Author

# Akira Hasegawa

Other affiliations: Kochi University of Technology, Bell Labs, Nagoya University ...read more

Bio: Akira Hasegawa is an academic researcher from Osaka University. The author has contributed to research in topics: Soliton & Dispersion (optics). The author has an hindex of 56, co-authored 259 publications receiving 16426 citations. Previous affiliations of Akira Hasegawa include Kochi University of Technology & Bell Labs.

Topics: Soliton, Dispersion (optics), Magnetic field, Plasma, Pulse (physics)

##### Papers published on a yearly basis

##### Papers

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TL;DR: Theoretical calculations supported by numerical simulations show that utilization of the nonlinear dependence of the index of refraction on intensity makes possible the transmission of picosecond optical pulses without distortion in dielectric fiber waveguides with group velocity dispersion.

Abstract: Theoretical calculations supported by numerical simulations show that utilization of the nonlinear dependence of the index of refraction on intensity makes possible the transmission of picosecond optical pulses without distortion in dielectric fiber waveguides with group velocity dispersion. In the case of anomalous dispersion (∂2ω/∂k2>0) discussed here [the case of normal dispersion (∂2ω/∂k2<0) will be discussed in a succeeding letter], the stationary pulse is a ``bright'' pulse, or envelope soliton. For a typical glass fiber guide, the balancing power required to produce a stationary 1‐ps pulse is approximately 1 W. Numerical simulations show that above a certain threshold power level such pulses are stable under the influence of small perturbations, large perturbations, white noise, or absorption.

2,509 citations

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AT&T

^{1}TL;DR: In this article, the authors presented the first experiment of all-optical solitons in a real optical fiber and showed that they can be used for information transfer in optical fibers.

Abstract: 1. Introduction.- 2. Wave Motion.- 2.1 What is Wave Motion?.- 2.2 Dispersive and Nonlinear Effects of a Wave.- 2.3 Solitary Waves and the Korteweg de Vries Equation.- 2.4 Solution of the Korteweg de Vries Equation.- 3. Lightwave in Fibers.- 3.1 Polarization Effects.- 3.2 Plane Electromagnetic Waves in Dielectric Materials.- 3.3 Kerr Effect and Kerr Coefficient.- 3.4 Dielectric Waveguides.- 4. Information Transfer in Optical Fibers and Evolution of the Lightwave Packet.- 4.1 How Information is Coded in a Lightwave.- 4.2 How Information is Transferred in Optical Fibers.- 4.3 Master Equation for Information Transfer in Optical Fibers: The Nonlinear Schrodinger Equation.- 4.4 Evolution of the Wave Packet Due to the Group Velocity Dispersion.- 4.5 Evolution of the Wave Packet Due to the Nonlinearity.- 4.6 Technical Data of Dispersion and Nonlinearity in a Real Optical Fiber.- 4.7 Nonlinear Schrodinger Equation and a Solitary Wave Solution.- 4.8 Modulational Instability.- 4.9 Induced Modulational Instability.- 4.10 Modulational Instability Described by the Wave Kinetic Equation.- 5. Optical Solitons in Fibers.- 5.1 Soliton Solutions and the Results of Inverse Scattering.- 5.2 Soliton Periods.- 5.3 Conservation Quantities of the Nonlinear Schrodinger Equation.- 5.4 Dark Solitons.- 5.5 Soliton Perturbation Theory.- 5.6 Effect of Fiber Loss.- 5.7 Effect of the Waveguide Property of a Fiber.- 5.8 Condition of Generation of a Soliton in Optical Fibers.- 5.9 First Experiments on Generation of Optical Solitons.- 6. All-Optical Soliton Transmission Systems.- 6.1 Raman Amplification and Reshaping of Optical Solitons-First Concept of All-Optical Transmission Systems.- 6.2 First Experiments of Soliton Reshaping and of Long Distance Transmission by Raman Amplifications.- 6.3 First Experiment of Soliton Transmission by Means of an Erbium Doped Fiber Amplifier.- 6.4 Concept of the Guiding Center Soliton.- 6.5 The Gordon-Haus Effect and Soliton Timing Jitter.- 6.6 Interaction Between Two Adjacent Solitons.- 6.7 Interaction Between Two Solitons in Different Wavelength Channels.- 7. Control of Optical Solitons.- 7.1 Frequency-Domain Control.- 7.2 Time-Domain Control.- 7.3 Control by Means of Nonlinear Gain.- 7.4 Numerical Examples of Soliton Transmission Control.- 8. Influence of Higher-Order Terms.- 8.1 Self-Frequency Shift of a Soliton Produced by Induced Raman Scattering.- 8.2 Fission of Solitons Produced by Self-Induced Raman Scattering.- 8.3 Effects of Other Higher-Order Dispersion.- 9. Polarization Effects.- 9.1 Fiber Birefringence and Coupled Nonlinear Schrodinger Equations.- 9.2 Solitons in Fibers with Constant Birefringence.- 9.3 Polarization-Mode Dispersion.- 9.4 Solitons in Fibers with Randomly Varying Birefringence.- 10. Dispersion-Managed Solitons (DMS).- 10.1 Problems in Conventional Soliton Transmission.- 10.2 Dispersion Management with Dispersion-Decreasing Fibers.- 10.3 Dispersion Management with Dispersion Compensation.- 10.4 Quasi Solitons.- 11. Application of Dispersion Managed Solitons for Single-Channel Ultra-High Speed Transmissions.- 11.1 Enhancement of Pulse Energy.- 11.2 Reduction of Gordon-Haus Timing Jitter.- 11.3 Interaction Between Adjacent Pulses.- 11.4 Dense Dispersion Management.- 11.5 Nonstationary RZ Pulse Propagation.- 11.6 Some Recent Experiments.- 12. Application of Dispersion Managed Solitons for WDM Transmission.- 12.1 Frequency Shift Induced by Collisions Between DM Solitons in Different Channels.- 12.2 Temporal Shift Induced by Collisions Between DM Solitons in Different Channels.- 12.3 Doubly Periodic Dispersion Management.- 12.4 Some Recent WDM Experiments Using DM Solitons.- 13. Other Applications of Optical Solitons.- 13.1 Soliton Laser.- 13.2 Pulse Compression.- 13.3 All-Optical Switching.- 13.4 Solitons in Fibers with Gratings.- 13.5 Solitons in Microstructure Optical Fibers.- References.

855 citations

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TL;DR: In this paper, a simple nonlinear equation is derived to describe the pseudo-three-dimensional dynamics of a nonuniform magnetized plasma with Te≫Ti by taking into account the three-dimensional electron, but two-dimensional ion dynamics in the direction perpendicular to B0.

Abstract: A simple nonlinear equation is derived to describe the pseudo‐three‐dimensional dynamics of a nonuniform magnetized plasma with Te≫Ti by taking into account the three‐dimensional electron, but two‐dimensional ion dynamics in the direction perpendicular to B0. The equation bears a close resemblance to the two‐dimensional Navier–Stokes equation. A stationary spectrum in the frequency range of drift waves is obtained using this equation by assuming a coexisting large amplitude long wavelength mode. The ω‐integrated k spectrum is given by k1.8(1+k2)−2.2, while the width of the frequency spectrum is proportional to k3(1+k2)−1, where k is normalized by cs/ωci. The result compares well with the recently observed spectrum in the ATC tokamak.

816 citations

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Bell Labs

^{1}TL;DR: The first observation of the modulational instability of light waves in dielectric material using a neodymium-doped yttrium aluminum garnet laser operated at 1.319 \ensuremath{\mu}m and single-mode optical fibers with anomalous group-velocity dispersion is reported.

Abstract: We report the first observation of the modulational instability of light waves in dielectric material using a neodymium-doped yttrium aluminum garnet laser operated at 1.319 \ensuremath{\mu}m and single-mode optical fibers with anomalous group-velocity dispersion. The observed results are in good agreement with the theoretical predictions. The relationship between the modulation instability and parametric four-wave mixing and the interplay with stimulated Raman and Brillouin scatterings are also presented.

712 citations

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TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

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Elsevier

^{1}TL;DR: The field of nonlinear fiber optics has advanced enough that a whole book was devoted to it as discussed by the authors, which has been translated into Chinese, Japanese, and Russian languages, attesting to the worldwide activity in the field.

Abstract: Nonlinear fiber optics concerns with the nonlinear optical phenomena occurring inside optical fibers. Although the field ofnonlinear optics traces its beginning to 1961, when a ruby laser was first used to generate the second-harmonic radiation inside a crystal [1], the use ofoptical fibers as a nonlinear medium became feasible only after 1970 when fiber losses were reduced to below 20 dB/km [2]. Stimulated Raman and Brillouin scatterings in single-mode fibers were studied as early as 1972 [3] and were soon followed by the study of other nonlinear effects such as self- and crossphase modulation and four-wave mixing [4]. By 1989, the field ofnonlinear fiber optics has advanced enough that a whole book was devoted to it [5]. This book or its second edition has been translated into Chinese, Japanese, and Russian languages, attesting to the worldwide activity in the field of nonlinear fiber optics.

15,770 citations

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TL;DR: A comprehensive review of spatiotemporal pattern formation in systems driven away from equilibrium is presented in this article, with emphasis on comparisons between theory and quantitative experiments, and a classification of patterns in terms of the characteristic wave vector q 0 and frequency ω 0 of the instability.

Abstract: A comprehensive review of spatiotemporal pattern formation in systems driven away from equilibrium is presented, with emphasis on comparisons between theory and quantitative experiments. Examples include patterns in hydrodynamic systems such as thermal convection in pure fluids and binary mixtures, Taylor-Couette flow, parametric-wave instabilities, as well as patterns in solidification fronts, nonlinear optics, oscillatory chemical reactions and excitable biological media. The theoretical starting point is usually a set of deterministic equations of motion, typically in the form of nonlinear partial differential equations. These are sometimes supplemented by stochastic terms representing thermal or instrumental noise, but for macroscopic systems and carefully designed experiments the stochastic forces are often negligible. An aim of theory is to describe solutions of the deterministic equations that are likely to be reached starting from typical initial conditions and to persist at long times. A unified description is developed, based on the linear instabilities of a homogeneous state, which leads naturally to a classification of patterns in terms of the characteristic wave vector q0 and frequency ω0 of the instability. Type Is systems (ω0=0, q0≠0) are stationary in time and periodic in space; type IIIo systems (ω0≠0, q0=0) are periodic in time and uniform in space; and type Io systems (ω0≠0, q0≠0) are periodic in both space and time. Near a continuous (or supercritical) instability, the dynamics may be accurately described via "amplitude equations," whose form is universal for each type of instability. The specifics of each system enter only through the nonuniversal coefficients. Far from the instability threshold a different universal description known as the "phase equation" may be derived, but it is restricted to slow distortions of an ideal pattern. For many systems appropriate starting equations are either not known or too complicated to analyze conveniently. It is thus useful to introduce phenomenological order-parameter models, which lead to the correct amplitude equations near threshold, and which may be solved analytically or numerically in the nonlinear regime away from the instability. The above theoretical methods are useful in analyzing "real pattern effects" such as the influence of external boundaries, or the formation and dynamics of defects in ideal structures. An important element in nonequilibrium systems is the appearance of deterministic chaos. A greal deal is known about systems with a small number of degrees of freedom displaying "temporal chaos," where the structure of the phase space can be analyzed in detail. For spatially extended systems with many degrees of freedom, on the other hand, one is dealing with spatiotemporal chaos and appropriate methods of analysis need to be developed. In addition to the general features of nonequilibrium pattern formation discussed above, detailed reviews of theoretical and experimental work on many specific systems are presented. These include Rayleigh-Benard convection in a pure fluid, convection in binary-fluid mixtures, electrohydrodynamic convection in nematic liquid crystals, Taylor-Couette flow between rotating cylinders, parametric surface waves, patterns in certain open flow systems, oscillatory chemical reactions, static and dynamic patterns in biological media, crystallization fronts, and patterns in nonlinear optics. A concluding section summarizes what has and has not been accomplished, and attempts to assess the prospects for the future.

6,145 citations

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04 Oct 2006TL;DR: In this paper, a review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime.

Abstract: A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

3,361 citations

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TL;DR: A comprehensive review of zonal flow phenomena in plasmas is presented in this article, where the focus is on zonal flows generated by drift waves and the back-interaction of ZF on the drift waves, and various feedback loops by which the system regulates and organizes itself.

Abstract: A comprehensive review of zonal flow phenomena in plasmas is presented. While the emphasis is on zonal flows in laboratory plasmas, planetary zonal flows are discussed as well. The review presents the status of theory, numerical simulation and experiments relevant to zonal flows. The emphasis is on developing an integrated understanding of the dynamics of drift wave–zonal flow turbulence by combining detailed studies of the generation of zonal flows by drift waves, the back-interaction of zonal flows on the drift waves, and the various feedback loops by which the system regulates and organizes itself. The implications of zonal flow phenomena for confinement in, and the phenomena of fusion devices are discussed. Special attention is given to the comparison of experiment with theory and to identifying directions for progress in future research.

1,739 citations