A structure of an optical grating coupler for tuning the center wavelength of signals which are propagated to a waveguide by changing the effective refractive index of the optical grating coupler is provided. The optical grating coupler includes a region for changing the effective refractive index of the optical grating coupler, which is included in the inside or outside of the optical grating coupler. The region receives a signal for changing the effective refractive index of the optical grating coupler.