Fabrication of periodically inverted domain structures in LiTaO3 and LiNbO3 using proton exchange

We report on the fabrication of a first‐order periodically inverted domain structure in LiTaO3 and LiNbO3 for quasi‐phase‐matched devices using proton exchange with one‐directional heating. First‐order periodically inverted domains with a 3.2 μm period and more than 40 μm depth were formed beyond the proton exchanged region. This domain inversion took place during the proton exchange process, far below the Curie temperatures. Taking advantage of these deep domains, we demonstrated second‐harmonic generation without fabricating a channel waveguide.