Browsing by Subject "Color filter"

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Open Access
Bismuth-based metamaterials: From narrowband reflective color filter to extremely broadband near perfect absorber
(De Gruyter, 2019) Ghobadi, Amir; Hajian, Hodjat; Gökbayrak, Murat; Bütün, Bayram; Özbay, Ekmel
In recent years, sub-wavelength metamaterials-based light perfect absorbers have been the subject of many studies. The most frequently utilized absorber configuration is based on nanostructured plasmonic metals. However, two main drawbacks were raised for this design architecture. One is the fabrication complexity and large scale incompatibility of these nano units. The other one is the inherent limitation of these common metals which mostly operate in the visible frequency range. Recently, strong interference effects in lithography-free planar multilayer designs have been proposed as a solution for tackling these drawbacks. In this paper, we reveal the extraordinary potential of bismuth (Bi) metal in achieving light perfect absorption in a planar design through a broad wavelength regime. For this aim, we adopted a modeling approach based on the transfer matrix method (TMM) to find the ideal conditions for light perfect absorption. According to the findings of our modeling and numerical simulations, it was demonstrated that the use of Bi in the metal-insulator-metal-insulator (MIMI) configuration can simultaneously provide two distinct functionalities; a narrow near unity reflection response and an ultra-broadband near perfect absorption. The reflection behavior can be employed to realize additive color filters in the visible range, while the ultra-broadband absorption response of the design can fully harvest solar irradiation in the visible and near infrared (NIR) ranges. The findings of this paper demonstrate the extraordinary potential of Bi metal for the design of deep sub-wavelength optical devices.
Open Access
Color generation and enhancement using large-scale compatible metamaterial design architectures
(2022-01) Köşger, Ali Cahit
Metamaterials are a type of artificial matt that can impose exotic functionalities beyond natural materials. These specifically designed sub-wavelength structures acquire these functionalities from their collective geometric arrangement rather than their individual single-unit properties. As a result, metamaterials have shown promising applications, including negative refraction, artificial magnetism, asymmetric transmission, lasing, and cloak of invisibility. Among all these applications, the concept of color generation and enhancement using metamaterial designs have attracted much attention in recent years. We can achieve color generation from two primary sources: i) filtering white light, and ii) generating light from emitting materials such as quantum dots. In color generation using white light, a metamaterial design reflects or transmits a narrow portion of the incident spectrum. Thus, the design acts as a color filter. However, the source is already a narrowband color light in the second category. Thus metamaterials merely amplify the color intensity rather than manipulate its spectral response. In this thesis, metamaterial structures are designed, fabricated, and characterized in both categories mentioned above; The content of this thesis consists of two parts; i) In the first part, we generated additive red-green-blue (RGB) colors in reflectance mode with near-unity amplitude. For this purpose, we designed a multilayer structure made of metal-insulator-metal-semiconductor-insulator (MIMSI) stacks to achieve >0.9 reflection peaks with full-width-at-half-maximum (FWHM) values <0.3λpeak. The proposed design also shows near-zero reflection in off-resonance spectral ranges, which, in turn, leads to high color purity. Finally, we fabricated the optimized designs and verified the simulation and theoretical results with characterization findings. This work demonstrates the potential of multilayer tandem cavity designs in realizing lithography-free large-scale compatible functional optical coatings. ii) In the second part, we utilized a large-scale compatible plasmonic nanocavity design platform to achieve almost an order of magnitude photoluminescence enhancement from light-emitting quantum dots. The proposed design is multi-sized/multi-spacing gold (Au) nano units that are uniformly wrapped with thin aluminum oxide (Al2O3) layer as a foreign host to form a metal-insulator-semiconductor (MIS) cavity, as we coated them with semiconductor quantum dots (QDs). Our numerical and experimental data demonstrate that, in an optimal insulator layer thickness, the simultaneous formation of broadband Fabry-Perot (FP) resonances and plasmonic hot spots leads to enhanced light absorption within the QD unit. This improvement in absorption response leads to the PL enhancement of QDs. This work demonstrates the potential and effectiveness of a host comprised of random plasmonic nanocavities in the realization of lithography-free efficient emitters. Overall, this thesis presents an alternative perspective on applying large-scale compatible metamaterials in color generation. Furthermore, the proposed designs and routes can be extended toward other functional photoelectronic designs, where high performances can be acquired in scaleable architectures.