Very deep nanoscale domain inversion in LiNbO3 for high-power and high-efficiency SHG devices

Very deep nanoscale domain inversion in lithium niobate (LiNbO₃) substrate have been realized utilizing the proposed circular form full cover electrode (CF-FCE) method. Initially, we highlighted the theory of QPM-SHG and the method of domain inversion in LiNbO₃ (hereafter referred as LN). We also analyzed the advantages and drawbacks of various electrodes utilized for periodic domain inversion in LN. Theoretical calculation of electric field distribution for conventional FCE shows that this method is not suitable for fine domain inversion patterns. We proposed the CF-FCE method for nanoscale domain inversion and the electric field distribution was calculated for this method. The calculated result shows that the CF-FCE is better than that of the conventional FCE for fine domain inversion patterns. Using the proposed CF-FCE, we successfully fabricated 2 mum periodic nanoscale domain patterns in a 500-mum-thick congruent LN (C-LN) crystal. We obtained very deep nanoscale domain inversion using this technique. Such a domain inversion technology is very important for next generation high-power and high-efficiency second harmonic generation (SHG) devices.