Publications by authors named "Eugenio Roldan"

Nonlinear optical cavities are crucial both in classical and quantum optics; in particular, nowadays optical parametric oscillators are one of the most versatile and tunable sources of coherent light, as well as the sources of the highest quality quantum-correlated light in the continuous variable regime. Being nonlinear systems, they can be driven through critical points in which a solution ceases to exist in favour of a new one, and it is close to these points where quantum correlations are the strongest. The simplest description of such systems consists in writing the quantum fields as the classical part plus some quantum fluctuations, linearizing then the dynamical equations with respect to the latter; however, such an approach breaks down close to critical points, where it provides unphysical predictions such as infinite photon numbers.

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We discuss the possibility of generating noncritical quadrature squeezing by spontaneous polarization symmetry breaking. We first consider Type II frequency-degenerate optical parametric oscillators but discard them for a number of reasons. Then we propose a four-wave-mixing cavity, in which the polarization of the output mode is always linear but has an arbitrary orientation.

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We study the influence of field diffusion on the spatial localized structures (cavity solitons) in bidirectional lasers. We find threefold positive role of the diffusion: 1) it allows for the existence of solitons in cavities with equal losses for the two fields; 2) it increases the stability range of the individual (isolated) solitons; and 3) it reduces the long-range interaction between cavity solitons, allowing for the independent manipulation (writing and erasing) of individual structures.

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We predict squeezed light generation through the spontaneous rotational symmetry breaking occurring in a degenerate optical parametric oscillator (DOPO) pumped above threshold. We show, within the linearized theory, that a DOPO with spherical mirrors, in which the signal and idler fields correspond to first-order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape of a Hermite-Gauss mode. This occurs at any pumping level above threshold; hence, the phenomenon is noncritical.

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We show theoretically that a broad area bidirectional laser with slightly different cavity losses for the two counterpropagating fields sustains cavity solitons (CSs). These are complementary; i.e.

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We report the experimental observation of the conversion of a phase-invariant nonlinear system into a bistable phase-locked one via rocking [G. J. de Valcárcel and K.

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We show that a parametrically driven cubic-quintic complex Ginzburg-Landau equation exhibits a hysteretic nonequilibrium Ising-Bloch transition for large enough quintic nonlinearity. These results help to understand the recent experimental observation of this phenomenon [A. Esteban-Martín, Phys.

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We report the controlled observation of the nonequilibrium Ising-Bloch transition in a broad area nonlinear optical cavity (a quasi-1D single longitudinal-mode photorefractive oscillator in a degenerate four-wave mixing configuration). Our experimental technique allows for the controlled injection of the domain walls. We use cavity detuning as control parameter and find that both Ising and Bloch walls can exist for the same detuning values within a certain interval of detunings; i.

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An anisotropic (dichroic) optical cavity containing a self-focusing Kerr medium is shown to display a bifurcation between static--Ising--and moving--Bloch--domain walls, the so-called nonequilibrium Ising-Bloch transition (NIB). Bloch walls can show regular or irregular temporal behavior, in particular, bursting and spiking. These phenomena are interpreted in terms of the spatiotemporal dynamics of the extended patterns connected by the wall, which display complex dynamical behavior as well.

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We show experimentally the feasibility of optically controlled location, individual addressing/erasure and steering of phase domain walls by injection of coherent addressing pulses into a phase-locked four-wave-mixing photorefractive oscillator.

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We demonstrate two alternative techniques for controlling and stabilizing domain walls (DW) in phase-sensitive, nonlinear optical resonators. The first of them uses input pumps with spatially modulated phase and can be applied also to dark-ring cavity solitons. An optical memory based on the latter is demonstrated.

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Parametrically driven systems sustaining sech solitons are shown to support a new kind of localized state. These structures are walls connecting two regions oscillating in antiphase that form in the parameter domain where the sech soliton is unstable. Depending on the parameter set the oppositely phased domains can be either spatially uniform or patterned.

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