Abstract

We previously reported that various types of Dirac cones, that is, isotropic linear dispersion relations, can be materialized in the zone center (Γ point) of photonic crystals (PhCs) by accidental degeneracy of eigenmodes with particular combinations of their spatial symmetries (See Ref. [1] and references therein). Those Dirac cones are characterized by a vanishing effective refractive index, so they can materialize cloaking and scatter-free wave guides. Recently another application to single-mode surface-emitting lasers was proposed [2]. Some of the Dirac cones were confirmed by experimental studies on two-dimensional PhCs (See Ref. [3], for example). However, the double Dirac cones were difficult to detect because of the dense distribution of eigenmodes in the vicinity of the Dirac point frequency although they have a unique character of the absence of flat bands, which is advantageous for their applications.

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