An optical diode and magnifier from a general function photonic crystals
  We have presented a new general function photonic crystals (GFPCs), which refractive index is a function of space position. Based on Fermat principle, we achieve the motion equations of light in one-dimensional general function photonic crystals, and calculate its transfer matrix. In this paper, we choose the line refractive index function for two mediums $A$ and $B$, and obtain new results: (1) when the line function of refractive indexes is up or down, the transmissivity can be far larger or smaller than 1. (2) when the refractive indexes function increase or decrease at the direction of incident light, the light intensity should be magnified or weaken, which can be made light magnifier or attenuator. (3) The GFPCs can also be made optical diode. The new general function photonic crystals can be applied to design more optical instruments. 
Xiang-Yao Wu, Bo-Jun Zhang, Xiao-Jing Liu, Si-Qi Zhang, Jing Wang, Nuo   Ba, Zhong Hua and Jing-Wu Li
physics.optics