The multiconversion processes in optical parametric oscillators based on periodically poled LiNbO3 are investigated. Interpretations based on simultaneous quasi- and birefringent phase matching are presented. Three parametric and three harmonic generation processes in a multigrating periodically poled LiNbO3 crystal were observed. Two of the parametric processes and two of the harmonics were quasi-phase matched, and the other conversion processes were phase matched through birefringence in the crystal. The primary parametric process (ωp → ωs + ωi) was obtained through first-order quasi-phase matching. The other quasi-phase-matched processes occurred within higher orders. The existence of even-order quasi-phase matching in the crystal is due to other than a 50% duty-cycle grating periods. The tuning range for each of the generated waves is obtained and compared with theoretical fittings.
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