Materials with negative refractive index attracted lots of interest recently because they can be realized with metamaterials or photonic crystals (PCs), which are usually periodic structures.

• 拥有负折射率的材料在最近是相当热门的，将人造复合材料或介电材料作周期性排列后，发现可产生负折射的现象，称此结构为超常材料或光子晶体。