Photonics / Fotonik

Permanent URI for this collectionhttps://hdl.handle.net/11147/2590

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Author: search.filters.author.Kocabaş, ÇoşkunCOAR Access Rights: search.filters.coarAccessRights.open access

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  • Article
    Citation - WoS: 17
    Citation - Scopus: 19
    Strong Coupling of Carbon Quantum Dots in Liquid Crystals
    (American Chemical Society, 2022) Sarısözen, Sema; Polat, Nahit; Mert Balcı, Fadime; Güvenç, Çetin Meriç; Kocabaş, Çoşkun; Yağlıoğlu, Halime Gül; Balcı, Sinan
    Carbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorption spectroscopy, and CDs display very stable and strong photoluminescence emission with a quantum yield of 35.4% and a lifetime of ∼2 ns. More importantly, we compare J-aggregate dyes with CDs in terms of their absorption line width, photostability, and ability to do strong coupling, and we conclude that highly fluorescent CDs have a bright future in the mixed light-matter states for emerging applications in future quantum technologies.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 11
    Graphene-Quantum Dot Hybrid Optoelectronics at Visible Wavelengths
    (American Chemical Society, 2018) Salihoğlu, Ömer; Kakenov, Nurbek; Balcı, Osman; Balcı, Sinan; Kocabaş, Çoşkun
    With exceptional electronic and gate-tunable optical properties, graphene provides new possibilities for active nanophotonic devices. Requirements of very large carrier density modulation, however, limit the operation of graphene based optical devices in the visible spectrum. Here, we report a unique approach that avoids these limitations and implements graphene into optoelectronic devices working in the visible spectrum. The approach relies on controlling nonradiative energy transfer between colloidal quantum-dots and graphene through gate-voltage induced tuning of the charge density of graphene. We demonstrate a new class of large area optoelectronic devices including fluorescent display and voltage-controlled color-variable devices working in the visible spectrum. We anticipate that the presented technique could provide new practical routes for active control of light-matter interaction at the nanometer scale, which could find new implications ranging from display technologies to quantum optics.
  • Article
    Citation - WoS: 134
    Citation - Scopus: 136
    Electrically Switchable Metadevices Via Graphene
    (American Association for the Advancement of Science, 2018) Balcı, Osman; Kakenov, Nurbek; Karademir, Ertuğrul; Balcı, Sinan; Çakmakyapan, Semih; Polat, Emre O.; Çağlayan, Hümeyra; Özbay, Ekmel; Kocabaş, Çoşkun
    Metamaterials bring subwavelength resonating structures together to overcome the limitations of conventional materials. The realization of active metadevices has been an outstanding challenge that requires electrically reconfigurable components operating over a broad spectrum with a wide dynamic range. However, the existing capability of metamaterials is not sufficient to realize this goal. By integrating passive metamaterials with active graphene devices, we demonstrate a new class of electrically controlled active metadevices working in microwave frequencies. The fabricated active metadevices enable efficient control of both amplitude (>50 dB) and phase (>90°) of electromagnetic waves. In this hybrid system, graphene operates as a tunable Drude metal that controls the radiation of the passive metamaterials. Furthermore, by integrating individually addressable arrays of metadevices, we demonstrate a new class of spatially varying digital metasurfaces where the local dielectric constant can be reconfigured with applied bias voltages. In addition, we reconfigure resonance frequency of split-ring resonators without changing its amplitude by damping one of the two coupled metasurfaces via graphene. Our approach is general enough to implement various metamaterial systems that could yield new applications ranging from electrically switchable cloaking devices to adaptive camouflage systems.