by exploiting a lithography-free method and only by coating a single Mn layer on a high-roughness substrate. Moreover, using the combination of the MIM cavity and an electro-optic material, we have shown that a lithography-free color filter can be achieved that covers the whole visible spectrum by changing the voltage from -12 to 12 volts. Finally, in a structure composed of Silicon nano-rods, an ultra-wideband and wide-angle highly-efficient beam deflection is obtained. What makes the same structure very promising is that it also has multifunctional applications as band-pass, band-stop, and low-pass angular filter.
Open Access
Observation of gate-tunable coherent perfect absorption of terahertz radiation in graphene
(American Chemical Society, 2016) Kakenov, N.; Balci, O.; Takan, T.; Ozkan, V. A.; Altan, H.; Kocabas, C.
We report experimental observation of electrically tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode, and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1 eV and to achieve a critical coupling condition at 2.8 THz with absorption of 99%. With the enhanced THz absorption, we were able to measure the Fermi energy dependence of the transport scattering time of highly doped graphene. Furthermore, we demonstrate flexible active THz surfaces that yield large modulation in the THz reflectivity with low insertion losses. We anticipate that the gate-tunable CPA will lead to efficient active THz optoelectronics applications.
Open Access
Plasmonically enhanced ZnO thin-film-photo-transistor with dynamic responsivity control
(IEEE, 2013) Özcan, Ayşe; Battal, Enes; Atar, Fatih Bilge; Okyay, Ali Kemal
We fabricated an ZnO based thin-film photo-transistor with electrically tunable photo-responsivity operating in the UV and visible spectra and designed plasmonic structures enhancing the device performance up to 6 folds below the band-gap of ZnO. © 2013 IEEE.
Open Access
Resonance broadening and tuning of split ring resonators by top-gated epitaxial graphene on SiC substrate
(AIP Publishing LLC, 2013) Cakmakyapan, S.; Sahin, L.; Pierini, F.; Strupinski, W.; Özbay, Ekmel
Split ring resonators (SRRs) are subwavelength structures that are able to localize and enhance the electromagnetic wave. Controlling the plasmonic resonance behavior of metallic nanostructures, such as SRRs, plays an important role in optoelectronics and nanophotonics applications. Electrically tunable carrier concentration of graphene provides hybrid devices, where the plasmonic structures and graphene are combined. In this paper, we report the design, fabrication, and measurement of a device comprising a SRR array on epitaxial graphene. We obtained resonance broadening and tuning of split ring resonators by utilizing an epitaxial graphene transistor with transparent top-gate.