Surface guided modes in photonic crystal ridges: the good, the bad, and the ugly

We discuss the existence and the optical properties of guided modes in photonic crystal ridges, where light confinement relies on a photonic band gap in the direction of the substrate and on total internal reflectance in the other directions. Photonic crystal ridges are known to support guided surface waves, but here we show that at least three different guided modes can be identified, and only one of them seems to possess all the characteristics of a proper guided surface wave. We also discuss the use of effective index approaches to drastically simplify the modeling of such modes. Photonics crystal ridges are already recognized as promising platforms in the field of optical sensing and for the study of the light-matter interaction at the fundamental level, and our results should be of use in exploiting the potential of these structures for the confinement and control of light.