Investigations On Nonlinear Effect And Quantum Interference Effect In Slot Waveguide

When light interact with matter (atoms, molecules) resonantly, there will be many interesting phenomenon. With the effect of Electromagnetically induced transparency which has been developed in recent years, the absorption of the probe light can be largely eliminated. EIT is the quantum destructive interfer-ence between excitation pathways induced by the quantum states of atoms or molecules coherently prepared by an extra induced field. Moreover, linear and nonlinear optical response can be significantly enhanced due to the resonant in-teraction. EIT also exhibits a steep dispersion curve in the resonance region, which lead to the slowing down of group velocity of the probe light. Based on these features, EIT is important for many applications such as optical delay de-vices, quantum storage, quantum communication and so on. With the enhanced nonlinear properties of EIT, optical effects under low light levels can be achieved, such as multi-wave mixing, quantum phase gate, quantum nondemolition mea-surement, ultraslow optical solitons. Investigations on EIT are of great signifi-cance in fundamental physics and technology applications.EIT has been proposed and realized for more than twenty years by now and people are paying more attention to the various applications of EIT, especially in the field of quantum information and quantum computing. Traditionally, inter-actions between optical field and atomic or molecular gases in free space involve following difficulties:(ⅰ) The density of the atoms and molecules is very low, so it is hard to enhance the EIT effect including absorption, slowing down of group velocity of light pulses, and nonlinear effects;(ⅱ) Usually there is strong Doppler effect when atomic gases are at room temperature and the EIT effect is not ideal. The temperature of the atoms or molecules has to be cooled down in order to e-liminate the Doppler effect and consequently the experimental setup is complex and expensive;(ⅲ) The traditional EIT system employs atomic and molecular gas in free space as the medium, so it is difficult to achieve the miniaturization of the optical device and large-scale integration.To overcome the difficulties mentioned above, solid materials come into con-sideration instead of atomic and molecular gas. But there are also some shortcom-ings in solids. Quantum interference effects and nonlinearity in solid medium is not enough to produce strong enough to meet the needs for the manipulation of quantum states at single-photon-level and related interaction. In addition, the energy level structure of the solid material is too complex with respect to the atomic and molecular gas and quantum decoherence effects caused by crystal field effect is also serious. Therefore, studies on combination of atoms, molecules and solid materials and micro/nano-sized hybrid quantum devices has attracted more and more attention. Micro/nano-structures can lead to light confinemen-t in subwavelength scale with a very small effective mode volume, which can greatly enhance the light field intensity and hence resulting in the enhancement of linear and nonlinear optical response. In recent years, with the development and improvement of manufacturing technology of micro/nano optical devices, hybrid systems combined with micro/nano structures and resonance atoms have become one of the most competitive candidate to achieve various applications of EIT.In this dissertation, we have investigated the quantum interference effec-t linear and nonlinear optical properties in the slot waveguide. The main work include the following aspects:1. We have investigated the electromagnetically induced transparency (EIT) and nonlinear pulse propagation in a∧-type three-level atomic gas filled in a slot waveguide. Due to the discontinuity of dielectric constant, the electric field is strongly confined inside the slot of the waveguide. As the width of the slot goes smaller, the electric field becomes stronger. We developed a theoretical model to treat the interaction of light and atoms in the slot waveguide. We find that EIT effect can be greatly enhanced due to the reduction of optical-field mode volume contributed by waveguide geometry. Comparing with the atomic gases in free space, the EIT transparency window in the slot waveguide system can be much wider and deeper. Finally, the nonlinear pulse propagation in the slot waveguide with low generation power are also discussed.2. We have studied the quantum interference effect in a doped solid em-bedded in a nanometer-wide slot waveguide. We investigate electromagnetical-ly induced transparency (EIT) and Autler-Townes splitting (ATS) and crossover from EIT to ATS. By using a averaging method and the residue theorem, we show that the quantum interference effect can be largely enhanced due to large increase and confinement of light field contributed by the slot-waveguide geometry. We give the explicit expressions of linear dispersion relation, width and depth of EIT transparency window and EIT condition. In particular, we show that inhomo-geneous broadening can be effectively suppressed with the slot waveguide. In addition, we make a detailed analysis on the quantum interference character of the system by adopting a spectrum-decomposition method, and demonstrate that a crossover from EIT to Autler-Townes splitting may occur if the Rabi frequency of control field is changed to different regions.3.We investigate the giant kerr nonlinearity and ultraslow soliton in a doped solid embedded in a slot waveguide. From Maxwell-Bloch equations, We derive the linear dispersion relation and nonlinear Schodinger equation by introducing a method of multiple scales asymptotic analysis. The third-order nonlinear sus-ceptibility is very sensitive to the changes of the size of the slot width. When the size of the slot width becomes small, the nonlinear Kerr effect can be significantly enhanced. We compared the third-order nonlinear susceptibility for the cases of different slot widths and analyze relationship between the third-order nonlinear susceptibility and the slot width. Giant Kerr nonlinearity and hence the enhanced self-phase modulation effects can be obtained by the using the slot waveguide for the electric field enhancement in the confined system. Thus, optical soliton can be generated efficiently with lower power in the confined system, compared to the unconfined system.The studies on nonlinear and quantum interference based on EIT in the slot waveguide effect are not only important for further studies on linear and nonlin-ear optical properties of confined system, but also have new findings and poten-tial applications in the field of optical information processing and transmission on a chip.