Abstract: In a first feature of the invention, an optical switching element is a semi-transparent, metallic film having variable absorption and transmission depending upon whether one or two optical signals are present. The metallic film can be illuminated from opposite sides in a direction perpendicular to its plane by two optical signals or can be illuminated obliquely at the same angle of incidence from opposite sides by two optical signals. In another embodiment, the metallic film is located between two optical waveguides. In a second feature of the invention, an optical switching element is an optically active material that rotates the plane of polarization of an optical input signal in the absence of an optical control signal and rotates the plane of polarization of the optical input signal to a lesser degree in response to an optical control signal. The optical input signal and the optical control signal have .pi. radians phase difference in the optical waveguide and have the same plane of polarization.