Light confinement at a Dirac point in honeycomb-like lattice photonic crystal

Optical waveguides and cavities are important components among modern optical devices. Traditional optical cavities rely on total internal reflection or photonic bandgaps to achieve field confinement. Recently, a new type of trapped mode, the Dirac mode, has been reported to occur in triangular or honeycomb lattice photonic crystal. This novel localized mode is attribute to neither of the traditional light-guiding mechanisms and owns different characteristics. Here we report the discovery of the Dirac mode in honeycomb-like photonic crystal lattice. The Dirac mode occurs at a Dirac frequency, which is beyond the complete photonic bandgaps. It has a different algebraic-decay feature. Our discovery extends applicability of the Dirac mode in designing for optical devices.