Abstract: A light modulating device for modulating incident light in a given wavelength band is provided. The light modulating device may include: a first semiconductor layer; an active layer provided on the first semiconductor layer and having a multiple quantum well structure and a refractive index that is variable according to an electric field applied thereto, and a second semiconductor layer provided on the active layer and including a grating pattern in which a plurality of gratings extending in a first direction are repeatedly arranged in a second direction perpendicular to the first direction. The light modulating device may have high modulation efficiency owing to guided mode resonance by the grating pattern.