Research On Slow Light Properties In Dual-periodic Photonic Crystals Based Slotted-waveguide Coupled Cavity

Today, in the developing era of all-optical network, all optical buffer and all-optical signal processor are the necessary premise of achieving all-optical network. Slow light technology is regarded as a solution with broad prospecting application for the achievement of all-optical buffer and all-optical signal processor. Compared with other slow light technologies, slow light in photonic crystal has the advantages of potentially larger bandwidth, lower dispersion and smaller device volume. Moreover, it is easy to be integrated into existing optical components and is able to be operated in room temperature, etc.In this paper, by utilizing the fact that slotted waveguide with low refractive index could confine and enhance light field in the slotted defect, and coupled micro-cavity with high refractive index could obtain slow light properties with smaller group velocity and low loss, we design a dual-periodic slotted-waveguide coupled cavity structure with high and low refractive index alternately. And we further analyze the influence of slow light properties by adjusting slot width and the period of cavity. The results show that the combination of high and low refractive index region can achieve better slow light property.The major work and innovation of this paper include the following.1. We establish a single-periodic slotted photonic crystal waveguide based on the conventional square structure. The slotted defect is achieved by dividing the dielectric rods of the perfect photonic crystal into two and symmetrically distributed on both sides of the central axis in a certain distance. The result reveals that group velocity slows down to 0.0679 times of the speed of light in vacuum when slotted width is 0.18 times of the lattice constant, which is the optimal slow light effect achieved by the slotted width as the only structural parameter. And the corresponding slow light bandwidth is 0.0073, the group velocity dispersion is maintained at [-1, 1]*105 magnitude. 2. We further optimize the slow light property of single-periodic slotted photonic crystal waveguide. We set slotted width to be 0.18 times of the lattice constant, and then adjust radius of dielectric rods adjacent to the slotted defect. The result reveals that group velocity slows down to 0.0474 times of the speed of light in vacuum when the radius of dielectric rods adjacent to the slotted defect is 0.8 times of the original radius of dielectric rods. This is the optimal slow light effect when we add the adjacent radius as the second structural parameter. Compared to slotted width as the only structural parameter, the minimum group velocity reduces 0.0205 times of the speed of light in vacuum, and slow light bandwidth reduces to 0.0052 and the normalized delay-bandwidth product reduces to 0.3242. 3. By utilizing the fact that slotted waveguide with low refractive index could confine and enhance light field in the slotted defect, and coupled micro-cavity with high refractive index could obtain slow light properties with smaller group velocity and low loss, we design a dual-periodic slotted waveguide coupled cavity structure with high and low refractive index alternately. The result reveals that group velocity slows down to 1.55*10-3 times of the speed of light in vacuum when slotted width is 0.54 times of the lattice constant in the dual-periodic slotted-waveguide coupled cavity structure. And the corresponding normalized delay bandwidth product is 0.243, the group velocity dispersion is maintained at [-1, 1]*108 magnitude. 4. We further optimize the slow light property of dual-periodic slotted-waveguide coupled cavity structure. We set slotted width to be 0.54 times of the lattice constant, and then adjust the period of cavity. The result reveals that we obtain the lowest group velocity, which is 7.94*10-4 times of speed of light in vacuum. Compared to slotted width as the only structural parameter in dual-periodic slotted-waveguide coupled cavity structure, the minimum group velocity further reduces an order of magnitude. And the corresponding normalized delay-bandwidth product is 0.244, which is a good indication for slow light bandwidth property.