Focusing analysis of a complex photonic crystal slab with negative refraction

The electromagnetic wave propagation in a two-dimensional (2D) complex triangular photonic crystal (PC) consisting of dielectric cylinders of different radii in air is investigated. The plane wave expansion (PWE) and finite element (FE) methods are used to study the optical and focusing properties of the complex PC. Interestingly, in contrast to a triangular PC consisting of dielectric cylinders of the same radius, the complex PC can generate a focusing effect with an effective refractive index of −1. Furthermore, a design is proposed using antireflection structures to enhance the transmission efficiency of light at the interfaces between the air and the PC slab. Numerical simulations show that appropriately adding antireflection structures to the surface of the slab can greatly improve the focusing resolution.