Temperature Effects on Liquid Crystal Nonlinearity

The effect of temperature variation on nonlinear refractive indices of several types of liquid crystal (LC) compounds has been reported. Five samples have been investigated: two pure components (E7, MLC 6241-000) and three mixtures are obtained by mixing the previous two in different proportions. Birefringence, the average refractive index and the temperature gradients of refractive indices of the LCs are determined. The variations in refractive indices and birefringence were fitted theoretically using the modified Vuks equation. Excellent agreement is obtained between the fitted values and experimental data. Finally, the bistability of nonlinear refractive indices with temperature of liquid crystal (LC) compounds has been studied. The bistability of liquid crystals based on temperature is clearly observed for all samples. Also, the extraordinary refractive index has larger bistability than the ordinary refractive index. The measurements are performed at 1550 nm wavelength using wedged cell refractometer method

Different Approaches of Synchronization in Chaotic-Coupled QD Lasers

The investigation of synchronization phenomena on measured theoretical data such as time series has recently become an increasing focus of interest. In this chapter, the synchronized states (including steady state, periodic or chaotic) in coupled quantum dot lasers (dimensionless rate equations) are considered with both bidirectional and unidirectional synchronization. Different approaches for measuring synchronization have been proposed that rely on certain characteristic features of the dynamical system under investigation. Results show that the measure to be applied to a certain task can be chosen according to information in test applications, although certain dynamical features of a system under investigation (e.g., bifurcation and amplitude correlation) may render certain measures more suitable than others

Experimental Evidence of Chaotic Resonance in Semiconductor Laser

تم في هذا البحث تقديم دراسة تجريبية بشأن إشارة الرنين في ليزر أشباه الموصلات الشواشي. تعتبر اضطرابات الرنين فعالة في تسخير مؤشرات التذبذب غير الخطية لتطبيقات مختلفة مثل إحداث الشواش والسيطرة على الشواش. تم الحصول على نتائج مثيرة للاهتمام فيما يتعلق بتأثير الرنين الشواشي عن طريق إضافة التردد على الأنظمة. يغير التردد القسري النظام الديناميكي غير الخطي من خلال قيمة حرجة ، وهناك انتقال من جاذب دوري إلى جاذب غريب. كما ان السعة لها تأثير وثيق الصلة للغاية بالنظام ، مما أدى إلى استجابة الرنين الأمثل للقيم المناسبة المتعلقة بزمن الارتباط. فيصبح النظام الشواشي منتظمًا تحت ترددات أو سعات معتدلة. كما تم تحليل هذه الديناميكيات لمخرجات الليزر من خلال السلاسل الزمنية واطياف القدرة المستخرجة (FFT) وقد تعززت بواسطة مخطط التشعب.In this paper, an experimental study has been conducted regarding the indication of resonance in chaotic semiconductor laser.  Resonant perturbations are effective for harnessing nonlinear oscillators for various applications such as inducing chaos and controlling chaos. Interesting results have been obtained regarding to the effect of the   chaotic resonance by adding the frequency on the systems. The frequency changes nonlinear dynamical system through a critical value, there is a transition from a periodic attractor to a strange attractor. The amplitude has a very relevant impact on the system, resulting in an optimal resonance response for appropriate values related to correlation time. The chaotic system becomes regular under a moderate frequencies or amplitudes. These dynamics of the laser output are analyzed by time series, FFT and bifurcation diagram as a result

Attractor selection in semiconductor laser chaos generated by optoelectronic feedback

In this paper, an experimental and numerical study for the evolution of the non-linear dynamics of semiconductor laser has been done under two conditions, when the dc bias current of Semiconductor laser is varied, and when the feedback strength is varied. These dynamics were analyzed by time series and their extracted(FFT) power spectrums, phase diagrams (attractors),inter-spike intervals(ISI), these measurements enhanced by bifurcation diagram which explained the chaotic regimes. The stability states using different control parameters have been demonstrated. The role of control parameters of laser such as: dc bias current and feedback strength is proved in spiking generation and chaos control in the laser output

Chaotic spiking and incomplete homoclinic scenarios in semiconductor lasers with optoelectronic feedback

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Exploring noise effects in chaotic optical networks

We report the experimental evidence coherence and stochastic resonance in a dynamics of fast chaotic spiking of a semiconductor laser with optical feedback using an external nonwhite noise in the pumping current. We characterize both coherence and stochastic resonance in the time and frequency domain. We show that the regularity of the chaotic pulses in the intensity of laser diod increases when adding noise and it is optimal for some intermediate value of the noise intensity. We find that the power spectrum of the signal develops a peak at a finite frequency at intermediate values of the noise. The results show that noise may help in extracting the periodic signal without synchronization in chaotic communication. Then we reported the effect of external noise numerically on a single system by using bifurcation diagram. Finally, we considered Chaos synchronization in a network of 28 distinct chaotic systems with independent initial conditions when a normal Gaussian noise is added. The transition between non-synchronization to synchronization states using a suitable spatio-temporal representation has been reported. The role of coherence has also been considered. Keywords: Coherence resonance, Stochastic resonance, Control, Nois

Chaos Theory

With a good background in nonlinear dynamics, chaos theory, and applications, the author of this leading book gives a systematic treatment of the basic principle of nonlinear dynamics in different fields. The contributions from leading international scientists active in the field provide a comprehensive overview of our current level of background on chaos theory and applications in different sciences. In addition, they show overlap with the traditional field of control theory in scientific community

Optoelectronic Feedback in Semiconductor Light Sources: Optimization of Network Components for Synchronization

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