Chaotic Free-Space Laser Communication over Turbulent Channel

The dynamics of errors caused by atmospheric turbulence in a self-synchronizing chaos based communication system that stably transmits information over a $\sim$5 km free-space laser link is studied experimentally. Binary information is transmitted using a chaotic sequence of short-term pulses as carrier. The information signal slightly shifts the chaotic time position of each pulse depending on the information bit. We report the results of an experimental analysis of the atmospheric turbulence in the channel and the impact of turbulence on the Bit-Error-Rate (BER) performance of this chaos based communication system.Comment: 4 pages, 5 figure

Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption

Optical chaos is a topic of current research characterized by high-dimensional nonlinearity which is attributed to the delay-induced dynamics, high bandwidth and easy modular implementation of optical feedback. In light of these facts, which adds enough confusion and diffusion properties for secure communications, we explore the synchronization phenomena in spatiotemporal semiconductor laser systems. The novel system is used in a two-phase colored image encryption process. The high-dimensional chaotic attractor generated by the system produces a completely randomized chaotic time series, which is ideal in the secure encoding of messages. The scheme thus illustrated is a two-phase encryption method, which provides sufficiently high confusion and diffusion properties of chaotic cryptosystem employed with unique data sets of processed chaotic sequences. In this novel method of cryptography, the chaotic phase masks are represented as images using the chaotic sequences as the elements of the image. The scheme drastically permutes the positions of the picture elements. The next additional layer of security further alters the statistical information of the original image to a great extent along the three-color planes. The intermediate results during encryption demonstrate the infeasibility for an unauthorized user to decipher the cipher image. Exhaustive statistical tests conducted validate that the scheme is robust against noise and resistant to common attacks due to the double shield of encryption and the infinite dimensionality of the relevant system of partial differential equations.Comment: 20 pages, 11 figures; Article in press, Optics Communications (2011

Corporate strategy in turbulent environments: Key roles of the corporate level

This paper analyzes the evolution during the period 1986-2002 of the corporate strategy of Lujan, a highly successful car components manufacturer headquartered in Spain, as a way to explore how the corporate level influences the successful evolution of a company exposed to a "turbulent" environment over a long period. We find that the corporate level plays three key roles. First, it drives a firm's evolution by developing a cognitive representation of the firm's competitive landscape. Second, it paces the company's evolution by alternately shifting the balance of organizational initiatives between static efficiency-based "local search" strategies, chosen in times of stability or economic slowdown, and dynamic efficiency-based "long jump" strategies, adopted during periods of major environmental turbulence. Long-jump corporate strategies, carried out through limited downside strategic initiatives such as real options and strategic alliances ("off-line long-jumps"), are particularly frequent in these circumstances. The third role consists of developing an organizational architecture that frames the self-organized coordination of the different business divisions. The Lujan story clearly illustrates the important role of corporate strategy in a firm that must undergo radical transitions as a result of major environmental changes.corporate strategy; turbulent environments; complexity theory; car components;