PHY
Maître de Conférences
Activité scientifique
Profil chercheur
Enseignant-chercheur à l’Université de Yaoundé I. Grade : Maître de Conférences.
Publications scientifiques
Lina Maureen Ndzia Wandji, Alain Djazet, Serge I. Fewo, Conrad B. Tabi, Timoléon C. Kofané
The European Physical Journal D
Eric Martial Signé, Alain Djazet, Laure Tiam Megne, Martin Djoko, Serge I. Fewo, Timoléon Crépin Kofané
Nonlinear Dynamics
S. Mounbou, Serge I. Fewo, Marius Romuald Kamsap, Maïk Delon Mboumba, E. Feddi, J. V. Nguepnang et 2 autre(s)
The Journal of Physical Chemistry C
High Resolution Image Download MS PowerPoint Slide We evaluate the effects of electromagnetic radiation and dielectric screening of substrates SiC and SiO 2 on the exciton-polaron state in a graphene monolayer. As in other two-dimensional (2D) materials deposited on polar substrates, the ground state energy was obtained by the Lee–Low–Pines variational method and the local disorder rate known as Tsallis entropy was calculated using Gibbs–Boltzmann statistics. Our results show that the ground state energy increases with the wave vector of the surface optical (SO) phonons, the strength of the Coulomb interaction and decreases with the frequency and the amplitude of the electromagnetic field. The entropy of the system decreases with the frequency and amplitude of the radiation and increases with the strength of the Coulomb interaction. These results suggest that the phonon wave vector, the dielectric screening of the substrates, the frequency, and the amplitude of the electromagnetic radiation are the key parameters useful to control the stability of exciton-polaron in graphene.
Marius Jeannot Nko’o Nko’o, Alain Djazet, Lucien Mandeng Mandeng, Serge I. Fewo, Clément Tchawoua, Timoléon Crépin Kofané et 1 autre(s)
Using the variational approach, we show that the anti-vortex vector solution is the best which can be managed using the coupling parameters of the system because it is more stable following its rapid soliton transformation.
Marius Jeannot Nko’o Nko’o, Alain Djazet, Lucien Mandeng Mandeng, Serge I. Fewo, Clément Tchawoua, Timoléon Crépin Kofané et 1 autre(s)
Physica Scripta
Abstract In this paper, we present a study of vortex and anti-vortex dynamics within a complex cubic-quintic Ginzburg-Landau vector equation (CCQGLVE). We employ a variational approach to address the analytical aspects, and the results obtained are subsequently confirmed numerically. The vortex vector (VV) and the anti-vortex vector (anti-VV) are defined with topological charges: m = 1 for VV and m = − 1 for anti-VV. Our investigation reveals that the stability zone map corresponds to the region where greater stability can be achieved for the two studied solutions. Notably, the radius of the vortex craters experiences variations either an increase or decrease depending on the competition between the coupling parameters associated with cubic and quintic cross-phase modulation (XPM). During the propagation, the interaction between a fundamental soliton and anti-VV transforms the soliton into a vortex after a short time, but both finally undergo self-confinement which probably will generates solitons. In the case of the interaction between a VV and a fundamental soliton, we observed a self-confinement and a transformation into solitons. Considering the interaction between a VV and an anti-VV, we found that both solutions are also self-confined but the anti-VV solution turns into a soliton faster than the VV solution. This confirms that the anti-VV is the better solution that can be managed with system coupling parameters than the VV one.
Stéphanie Ganyou, Serge I. Fewo, Chérif S. Panguetna, Timoléon Crépin Kofané
Results in Physics
The dynamics of propagation of (2+1)-dimensional ion-acoustic wave (IAW) packets in magnetized electronegative plasma made of negative ions with electrons, both in boltzmann distribution and cold mobile positive ions is studied. For this purpose, the standard reductive perturbation method is used to derive the (2+1)-dimensional nonlinear Schrödinger (NLS) equation, which governs the modulation of positive IAW packets. The coefficients of the obtained NLS equation do not only depend on the system parameters specially the electronegative parameters such as the negative ion concentration ratio and the elcectron-to-negative ion temperature ratio (α and σn, respectivetly), but also on the magnetic field (ωp). The modulational instability is studied to analyse the areas of the emergence of waves. In order to describe the main characteristics of IAWs, the variational method is performed involving trial function solution of NLS equation and the exact (input profile) and numerical (output profile) solutions are also discussed.
Alain Djazet, Serge I. Fewo, Martin Djoko, E. Tchomgo Felenou, Timoléon Crépin Kofané
Chaos Solitons & Fractals
Dieudonné Zanga, Serge I. Fewo, Conrad Bertrand Tabi, Timoléon Crépin Kofané
Physical Review A
The generation of dissipative optical solitons is explored in doped fibers with correction effects under the activation of modulational instability (MI). The model, described by the cubic-quintic-septic complex Ginzburg-Landau equation, includes higher-order dispersion and nonlinear gradient terms. The Lange-Newell's criterion for MI of Stokes wave, boundary domains of MI, and integrated gain of MI are obtained via the linear stability analysis. Particular attention is given to the physical effect on the critical frequency detuning, especially in the normal regime, when varying the values of odd dispersion coefficients. Numerical simulations are undertaken and confronted with analytical predictions. Beyond the agreement between the linear stability analysis and trains of soliton generation, the soliton map induced by MI, along with the subsequent physical effects, is debated via bifurcation diagrams. This allows accurate prediction of transitions between various types of localized modes and well-calibrated generation of a wide variety of solitons with different energies. It is argued that knowing the center of mass and the energy of the generated structures can better characterize the long-time evolution of MI and, eventually, its nonlinear manifestations.
Alain Djazet, Serge I. Fewo, Conrad Bertrand Tabi, Timoléon Crépin Kofané
Applied Physics B
C. Kenfack-Sadem, S. Mounbou, Serge I. Fewo, M. F. C. Fobasso, A. J. Fotué, Lukong Cornelius Fai
Journal of Low Temperature Physics
Alain Djazet, Serge I. Fewo, E B Ngompe Nkouankam, Timoléon Crépin Kofané
The European Physical Journal D
S.C. Kenfack, S. Mounbou, N. Issofa, Serge I. Fewo, A. V. Wirngo, M. F. C. Fobasso et 2 autre(s)
Physica B Condensed Matter
Dieudonné Zanga, Serge I. Fewo, Conrad Bertrand Tabi, Timoléon Crépin Kofané
Communications in Nonlinear Science and Numerical Simulation
A.B. Togueu Motcheyo, J.D. Tchinang Tchameu, Serge I. Fewo, Clément Tchawoua, Timoléon Crépin Kofané
Communications in Nonlinear Science and Numerical Simulation
Chancelor Pokam Nguewawe, Serge I. Fewo, David Yemélé
Physical review. E
The effects of higher-order (HO) terms on the properties of the compact bright (CB) pulse described by the dispersionless nonlocal nonlinear Schrödinger (DNNLS) equation are investigated. These effects include third-order dispersion (TOD), the Raman term, and the time derivative of the pulse envelope. By means of the collective variable method, the dynamical behavior of the pulse amplitude, width, frequency, velocity, phase, and chirp during propagation is pointed out. The results indicate that the CB pulse experiences a self-frequency shift and self-steepening, respectively, in the presence of an isolated Raman term and the time derivative of the pulse envelope and acquires a velocity as the result of the TOD effect. In addition, TOD may also induce the breathing mode inside the variation of the pulse parameters when the width of the input pulse is slightly less than that of the unperturbed CB pulse. The combination of these terms, indispensable for describing ultrashort pulses, reproduces all these phenomena in the CB pulse behavior. Further, other properties are observed, namely, the pulse decay, the breathing mode even when the unperturbed CB pulse is taken as the input signal, and the attenuated pulse. These results are in good agreement with the results of the direct numerical simulations of the DNNLS equation with HO terms.
Anderson S. L. Gomes, Ernesto P. Raposo, André L. Moura, Serge I. Fewo, Pablo I. R. Pincheira, Vladimir Jerez et 2 autre(s)
Scientific Reports
Random lasers have been recently exploited as a photonic platform for studies of complex systems. This cross-disciplinary approach opened up new important avenues for the understanding of random-laser behavior, including Lévy-type distributions of strong intensity fluctuations and phase transitions to a photonic spin-glass phase. In this work, we employ the Nd:YBO random laser system to unveil, from a single set of measurements, the physical origin of the complex correspondence between the Lévy fluctuation regime and the replica-symmetry-breaking transition to the spin-glass phase. A novel unexpected finding is also reported: the trend to suppress the spin-glass behavior for high excitation pulse energies. The present description from first principles of this correspondence unfolds new possibilities to characterize other random lasers, such as random fiber lasers, nanolasers and small lasers, which include plasmonic-based, photonic-crystal and bio-derived nanodevices. The statistical nature of the emission provided by random lasers can also impact on their prominent use as sources for speckle-free laser imaging, which nowadays represents one of the most promising applications of random lasers, with expected progress even in cancer research.
Anderson S. L. Gomes, Ernesto P. Raposo, André L. Moura, Serge I. Fewo, Pablo I. R. Pincheira, Vladimir Jerez et 2 autre(s)
arXiv (Cornell University)
Random lasers have been recently approached as a photonic platform for disordered complex systems, such as spin glasses. In this work, using a Nd$^{3+}$:YBO$_3$ random laser system operating in the nonresonant (diffusive) feedback regime, we measured the distinct statistics of intensity fluctuations and show the physical origin of the complex interplay between the Lévy regime and the replica-symmetry-breaking transition to the photonic spin-glass phase. A novel result is reported: the unsaturated spin-glass behavior for high excitation pulse energies, not observed for systems with coherent feedback. Our experimental findings are corroborated by the present theoretical analysis. The results herein presented universalize the recent observation consistent with replica symmetry breaking in random lasers with coherent feedback, and also advance on the characterization of the fluctuation statistics of the photonic spin-glass phase, supported by recent theoretical works on the nonlinear optics of complex photonic systems.
André L. Moura, Serge I. Fewo, Mariana T. Carvalho, Andrey N. Kuzmin, Paras N. Prasad, Anderson S. L. Gomes et 1 autre(s)
Journal of Applied Physics
Random laser (RL) emission in Nd3+ doped potassium gadolinium tungstate—KGd(WO4)2:Nd3+—crystal powder is demonstrated. The powder was excited at 813 nm in resonance with the Nd3+ transition 4I9/2→4F5/2. RL emission at 1067 nm due to the 4F3/2→4I11/2 transition was observed and characterized. An intensity threshold dependent on the laser spot area and bandwidth narrowing from ≈2.20 nm to ≈0.40 nm were observed and measured. For a beam spot area of 0.4 mm2, a RL threshold of 6.5 mJ/mm2 (90 MW/cm2) was determined. For excitation intensity smaller than the RL threshold, only spontaneous emission from level 4F3/2 with decay time in the tens microsecond range was observed, but for excitation above the RL threshold, significant shortening of excited level lifetime, characteristic of a stimulated process was found. The overall characteristics measured show that KGd(WO4)2:Nd3+ is an efficient material for operation of solid state RLs in the near-infrared.
Lucien Mandeng Mandeng, Serge I. Fewo, Clément Tchawoua, Timoléon Crépin Kofané
Journal of Modern Optics
In a linear dispersive optical medium under fourth-order dispersion (FOD), we study the dynamics of the chirped pulse compression with the help of trial Gaussian and raised-cosine (RC) ansätze pulses. The analysis based on the variational approach leads to the occurrence of compression conditions, highlighting the cases where both the group-velocity dispersion (GVD) and the chirp could have the same sign or the case where both the FOD and the GVD have the same sign. Furthermore, we show that the compression process is dependent on the considered input profile. Particularly, a condition supposing that the GVD, the FOD and the chirp have the same sign leads to a compression only for the RC pulse in comparison to the previous results obtained for the Gaussian pulse. Numerical simulations, which confirm these features, are presented for the 380-fs input pulses undergoing value in the FOD.
Lucien Mandeng Mandeng, Serge I. Fewo, Clément Tchawoua, Timoléon Crépin Kofané
Journal of Optics
We report the analysis of the compression mechanism for chirped femtosecond pulses in silicon-on-insulator waveguides under the effect of fourth-order dispersion (FOD) using the modified variational approach that involves Rayleighʼs dissipation function (RDF). Our results show that the nonlinear compression in these waveguides is input pulse dependent. Moreover, this study leads to a nearly periodic-like dynamic induced by the interplay between self-phase modulation and FOD in a normal group-velocity dispersion. In addition, when large values of the initial chirp and absorption coefficients present in these waveguides are considered, the compression mechanism is completely destroyed, with the observation of at least one pulse amplification over a short distance of propagation prior to pulse broadening.
Lucien Mandeng Mandeng, Serge I. Fewo, Clément Tchawoua
The European Physical Journal D
Serge I. Fewo, Hermance Moussambi, Timoléon Crépin Kofané
Physica Scripta
Based on the nonlinear Helmholtz equation, we consider a model of the propagation of non-paraxial optical solitons, namely the non-paraxial nonlinear Schrödinger equation. Using this model, we present a theoretical treatment leading to dynamical equations of motion by means of the collective variable (CV) approach. We show that the non-paraxiality parameter leads to a more complicated analysis of the dynamics of the relevant parameters, called CVs, associated with the soliton in comparison with those behaviors taking into account the approximation of the slowly varying amplitude of the propagating beam. We provide some propagation results of the analysis on a typical semi-infinite Kerr medium for some coefficient values of the model. Also, we find that stable propagation of non-paraxial solitons can be achieved for an appropriate choice of parameters.
Serge I. Fewo, Timoléon Crépin Kofané
Optics Communications
Serge I. Fewo, C. M. Ngabireng, Timoléon Crépin Kofané
Journal of the Physical Society of Japan
Serge I. Fewo, C. M. Ngabireng, Timoléon Crépin Kofané
Journal of the Physical Society of Japan
With the help of the Maxwell equations, a basic equation modeling the propagation of ultrashort optical solitons in optical fiber is derived, namely the higher-order complex Ginzburg–Landau equation (HCGLE). Considering this one-dimensional HCGLE, we obtain a set of differential equations characterizing the variation of the pulse parameters called collective variables (CVs), of a pulse propagating in dispersion-managed (DM) fiber optic-links. Equations obtained are investigated numerically in order to observe the behaviour of pulse parameters along the optical fiber. A fully numerical simulation of the one-dimensional HCGLE finally tests the results of the CV theory. A good agreement between both methods is observed. Among various behaviours, chaotic pulses, attenuate pulses and stable pulses can be obtained under certain parameter values.
Serge I. Fewo, A. Kenfack-Jiotsa, Timoléon Crépin Kofané
Journal of Physics A Mathematical and General
Author: Fewo, S. I. et al.; Genre: Journal Article; Issued: 2006-02-10; Title: A collective variable approach and stabilization for dispersion-managed optical solitons in the quintic complex Ginzburg-Landau equation as perturbations of the nonlinear Schrödinger equation
A. Kenfack-Jiotsa, Serge I. Fewo, Timoléon Crépin Kofané
Physica Scripta
Considering a pulse-like ansatz, we derive different classes of exact soliton solutions of the modified complex Ginzburg–Landau equation. We then present the important variations which occur in the domain of stability of these solutions depending on the values of the renormalization coeffecients. This means that this term which can be considered for nonzero solutions and which does not generally occur in the literature could explain the lack of concordance between some theory and experiments.
Serge I. Fewo, Jacques Atangana, A. Kenfack-Jiotsa, Timoléon Crépin Kofané
Optics Communications
C. Koyandoulou, J. S. Njem Njem, Clovis Ntahkie Takembo, Serge I. Fewo, H. P. Ekobena Fouda, Timoléon Crépin Kofané
Chaos Solitons & Fractals
S. Mounbou, Serge I. Fewo, Luiz Antônio Ribeiro, C. Kenfack-Sadem
arXiv (Cornell University)
Polarons are the primary charge carriers in organic materials. A deep understanding of their properties can open channels for novel optoelectronic applications. By applying electric and magnetic fields, we investigate the influence of polaron interactions on the linear and nonlinear optical properties of a graphene monolayer between a substrate and air. Using the density matrix approach, we derive the linear and nonlinear optical absorption coefficients and the relative refractive index by incorporating the zero-energy level. Our numerical results reveal that the polaron effect and the magnetic field induce shifts in the peak positions of the optical absorption coefficients and refractive index. Moreover, while the presence of electric and magnetic fields significantly alters the amplitude of the absorption coefficients, only the magnetic field affects the refractive index amplitude. Additionally, we find that the magnetic field amplifies the influence of surface optical phonons on the optical properties of graphene. These findings provide deeper insights into the optical behavior of graphene in external fields, which could be relevant for optoelectronic applications.
S. Mounbou, Serge I. Fewo, Luiz Antônio Ribeiro, C. Kenfack-Sadem
ACS Omega
High Resolution Image Download MS PowerPoint Slide Polarons are the primary charge carriers in organic materials. A deep understanding of their properties can open channels for novel optoelectronic applications. By applying electric and magnetic fields, we investigate the influence of polaron interactions on the linear and nonlinear optical properties of a graphene monolayer between a substrate and air. Using the density matrix approach, we derive the linear and nonlinear optical absorption coefficients and the relative refractive index by incorporating the zero-energy level. Our numerical results reveal that the polaron effect, the magnetic and electric fields induce shifts in the peak positions of the optical absorption coefficients and refractive index. Moreover, while the presence of electric and magnetic fields significantly alters the amplitude of the absorption coefficients, only the magnetic field affects the refractive index amplitude. Additionally, we find that (i) the magnetic field amplifies the influence of surface optical phonons on the optical properties of graphene on polar substrate and (ii) surface optical phonons contribute significantly to the improved optical response of SiCand SiO 2 substrates due to their strong electron–phonon coupling strength. These findings provide deeper insights into the optical behavior of graphene on polar substrate in external fields, which could be relevant for optoelectronic applications.
Eric Martial Signé, Alain Djazet, Laure Tiam Megne, Martin Djoko, Serge I. Fewo, Timoléon Crépin Kofané
Chaos Solitons & Fractals
Stéphanie Ganyou, Chérif S. Panguetna, Serge I. Fewo, Conrad Bertrand Tabi, Timoléon Crépin Kofané
Pramana
J. S. Njem Njem, Clovis Ntahkie Takembo, Zeric Tabekoueng Njitacke, Serge I. Fewo, Timoléon Crépin Kofané
The European Physical Journal Plus
Loic Z. Ngou, HYACINTHE SIMO KAPTUE, Benjamin K. Lekama, Serge I. Fewo, Yves C. Mbono Samba
Journal of Mechanical Science and Technology
Loïc Ngou Zeufo, Hyacinthe Simo Kaptue, Benjamin Lekama Nkama, Serge I. Fewo, Yves Mbono Samba
SSRN Electronic Journal
Alain Djazet, Conrad Bertrand Tabi, Serge I. Fewo, Timoléon Crépin Kofané
Applied Physics B
Alain Djazet, Serge I. Fewo, Conrad Bertrand Tabi, Timoléon Crépin Kofané
Preprints.org
Interaction of an electromagnetic field with matter in a laser cavity without the assumption of a fixed direction of the transverse electric field, described by the two-level Maxwell-Bloch equations, is studied. By using a perturbative nonlinear analysis, performed near the laser threshold, we report on the derivation of the laser (3+1)D vectorial complex cubic-quintic complex Ginzburg-Landau equation. Furthermore, we study the modulational instability of the plane waves both theoretically using the linear stability analysis, and numerically, using direct simulations via the split-step Fourier method. The linear theory predicts instability for any amplitude of the primary waves. Our numerical simulations confirm the theoretical predictions of the linear theory as well as the threshold of the amplitude of perturbations. The system understudy shows a deep dependence on the laser cavity parameters, for which there appear wave patterns in accordance with the predictions from the gain spectrum.
Pablo I. R. Pincheira, Andréa F. Silva, Sandra J. M. Carreño, Serge I. Fewo, André L. Moura, Ernesto P. Raposo et 2 autre(s)
Replica symmetry break and a photonic paramagnetic to spin-glass phase transition in a random laser based on ethanol solution of Rhodamine 6G and specially designed amorphous TiO2 nanoparticles is demonstrated.
Profil chercheur
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