Abstract: Methods of characterizing non-linear optical materials and fabricating wavelength conversion devices are provided. The method of characterizing non-linear optical materials comprising a periodically poled waveguide layer and at least one waveguide region includes coupling at least one diagnostic laser beam into the waveguide region at one or more input locations positioned on the waveguide layer of the non-linear optical material, and out-coupling the diagnostic laser beam from the waveguide region by applying an electric field to the periodically poled domains at one or more output locations positioned on the waveguide layer. The method also includes measuring an intensity level of the out-coupled beam and determining at least one optical property of the waveguide region based at least in part on the measured intensity level of the out-coupled beam. The characterization method may be implemented into a wavelength conversion fabrication process.