Patent ID: 8050555

Claim:
An optical waveguide device, comprising: an input optical port for launching light therein; an output optical port for emitting modulated light; a first waveguide phase modulator (WPM) optically coupled between the input and output optical ports for imparting a first phase shift onto light propagating therethrough in response to an electrical drive signal; and, a first waveguide monitoring structure (WMS) coupled optically in parallel with the first WPM so as to form a Mach-Zehnder interferometer (MZI) therewith for producing monitor light indicative of the first phase shift imparted by the first WPM; wherein the first waveguide monitoring structure comprises: a first optical tap for tapping off a fraction of light entering the first WPM for providing first tapped-off light, a second optical tap for tapping off a fraction of light exiting the first WPM for providing second tapped off light, a monitor port optically coupled to the first and second optical taps for providing the monitor light wherein the first tapped-off light is mixed with the second tapped-off light, and an ancillary phase modulator (APM) for modulating the optical phase of one of the first and second tapped-off light with a test signal so as to modulate the intensity of the monitor light in dependence upon the first phase shift.