Browsing by Author "Valuckas, V."

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Open Access
Control of LED emission with functional dielectric metasurfaces
(Wiley, 2020) Khaidarov, E.; Liu, Z.; Paniagua-Domínguez, R.; Ha, S. T.; Valuckas, V.; Liang, X.; Akimov, Y.; Bai, P.; Png, C. E.; Demir, Hilmi Volkan; Kuznetsov, A. I.
The improvement of light‐emitting diodes (LEDs) is one of the major goals of optoelectronics and photonics research. LED integration to complex photonic devices requires precise control of the wavefront of the emitted light. Metasurfaces are spatial arrangements of engineered scatters that may enable this light manipulation capability with unprecedented resolution. Most of these devices, however, are only able to function properly under irradiation of laser light with a large spatial coherence. LEDs, on the other hand, have angularly broad, Lambertian‐like emission patterns characterized by a low spatial coherence, which makes the integration of metasurface devices on LEDs challenging. A novel concept for metasurface integration on LED is proposed, using a cavity to increase the LED spatial coherence through an angular collimation. The experimental demonstration of the proposed concept is implemented on a GaP LED architecture including a hybrid metallic‐Bragg cavity. By integrating a silicon metasurface on top, two different functionalities of these compact devices are demonstrated: directional LED emission at a desired angle and LED emission of a vortex beam with an orbital angular momentum. The presented concept is general, being applicable to other incoherent light sources and enabling metasurfaces designed for plane waves to work with incoherent light emitters.
Open Access
High-efficiency and low-loss gallium nitride dielectric metasurfaces for nanophotonics at visible wavelengths
(American Institute of Physics Inc., 2017) Emani, N. K.; Khaidarov, E.; Paniagua-Domínguez, R.; Fu, Y. H.; Valuckas, V.; Lu S.; Zhang X.; Tan S.T.; Demir, Hilmi Volkan; Kuznetsov, A. I.
The dielectric nanophotonics research community is currently exploring transparent material platforms (e.g., TiO2, Si3N4, and GaP) to realize compact high efficiency optical devices at visible wavelengths. Efficient visible-light operation is key to integrating atomic quantum systems for future quantum computing. Gallium nitride (GaN), a III-V semiconductor which is highly transparent at visible wavelengths, is a promising material choice for active, nonlinear, and quantum nanophotonic applications. Here, we present the design and experimental realization of high efficiency beam deflecting and polarization beam splitting metasurfaces consisting of GaN nanostructures etched on the GaN epitaxial substrate itself. We demonstrate a polarization insensitive beam deflecting metasurface with 64% and 90% absolute and relative efficiencies. Further, a polarization beam splitter with an extinction ratio of 8.6/1 (6.2/1) and a transmission of 73% (67%) for p-polarization (s-polarization) is implemented to demonstrate the broad functionality that can be realized on this platform. The metasurfaces in our work exhibit a broadband response in the blue wavelength range of 430-470 nm. This nanophotonic platform of GaN shows the way to off- and on-chip nonlinear and quantum photonic devices working efficiently at blue emission wavelengths common to many atomic quantum emitters such as Ca+ and Sr+ ions.
Open Access
Hybrid dielectric-plasmonic nanoantenna with multiresonances for subwavelength photon sources
(American Chemical Society, 2023-03-15) Dmitriev, P. A.; Lassalle, E.; Ding, L.; Pan, Z.; Neo, D. C. J.; Valuckas, V.; Paniagua-D., R.; Yang, J. K. W.; Demir, Hilmi Volkan; Kuznetsov, A. I.
The enhancement of the photoluminescence of quantum dots induced by an optical nanoantenna has been studied considerably, but there is still significant interest in optimizing and miniaturizing such structures, especially when accompanied by an experimental demonstration. Most of the realizations use plasmonic platforms, and some also use all-dielectric nanoantennas, but hybrid dielectric-plasmonic (subwavelength) nanostructures have been very little explored. In this paper, we propose and demonstrate single subwavelength hybrid dielectric-plasmonic optical nanoantennas coupled to localized quantum dot emitters that constitute efficient and bright unidirectional photon sources under optical pumping. To achieve this, we devised a silicon nanoring sitting on a gold mirror with a 10 nm gap in-between, where an assembly of colloidal quantum dots is embedded. Such a structure supports both (radiative) antenna mode and (nonradiative) gap mode resonances, which we exploit for the dual purpose of out-coupling the light emitted by the quantum dots into the far-field with out-of-plane directivity, and for enhancing the excitation of the dots by the optical pump. Moreover, almost independent control of the resonance spectral positions can be achieved by simple tuning of geometrical parameters such as the ring inner and outer diameters, allowing us to conveniently adjust these resonances with respect to the quantum dots emission and absorption wavelengths. Using the proposed architecture, we obtain experimentally average fluorescence enhancement factors up to 654× folds mainly due to high radiative efficiencies, and associated with a directional emission of the photoluminescence into a cone of ±17° in the direction normal to the sample plane. We believe the solution presented here to be viable and relevant for the next generation of light-emitting devices.
Open Access
Lasing action in single subwavelength particles supporting supercavity modes
(American Chemical Society, 2020-05) Mylnikov, V.; Ha, S. T.; Pan, Z.; Valuckas, V.; Paniagua-Domínguez, R.; Demir, Hilmi Volkan; Kuznetsov, A. I.
On-chip light sources are critical for the realization of fully integrated photonic circuitry. So far, semiconductor miniaturized lasers have been mainly limited to sizes on the order of a few microns. Further reduction of sizes is challenging fundamentally due to the associated radiative losses. While using plasmonic metals helps to reduce radiative losses and sizes, they also introduce Ohmic losses hindering real improvements. In this work, we show that, making use of quasibound states in the continuum, or supercavity modes, we circumvent these fundamental issues and realize one of the smallest purely semiconductor nanolasers thus far. Here, the nanolaser structure is based on a single semiconductor nanocylinder that intentionally takes advantage of the destructive interference between two supported optical modes, namely Fabry–Perot and Mie modes, to obtain a significant enhancement in the quality factor of the cavity. We experimentally demonstrate the concept and obtain optically pumped lasing action using GaAs at cryogenic temperatures. The optimal nanocylinder size is as small as 500 nm in diameter and only 330 nm in height with a lasing wavelength around 825 nm, corresponding to a size-to-wavelength ratio as low as 0.6.
Open Access
Near-unity emitting, widely tailorable, and stable exciton concentrators built from doubly gradient 2D semiconductor nanoplatelets
(American Chemical Society, 2023-10-24) Liang, X.; Durmuşoğlu, E. G.; Lunina, M.; Hernandez-Martinez, P. L.; Valuckas, V.; Yan, F.; Lekina, Y.; Sharma, V. K.; Yin, T.; Ha, S. T.; Shen, Z. X.; Sun, H.; Kuznetsov, A.; Demir, Hilmi Volkan
The strength of electrostatic interactions (EIs) between electrons and holes within semiconductor nanocrystals profoundly affects the performance of their optoelectronic systems, and different optoelectronic devices demand distinct EI strength of the active medium. However, achieving a broad range and fine-tuning of the EI strength for specific optoelectronic applications is a daunting challenge, especially in quasi two-dimensional core–shell semiconductor nanoplatelets (NPLs), as the epitaxial growth of the inorganic shell along the direction of the thickness that solely contributes to the quantum confined effect significantly undermines the strength of the EI. Herein we propose and demonstrate a doubly gradient (DG) core–shell architecture of semiconductor NPLs for on-demand tailoring of the EI strength by controlling the localized exciton concentration via in-plane architectural modulation, demonstrated by a wide tuning of radiative recombination rate and exciton binding energy. Moreover, these exciton-concentration-engineered DG NPLs also exhibit a near-unity quantum yield, high photo- and thermal stability, and considerably suppressed self-absorption. As proof-of-concept demonstrations, highly efficient color converters and high-performance light-emitting diodes (external quantum efficiency: 16.9%, maximum luminance: 43,000 cd/m2) have been achieved based on the DG NPLs. This work thus provides insights into the development of high-performance colloidal optoelectronic device applications.