Research Paper: Designing Slow Light Waveguides Consisting of Two-dimensional Photonic Crystals and Investigating its Tunability

The purpose of this research is to investigate the group velocity of tunable two-dimensional photonic crystals. The first step considers a square lattice consisting of dielectric rods in the liquid crystal background. In the next step, this structure was rotated by 45 degrees and its photonic band structure was investigated. Then, by removing a row of dielectric material (silicon) rods a waveguide is made in the photonic crystal. The waveguide mode and the related group velocity of the waveguide mode were investigated. In the following, the effect of applying an external voltage and changing the refractive index of the background material on the group velocity was studied. Afterward, by applying geometrical changes to the size of waveguide side rods, the effect of mentioned geometrical change on the properties of the waveguide mode and the group velocity was investigated. The calculation results show that the group velocity is reduced and as a result, the group index is increased. The investigations carried out show that quantitatively, by applying an external voltage in the ordinary waveguides, the range of changes in the group index is between 7 and 10, but by applying changes in modified waveguides, this quantity changes in the range of 14 to 27, which can be adjusted by applying an external electric field.