Quadratic simultons in linear and nonlinear photonic bandgaps

Energy localization and Bragg solitons can be sustained by the interplay of distributed feedback and quadratic nonlinearity. With reference to second harmonic generation, we review the main features of slowly-moving and stati onary two-color solitons or simultons both in singly and doubly resonant st ructures, and discuss their experimental feasibility and potential applicat ions. Finally, with reference to the case of purely nonlinear feedback thro ugh short-period quasi-phase-matching, we show that cavityless parametric o scillations can occur in the presence of gain.