Self-phase-locking in a type II phase-matched optical parametric oscillator

Summary form only given.In optical frequency metrology, cw optical parametric oscillators (OPOs) have attracted considerable interests as tunable optical frequency dividers. Type II phase-matching is often utilized because the crystal birefringence affords fine frequency tuning and good frequency stability, especially near-frequency degeneracy, which are essential in this type of high precision application. However, at exact frequency degeneracy, the type II phasematched OPO remains nondegenerate because the signal and idler fields are orthogonally polarized, and hence no self-phase-locking is possible.