Fig. 4

(a) Wavefield (modulus) in a finite periodic waveguide (\(M= 6\), \(d = 2\)), as generated by a point source located at two different positions (\({\varvec{\odot }}\)), at a frequency, \(k = 6.23 \pi\), in a band with only one pair of right- and left-going propagating Bloch modes (see. Fig. 3). (b) Pattern of the transmitted field \(|\psi (x = Md, y)|\), \(y \in [0, 1]\). (c) Similarity function F(x), as defined by Eq. (6). Numerics are performed using a finite element method (Comsol Multiphysics).