Light localization in periodic waveguides due to random fabrication imperfections, even very small ones, is a well-known phenomenon in optics and photonics. It is generally attributed to the fact that light propagation becomes very sensitive to perturbations when its group velocity diminishes, for instance, at frequencies near the edge of the dispersion curve.
In a recent study published in Scientific Reports, researchers at LP2N, in collaboration with researchers at ICB (Dijon, France) and at the University of St-Andrews (UK), have revealed that the parameter that drives the size of the smallest possible localized modes is the effective photon mass, rather than the group index.
These results suggest that an engineering of photonic-crystal waveguides can make them less sensitive to imperfections, which often constitutes a strong limitation for the realization of photonic components, or inversely, enhance the spatial confinement of light for applications such as sensing or quantum optics.
R. Faggiani, A. Baron, X. Zang, L. Lalouat, S. A. Schulz, B. O’Regan, K. Vynck, B. Cluzel, F. de Fornel, T. F. Krauss, P. Lalanne, Lower bound for the spatial extent of localized modes in photonic-crystal waveguides with small random imperfections, Scientific Reports 6, 27037 (2016). (link)