Note for practical consideration of using PPLN-QPM materials:
Above describes general QPM principle. However, in practical applications, different experimental setup may require different detailed considerations of using a PPLN crystal, which includes polarization, wavelength, temperature, and linewidth, etc.
Polarization: As mentioned, the input beam should be polarized at a certain direction to utilize the corresponding nonlinear coefficient. For example, type-0 need all e-polarized waves while o-polarized waves will be needed in type-I SHG.
Temperature/Wavelength: Since the period form by periodical poling compensates only the design wavelength at a certain temperature, temperature/wavelength adjusting is needed for efficiency optimization. Example tuning curve (Normalized efficiency vs. wavelength) is shown in the figure 9 below.