We report on electric-field poling of MgO:LiNbO3 (MgLN) using patterned electrodes. Investigation of electric properties of MgLN reveals that polarization switching causes reversible resistance change and that this phenomenon can explain the physical mechanism of random domain growth. Based on these results, we propose a domain-control method in MgLN single crystals by suppressing resistance reduction during the poling process. Using this method, short periodic structures consisting of submicron domain geometries have been achieved in X-, Y-, and Z-cut MgLN crystals. High performances of these periodic domain-inverted structures are also demonstrated by evaluating their potentials as second-harmonic generation devices.

We present a method of controlling the shape of the domain-inverted structure in an off-cut MgO:LiNbO(3) crystal by utilizing a two-dimensional high-voltage application. With this technique a periodically domain-inverted structure with a period of 3.2 microm and a thickness of 2.0 microm was fabricated over a 10-mm interaction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated cw blue second-harmonic generation of 17.3 mW of power at a wavelength of 426 nm with single-pass 55-mW cw AlGaAs laser diode input, which corresponded to 31% power-conversion efficiency.

Quasi-phase-matched (QPM) UV second-harmonic generation (SHG) in a periodically poled MgO:LiNbO3 waveguide is presented. A ridge-type waveguide with high nonlinearity and strong resistance to photorefractive damage was achieved by use of an ultraprecision machining technique. By use of this waveguide in 1.4-microm periodically poled MgO:LiNbO3, a first-order QPM SHG device for 340-nm UV radiation was demonstrated. In a single-pass configuration, continuous-wave 22.4-mW UV light was generated for a fundamental power of 81 mW, corresponding to a normalized conversion efficiency of 340%/W.

Continuous-wave high-power green light generation at room temperature is reported in a single-pass frequency-doubling configuration with bulk periodically poled MgO:LiNbO3 crystal placed outside a diode end-pumped Nd:GdVO4 laser. The MgO:LiNbO3 samples of 6.95-microm domain period, uniform periodicity, and 50% duty cycle along the entire crystal length are fabricated by use of a high-voltage multipulse poling method. A maximum power of 1.18 W at 531 nm with 16.8% conversion efficiency is obtained from a 2-mm-thick, 25-mm-long MgO:LiNbO3 crystal; the corresponding internal green power and conversion efficiency are 1.38 W and 19.6%, respectively, whereas the normalized conversion efficiency is 3.3%/W.

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