Fig. 1: Geometric structure, bulk bands, and Zak phase.
a Schematic diagram of the topological rainbow configuration. a1, a2 denote the lattice vectors. The red and blue regions denote the barrier and dispersing regions, respectively. The displacement vector of ith layer is denoted by ξia2. Na, Nξ, Nb denote the number of layers of regions I, III along a1 direction, and Nu, Nd denote the number of layers of undeformed region and the deformed region in region II. Light is incident from the dielectric waveguide with a width w = 8 μm. b Evolution of Zak phases with parameter ξ. The inset shows the geometric structure for different ξs. c The TE-like bands of triangular hole structure with side length l = 0.75a and thickness h = 220 nm. The geometry of the unit cell is shown in the inset.
