KEYWORDS: Resonators, Dielectrics, Simulations, Electrical conductivity, Signal detection, Sensors, Electric fields, Signal to noise ratio, Infrared detectors
Here, simulations of a photoconductive scatterer in a system of two parallel dielectric resonators operating at a non-Hermitian degeneracy, or exceptional point (EP) are explored. Systems operating at an EP exhibit unique characteristics such as increased sensitivity to low-level perturbation that can be exploited to enhanced sensing applications. To elucidate this functionality, two-dimensional eigenfrequency simulations of this novel system operating at an EP with the scatterer is used to introduce perturbations to the system. The EP is identified through the variation of two physical parameters viz. the distance of the scatterer from the resonators and the gap between the resonators. A systematic parametric sweep of these variables shows the distinctive characteristics of a system with EPs including a crossing of real eigenfrequencies, repulsion of imaginary eigenfrequencies, simultaneous mode excitation, self-intersecting Riemann sheets, and eigenvalue splitting in response to perturbation. These results show how this EP-based systems can be used to significantly improve sensitivity low-level light detection.
Epsilon-near-zero (ENZ) materials such as indium tin oxide (ITO), have recently emerged as a new platform to enhance optical nonlinearities. In this talk I will report on our recent theoretical and experimental results on the origin of ultrafast nonlinearities in ITO films that are dominated by intraband and interband transitions. We show that there are two competing factors that jointly contribute to a spectrally-invertible nonlinearity of ITO near its ENZ region i.e. the nonparabolicity of the bands that results in a larger effective mass and the Fermi energy shift, which determines the free carrier density. Our work reveals the relationship between the large nonlinearity and the intrinsic material properties of the ITO films which will enable design and development of photonic materials and nonlinear devices made of transparent conductive oxides.
While two-dimensional (2D) structural photonic materials have led to many new innovations in the field of optics, the preferential alignment and assembly of colloidal particle arrays over large areas remains a challenge. Here, we develop a theoretical model based on the constructal law in order to describe this particle assembly behavior. The constructal model was then used to predict and tune the resulting particle alignment with and without the presence of an external driving force. Ultimately, this model provides a generalized framework that could be expanded upon to predict the self/directed-assembly of colloidal particles in a range of dynamically tunable and reconfigurable systems.
The mid-infrared (mid-IR) region of the electromagnetic spectrum has a range of applications in defense, sensing, and free space optical communications. However, most mid-IR sources, particularly incoherent emitters, are practically limited as a result of significant non-radiative losses such as Auger and Shockley-Read-Hall recombination as well as phonon-assisted scattering. Recently, plasmonic materials have been a topic of interest due to their ability to overcome traditional limitations of light confinement as well as enhance light-matter interactions. For inherently inefficient sources, such as many mid-IR emitters, coupling of the emitting element to a plasmonic structure could enhance emission efficiency. In this work, we propose and experimentally evaluate the use of plasmon-mediated photoluminescence as a potential method for improving efficiency in mid-IR emitters.
We assess the effectiveness of 3% gallium-doped zinc oxide (G3ZO) as a mid-IR plasmonic material. We design, simulate, fabricate, and characterize a two-dimensional periodic array of bow-tie nanoantennas (nantennas). Our structures are designed to enhance the overlap of the nantenna optical field with underlying In(Ga)Sb/InAs quantum well structures emitting at λ ≈ 4.0μm. Thin films of G3ZO are grown by pulsed laser deposition and are characterized electrically and optically, with the extracted material parameters used as inputs in our simulations. G3ZO plasmonic nantennas are then fabricated by electron-beam lithography and dry-etching. The spectral response of the patterned nantennas is characterized using Fourier transform infrared reflection spectroscopy. Samples are then characterized by temperature and polarization dependent photoluminescence spectroscopy in order to determine the extent to which the emission efficiency improves as a result of coupling to the nanostructures.
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