Photonic-Crystal Waveguides with Disorder: Measurement of a Band-Edge   Tail in the Density of States
  We measure localized and extended mode profiles at the band edge of slow-light photonic-crystal waveguides using phase-sensitive near-field microscopy. High-resolution band structures are obtained and interpreted, allowing the retrieval of the optical density of states (DOS). This constitutes a first observation of the DOS of a periodic system with weak disorder. The Van Hove singularity in the DOS expected at the band edge of an ideal 1D periodic structure is removed by the disorder. The Anderson-localized states form a "tail" in the density of states, as predicted by Lifshitz for solid-state systems. 
S. R. Huisman, G. Ctistis, S. Stobbe, A. P. Mosk, J. L. Herek, A.   Lagendijk, P. Lodahl, W. L. Vos, and P. W. H. Pinkse
physics.optics