An optical radiator for use in an optical phased array antenna includes an optical waveguide including a waveguide core using a semiconductor material and a waveguide cladding, and a grating that utilizes scattering of input light waves incident in one direction of the optical waveguide to radiate a light wave to the free space. The optical radiator changes the effective refractive index of the grating in order to adjust a radiation angle of the light wave radiated to the free space.