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.

/pdf/optical-communication-in-space-challenges-and-mitigation-41d8by09lh.pdf

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.

/pdf/athermally-photoreduced-graphene-oxides-for-three-4pedaj3yu4.pdf

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

Electromagnetic propagation through MVKS-type turbulence is examined assuming a slanted path using the Hufnagel-Valley model for the structure parameter. The propagation path consists of turbulent (Lt) and non-turbulent (LD) zones; using a split-step approach, the diffracted field characteristics for Gaussian-profile and Bessel beams are examined under varying turbulence strengths, and Lt/ Ld ratios. Cross-correlation (CC) products are computed as performance measures relative to non-turbulent recovery.

Slanted electromagnetic wave propagation through atmospheric phase turbulence using altitude-dependent structure parameter

Electromagnetic (EM) propagation velocities play an important role in the determination of power and energy flow in
materials and interfaces. It is well known that group and phase velocities need to be in opposition in order to achieve
negative refractive index. Recently, we have shown that considerable differences may exist in phase, group and
signal/energy velocities for normal and anomalous dispersion, especially near dielectric resonances. This paper examines
the phase and group velocities in the presence of normal and anomalous dispersion, and group velocity dispersion
(GVD), which requires introduction of the second order coefficient in the permittivity and permeability models.

/pdf/consideration-of-dispersion-and-group-velocity-dispersion-in-54nb0dsxzg.pdf

Consideration of dispersion and group velocity dispersion in the determination of velocities of electromagnetic propagation

Negative index in a dispersive chiral material with first-order sideband dispersion under dielectric losses

The properties of thick lenses are altered substantially in the presence of chirality and material dispersion. Recent work has involved examining of a chiral thick lens by re-deriving the related ABCD matrices based on standard paraxial and meridional conditions. A salient feature of a chiral thick lens is the inherent bimodal propagation via circular polarizations. Additionally, determination of image intensities requires the electromagnetic transmission properties expressed via the Fresnel coefficients. Three different scenarios are considered, viz., first-order frequency-dependent material dispersion of the dielectric permittivity, the lens material being chiral, and the case of an air gap (shaped like a thick lens) embedded in a chiral host. Under chirality, two sets of ABCD matrices are derived for right- and left-circularly polarized modes. The analyses and results are compared with the standard achiral problem. For imaging purposes, a simple 1D colored transparency is placed as an object before the thick lens in each scenario, with the transmission across the spherical boundaries examined via the ABCD parameters; also, the plane-wave amplitude transmitted across the system under different chirality bands and physical parameters is examined using the corresponding Fresnel coefficients. Under dispersion, image characteristics such as foci, location, magnification, and amplitude are controlled by narrow sidebands around a monochromatic carrier and the chirality. It is found that significant differences arise in the three imaging systems leading to the comparisons presented here.

Electromagnetic and imaging properties of chiral dispersive spherical interfaces under bimodal propagation using ABCD matrices.

Anisoplanatic electromagnetic (EM) propagation across a turbulent atmosphere has been recently examined for an unmodulated carrier propagating over an image-bearing transparency through opt...

Monish Ranjan Chatterjee

Papers

Slanted electromagnetic wave propagation through atmospheric phase turbulence using altitude-dependent structure parameter

Consideration of dispersion and group velocity dispersion in the determination of velocities of electromagnetic propagation

Negative index in a dispersive chiral material with first-order sideband dispersion under dielectric losses

Electromagnetic and imaging properties of chiral dispersive spherical interfaces under bimodal propagation using ABCD matrices.

Non-chaotic and chaotic propagation of stationary and dynamic images through MVKS turbulence