PPLN based on congruent Lithium Niobate

Congruent PPLN chips can be produced with thickness up to 1mm and lengths over 50mm. The domain pattern is generated using the electrical field poling process. This allows not only single grating devices where one interaction is phase-matched, but multiple gratings along the propagation direction, chirped gratings, and fan-out gratings . Most PPLN devices fabricated from congruent.

Lithium niobate are used for difference frequency generation5 or OPO applications pumped in the near infrared, but SHG is also possible, e.g. from a fiber laser at 1.55µm.

The most common OPO using PPLN is pumped with a Q-switched laser at 1064 or 1047nm with a signal resonating around 1500nm. The risk of spurious visible light generation causing photo-refractive damage (PRE) can be lowered by heating the crystal (120° to 180°C). An alternative option for reducing PRE is to use MgO doped PPLN.

To utilize the high nonlinear optical coefficient of PPLN, all interacting waves need to be polarized along the polar Z-axis (across the thin dimension of the aperture, either 0.5mm or 1mm). The propagation direction for the laser beams is the crystallographic X-axis.