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Complex dynamics of photonic delay systems: a story of consistency and unpredictability

AuthorsOliver, Neus
AdvisorFischer, Ingo
Issue DateNov-2015
PublisherCSIC-UIB - Instituto de Física Interdisciplinar y Sistemas Complejos (IFISC)
Universidad de las Islas Baleares
AbstractThe field of photonics is revolutionizing the current industry and society, analogously to what electronics did during the 20th century. The uses of photonics seem endless and are not restricted to advanced science. Some of its applications have already become mature tech- nologies, and belong now to our everyday life: internet relies on optical fiber communications, lasers are an integrated tool in medical surgery and industrial manufacturing, and the use of light has facilitated the measurement techniques in metrology, among many others. The rich phenomenology in photonics makes it an emerging field with open perspectives, whose full capabilities are still to be exploited. Specifically, two of the promising areas for photonics are information processing and secure optical communications. Complex phenom- ena in photonics can serve as a backbone for both applications. This Thesis comprises the study of the emerging complex behavior in concrete photonic systems: semiconductor laser systems with delay. These simple systems can generate an interesting variety of dynamical regimes, like deterministic chaos and, therefore, we use them to contribute to the above men- tioned areas. More precisely, we address the consistency properties for bio-inspired photonic information processing and the optical generation of random numbers, thereby telling a story of consistency and unpredictability.
On consistency or how to perform reliably photonic information processing. Our brain is a fast and efficient organ, capable of performing reliably tasks that for any com- puter would be rather hard, such as face recognition. Inspired by our brain, technical systems have been introduced to mimic information processing in neural networks. Understanding how these systems process information can lead to faster, low-energy demanding computing. A recent technique for photonic information processing is Reservoir Computing. In Reser- voir Computing, a nonlinear system performs computationally hard tasks, like spoken digit recognition. Its operation is based on providing a consistent nonlinear response with respect to an input signal, exactly as neurons do: they respond reliably to electrical and chemical signals when processing information. Consistency, as the ability of the system to respond in a similar way to similar inputs, is therefore a key-ingredient to be studied. Surprisingly, consistency in nature is not always a given, and a system might change from a consistent response to an inconsistent one. The mechanisms underlying consistency as well as its quantification are thus pertinent proper questions. Semiconductor lasers with feedback represent an excellent platform for its inves- tigation. We approach these aspects by designing three experiments to investigate and characterize the consistency properties of semiconductor laser with del ayed optical feedback and an optoelectronic system. The high quality of the experiments allo w us to illustrate the occurrence of transitions between consistent and inconsistent respon ses in the laser, and characterize their dependence on the drive signal. Thus, we utilize vario us drive signals, both optical and electrical, and present different ways to quantify consis tency, including correlations and a direct measure for the sub-Lyapunov exponent. Beyond phot onics, consistency in driven systems is a fundamental and far-reaching concept, present in nature and technology. Therefore, the fundamental properties and the developed method r epresent valuable findings for further fundamental investigations and applications.
On unpredictability or how to implement an optical random number generator. Random numbers (or random bits) are crucial for information security, online-gaming, complex numerical simulations and cryptography. Their ubiqui ty has led to the emergence of random number generators (RNGs) based on photonic componen ts, given the intrinsic advantages of photonics: first, an optical RNG is easy to integr ate into telecommunication systems; and second, a photonic approach to random number generation allows for high generation speeds of order of gigabits per second (Gbit/s), a key demand of current random number generators. Although some optical approaches to random bit generation had been successfully put forward, open questions still remain ed: Is it possible to employ simpler schemes to generate random numbers? Are we using the RNG opti mally or can its performance be enhanced? What is the maximum bit rate attainable wi th a given RNG? Can we know it in advance? In this Thesis, we contribute significant ly to answer these questions. We propose a strikingly simple experimental setup based on a si ngle semiconductor laser with optical feedback, benefiting from the unpredictability and randomness of the chaotic output of the laser. Nevertheless, chaotic dynamics is only a neces sary but not a sufficient condition to obtain random numbers. We present guidelines on the i nterplay between dynamics, acquisition procedures and post-processing, and predict t he potential of any RNG by using Information Theory to estimate the maximum achievable bit r ate. The relevance of this work relies not only on the high speed of the bit rate, up to 160Gbit/s, but also on the understanding of the factors involved in the random bit generation process to guarantee the optimal operation of any laser-based generator.
DescriptionTesis presentada en el Departamento de Física de la Universitat de les Illes Balears.
Appears in Collections:(IFISC) Tesis
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