Self-structuration of Three-Wave Dissipative Solitons in CW-Pumped Backward Optical Parametric Oscillators

Abstract

Generation of ultra-short optical pulses in cw-pumped cavities are mostly associated to mode locking in active media, as doped fibers or solid-state lasers. The cavity contains not only a gain element (atoms or ions) but also a nonlinear element of the host medium, such as self-phase modulation (SPM) or intensity dependent absorption. Our aim here is to present another mechanism for pulse generation in an optical cavity due to the nonlinear three-wave counter streaming interaction. We show that the same mechanism, responsible for symbiotic solitary wave morphogenesis in the Brillouin-fiber-ring laser, may act for picosecond pulse generation in a quadratic optical parametric oscillator (OPO). The resonant condition is automatically satisfied in stimulated Brillouin backscattering (SBS); however, in order to achieve counter-streaming quasi-phase matching (QPM) between the three optical waves in the χ(2) medium, a grating of sub-μm period is required. Such a quadratic medium supports solitary waves that result from energy exchanges between dispersionless waves of different velocities. The structure of these temporal localized solitary waves is determined by a balance between the energy exchange rates and the velocity mismatch between the three interacting waves. The backward QPM configuration spontaneously generates tunable picosecond solitary pulses from noise when the quadratic material is placed inside a single resonant OPO. We show, by a stability analysis of the degenerate backward OPO in the QPM decay interaction between a CW-pump and a backward signal, that the inhomogeneous stationary solutions are always unstable, whatever the cavity length and pump power above single OPO threshold. Starting from any initial condition, the nonlinear dynamics exhibits self-pulsing of the backward signal with unlimited amplification and compression. Above a critical steepening, dispersion may saturate this singular behavior leading to a new type of dynamical solitary structures.