Enhanced light emission from gap plasmons in nano-strip MIM tunnel junctions

Electrical excitation of light using inelastic electron tunneling is a promising approach for the realization of ultra-compact on-chip optical sources with high modulation bandwidth. However, the practical implementation of these nanoscale light sources presents a challenge due to the low electron-to-photon transduction efficiencies. Here, we investigate designs for the enhancement of light generation and out-coupling in a periodic Ag-SiO2-Ag tunnel junction due to inelastic electron tunneling. The structure presents a unique advantage of a simple fabrication procedure as compared to the other reported structures. By efficiently coupling the gap plasmon mode and the lattice resonance, we achieve a resonant enhancement in the local density of optical states up to three orders of magnitude and enhanced radiative efficiency of ~0.53, 30% higher as compared to the uncoupled structure.Comment: This is the version of the article before peer review or editing, as submitted by an author to IoP Journal of Optics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/2040-8986/ababe

Enhancement of the optical gain in GaAs nanocylinders for nanophotonic applications

Semiconductor nanolasers based on micro disks, photonic crystal cavities, and metallo-dielectric nanocavities have been studied during the last decade for on-chip light source applications. However, practical realization of low threshold, room temperature operation of semiconductor nanolasers is still a challenge due to the large surface-to-volume ratio of the nanostructures, which results in low optical gain and hence higher lasing threshold. Also, the gain in nanostructures is an important parameter for designing all-dielectric metamaterial-based active applications. Here, we investigate the impact of p-type doping, compressive strain, and surface recombination on the gain spectrum and the spatial distribution of carriers in GaAs nanocylinders. Our analysis reveals that the lasing threshold can be lowered by choosing the right doping concentration in the active III-V material combined with compressive strain. This combination of strain and p-type doping shows 100x improvement in gain and ~5 times increase in modulation bandwidth for high-speed operation.Comment: 19 pages, 6 figure

Graphene: A Dynamic Platform for Electrical Control of Plasmonic Resonance

Abstract:Graphene has recently emerged as a viable platform for integrated optoelectronic and hybrid photonic devices because of its unique properties. The optical properties of graphene can be dynamically controlled by electrical voltage and have been used to modulate the plasmons in noble metal nanostructures. Graphene has also been shown to support highly confined intrinsic plasmons, with properties that can be tuned in the wavelength range of 2 μm to 100 μm. Here we review the recent development in graphene-plasmonic devices and identify some of the key challenges for practical applications of such hybrid devices.</jats:p

Dynamic control of plasmonic resonances with graphene based nanostructures

Light incident on a metallic structure excites collective oscillations of electrons termed as plasmons. These plasmons are useful in control and manipulation of information in nanoscale dimensions and at high operating frequencies. Hence, the field of plasmonics opens up the possibility of developing nanoscale optoelectronic circuitry for computing and sensing applications. One of the challenges in this effort is the lack of tunable plasmonic resonance. Currently, the resonant wavelength of plasmonic structure is fixed by the material and structural parameters. Post-fabrication dynamic control of a plasmonic resonance is rather limited. In this thesis we explore the combination of optoelectrical properties of graphene and plasmon resonances in metallic nanostructures to achieve dynamic control of plasmon resonances. First, we show that it is possible to use the highly tunable interband transitions in graphene to effectively control the plasmonic resonance in mid-infrared (MIR) wavelengths. We then outline the current challenges in achieving modulation in the technologically relevant near-infrared (NIR) wavelengths. One potential solution is to combine Fano resonances in metallic structures with graphene to realize a higher degree of tunability at NIR wavelengths. In addition to modulating resonances in metallic nanostructures, graphene itself supports highly confined and tunable plasmons in MIR wavelengths. We report experimental studies on the plasmonic resonance in multilayer graphene, and the interaction of graphene plasmons with the substrate phonons. Finally, we conclude with the current challenges and present directions for further improvements so as to enable practical devices

Design of photonic waveguides at Mid-infrared wavelengths on a SOI platform

The need of designing the waveguide from near infrared region and extending the work to midinfrared region is discussed. A rib waveguide is designed to work at telecommunication wavelength 1.55 µm in the regime of silicon photonics and the modes are reviewed. By optimising geometric parameters of the waveguide design on SOI (Silicon-on-insulator) platform, the mode profiles have been obtained up to 10 µm range of wavelength. The commercial Lumerical FDE mode solver has been used throughout the simulations of the waveguide design, exploring the spectral and geometric parametric sweep. We have discussed the optimised widths and heights with higher effective index of SOI rib waveguide for mid-IR wavelengths - 3.6 µm, 4.74 µm and 9.14 µm. The results of the modes of the rib waveguide for mid-IR range are discussed around the phononic absorption peak of SiO2 with the help of its dispersion curve. Our future interest is to fabricate waveguides for the above mentioned wavelengths and characterize using MIRcat 2400-QT, Daylight Solutions Inc. available in lab

Tunable Spectral Singularities with Asymmetric Directional Response in PT-symmetric 2D Nanoantenna Array

We investigate GaInP PT-symmetric 2D nanoantenna array and show that the proposed metasurface supports spectral singularities with highly asymmetric scattering response. Broader design parameter space allows to control wavelength, and scattering direction. © OSA 2020 © 2020 The Author(s

Study of Gap Plasmons in 2D Finite Metal-Insulator-Metal Tunnel Junctions

The electrical excitation of surface plasmons/photons from MIM tunnel junctions has attracted significant research attention in recent times [1]-[3]. These devices, though are promising for future on-chip plasmonic applications, are plagued with low quantum efficiencies. In an effort towards increasing the effectiveness of such devices, we study the behaviour of gap plasmons in Ag-SiO2-Ag and Al-Al2O3-Au structures, with a 3 nm oxide and confined in two dimensions. We find that the out-coupling of leaky modes due to the Fabry-Pérot resonances in the oxide region contributes to the lower efficiencies of MIM tunnel junctions

Spectral singularities and asymmetric light scattering in PT-symmetric 2D nanoantenna arrays

The intriguing physics of non-Hermitian systems satisfying parity-time (PT) symmetry has spurred a surge of both theoretical and experimental research in interleaved gain-loss systems for novel photonic devices. In this work, we investigate vertically stacked GaInP PT-symmetric nanodisk resonators arranged in two-dimensional periodic lattice using full-wave numerical simulations and scattering matrix theory. The proposed dielectric metasurface supports lasing spectral singularities with asymmetric reflection and highly anisotropic far-field scattering patterns. It offers a much broader design parameter space to control wavelength, scattering direction, and efficiency of optical emission when compared to the predominantly one-dimentional (1D) or quasi-1D structures studied so far. The proposed system with Q-factor >105 serves as a powerful platform for enhanced light-matter interaction by enabling extensive control of asymmetric light scattering, amplification, and unprecedented localization of electromagnetic fields. © 2020 Optical Society of Americ

Wavelength Selective Beam Switching Using Electrically Driven Nano-Strip MIM Tunnel Junctions

Tunable directional emission from electrically driven sources is essential for applications involving on-chip nano-circuits, sensing and quantum information processing. Here, we numerically demonstrate wavelength selective, switchable directional emission from periodic, nano-strip metal-insulator-metal tunnel junctions. Using two excitation sources, we show that our structure can efficiently redirect two different wavelengths in opposite directions when the excitation is switched. We achieved a peak directivity of 21.5 and 25.8 for wavelengths of 692 nm and 738 nm, respectively. The emission angle can be tuned by varying the periodicity, thereby paving the way for on-chip multiplexing. © 2022 IEEE