Ibanescu Mihai, Reed Evan J, Joannopoulos J D
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239, USA.
Phys Rev Lett. 2006 Jan 27;96(3):033904. doi: 10.1103/PhysRevLett.96.033904. Epub 2006 Jan 26.
We show that a saddle point Van Hove singularity in a band adjacent to a photonic crystal band gap can lead to situations which defy the conventional wisdom that the strongest band-gap confinement is found at frequencies near the midgap. As an example, we present a two-dimensional square photonic crystal waveguide where the strongest confinement is close to the band edge. The underlying mechanism can also apply to any system that is described by a band structure with a gap. In general, the saddle point favors the appearance of a very flat band, which in turn results in an enhanced confinement at band-gap frequencies immediately above or below the flat band.
