The band gaps structure of two-dimensional function photonic crystals for the triangle lattice, , , function coefficient , medium column radius . (a) TE wave, there are two semi-Dirac points A and B for the TE wave. In the vicinity of the A point, the dispersion relation is linear along the XM direction and quadratic along the direction. In the vicinity of the B point, the dispersion relation is linear along the MX direction and quadratic along the direction. (b) TM wave, there is one semi-Dirac point C for the TM wave. In the vicinity of the C point, the dispersion relation is linear along the MX direction and quadratic along the direction.