Active lens realized by two-dimensional photonic crystal

It has been suggested that photonic crystals can be utilized to make a microsuperlens due to the presence of negative refraction in them. However, the losses of intensity for the image and focusing are inevitable. There are two kinds of losses, one is from the absorption of materials and another is associated with a finite reflection on the interface of the sample. In this Letter, we introduce optical gain in 2D photonic-crystal-based flat lens to compensate the losses. We find that both of losses can be compensated by introducing optical gain. Thus, an active flat lens has been designed by using such a 2D photonic crystal, which the non-loss image and focusing can be realized by it.