1,859 research outputs found

    Chalcogenide Glass-on-Graphene Photonics

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    Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators

    Computational Explorations of Enhanced Nonlinearities and Quantum Optical Effects in Photonic Nanostructures

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    In this thesis, we present a comprehensive theoretical analysis and computataional study of optical nonlinearities in the graphene-based and silicon-based metamaterials. The novel numerical methods and corresponding results described in this work give a significant impact on our understanding of surface plasmon resonance in artificial optical materials, which facilitates the design and fabrication of new photonic devices with enhanced nonlinear optical functionalities. // Two generic nonlinear metasurfaces are elaborated in this dissertation, namely, graphene-based metasurfaces and silicon-based metasurfaces. Employing a novel homogenization technique, the effective second-order susceptibility of graphene metasurfaces is calculated, which can be enhanced by more than two orders of magnitude as compared to the intrinsic value of graphene sheet. There is excellent agreement between the predictions of the homogenization method and those based on rigorous numerical solutions of Maxwell equations. Moreover, we also illustrate that the effective Raman susceptibilities of silicon-based metasurfaces can be enhanced by 3 to 4 orders of magnitude as compared to the intrinsic value of silicon. Even though the homogenization method for silicon-based metasurfaces is not as accurate as graphene-based, this result still gives a qualitative analysis on the effective Raman susceptibility of silicon-based metasurfaces. // Additionally, the optical nonlinearity is utilized to design a two-mode quantum waveguide made of coupled silicon photonic crystal nanocavities in the last part of the thesis. Finally, we also explore the implications of our work to the development of new active photonic nano devices with new or improved functionalities

    Broadband 10 Gb/s operation of graphene electro-absorption modulator on silicon

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    High performance integrated optical modulators are highly desired for future optical interconnects. The ultrahigh bandwidth and broadband operation potentially offered by graphene based electro-absorption modulators has attracted a lot of attention in the photonics community recently. In this work, we theoretically evaluate the true potential of such modulators and illustrate this with experimental results for a silicon integrated graphene optical electro-absorption modulator capable of broadband 10 Gb/s modulation speed. The measured results agree very well with theoretical predictions. A low insertion loss of 3.8 dB at 1580 nm and a low drive voltage of 2.5 V combined with broadband and athermal operation were obtained for a 50 mu m-length hybrid graphene-Si device. The peak modulation efficiency of the device is 1.5 dB/V. This robust device is challenging best-in-class Si (Ge) modulators for future chip-level optical interconnects

    Theoretical and computational analysis of second- and third-harmonic generation in periodically patterned graphene and transition-metal dichalcogenide monolayers

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    Remarkable optical and electrical properties of two-dimensional (2D) materials, such as graphene and transition-metal dichalcogenide (TMDC) monolayers, offer vast technological potential for novel and improved optoelectronic nanodevices, many of which relying on nonlinear optical effects in these 2D materials. This article introduces a highly effective numerical method for efficient and accurate description of linear and nonlinear optical effects in nanostructured 2D materials embedded in periodic photonic structures containing regular three-dimensional (3D) optical materials, such as diffraction gratings and periodic metamaterials. The proposed method builds upon the rigorous coupled-wave analysis and incorporates the nonlinear optical response of 2D materials by means of modified electromagnetic boundary conditions. This allows one to reduce the mathematical framework of the numerical method to an inhomogeneous scattering matrix formalism, which makes it more accurate and efficient than previously used approaches. An overview of linear and nonlinear optical properties of graphene and TMDC monolayers is given and the various features of the corresponding optical spectra are explored numerically and discussed. To illustrate the versatility of our numerical method, we use it to investigate the linear and nonlinear multiresonant optical response of 2D-3D heteromaterials for enhanced and tunable second- and third-harmonic generation. In particular, by employing a structured 2D material optically coupled to a patterned slab waveguide, we study the interplay between geometric resonances associated to guiding modes of periodically patterned slab waveguides and plasmon or exciton resonances of 2D materials.Comment: 28 pages, 21 figure

    Enhanced Light Absorption and Electro-absorption Modulation Based on Graphene and Conductive Oxide

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    The development of integrated photonics is limited by bulky and inefficient photonic component compared to their electronic counterparts due to weak light-matter interactions. As the key devices that determine the performance of integrated photonic circuits, electro-optical (EO) modulators are inherently built on the basis of enhancing light-matter interactions. Current EO modulators often deploy conventional materials with poor EO properties, or ring resonator structure with narrow bandwidth and thermal instability, so their dimensions and performance have nearly reached their physical limits. Future integrated photonic interconnects require EO modulators to be ultra-compact, ultra-fast, cost-effective and able to work over a broad bandwidth. The key to achieving this goal is to identify an efficient and low-cost active material. Meanwhile, novel waveguides and platforms need to be explored to significantly enhance light-active medium interaction. As widely investigated novel materials, graphene and conductive oxide (COx) have shown remarkable EO properties. The objective of this dissertation is to realize enhanced light-matter interaction based on these two novel materials and waveguiding platforms, and further develop ultra-compact, ultra-fast EO modulators for future photonic integrated circuits. The first part of this dissertation covers the theory of EO modulation mechanisms, several types of EO materials including graphene and COx, as well as fabrication techniques. The second part demonstrates greatly enhanced light absorption based on mono-/multi-layer graphene. The third part proposes the theoretical study of nanoscale EA modulators based on ENZ-slot waveguide. The fourth part explores the field effect within a MOS-like structure, and verifies the ENZ behavior of COx. The fifth part experimentally demonstrates both plasmonic and dielectric configurations for ultra-compact and ultra-fast EA modulators. The final part summarizes the work presented in this dissertation and also discusses some future work for photonic applications
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