Devices in periodically poled glass must have a large periodic variation of the built-in field. We show that the periodic variation can be severely degraded by charge dynamics taking place at the external (glass–air) interface or at internal (glass–glass) interfaces if the interfaces have imperfections. The problem of the external interface can be solved by poling with periodic electrodes that are buried inside the glass, in many cases improving the poling efficiency dramatically. Internal interfaces can be addressed by the proper choice of waveguide design and processing. Without poling the device, one can reveal the existence of imperfect interfaces by use of electric field induced second-harmonic generation.