Impact Of Kerr Nonlinearity Research Articles

The influence of Kerr nonlinear effect on the signal and pump intensities in parabolic and triangular index EDFAs

Erbium-doped fiber amplifiers (EDFAs) is an integral part of all-optical communication system. Intensities of pump and signal within EDFAs is one of the significant parameters in its application perspective. Nonlinear effect on pump and signal may affect the performance aspect of EDFAs. In this work, we study intensity profile of pump and signal at different wavelengths of interest in EDFAs for the first higher order (LP11) excited mode considering the nonlinear impact. In this comparative analysis, EDFAs made up of some parabolic-index and triangular-index fibers of several V-numbers have been chosen. Our study involves the power series expression of the LP11 field prescribed by Chebyshev’s technique. A short computation is needed for achieving the objective by this method. Outcomes of this exercise are in superb conformity with those derived through the cumbersome finite element method (FEM) proving reliability of the Chebyshev’s method. The analysis is important in the context of use of dual mode optical fiber in EDFAs. The impact of Kerr nonlinearity on the performance of EDFAs involving dual mode optical fiber is also investigated. This analytical exercise through a handy and reliable mathematical instrument may be a dependable option for photonic EDFAs designers in practical realization of nonlinear EDFAs.

Efficiency enhancement of phase-conjugated twin waves technique by shaping envelopes of subcarriers in all-optical OFDM systems

All-optical orthogonal frequency division multiplexing (AO-OFDM) transmission, which employs high-order modulation formats, opens up a new field of advanced optical transmission. However, a major limitation is the impact of Kerr nonlinearity on AO-OFDM systems that induces nonlinear phase noise (NPN). In this work, we proposed a new method for suppressing NPN in AO-OFDM systems based on shaping envelopes of phase-conjugated twin waves (PCTWs). In the proposed method, each subcarrier and its phase-conjugated replica are firstly modulated with m-array quadrature amplitude modulation (mQAM) format and then shaped by return-to-zero (RZ) coding format. Sequentially, the subcarriers are multiplexed to form twin AO-OFDM signals, which are sent into two similar fiber links. At receiver, both waveforms are separately detected and twin subcarriers are coherently added for suppressing the NPN. An analytical model that characterizes NPN in proposed system is also developed. In addition, the performance of proposed system with 15 subcarriers that modulated by a RZ-4QAM format is numerically demonstrated. The results show that the NPN is considerably suppressed and system performance is highly improved. A signal-to-noise ratio (SNR) is enhanced by 5.7 dB and transmission length is lengthened by 150% as compared to conventional 4QAM-AO-OFDM system.

The Impact of Kerr Nonlinearity on the SNR Variability Induced by Polarization-Dependent Loss

We provide through numerical simulations new insights on the polarization-dependent loss (PDL)-induced variability of the signal-to-noise ratio (SNR) in dual-polarization coherent systems when Kerr nonlinearity is significant. We show that the interplay between PDL and nonlinearities provides an SNR distribution broader than the one induced by PDL in the only presence of amplified spontaneous emission noise. Such a broadening is missed by handy state-of-art models as the reverse channel method (RCM) that do not account for fiber nonlinearity, thus resulting inaccurate to estimate the SNR variability at practical launch powers. We show that such an inaccuracy persists even by considering in the RCM the nonlinear noise contribution. We show that the SNR distribution broadening in the presence of fiber nonlinearity is the result of a change in dynamics between the performance of those that can be identified for each PDL draw as best- and worst-performing polarization tributaries. By numerically decoupling the main contributions to fiber nonlinearity we also identify the nonlinear effects responsible for such a change of dynamics. Finally, we qualitatively validate our findings by mean of an experimental result.

Diffraction control inPT-symmetric photonic lattices: From beam rectification to dynamic localization

We address the propagation of light beams in longitudinally modulated PT-symmetric lattices, built as arrays of couplers with periodically varying separation between their channels, and show a number of possibilities for efficient diffraction control available in such non-conservative structures. The dynamics of light in such lattices crucially depends on the ratio of the switching length for the straight segments of each coupler and the longitudinal lattice period. Depending on the longitudinal period, one can achieve either beam rectification, when the input light propagates at a fixed angle across the structure without diffractive broadening, or dynamic localization, when the initial intensity distribution is periodically restored after each longitudinal period. Importantly, the transition between these two different propagation regimes can be achieved by tuning only gain and losses acting in the system, provided that the PT-symmetry remains unbroken. The impact of Kerr nonlinearity is also discussed.

Impact of Kerr nonlinearity on the whispering gallery modes of a microsphere.

To describe the temporal evolution of the mode amplitude of a spherical microcavity, a nonlinear equation is developed by considering loss and Kerr nonlinear effect as perturbations. In order to study the impact of Kerr nonlinearity, the tensor components of χ((3)) in spherical coordinates are calculated. To describe the impact of Kerr nonlinearity, effective mode volume and effective nonlinear coefficient are defined. We found that the resonant modes undergo a negative frequency shift proportional to the injected energy, consistant with the reported experimental observations.