0 Theory of self phase - locked optical parametric oscillators

The plane-wave dynamics of 3ω → 2ω, ω subharmonic optical parametric oscillators containing a second harmonic generator of the idler-wave ω is analyzed analytically by using the meanfield approximation and numerically by taking into account the field propagation inside the media. The resonant χ(−3ω; 2ω, ω) : χ(−2ω;ω,ω) cascaded second-order nonlinearities induce a mutual injection-locking of the signal and idler waves that leads to coherent self phase-locking of the pump and subharmonic waves, freezing the phase diffusion noise. In case of signal-and-idler resonant devices, largely detuned sub-threshold states occur due to a subcritical bifurcation, broadening out the self-locking frequency range to a few cavity linewidths. PACS: 42.65.-k, 42.65.Yj, 42.65.Sf, 42.65.Ky