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The nonlinear dynamics of two semiconductor laser systems: (i) with optical feedback, and (ii) with optical feedback and direct current modulation are evaluated from multi-GHz-bandwidth output power time-series. Animations of compilations of the RF spectrum (from the FFT of the time-series) as a function of optical feedback level, injection current and modulation signal strength is demonstrated as a new tool to give insight into the dynamics. The results are contrasted with prior art and new observations include fine structure in the RF spectrum at low levels of optical feedback and non-stationary switching between periodic and chaotic dynamics for some sets of laser system parameters. Correlation dimension analysis successfully identifies periodic dynamics but most of the dynamical states are too complex to be extracted using standard algorithms.
Asunto(s)
Láseres de Semiconductores , Luz , Dinámicas no Lineales , Procesamiento de Señales Asistido por Computador/instrumentación , Algoritmos , Diseño de Equipo , RetroalimentaciónRESUMEN
This paper provides a report of chaos synchronization regimes which may be accessed in both unidirectionally and bidirectionally coupled multiple-time-delay semiconductor lasers. We demonstrate that in bidirectionally coupled multiple-time-delay lasers additional feedback can considerably enhance synchronization quality.
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We investigate the generalized synchronization between two unidirectionally linearly and nonlinearly coupled chaotic nonidentical Ikeda models and find existence conditions of the generalized synchronization. Also we study the chaos synchronization between nonidentical Ikeda models with variable feedback-delay times and find the existence and sufficient stability conditions for the retarded synchronization manifold with the coupling-delay lag time. Generalization of the approach to the wide class of nonlinear chaotic systems is also presented.
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We derive conditions for achieving inverse anticipating synchronization where a driven time-delay chaotic system synchronizes to the inverse future state of the driver. The significance of inverse anticipating chaos in delineating synchronization regimes in time-delay systems is elucidated. The concept is extended to cascaded time-delay systems.
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We study perfect chaos synchronization between two bidirectionally coupled external cavity semiconductor lasers and demonstrate that mismatches in laser photon decay rates can explain the experimentally observed anticipating time in synchronization.
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We report an analysis of synchronization between two unidirectionally coupled chaotic external cavity master and 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 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.
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Chaos data analysis has been performed on the chaotic output power time series data from a synchronized transmitter-receiver pair of semiconductor lasers. The system uses an asymmetric, bidirectional coupling configuration between the master (transmitter), which is a laser diode with optical feedback, and a stand-alone slave semiconductor laser. The correlation dimension of the chaotic time series has a minimum value of 4, which was obtained from high-bandwidth measurements. The correlation dimensions for both the master and the synchronized slave are identical when the cross-correlation coefficient of the synchronized chaos is above 0.9. These results establish correlation dimension analysis as an effective tool for the determination of the quality of wideband chaos synchronization.
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Nearly degenerate four-wave mixing in two-section single-mode laser diodes with unequal (asymmetric) facet reflectivities is studied theoretically. It is demonstrated that, under appropriate biasing conditions, the device exhibits a uniform phase-conjugate reflectivity over a frequency detuning range of more than 10 GHz. We can simultaneously achieve enhancement of the four-wave-mixing bandwidth and efficiency by injecting the probe signal at and deriving the conjugate output from the low-reflectivity facet of an asymmetric two-section laser diode.
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An experimental demonstration of optical synchronization of chaotic external-cavity semiconductor laser diodes is reported for what is believed to be the first time. It is shown that at an optimum coupling strength between the master and the slave lasers high-quality synchronization can be obtained.
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Amplitude modulation is used to encode a message into the output of a chaotic laser-diode optical transmitter, and decoding of the message by use of a synchronized chaotic laser-diode receiver is demonstrated experimentally. The chaotic carrier is shown to effectively mask the transmitted message.
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Experimental observation of optical bistability in a semiconductor laser under intermodal injection locking is reported for what is believed to be the first time. It is seen that a change in injection power of several microwatts or master laser frequency detuning of a few hundred megahertz can induce a change of as much as several hundred gigahertz in the lasing frequency of the slave laser. The results are in qualitative agreement with theoretical predictions.
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An experimental demonstration of optical synchronization of a chain of chaotic external-cavity laser diodes is reported for what is believed to be the first time. The experiment is performed in the low-frequency-fluctuation regime.
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Dynamical and noise properties of laser diodes subject to strong optical feedback have been investigated. Under strong optical feedback a conventional rate-equation approach is not valid, and thus an iterative traveling-wave model has been developed to describe this operating regime. Attention has been given to identifying the transition from stable strong-feedback operation to the coherence collapse regime obtained with moderate optical feedback.
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A practical scheme for polarization-insensitive and frequency-conversion interval-independent four-wave mixing in an optical loop configuration is proposed that uses one conventional semiconductor optical amplifier device and two perpendicular polarized pump sources. The significant advantages of this technique are simplicity of configuration, efficient conjugate power generation, effective suppression of the signal and one pump wave at the output port, and reduction in noise.
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A method that uses discrete wavelet transforms for the solution of evolution equations that describe optical pulse propagation in nonlinear media is presented. The theory of orthogonal wavelet transforms is outlined and applied to the representation of optical pulses. Wavelet transform representations of propagation operators are presented and applied to the nonlinear Schrödinger equation, yielding results that are indistinguishable from traditional Fourier-based simulations. The compression properties of wavelet representations of optical pulses permit significant improvement in execution speed compared with that of the split-step Fourier method.
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A simple method of targeting periodic dynamics appearing in semiconductor lasers subject to optical feedback is demonstrated. Possible applications of the technique in chaotic communications are identified, and its advantages for chaos control are discussed.
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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.
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Chaotic synchronization is investigated by use of two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of 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.
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Synchronization of three chaotic diode lasers is effected in a transmitter-mediator-receiver configuration. The transmitter laser's output is bidirectionally coupled to the mediator laser to achieve anticipating synchronization in their output intensities. The mediator laser's output is unidirectionally coupled to the receiver laser to achieve lag synchronization in their output intensities. This combination of lead and lag synchronization nullifies the time-of-flight lead-lag in synchronization between the transmitter and receiver lasers. This approach provides a means of eliminating time-of-flight delays in the synchronization of remote transmitters and receivers.
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We report the first experimental observation of anticipating chaotic synchronization in an optical system 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. It is found that the anticipation time does not depend on the external-cavity round trip time of the transmitter.