Tunable sharp angular defect mode with invariant transmitted frequency range in one-dimensional photonic crystals containing negative index materials.
We propose a different photonic crystal structure with a novel defect mode. In this defect mode, the transmitted angle is sharp and the pass band is of rectangular shape. Surprisingly, there is a critical refractive index of the defect layer in the crystal. By changing the refractive index in a range higher than this critical value, the sharp transmitted angle can be tuned with transmitted frequency range maintained; when the refractive index is lower than this critical value, only the transmittance of the defect mode is adjusted, with the sharp transmitted angle and transmitted frequency kept unchanged. All these phenomena provide possible mechanisms for angular filtering, optical switching (i.e., an optical switch working in the angular domain) and setting optical limits.