quasi-phase-matched (qpm) wavelength converters are highly desirable for emerging nonlinear optics applications in photonic integrated circuits, but available waveguide and quasi-phase-matching technologies have so far constrained their realization. in this work, we present a periodically poled lithium niobate (ln) waveguide on a silicon nitride-thin film ln platform. it contains a submicrometer waveguide core for enhancing nonlinear interactions that is more than one order of magnitude smaller than those of previous qpm waveguides. periodic poling was applied directly to the thin film ln for quasi-phase-matching by a new surface poling technology. we demonstrated 160% w-1.cm(-2) normalized efficiency for second harmonic generation at 1530 nm with ultralow propagation loss (0.3 db/cm) in the telecom band. this highly efficient and compact wavelength converter has the potential for straightforward integration with various photonic platforms, e.g., on-chip microsystems such as optical communication networks, quantum storage, and optical frequency referencing. (c) 2016 optical society of america