Modulation Of Group Velocity By Coupled-resonator Optical Waveguide

Photonic crystal is artificial structure, consists of two or more mediums which are arranged in period and have different indexes of refraction. The remarkable optical property of photonic crystal is existence of photonic band gaps in the frequency spectrum of electromagnetic waves.This prominent characteristic enables us to control the propagation of the electromagnetic waves in the dielectric medium as in semiconductor. By introducing different defects with in the medium, a large variety of optical devices, for example, resonator cavities, light-emitting diodes, optical waveguides, and ultrafast optical switches, can be realized.There are two kinds of waveguides in photonic crystals. One is line defect formed in the otherwise perfect photonic crystal. The other is constructed with a chain of strongly confined point defects or cavities, commonly known as a coupled-resonator optical waveguides,coupled-resonator optical waveguides have many peculiar optical characteristics, for example the low group velocity, that promise a bright future in optical communication. In addition, coupled-resonator optical waveguides can realize both the low group velocity and the large optical field amplitude, so they can be used for pulse compression, strongly wavelength-dependent delay line and the enhancement of stimulated emission.The transmission properties of coupled-resonator optical waveguides constructed in periodic PCs have been studied extensively. And it was found that electromagnetic waves can transmit in coupled-resonator optical waveguides, in general, the maximal value of the group velocity is reduced to a value that is two orders of magnitude smaller than the light speed in a vacuum, but this can not satisfy the need of some optical device. Therefore, how to reduce the group velocity of coupled-resonator optical waveguides becomes an important question in this field. The thesis studies the optical properties of coupled-resonator optical waveguides constructed in two-dimensional square lattice photonic crystal,reduce the group velocity by two methods and studies the transmission properties of new coupled-resonator optical waveguide utilizing the finite-difference time-domain method and the multiple-scattering method. The whole works contain two parts:one part is the influence of cavity rotation on the group velocities of the coupled-resonator optical waveguides,which consists of the two-dimensional square lattice photonic crystal;another part is about the effect on the group velocity when some triangular lattice dielectric robs are inserted between two point cavities made in two-dimensional square lattice photonic crystal.The main contents and results are represented as follows.The content of this thesis is as follows. The first chapter gives a brief introduction of the physical properties and the developing process of and coupled-resonator optical waveguides.In the second chapter, some physical theories of studying the photonic crystal are summarized, and the coupling theory of coupled-resonator optical waveguides is given. In the third chapter, the finite-difference time-domain method and the multiple-scattering method are introduced which are needed in this thesis. The influence of cavity rotation on the group velocities of the coupled-resonator optical waveguides,which consists of the two-dimensional square lattice photonic crystal are discussed in the fourth chapter, In the fifth chapter, the group velocity and the transmission property of the coupled-resonator optical waveguides made in two-dimensional super-lattice photonic crystal are researched. In the last chapter, the summery and the prospect are represented.