Study on self-collimated light-focusing device using the 2-D photonic crystal with a parallelogram lattice

This paper investigates the optical characteristics of a light-focusing device (LFD) consisting of two-dimensional (2-D) photonic crystals (PCs) configured in a parallelogram lattice structure. The LFD is composed of two jointed symmetric PCs that have a strong self-collimation effect. This self-collimation effect focuses the incident light wave. For a square lattice, however, in which the equi-frequency contours have fourfold symmetry (π/2 rotation symmetry), the band structure needed to realize an LFD was not obtained. The proposed solution was to consider the parallelogram lattice arrangement since its equi-frequency contours do not have π/2 rotation symmetry; a prototype LFD composed of 2-D PCs with parallelogram lattice structure exhibits desirable focusing performance. The authors also investigate the asymmetry of light wave transmission through the LFD. Finite-division time-domain (FDTD) simulations of the optical property of the LFD show that the LFD has distinct transmission asymmetry.