Bound states in the continuum that rest on a spatial symmetry or a tuned parameter are usually destroyed by fabrication disorder. In the Su-Schrieffer-Heeger chain, chiral symmetry confines the edge state to one sublattice, so a lead on the other sublattice has zero coupling to it. Tight-binding models assume this symmetry is exact; a coupled-waveguide array described by full-wave Maxwell equations breaks it. We test whether the sublattice decoupling survives on a fabricable silicon array. A next-nearest-neighbor hopping and a terminal index offset break chiral symmetry, yet the edge state keeps a weight of order ${10}^{-3}$ on the complementary sublattice and couples to a lead there 11 to 13 times more weakly than on its own sublattice. In a three-dimensional directional coupler, a probe over the complementary sublattice transmits as it does over a trivial array at every coupling length, while a probe over the mode's own sublattice exchanges power with the edge state. Gap disorder, which preserves chiral symmetry to leading order, leaves the edge-state index pinned; on-site disorder of the same physical strength moves it 30 times more. The protection therefore covers errors in waveguide placement and spacing; variations of waveguide width or thickness break it.

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• Bound states in the continuum
• Topological effects in photonic systems
• Waveguide arrays
• Su-Schrieffer-Heeger model