Research On Coupled-Cavity Structure And Slow Light Properties In Two-Dimensional Nested Magnetic Fluid Photonic Crystal Waveguide

Optical buffer and all-optical delay line technology are the key technologies to achieve all-optical network. It is crucial to select the appropriate material to achieve optical buffer.Compared with other materials which can acquire slow light, photonic crystal waveguide(PCW),due to its large bandwidth, small size, diversified design of the waveguide structures and easy to integration with other optical devices, represents a breakthrough in the field of optical buffer.Because photonic crystal has unique photonic band gap characteristics and optical properties, it is beneficial to the realization of optical buffer.Here, a nested structure with ferrite magnetic fluid(MF) infiltrated photonic crystal coupled-cavity waveguides(PC-CCW). Specifically, three types of coupled cavities, i.e.,horizontal-, vertical-, and cross-defect cavity are studied with different concentrations of magnetic fluid. This paper studies mainly on the characteristics of slow light of these three coupled-cavity waveguides. We also designed the structures of two-dimensional nested photonic crystal coupled cavity with air filled and analyze and compare the slow light performance of these coupled-cavity structures.The major work and innovation of the paper as following.1. The plane wave expansion method(PWM) is used to study slow light properties of four structures of two-dimensional nested photonic crystal coupled cavity with air filled. Four different types of coupled cavity models whose slow light characters are influenced by radius of defect rod in cavity and the distance between two cavities are investigated. The result shows that double-defect cavities have better slow light performance compared with single defect cavity.But in three double-defect coupled cavity waveguide structures, the best performance of slow light is realized in double- defect coupled cavity waveguide structure of type one whose maximum group velocity reaches the magnitude of310 c-corresponding maximum NDBP reaches 0.284. In addition, the bandwidth of the single defect cavity, the largest group velocity and NDBP decreased as the distance between two cavities increases. When L=3a, the maximum group velocity is only around210 c-.Then increase L to 5a, it could get three orders of magnitude smaller than the speed of light in vacuum.2. Three kinds of reconfigurable two-dimensional nested ferrite magnetic fluid photonic crystal coupled-cavity waveguides named horizontal-, vertical-, and cross-defect cavity are established. Firstly, we obtain the optimal structure of three kinds of novel nested magnetic fluid coupled cavity structures by simulation and optimization. Then we studied the characteristics of slow light with the variation of the magnetic fluid material. Simulation results show that: The group velocities are all three orders of magnitude smaller than the speed of light in vacuum, and that the corresponding Normalized Delay-Bandwidth Product(NDBP) values are all larger than0.35. Among them, vertical-defect coupled cavity possesses the best slow light property in three kinds of novel nested coupled cavity structures which are infiltrated with magnetic fluids. The minimum value of maximum group velocity can reach to32.56 10 c-?, the bandwidth is about0.0002, the maximum value of NDBP comes to around 0.408, and Q factor reaches the magnitude of310.3. The facile and practical strategy that involves infiltrating the novel nested PC-CCW structures with magnetic fluid, which realizes both the adjustability of the slow light property and reconfiguration of PCW. By this means, three structures of PC-CCW were generated and the slow light properties were regulated flexibly. The results of this work have further improved the slow light property in slow light devices and realized the tunable slow light. By simulation we come to the conclusion that: Bandwidth, group velocity, NDBP and Q values in the new nested ferrite magnetic fluid photonic crystal coupled-cavity waveguides are adjusted continuously as the concentration changes, and are superior to the two-dimensional nested coupled cavity structures with air filled.