Optical confinement of spatial frequencies in the photonic crystal waveguide

The optical confinement of spatial frequencies in the photonic crystal waveguide has been investigated theoretically and simulated numerically. It is found that the enhanced gap confinement is at frequency close to the upper band edge, in contrary to the conventional concept that the strongest optical confinement is found at frequencies near the mid-gap. The anomalous phenomenon may be attributed to a Van Hove saddle point singularity in a band adjacent to a photonic crystal band gap. In general, the saddle point favors the appearance of a very flat band, which in turn causes an enhanced confinement at band-gap frequencies.