We studies a three-variable dimensionless model for a quantum dot light emitting diode (QD-LED) subject to optoelectronic feedback (OEFB). In dependence of the feedback strength and delay-time we analyze complex bifurcation scenarios for the intensity of the emitted light as well as time series, fast Fourier translate (FFT) and phase plane of all dynamic variables in order to elucidate the dynamics of the light emitting diode. The chaotic dynamic is completely determined by both the variation of the OEFB strength and delay-time of the QD-LED, as evidenced by bifurcation diagram. Our results show that small delay time lead to repeat periodicity of the light emitting towards OEFB. Furthermore, we study chaos synchronization of two QD-LED which are coupled via a unidirectional and bidirectional coupling system. When periodic systems are non-identical, both unidirectional and bidirectional systems depending on the coupling strength parameter the system exhibits completely synchronization. Residual chaos, the mean coherence and entropy are discussed as well.

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.

A communication scheme based on the synchronization of two chaotic quantum dot light emitting diodes (QD-LEDs) is theoretically examined. The Chaos in the QD-LED is generated by means of an optical feedback. Synchronization of the chaos is achieved by varying coupling strength between the transmitter and the receiver as unidirectional coupling. The proposed communication schemes is test a by successfully transmitting messages.

An optical communication scheme based on the synchronization of two chaotic semiconductor lasers is investigated experimentally. Two schemes of optical feedback injection, bidirectional and unidirectional, have been used. Synchronization of the chaos is achieved by coupling a fraction of the transmitter's output power to the driving current of the receiver. We present experimental results on the different routes of chaos synchronization. First is by using different current densities from master to slave-making synchronization, second is to apply different frequencies with fixed amplitude by using an external perturbation, and third is by applying a different amplitude white noises signals. Our results show that the third route has perfect results of synchronization. The last two routes are new methods and their experimental results are presented for the first time in making chaos synchronization. Finally, the quality of the synchronization was studied by different methods such as a Cross-Correlation Coefficient and Residual Chaos.

In this research, the frequency-frequency interactions in chaotic systems has been experimentally and numerically studied. We have injected two frequencies on chaotic system where one of these frequencies is modulated with chaotic waveform and the other is untiled as a scanning frequency to find modulating frequency. It is observed that the Fast Fourier Transformation (FFT) peaks amplitude increased when the value of the two frequencies are matched. Thus, the modulating frequency could be observed, this leads to discover a new method to detect the modulating frequency without synchronization.

The influence of bias current on the bandwidth of chaotic signals in semiconductor lasers by optical feedback has been studied experimentally and numerically. The measured data reveal that the bandwidth increase when the system becomes chaotic and this chaotic signal has a broadband spectrum so it can be used as a carrier for the quantum key. Mixing chaotic signal and quantum key make a very small change in chaotic bandwidth that does not affect the security of data transmitted.

The experimental and numerical study of chaos modulation will be presented in two stats, first, when the frequency of the external perturbation is varied, secondly, when the amplitude of this perturbation is changed. The dynamics of the laser output are analyzed by Fast Fourier Transformation, attractors and bifurcation Diagram. Some frequencies could be hidden other appeared, when the frequencies are hidden, the communication link considered as secure.

we study how to control the dynamics of excitable systems by using the phase control technique.We study how to control nonlinear semiconductor laser dynamics with optoelectronic feedback using the phase control method. The phase control method uses the phase difference between a small.added frequenc y and the main driving frequency to suppress chaos, which leads to various periodic orbits. The experimental studying for the evaluation of chaos modulation behavior are considered in two conditions, the first condition, when one frequency of the external perturbation is varied, secondly, when two of these perturbations are changed. The chaotic system becomes regular under one frequency or two frequencies, But in two frequencies, phase control showed an excellent ability to maintain regular behavior in chaotic window and reexcite chaotic behavior when destroyed. This dynamics of the laser output are analyzed by time series and bifurcation diagram.

In this paper the experimental and the numerical study of an optical key distribution quantum cryptography using BB84 protocol has been achieved. We create secret quantum key and the security of BB84 protocol is tested by inserting Eve in the system, the presence of Eve will cause disturbance to the synchronization of qubits between Alice and Bob and lead to bits errors. Finally we enhance the security of quantum cryptography using one-time pad technique and chaotic signal generated by semiconductor laser with an optical feedback. Mixing quantum key with chaotic signal will make ultimate security of the system.

The electrical and optical properties results were studied for Cadmium Sulphide (CdS) Nanoparticles/ Nematic liquid crystal (5CB) mixtures. Doping of CdS nanoparticles increases the spontaneous polarization and response time, the increase is due to large dipole-dipole interaction between the liquid crystal (LC) molecules and CdS nanoparticles, which increase the anchoring energy. The electro-optic measurements revealed a decrease (similar to 40%) in threshold voltage, and faster response time in doped sample cells than Pure 4'-n-pentyl-4-cyanobiphenyl (5CB) nematic liquid crystal.

The existence of high chaotic spiking in the dynamics of semiconductor lasers with an AC-coupled optical feedback is investigated experimentally. After chaos signal generation, the effect of attenuation feedback strength as a control parameter is studied, and the time evolution of photon density is analyzed. The chaotic instability is tested; our results exhibit monostability in dynamics. By applying different frequencies to observe the hidden regions, the chaotic dynamic results are indicated as a good candidate to hide information for satisfying the resonance phenomenon, to evaluate secure optical communication.

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.

We report phase control in a periodically driven chaotic nanosystem consisting of a quantum dot light-emitting diode. Such a dynamical system is a class C laser, whence the charactering features are intrinsically chaotic. Phase control relies on the addition of small parametric harmonic perturbations with adjustable phase. Phase control is demonstrated by changing both frequency and strength of the controlling perturbations. Our results show that phase control has two crucial effects on a quantum dot light-emitting diode. First, it can enhance the spiking behavior in either regular or chaotic regimes; second, it is able to turn periodic behavior to chaotic behavior with a minimal perturbation when a resonance condition at half of the driving frequency is achieved.

The non-linear optical properties of Spatial Light Modulator(SLM) represented by Nonlinear Refractive Index (NLR) and nonlinear Absorption coefficient has been measured in this work using highly sensitive method known as Z-scan technique for different wavelengths (red and green). The capability to do instant measurements of different nonlinear optical parameters lead to consider these techniques as a one of the most desired and effective methods that could apply for different materials. The results showed that the NLR were in the same power for the different wavelengths while the nonlinear absorption is higher in case of green laser.

An experimentally observations of chaos synchronization have been investigated between two optically coupled laser diodes. Two schemes of optical injection, bidirectional and unidirectional optical injections have been used. One of the two lasers MLD exhibits optical chaos due to external optical feedback by fiber mirror and the other laser diode SLD exhibits optical chaos by optical injection from the first one. The chaotic dynamics of both lasers were a function of laser diodes drive current. Synchronization and Anti-synchronization between two coupled laser diodes have been observed, and ensured by different measurements like time series matching ,correlation diagram(phase form)of amplitudes of coupled chaotic signals ,spectrum components coinciding of coupled chaotic signals, and coherence have been used for both injection schemes.

This research reports a theoretical investigation on the role of filtered optical feedback (FOF) in the quantum dot light emitting diode (QD-LED). The underlying dynamics is affected by a sidle node, which returns to an elliptical shape when the wetting layer (WL) is neglected. Both filter width and time delay change the appearance of different dynamics (chaotic and mixed mode oscillations ,MMOs). The results agrees with the experimental observations. Here, the fixed point analysis for QDs was done for the first time. For QD-LED with FOF, the system transits from the coherence collapse (CC) case in conventional optical feedback (COF) to a coherent case with a filtered mode in FOF. It was found that the WL washes out the modes which is an unexpected result. This may attributed to the longer capture time of WL compared with that between QD states. Thus, WL reduces the chaotic behavior.

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.

Chaotic behavior with multiscroll attractors and equilibrium points of semiconductor laser dynamics subjected to optical delay feedback and sinusodial injection current modulation observed numerically. The complicated dynamical behavior performed based on numerical simulation of modified Lang-Kobayashi model with direct current modulation term. The results reveal different dynamical regimes involving steady state, periodic, quas-periofdic, mixed modes, chaotic state with high power and 1-D 10 scrll attractors. These dynamics analyzed by sequences of observation analysis, FFT, phase portrait in two and three dimensions that qualify sensitivity of the system to initial conditions and give measure of the rate at which the trajectories separate one from the other(fixed point attractor ). These prove important use in Chaos synchronization and networks.

Nonlinear dynamics of a semiconductor laser subjected optical feedback observed numerically. The investigation performed based on numerical simulation of Lang-Kobayashi time delay rate equations over wide range of optical feedback strength. The results show that under small, moderate and high optical feedback strength semiconductor laser output power goes different dynamical regimes involving steady state, periodic, mixed modes and chaotic spiking. These dynamics analyzed by time series and their FFt power spectrum with phase space trajectory. The bifurcation diagram is drawn as a function of optical feedback strength. Chaos synchronization in unidirectional coupling scheme numerically presented.

The Chaos in single-mode semiconductor lasers is generated by means of an optoelectronic feedback. Chaotic dynamics have been generated due to the semiconductor laser model with optoelectronics feedback under appropriate conditions. MATLAB packages have been used to simulate the behavior of the semiconductor laser diodes with optoelectronics feedback. According to the chaos simulation technique, we have studied the model properties. And determine the control parameters that lead to regular behavior. Chaotic behavior has been generated by use the simulated model of OEFSL under appropriate conditions. We have a lot consider effectively analyze the behavior of a dynamical system under the influence control parameters such as bias current (δ 0 ), feedback strength (ε) and the population inversion (γ).