  By altering the lattice geometry of the photonic crystal surface-emitting
lasers (PCSELs), we tune the regular lasing band edges of quadratic dispersions
to form a single accidental Dirac point of linear dispersion at the Brillouin
zone center. This not only increases the mode spacing by orders of magnitude,
but also eliminates the distributed in-plane feedback to enable single-mode
PCSELs of substantially larger area thus substantially higher output power. The
advantages of using accidental Dirac cones are systematically evaluated through
two-dimensional in-plane calculations and confirmed by three-dimensional
simulations of photonic crystal slab devices.
