Flavio R. Ruiz-Oliveras

Optical Chaotic Communication Using Generalized and Complete Synchronization

We propose a secure optical communication system based on the principles of generalized and complete chaotic synchronization. A transmitter and a receiver both composed by two chaotic external-cavity semiconductor lasers are coupled in a master-slave configuration to provide generalized synchronization, while the master lasers in the transmitter and in the receiver are completely synchronized through the synchronization channel via an optical fiber. A message is added to the transmitter slave laser and sent to the receiver through the information channel to be compared with the output of the receiver slave laser. The system is robust to a small mismatch of the laser parameters or of the coupling between the master and slave lasers, unavoidable in a real system, and can even enable a good communication up to a 5 Gb/s transmission rate using the chaos masking encryption method, when the master laseres are coupled bidirectionally.

Phase-locking phenomenon in a semiconductor laser with external cavities

Phase-locked solutions are found numerically in a semiconductor laser with one and two external cavities. Different periodic, quasiperiodic, chaotic, and steady-state regimes form Arnolds tongues in bi-dimensional parameter spaces of the length and feedback strengths of the external cavities and the pump parameter. This rich structure gives additional possibility for controlling complex dynamics and chaos in a semiconductor laser with external cavities by properly adjusting their lengths and feedback strengths.

Information Encoding and Decoding Using Unidirectionally Coupled Chaotic Semiconductor Lasers Subject to Filtered Optical Feedback

We present a detailed numerical study of the dynamics of two unidirectionally coupled semiconductor lasers subject to filtered optical feedback. We show that this chaos-based communication scheme allows for an improvement in the decoding of encrypted messages in comparison with the conventional feedback scheme. We found that the performance of the system is optimal when the closed-loop configuration and similar filters are used in the emitter and receiver systems.

Route to Chaos in a Ring of Three Unidirectionally-Coupled Semiconductor Lasers

Complex dynamics of a ring of three unidirectionally-coupled semiconductor lasers are studied with respect to the coupling strength. While uncoupled, the lasers stay in a continuous-wave regime; they begin to oscillate as the coupling strength reaches a certain threshold value. When the coupling further increases, the dynamics exhibit a route to chaos via a sequence of Hopf bifurcations resulting in periodic, quasiperiodic, and chaotic oscillations. In the chaotic range, different synchronization states, ranging from asynchronous behavior to phase and near synchronization, are observed. The analytical solution yields a large number of fixed points.

Stable Cnoidal Wave Formation in an Erbium-Doped Fiber Laser

We demonstrate the formation of stable cnoidal waves in an erbium-doped fiber laser using an electrooptic modulator in the laser cavity. Properties of the cnoidal wave such as pulse shape, width, intensity, and frequency can be controlled through the electrooptic modulator or the length of the doped fiber. This system can be described using a three-level laser model, which shows that for any cavity loss there is a modulation frequency that makes stable cnoidal waves possible. Numerical and experimental results are presented.

Dynamics of a Semiconductor Laser with Two External Cavities

We study numerically complex dynamics of a semiconductor with one and two external cavities. We show that dynamical regimes in the laser with one external cavity can be controlled by adding another external cavity and properly adjusting its length and feedback strength. We demonstrate the existence of difierent stable periodic, quasiperiodic, chaotic, and steady-state regimes which form Arnolds tongues in bi-dimensional parameter spaces of the length and feedback strength of the external cavities and the pump parameter. The dynamics of a semiconductor laser subjected to external optical feedback has been studied by many researchers, since this laser has many applications in optical communications, interferometric sensors, frequency stability, etc. (see, for example, Ref. 1 and references therein). For moderate and strong feedback strengths this laser can display a very rich dynamical behavior, from periodic and quasiperiodic oscillations to chaos and coherence collapse (2,3). When the laser injection current is close to the solitary laser threshold, the laser operates in a stable steady-state regime. As the pump current is increased, intermittent drops of the laser intensity appear, that gives rise to low- frequency ∞uctuations (LFF). At higher currents, the laser optical bandwidth broadens that is known as coherence collapse (4,5). The dynamical behavior of a semiconductor lasers with a single feedback was studied extensively and the basic mechanism for LFF is well understood (6,7). The possibility for controlling LFF in a semiconductor laser with an external cavity by using a second delayed optical feedback was initially deduced by Liu and Ohtsubo (8). Later their idea was developed by Rogister, etal., (9,10), who realized the suppression of antimodes, responsible for LFF crises by properly adjusting the second feedback strength. Recently Mendez, etal., (11) have demonstrated experimentally that the frequency of LFF can be locked by external periodic modulation applied to the feedback strength of the external cavity. They have found difierent periodic and quasiperiodic regimes which formed Arnolds tongues in the space of the amplitude and frequency of the external modulation. In this paper we demonstrate that the locking efiect can be achieved without any external forcing. We show how LFF in a semiconductor laser with external cavity can be adequately controlled by adjusting properly both the length and the feedback strength of the second external cavity. The feedback time and the feedback strength of the second external cavity act in a similar manner as the period and amplitude of external modulation. We demonstrate that the variation of the parameters of the second external cavity allows one to obtain difierent dynamical regimes of the laser operation without any modiflcations in the solitary laser with a single external cavity. A single-mode semiconductor laser with delayed feedback is usually modeled by the Lang- Kobayashi rate equations (12). Due to the inflnite dimension of the system, an analytical study is very di-cult. Therefore, to study the dynamics of a semiconductor laser with two external cavities shown in Figure 1, we make numerical calculations of the modifled equations similar to those ex- plored previously by Sivapakrasam, etal., (13) and Carr (14). For weak or moderate feedback the modifled equations can be written as follows d ¢ E0(t) = (1=2)G(N (t) i Nth)E0 (t) + •1E0 (t i ?1)cos(ˆ1 + `(t) i `(t i ?1))

Synchronization of Delayed-Feedback Semiconductor Lasers and Its Application in Optical Communication

Semiconductor lasers with optical injection or delayed feedback have been widely studied because of their potential applications in optical communication using chaos synchronization. The delayed feedback through an external cavity or mirror enriches the laser dynamics so that different bifurcations (saddle-node, Hopf, period-doubling, torus, and crisis) arise when the coupling strength and/or delay time are varied. Recent research works on coupled semiconductor lasers have examined various mechanisms for their synchronization that may be useful to design optical communication networks. When the coupled lasers behave in a chaotic manner, different synchronization types can be achieved ranging from lag and phase synchronization to a completely synchronized motion. The route to synchronization of these lasers in a bistability domain displays a series of bifurcations with respect to the coupling strength. Complete chaos synchronization between the master and the slave lasers has been used to send information using the chaotic carrier. The message is encrypted in the chaotic output of the laser in the transmitter and then recovered by comparing with the chaotic output of the laser in the receiver. In the current chapter, a novel method of optical communication based on the combination of complete and generalized synchronization of chaotic semiconductor lasers is described.

Control of self-oscillations in a diode laser with external cavity

We study possibilities of controlling instabilities in a diode laser with external cavity by adding a second external cavity and adjusting its length and feedback strength. This method is approved numerically with a model of Lang-Kobayashi equations for the laser with two external cavities. We find that chaotic behaviour of the laser output can be completely stabilized to periodic orbits of different periods.