Orbital angular momentum generation from a defect in photonic crystals

Orbital angular momentum (OAM) is generated from a defect in two-dimensional (2-D) photonic crystals (PC). By breaking the translation symmetry along the two orthogonal directions, the localized defect states can be supported within photonic bandgap of the PC. Particularly, we examine the characteristics of the point defect states along the azimuthal direction by the finite-difference (FD) based eigenvalue analysis. We find that vortex beam carrying OAM can be generated from the defect. The novel design can be easily integrated in optical circuits.