Browsing by Author "Takan, T."

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    Compressive sensing imaging with a graphene modulator at THz frequency in transmission mode
    (IEEE, 2016) Özkan, V. A.; Takan, T.; Kakenov, Nurbek; Kocabaş, Coşkun; Altan, H.
    In this study we demonstrate compressive sensing imaging with a unique graphene based optoelectronic device which allows us to modulate the THz field through an array of columns or rows distributed throughout its face.
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    Electrically controlled terahertz spatial light modulators with graphene arrays
    (IEEE, 2016) Kakenov, Nurbek; Takan, T.; Özkan, V. A.; Balcı, Osman; Polat, Emre Ozan; Altan, H.; Kocabaş, Coşkun
    Gate-tunable high-mobility electrons on atomically thin graphene layers provide a unique opportunity to control electromagnetic waves in a very broad spectrum. In this paper, we describe an electrically-controlled multipixel terahertz light modulators. The spatial light modulator is fabricated using two large-area graphene layers grown by chemical vapor deposition and transferred on THz transparent and flexible substrates. Room temperature ionic liquid, inserted between the graphene, provides mutual gating between the graphene layers. We used passive matrix addressing to control local charge density thus the THz transmittance. With this device configuration, we were able to obtain 5×5 arrays of graphene modulator with 65% modulation between 0.1 to 1.5 THz.
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    Graphene-enabled electrically controlled terahertz spatial light modulators
    (Optical Society of America, 2015-05-01) Kakenov, N.; Takan, T.; Ozkan, V. A.; Balcı, O.; Polat, E. O.; Altan, H.; Kocabas, C.
    In this Letter, we demonstrate a broadband terahertz (THz) spatial light modulator using 5×5 arrays of large area graphene supercapacitors. Our approach relies on controlling spatial charge distribution on a passive matrix array of patterned graphene electrodes. By changing the voltage bias applied to the rows and columns, we were able to pattern the THz transmittance through the device with high modulation depth and low operation voltage. We anticipate that the simplicity of the device architecture with high contrast THz modulation over a broad spectral range could provide new tools for THz imaging and communication systems.
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    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.