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The energy-exchange process between the fundamental and its second-harmonic fields copropagating in an optical medium is facilitated by the spatially periodic dc poling field. The nonlinear dynamics of this system is investigated in the context of an effective Hamiltonian formalism. The explicitly included cross-modulation and self-phase-modulation nonlinear terms lead to the bifurcation instability interpreted as a new switching phenomenon in which both up- and down-conversion efficiencies can be precisely controlled by the external field. Experiments testing predicted effects are suggested

We investigate the tunneling of carriers in a quasi-one-dimensional array of semimagnetic quantum dots. The large magnetopolaron effects due to the exchange interaction of carriers with magnetic ions result in a transmission via solitonlike electronic states. The intensity-dependent transmission coefficient shows the opening of intensity-dependent gaps in the transmission spectrum.

We consider a semiconductor superlattice built of quasi-two-dimensional layers of narrow-band-gap material sandwiched by barriers of wide-band-gap material. We show that when the electromagnetic wave with frequency below the band gap of the superlattice propagates along the superlattice axis, it induces intensity-dependent gaps in the spectrum. The connection between these unusual gaps and spatial chaos is explored. The possibility of bistable devices is discussed.