Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

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Thesis(Ph.D.)--Case Western Reserve University, 2010 / Title from PDF (viewed on 2010-04-12) Department of Physics Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

As natural chiral materials demonstrate limited circularly dichroic contrasts, enhancement of these polarization dependent signals has long been the focus of chiral metamaterial research. By manipulating the geometric chirality of resonant plasmonic nanostructures, we are capable of enhancing light confinement to amplify chiral modified, nonlinear signals from quantum emitters. The metamaterial demonstrates a linear transmission contrast of 0.5 between left and right circular polarizations and a 20× contrast between second harmonic responses from the two incident polarizations. Nonlinear and linear response images probed with circularly polarized lights show strongly defined contrast. As a second set of experimentation, the chiral center of the metamaterial is opened, providing direct access to place emitters to occupy the most light-confining and chirally sensitive regions. The resulting two-photon emission profiles from circularly polarized excitation displays mirrored symmetry for the two enantiomer structures. The efficiency of the nonlinear signal directly correlates to the chiral resonance of the linear regime. The nonlinear emission signal is enhanced by 40× that of the emitters not embedded in the metamaterial and displays a 3× contrast for the opposite circular polarization. Such manipulations of nonlinear signals with metamaterials open pathways for diverse applications where chiral selective signals are monitored, processed, and analyzed.

The fundamental limitations on the operation of optical bistable devices in a ring cavity and in GaAs etalons are investigated. Experimental results of spontaneous transitions due to shot noise fluctuations are found in good agreement with various "ladder" models, if one allows the counting rates to vary accordingly. Stability analysis for two-photon homogeneously broadened media reveals single-wavelength instabilities for the laser but not for absorptive optical bistability. Appreciable regions of sidemode gain exist for both problems allowing for multiwavelength instabilities to occur. GaAs bistable devices show attractive features such as low power and high speed at room temperature for optical processing. However, experimental evidence in GaAs confirm the computer simulations of bistability that cavity losses, due to unsaturable background absorption, limit the switching power at room temperature. Methods to overcome the different limitations in GaAs devices toward parallel computation are then addressed from a system approach.

Nonlinear optical transverse effects, which arise from the interaction of a Gaussian beam with a nonlinear medium, are discussed. They are cw on-resonance enhancement (CORE), cw off-resonance rings, crosstalk, intracavity phase switching, self-defocusing of a bistable etalon, and thin-sample-encoding (TSE) self-lensing (i.e., self-focusing or self-defocusing) bistability and instabilities. CORE is the enhancement of the on-axis intensity of an on-resonance laser beam in a two-level medium. We report the first observation of CORE using sodium vapor. Cw off-resonance rings, resulting from a pure phase encoding or from simultaneous phase and amplitude encodings, are observed using sodium vapor. These rings have been observed many time before, but we have made the first careful comparison with numerical calculations. Parallel operation and external switching are two crucial themes for the application of bistable optical devices (BODs). For parallel operation, crosstalk between nearby BODs on the same etalon due to diffraction coupling may need to be avoided. Minimum separations needed to ensure independent operation are computed. For external switching, intracavity phase switching using a plane-wave input can switch on (or off) a BOD using an external pulse. The validity of this concept for a Gaussian input is numerically simulated. Self-defocusing effects, resulting in some interesting effects in the transverse bistable loops, are observed using a GaAs-GaAlAs bistable etalon. The results are confirmed by numerical simulations. TSE self-lensing bistability is observed using a short sodium cell and a single mirror. TSE self-lensing bistability results from an enhancement in the feedback via self-lensing of the beam. The lack of an optical resonator and the use of a thin medium make TSE setup a good candidate to study the Ikeda instability. We report the first observation of the Ikeda instability in this all-optical passive system using a cw input. Numerical simulations show a rich bifurcation sequence not yet fully studied experimentally.

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在適當的條件下，正向入射激光束令GaAs量子阱微腔產生方向的不穩定性，並生成橫向光學圖案。方向不穩定性的形成是由於極化子，即光子及量子阱激子的強非線性耦合的本徵態，在微腔內散射的結果。電腦模擬顯示，通過一個非常弱的控制激光束，橫向光學圖案可以從一個方向切換到另一個。它可以作為一個全光學開關，而全光開關可有效地改善計算機的性能。 / 本論文先介紹GaAs量子阱微腔的理論及其數值模擬，以顯示GaAs量子阱微腔能夠產生光學圖案和全光學開關。然而，透過複雜的模擬數據去理解其規律及原理實在太困難。為此，我們發展一個低維的群種競爭模型，以理解這些現象。 / 為了分析群種競爭模型，我們應用了一些數學工具，如Gröbner bases 和廣義判式，以減少計算模型的相圖所需的電腦負荷。此外，我們也利用了突變理論來分類和解釋所有相圖中的相界。這個人口競爭模型使我們對不同物理系統中的圖案生成現象有一個全面的定性理解。 / 在本論文的最後一部分，我們研究量子阱雙微腔，即兩個耦合的微腔，而每個微腔中間也有一個量子阱。透過傳輸矩陣的方法，我們獲得了雙微腔的色散關係，並與實驗結果作比較。我們預期沿著這個研究方向在未來能夠加快實現全光開關。 / Under favorable conditions, laser beams incident normally to a GaAs quantumwell microcavity develop directional instabilities and generate transverse patterns in the far field. The directional instabilities are driven by scattering among polaritons inside the microcavity, where the polaritons are the eigenstates of strong linear coupling between the cavity photons and the excitons inside the quantum-well. It has been predicted that the transverse pattern can be switched from one to another by the use of a very weak control beam. It can serve as an all-optical switching, which can potentially be used to improve computers’ performance. / In this thesis, the theory of the GaAs quantum-well microcavity is first introduced and numerical results showing the formation of patterns and the all-optical switching scheme are presented. However, understanding the patterns and their dynamics through numerical simulations turns out to be very complicated. To this end, we derive a low-dimensional population-competition model for the interpretation of these behaviors. / To facilitate the analysis the population-competition model, we apply mathematical tools such as the Gröbner basis and the generalized discriminant to reduce the computational load in finding the ‘phase diagrams’ of the populationcompetition model. Besides, we also make use of the catastrophe theory to classify and explain all the phase boundaries in the phase diagrams. This population-competition model enables us to acquire an overall qualitative picture of pattern formation in various physical systems. / In the last part of this thesis, we use the transfer-matrix method to study the polariton spectrum of a quantum-well double-microcavity, which is two coupled optical cavities each containing a quantum well, and compare the spectrum with the experimental results. We expect our efforts along this direction could expedite realization of all-optical switching in the future. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Tse, Yuen Chi = 分析橫向光學圖案的低維群種競爭模型 / 謝沅志. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 112-119). / Abstracts also in Chinese. / Tse, Yuen Chi = Fen xi heng xiang guang xue tu an de di wei qun zhong jing zheng mo xing / Xie Yuanzhi. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Optical computation and all-optical switching --- p.3 / Chapter 1.2 --- Nonlinear optics and low-intensity ultra-fast all-optical switching of transverse optical pattern --- p.4 / Chapter 1.3 --- Pattern formation and amplitude equation formalism --- p.6 / Chapter 1.4 --- Semiconductor quantum-well double-microcavity and transfermatrix method --- p.9 / Chapter 2 --- Semiconductor quantum-well microcavity --- p.10 / Chapter 2.1 --- Physical configuration and theroy --- p.10 / Chapter 2.2 --- Simplified models --- p.19 / Chapter 2.3 --- Directional instability and the effect of anisotropy in model PCO-Q --- p.25 / Chapter 2.4 --- Effect of control beam and all-optical switching in PCO-Q --- p.30 / Chapter 2.5 --- Simulation results of model PCO-L, a model without quadratic dependence --- p.33 / Chapter 3 --- Population-competition model --- p.37 / Chapter 3.1 --- Derivation of PC model --- p.37 / Chapter 3.1.1 --- Approximation from the simulation results --- p.38 / Chapter 3.1.2 --- Adiabatic approximation for the field equations --- p.39 / Chapter 3.1.3 --- Revised dynamical equations --- p.40 / Chapter 3.1.4 --- Taylor expansion approximation about phase locking --- p.42 / Chapter 3.1.5 --- Comparison with the simulation results --- p.45 / Chapter 3.1.6 --- Modelling of the control beam --- p.47 / Chapter 3.1.7 --- Reduction in the number of parameters --- p.47 / Chapter 3.2 --- Physical meaning of the simplified PC model --- p.49 / Chapter 3.3 --- Comparison with amplitude equations formalism and others competition models --- p.49 / Chapter 4 --- Mathematical tools --- p.52 / Chapter 4.1 --- Steady states and linear stability analysis --- p.52 / Chapter 4.2 --- Gröbner basis --- p.54 / Chapter 4.3 --- Generalized discriminant --- p.55 / Chapter 4.4 --- Algorithm for conditions for qualitative changes --- p.56 / Chapter 4.5 --- Reduction in computational power --- p.57 / Chapter 4.6 --- Elementary catastrophe theory --- p.58 / Chapter 5 --- Population-competition model analysis --- p.66 / Chapter 5.1 --- Symmetric model L without source term --- p.67 / Chapter 5.2 --- Symmetric model Q without source term --- p.70 / Chapter 5.3 --- Asymmetric model L and Q without source term --- p.74 / Chapter 5.4 --- Symmetric models L and Q with control beam S₂ --- p.80 / Chapter 5.5 --- Asymmetric Model L and Q with control beam S₂ --- p.81 / Chapter 6 --- Semiconductor quantum-well double-microcavity --- p.91 / Chapter 6.1 --- Motivation --- p.91 / Chapter 6.2 --- Transfer-matrix method inside dielectrics --- p.94 / Chapter 6.3 --- Transfer-matrix method across QW --- p.97 / Chapter 6.4 --- Analysis of the QWDM through transfer-matrix method --- p.98 / Chapter 7 --- Conclusion and Outlook --- p.105 / Chapter 7.1 --- Conclusion --- p.105 / Chapter 7.2 --- Outlook --- p.107 / Chapter 7.2.1 --- Extension of the PC model --- p.107 / Chapter 7.2.2 --- Extension of the transfer-matrix method to nonlinear analysis --- p.109 / Bibliography --- p.112 / Chapter A --- Dispersion relations inside QWM --- p.120 / Chapter B --- Analysis on the steady states with and without off-axis instability --- p.122 / Chapter B.1 --- Steady states of E₀ and p₀ --- p.122 / Chapter B.2 --- Analysis on the steady states without off-axis instability --- p.123 / Chapter B.3 --- The effects of instability on E₀ and p₀ --- p.124 / Chapter C --- Analytical derivation of the phase diagram asymmetry versus quadratic terms (δβ1 vs γ) without control beam (S₂ = 0) --- p.127 / Chapter D --- Verification of the elliptic umbilic (D₋₄) singularity --- p.129

An Zhong. / "November 30, 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. [167]-173). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.