Packaged MZIs passively balanced by means of multimode grating couplers

We present a novel Mach-Zehnder Interferometer configuration that can be passively balanced by adjusting the position of the input fiber over a multimode input coupler, thus correcting phase deviations typically arising from fabrication asymmetries. Characterization after permanent fiber array attachment by means of a UV curable epoxy shows high thermal stability resulting in less than 0.5 dB power imbalance at the output of the interferometer over a temperature range of 20 to 80°C.