Controlling Interface States in 1D Photonic Crystals by tuning Bulk   Geometric Phases
  Interface states in photonic crystals usually require defects or surface/interface decorations. We show here that one can control interface states in 1D photonic crystals through the engineering of geometrical phase such that interface states can be guaranteed in even or odd, or in all photonic bandgaps. We verify experimentally the designed interface states in 1D multilayered photonic crystals fabricated by electron beam vapor deposition. We also obtain the geometrical phases by measuring the reflection phases at the bandgaps of the PCs and achieve good agreement with the theory. Our approach could provide a platform for the design of using interface states in photonic crystals for nonlinear optic, sensing, and lasing applications 
Wensheng Gao, Meng Xiao, Baojie Chen, Edwin Y. B. Pun, C. T. Chan, and   Wing Yim Tam
physics.optics