Directed diffraction without negative refraction

摘要: Using the FDTD method, we investigate electromagnetic propagation in two-dimensional photonic crystals, formed by parallel air cylinders a dielectric medium. The corresponding frequency band structure is computed using standard plane-wave expansion method. It shown that within partial gaps, waves tend to bend away from forbidden directions. This phenomenon perhaps need not be explained terms of negative refraction or ``superlensing'' behavior, contrast what has been conjectured. Rather it related collimation property crystals.