| After years of rapid development,electronic information technology has encountered the "electronic bottleneck",and Moore's Law is also approaching its limits.Light,as an information carrier,has many advantages such as the large bandwidth,fast transmission speed,good anti-interference,safety and reliability,and so on.Therefore,people are looking forward to the realization of an all-optical network that carries information by light throughout the process from sending to receiving.To do this,technology of light storage is essential,which plays an important role in optical signal processing,quantum computing,and on-chip optical interconnection.To store photons on-chip,the speed of light should be significantly slowed down and even stopped.In past decades,electromagnetically induced transparency(EIT),a quantum destructive interference effect in multi-level atomic systems,is widely used in slowing/stopping light.Currently,the proposed slow-light systems that base on the all-optical EIT effect are mainly composed of two or more static resonators to produce an extremely narrow EIT peak,which will cause the group velocity of the optical pulse to decrease greatly.However,these slow-light mechanisms are limited by the delay-bandwidth product: in order to obtain a large amount of delay,an extremely narrow EIT peak that owns a small linewidth is needed,which makes the operating bandwidth very small,resulting in a small delay-bandwidth product.To break this limit,dynamic tuning the coupling strength between the resonators and WGs is demanded.So far,various mechanisms have been proposed to realize dynamically tuning the coupling strength.These mechanisms suffer different challenges:they either request a rigorous dynamic-phase-matching condition or need ultrahigh-speed periodical refractive index modulation.In addition,most of the proposed EIT-like effects are realized in coupled travelling-wave resonators(such as microrings or microtoroids),which commonly have large modal volumes accompanied by many undesirable resonant modes.In order to overcome the above shortcomings,we designed a standing wave resonance system based on the photonic crystal cascade nanocavities.The linewidth of the EIT peak is controlled by modulating the refractive index of the nanocavity dynamically,so that the nanocavity can be switched between a low-Q state and a high-Q state,so as to achieve effective pulse trapping,long-term storing and on-demand releasing.In this way,we break the delay-bandwidth limit.To breakthrough the limitation of the existing optical storage mechanisms,in this thesis we propose a general theory to describe a dynamic photonic crystal system,revealing the underlying physical principle of how to effectively store a signal pulse dynamically.Based on these analytical results,we design a compact silicon photonic crystal systemwith a long storing time over 240 ps and a delay-bandwidth product over 460,and the trapped signal pulse can be released on demand.Besides,the distortion of the light pulse after releasing is relatively slighter.In the first chapter,we introduce the basic concepts,main characteristics,fabrication methods and practical applications of photonic crystal and the development of light storage.In the second chapter,we introduce several numerical methods for photonic crystal investigation: Plane Wave Expansion Method and Finite-Difference Time-Domain Method.In Chapter 3,we focus on designing a photonic crystal cascade nanocavity system that produces an EIT-like effect;In Chapters 4 and 5,we theoretically and numerically investigate how to realize dynamic light storage and eventually break the delay-bandwidth limit. |
PDF Full Text Request