178 research outputs found

    Antenna-coupled silicon-organic hybrid integrated photonic crystal modulator for broadband electromagnetic wave detection

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    In this work, we design, fabricate and characterize a compact, broadband and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. The large electro-optic (EO) coefficient of organic polymer, the slow-light effects in the silicon slot photonic crystal waveguide (PCW), and the broadband field enhancement provided by the bowtie antenna, are all combined to enhance the interaction of microwaves and optical waves, enabling a high EO modulation efficiency and thus a high sensitivity. The modulator is experimentally demonstrated with a record-high effective in-device EO modulation efficiency of r33=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB bandwidth of 11GHz. The slot PCW has an interaction length of 300um, and the bowtie antenna has an area smaller than 1cm2. The bowtie antenna in the device is experimentally demonstrated to have a broadband characteristics with a central resonance frequency of 10GHz, as well as a large beam width which enables the detection of electromagnetic waves from a large range of incident angles. The sensor is experimentally demonstrated with a minimum detectable electromagnetic power density of 8.4mW/m2 at 8.4GHz, corresponding to a minimum detectable electric field of 2.5V/m and an ultra-high sensitivity of 0.000027V/m Hz^-1/2 ever demonstrated. To the best of our knowledge, this is the first silicon-organic hybrid device and also the first PCW device used for the photonic detection of electromagnetic waves. Finally, we propose some future work, including a Teraherz wave sensor based on antenna-coupled electro-optic polymer filled plasmonic slot waveguide, as well as a fully packaged and tailgated device.Comment: 20 pages, 16 figure

    Design and Optimization of Polarization Splitting and Rotating Devices in Silicon-on-Insulator Technology

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    We review polarization splitting and rotating photonic devices based on silicon-on-insulator technology platform, focusing on their performance and design criteria. In addition, we present a theoretical investigation and optimization of some rotator and splitter architectures to be employed for polarization diversity circuits. In this context, fabrication tolerances and their influences on device performance are theoretically estimated by rigorous simulations too

    Doctor of Philosophy

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    dissertationPhotonic integration circuits (PICs) have received overwhelming attention in the past few decades due to various advantages over electronic circuits including absence of Joule effect and huge bandwidth. The most significant problem obstructing their commercial application is the integration density, which is largely determined by a signal wavelength that is in the order of microns. In this dissertation, we are focused on enhancing the integration density of PICs to warrant their practical applications. In general, we believe there are three ways to boost the integration density. The first is to downscale the dimension of individual integrated optical component. As an example, we have experimentally demonstrated an integrated optical diode with footprint 3 Ã- 3 m2, an integrated polarization beamsplitter with footprint 2.4 Ã- 2.4 m2, and a waveguide bend with effective bend radius as small as 0.65 m. All these devices offer the smallest footprint when compared to their alternatives. A second option to increase integration density is to combine the function of multiple devices into a single compact device. To illustrate the point, we have experimentally shown an integrated mode-converting polarization beamsplitter, and a free-space to waveguide coupler and polarization beamsplitter. Two distinct functionalities are offered in one single device without significantly sacrificing the footprint. A third option for enhancing integration density is to decrease the spacing between the individual devices. For this case, we have experimentally demonstrated an integrated cloak for nonresonant (waveguide) and resonant (microring-resonator) devices. Neighboring devices are totally invisible to each other even if they are separated as small as /2 apart. Inverse design algorithm is employed in demonstrating all of our devices. The basic premise is that, via nanofabrication, we can locally engineer the refractive index to achieve unique functionalities that are otherwise impossible. A nonlinear optimization algorithm is used to find the best permittivity distribution and a focused ion beam is used to define the fine nanostructures. Our future work lies in demonstrating active nanophotonic devices with compact footprint and high efficiency. Broadband and efficient silicon modulators, and all-optical and high-efficiency switches are envisioned with our design algorithm

    Gradient metasurfaces: a review of fundamentals and applications

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    In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic

    도파로와 메타표면에서의 비대칭 광모드 변환

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    학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 이병호.In this dissertation, asymmetric characteristics of photonic mode conversion structures in waveguides and metasurfaces have been discussed. More specifically, I propose design schemes for i) adjustment of mode conversion asymmetry in tri-mode waveguide system, ii) compact unidirectional mode converter in plasmonic waveguide and iii) unidirectional scattering of polarization-converted wave from bilayer metasurface. Firstly, a Lorentz reciprocal mode conversion asymmetry in reflectionless tri-mode waveguide system with weak waveguide gratings is discussed. In particular, the dark-mode which is the photonic analogue of atomic dark-state has been exploited for independent design of forward and backward direction characteristics. Due to the stationary property of the dark-mode, the mode conversion characteristics in one propagation direction could be fixed regardless of the length of the grating that defines the dark-mode. By carefully selecting the dark-mode and the length of the waveguide grating, the mode conversion asymmetry could be controlled. Secondly, a compact spatial plasmonic mode converter with unidirectional mode conversion characteristics is proposed. By combining mode-selective blockers with simple stub mode converter, unidirectional mode conversion characteristics could be achieved. Furthermore, it was found that the redundant scattering and the backward reflection can be completely eliminated by mode filtering and destructive interference, respectively. An application of the design strategy using the mode-selective blockers is also presented for the problem of near-complete out-coupling from subwavelength nanoslits. Lastly, a bilayer metasurface which transmits polarization converted signal only to the forward direction is proposed. The bilayer metasurface was designed by assembling two identical thin metasurfaces, the property of which is well-known. After numerical design of the bilayer metasurface, the designed structure was fabricated and its transmission and reflection characteristics were measured. It was found that the reflectance of the fabricated structure is successfully suppressed. The issue of amplitude distortion and its compensation is discussed and experimentally verified. The results on the dark-mode based asymmetric conversion device offer a method to control the transmission asymmetry and this capability can pave a way to actively tunable asymmetry of optical systems. Furthermore, by using mode selective blockers, asymmetric mode converters can be constructed in a compact form which is suitable for nanophotonic applications. The bilayer metasurface can be easily extended to the reflection-type and the multiplexing of transmitted signal and reflected signal can be made possible by making a supercell of a transmission-type cell and a reflection-type cell. This opens a new way of metasurface function multiplexing.Chapter 1 Introduction 1 1.1 Overview 1 1.1.1 Asymmetric transmission characteristics in multimode systems 2 1.1.2 Metasurfaces 6 1.2 Motivation and organization of this dissertation 9 Chapter 2 Adjustment of waveguide mode conversion asymmetry by using photonic dark-states 13 2.1 Introduction 13 2.1.1 Asymmetric transmission in tri-mode waveguide system allowed by Lorentz reciprocity 13 2.1.2 Photonic analogue of dark-state in coupled-mode theory 14 2.2 Designed asymmetry by using dark-modes 16 2.3 Specification of dark-mode 21 2.4 Asymmetric mode conversion by cascaded gratings 25 2.5 Conclusion 33 Chapter 3 Compact plasmonic spatial mode converter with mode conversion asymmetry 34 3.1 Introduction 34 3.1.1 Asymmetric spatial mode converters in waveguides 34 3.1.2 Mode conversion by using mode-selective blocking filters 35 3.2 Plasmonic spatial mode conversion by using a stub mode converter 37 3.2.1 Dispersion relation of the plasmonic waveguide 37 3.2.2 Stub mode converter 39 3.3 Asymmetric mode conversion by using spatial mode filters 44 3.3.1 Configuration of the proposed structure 44 3.3.2 Design of the anti-symmetric mode barrier (F2) 45 3.3.3 Design of the notch filter (F1) 47 3.3.4 Unidirectional mode conversion characteristics of the whole structure 50 3.4 Tuning of the mode-selective cavity for idle scattering component elimination 51 3.4.1 Modelling of the mode-selective cavity and optimization conditions 51 3.4.2 Cavity length optimization 54 3.5 Application of the design strategy to out-coupler design problem 56 3.5.1 Scattering components at the end of nanoslit 56 3.5.2 Trench-type antenna near nanoslit and its working principle 57 3.5.3 Design of the SPP blocking trench 60 3.5.4 Radiation pattern from the optimized structure 63 3.6 Conclusion 66 Chapter 4 Unidirectional launching of polarizationconverted waves from bilayer metasurfaces 67 4.1 Introduction 67 4.1.1 Properties of thin, single layer metasurfaces and the symmetry of scattering characteristics 67 4.1.2 Multiplexing of the transmitted and reflected wavefronts 70 4.2 Numerical design 72 4.2.1 Configuration of the bilayer metasurface and reduction into a single layer metasurface design problem 72 4.2.2 Unit cell structure and gap distance optimization 75 4.2.3 Effective material parameter point of view 78 4.2.4 Amplitude distortion and its compensation 79 4.3 Experiment 82 4.3.1 Fabrication and experimental setup 82 4.3.2 Antenna resonance condition specification 85 4.3.3 Transmission and reflection characterization 87 4.3.4 Amplitude distortion and its reduction by polarization basis change 90 4.4 Conclusion 92 Chapter 5 Summary 93 Bibliography 96 Appendix 105 초 록 106Docto

    Spoof Surface Plasmon Polariton Based THz Circuitry

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    Terahertz, abbreviated as THz, is defined as the frequency band spanning from 300 GHz to 10 THz, which is located between the microwave from the electronic side of the electromagnetic (EM) spectrum to mid-Infra-Red on the photonic side of the EM spectrum. As accelerated research and innovations over the past seven decades have resulted in widespread commercialization of both electronic and photonic components, THz band has remained underdeveloped, underexploited, and mostly unallocated by the Federal Communications Commission (FCC). Though certain definitive merits of EM waves at THz have evoked interests of physicists, chemists, biologists and material scientists to deploy THz in Time-Domain Spectroscopy (TDS), bio-sensing, and classical imaging applications, the field of THz circuits (also known as THz electronics) has continued to remain in embryonic stage due to the speed limitations of conventional Silicon and compound semiconductor devices like Field Effect Transistors (FETs), Hetero-junction Bipolar Transistors (HBTs), and Hot Electron Mobility Transistors (HEMTs). On the other hand, conventional photonic devices cannot be readily adopted to design new THz circuits and systems. Our research vision in THz circuits and systems is to study the meta-material properties of THz in various forms of sub-wavelength structures and exploit those unique properties to invent the designs of large THz systems like the THz switch, Analog-to-Digital Converter (ADC), etc. The potential large bandwidth and high propagation speed helps photonic circuitry to be proposed against the above-mentioned challenges faced by its electronic counterpart. Optical-assisted as well as all-optical systems in various forms have been reported to realize different data-processing functionalities. For example, analog-to-digital converters (ADC) with the potential of high speed operation have been demonstrated by optical-assisted or all-optical approaches. Photonic logic has also been reported in numerous works by coding the Boolean information in the amplitude, phase or wavelength of the optical signals. Despite these efforts, however, the key element to address the fundamental deficiencies of CMOS circuit remained missing. The use of optical frequencies in these works brought about common shortcomings including dimension mismatch, lack of coherent detection, inflexibility, susceptibility to mechanical and environmental variations, and the presence of bulky optical elements (i.e., mirrors, beam splitters, lenses, etc.). More seriously, these works inherited sequential circuit designs directly from CMOS. It indicates that the cumulative delay still dominated the speed performance, which prevented further decrease of the circuit latency. In light of these problems, we foresee the implementation of THz circuitry as the next reasonable step to take in designing high-speed analog as well as digital circuits. Spoofed Surface Plasmon Polariton (SSPP) is known as a pseudo-surface mode in THz frequencies that mimics the slow wave nature and localized E-M field distribution of the plasmon mode typically observed in optical domain. By introducing periodic corrugations on the surfaces of a metal-dielectric-metal structure, SSPP mode is realized for propagating THz signal, and its mode dispersion is strongly dependent on the geometric dimensions as well as the material properties of the architecture. Recently propagation of THz wave utilizing Spoof surface plasmon polariton (SSPP) earned a great deal of attention due to the ability of SSPP modes to guide THz waves at very low dispersion. In this research, we exploit and investigate the SSPP modes in different periodic structure and utilizing them in different structure to introduce new THz devices, such as, polarization rotator, THz switch, ADC, etc.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144105/1/mahdia_1.pd

    Recent Advances and Future Trends in Nanophotonics

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    Nanophotonics has emerged as a multidisciplinary frontier of science and engineering. Due to its high potential to contribute to breakthroughs in many areas of technology, nanophotonics is capturing the interest of many researchers from different fields. This Special Issue of Applied Sciences on “Recent advances and future trends in nanophotonics” aims to give an overview on the latest developments in nanophotonics and its roles in different application domains. Topics of discussion include, but are not limited to, the exploration of new directions of nanophotonic science and technology that enable technological breakthroughs in high-impact areas mainly regarding diffraction elements, detection, imaging, spectroscopy, optical communications, and computing
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