Effect of second-order coupling on photon-pair statistics in waveguide structures

We investigate a quasi-one-dimensional periodic array of coupled waveguides, with one extended and one bound dimension, incorporating both first-and second-order coupling. We study the evolution of optical fields in this system, and measure quantum correlations when path-entangled photon pairs are launched into them. We observe a surprisingly large and nontrivial effect of second-order coupling on these correlations-while quantum correlations are symmetric when only first-order coupling is present, the introduction of next-nearest-neighbor coupling often breaks the symmetry to reflections.