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.

/pdf/optical-communication-in-space-challenges-and-mitigation-4wng3q8rfl.pdf

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

Concepts of energy and group velocities, Poynting and propagation vectors are examined for both positive and negative index materials. Known definitions for these entities are explored in terms of the interplay of chirality and dispersion.

/pdf/examination-of-energy-and-group-velocities-in-positive-and-2x9cyhg76g.pdf

Examination of Energy and Group Velocities in Positive and Negative Index Chiral Materials With and Without Dispersion

Propagation of a Gaussian-profile beam through extended MVKS phase turbulence under interchangeable source and receiver positions

In this paper, we consider a 2D polychromatic transparency serving as an object in front of a dispersive thick lens. The RGB based constituent colors are treated in terms of a center wavelength with a spectral spread, thereby enabling the phasor interpretation and tracking along axial image planes. It turns out that any individual color of the input transparency has a unique focal length or image position in the (meridional) observation plane after propagation through the lens. Under dispersion, image characteristics such as foci, axial location, magnification, and amplitude are controlled by narrow sidebands around a monochromatic carrier. The analytical results (derived numerically) are compared with standard non-dispersive imaging. Particular attention is given to the nature of transverse paraxial images in fixed axial planes, whereby defocusing effects due to dispersion are demonstrated in the manner of spherical aberration. Such selective axial focusing of individual wavelengths may find applications in improving the conversion efficiency of solar cells and photodetectors exposed to white light illumination.

Two-dimensional imaging under meridional propagation through a dispersive thick lens based on RGB distributions and defocused planes.

The use of acousto-optic chaos, as manifested via first-order feedback in an acousto-optic Bragg cell, in
encrypting a message wave and subsequently recovering the message in the receiver using a chaotic heterodyne
strategy, has been reported recently [1-3]. In examining the dynamical system analytically using computer
simulation, (expected) modulated chaos waveforms are obtained within specified observation windows. Because of
the relatively random nature inherent in chaos waveforms, it is essentially impossible to ascertain from the visual
display of the chaotic wave whether a given message signal has in fact modulated the chaotic "carrier". In fact, it
has been observed from earlier work that by appropriately controlling the chaos parameters, one may "hide" the
silhouette of the message from the envelope of the modulated chaos [1]. This was found to be especially true for
low-frequency chaos (in the KHz range). For chaos in the mid-RF (up to 10s of MHz) range, it is seen that the
silhouette is more difficult to suppress (even though this does not affect the robustness of the encryption). To
adequately determine whether modulation has in fact occurred by passing the AC signal through the sound cell bias
input, one needs to examine the spectral content of the chaos wave. In this paper, we discuss the results of such
spectral analyses using two different approaches, (i) fast Fourier transforms applied to the displayed waveform; and
(ii) transferring the intensity-vs-time data to an Excel spreadsheet, and then applying this information to a laboratory
spectrum analyzer with adequate bandwidth. The results are mutually compared and interpreted in terms of
encryption and decryption properties.

/pdf/spectral-analysis-of-encrypted-chaotic-signals-using-fast-3d6bpxr7ue.pdf

Spectral Analysis of Encrypted Chaotic Signals Using Fast Fourier Transforms and Laboratory Spectral Analyzers

Andrew Zangwill’s March 2022 article (page 28) presents an insightful portrait of Philip Anderson in dynamic, human terms. I was particularly drawn in by Zangwill’s mention of Anderson’s Anglophilia and his association with leading researchers at the University of Cambridge. In that context, two of Anderson’s “four facts”—that computers will not replace scientists and that good science has aesthetic qualities—resonate with Brian Josephson’s interests in the past 20-odd years.I met Josephson at an international conference, titled Home and the World: Rabindranath Tagore at the End of the Millennium, which was held by the University of Connecticut in September 1998. Josephson spoke about the poet-philosopher Tagore (1861–1941) and science.11. B. Josephson, in Rabindranath Tagore: Universality and Tradition, P. C. Hogan, L. Pandit, eds., Fairleigh Dickinson U. Press (2003), p. 107. From my relatively brief encounter with him, I understood at the time that Josephson was especially interested in the area of mind–matter interactions, and that, of course, had some relevance to the well-known 1930 conversation that Tagore had with Albert Einstein on reality and the human mind.22. M. Popova, “When Einstein met Tagore: A remarkable meeting of minds on the edge of science and spirituality,” Marginalian (27 April 2012). Mind–matter interactions have also been an area of sustained interest for many leading scientists, including Ilya Prigogine and Roger Penrose.It is also quite noteworthy that Zangwill mentions Charles Kittel as one of Anderson’s mentors at Bell Labs. Many of us pursuing physics and engineering in India in the 1970s were introduced to Kittel’s classic textbook Introduction to Solid State Physics, which was foundational to our understanding of the subject.ReferencesSection:ChooseTop of pageReferences <<1. B. Josephson, in Rabindranath Tagore: Universality and Tradition, P. C. Hogan, L. Pandit, eds., Fairleigh Dickinson U. Press (2003), p. 107. Google Scholar2. M. Popova, “When Einstein met Tagore: A remarkable meeting of minds on the edge of science and spirituality,” Marginalian (27 April 2012). Google Scholar© 2023 American Institute of Physics. 

https://physicstoday.scitation.org/doi/pdf/10.1063/PT.3.5169

Monish Ranjan Chatterjee

Papers

Examination of Energy and Group Velocities in Positive and Negative Index Chiral Materials With and Without Dispersion

Propagation of a Gaussian-profile beam through extended MVKS phase turbulence under interchangeable source and receiver positions

Two-dimensional imaging under meridional propagation through a dispersive thick lens based on RGB distributions and defocused planes.

Spectral Analysis of Encrypted Chaotic Signals Using Fast Fourier Transforms and Laboratory Spectral Analyzers

Mind and matter