Doubly resonant photonic crystal cavity using merged bound states in the continuum

In this work, a doubly resonant photonic crystal (PhC) cavity using the merged bound states in the continuum (BICs) is proposed to obtain a higher second harmonic generation (SHG) efficiency. Firstly by scanning geometry parameters the accidental BICs and a band-edge mode outside the light cone can be obtained. Then as the lattice constant or the thickness of the slab is adjusted the accidental BICs will merge. A supercell with large and small holes is constructed and the band-edge mode outside the light cone can be mode-matched with the merged BICs mode. Finally the heterostructure PhC cavity is designed. The merged BICs show a high quality factor for the photonic crystal with finite size. Consequently, the SHG efficiency of the lattice constant near merged BICs of ~6000% W-1 is higher than the one of the isolated BIC

Logic functions, devices, and circuits based on parametric nonlinear processes

Second-harmonic generation and parametric down-conversion processes have been studied as the basis of all-optical logic gates. All possibilities that are obtainable with both the low and high conversion efficiencies of such processes have been analyzed here. XOR and AND gates are also experimentally proven by using 1-ps pulses at 800 nm within a beta-BaB(2)O(4) crystal, reaching conversion efficiencies of as high as 80%. Based on these phenomena, complex algebraic operations are proposed for performing several different logic functionalities particularly concerning network switching and arithmetic calculation

Distributed Quantum Computation Architecture Using Semiconductor Nanophotonics

In a large-scale quantum computer, the cost of communications will dominate the performance and resource requirements, place many severe demands on the technology, and constrain the architecture. Unfortunately, fault-tolerant computers based entirely on photons with probabilistic gates, though equipped with "built-in" communication, have very large resource overheads; likewise, computers with reliable probabilistic gates between photons or quantum memories may lack sufficient communication resources in the presence of realistic optical losses. Here, we consider a compromise architecture, in which semiconductor spin qubits are coupled by bright laser pulses through nanophotonic waveguides and cavities using a combination of frequent probabilistic and sparse determinstic entanglement mechanisms. The large photonic resource requirements incurred by the use of probabilistic gates for quantum communication are mitigated in part by the potential high-speed operation of the semiconductor nanophotonic hardware. The system employs topological cluster-state quantum error correction for achieving fault-tolerance. Our results suggest that such an architecture/technology combination has the potential to scale to a system capable of attacking classically intractable computational problems.Comment: 29 pages, 7 figures; v2: heavily revised figures improve architecture presentation, additional detail on physical parameters, a few new reference

Photonic based Radar: Characterization of 1x4 Mach-Zehnder Demultiplexer

This work is based on a research activity which aims to implement an optical transceiver for a photonic-assisted fully–digital radar system based on optic miniaturized optical devices both for the optical generation of the radiofrequency (RF) signal and for the optical sampling of the received RF signal. The work is more focused on one very critical block of receiver which is used to parallelize optical samples. Parallelization will result in samples which will be lower in repetition rate so that we can use commercial available ADCs for further processing. This block needs a custom design to meet all the system specifications. In order to parallelize the samples a 1x4 switching matrix (demux) based on Mach Zehnder (MZ) interferometer has been proposed. The demux technique is Optical Time Division Demultiplexing. In order to operate this demux according to the requirements the characterization of device is needed. We need to find different stable control points (coupler bias and MZ bias) of demux to get output samples with high extinction ratio. A series of experiments have been performed to evaluate the matrix performance, issues and sensitivity. The evaluated results along with the whole scheme has been discussed in this document

복소, 무질서 및 광학적 비선형 퍼텐셜에서의 대칭성 붕괴를 통한 빛의 흐름 제어

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 박남규.매질 내 빛의 흐름은 통상적으로 거시적 맥스웰 방정식에 의해 정의된다. 동질성 및 등방성을 가지고, 선형적이며, 시간에 대해 일정한 광학 매질 변수를 갖는 이상적인 매질에서는 광파의 양상이 페르마의 원리의 직접적인 예인 진동하는 전자기장의 직진 형태로, 간단하며 직관적이다. 이러한 평면파적 특성은 기하 광학의 바탕이며, 슈뢰딩거 방정식 형태의 파동 방정식이 갖는 다양한 대칭성 (병진 대칭, 키랄 대칭, 에르미트 대칭, 로렌츠 대칭 및 시간 반전 대칭)의 보존에서 그 원리을 찾을 수 있다. 렌즈, 거울 및 프리즘과 같은 고전적인 방식에서조차, 빛의 흐름을 조절키 위해서는 일부 광학적 대칭성의 붕괴를 필요로 한다. 비균질 매질에서의 병진 대칭의 붕괴는 굴절, 반사, 회절과 같은 산란 기반 빛 제어를 위한 고전적인 방법이다. 전파 시의 빛 에너지의 소모 또는 증폭은 파동 방정식의 비에르미트 헤밀토니안에 의해 정량화된다. 키랄 분자로 이루어진 매질은 광학 활성, 즉 빛의 편광을 돌릴 수 있도록 한다. 천문학에서 별 및 은하 움직임의 관찰에 이용되는 광학적 도플러 효과는 로렌츠 대칭성을 붕괴시키는 광원의 시간에 따른 변화에 기반한다. 비직관적인 이론적 결과물 및 향상된 공정 기술을 포함하는 광학 분야의 최근 성과들은 이제 비고전적인 빛의 흐름을 이끌어내기 위한 광학적 퍼텐셜 제어의 새로운 영역을 개척하고 있다. 메타 물질 개념과 연계된 나노 스케일 기술은 단방향 빛 전파, 변형된 스넬의 법칙, 음굴절율, 투명 망토, 완전 흡수체와 같은 특이한 빛의 흐름을 지원하는, 이론적으로 증명된 인조 매질의 설계를 가능케 한다. 광 증폭 기술의 발전은 양자역학적 개념인 패리티-시간 대칭성의 구현에 적용되어, 복소 퍼텐셜에서의 새로운 종류의 광학을 탄생시켰다. 이러한 성취물들은 맥스웰 방정식에서의 더 넓고 급격한 형태의 대칭성 붕괴에 기반하기 때문에, 의도된 빛의 흐름 조절을 위해서는 다양한 대칭성 붕괴에 관한 심도있는 연구가 필요하다. 본 학위 논문에서는 복소, 불규칙, 비선형 광학 퍼텐셜과 같은 다양한 플랫폼에서의 대칭성 붕괴에 대하여 살펴보고자 한다. 본 연구는 패리티-시간 대칭성, 키랄 특성, 인과율, 초대칭, 생물 모방 기술, 모드 경계 광학 및 느린 빛 원리와 연계된 빛의 특이한 흐름에 집중한다. 본 연구진이 이끌어낸 비직관적인 개념 및 광소자의 새로운 설계 기법 관련 결과들은 비고전적인 빛의 흐름에 기반한 미래 광학 발전에 도움이 될 것이다.The flow of light in matters is usually defined by macroscopic Maxwells equations. In ideal media with homogeneous, isotropic, linear, and time-invariant optical material parameters, the aspect of light wave dynamics is simple and intuitive: propagating straight with oscillated electromagnetic fields, as the direct example of Fermats principle. This planewave dynamics, the basis of geometric optics, originates from the conservation of various symmetries of the Schrodinger-like wave equation, including translational and chiral symmetry, Hermitian symmetry, Lorentz reciprocity, and time-reversal symmetry. To control the flow of light even in a classical manner such as lens, mirror, and prism, some parts of the symmetries in optics should be broken. Breaking the translational symmetry with inhomogeneous materials is the traditional method of controlling light by scattering such as refraction, reflection, and diffraction. The dissipation or amplification of optical energy during the propagation is quantified by the non-Hermitian Hamiltonian of the wave equation. The materials composed of chiral molecules allow the rotation of the polarization of light, i.e. optical activity. The optical Doppler effect, which has been employed in astronomy for the observation of the motion of stars and galaxies, is based on the time-varying position of light sources, breaking Lorentz reciprocity. Recent achievements in optics, including counterintuitive theoretical results and improved fabrication technologies, have now been pioneering unprecedented regimes of controlling optical potentials which derive non-classical flow of light. Nano-scale technologies linked with the concept of metamaterials have opened a path to the design of theoretically-demonstrated artificial media supporting extraordinary light flows: such as unidirectional light flow, modified Snells law, negative index, cloaking, and perfect absorption. The development of optical amplification techniques has been applied to the realization of the quantum-mechanical notion of parity-time symmetry: stimulating a new class of optics in complex potentials. Because these achievements have been based on broader and drastic forms of symmetry breaking in Maxwells equations, in-depth investigation of various symmetry breakings is now imperative to realize designer manipulation of light flow. In this dissertation, we explore symmetry breakings in various platforms: complex, disordered, and nonlinear optical potentials. The investigation is focused on unconventional flows of light linked with the notions of parity-time symmetry, chirality, causality, supersymmetry, biomimetics, mode junction photonics, and slow-light. We believe that our results including counterintuitive concepts and novel design methods for optical devices will be the foundation of future development in optics based on non-classical flow of light.Table of Contents Abstract i Table of Contents iv List of Figures viii Chapter 1 Introduction １ 1.1 Why should we break the symmetry of light? １ 1.2 Outline of the dissertation ２ Chapter 2 Parity-Time Symmetric Optics ４ 2.1 Introduction to PT-symmetric optics ５ 2.2 PT-symmetric waves in the spatial domain １１ 2.2.1 2-level chirped system １１ 2.2.2 N-level photonic molecule ２４ 2.3 PT-symmetric waves in momentum domains ４３ 2.3.1 Optical chirality in low-dimensional eigensystems ４４ 2.3.2 Interpretation of PT-symmetry in k-space ６３ 2.4 Conclusion ７５ Chapter 3 Disordered Optics ７６ 3.1 Introduction to disordered optics ７７ 3.2 Supersymmetric bandgap in disorder ７８ 3.2.1 Wave dynamics in random-walk potentials ７９ 3.2.2 Supersymmetric transformation for isospectrality ８３ 3.2.3 Bloch-wave family with tunable disorder ８６ 3.3 Biomimetic disordered surface ９１ 3.4 Conclusion ９８ Chapter 4 All-Optical Devices with Nonlinearity ９９ 4.1 Introduction to all-optical devices １００ 4.2 Mode junction photonics １０１ 4.2.1 Photonic Junction Diode １０５ 4.2.2 Multi-Junction Half Adder １１３ 4.3 Slow-light enhanced optical functionalities １１５ 4.3.1 Multiband slow light １１６ 4.3.2 Optical A/D converter １２６ 4.3.3 All-optical A/D converter １３７ 4.3.4 Travelling-wave all-optical isolator １４３ 4.4 Conclusion １４９ Chapter 5 Conclusion １５０ Appendix A Eigenvalues in PT-Meta-molecules １５２ Appendix B Supplements for Section 2.3.1 １５７ B.1 Planewave solution of a PT-symmetric optical material １５７ B.2 Density of optical chirality for complex eigenmodes １５８ B.3 Effect of imperfect PT symmetry on the modal chirality １５９ B.3.1 Broken symmetry in the real part of permittivity １５９ B.3.2 Broken anti-symmetry in the imaginary part of the permittivity １６１ B.4 Transfer between RCP and LCP modes in the PT-symmetric chiral material １６２ B.4.1 Propagation of complex eigenmodes １６２ B.4.2 Strength of chiral conversion CCS before the EP １６３ B.5 The state of polarization (SOP) at the EP: Optical spin black hole １６４ B.6 Giant chiral conversion in the resonant structure １６５ B.7 Detailed information of fabrication and experiment in THz chiral polar metamaterials １６６ B.7.1 Fabrication process of THz chiral polar metamaterials １６６ B.7.2 THz-TDS system for the measurement of intermodal chirality １６７ B.8 Realization of PT-symmetric permittivity in metamaterial platforms １６７ B.9 Design parameters of chiral waveguides １７１ B.10 Low-dimensional linear polarization １７１ Appendix C Detailed Derivation for Section 2.3.2 １７３ C.1 Detailed derivation of Eq. (2.20) １７３ C.2 Serial calculation of discretized coupled mode equations １７５ Appendix D Analytical Methods for Section 3.2 １７７ D.1 Details of the FDM and FGH method １７７ D.2 Calculation of the Hurst exponent １７７ Appendix E Supplements for Section 4.2 １７９ E.1 Details of the device structures and numerical method used in the study １７９ E.2 Coupled mode theory for the di-atomic photonic junction diode １８１ E.2.1 Analytical model and coupled mode equations １８１ E.2.2. Solution of resonator field (a1, a2, a3) １８３ E.2.3 Implementation of Kerr nonlinearity and calculation of diode throughput １８５ Bibliography １８７ Abstract in Korean ２０３Docto