optics

We theoretically describe the quasi one-dimensional transverse spreading of a light pulse propagating in a defocusing nonlinear optical material in the presence of a uniform background light intensity. For short propagation distances the pulse can be described within a nondispersive approximation by means of Riemann's approach. We are also able to calculate the wave-breaking time, at which nonlinear nondispersive spreading leads to a gradient catastrophe. The theoretical results are in excellent agreement with numerical simulations. Experimental and theoretical studies have demonstrated the occurence of wave breaking even in absence of background. Our results exhibit this feature and the corresponding theoretical wave-breaking time agrees very well with simulations.

We present the main features of a recently introduced system capable of laser action: the complex active optical network, or lasing network (LANER). The system is experimentally realized with optical fibers linked each other with couplers and with one or more coherently amplifying sections. A linear theoretical description shows how the LANER can be considered as a generalization of the laser with the physical network acting as a complicated cavity, and can be represented by directed graphs disclosing the analogies with the problem of quantum chaos on graphs. Experiments in simple configurations are reported, with evidence of lasing action and its characterization. Examples of spectra of the detected emitted intensity are obtained in different cases, in a phenomenological agreement with the numerical findings of the theory.