Gonzalo Izús

System size stochastic resonance: General nonequilibrium potential framework

We study the phenomenon of system size stochastic resonance within the nonequilibrium potential framework. We analyze three different cases of spatially extended systems, exploiting the knowledge of their nonequilibrium potential, showing that through the analysis of that potential we can obtain a clear physical interpretation of this phenomenon in wide classes of extended systems. Depending on the characteristics of the system, the phenomenon is associated with a breaking of the symmetry of the nonequilibrium potential or a deepening of the potential minima yielding an effective scaling of the noise intensity with the system size.

Bloch domain walls in type II optical parametric oscillators

Evidence of Bloch domain walls in nonlinear optical systems is given. These walls are found in the transverse fields of optical parametric oscillators when the polarization degree of freedom, the cavity birefringence, and (or) dichroism are taken into account. These domain walls arise spontaneously and exhibit defects where Bloch walls of different chirality join together. Two dynamic regimes are found:In the first one the vector field approaches a final homogeneous state, and in the other the walls are continually generated and annihilated. This dynamic behavior is caused by the fact that walls of opposite chirality move spontaneously with opposite velocity.

Stochastic resonance between dissipative structures in a bistable noise-sustained dynamics

We study an extended system that without noise shows a monostable dynamics, but when submitted to an adequate multiplicative noise, an effective bistable dynamics arises. The stochastic resonance between the attractors of the noise-sustained dynamics is investigated theoretically in terms of a two-state approximation. The knowledge of the exact nonequilibrium potential allows us to obtain the output signal-to-noise ratio. Its maximum is predicted in the symmetric case for which both attractors have the same nonequilibrium potential value.

Pattern formation in the presence of walk-off for a type II optical parametric oscillator

We show the relevance of walk-off effects in pattern formation in a type II optical parametric oscillator at frequency degeneracy. With walk-off neglected only phase patterns are formed, and the intensity distribution is homogeneous. Walk-off changes the instability from absolute to convective for some parameter range. In the absolutely unstable regime it induces for each polarization component of light a competition between two phase stripe patterns (traveling waves) of different wavelength. Phase stripe patterns at each of the wavelengths are equally likely to be selected, and, after a transient regime of coexistence, one of them takes over. In the convectively unstable regime the existence of intensity patterns sustained by noise is shown. The patterns arise from the interference between traveling waves that are generated by the dynamical amplification of noise.

Quantum correlations in noise-sustained optical patterns

Noise-sustained patterns have been recently predicted in several systems including a Kerr cavity and an optical parametric oscillator. In these systems a regime of convective instability can appear, in which a transverse pattern arises as a macroscopic manifestation of amplified and spatially structured quantum noise, with magnification factors of several order of magnitudes. We study quantum correlations in the convective regime of a degenerate type-I optical parametric oscillator (OPO) using a time dependent parametric approximation, in which the intracavity pump field is taken as a classical stochastic field.

Transverse Patterns in Type-II Optical Parametric Oscillators

We study the effects produced by walk-off and cavity induced polarization coupling in the process of pattern formation in a type-II optical parametric oscillator (OPO). Walk-off generates a convectively unstable regime in which intensity patterns sustained by noise are produced. An absolute unstable regime is also present. In this regime a competition between two traveling waves of different wavelength takes place. The presence of a birefringent and/or dichroic mirror produces homogeneous phase locked solutions separated by Domain Walls similar to Bloch walls in magnetic systems. The spontaneous motion of these walls around point defects produces persistent spatio-temporal states.

Bloch domain walls in transverse patterns in type-II optical parametric oscillators

Summary form only given. We show that the presence of a birefringent and/or dichroic mirror into a type-II optical parametric oscillator (OPO) yields to a new kind of domain walls. In these walls the field amplitude remains constant while the phase rotates when going from one domain to the neighboring one. These domain walls are similar to Bloch walls in magnetic systems. They appear here for positive or null detunings, where the zero wavenumber is selected. Idler and signal fields show a similar pattern.