In recent years, free space optical (FSO) communication has gained significant importance owing to its unique features: large bandwidth, license free spectrum, high data rate, easy and quick deployability, less power, and low mass requirements. FSO communication uses optical carrier in the near infrared band to establish either terrestrial links within the Earth’s atmosphere or inter-satellite/deep space links or ground-to-satellite/satellite-to-ground links. It also finds its applications in remote sensing, radio astronomy, military, disaster recovery, last mile access, backhaul for wireless cellular networks, and many more. However, despite of great potential of FSO communication, its performance is limited by the adverse effects (viz., absorption, scattering, and turbulence) of the atmospheric channel. Out of these three effects, the atmospheric turbulence is a major challenge that may lead to serious degradation in the bit error rate performance of the system and make the communication link infeasible. This paper presents a comprehensive survey on various challenges faced by FSO communication system for ground-to-satellite/satellite-to-ground and inter-satellite links. It also provides details of various performance mitigation techniques in order to have high link availability and reliability. The first part of this paper will focus on various types of impairments that pose a serious challenge to the performance of optical communication system for ground-to-satellite/satellite-to-ground and inter-satellite links. The latter part of this paper will provide the reader with an exhaustive review of various techniques both at physical layer as well as at the other layers (link, network, or transport layer) to combat the adverse effects of the atmosphere. It also uniquely presents a recently developed technique using orbital angular momentum for utilizing the high capacity advantage of optical carrier in case of space-based and near-Earth optical communication links. This survey provides the reader with comprehensive details on the use of space-based optical backhaul links in order to provide high capacity and low cost backhaul solutions.

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Optical Communication in Space: Challenges and Mitigation Techniques

In recent years, free space optical communication has gained significant importance owing to its unique features: large bandwidth, license-free spectrum, high data rate, easy and quick deployability, less power and low mass requirements. FSO communication uses the optical carrier in the near infrared band to establish either terrestrial links within the Earth's atmosphere or inter-satellite or deep space links or ground-to-satellite or satellite-to-ground links. However, despite the great potential of FSO communication, its performance is limited by the adverse effects viz., absorption, scattering, and turbulence of the atmospheric channel. This paper presents a comprehensive survey on various challenges faced by FSO communication system for ground-to-satellite or satellite-to-ground and inter-satellite links. It also provides details of various performance mitigation techniques in order to have high link availability and reliability. The first part of the paper will focus on various types of impairments that pose a serious challenge to the performance of optical communication system for ground-to-satellite or satellite-to-ground and inter-satellite links. The latter part of the paper will provide the reader with an exhaustive review of various techniques both at physical layer as well as at the other layers i.e., link, network or transport layer to combat the adverse effects of the atmosphere. It also uniquely presents a recently developed technique using orbital angular momentum for utilizing the high capacity advantage of the optical carrier in case of space-based and near-Earth optical communication links. This survey provides the reader with comprehensive details on the use of space-based optical backhaul links in order to provide high-capacity and low-cost backhaul solutions.

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Since the early 1990s, a large number of chaos-based communication systems have been proposed exploiting the properties of chaotic waveforms. The motivation lies in the significant advantages provided by this class of non-linear signals. For this aim, many communication schemes and applications have been specially designed for chaos-based communication systems where energy, data rate, and synchronization awareness are considered in most designs. Recently, the major focus, however, has been given to the non-coherent chaos-based systems to benefit from the advantages of chaotic signals and non-coherent detection and to avoid the use of chaotic synchronization, which suffers from weak performance in the presence of additive noise. This paper presents a comprehensive survey of the entire wireless radio frequency chaos-based communication systems. First, it outlines the challenges of chaos implementations and synchronization methods, followed by comprehensive literature review and analysis of chaos-based coherent techniques and their applications. In the second part of the survey, we offer a taxonomy of the current literature by focusing on non-coherent detection methods. For each modulation class, this paper categorizes different transmission techniques by elaborating on its modulation, receiver type, data rate, complexity, energy efficiency, multiple access scheme, and performance. In addition, this survey reports on the analysis of tradeoff between different chaos-based communication systems. Finally, several concluding remarks are discussed.

Wireless Chaos-Based Communication Systems: A Comprehensive Survey

The emerging graphene-based material, an atomic layer of aromatic carbon atoms with exceptional electronic and optical properties, has offered unprecedented prospects for developing flat two-dimensional displaying systems. Here, we show that reduced graphene oxide enabled write-once holograms for wide-angle and full-colour three-dimensional images. This is achieved through the discovery of subwavelength-scale multilevel optical index modulation of athermally reduced graphene oxides by a single femtosecond pulsed beam. This new feature allows for static three-dimensional holographic images with a wide viewing angle up to 52 degrees. In addition, the spectrally flat optical index modulation in reduced graphene oxides enables wavelength-multiplexed holograms for full-colour images. The large and polarization-insensitive phase modulation over π in reduced graphene oxide composites enables to restore vectorial wavefronts of polarization discernible images through the vectorial diffraction of a reconstruction beam. Therefore, our technique can be leveraged to achieve compact and versatile holographic components for controlling light.

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Athermally photoreduced graphene oxides for three-dimensional holographic images

The direct algebraic method for constructing travelling wave solutions on nonlinear evolution and wave equations has been generalized and systematized The class of solitary wave solutions is extended to analytic (rather than rational) functions of the real exponential solutions of the linearized equation Expanding the solutions in an infinite series in these real exponentials, an exact solution of the nonlinear PDE is obtained, whenever the series can be summed Methods for solving the nonlinear recursion relation for the coefficients of the series and for summing the series in closed form are discussed The algorithm is now suited to solving nonlinear equations by any symbolic manipulation program This direct method is illustrated by constructing exact solutions of a generalized KdV equation, the Kuramoto-Sivashinski equation and a generalized Fisher equation

https://inside.mines.edu/~whereman/papers/Hereman-Takaoka-JPA-v23(21)-(1990)4805-4822.pdf

Solitary wave solutions of nonlinear evolution and wave equations using a direct method and MACSYMA

In a parallel approach to recently-used transfer function formalism, a study involving diffraction of modulated electromagnetic (EM) waves through uniform and phase-turbulent atmospheres is reported in this paper. Specifically, the input wave is treated as a modulated optical carrier, represented by use of a sinusoidal phasor with a slowly timevarying envelope. Using phasors and (spatial) Fourier transforms, the complex phasor wave is transmitted across a uniform or turbulent medium using the Kirchhoff-Fresnel integral and the random phase screen. Some preliminary results are presented comparing non-chaotic and chaotic information transmission through turbulence, outlining possible improvement in performance utilizing the robust features of chaos.

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Diffractive propagation and recovery of modulated (including chaotic) electromagnetic waves through uniform atmosphere and modified von Karman phase turbulence

Following up on recent work involving investigation of polarization states and Fresnel coefficients (FCs) at an
achiral/chiral (ACC) interface, this paper will consider extensions to the case of two interfaces whereby the front end will
be ACC and the back end chiral/achiral (CAC) leading to entirely different optical characteristics. Specifically, the work
examines the FCs for ACC and CAC, and explores the corresponding changes in the polarization states of the reflected
and transmitted light-waves. Additionally, the paper tracks the nature of the transmission through the chiral slab and the
emerging fields corresponding to linear as well as arbitrary input polarizations. Keeping in mind that left- and right-circular
modes are characteristic of propagation in a chiral material, amplitude and power reflection and transmission
characteristics are also examined for the device.

Polarization, reflection, and transmission states of plane electromagnetic propagation through a reciprocal chiral slab

Negative refractive index arises typically in metamaterials via multiple routes. One such avenue is the condition where the Poynting vector of the electromagnetic wave is in opposition to the group velocity in the material. An earlier work along this route in a chiral material led to the well-known result of requiring very large (non-realizable) chirality. Thereafter, a combination of chirality together with first-order dispersion was examined using plane wave electromagnetic analysis. To arrive at the conclusions in that approach, the three wave velocities (energy, group and phase) were derived under first-order dispersion in permittivity, permeability and chirality. Negative index in this approach was established under the condition of contra-propagating group and phase velocities. Regions of negative index were found analytically by assuming standard dispersive models (such as Condon). In this paper, we will re-visit the negative index problem under higher-order dispersion. In addition, we will re-examine the plane wave propagation model under parametric dispersion where each material parameter (e, μ, κ) is dispersively expanded up to the second order in frequency. Such a physical effect may be traced to group velocity dispersion (GVD) in the material. Field solutions are then obtained under the GVD effect, and extended to the evaluation of the energy, phase and group velocities.

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Investigation of negative index in dispersive, chiral materials via contra-propagating velocities under second-order dispersion (GVD)

Signal encryption and recovery using chaotic optical waves has been a subject of active research in the past 10 years. Since an acousto-optic Bragg cell with zeroth- and first-order feedback exhibits chaotic behavior past the threshold for bistability, such a system was recently ex amined for possible chaotic encryption us ing a low-amplitude sinusoidal signal applied via the bias input of the sound cell driver 1, 2 . Subsequent recovery of the me ssage signal was carried out via a heterodyne strategy employing a locally generated chaotic carrier, with threshold parameters matched to the transmitting Bragg cell. The simulation results, though encouraging, were limited to relatively low chaos frequencies and sinusoidal message signals only. In this paper, we extend the previous work by (i) increasing the chaos frequency using appropriate parameter control; (ii) carefully examining the system sensitivity to three system parameters, viz., feedback delay, feedback gain, and dc bias level; (iii) examine signal recovera bility relative to shifts in the three parameters mentioned above relative to the transmitter; and (iv) determining the robu stness of such a system relative to the primary transmitter parameters. Additionally, we consider also the effect of the additive bandpass noise (obtained from white Gaussian noise in the simulator) on signal recovery in such a system from a performance standpoint. It is also conjectured that signal recovery can be effected by passing the modulated light through a second sound cell in a matched chaotic regime. This aspect is also under investigation. Keywords : Acousto-optics, chaos, feedback, modulation, encryption, heterodyne, recovery, nonlinear dynamics

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Performance measures in acousto-optic chaotic signal encryption system subject to parametric variations and additive noise

Negative refractive index is introduced in metamaterials whereby the Poynting vector of the electromagnetic (EM) wave is in opposition to the group velocity, or alternatively, when the group and phase velocities in the medium are in opposition. In recent years, considerable research has been carried out relative to the EM propagation and refraction characteristics in metamaterials with emphasis on the origins of negative refractive index. The latter phenomenon has been extensively investigated in the literature, including recent work involving chiral metamaterials with material dispersion up to the first and second orders. An EM propagation in a chiral, dispersive material up to the first order is examined for possible emergence of negative refractive index under non-conductive losses. Three loss scenarios are considered, viz., dielectric losses (complex permittivity), magnetic losses (complex permeability), and a combination of both types of losses. A spectral approach combined with a slowly time-varying phasor analysis is applied, leading to the analytic derivation of EM phase and group velocities and corresponding indices. The velocities and indices are examined by selecting arbitrary dispersion parameters based on published practical values. The results indicate the emergence of negative index within specific radio frequency modulation bands. The resulting polarization states of the fields are examined under loss conditions. Finally, a method is suggested whereby the effects of dielectric and magnetic losses may be combined via appropriate Taylor coefficients such that the effective attenuation constant may be driven to zero via induced gain mechanisms arising from the dielectric and magnetic loss models.

Impact of losses on the negative index behavior in a chiral dielectric and tradeoffs between dielectric and magnetic losses toward zero effective attenuation

Monish Ranjan Chatterjee

Papers

Diffractive propagation and recovery of modulated (including chaotic) electromagnetic waves through uniform atmosphere and modified von Karman phase turbulence

Polarization, reflection, and transmission states of plane electromagnetic propagation through a reciprocal chiral slab

Investigation of negative index in dispersive, chiral materials via contra-propagating velocities under second-order dispersion (GVD)

Performance measures in acousto-optic chaotic signal encryption system subject to parametric variations and additive noise

Impact of losses on the negative index behavior in a chiral dielectric and tradeoffs between dielectric and magnetic losses toward zero effective attenuation