PROBLEM TO BE SOLVED: To provide a two-dimensional photonic crystal which controls the top/reverse radiation ratio of light from an optical resonator.
SOLUTION: A refractive index member 13 formed of a material having a different refractive index from air is mounted on the top surface of two-dimensional photonic crystal which has holes 12 periodically formed in a main body 11. Consequently, the main body 11 and refractive index member 13 constitute an optical resonator together at the position where the refractive index member 13 is mounted. This optical resonator radiates light intensely to a high-refractive-index side, i.e. the side of the surface where the refractive index member is mounted. Consequently, light 191 radiated to the surface side where the refractive index member 12 is arranged has larger intensity than light 192 radiated to its opposite surface side. The refractive index, shape, and size of the refractive index member are varied to control the top/reverse radiation ratio which is the intensity ratio of the light 191 and light 192.