The device includes a waveguide on a base. A light-absorbing portion of the waveguide receives a light signal, absorbs a portion of the light signal and guides a transmitted portion of the light signal to the output portion of the waveguide. A light-absorbing portion of the waveguide is partially defined by a light-absorbing medium that has lateral sides that each extends between a top side and a bottom side of the light-absorbing medium. The device also includes a monitor absorption of the absorbed portion of the light signal. The monitor includes field sources that are each configured to serve as a source of an electrical field in the light-absorbing medium. The field sources each contacts one of the lateral sides of the light-absorbing medium.