Tuning of a phase shift to reduce the polarization-dependent loss in an interferometer-type variable optical attenuator built in lithium niobate

摘要

A method to adjust the phase mismatch between two paths of a Mach-Zehnder interferometer built in lithium niobate is presented. The importance of phase adjustment is that, in reducing polarization-dependent loss (PDL) in an optical attenuator based on lithium niobate z-propagation geometry, the phase shifts of two polarizations must be minimized or equalized. The method employs partially covering a waveguide arm with resin droplets using a microdispenser. In interferometer-type variable optical attenuators built in lithium niobate in x-cut/z-propagation geometry, the phase mismatch contribution to the PDL of less than 0.7 dB was shown to be achievable by the present phase tuning method.