A comprehensive model has been developed to construct phase matching conditions, including Poynting vector directions, parametrically interacting beam wavelengths, relative walk-off angles and polarization states in a biaxial nonlinear single crystal with known refractive index dispersion. The model optimizes
phase matching conditions by providing a strategy for walk-off compensation that determines the optimum
periodicity of twist-twin Adhesive-Free Bond (AFB(R)) composite pair designs. The model is validated experimentally by measuring the calculated walk-off angles and the crystal
orientation of KTP that correlates to the given Poynting vector. The method is useful in reducing uncertainties of OPO designs, in providing walk-off compensation design data, and in confirming the final walk-off corrected design configuration. It is generally applicable to biaxial and uniaxial nonlinear crystals.