R.J. Jones

Influence of detuned injection locking on the relaxation oscillation frequency of a multimode semiconductor laser

Abstract The injection locking characteristics of a multi-mode semiconductor laser are considered. A formalism is developed to investigate the stability properties of an arbitrary laser mode subject to optical injection. The formalism is used to show that the relaxation oscillation frequency (ROF) in a semiconductor laser subject to optical injection is increased relative to that of the free running laser diode. Methods of utilizing positive detuning to determine the best approach of increasing the ROF of a semiconductor laser via injection locking are considered.

Integrity of semiconductor laser chaotic communications to naïve eavesdroppers.

The integrity of a chaotic encoding technique based on an external-cavity semiconductor laser transmitter-receiver system is experimentally examined. A semiconductor laser placed in the transmission path of the system is used to represent an eavesdropper intercepting a chaotic communication. The eavesdropper is able to obtain a copy of the transmission but is unable to decode the message. A chaotic communication system based on external-cavity semiconductor lasers is seen therefore to be secure against this form of interception.

Theoretical analysis of synchronization of chaotic self-pulsating semiconductor lasers

Chaotic dynamics in a self-pulsating laser diode has been shown theoretically to occur by modulation of the laser current. It has been also shown that synchronization of two chaotic self-pulsating lasers can be achieved by small amounts of optical coupling. This result has been obtained with a deterministic model for the laser intensity. We study coherent synchronization of single mode self-pulsating laser diodes by means of a field-equation model that takes into account phase-effects and spontaneous emission noise. It is shown that the size of the coupling required to achieved synchronization is influenced by spontaneous emission noise and by the linewidth enhancement factor. Numerical simulations are then used to identify the optimum regime for efficient synchronization. It is found that good synchronization can be obtained for large values of the bias current, such that the spontaneous emission plays a minor role. The degree of synchronization is studied as a function of the differences between the master and slave laser parameters. Finally, a sinusoidal signal is used to analyze a chaotic communication system based on self-pulsating laser diodes.

Communicating with chaos

This paper presents an overview of work undertaken and directed at the utilization of chaotic laser diodes in secure optical communications systems. Particular emphasis will be given to experimental work using external cavity laser diodes.

Output power changes in laser diodes subject to sub-wavelength variations in external cavity length: theory and experiment

Summary form only. Recent experiments have shown that the five regimes of feedback commonly used to characterise the dynamical performance of laser diodes subject to optical feedback poorly describe the behaviour for short external cavity laser diodes. Experimental investigations have shown that the output power of the laser can be dramatically affected by sub-wavelength variation in the external cavity length. A theoretical investigation using the Lang-Kobayashi model has shown excellent agreement with experimental results, and has thus elucidated the mechanisms that induces the observed experimental behaviour.

Chaotic synchronization with self-pulsating semiconductor lasers

Summary form only given. Considerable attention has been given to using chaos to implement secure optical communication systems. A message is encoded onto a chaotic carrier generated in a transmitter laser. Decoding of the message can be effected using a chaotic receiver if it is synchronized to the transmitter. In this paper we show that chaotic synchronization can be achieved using self-pulsating semiconductor lasers such as CD laser diodes. Chaotic dynamics are introduced by modulation of the lasers drive current. The intrinsic nature of the chaos allows the use of a simple low-cost stand-alone device to effect chaotic data encryption.