Backward three-wave optical solitons |
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Authors: | C Montes A Picozzi C Durniak and M Taki |
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Institution: | (1) CNRS, Laboratoire de Physique de la Matière Condensée, Université de Nice - Sophia Antipolis, 06108 Nice Cedex 2, France;(2) CNRS, Institut Carnot de Bourgogne, 21078 Dijon Cedex, France;(3) Laboratoire de Physique des Lasers, Atomes et Molécules, Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Asq Cedex, France |
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Abstract: | Backward symbiotic solitary waves in quadratic media with absorption losses are generated through the nonlinear non-degenerate
three-wave interaction. We study these solitary waves in the particular case of a doubly backward quasi-phase matching configuration.
The same mechanism responsible for nanosecond solitary wave morphogenesis in the c.w. pumped Brillouin-fiber-ring laser may
act for picosecond pulse generation in a quadratic c.w. pumped optical parametric oscillator (OPO). The resonant condition
is automatically satisfied in stimulated Brillouin backscattering when the fiber-ring laser contains a large number of longitudinal
modes beneath the gain curve. However, in order to achieve quasi-phase matching between the three optical waves in the Χ(2) medium, a nonlinear susceptibility inversion 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. We show, by a stability analysis
of the non-degenerate backward OPO in the QPM decay interaction between a c.w. pump and backward signal and idler waves that
the inhomogeneous stationary solution exhibits a Hopf bifurcation with a single control parameter. Above OPO threshold, the
nonlinear dynamics yields self-structuration of a backward symbiotic solitary wave, which is stable for a finite temporal
walk-off (i.e. different group velocities) between signal and idler waves.
We also study the dynamics of singly backward mirrorless OPO’s (BMOPO’s) pumped by an incoherent field, in line with the recent
experimental demonstration of this OPO configuration. We show that this system is characterized, as a general rule, by the
generation of a highly coherent backward field, despite the high degree of incoherence of the pump field. This remarkable
property finds its origin in two distinct phase-locking mechanisms that originate respectively in the convection and the dispersion
properties of the fields. In both cases we show that the incoherence of the pump is transferred to the co-moving field, which
thus allows the backward field to evolve towards a highly coherent state. We propose realistic experimental conditions that
may be implemented with currently available technology and in which backward coherent wave generation from incoherent excitation
may be observed and studied. |
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