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Appl. Sci. 2017, 7(7), 645; doi:10.3390/app7070645

Modulational Instability in Linearly Coupled Asymmetric Dual-Core Fibers

1
Department of Physics, Presidency College, Chennai 600 005, Tamilnadu, India
2
Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel
3
Laboratory of Nonlinear-Optical Informatics, ITMO University, St. Petersburg 197101, Russia
4
Department of Physics, Anna University, Chennai 600 025, Tamilnadu, India
Current address: Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamilnadu, India.
*
Authors to whom correspondence should be addressed.
Academic Editor: Christophe Finot
Received: 25 April 2017 / Revised: 12 June 2017 / Accepted: 13 June 2017 / Published: 22 June 2017
(This article belongs to the Special Issue Guided-Wave Optics)

Abstract

We investigate modulational instability (MI) in asymmetric dual-core nonlinear directional couplers incorporating the effects of the differences in effective mode areas and group velocity dispersions, as well as phase- and group-velocity mismatches. Using coupled-mode equations for this system, we identify MI conditions from the linearization with respect to small perturbations. First, we compare the MI spectra of the asymmetric system and its symmetric counterpart in the case of the anomalous group-velocity dispersion (GVD). In particular, it is demonstrated that the increase of the inter-core linear-coupling coefficient leads to a reduction of the MI gain spectrum in the asymmetric coupler. The analysis is extended for the asymmetric system in the normal-GVD regime, where the coupling induces and controls the MI, as well as for the system with opposite GVD signs in the two cores. Following the analytical consideration of the MI, numerical simulations are carried out to explore nonlinear development of the MI, revealing the generation of periodic chains of localized peaks with growing amplitudes, which may transform into arrays of solitons. View Full-Text
Keywords: modulational instability; asymmetric nonlinear fiber couplers; linear stability approach; coupled nonlinear Schrödinger equations modulational instability; asymmetric nonlinear fiber couplers; linear stability approach; coupled nonlinear Schrödinger equations
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Govindarajan, A.; Malomed, B.A.; Mahalingam, A.; Uthayakumar, A. Modulational Instability in Linearly Coupled Asymmetric Dual-Core Fibers. Appl. Sci. 2017, 7, 645.

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