Siva Sivaprakasam

Parameter mismatches and perfect anticipating synchronization in bidirectionally coupled external cavity laser diodes.

We study perfect chaos synchronization between two bi-directionally coupled external cavity semiconductor lasers and demonstrate for the first time that mismatches in laser photon decay rates can explain the experimentally observed anticipating time in synchronization.

Dual-time and cascaded anticipation of chaos synchronization

Using an Ikeda model, which was introduced to describe the dynamics of an optical bistable resonator it is demonstrated analytically that anticipating synchronization can be obtained in chaotic time-delay systems governed by two characteristic delay times. We derive existence and stability conditions for the dual-time anticipating synchronization manifold. We also show that increased anticipation times for chaotic time-delay systems with two characteristic delay times can be obtained by the use of cascaded systems. The theory is in excellent agreement with numerical simulations. We also derive existence conditions for cascaded anticipating synchronization in external cavity semiconductor lasers.

Transition between anticipating and lag synchronization in chaotic external-cavity laser diodes

Chaotic synchronization is investigated using two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of an optical feedback in an external-cavity configuration. Changes in the spectrum of the synchronized system are shown to be associated with the transition between anticipating and lag synchronization.

Enhanced intensity fluctuations in a laser diode subject to optical feedback

The effects of optical feedback in edge-emitting semiconductor lasers and vertical cavity surface emitting lasers (VCSELs) have attracted considerable attention because the characteristics of both kind of lasers are very sensitive to the effects of reflected light. The phenomena arising in laser diodes subject to optical feedback can be classified according to operating five regimes conventionally identified as regimes I-V. Optical feedback also affects the noise properties of semiconductor lasers. There have been a number of investigations of the noise properties of semiconductor lasers and VCSELs subject to optical feedback. However, such work has been concerned with only some of the above-mentioned regimes of operation. A thorough experimental investigation of the effect of optical feedback in RIN of edge-emitting semiconductor lasers has yet to appear in the literature. In this paper, we present a detailed study of the effect of optical feedback on the average RIN of edge-emitting semiconductor lasers at different bias currents. An experimental study has been performed of the relative intensity noise (RIN) of a semiconductor laser in optical feedback regimes I to V. At low bias current, a low RIN is observed with low feedback feedback ratio, the RIN increased in the coherence collapse regime, then decreased again in regime V. The RIN in regime V is lower than that of the solitary laser. It is observed experimentally that an increase of the RIN occurs for intermediate levels of feedback. Such an increase in RIN appears to be related to enhanced intensity fluctuations. We will consider theoretical approaches to explaining the observed RIN characteristics.

Chaotic data encryption using semiconductor laser diodes

Synchronized external-cavity diode lasers are used for chaotic optical communication. A 1 GHz message is encoded by current modulation of the chaotic transmitter laser and decoded by a synchronzied chaotic receiver laser diode. The effect of introducing the message by optical injection into the receiver laser instead of direct current modulation is then investigated. Finally, we show how the signal masking can be enhacned by the appropriate choice of external cavity length for a given message frequency.

Optical feedback dependence of laser diode relative intensity noise

The relative intensity noise (RIN) of a semiconductor laser subject to optical feedback ahs been experimentally studied. At low bias current, a low RIN is observed with low feedback ration, the RIN increased in the coherence collapse regime (regime IV) and decreased in regime V. The RIN in regime V is lower than that of the solitary laser. The measurements are found to be in good qualitative and quantitative agreement with theoretical predictions. For higher bias current, a higher feedback ratio is needed for the semiconductor laser to transit from regime IV to V.

Cavity length as a key to security in a chaotic optical communication scheme

Three diode lasers are used as message, transmitter and receive lasers. The message laser is amplitude modulated by a simple message and its output is optically coupled to the transmitter laser ensuring optical modulation of message. The transmitter laser is rendered chaotic by application of appropriate optical feedback. The receiver laser is used to decode the message. Effective signal masking is enhanced by the selection of an appropriate external cavity length, which could be a possible key for chaotic optical communication security.

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.

Mechanisms for inducing chaos in broad and narrow linewidth external-cavity laser diodes

Abstract Optical power spectra of two chaotic external-cavity diode lasers with different single mode linewidths are compared. We report what we believe is the first observation of a novel mechanism for the onset of chaos in broad linewidth external-cavity laser diodes.