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We investigate experimentally and numerically the existence of fast chaotic spiking in the dynamics of a semiconductor laser with ac-coupled optical feedback. The observed dynamics is chaotic in the explored range of both bias current optical feedback strength. The effects of a modulation applied to the bias current are also investigated. We eventually indicate that the observed chaotic dynamics is a good candidate to hide information to satisfy secure communications. [ABSTRACT FROM AUTHOR]

Abstract: We report on neurocomputing performed with real Euglena cells confined in micro-aquariums, on which two-dimensional optical feedback is applied using the Hopfield–Tank algorithm. Trace momentum, an index of swimming activity of Euglena cells, is used as the input/output signal for neurons in the neurocomputation. Feedback as blue-light illumination results in temporal changes in trace momentum according to the photophobic reactions of Euglena. Combinatorial optimization for a four-city traveling salesman problem is achieved with a high occupation ratio of the best solutions. Two characteristics of Euglena-based neurocomputing desirable for combinatorial optimization are elucidated: (1) attaining one of the best solutions to the problem, and (2) searching for a number of solutions via dynamic transition between the best solutions. Mechanisms responsible for the two characteristics are analyzed in terms of network energy, photoreaction ratio, and dynamics/statistics of Euglena movements. The spontaneous fluctuation in input/output signals and reduction in photoreaction ratio were found to be key factors in producing characteristic (1), while the photo-insensitive Euglena cells or the accidental evacuation of cells from non-illuminated areas causes characteristic (2). Furthermore, we show that the photophobic reactions of Euglena involves various survival strategies such as adaptation to blue-light or awakening from dormancy, which can extend the performance of Euglena-based neurocomputing toward deadlock avoidance or program-less adaptation. Finally, two approaches for achieving a high-speed Euglena-inspired Si-based computation are described. [Copyright &y& Elsevier]

Abstract: In this paper, semiconductor microring lasers with integrated phase sections in the bus waveguide are numerically evaluated, using a dynamic multimode laser model, and investigated as low-cost, integrated, potential tunable directly modulated transmitters for future hybrid optical–wireless networks. The effect of optical feedback through bus waveguide is revealed as a promising mechanism for improving nonlinear distortion. Additionally, tunability is achieved with the aid of phase-tuning. The underlying laser dynamics beyond this behavior are analyzed. [Copyright &y& Elsevier]

Abstract: A novel nanometer-resolution displacement measurement system based on weak feedback effect of Zeeman-birefringence dual-frequency laser has been demonstrated. An experimental setup based on an optical feedback dual-frequency laser is developed to realize displacement division and direction discrimination utilizing phase delay between the optical feedback fringes of the two orthogonally polarized lights. The sub-division circuits of fringes are mainly composed of Field Programmable Gate Array (FPGA) and Micro Controller Unit (MCU), can realize 400 subdivisions for each fringe. The FPGA is used to realize the division of integral number fringes, and the MCU is used to realize the “division” of the fractional number fringes through program of look-up table. The total measured displacement is the value sum of both the integral part and the fractional part. A comparison experiment with the HP5529A interferometer was carried out resulting in a linearity of about 5×10−6, and a concise theoretical model is given to explain the experimental results. The proposed system has a theoretical resolution as high as 0.791 nm, as well as a function of direction discrimination. Thereby, it can meet some demands of high-precision displacement measurements. [Copyright &y& Elsevier]