Short-period domain patterning by ion beam irradiation in lithium niobate waveguides produced by soft proton exchange

•We propose a focused ion-beam irradiation for periodical poling in lithium niobate waveguides.•The ion-beam irradiation is realized after waveguide creation by soft proton exchange method.•This method allowed to create the 1-mm-long 2-μm-period domain structure in a channel waveguide.•The obtained second harmonic generation efficiency for pulsed 756–378 nm wavelength conversion was up to 6·107% W−1 cm−2 for average power.