PURPOSE: To obtain an optical device provided with a circular waveguide with high conversion efficiency by arranging refracting gratings in radial shape at the outside of an annular optical waveguide.

CONSTITUTION: The circular waveguide 62 and a linear waveguide 64 to introduce light to the waveguide are provided at a substrate 66. The radius, width thickness, and refracting index distribution of the circular waveguide 62 are set so as to circulate continuously light of 2πr/n(r: radius of circular waveguide, n: certain natural number) in the inside of the waveguide in a direction of arrowhead. A grating 68 is formed on the upper plane of the circular waveguide 62 at pitch of 2πr/(n+1). Also, another grating 70 is provided on the upper plane of the substrate 66. The grating 70 is provided with the same number of teeth as that of the grating 68.