Demonstration of optical synchronization of chaotic external-cavity laser diodes

Sivaprakasam, S.; Shore, K.A.

doi:10.1364/ol.24.000466

Cited by 160 publications

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“…Two coupled semiconductor lasers exhibit chaos synchronization. Different coupling setups such as unidirectional or mutual coupling and variations of the strength of the self and coupling feedback result in different synchronization states: the two lasers can synchronize in a leaderlaggard or anticipated mode [3,4], as well as in two different synchronization states; achronal synchronization in which the lasers assume a fluctuating leading role, or isochronal synchronization where there is no time delay between the two lasers' chaotic signals [2,5,6,7,8].In this Letter we focus on a symmetric setup, the time delay between the lasers is denoted by τ c and the time delay of the self-feedback is denoted by τ d . In the event of τ c = τ d = τ and for a wide range of the mutual coupling strength, σ, and the strength of the self-feedback, κ, the stationary solution is isochronal synchronization [2,5,9].…”

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Synchronization of Mutually Coupled Chaotic Lasers in the Presence of a Shutter

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Two mutually coupled chaotic diode lasers exhibit stable isochronal synchronization in the presence of self feedback. When the mutual communication between the lasers is discontinued by a shutter and the two uncoupled lasers are subject to self-feedback only, the desynchronization time is found to scale as A d τ where A d > 1 and τ corresponds to the optical distance between the lasers. Prior to synchronization, when the two lasers are uncorrelated and the shutter between them is opened, the synchronization time is found to be much shorter, though still proportional to τ . As a consequence of these results, the synchronization is not significantly altered if the shutter is opend/closed faster than the desynchronization time. Experiments in which the coupling between two chaotic-synchronized diode lasers is modulated with an electro-optic shutter are found to be consistent with the results of numerical simulations.PACS numbers: 05.45. Vx, 42.65.Sf, 42.55.Px Chaotic systems are characterized by an irregular motion which is sensitive to initial conditions and tiny perturbations. Nevertheless, two chaotic systems can synchronize their irregular motion when they are coupled [1]. When the coupling is switched off, any tiny perturbation drives the two trajectories apart. The separation is exponentially fast, and it is described by the largest Lyapunov exponents of a single system.In this Letter we show that the trajectory dynamics of coupled chaotic systems which also poses time-delayed self-feedback, is different. In a system with self-feedback, which has also been investigated in the context of secure communication with chaotic lasers [2], the time scale for the separation of the trajectories is found to be much longer than the coupling time. On the other hand, when the coupling is switched on, resynchronization occurs on a faster time scale. We investigate this phenomenon numerically and show first experiments which support our numerical simulations. The demonstrated difference between de-and re-synchronization can be used to improve the security of public-channel communication with chaotic lasers [2].Semiconductor (diode) lasers subjected to delayed optical feedback are known to displays chaotic oscillations. Two coupled semiconductor lasers exhibit chaos synchronization. Different coupling setups such as unidirectional or mutual coupling and variations of the strength of the self and coupling feedback result in different synchronization states: the two lasers can synchronize in a leaderlaggard or anticipated mode [3,4], as well as in two different synchronization states; achronal synchronization in which the lasers assume a fluctuating leading role, or isochronal synchronization where there is no time delay between the two lasers' chaotic signals [2,5,6,7,8].In this Letter we focus on a symmetric setup, the time delay between the lasers is denoted by τ c and the time delay of the self-feedback is denoted by τ d . In the event of τ c = τ d = τ and for a wide range of the mutual coupling strength, σ, and the stre...

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Synchronization of Mutually Coupled Chaotic Lasers in the Presence of a Shutter

et al. 2007

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“…Most experimental investigations of chaos synchronization in unidirectionally coupled external cavity semiconductor lasers [4] have found that the lag time between the master and slave lasers' intensities is equal to the coupling delay, whereas numerical results [5] show that the lag time should be equal to the difference between the delay time in the coupling and round-trip time of the light in the transmitter's external cavity. Knowledge of the exact lag time is of considerable practical importance, as experiments on message transmission using fibre lasers and diode lasers have shown that the recovery of message at the receiver critically depends on the correction made for the lag time [4,6].…”

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“…Knowledge of the exact lag time is of considerable practical importance, as experiments on message transmission using fibre lasers and diode lasers have shown that the recovery of message at the receiver critically depends on the correction made for the lag time [4,6].…”

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Lag times and parameter mismatches in synchronization of unidirectionally coupled chaotic external cavity semiconductor lasers

2002

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We report an analysis of synchronization between two unidirectionally coupled chaotic external cavity master/slave semiconductor lasers with two characteristic delay times, where the delay time in the coupling is different from the delay time in the coupled systems themselves. We demonstrate for the first time that parameter mismatches in photon decay rates for the master and slave lasers can explain the experimental observation that the lag time is equal to the coupling delay time. PACS number(s):05.45. Xt, 05.45.Vx, 42.55.Px, 42.65.Sf Chaos synchronization [1] is of fundamental importance in a variety of complex physical, chemical and biological systems [2]. Application of chaos synchronization has been advanced in secure communications, optimization of non-linear systems' performance, modeling brain activity and pattern recognition [2]. Time-delay systems are ubiquitous in nature, technology and society because of finite signal transmission times, switching speeds and memory effects [3]. Therefore the study of chaos synchronization in these systems is of considerable practical significance. Because of their ability to generate high-dimensional chaos, time-delay systems are good candidates for secure communications based on chaos synchronization. In this context particular emphasis is given to the use of chaotic external cavity semiconductor lasers, because laser systems with optical feedback are prominent representatives of time-delay systems which can generate hyperchaos [4].Most experimental investigations of chaos synchronization in unidirectionally coupled external cavity semiconductor lasers [4] have found that the lag time between the master and slave lasers' intensities is equal to the coupling delay, whereas numerical results [5] show that the lag time should be equal to the difference between the delay time in the coupling and round-trip time of the light in the transmitter's external cavity. Knowledge of the exact lag time is of considerable practical importance, as experiments on message transmission using fibre lasers and diode lasers have shown that the recovery of message at the receiver critically depends on the correction made for the lag time [4,6].Recently there have been several attempts to explain the coupling-delay lag time synchronization in unidirectionally coupled external cavity semiconductor lasers. In [7] this phenomenon was related to a strong coupling and/or frequency detuning between the two lasers. However in a recent paper [8], where a numerical study of two unidirectionally coupled single-mode semicon-

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