Patent ID: 7136561

Claim:
A two-dimensional photonic crystal formed by a periodical two-dimensional arrangement of plural unit lattices, comprising: a prism-shaped first dielectric area arranged at each lattice point of each unit lattice; a prism-shaped second dielectric area arranged at an approximate center of each unit lattice; and a third dielectric area adjacent to and around the first and second dielectric areas, wherein the third dielectric area has a relative dielectric constant different from relative dielectric constants of the first and second dielectric areas, the unit lattice is a tetragonal lattice, and the first dielectric area and the second dielectric area have a substantially cylindrical shape and satisfy a relationship: 0.4 a≦r 1 +r 2 ≦ 0 . 6 a, wherein r 1 indicates a radius of the cylindrical first dielectric area, r 2 indicates a radius of the cylindrical second dielectric area, and a indicates a unit length of a lattice axis of the tetragonal lattice.