Observation of nonlinear bands in near-field scanning optical microscopy   of a photonic-crystal waveguide
  We have measured the photonic bandstructure of GaAs photonic-crystal waveguides with high energy and momentum resolution using near-field scanning optical microscopy. Intriguingly, we observe additional bands that are not predicted by eigenmode solvers, as was recently demonstrated by Huisman et al. [Phys. Rev. B 86, 155154 (2012)]. We study the presence of these additional bands by performing measurements of these bands while varying the incident light power, revealing a non-linear power dependence. Here, we demonstrate experimentally and theoretically that the observed additional bands are caused by a waveguide-specific near- field tip effect not previously reported, which can significantly phase-modulate the detected field. 
Amandev Singh, Georgios Ctistis, Simon R. Huisman, Jeroen P. Korterik,   Allard P. Mosk, Jennifer L. Herek, and Pepijn W. H....
physics.optics