a, Illustration of the experimental setup for the case of N_y=3. b, The band structure for N_y=3 (The gray region is projected band structure). c-d, Measured (color code) and simulated (lines) band structures for N_y= 2 and 3, respectively. e-f, Simulated and experimental electric field distributions for N_y= 4 at a non-node frequency and a node frequency.

a, The photo of the sample with N_y= 2 and the eigenfield amplitude distribution at the nodal wave vector. b, The band structure for N_y= 2, the corresponding Q factor of boundary mode, the definition of geometric parameter η and the topological characters of the FBIC. c-d, The field distribution and attenuation characteristics of boundary modes in the second configuration.