Fabrication of ferroelectric‐domain‐inverted gratings for LiNbO3 second harmonic generation devices by voltage application

To realize a compact short‐wavelength coherent light source, development of an LiNbO3 waveguide quasi‐phase matched second harmonic generation devices is expected. To realize these devices, fabrication of the domain‐inverted grating is important. The authors discuss the fabrication of a grating with a period of about 3 μm near the surface of the z‐cut LiNbO3 crystal (with a thickness of 0.5 mm) by applying voltage. As the periodic electrode structure, the ladder electrode and the corrugation electrode were investigated. The distribution of the z component of the electric field induced under the periodic electrode was computed theoretically so that the structure of the periodic electrode effective for the grating fabrication was determined. From the experimental investigation, it was found that the domain inversion was more likely to occur on the +z side and the application of the current limited pulse voltage (∼ 10 kV, width of 1 ∼ 40 ms) was effective and that a domain‐inverted grating could be fabricated almost uniformly under the entire electrode if the current‐limiting value and the pulsewidth were adequate. When a ladder electrode (electrode linewidth/period ∼ 0.2) is used in vacuum and when a corrugation electrode was used in insulation oil, suitable structures can be fabricated for the device, which is uniform in the waveguide cross section and the inverted width to the uninverted width was close to one to one under the periodic electrode.