Experimental Observation of Non-Orthogonal Modes in Tight-Binding Lattices

The concept of coupled modes in electromagnetic system was first described in 1954 [1]. Coupled mode theory has since become a well established tool in the description of parametric nonlinear devices, harmonic gerneration, waveguide structures, optical fiber networks and various other optoelectronic structures[2, 3, 4]. In tight-binding structures it reduces otherwise complex systems to discrete coupled mode equations that often describe the dynamics with high accuracy. However, a number of simplifications are typically made that neglect potentially important parameters. In particular, the orthogonality of the coupled modes is typically taken for granted.