Zero phase delay with relax incident condition in photonic crystals.

Based on the wavefront modulation of photonic crystal (PhC), zero phase delay of propagating electromagnetic wave (EMW) can be realized with a relaxed incident condition in the PhC. The phase velocity is modulated perpendicular to the group velocity with wavefronts extending along the direction of energy flow, which lead to the phenomenon of zero phase delay with a finite spatial period. This effect can be realized simultaneously in both positive and negative refracted waves. The phase difference between the incident and transmitted waves are measured within a wide incident angle region to demonstrate zero phase delay can be realized easily instead of zero-n or zero-averaged-n materials. Further investigations prove that the phenomena of zero phase delay induced by this way can also be realized easily in various PhC configurations and can be accurately manipulated by changing the incident angle or the flexible design of PhC configuration.