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Dynamics of semiconductor lasers subjected to polarization rotated feedback and its application to fast random bit generation

AuthorsOliver, Neus
AdvisorFischer, Ingo ; Soriano, Miguel C.
Issue Date15-Mar-2012
PublisherUniversidad de las Islas Baleares
CSIC-UIB - Instituto de Física Interdisciplinar y Sistemas Complejos (IFISC)
AbstractIn this Master Thesis we study the dynamics of semiconductor lasers subjected to de layed optical feedback, in particular, polarization rotated optical feedback (PROF). Optical feedback o ccurs when a fraction of the laser output is reinjected back into the laser cavity, normally due to the re ection of the light from a distant mirror. It has b een observed that when a semiconductor laser is sub jected to delayed optical feedback, the laser emission can b e disturb ed, exhibiting nonlinear dynamical behavior. These dynamics were contemplated as a nuisance that should be avoided, until it recently b egan to b e considered as b ene cial, taking advantage of the dynamical op eration. Nevertheless, a complete understanding of the delay dynamics is lacking. Many studies have b een presented with lasers and optical feedback but less attention has b een given to feedback in which the p olarization state of light is rotated. It was not until the early 1990s when thorough research and characterization of the dynamics of semiconductor lasers with PROF began. Interest in this typ e of feedback has b een increasing since then, prompting the emergence of new exp erimental work together with di erent mathematical mo dels. Still, the studies so far have b een inconclusive, as explained in Chapter 2, requiring a better description of the sp ectral and temp oral features present in this system. This lack of exp erimental investigations with a complete characterization of the dynamical behavior motivated part of this thesis. In addition, we believe that this characterization of the dynamics of semiconductor lasers under PROF, interesting in itself, was also necessary to understand the p otential and increase the applicability of the system. In fact, the dynamical properties of the semiconductor laser sub jected to PROF are signi cantly di erent from the dynamics of other optical feedback typ es, b eing sp ecially favorable for chaotic applications. Within chaotic applications, one of current interest is the generation of sequences of random bits. Random bits play an imp ortant role in information security, complex numerical simulations, cryptography and gambling. Until recently, most of these demands were using the so called "pseudorandom generators" which are only deterministic algorithms utilized to generate the pseurandom bits. These pseudorandom generators have two fundamental problems. On the one hand, the data generation sp eed is always limited by the sp eed of the electronic hardware. On the other hand, due to its deterministic nature, the unpredictability is bounded by the p erio dicity of the bit sequence. Consequently, the development of a system capable of generating true random bits was necessary. Many random bits generators have b een presented up to to day. Some are based on quantum mechanical uncertainty, b eing known as Quantum Random Bit Generators (QRBG) but their main disadvantage lies in the generation rate, which for the moment is in the order of Mbit/s while the mo dern data rates demand sp eeds three orders of magnitude faster. Other systems are laser-based, which generate random bits with diferent methods like using phase noise of the laser or injecting light from a chaotic laser into a second laser. The former has the same problem as the QRBGs, generating random bits at sp eeds up to 20Mbit/s. The latter, capable of generating bits at competitive rates, requires a system which enhances the bandwidth and where the polarization state is maintained along the entire setup, thus making it more expensive. To the b est of our knowledge, this is the rst work in which a single laser subjected to PROF is succesfully used to generate fast random bits.
DescriptionTesis presentada para la obtención del grado de doctor en la Universidad de las Islas Baleares en marzo de 2012.
Appears in Collections:(IFISC) Tesis
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