Patent ID: 8743371

Claim:
A tunable Mach-Zehnder interferometer comprising: an optical splitter comprising at least one input waveguide and two output waveguides; an optical recombiner comprising two input waveguides and two output waveguides; a pair of interferometer arms, each optically coupled between one of the output waveguides of the optical splitter and one of the input waveguides of the optical recombiner; an arm photodetector section provided within each interferometer arm, the arm photodetector sections configured to measure the intensities of light passing therethrough so as to measure an effective split ratio (SRe) of the intensities of the light; an output photodetector section provided within each output waveguide of the optical recombiner, the output photodetector sections configured to measure an output ratio (R out ) of intensities of light within the output photodetector sections; wherein each of the optical splitter and recombiner further comprises a tunable multimode interference (MMI) coupler, the tunable MMI coupler comprising a tunable MMI region and a tuning electrode on a surface of the tunable MMI region, and wherein a tuning current to the tuning electrode of the MMI coupler of at least one of the splitter and recombiner is controlled in correspondence with the effective split ratio (SRe), and the tuning current to the tuning electrode is controlled such the output ratio (R out ) and effective split ratio (SRe) are in the relationship Rout=(SRe+1/SRe)/2.