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付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第23904号 / 工博第4991号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 竹内 繁樹, 教授 川上 養一, 准教授 浅野 卓 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The ever-increasing bandwidth requirements to support telecommunications infrastructure necessitates large-scale fabrication of low-cost and scalable silicon photonic integrated circuits. Wavelength-division multiplexing (WDM) schemes are fundamentally limited in the number of channels supported in long-haul transmission by the erbium doped fiber amplifier (EDFA). To address this, researchers have turned focus toward the thulium doped fiber amplifier (TDFA), which provides 3× more bandwidth. This thesis describes the development of high-speed silicon-on-insulator (SOI) micro-ring resonator (MRR) modulators optimized for wavelengths in the TDFA band. Chapter 2 presents a theoretical performance comparison between MRR modulators designed for optimized use at EDFA and TDFA wavelengths. Chapter 3 presents an experimental study of optical loss mechanisms at extended wavelengths which suggests reduced waveguide scattering and enhanced divacancy defect absorption as well as larger bending and substrate leakage losses when compared with shorter wavelengths. An electronic variable optical attenuator is characterized in Chapter 4 to experimentally verify the predicted 1.7× TDFA-band free-carrier effect enhancement over EDFA-band wavelengths. The first steady-state operation of an MMR modulator near a central wavelength of 1.97 µm is also demonstrated under the enhanced free-carrier effect. Chapter 5 demonstrates the first high-speed reverse bias operation of an MRR modulator with a measured bandwidth of 12.5 GHz, and an on-chip optical link consisting of a modulator followed by a defectmediated detector with open eye-diagrams up to data rates of 12.5 Gbps. Chapter 6 introduces an electrically-driven post-fabrication defect-assisted resonance trimming technique via local annealing for use in MRR devices. Chapter 7 presents a Monte Carlo simulation of resonance alignment in multi-MRR systems subjected to spatially-correlated wafer variation created through the Virtual Wafer Model process to predict thermal power consumption and power reduction through resonance trimming. / Thesis / Doctor of Philosophy (PhD)

Yes / In this paper, a compact dielectric resonator antenna (DRA) with band-notched characteristics for ultra-wideband applications is presented. A comprehensive parametric study was carried out using CST Microwave Studio Suite TM 2011 to analyze and optimize the characteristics of the proposed antenna. Three shapes for the coupling slot were investigated. Simulation results show that the proposed DRA had a −10 dB impedance bandwidth of 23% from 9.97 GHz to 12.558 GHz, and a maximum gain of 7.23 dBi. The antenna had a notched band centered at 10.57 GHz, which increased the reflection coefficient by 23.5 dB, and reduced the gain by 6.12 dB. The optimized designs were verified by experimental tests on fabricated samples.

Yes / In this paper, we present the design of a compact and highly sensitive microwave sensor based on a metamaterial complementary split-ring resonator (CSRR), for liquid characterization at microwave frequencies. The design consists of a two-port microstrip-fed rectangular patch resonating structure printed on a 20 × 28 mm2 Roger RO3035 substrate with a thickness of 0.75 mm, a relative permittivity of 3.5, and a loss tangent of 0.0015. A CSRR is etched on the ground plane for the purpose of sensor miniaturization. The investigated liquid sample is put in a capillary glass tube lying parallel to the surface of the sensor. The parallel placement of the liquid test tube makes the design twice as efficient as a normal one in terms of sensitivity and Q factor. By bending the proposed structure, further enhancements of the sensor design can be obtained. These changes result in a shift in the resonant frequency and Q factor of the sensor. Hence, we could improve the sensitivity 10-fold compared to the flat structure. Subsequently, two configurations of sensors were designed and tested using CST simulation software, validated using HFSS simulation software, and compared to structures available in the literature, obtaining good agreement. A prototype of the flat configuration was fabricated and experimentally tested. Simulation results were found to be in good agreement with the experiments. The proposed devices exhibit the advantage of exploring multiple rapid and easy measurements using different test tubes, making the measurement faster, easier, and more cost-effective; therefore, the proposed high-sensitivity sensors are ideal candidates for various sensing applications. / This work was supported by the Moore4Medical project, funded within ECSEL JU in collaboration with the EU H2020 Framework Programme (H2020/2014–2020) under grant agreement H2020-ECSEL-2019-IA-876190, and the Fundação para a Ciência e Tecnologia (ECSEL/0006/2019). This project received funding in part from the DGRSDT (Direction Générale de la Recherche Scientifique et du Développement Technologique), MESRS (Ministry of Higher Education and Scientific Research), Algeria. This work was also supported by the General Directorate of Scientific Research and Technological Development (DGRSDT)–Ministry of Higher Education and Scientific Research (MESRS), Algeria, and funded by the FCT/MEC through national funds and, when applicable, co-financed by the ERDF, under the PT2020 Partnership Agreement under the UID/EEA/50008/2020 project.

A desirable goal in wireless communication systems is to achieve a high-rate data transmission through electrically small antennas. However, the overall transmission bandwidth is limited by the antenna size. As a well-known physical limitation, maximum achievable bandwidth of a small antenna is governed by the fundamental limit which defines a lower bound on the antenna quality factor. This limit is a function of electrical size of the antenna and therefore, as the antenna shrinks in size the bandwidth decreases as well. This dissertation presents a new technique to decouple the impedance bandwidth of a high-Q antenna from the information bandwidth in order to provide a wideband data-transmission. This technique controls the natural resonant frequencies of an electrically small antenna in a time-varying fashion such that ultra-fast frequency-shift keying modulation can be achieved regardless of the narrow bandwidth of the antenna. A major advantage of the proposed technique is that the high-Q property of a miniaturized antenna is a desirable design parameter rather than a limiting factor. Therefore, the antenna size can be reduced as much as required. It is shown that if the fundamental resonance of an antenna is shifted in time, the frequency of the near-zone fields which construct the reactive stored energy, changes momentarily and hence, the radiating fields track any instantaneous variation of the antenna fundamental resonance. This characteristic is utilized to employ a single-mode high-Q antenna in the transient state and modulate the fundamental resonant frequency according to the baseband data information. This approach leads to a new class of compact transmitters with a minimized architecture and high data-rate transmission capability. / Ph. D.

Yes / In this paper, a compact two-element cylindrical dielectric resonator antenna (CDRA) array with corporate feeding is proposed for X-band applications. The dielectric resonator antenna (DRA) array is excited by a microstrip feeder using an efficient aperture-coupled method. The designed array antenna is analyzed using a CST microwave studio. The fabricated sample of the proposed CDRA antenna array showed bandwidth extending from 10.42GHz to 12.84GHz (20.8%). The achieved array gain has a maximum of 9.29dBi at frequency of 10.7GHz. This is about 2.06dBi enhancement of the gain in comparison with a single pellet CDRA. The size of the whole antenna structure is about 50 x 50mm2.

Attenuation of low frequency turbofan engine noise has been a challenging task in an industry that requires low weight and tightly-packed solutions. Without innovative advancements, the technology currently used will not be able to keep up with the increasingly stringent requirements on aircraft noise reduction. A need exists for novel technologies that will pave the way for the future of quiet aircraft. This thesis investigates acoustic metamaterials and their ability to achieve superior transmission loss characteristics not found in traditional honeycomb liners. The acoustic metamaterials investigated are an array of Helmholtz resonators with and without coupled cavities periodically-spaced along a duct wall. Analytical, numerical, and experimental developments of these acoustic metamaterial systems are used herein to study the effects of this technology on the transmission loss. Particularly focusing on analytical modeling will aid in understanding the underlying physics that governs their interesting transmission loss behavior. A deeper understanding of the physics will be used to aid in future acoustic metamaterial liner design. A parameter study is performed to understand the effects of the geometry, spacing, and number of resonators, as well as resonator cavity coupling on performance. Increased broadband transmission loss, particularly in low frequencies, is achieved through intelligent manipulation of these parameters. Acoustic metamaterials are shown to have appealing noise cancellation characteristics that prove to be effective for aircraft engine liner applications. / Master of Science / Aircraft noise reduction is an ongoing challenge for the aerospace industry. Without innovative advancements, the next generation of aircraft will not be able to keep up with increasingly stringent noise regulations; novel acoustic technology is needed to pave the way for a future of quieter aircraft. This thesis investigates acoustic metamaterials and their ability to achieve superior noise reduction over traditional methods. Modeling techniques were developed, and experimental tests were conducted to quantitatively evaluate the effectiveness of a new acoustic metamaterial system. The acoustic metamaterial design explored herein was proven to reduce noise effectively and shows promise for a world of quieter aircraft.

Liquid microdroplet resonators provide an excellent tool for optical studies due to their innate smoothness and high quality factors, but they can be difficult to control. By using 3D printed mounts to support the droplets, we can obtain precise control over the droplet geometries and positions. We here present our work with oil, water, and ice microdroplets, as well as tools required to enable their study. We first present methods for creating 3D printed mounts for oil microdroplet resonators. The mounts enable precise positioning of the droplets relative to a tapered optical fiber. The oil microdroplet resonators exhibited quality factors of over 4 × 10^5. Water microdroplet resonators are more difficult to create due to the evaporation of water. By supporting the droplet on a 3D printed structure that supplies water to the droplet, we can maintain a water microdroplet resonator in an ambient environment while also controlling its shape and size. The resulting resonators have high quality factors, with values measured as high as 6 × 10^8. Ice microdroplets may be useful as optical resonators; however, typically ice appears cloudy due to trapped air bubbles. We present a method for freezing clear ice microdroplets in both humid and dry environments, enabling the formation of a clear ice droplet without the risk of additional crystal growth. To facilitate the freezing of droplets in a low-humidity environment, we have developed an environmental control chamber capable of maintaining an arbitrary humidity level and controlling the temperature of a small sample. We here present instructions for its manufacture as well as validation of its function. Finally, we present an automated fabrication system for the creation of tapered and dimpled optical fibers. Tapered fibers have been essential in our work as tools for optical coupling to microdroplet resonators, and dimpled fibers allow for coupling to on-chip structures. The system we present allows for their fabrication with no user input and is able to produce fibers with efficiencies over 90% at a high yield.