I. Pierce

Experimental Investigations of Time-Delay Signature Concealment in Chaotic External Cavity VCSELs Subject to Variable Optical Polarization Angle of Feedback

Time-delay (TD) signature concealment in a chaotic vertical-cavity surface-emitting laser (VCSEL) is studied experimentally. The VCSEL is subject to variable optical polarization angle of feedback along with variable optical feedback strength and bias current. The TD signature concealment is determined through the use of autocorrelation and information theory-based permutation entropy functions. It is found that the TD signature is concealed at low feedback of strength of order -18 dB. At moderate feedback strength, the TD signature is sensitive to the rotation of optical polarization angle of feedback with TD concealment being observed for polarization angles in the range from 45° to 90°.

A theoretical analysis of optical clock extraction using a self pulsating laser diode

The potential for using inexpensive compact disc laser diodes as optical clock extraction elements in transparent networks has led to an increase in research into the dynamics of self-pulsating laser diodes. We use a rate-equation model to simulate the synchronization of the self-pulsating laser output pulses to a periodic optical signal, In particular, we investigate the time it takes for the laser to synchronize to the input signal and also, the time taken for the laser to unlock when the signal is removed. The effect of varying the power of the optical signal and the detuning of the input signal frequency relative to the lasers self-pulsation frequency are determined. Our results enable us to identify important issues which need to be addressed when a self-pulsating laser diode is used in a clock extraction subsystem, In particular, we find that the signal frequency and laser free-running frequency must be as close as possibility to minimize errors. Also, the higher the signal power the quicker the laser synchronizes to the signal, although we find that if the power becomes too large the laser can no longer lock, which would cause a significant increase in detection errors.

Identification of the optimum time-delay for chaos synchronization regimes of semiconductor lasers

It is shown that the optimum correlation for chaos synchronization of master-slave semiconductor lasers occurs at a delay time that is sensitive to both the injection strength and the frequency detuning of the driving field. This effect may be overlooked if the correlation function is not evaluated globally. The correlation function has been used as the de facto method for quantitatively determining the degree of synchronization achieved between unidirectional coupled chaotic semiconductor lasers, see for example . The correlation function is a continuous function of the delay time but is normally evaluated at only two delay times. It is shown that this approach can cause a misidentification of the dominant synchronization process and can also mask important temporal fluctuations in the nature and quality of the chaos synchronization. In essence, two factors contribute to the potential for misidentification, the first is the inherent small time shift required to obtain the optimum correlation and the second is the quasi-periodicity that is present in certain chaotic regimes. This paper shows that a reevaluation of some of the published numerical studies of chaos synchronization is necessary.

Frequency-detuned synchronization switching in chaotic DFB laser diodes

Synchronization switching between complete and generalized synchronization via frequency detuning of chaotic laser diodes has been observed. Maximum cross-correlation coefficients for the two forms of synchronization have been used to demonstrate such synchronization switching. The regime of synchronization achieved has also been confirmed by measurement of the time lag between the synchronized laser outputs.

Multi-modal biometric emotion recognition using classifier ensembles

We introduce a system called AMBER (Advanced Multimodal Biometric Emotion Recognition), which combines Electroencephalography (EEG) with Electro Dermal Activity (EDA) and pulse sensors to provide low cost, portable real-time emotion recognition. A single-subject pilot experiment was carried out to evaluate the ability of the system to distinguish between positive and negative states of mind provoked by audio stimuli. Eight single classifiers and six ensemble classifiers were compared using Weka. All ensemble classifiers outperformed the single classifiers, with Bagging, Rotation Forest and Random Subspace showing the highest overall accuracy.

Optimal operating conditions for external cavity semiconductor laser optical chaos communication system

In optical chaos communications a message is masked in the noise-like broadband output of a chaotic transmitter laser, and message recovery is enabled through the synchronization of the transmitter and the (chaotic) receiver laser. Key issues are to identify the laser operating conditions which provide the highest quality synchronization conditions and those which provide optimized message extraction. In general such operating conditions are not coincident. In this paper numerical simulations are performed with the aim of identifying a regime of operation where the highest quality synchronization and optimizing message extraction efficiency are achieved simultaneously. Use of such an operating regime will facilitate practical deployment of optical chaos communications systems without the need for re-adjustment of laser operating conditions in the field.

Wavelet operators for nonlinear optical pulse propagation

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.

Theoretical optimization of self-pulsating 650-nm-wavelength AlGaInP laser diodes

Self-pulsating laser diodes operating at a wavelength of 650 nm are attractive for high-density optical storage. The main candidate for such a device is an AlGaInP laser diode including an epitaxially integrated saturable absorber. The characteristic self-pulsation occurs due to the interplay between gain in the active region and the absorption within the structure. In the paper, we calculate the dynamics of self-pulsation in this type of AlGaInP laser diode, including a detailed description of gain and absorption within the relative sections. In particular, we identify how, by modifying the structure of the epitaxial absorber layers, we can alter the operating characteristics of these laser diodes.

Self-consistent optical gain and threshold current calculations for near infrared intersubband semiconductor lasers

Abstract A theoretical investigation of the optical gain of electrically pumped intersubband lasers is presented. Using a prototype four-level near-infrared (1.55 μm) triple quantum well structure, self-consistent numerical simulations of the rate equations, energy density equations, optical gain and spontaneous emisson spectra of triple quantum well structures have been implemented at temperatures of 100 K and 300 K. It is predicted that the threshold currents of such lasers are significantly smaller than those for mid-infrared quantum cascade lasers.

Experimental analysis of self-pulsation 650-nm-wavelength AlGaInP laser diodes with epitaxial absorbing layers

We have produced self-pulsating 650-nm-wavelength AlGaInP lasers by the inclusion of saturable absorbing quantum quantum wells (QWs) within the p-doped cladding layer. To maintain the pulsation characteristics at high temperature, a multiple QW design has been used. This reduces the saturation of the absorbing layers due to thermally activated charge leakage from the active region of the laser, thus enabling strong self-pulsation up to a maximum temperature of 100/spl deg/C. The dynamic characteristics of the absorber wells have been measured using time-resolved photoluminesence techniques on the laser structures. The results indicate that the carrier lifetime in the absorber is determined by nonradiative processes with a typical decay time of 0.3 ns.