Abstract: An integrated optical modulator of the Mach-Zehnder type has a waveguide which, for part of its length, is divided into two waveguide sections (11, 12) arranged logically in parallel. Incoming light is divided to pass along the two sections (11, 12) and is then recombined before leaving the modulator. Each waveguide section has a pair of electrodes (13, 14) and (14, 15) associated therewith to generate an electric field through which the respective waveguide section passes, though there may be a single electrode (14) between the two waveguide sections (11, 12) to serve as one electrode of each pair, with the other electrode of each pair commoned.

Abstract: An optical modulator for duobinary modulation is based on a Mach-Zehnder interferometer but has parallel optical waveguides of a greater length than normally is employed with an optical modulator. A pair of similar electrode structures are arranged in series on the waveguides, the electrodes of the two structures being separately addressable by binary electrical signals. The phase shifts induced in the light propagating along the parallel waveguides by voltages applied to the separate electrode structures allows the output to take values of 0, 1 or 2 for binary inputs applied to the structures.

Abstract: A method of aligning a bi-refringent optical fiber with a polarisation sensitive component positioned within a package so that the bi-refrigence axes of the fiber are set in a pre-defined relation to a light guide within the component. The fiber is inserted through an aperture in the package and is approximately aligned with the light guide of the component. An optical probe having a tip provided with an optical polariser is positioned with the tip between the end of the fiber and the component, to collect light from the fiber. The free end of the fiber is manipulated and the output from the probe is monitored until the desired polarisation alignment is achieved whereafter the probe is removed from the package whilst the rotational relationship between the fiber and the component is maintained. Then, the fiber end is moved to optically couple wish the component and the fiber is secured in position. The package may thereafter be completed in the usual way.