Sharma, Chaitanya

We report on the efficient second harmonic generation at a near-UV wavelength of 399.7 nm in periodically poled Zr-doped LiTaO3 waveguides. High-temperature in-diffusion of ZrO2 layers into congruent LiTaO3 substrates with simultaneous improvement of crystal stoichiometry by vapor transport equilibration in a Li-rich atmosphere was performed for the fabrication of planar waveguides. This new method enables very high photorefractive damage thresholds and allows us to avoid the known disadvantages of, e.g., proton exchange or titanium in-diffusion waveguide fabrication methods, which lower resistance to photorefractive damage. Low-loss ridge waveguides were then fabricated using a diamond blade saw. At a maximum available coupled power of 540 mW of the near-infrared pump laser, 49 mW of second harmonic light was generated in a 22 mm long sample with a normalized conversion efficiency of 3.5%·W-1·cm-2, exceeding the previously reported powers for LiTaO3 waveguides in this wavelength range. Furthermore, by heating the sample, a temperature tuning coefficient of 32 pm/°C was measured for the generated second harmonic wave.

Optical damage resistant ridge waveguides for blue and near UV wavelengths have been fabricated using high-temperature Zr and Zn diffusion doping and vapor transport equilibration (VTE) of congruent LiTaO_3 crystals. For both dopants high optical damage thresholds >10 MW/cm^2 for 532 nm light were demonstrated at room temperature, which can be increased by a factor ~3 when heating the samples to ~150°C. Ridge waveguides with low optical losses of ~0.4 dB/cm were fabricated using diamond-blade dicing. First-order periodic poling with grating periods of ~3 μm can be used for efficient nonlinear frequency conversion for both SHG (800 nm pump) or SPDC (400 nm pump) processes.