Fabrication of periodically reversed domain structure for second-harmonic- generation in LiNbO3 by applying voltage

Recently there has been much interest in quasi-phase-matched(QPM) second harmonic generation (SHG) to obtain coherent blue light in LiNbO3 waveguide1) Several techniques for the domain reversal of LiNbO3 have been proposed2)3). By using these techniques, the domain shape is triangle and the domain region has the change in refractive index. This shape is not enough for making a fine and deep periodical domain structure of the QPM-SHG, so the conversion efficiency can not become so high4).