C.w. optical parametric oscillators: single mode or multimode?

This paper details the conditions for which a c.w. OPO pumped by a single m ode field is working in a single or multimode regime. It shows that c.w. OP Os are intrinsically single mode systems in the steady state regime, both f or the longitudinal and transverse modes, unless special conditions of mode degeneracy or mode coupling are met. Complex optical patterns may appear i n such cicumstances, that we have recently observed. Furthermore, if one ad ds a linear coupling between the signal and idler modes, these two modes ca n phase-lock on each other: one then obtains a perfect degenerate single mo de operation for the c.w. OPO. (C) 2000 Academie des sciences/Editions scie ntifiques et medicales Elsevier SAS.