Abstract: An optical test instrument, for testing response of an optical medium to optical energy, comprises a light source for emitting optical energy in response to electrical energy, a detector for providing an electrical output signal in response to incident optical energy, and a propagation path for delivering optical energy from the light source to the medium under test and for delivering optical energy from the medium under test to the detector. A positioning mechanism displaces an optical attenuator element between a first position, in which it is out of the propagation path, and a second position, in which it is interposed in a segment of the path in which the optical energy is propagated as a beam.

Abstract: An electrooptical device comprises a substrate of electrooptic material having first, second and third optical waveguide formed therein. The first and second waveguides have first and second waveguide segments respectively, and the third waveguide has third and fourth waveguide segments extending adjacent the first and second waveguide segments respectively, so that first and second directional couplers are formed. The interaction length of the first directional coupler is slightly greater than an optimum interaction length for a predetermined wavelength and the interaction length of the second directional coupler is slightly less than an optimum interaction length for the predetermined wavelength. A first electrode structure influences the first directional coupler and a second electrode structure influences the second directional coupler.

Abstract: Apparatus for depolarizing light received from a source of light comprises a body of material that defines an optical waveguide, the material of the body and the length of the waveguide being such that when polarized light is propagated through the waveguide, light in one of two polarization eigen states is retarded relative to light in the other polarization eigen state by a time such as to destroy phase coherence between the polarization eigen states of the light emitted by the source. The relative amplitudes of the two polarization eigen states of polarized light entering the wave-guide are adjusted.