Physics and Applications of Laser Diode Chaos

An overview of chaos in laser diodes is provided which surveys experimental achievements in the area and explains the theory behind the phenomenon. The fundamental physics underpinning this behaviour and also the opportunities for harnessing laser diode chaos for potential applications are discussed. The availability and ease of operation of laser diodes, in a wide range of configurations, make them a convenient test-bed for exploring basic aspects of nonlinear and chaotic dynamics. It also makes them attractive for practical tasks, such as chaos-based secure communications and random number generation. Avenues for future research and development of chaotic laser diodes are also identified.Comment: Published in Nature Photonic

DSP Prototype of a Chaos-Based Multi-User Communication System: Design and Performance Analysis

This paper presents the implementation of a multi-user chaos-based communication system in DSP (digital signal processor) technology. The system is based on the chaotic phase shift keying (CPSK) digital modulation scheme, where chaotic signals are used as the spreading sequences of a CDMA (code division multiple access) system. Using chaotic signals offers the advantages of increased security and higher system capacity compared with conventional sequences. The aim of this hardware implementation was to enable a comparison against analytical performance results for CPSK. The transceiver prototype was implemented on a 32-bit floating-point TigerSHARC DSP. Its bit error rate (BER) characteristics were measured in the presence of additive white Gaussian noise. The prototype achieves excellent BER performance, matching that of theoretical CPSK. The effects of the limited number precision of the hardware platform are thus negligible. However, due to the limited concurrency of DSP, the multi-user system only supports low data rates. Despite this, the prototype demonstrates that the CPSK scheme is a promising and viable CDMA option for the future

Performance Analysis of a Chaos-Based Multi-User Communication System Implemented in DSP Technology

This paper presents the implementation of a multi-user chaos-based communication system in DSP. The system is based on the chaotic phase shift keying (CPSK) digital modulation scheme, where chaotic signals are used as the spreading sequences of a CDMA system. Using chaotic signals offers the advantages of increased security and higher system capacity compared with conventional sequences. The aim of this hardware implementation was to enable a comparison against analytical performance results for CPSK. The transceiver prototype was implemented on a 32-bit floating-point TigerSHARC DSP. Its bit error rate (BER) characteristics were measured in the presence of additive white Gaussian noise. The prototype achieves excellent BER performance, matching that of theoretical CPSK. The effects of the limited number precision of the hardware platform are thus negligible. However, due to the limited concurrency of DSP, the multi-user system only supports low data rates

Security performance and protocol consideration in optical communication system with optical layer security enabled by optical coding techniques

With the fast development of communication systems, network security issues have more and more impact on daily life. It is essential to construct a high degree of optical layer security to resolve the security problem once and for all. Three different techniques which can provide optical layer security are introduced and compared. Optical chaos can be used for fast random number generation. Quantum cryptography is the most promising technique for key distribution. And the optical coding techniques can be deployed to encrypt the modulated signal in the optical layer. A mathematical equation has been derived from information theory to evaluate the information-theoretic security level of the wiretap channel in optical coding schemes. And the merits and limitation of two coherent optical coding schemes, temporal phase coding and spectral phase coding, have been analysed. The security scheme based on a reconfigurable optical coding device has been introduced, and the corresponding security protocol has been developed. By moving the encryption operation from the electronic layer to the optical layer, the modulated signals become opaque to the unauthorised users. Optical code distribution and authentication is the one of the major challenges for our proposed scheme. In our proposed protocol, both of the operations are covered and defined in detail. As a preliminary draft of the optical code security protocol, it could be a useful guidance for further research

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

Design and Implementation of Secure Chaotic Communication Systems

Chaotic systems have properties such as ergodicity, sensitivity to initial conditions/parameter mismatches, mixing property, deterministic dynamics, structure complexity, to mention a few, that map nicely with cryptographic requirements such as confusion, diffusion, deterministic pseudorandomness, algorithm complexity. Furthermore, the possibility of chaotic synchronization, where the master system (transmitter) is driving the slave system (receiver) by its output signal, made it probable for the possible utilization of chaotic systems to implement security in the communication systems. Many methods like chaotic masking, chaotic modulation, inclusion, chaotic shift keying (CSK) had been proposed however, many attack methods later showed them to be insecure. Different modifications of these methods also exist in the literature to improve the security, but almost all suffer from the same drawback. Therefore, the implementation of chaotic systems in security still remains a challenge. In this work, different possibilities on how it might be possible to improve the security of the existing methods are explored. The main problem with the existing methods is that the message imprint could be found in the dynamics of the transmitted signal, therefore by some signal processing or pattern classification techniques, etc, allow the exposition of the hidden message. Therefore, the challenge is to remove any pattern or change in dynamics that the message might bring in the transmitted signal

Performance Analysis of a Chaos-Based Multi-User Communication System Implemented in DSP Technology

Abstrac

SEQUENCE SYNCHRONIZATION IN A WIDEBAND CDMA SYSTEM

A mathematical model of a synchronization block of a DS-CDMA system is developed and then investigated using a simulation. For this synchronization a pilot sequence has been used that can be a pseudorandom sequence or a chaotic sequence of a limited length. The theoretical model is tested by simulation. It was shown that the system can be synchronized using a pilot sequence represented by a periodically repeated chaotic sequence