Provided are an optical device and a method of controlling propagation directions of light and a surface plasmon using the optical device. The optical device includes a light source, a substrate, and a metal layer that is disposed on the substrate, the metal layer includes at least two slots, and propagation directions of light and a surface plasmon may be controlled by using the light that is polarized in a direction parallel to a direction of a long length of any one of the at least two slots.