Super-collimation by axisymmetric diffractive metamirror.

We propose and demonstrate experimentally super-collimation of light beams by an axisymmetric diffractive metamirror-an axisymmetric concentric dielectric ring structure positioned in front of a mirror at a distance of several micrometers. By super-collimation, we mean the formation of a well-collimated beam characterized by a substantial enhancement of its axial component in the far-field domain. In the reported experiments, the axial intensity of the field was enhanced by around six times. Such axisymmetric super-collimators could be especially useful for improving the emission spatial quality of micro-lasers, when integrated as one (or both) resonator mirrors.

Controlled observation of a nonequilibrium Ising-Bloch transition in a nonlinear optical cavity.

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.e., the Ising-Bloch transition is hysteretic in our case. A complex Ginzburg-Landau model is used for supporting the observations.

Spatial resonator solitons.

Spatial solitons can exist in various kinds of nonlinear optical resonators with and without amplification. In the past years different types of these localized structures such as vortices, bright, dark solitons, and phase solitons have been experimentally shown to exist. Many links appear to exist to fields different from optics, such as fluids, phase transitions, or particle physics. These spatial resonator solitons are bistable and due to their mobility suggest schemes of information processing not possible with the fixed bistable elements forming the basic ingredient of traditional electronic processing. The recent demonstration of existence and manipulation of spatial solitons in semiconductor microresonators represents a step in the direction of such optical parallel processing applications. We review some proof of principle soliton experiments on slow systems, and describe in more detail the experiments on semiconductor resonator solitons which are aimed at applications.

Spatial solitons in a pumped semiconductor resonator.

Bright and dark spatial solitons are observed in an optically pumped semiconductor resonator. The pumping allows us to reduce considerably the light intensity necessary for the existence of the solitons and alleviates thermal load problems. Experiments are found to agree qualitatively with calculations based on a simple large-aperture semiconductor resonator model. The role of the signs of the absorptive and reactive nonlinearities in soliton existence is discussed in relation to the nonlinear resonance effect, the tilted-wave mechanism of pattern formation, and the sign of the population inversion.

Nonlinear coherent polarimetry for measuring the complex nonlinear index.

A novel polarimetric technique for measuring the nonlinear change of optical polarization at a vector two-wave mixing interaction is described and demonstrated as an absorption and refraction of bacteriorhodopsin.