Abstract: An optical device may include a substrate, a metal layer on the substrate, at least one first nano-structure in the layer, and at least one second nano-structure in the layer. The at least one first nano-structure may include a light source. The at least one first and second nano-structures may be spaced apart. A method of controlling a propagation direction of light output from an optical device that includes a metal layer on a substrate may include disposing first and second nano-structures in the layer; disposing at least one light source in the first nano-structure; and controlling the propagation direction of the light output from the at least one light source by changing at least one of a shape of the first nano-structure, a shape of the second nano-structure, a size of the first nano-structure, a size of the second nano-structure, and an interval between the first and second nano-structures.