Browsing by Subject "Optical modulator"

Now showing 1 - 4 of 4

Open Access
Broadband optical modulators based on graphene supercapacitors
(American Chemical Society, 2013) Polat, E. O.; Kocabas, C.
Optical modulators are commonly used in communication and information technology to control intensity, phase, or polarization of light. Electro-optic, electroabsorption, and acousto-optic modulators based on semiconductors and compound semiconductors have been used to control the intensity of light. Because of gate tunable optical properties, graphene introduces new potentials for optical modulators. The operation wavelength of graphene-based modulators, however, is limited to infrared wavelengths due to inefficient gating schemes. Here, we report a broadband optical modulator based on graphene supercapacitors formed by graphene electrodes and electrolyte medium. The transparent supercapacitor structure allows us to modulate optical transmission over a broad range of wavelengths from 450 nm to 2 μm under ambient conditions. We also provide various device geometries including multilayer graphene electrodes and reflection type device geometries that provide modulation of 35%. The graphene supercapacitor structure together with the high-modulation efficiency can enable various active devices ranging from plasmonics to optoelectronics. © 2013 American Chemical Society.
Open Access
Graphene based optoelectronics in the visible spectrum
(2015) Polat, Emre Ozan
Graphene, a two dimensional crystal of carbon atoms, emerges as a viable material for optoelectronics because of its electrically-tunable broadband optical properties. Optical response of graphene at visible and near infrared frequencies is defined by inter-band electronic transitions. By electrical tuning of the Fermi energy, the inter-band transitions can be blocked due to Pauli blocking. However, controlling inter-band transitions of graphene in the visible and near infrared wavelengths, has been an outstanding challenge. We developed a new device to control optical properties of graphene in the visible spectra. Our device relies on a graphene supercapacitor which includes two parallel graphene electrodes and electrolyte between them. Mutual gating between graphene electrodes enables us to fabricate optical modulators which can operate in the visible and near-infrared. Single layer graphene, however, has performance limits due to its small optical absorption defined by fundamental constants. We extend our method and we developed a new class of electrochromic devices using multilayer graphene. Fabricated devices undergo a reversible color change with the electrically controlled intercalation process. The electrical and optical characterizations of the electrochromic devices reveal the broadband optical modulation up to 55 per cent in the visible and near-infrared. Integration of semiconducting materials on unconventional substrates enables optoelectronic devices with new mechanical functionalities that cannot be achieved with wafer-based technologies. As a novel application, we demonstrate ultra thin electronic paper displays using the multilayer graphene as a reconfigurable optical medium. We anticipate that the developed devices would find wide range of applications in optoelectronics.
Open Access
Organic Electrolytes for Graphene-Based Supercapacitor: Liquid, Gel or Solid
(Elsevier Ltd, 2016) Kovalska, E.; Kocabas, C.
The electrolyte is an important and decisive factor in battery, capacitor and supercapacitor fabrication. Here we report how electrolyte's provenance and structure effect on the electro-optical properties of the graphene-based supercapacitor. The three organic electrolytes were synthesized: liquid electrolyte, which on the basis of propylene carbonate (PC), gel electrolyte - polyvinyl alcohol (PVA) and solid electrolyte - polyvinylidene fluoride (PVDF). As an application, we demonstrate an optical modulator using supercapacitor structure built by graphene electrodes and prepared electrolytes. All organic electrolyte-based supercapacitors potentiate optical modulation of graphene electrodes over a broad range of wavelengths, under ambient conditions. We reveal higher capacitance (78 μF/cm2) for a supercapacitor with gel electrolyte during various bias voltages. We represent the increasing of light transmission at 3 times using solid electrolyte, in comparison with liquid and gel electrolytes and illustrate the supercapacitor possibility with gel electrolyte to operate under negative voltage. Consequently, we suggest applying of solid electrolyte as a more appropriate electrolyte for fabrication of graphene-based supercapacitor. We anticipate that using of solid electrolyte allows us to get desired electro-optical properties, minimize the size of the device and vary it shape.
Open Access
ZnO based optical modulator in the visible wavelengths
(SPIE, 2013) Okyay, Ali Kemal; Aygun, Levent E.; Oruç, Feyza B.
In order to demonstrate tunable absorption characteristics of ZnO, photodetection properties of ZnO based thin-film transistors are investigated. By controlling the occupancy of the trap states, the optical absorption coefficient of ZnO in the visible light spectrum is actively tuned with gate bias. An order of magnitude change of absorption coefficient is achieved. An optical modulator is proposed exploiting such tunable absorption mechanism. © 2013 SPIE.