Ab initio Design, Experimental Validation, and Scope of Coupling Coefficients in Waveguide Arrays and Discrete Photonics Patterns

In coupled waveguide arrays, well-defined coupling coefficients are still required to demonstrate advanced effects on a quantitative basis, especially in patterned arrays where new discrete photonics functions need accurate coupling gradients. We show that adequate arrays of strip loaded waveguides designed within an extended second-neighbor coupled-mode theory can actually be constructed by means of state-of-the-art technologies, with the necessary coupling coefficient ratios (similar to 0.5) and accuracies (similar to 10%). We also specify for literature systems the weak coupling regime where the conventional coupled-mode theory truly applies, and the moderate coupling regime where the extended theory is required but can be approximated by the conventional theory with an apparent coupling coefficient.