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[IEEE 2019 International Conference on Vision Towards Emerging Trends in Communication and Networking (ViTECoN) - Vellore, India (2019.3.30-2019.3.31)] 2019 International Conference on Vision Towards Emerging Trends in Communication and Networking (ViTECoN) - Modeling and Analysis of Hybrid SIM with L-PPM and MSK over Double Generalized Gamma Distribution in Free Space Optical Communication System
摘要： In this paper, we use Double Generalized Gamma (GG) distribution in turbulence induced fading to model the communication channel under weak, moderate and strong turbulence condition. In order to further improve the performance of Free Space Optical (FSO) Communication system over Double GG distribution, we use Hybrid Subcarrier Intensity Modulation (SIM) with L-Pulse Position Modulation (L-PPM) and Minimum Shift Keying (MSK) and analyze its Bit Error Rate (BER) performance for average received irradiance between -12 dBm and 4 dBm. From the simulation results, we observe that BER decreases with decrease in average length of PPM symbol L under different turbulence conditions in FSO Communication system.
关键词： FSO Communication System,Subcarrier Intensity Modulation,Atmospheric Turbulence,Bit Error Rate,Average Irradiance
更新于2025-09-12 10:27:22
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Complex Dynamics of Long Cavity Lasers
摘要： In this paper, we will discuss the properties of long cavity frequency sweeping lasers and demonstrate various scenarios of coherence deterioration in such lasers. The long cavity lasers are known to demonstrate rich variety of dynamical regimes including formation of localised structures and transition to turbulence. The interest to frequency sweeping long cavity lasers has also recently increased due to their application for imaging and sensing. For these applications, the stability of the laser is an important parameter as it directly influences its coherence and therefore, for example, the quality of the obtained images. We investigated static, quasi static and synchronisation regimes of such lasers and analysed possible instabilities in such system. Experimentally, we considered different laser configurations which has allowed us to study the influence of the cavity length, frequency sweeping speed and the detuning. Numerically, we used a model based on a system of delayed differential equations. The numerical simulation of our model showed excellent agreement with the experimental data. In particularly, we studied the formation of dark pulses, both periodic and non-periodic, and showed that they are closely connected to Nozaki-Bekki holes previously predicted in the complex Ginzburg-Landau equation.
关键词： turbulence,optical coherence tomography,swept sources lasers,long cavity lasers,nonlinear dynamics,localised structures
更新于2025-09-12 10:27:22
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Complexity in Biological and Physical Systems - Bifurcations, Solitons and Fractals || Self-Organization, Coherence and Turbulence in Laser Optics
摘要： In the last decades, rapid progress in modern nonlinear science was marked by the development of the concept of dissipative soliton (DS). This concept is highly useful in many different fields of science ranging from field theory, optics, and condensed matter physics to biology, medicine, and even sociology. This chapter aims to present a DS appearance from random fluctuations, development and growth, the formation of the nontrivial internal structure of mature DS and its breakup, in other words, a full life cycle of DS as a self-organized object. Our extensive numerical simulations of the generalized cubic-quintic nonlinear Ginzburg-Landau equation, which models, in particular, dynamics of mode-locked fiber lasers, demonstrate a close analogy between the properties of DS and the general properties of turbulent and chaotic systems. In particular, we show a disintegration of DS into a noncoherent (or partially coherent) multisoliton complex. Thus, a DS can be interpreted as a complex of nonlinearly coupled coherent “internal modes” that allows developing the kinetic and thermodynamic theory of the nonequilibrious dissipative phenomena. Also, we demonstrate an improvement of DS integrity and, as a result, its disintegration suppression due to noninstantaneous nonlinearity caused by the stimulated Raman scattering. This effect leads to an appearance of a new coherent structure, namely, a dissipative Raman soliton.
关键词： dissipative solitons,chaos in nonlinear optical systems,generalized cubic-quintic nonlinear Ginzburg-Landau equation,dissipative Raman soliton,optical turbulence
更新于2025-09-12 10:27:22
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Fiber Optic and Atmospheric Optical Communication || Atmospheric Communication Channels
摘要： The atmosphere is a gaseous envelope that surrounds the Earth from the ground surface up to several hundred kilometers. The atmosphere consists of different kinds of gaseous, liquid, and crystal structures, including effects of gas molecules (atoms), aerosol, cloud, fog, rain, hail, dew, rime, glaze, and snow. Except for the first two, the others are usually called hydrometeors in the literature. Furthermore, due to irregular and sporadic air streams and motions, that is, irregular wind motions, chaotic structures defined as atmospheric turbulence are also present in the atmosphere.
关键词： Hydrometeors,Atmosphere,Aerosol,Turbulence,Optical Communication
更新于2025-09-12 10:27:22
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Phase Offset Tracking for Free Space Digital Coherent Optical Communication System
摘要： The coherent receiving method can improve the sensitivity of an optical signal receiver for free space optical communication system effectively. To implement coherent receiving, the phase offset between the local laser in the receiver and the received optical signal through the atmosphere needs to be measured and estimated. The commonly used algorithm is the Viterbi-Viterbi phase offset estimation method (VVPE) and this method always produces great errors especially with low SNR (signal to noise ratio). To improve the estimation performance, we present a new method combing the VVPE with the Kalman filter (VVPE-KF) to estimate the phase offset. This method can lower the estimation error by no less than 60%, when the SNR is low. To verify the performance of this new method, the constant parameter channel and atmosphere turbulence channel are employed to evaluate the algorithm. The impact of the atmosphere turbulence intensity on the tracking error is discussed.
关键词： estimation method,Kalman filter,estimation error,atmosphere turbulence,Viterbi-Viterbi algorithm,phase offset
更新于2025-09-12 10:27:22
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[IEEE 2019 15th International Conference on Telecommunications (ConTEL) - Graz, Austria (2019.7.3-2019.7.5)] 2019 15th International Conference on Telecommunications (ConTEL) - Beam Quality Factor and Its Effect on Laser Beam through Anisotropic Turbulence for OWC
摘要： For optical wireless communication (OWC), beam quality factor is used as an important parameter to evaluate the propagation of laser beam through atmospheric turbulence. The beam quality factor and its effect on laser beam are investigated using the generalized anisotropic non-Kolmogorov power spectrum such that anisotropy property of turbulence, general spectral power law, and turbulence inner and outer scales can be considered together. We derive new expressions of beam quality factor for the lowest-order Gaussian beam and higher-mode Hermite-Gaussian beam. The effect of beam quality factor on the beam intensity through turbulence is also analyzed. Numerical results are presented to exhibit influences of different turbulence parameters on the beam quality factor and further on the propagation of laser beam, which provides a better understanding for OWC over free space.
关键词： beam quality factor,inner and outter scales,non-Kolmogorov turbulence,anisotropy,general spectral power law
更新于2025-09-12 10:27:22
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Decoy State Quantum Key Distribution via Beam-Wandering Modeled Atmosphere Channel
摘要： We investigate the decoy state quantum key distribution via the atmosphere channels. We consider the efficient decoy state method with one-signal state and two-decoy states. Our results show that the decoy state method works even in the channels with fluctuating transmittance. Nevertheless, the key generation rate will be dramatically decreased by atmosphere turbulence, which sheds more light on the characterization of atmosphere turbulence in realistic free-space based quantum key distributions.
关键词： quantum key distribution,atmosphere turbulence,decoy state,beam-wandering model
更新于2025-09-12 10:27:22
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Experimental study of the effects of thermally induced optical turbulence on underwater wireless optical communication link parameters
摘要： In this experimental research, the effects of refractive index fluctuations resulting from temperature fluctuations on some of the most important underwater communication link parameters such as the average received power, Signal to Noise Ratio (SNR) and normalized power variance (aperture averaged scintillation) has been experimentally investigated. Moreover, by introducing a new probability density function which is fitted more appropriately to the experimental data obtained from our simulator tank, the Bit Error Rate (BER) behavior of an Underwater Wireless Optical Communication (UWOC) link is also studied. These investigations are essential due to the optical turbulence limiting effects on the performance of UWOC systems. The experimental results indicate that reduction of the aperture averaged scintillation effects by using of optical components in the transmitter and receiver of UWOC links can enhance their performance. In general, increasing the strength of the optical turbulence (by increasing the temperature gradient induced by the rod heater) or the distance of the localized turbulence screen generated by temperature gradient from the transmitter plane, the aperture averaged scintillation decreases and consequently the SNR raises whilst the BER declines. Also, expanding the aperture diameter of the receiver optics reduces the normalized power variance which leads to decrease and increase in the BER and the SNR amounts respectively. The results are presented as experimental simulation graphs.
关键词： Laser beam propagation through turbulence,aperture averaged scintillation,Probability density function,BER,SNR,Underwater optical communication link
更新于2025-09-12 10:27:22
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Free Space Optical Communication (System Design, Modeling, Characterization and Dealing with Turbulence) || 2. Real-time measurement of meteorological parameters for estimating low altitude atmospheric turbulence strength (C2 n)
摘要： The major factor that limits the performance of Free Space Optical Communication (FSOC) is atmospheric turbulence which fluctuates over time in accordance with the variations in local meteorological parameters. Estimating the atmospheric turbulence strength (C2n) from measurement data is significant for finding the data rate the system is capable of operating at under different outdoor local environmental conditions. Hence, a low cost customized system for continuously measuring local meteorological data is developed and presented in this chapter. A field test scintillometer setup is established for a link range of 0.5 km at an altitude of 15.25 m. Specialized sensors are interfaced to the digital architectures to acquire the real-time data corresponding to atmospheric changes. The accuracy and performance of the measurement system are tested against standard instruments and the maximum correlation coefficients of 99.92 %, 99.63 %, 99.73 %, and 99.88 % are achieved for wind speed, temperature, relative humidity and pressure respectively. Atmospheric turbulence strength is estimated for the diurnal period using measured meteorological data. The validations of the estimated results with the scintillometer measurement are also analyzed. The weather profile and corresponding C2n variations at our test field for different seasons over a one year period are presented and the results are analyzed.
关键词： atmospheric turbulence,meteorological parameters,scintillometer,PAMELA model,Free Space Optical Communication (FSOC)
更新于2025-09-12 10:27:22
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Free Space Optical Communication (System Design, Modeling, Characterization and Dealing with Turbulence) || 4. Mitigation of beam wandering due to atmospheric turbulence and prediction of control quality using intelligent decision making tools
摘要： In a Free Space Optical Link (FSOL), atmospheric turbulence causes fluctuations in both intensity and phase of the received beam and impairs link performance. Beam motion is one of the main causes for major power loss. This chapter presents an investigation of the performance of two types of controller designed for aiming a laser beam at a particular spot under dynamic disturbances. Multiple experiment observability nonlinear input-output data mapping is used as the principal component for the controllers’ design. The first design is based on the Taguchi method while the second is the Artificial Neural Network (ANN) method. These controllers process the beam location information from a static linear map of a 2D plane: Optoelectronic Position Detector (OPD) as observer, and then generate the necessary outputs to steer the beam with a micro-electromechanical mirror: Fast Steering Mirror (FSM). The beam centroid is computed using a Mono-Pulse Algorithm (MPA). Evidence of suitability and effectiveness of the proposed controllers are comprehensively assessed and quantitatively measured in terms of coefficients of correlation, correction speed, control exactness, centroid displacement and stability of the receiver signal through the experimental results from the FSO link setup established for the horizontal range of 0.5 km at an altitude of 15.25 m. The test field type is open flat terrain, grass and a few isolated obstacles.
关键词： atmospheric turbulence,Artificial Neural Network (ANN),Mono-Pulse Algorithm (MPA),Fast Steering Mirror (FSM),beam wandering,Taguchi method,Free Space Optical Link (FSOL),Optoelectronic Position Detector (OPD)
更新于2025-09-12 10:27:22