a b s t r a c tWe consider two variants of the task of spreading a swarm of agents uniformly on a ring graph. Ant-like oblivious agents having limited capabilities are considered. The agents are assumed to have little memory, they all execute the same algorithm and no direct communication is allowed between them. Furthermore, the agents do not possess any global information. In particular, the size of the ring (n) and the number of agents in the swarm (k) are unknown to them. The agents are assumed to operate on an unweighted ring graph. Every agent can measure the distance to his two neighbors on the ring, up to a limited range of V edges.The first task considered, is dynamical (i.e. in motion) uniform deployment on the ring.We show that if either the ring is unoriented, or the visibility range is less than ⌊n/k⌋, this is an impossible mission for the agents. Then, for an oriented ring and V ≥ ⌈n/k⌉, we propose an algorithm which achieves the deployment task in optimal time. The second task discussed, called quiescent spread, requires the agents to spread uniformly over the ring and stop moving. We prove that under our model, in which every agent can measure the distance only to his two neighbors, this task is impossible. Subsequently, we propose an algorithm which achieves quiescent but only almost uniform spread. The algorithms we present are scalable and robust. In case the environment (the size of the ring) or the number of agents changes during the run, the swarm adapts and re-deploys without requiring any outside interference.

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We experimentally demonstrate a phasematching technique for frequency conversion in nonlinear semiconductor structures by employing linear long-period gratings. We designed a specific semiconductor photonic device for second harmonic generation using coupled-mode equations with parameters extracted from beam propagation method simulations. Optical frequency converters were fabricated according to the design with the main feature; linear long-period weak gratings imprinted on semiconductor waveguides, providing the required photon momentum difference for matching the phases of the different-wavelength photons. The measured nonlinear conversion efficiency and its spectrum comply with our theoretical predictions.

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