Previous studies of lasers and nonlinear resonators
have revealed that the polarisation degree of freedom allows for the
formation of polarisation patterns and novel localized structures, such
as vectorial defects. Type II optical parametric oscillators are characterised
by the fact that the down-converted beams are emitted in orthogonal
polarisations. In this paper we show the results of the study
of pattern and defect formation and dynamics in a Type II degenerate optical
parametric oscillator for which the pump field is not resonated in the
cavity. We find that traveling waves are the predominant solutions and
that the defects are vectorial dislocations which appear at the boundaries
of the regions where traveling waves of different phase or wave-vector
orientation are formed. A dislocation is defined by two topological charges, one
associated with the phase and another with the wave-vector orientation. We also
show how to stabilize a single defect in a realistic experimental
situation. The effects of phase mismatch of nonlinear interaction are
finally considered.
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http://www.imedea.uib.es/Nonlinear/research_topics/OPO/.